[ { "id": "authors:sk1hx-x9e39", "collection": "authors", "collection_id": "sk1hx-x9e39", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190710-110611418", "type": "article", "title": "Hans Herbert Brintzinger (1935\u20132019)", "author": [ { "family_name": "Bercaw", "given_name": "John", "clpid": "Bercaw-J-E" }, { "family_name": "Berke", "given_name": "Heinz", "clpid": "Berke-H" }, { "family_name": "Mecking", "given_name": "Stefan", "clpid": "Mecking-S" } ], "abstract": "Hans Brintzinger sadly passed away on June 2, 2019 unexpectedly. This is a great loss not only for his family but also for his former students, colleagues, friends, and the entire scientific community. His discovery of molecular catalysts capable of stereoregular 1\u2010olefin polymerization defined a whole new field. His legacy extends to numerous young researchers influenced by him, who succeeded in academic and industrial careers.", "doi": "10.1002/anie.201907530", "issn": "1433-7851", "publisher": "Wiley", "publication": "Angewandte Chemie International Edition", "publication_date": "2019-08-19", "series_number": "34", "volume": "58", "issue": "34", "pages": "11569" }, { "id": "authors:c17st-r9r59", "collection": "authors", "collection_id": "c17st-r9r59", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190531-091631225", "type": "article", "title": "Catalyst Speciation During ansa-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy\u2014Formation and Partial Re-Activation of Zr-Allyl Intermediates", "author": [ { "family_name": "Panchenko", "given_name": "Valentina N.", "orcid": "0000-0003-3771-8019", "clpid": "Panchenko-Valentina-N" }, { "family_name": "Babushkin", "given_name": "Dmitrii E.", "clpid": "Babushkin-Dmitrii-E" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Brintzinger", "given_name": "Hans H.", "clpid": "Brintzinger-Hans-H" } ], "abstract": "Catalyst speciation during polymerization of 1-hexene in benzene or toluene solutions of the catalyst precursor SBIZr(\u03bc-Me)_2AlMe_2^+ B(C_6F_5)_4^\u2212 (SBI = rac-dimethylsilyl-bis(1-indenyl)) at 23 \u00b0C is studied by following the accompanying UV-vis-spectral changes. These indicate that the onset of polymerization catalysis is associated with the concurrent formation of two distinct zirconocene species. One of these is proposed to consist of SBIZr-\u03c3-polyhexenyl cations arising from SBIZr-Me^+ (formed from SBIZr(\u03bc-Me)_2AlMe_2^+ by release of AlMe_3) by repeated olefin insertions, while the other one is proposed to consist of SBIZr-\u03b7^3-allyl cations of composition SBIZr-\u03b7^3-(1-R-C_3H_4)^+ (R = n-propyl), formed by \u03c3-bond metathesis between SBIZr-Me^+ and 1-hexene under release of methane. At later reaction stages, all zirconocene-\u03c3\u2212polymeryl cations appear to decay to yet another SBIZr-allyl species, i.e., to cations of the type SBIZr- \u03b7^3-(x-R-(3-x)-pol-C_3H_3)^+ (pol = i-polyhexenyl, x = 1 or 2). Renewed addition of excess 1-hexene is proposed to convert these sterically encumbered Zr-allyl cations back to catalytically active SBIZr-\u03c3\u2212polymeryl cations within a few seconds, presumably by initial 1-hexene insertion into the \u03b7^1- isomer, followed by repeated additional insertions, while the initially formed, less crowded allyl cations, SBIZr-\u03b7^3-(1-R-C_3H_4)^+ appear to remain unchanged. Implications of these results with regard to the kinetics of zirconocene-catalyzed olefin polymerization are discussed.", "doi": "10.3390/polym11060936", "pmcid": "PMC6630943", "issn": "2073-4360", "publisher": "MDPI", "publication": "Polymers", "publication_date": "2019-06", "series_number": "6", "volume": "11", "issue": "6", "pages": "Art. No. 936" }, { "id": "authors:3ackj-3n608", "collection": "authors", "collection_id": "3ackj-3n608", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190103-131505166", "type": "article", "title": "Malcolm L. H. Green: Reminiscences and Appreciations", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" } ], "abstract": "We are greatly pleased to participate in this special issue of Inorganica Chimica Acta celebrating Malcolm Green. Having no new science worthy of the occasion to report (and feeling no great urge to recycle older work yet one more time), we offer instead a brief appreciation of Malcolm's contributions to inorganic chemistry, as well as what he has meant to us throughout our careers, both personally and professionally.\n\nMalcolm was one of the earliest products of the Geoffrey Wilkinson school of organotransition metal chemistry, a group which, as one of us has documented [1], was a major factor in the mid-20th century \"renaissance\" of inorganic chemistry, in which Malcolm himself played no small part. Many of his early studies, both during his graduate student days and in his independent career at Oxford (following a brief sojourn at Cambridge), were focused on bent metallocenes and transition metal hydride complexes (often both): papers that had a significant influence on our own research programs. But even more importantly, his special ability to identify and delineate patterns of structure and reactivity was central to the transformation of organotransition metal chemistry, from a collection of interesting but poorly understood observations to the systematic and powerfully unified field it is today.", "doi": "10.1016/j.ica.2018.12.044", "issn": "0020-1693", "publisher": "Elsevier", "publication": "Inorganica Chimica Acta", "publication_date": "2019-03-01", "volume": "487", "pages": "405-408" }, { "id": "authors:5he8a-10062", "collection": "authors", "collection_id": "5he8a-10062", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180425-170103696", "type": "article", "title": "Jack Halpern (1925\u20132018): Pioneer of homogeneous catalysis", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Jack Halpern, a preeminent scholar and father of modern organometallic chemistry and homogeneous catalysis, died January 31, 2018 at the age of 93. Homogeneous catalysis by transition metal complexes, a field that has many important scientific and technological applications, can be traced to his early contributions. Jack developed methodologies to investigate the mechanisms and thermodynamics of fundamental chemical transformations that underpin organometallic and bioinorganic chemistry. Perhaps most notably, he reported the first molecular catalyst for hydrogenation of olefins and later elucidated the principles of catalytic asymmetric hydrogenation of olefins. Halpern helped, more so than any other chemist, to define the intellectual basis of modern catalytic science.", "doi": "10.1073/pnas.1806116115", "pmcid": "PMC5960341", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "2018-05-15", "series_number": "20", "volume": "115", "issue": "20", "pages": "5049-5050" }, { "id": "authors:t46kg-n6p81", "collection": "authors", "collection_id": "t46kg-n6p81", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170616-130503051", "type": "article", "title": "Mechanistic Studies on Selective Trimerization of Linear \u03b1-Olefins over a Supported Titanium Catalyst", "author": [ { "family_name": "Steelman", "given_name": "D. Keith", "clpid": "Steelman-D-K" }, { "family_name": "Aluthge", "given_name": "Dinesh C.", "clpid": "Aluthge-D-C" }, { "family_name": "Lehman", "given_name": "Matthew C.", "clpid": "Lehman-M-C" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The supported titanium catalyst s(FI)Ti, generated by adding (FI)TiCl3 to MAO-treated SiO2 (FI = (N-(5-methyl-3-(1-adamantyl)salicylidene)-2'-(2\"-methoxyphenyl)anilinato)], effects the selective trimerization of the linear \u03b1-olefins (LAOs) propene, 1-pentene, 1-hexene, 1-decene, with >95% selectivity for trimers and ~85% selectivity to a single isomer thereof (2,3,5-trialkyl-1-hexene). Mechanistic interpretations are offered for the high regioselectivity as well as for some unusual kinetics behavior, including third-order dependence on LAO concentration and nearly identical initial rates at 0 and 25 \u00b0C.", "doi": "10.1021/acscatal.7b00256", "issn": "2155-5435", "publisher": "American Chemical Society", "publication": "ACS Catalysis", "publication_date": "2017-08-04", "series_number": "8", "volume": "7", "issue": "8", "pages": "4922-4926" }, { "id": "authors:nnkka-jv888", "collection": "authors", "collection_id": "nnkka-jv888", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160912-085645255", "type": "article", "title": "Cosupported Tandem Catalysts for Production of Linear Low-Density Polyethylene from an Ethylene-Only Feed", "author": [ { "family_name": "Aluthge", "given_name": "Dinesh C.", "clpid": "Aluthge-D-C" }, { "family_name": "Sattler", "given_name": "Aaron", "clpid": "Sattler-A" }, { "family_name": "Al-Harthi", "given_name": "Mamdouh A.", "clpid": "Al-Harthi-M-A" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Linear low-density polyethylene (LLDPE) is produced from an ethylene-only feed over a tandem catalyst system consisting of a phenoxy\u2013imine titanium trimerization catalyst and a silylene-linked cyclopentadienyl/amido titanium polymerization catalyst cosupported on the same methylaluminoxane/silica particles. The level of 1-hexene incorporation can be controlled by varying the ethylene pressure.", "doi": "10.1021/acscatal.6b02370", "issn": "2155-5435", "publisher": "American Chemical Society", "publication": "ACS Catalysis", "publication_date": "2016-10-07", "series_number": "10", "volume": "6", "issue": "10", "pages": "6581-6584" }, { "id": "authors:ayfdz-6at82", "collection": "authors", "collection_id": "ayfdz-6at82", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151130-153147009", "type": "article", "title": "Enhanced Productivity of a Supported Olefin Trimerization Catalyst", "author": [ { "family_name": "Sattler", "given_name": "Aaron", "clpid": "Sattler-A" }, { "family_name": "Aluthge", "given_name": "Dinesh C.", "clpid": "Aluthge-D-C" }, { "family_name": "Winkler", "given_name": "Jay R.", "orcid": "0000-0002-4453-9716", "clpid": "Winkler-J-R" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Treatment of dry silica with methylaluminoxane (MAO) followed by (FI)TiCl_3 (FI = (N-(5-methyl-3-(1-adamantyl)salicylidene)-2\u2032-(2\u2033-methoxyphenyl)anilinato) gives a heterogeneous supported ethylene trimerization catalyst, s(FI)Ti, which exhibits productivity more than an order of magnitude higher than its homogeneous analogues. This increase in productivity is attributed to a decreased rate of catalyst decomposition, a process that is proposed to occur via comproportionation to an inactive TiIII species; immobilization retards this process. In addition, s(FI)Ti catalyzes trimerization of \u03b1-olefins with high selectivity. Based on regioisomer distributions, catalysis by s(FI)Ti involves the same active species as the previously reported homogeneous systems (FI)TiR_2Me/B(C_6F_5)_3 (R = Me, CH_2SiMe_3, CH_2CMe_3).", "doi": "10.1021/acscatal.5b02604", "issn": "2155-5435", "publisher": "American Chemical Society", "publication": "ACS Catalysis", "publication_date": "2016-01", "series_number": "1", "volume": "6", "issue": "1", "pages": "19-22" }, { "id": "authors:mwagp-p6m81", "collection": "authors", "collection_id": "mwagp-p6m81", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151105-082822906", "type": "article", "title": "Mechanistic Insights on the Controlled Switch from Oligomerization to Polymerization of 1-Hexene Catalyzed by an NHC-Zirconium Complex", "author": [ { "family_name": "Despagnet-Ayoub", "given_name": "Emmanuelle", "orcid": "0000-0002-9013-7574", "clpid": "Despagnet-Ayoub-E" }, { "family_name": "Takase", "given_name": "Michael K.", "orcid": "0000-0001-8365-3645", "clpid": "Takase-M-K" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The benzimidazolylidene zirconium complex 1 switches from an oligomerization (without additive) to a polymerization catalyst by addition of an L-type ligand such as trimethylphosphine, while larger phosphines or amines completely inhibit catalysis. On the basis of the regioselectivity of the oligomers/polymers obtained, the time profiles of reactions as a function of added ligand, and the molecular structures of several cationic zirconium complexes, we propose a mechanistic framework for interpreting this complex catalytic behavior.", "doi": "10.1021/acs.organomet.5b00472", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2015-10-12", "series_number": "19", "volume": "34", "issue": "19", "pages": "4707-4716" }, { "id": "authors:9s2pe-2y520", "collection": "authors", "collection_id": "9s2pe-2y520", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151105-084413995", "type": "article", "title": "Gregory L. Hillhouse: His Life, His Art, His Science, and the Rise of \"Double Nickel\"", "author": [ { "family_name": "Mindiola", "given_name": "Daniel J.", "clpid": "Mindiola-D-J" }, { "family_name": "Smith", "given_name": "Milton R.", "clpid": "Smith-M-R" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Professor Gregory Lee Hillhouse was a purist who explored at a fundamental level structure, bonding, and reactivity of organic and inorganic molecules. Whether at the canvas or in the laboratory, he was a creative artist who lived life to its fullest, and enriched the lives of those around him. As an undergraduate at the University of South Carolina with Professor Edward Mercer, Greg became interested in the chemistry of transition metals. In his graduate and postdoctoral studies, Greg focused on the roles of transition metals in stabilizing reactive molecules and activating inert ones, which would become hallmarks of his independent career. In his early days as a graduate student in the laboratories of Professor Barry Haymore (Figure 1) at the Indiana University\u2014Bloomington, Greg (Figures 1 and 2) began exploring fundamental chemistry of energy-rich nitrogen compounds such as organic azides and diazoalkanes.(1-3) In parallel, he pursued the synthesis of metal hydride complexes that underwent insertion reactions with unsaturated molecules.(2, 4) At this early stage of his career, the seeds of Greg's passion for metal\u2013ligand multiple bonding were sown.(2, 5)", "doi": "10.1021/acs.organomet.5b00527", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2015-10-12", "series_number": "19", "volume": "34", "issue": "19", "pages": "4633-4636" }, { "id": "authors:4tahc-nq790", "collection": "authors", "collection_id": "4tahc-nq790", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150223-082637024", "type": "article", "title": "Mechanistic studies on the Shilov system: A retrospective", "author": [ { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Following a brief account of our personal encounters with Alex Shilov, we summarize our 20+ years work on the mechanism of the Shilov system and related C\u2013H activation chemistry.", "doi": "10.1016/j.jorganchem.2015.01.027", "issn": "0022-328X", "publisher": "Elsevier", "publication": "Journal of Organometallic Chemistry", "publication_date": "2015-09-15", "volume": "793", "pages": "47-53" }, { "id": "authors:x1t6d-qd515", "collection": "authors", "collection_id": "x1t6d-qd515", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150917-154149857", "type": "article", "title": "Reversible 1,2-Alkyl Migration to Carbene and Ammonia Activation in an N-Heterocyclic Carbene\u2013Zirconium Complex", "author": [ { "family_name": "Despagnet-Ayoub", "given_name": "Emmanuelle", "orcid": "0000-0002-9013-7574", "clpid": "Despagnet-Ayoub-E" }, { "family_name": "Takase", "given_name": "Michael K.", "orcid": "0000-0001-8365-3645", "clpid": "Takase-M-K" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Addition of trimethylphosphine to a bis(phenolate)benzylimidazolylidene(dibenzyl)zirconium complex induces migration of a benzyl ligand from the metal center to the C_(carbine) atom. This process may be reversed, resulting in C_(sp)^3\u2013C_(sp)^3 activation, by abstraction of the phosphine, an example of regulated, reversible alkyl migration. Addition of ammonia to the dibenzyl complex results in migration of one benzyl group and protonolysis of the other to generate a bis(NH_2)-bridged dimer via an NMR-observable intermediate NH_3 adduct.", "doi": "10.1021/jacs.5b06695", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2015-08-26", "series_number": "33", "volume": "137", "issue": "33", "pages": "10500-10503" }, { "id": "authors:qpyay-2bm23", "collection": "authors", "collection_id": "qpyay-2bm23", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150407-092610476", "type": "article", "title": "Upgrading Light Hydrocarbons: A Tandem Catalytic System for Alkane/Alkene Coupling", "author": [ { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Leitch", "given_name": "David C.", "clpid": "Leitch-D-C" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Deimund", "given_name": "Mark A.", "clpid": "Deimund-M-A" }, { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" } ], "abstract": "Light hydrocarbons, with relatively low fuel value, are abundant from several sources, including mixed alkane/alkene refinery byproduct streams. A tandem system consisting of a compatible combination of a homogeneous alkane dehydrogenation catalyst (known to be kinetically efficient but thermodynamically disfavored at low temperatures) with an olefin dimerization catalyst could effect the coupling of an alkane and alkene to produce a heavier, more valuable fuel molecule (C_nH_(2n+2) + CnH_(2n) = C_(2n)H_(4n+2)), a reaction that is thermodynamically favorable below 250 \u00b0C. We have demonstrated that coupling with a tandem homogeneous catalyst, consisting of a pincer-ligated iridium alkane dehydrogenation catalyst and an organometallic tantalum alkene dimerization catalyst; the combination couples 1-hexene/n-heptane to C_(13)/C_(14) products at temperatures ranging from 100 to 150 \u00b0C, operating with up to 90 % cooperativity. This particular combination generates alkene products rather than the desired alkanes, however, because the regioselectivity of the dimerization catalyst preferentially yields highly substituted alkenes that are not reactive towards hydrogen transfer. A complete cycle should be attainable by combining the dehydrogenation catalyst with an alternate dimerization catalyst that gives mostly linear and monosubstituted alkenes; we have synthesized a novel class of nickel-exchanged zincosilicates that exhibit the desired dimerization catalytic behavior.", "doi": "10.1007/s11244-015-0380-2", "issn": "1022-5528", "publisher": "Springer", "publication": "Topics in Catalysis", "publication_date": "2015-05", "series_number": "7-9", "volume": "58", "issue": "7-9", "pages": "494-501" }, { "id": "authors:j7jvp-saw80", "collection": "authors", "collection_id": "j7jvp-saw80", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140902-111856267", "type": "article", "title": "Palladium(II) Complexes Supported by a Bidentate Bis(secondary)phosphine Linked by Pyridine", "author": [ { "family_name": "Winston", "given_name": "Matthew S.", "clpid": "Winston-M-S" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A series of complexes of the type (PNP-H_2)PdX_2 (X = Cl, Br, I) have been synthesized, where PNP-H_2 is a bis(secondary)phosphine ligand linked by a pyridine, 2,6-(Ph(H)P)_2(C_5H_3N). Due to chirality at phosphorus, the parent ligand exists as a mixture of nearly equivalent rac and meso diastereomers non-interconverting at room temperature. When ligated to Pd(II) halides, however, the diastereomeric ratio is dependent upon the halide. The chloro, bromo, and iodo complexes have been characterized crystallographically. Conformationally similar meso diastereomers of each dihalide are roughly C_s symmetric in the solid state, while the rac diastereomers (identified only for X = Br, I) show substantially different solid-state conformations.", "doi": "10.1016/j.ica.2014.08.002", "issn": "0020-1693", "publisher": "Elsevier", "publication": "Inorganica Chimica Acta", "publication_date": "2014-10-01", "volume": "422", "pages": "30-35" }, { "id": "authors:y8pfw-emr29", "collection": "authors", "collection_id": "y8pfw-emr29", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140804-164958436", "type": "article", "title": "Guanidine-Functionalized Rhenium Cyclopentadienyl Carbonyl Complexes: Synthesis and Cooperative Activation of H\u2013H and O\u2013H Bonds", "author": [ { "family_name": "Teets", "given_name": "Thomas S.", "clpid": "Teets-T-S" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Catalytic reactions utilizing carbon monoxide as a substrate are numerous, and they typically involve selective functionalization of a metal-bound CO. We have developed group 7 carbonyl complexes where secondary coordination sphere, Lewis acidic functionalities can assist in the activation of substrate molecules, mainly in the context of syngas conversion. This work describes a new class of cyclopentadienyl (Cp) rhenium carbonyl compounds of the type [Re(\u03b7^5-C_5H_4DMEG)(CO)_(3\u2013n)(NO)_n]^n (DMEG = dimethylethyleneguanidine, n = 0, 1), where a tethered guanidine base is appended to the Cp ring to participate in cooperative substrate activation with the electrophilic carbonyl. A reliable synthetic route for these complexes is presented, with crystallographic characterization of the free-base and protonated forms for both the carbonyl and mixed carbonyl-nitrosyl complexes. The latter are employed as platforms to study heterolytic H\u2013H and O\u2013H bond cleavage reactions that result in nucleophilic CO functionalization. The corresponding formyl complex is prepared by hydride transfer, and by measuring its hydricity (\u0394G^\u00b0_(H\u2013)) and pK_a of the protonated base, the free energy of H_2 cleavage is found to be +3.3(6) kcal/mol. The activation of methanol to form methoxycarbonyl complexes is found to be more favorable, with \u0394G^\u00b0 \u2248 0 for the intramolecular addition of methanol to the guanidine-appended carbonyl complex. A detailed thermodynamic study is described for both the intramolecular methanol activation reaction and related intermolecular reactions with external bases. The results highlight some tangible thermodynamic benefits of tethering the base in the secondary coordination sphere.", "doi": "10.1021/om500650b", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2014-08-11", "series_number": "15", "volume": "33", "issue": "15", "pages": "4107-4117" }, { "id": "authors:cak37-24a77", "collection": "authors", "collection_id": "cak37-24a77", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150324-150701311", "type": "article", "title": "N-Heterocyclic carbene group 4 transition metal catalysts: Synthesis and reactivity towards oligomerization/polymerization of \u03b1-olefins", "author": [ { "family_name": "Despagnet-Ayoub", "given_name": "Emmanuelle", "orcid": "0000-0002-9013-7574", "clpid": "Despagnet-Ayoub-E" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Carbene ligands, esp. N-heterocyclic carbenes (NHC), are widely used in late transition metal catalysts,\noften enhancing catalytic activity due to their strong \u03c3-donation ability helping to stabilize the active species. In\ncontrast, limited examples of early transition metal catalysts contg. NHCs have been reported, esp. group 4\nolefin polymn. catalysts, due to their poor binding affinity to early transition metals. Indeed, the increasing\ninterest in \"post-metallocene\" catalysts for olefin polymn. has generated many active catalysts that exploit\nthe modularity of the ligand to afford in particular interesting tacticity control. In this regard, we are\ninvestigating the use of tridentate dianionic carbenes bearing bisphenolate arms as ligands for olefin polymn. In\nthis talk, we will present the coordination chem. of these new carbenes with group 4 metal complexes and\ntheir application as catalysts for the polymn./oligomerization of \u03b1-olefins.", "issn": "0065-7727", "publisher": "American Chemical Society", "publication": "Abstracts of Papers of the American Chemical Society", "publication_date": "2014-08-10", "volume": "248", "pages": "527-INOR" }, { "id": "authors:p1nj1-gnj90", "collection": "authors", "collection_id": "p1nj1-gnj90", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140829-112317640", "type": "article", "title": "Lewis Acid Promoted Titanium Alkylidene Formation: Off-Cycle Intermediates Relevant to Olefin Trimerization Catalysis", "author": [ { "family_name": "Sattler", "given_name": "Aaron", "clpid": "Sattler-A" }, { "family_name": "VanderVelde", "given_name": "David G.", "orcid": "0000-0002-2907-0366", "clpid": "VanderVelde-D-G" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Two new precatalysts for ethylene and \u03b1-olefin trimerization, (FI)Ti(CH_2SiMe_3)_2Me and (FI)Ti(CH_2CMe_3)_2Me (FI = phenoxy-imine), have been synthesized and structurally characterized by X-ray diffraction. (FI)Ti(CH_2SiMe_3)_2Me can be activated with 1 equiv of B(C_6F_5)_3 at room temperature to give the solvent-separated ion pair [(FI)Ti(CH_2SiMe_3)_2][MeB(C_6F_5)_3], which catalytically trimerizes ethylene or 1-pentene to produce 1-hexene or C_(15) olefins, respectively. The neopentyl analogue (FI)Ti(CH_2CMe_3)_2Me is unstable toward activation with B(C_6F_5)_3 at room temperature, giving no discernible diamagnetic titanium complexes, but at \u221230 \u00b0C the following can be observed by NMR spectroscopy: (i) formation of the bis-neopentyl cation [(FI)Ti(CH_2CMe_3)_2]^+, (ii) \u03b1-elimination of neopentane to give the neopentylidene complex [(FI)Ti(\u2550CHCMe_3)]^+, and (iii) subsequent conversion to the imido-olefin complex [(MeOAr_2N\u2550)Ti(OArHC\u2550CHCMe_3)]^+ via an intramolecular metathesis reaction with the imine fragment of the (FI) ligand. If the reaction is carried out at low temperature in the presence of ethylene, catalytic production of 1-hexene is observed, in addition to the titanacyclobutane complex [(FI)Ti(CH(CMe_3)CH_2CH_2)]^+, resulting from addition of ethylene to the neopentylidene [(FI)Ti(\u2550CHCMe_3)]^+. None of the complexes observed spectroscopically subsequent to [(FI)Ti(CH_2CMe_3)_2]^+ is an intermediate or precursor for ethylene trimerization, but notwithstanding these off-cycle pathways, [(FI)Ti(CH_2CMe_3)_2]^+ is a precatalyst that undergoes rapid initiation to generate a catalyst for trimerizing ethylene or 1-pentene.", "doi": "10.1021/ja5055687", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2014-07-30", "series_number": "30", "volume": "136", "issue": "30", "pages": "10790-10800" }, { "id": "authors:jz7e2-cj251", "collection": "authors", "collection_id": "jz7e2-cj251", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140623-133736607", "type": "article", "title": "Scope and Mechanism of Homogeneous Tantalum/Iridium Tandem Catalytic Alkane/Alkene Upgrading using Sacrificial Hydrogen Acceptors", "author": [ { "family_name": "Leitch", "given_name": "David C.", "clpid": "Leitch-D-C" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "An in-depth investigation of a dual homogeneous catalyst system for the coupling of alkanes and alkenes based on an early-/late-transition-metal pairing is reported. The system is composed of Cp*TaCl_2(alkene) for alkene dimerization and pincer-iridium hydrides for alkane/alkene transfer hydrogenation. Because there is no kinetically relevant interaction between the two catalysts, the tandem mechanism can be entirely described using the two independent catalytic cycles. The alkene dimerization mechanism is characterized by an entropically disfavored pre-equilibrium between Cp*TaCl_2(1-hexene) + 1-hexene and Cp*TaCl_2(metallacyclopentane) (\u0394H\u00b0 = \u221222(2) kcal/mol; \u0394S\u00b0 = \u221216(2) eu); thus, the overall rate of alkene dimerization is positive order in 1-hexene (exhibiting saturation kinetics), and increases only modestly with temperature. In contrast, the rate of 1-hexene/n-heptane transfer hydrogenation catalyzed by t-Bu[PCP]IrH_4 is inverse order in 1-hexene and increases substantially with temperature. Styrene has been investigated as an alternate sacrificial hydrogen acceptor. Styrene dimerization catalyzed by Cp*TaCl_2(alkene) is considerably slower than 1-hexene dimerization. The conversion of styrene/heptane mixtures by the Ta/Ir tandem system leads to three product types: styrene dimers, coupling of styrene and heptane, and heptene dimers (from heptane). Through careful control of reaction conditions, the production of heptene dimers can be favored, with up to 58% overall yield of heptane-derived products and cooperative TONs of up to 12 and 10 for Ta and Ir catalysts, respectively. There is only slight inhibition of Ir-catalyzed styrene/n-heptane transfer hydrogenation under the tandem catalysis conditions.", "doi": "10.1021/om500231t", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2014-07-14", "series_number": "13", "volume": "33", "issue": "13", "pages": "3353-3365" }, { "id": "authors:yvc96-ga626", "collection": "authors", "collection_id": "yvc96-ga626", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140701-092911451", "type": "article", "title": "Investigations into Asymmetric Post-Metallocene Group 4 Complexes for the Synthesis of Highly Regioirregular Polypropylene", "author": [ { "family_name": "Klet", "given_name": "Rachel C.", "clpid": "Klet-R-C" }, { "family_name": "Theriault", "given_name": "Curt N.", "clpid": "Theriault-C-N" }, { "family_name": "Klosin", "given_name": "Jerzy", "clpid": "Klosin-J" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A series of asymmetric post-metallocene group 4 complexes based on a modular anilide(pyridine)phenoxide framework have been synthesized and tested for propylene polymerization activity. These complexes, upon activation with methylaluminoxane (MAO), produce highly regioirregular and stereoirregular polypropylene with moderate to good activities. Surprisingly, modification of the anilide R-group substituent from 1-phenethyl to benzyl or adamantyl did not significantly change the polymer microstructure as determined by ^(13)C NMR spectroscopy. Although polymer molecular weights and polydispersities vary with propylene pressure, temperature, and activator, regio- and stereoirregularity were also found to be relatively insensitive to these variables. When the polymerization is conducted at 70 \u00b0C under dihydrogen, partial decomposition to a highly active catalyst that produces an isotactic microstructure occurs; the undecomposed catalyst continues to produce highly regioirregular and stereoirregular polypropylene under these conditions.", "doi": "10.1021/ma500453t", "issn": "0024-9297", "publisher": "American Chemical Society", "publication": "Macromolecules", "publication_date": "2014-05-27", "series_number": "10", "volume": "47", "issue": "10", "pages": "3317-3324" }, { "id": "authors:3x2yh-s6g26", "collection": "authors", "collection_id": "3x2yh-s6g26", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131203-152859954", "type": "article", "title": "Highly Selective Olefin Trimerization Catalysis by a Borane-Activated Titanium Trimethyl Complex", "author": [ { "family_name": "Sattler", "given_name": "Aaron", "clpid": "Sattler-A" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Reaction of a trimethyl titanium complex, (FI)TiMe_3 (FI = phenoxy-imine), with 1 equiv of B(C_6F_5)_3 gives [(FI)TiMe_2][MeB(C_6F_5)_3], an effective precatalyst for the selective trimerization of ethylene. Mechanistic studies indicate that catalyst initiation involves generation of an active TiII species by olefin insertion into a Ti\u2013Me bond, followed by \u03b2-H elimination and reductive elimination of methane, and that initiation is slow relative to trimerization. (FI)TiMe_3/B(C_6F_5)_3 also leads to a competent catalyst for the oligomerization of \u03b1-olefins, displaying high selectivity for trimers (>95%), approximately 85% of which are one regioisomer. This catalyst system thus shows promise for selectively converting light \u03b1-olefins into transportation fuels and lubricants.", "doi": "10.1021/om401098m", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2013-12-09", "series_number": "23", "volume": "32", "issue": "23", "pages": "6899-6902" }, { "id": "authors:5g2gt-8p958", "collection": "authors", "collection_id": "5g2gt-8p958", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131205-151235905", "type": "article", "title": "Spectral Studies of a Cr(PNP)\u2212MAO System for Selective Ethylene Trimerization Catalysis: Searching for the Active Species", "author": [ { "family_name": "Do", "given_name": "Loi H.", "clpid": "Do-Loi-H" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Variable temperature spectroscopic, kinetic, and chemical studies were performed on a soluble Cr^(III)Cl_3(PNP) (PNP = bis(diarylphosphino)alkylamine) ethylene trimerization precatalyst to map out its methylaluminoxane (MAO) activation sequence. These studies indicate that treatment of Cr^(III)Cl_3(PNP) with MAO leads first to replacement of chlorides with alkyl groups, followed by alkyl abstraction, and then reduction to lower\u2013valent species. Reactivity studies demonstrate that the majority of the chromium species detected are not catalytically active.", "doi": "10.1021/cs400778a", "pmcid": "PMC3855459", "issn": "2155-5435", "publisher": "American Chemical Society", "publication": "ACS Catalysis", "publication_date": "2013-11", "series_number": "11", "volume": "3", "issue": "11", "pages": "2582-2585" }, { "id": "authors:bfj5d-fq296", "collection": "authors", "collection_id": "bfj5d-fq296", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131125-143704208", "type": "article", "title": "A Thermodynamic Analysis of Rhenium(I)\u2212Formyl C\u2212H Bond\n Formation via Base-Assisted Heterolytic H_2 Cleavage in the\n Secondary Coordination Sphere", "author": [ { "family_name": "Teets", "given_name": "Thomas S.", "clpid": "Teets-T-S" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Conversion of synthesis gas, a mixture of carbon monoxide and hydrogen, into value-added Cn\u22652 products requires both C\u2013H and C\u2013C bond-forming events. Our group has developed a series of molecular complexes, based on group 7 (manganese and rhenium) carbonyl complexes, to interrogate the elementary steps involved in the homogeneous hydrogenative reductive coupling of CO. Here, we explore a new mode of H2 activation, in which strong bases in the secondary coordination sphere are positioned to assist in the heterolytic cleavage of H2 to form a formyl C\u2013H bond at a rhenium-bound carbonyl. A series of cationic rhenium(I) complexes of the type [ReI(PB:-\u03ba1-P)(CO)5]n (n = 0, +1), where PB: is a phosphine ligand with a tethered strong base, are prepared and characterized; measurement of their protonation equilibria demonstrates a pronounced attenuation of the basicity upon coordination. Formyl complexes supported by these ligands can be prepared in good yield by hydride delivery to the parent pentacarbonyl complexes, and several of the free-base formyl complexes can be protonated, generating observable [ReI(PBH-\u03ba1-P)(CHO)(CO)4]n complexes. Intramolecular hydrogen bonding is evident for one of the complexes, providing additional stabilization to the protonated formyl complex. By measuring both the hydricity of the formyl, \u0394G\u00b0H\u2013, and its pKa, the overall free energy of H2 cleavage is calculated from an appropriate cycle and found to be thermodynamically uphill in all cases (in the best case by only about 8 kcal/mol), although significantly dependent upon the properties of the supporting ligand.", "doi": "10.1021/om400810v", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2013-10-14", "series_number": "19", "volume": "32", "issue": "19", "pages": "5530-5545" }, { "id": "authors:g7gvw-j5e42", "collection": "authors", "collection_id": "g7gvw-j5e42", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131204-094018041", "type": "article", "title": "Addition of a phosphine ligand switches an N-heterocyclic carbene-zirconium catalyst from oligomerization to polymerization of 1-hexene", "author": [ { "family_name": "Despagnet-Ayoub", "given_name": "Emmanuelle", "orcid": "0000-0002-9013-7574", "clpid": "Despagnet-Ayoub-E" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A catalyst for the oligomerization of 1-hexene, generated by the activation of a benzimidazolylidene zirconium dibenzyl complex, switches to a polymerization catalyst on addition of a trialkylphosphine.", "doi": "10.1039/C3DT52342J", "issn": "1477-9226", "publisher": "Royal Society of Chemistry", "publication": "Dalton Transactions", "publication_date": "2013-09-06", "series_number": "44", "volume": "42", "issue": "44", "pages": "15544-15547" }, { "id": "authors:m5hw0-a8e50", "collection": "authors", "collection_id": "m5hw0-a8e50", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230411-407247000.4", "type": "article", "title": "Crystallization analysis fractionation of poly(ethylene-co-styrene) produced by metallocene catalysts", "author": [ { "family_name": "Kamal", "given_name": "Muhammad Shahzad", "orcid": "0000-0003-2359-836X", "clpid": "Kamal-Muhammad-Shahzad" }, { "family_name": "Bahuleyan", "given_name": "Bijal Kottukkal", "orcid": "0000-0002-5777-3448", "clpid": "Bahuleyan-Bijal-K" }, { "family_name": "Bin Sohail", "given_name": "Omer", "orcid": "0000-0002-3901-9089", "clpid": "Bin-Sohail-Omer" }, { "family_name": "Emwas", "given_name": "Abdul-Hamid M.", "clpid": "Emwas-Abdul-Hamid -M" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Al-Harthi", "given_name": "Mamdouh A.", "orcid": "0000-0002-6500-7532", "clpid": "Al-Harthi-Mamdouh-A" } ], "abstract": "Ethylene homo polymer and ethylene\u2013styrene copolymers were synthesized using Cp\u2082ZrCl\u2082 (1)/methyl aluminoxane (MAO) and rac-silylene-bis (indenyl) zirconium dichloride (2)/MAO catalyst systems by varying styrene concentration and reaction conditions. Crystallization analysis fractionation (CRYSTAF), DSC, FTIR and \u00b9H NMR spectroscopy were used for characterizing the synthesized polymers. Interestingly, styrene was able to increase the activity of 1/MAO and 2/MAO catalyst systems at low concentrations, but at higher concentrations the activity decreases. The 1/MAO system at low and high pressure was unable to incorporate styrene, and the final product was pure polyethylene. On the other hand, with 2/MAO polymerization of ethylene and styrene yielded copolymer containing both styrene and ethylene. Results obtained from CRYSTAF and DSC reveal that on using 1/MAO system at high pressure, the resulting polymer in the presence of styrene has similar crystallinity as the polymer produced without styrene. Using both 1/MAO at low pressure and 2/MAO leads to decrease in crystallinity with increase in styrene concentration, even though the former does not incorporate styrene.", "doi": "10.1007/s00289-013-0980-6", "issn": "0170-0839", "publisher": "Springer", "publication": "Polymer Bulletin", "publication_date": "2013-09", "series_number": "9", "volume": "70", "issue": "9", "pages": "2645-2656" }, { "id": "authors:5sqgr-qnq10", "collection": "authors", "collection_id": "5sqgr-qnq10", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130925-111719370", "type": "article", "title": "Frontiers, Opportunities, and Challenges in Biochemical and Chemical Catalysis of CO_2 Fixation", "author": [ { "family_name": "Appel", "given_name": "Aaron M.", "clpid": "Appel-A-M" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Bocarsly", "given_name": "Andrew B.", "clpid": "Bocarsly-A-B" }, { "family_name": "Dobbek", "given_name": "Holger", "clpid": "Dobbek-H" }, { "family_name": "DuBois", "given_name": "Daniel L.", "clpid": "DuBois-D-L" }, { "family_name": "Dupuis", "given_name": "Michel", "clpid": "Dupuis-M" }, { "family_name": "Ferry", "given_name": "James G.", "clpid": "Ferry-J-G" }, { "family_name": "Fujita", "given_name": "Etsuko", "clpid": "Fujita-E" }, { "family_name": "Hille", "given_name": "Russ", "clpid": "Hille-R" }, { "family_name": "Kenis", "given_name": "Paul J. A.", "clpid": "Kenis-P-J-A" }, { "family_name": "Kerfeld", "given_name": "Cheryl A.", "clpid": "Kerfeld-K-A" }, { "family_name": "Morris", "given_name": "Robert H.", "clpid": "Morris-R-H" }, { "family_name": "Peden", "given_name": "Charles H. F.", "clpid": "Peden-C-H-F" }, { "family_name": "Portis", "given_name": "Archie R.", "clpid": "Portis-A-R" }, { "family_name": "Ragsdale", "given_name": "Stephen W.", "clpid": "Ragsdale-S-W" }, { "family_name": "Rauchfuss", "given_name": "Thomas B.", "clpid": "Rauchfuss-T-B" }, { "family_name": "Reek", "given_name": "Joost N. H.", "clpid": "Reek-J-N-H" }, { "family_name": "Seefeldt", "given_name": "Lance C.", "clpid": "Seefeldt-L-C" }, { "family_name": "Thauer", "given_name": "Rudolf K.", "clpid": "Thauer-R-K" }, { "family_name": "Waldrop", "given_name": "Grover J.", "clpid": "Waldrop-G-J" } ], "abstract": "Two major energy-related problems confront the world in the\nnext 50 years. First, increased worldwide competition for\ngradually depleting fossil fuel reserves (derived from past\nphotosynthesis) will lead to higher costs, both monetarily and politically. Second, atmospheric CO_2 levels are at their highest recorded level since records began. Further increases are predicted to produce large and uncontrollable impacts on the world climate. These projected impacts extend beyond climate to ocean acidification, because the ocean is a major sink for atmospheric CO2.1 Providing a future energy supply that is secure and CO_2-neutral will require switching to nonfossil energy sources such as wind, solar, nuclear, and geothermal energy and developing methods for transforming the energy produced by these new sources into forms that can be stored, transported, and used upon demand.", "doi": "10.1021/cr300463y", "pmcid": "PMC3895110", "issn": "0009-2665", "publisher": "American Chemical Society", "publication": "Chemical Reviews", "publication_date": "2013-08-14", "series_number": "8", "volume": "113", "issue": "8", "pages": "6621-6658" }, { "id": "authors:cj01j-z9q16", "collection": "authors", "collection_id": "cj01j-z9q16", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131008-104804358", "type": "article", "title": "Formation of Trivalent Zirconocene Complexes from ansa-Zirconocene-Based Olefin-Polymerization Precatalysts: An EPR- and NMR-Spectroscopic Study", "author": [ { "family_name": "Lenton", "given_name": "Taylor N.", "clpid": "Lenton-T-N" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Panchenko", "given_name": "Valentina N.", "orcid": "0000-0003-3771-8019", "clpid": "Panchenko-V-N" }, { "family_name": "Zakharov", "given_name": "Vladimir A.", "clpid": "Zakharov-V-A" }, { "family_name": "Babushkin", "given_name": "Dmitrii E.", "clpid": "Babushkin-D-E" }, { "family_name": "Soshnikov", "given_name": "Igor E.", "clpid": "Soshnikov-I-E" }, { "family_name": "Talsi", "given_name": "Evgenii P.", "clpid": "Talsi-E-P" }, { "family_name": "Brintzinger", "given_name": "Hans H.", "clpid": "Brintzinger-H-H" } ], "abstract": "Reduction of Zr(IV) metallocenium cations with sodium amalgam (NaHg) produces EPR signals assignable to Zr(III) metallocene complexes. The chloro-bridged heterodinuclear ansa-zirconocenium cation [(SBI)Zr(\u03bc-Cl)_2AlMe_2]^+ (SBI = rac-dimethylsilylbis(1-indenyl)), present in toluene solution as its B(C_6F_5)_4^\u2013 salt, thus gives rise to an EPR signal assignable to the complex (SBI)Zr^(III)(\u03bc-Cl)_2AlMe_2, while (SBI)ZrIII-Me and (SBI)Zr^(III)(\u03bc-H)_2Al^(i)Bu_2 are formed by reduction of [(SBI)Zr(\u03bc-Me)_2AlMe_2]^+ B(C_6F_5)_4\u2013 and [(SBI)Zr(\u03bc-H)_3(AliBu_2)_2]^+ B(C_6F_5)_4^\u2013, respectively. These products can also be accessed, along with (SBI)ZrIII-iBu and [(SBI)ZrIII]^+ AlR_4^\u2013, when (SBI)ZrMe_2 is allowed to react with HAl^(i)Bu_2, eliminating isobutane en route to the Zr(III) complex. Further studies concern interconversion reactions between these and other (SBI)Zr(III) complexes and reaction mechanisms involved in their formation.", "doi": "10.1021/ja403170u", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2013-07-24", "series_number": "29", "volume": "135", "issue": "29", "pages": "10710-10719" }, { "id": "authors:s3vrg-vc253", "collection": "authors", "collection_id": "s3vrg-vc253", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130923-085459949", "type": "article", "title": "Upgrading Light Hydrocarbons via Tandem Catalysis: A Dual Homogeneous Ta/Ir System for Alkane/Alkene Coupling", "author": [ { "family_name": "Leitch", "given_name": "David C.", "clpid": "Leitch-D-C" }, { "family_name": "Lam", "given_name": "Yan Choi", "orcid": "0000-0001-7809-4471", "clpid": "Lam-Yan-Choi" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Light alkanes and alkenes are abundant but are underutilized as energy carriers because of their high volatility and low energy density. A tandem catalytic approach for the coupling of alkanes and alkenes has been developed in order to upgrade these light hydrocarbons into heavier fuel molecules. This process involves alkane dehydrogenation by a pincer-ligated iridium complex and alkene dimerization by a Cp*TaCl_2(alkene) catalyst. These two homogeneous catalysts operate with up to 60/30 cooperative turnovers (Ir/Ta) in the dimerization of 1-hexene/n-heptane, giving C_(13)/C_(14) products in 40% yield. This dual system can also effect the catalytic dimerization of n-heptane (neohexene as the H_2 acceptor) with cooperative turnover numbers of 22/3 (Ir/Ta).", "doi": "10.1021/ja405191a", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2013-07-17", "series_number": "28", "volume": "135", "issue": "28", "pages": "10302-10305" }, { "id": "authors:mjja3-v7810", "collection": "authors", "collection_id": "mjja3-v7810", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130814-085742329", "type": "article", "title": "Alkyne Hydroamination and Trimerization with Titanium Bis(phenolate)pyridine Complexes: Evidence for Low-Valent Titanium Intermediates and Synthesis of an Ethylene Adduct of Titanium(II)", "author": [ { "family_name": "Tonks", "given_name": "Ian A.", "clpid": "Tonks-I-A" }, { "family_name": "Meier", "given_name": "Josef C.", "clpid": "Meier-J-C" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A class of titanium precatalysts of the type (ONO)TiX_2 (ONO = pyridine-2,6-bis(4,6-di-tert-butylphenolate); X = Bn, NMe_2) has been synthesized and crystallographically characterized. The (ONO)TiX_2 (X = Bn, NMe_2, X_2 = NPh) complexes are highly active precatalysts for the hydroamination of internal alkynes with primary arylamines and some alkylamines. A class of titanium imido/ligand adducts, (ONO)Ti(L)(NR) (L = HNMe_2, py; R = Ph, ^tBu), have also been synthesized and characterized and provide structural analogues to intermediates on the purported catalytic cycle. Furthermore, these complexes exhibit unusual redox behavior. (ONO)TiBn_2 (1) promotes the cyclotrimerization of electron-rich alkynes, likely via a catalytically active Ti^(II) species that is generated in situ from 1. Depending on reaction conditions, these Ti^(II) species are proposed to be generated through Ti benzylidene or imido intermediates. A formally Ti^(II) complex, (ONO)Ti^(II)(\u03b7^2-C_2H_4)(HNMe_2) (7), has been prepared and structurally characterized.", "doi": "10.1021/om400080g", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2013-06-24", "series_number": "12", "volume": "32", "issue": "12", "pages": "3451-3457" }, { "id": "authors:1c8ga-4fj11", "collection": "authors", "collection_id": "1c8ga-4fj11", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130808-105416699", "type": "article", "title": "Kinetics and Mechanism of Indene C\u2013H Bond Activation by [(COD)Ir(\u03bc_2-OH)]_2", "author": [ { "family_name": "Ahmed", "given_name": "Tonia S.", "clpid": "Ahmed-T-S" }, { "family_name": "Tonks", "given_name": "Ian A.", "clpid": "Tonks-I-A" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The hydroxy-bridged dimer [(COD)Ir(\u03bc_2-OH)]_2 (COD = 1,5-cyclooctadiene) cleanly cleaves C\u2013H bonds in indene and cyclopentadiene to produce (COD)Ir(\u03b7^3-indenyl) and (COD)Ir(\u03b7^5-C_(5)H_5), respectively. The kinetics of the formation of (COD)Ir(\u03b7^3-indenyl) are consistent with a mechanism that involves coordination of indene to [(COD)Ir(\u03bc_2-OH)]_2 followed by rate-determining C\u2013H activation from the iridium dimer\u2013indene unit. Transition-state analysis of the Ir and Rh hydroxy dimers indicates that the C\u2013H activation proceeds through a direct deprotonation of indene by the M\u2013OH unit rather than a stepwise oxidative addition/reductive elimination mechanism. The crystal structure of [(COD)Ir]_5(\u03bc_4-O)(\u03bc_3-O)(\u03bc_2-OH), a dehydration product of [(COD)Ir(\u03bc_2-OH)]_2, is presented.", "doi": "10.1021/om400230j", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2013-06-10", "series_number": "11", "volume": "32", "issue": "11", "pages": "3322-3326" }, { "id": "authors:w3wfm-4x405", "collection": "authors", "collection_id": "w3wfm-4x405", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130712-133515989", "type": "article", "title": "Group 4 Transition-Metal Complexes of an Aniline\u2013Carbene\u2013Phenol Ligand", "author": [ { "family_name": "Despagnet-Ayoub", "given_name": "Emmanuelle", "orcid": "0000-0002-9013-7574", "clpid": "Despagnet-Ayoub-E" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Attempts to install a tridentate aniline\u2013NHC\u2013phenol (NCO) ligand on titanium and zirconium led instead to complexes resulting from unexpected rearrangement pathways that illustrate common behavior in carbene\u2013early-transition-metal chemistry.", "doi": "10.1021/om4001567", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2013-05-27", "series_number": "10", "volume": "32", "issue": "10", "pages": "2934-2938" }, { "id": "authors:4mnaa-3b492", "collection": "authors", "collection_id": "4mnaa-3b492", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130507-074545359", "type": "article", "title": "Unexpected rearrangements in the synthesis of an\n unsymmetrical tridentate dianionic N-heterocyclic\n carbene", "author": [ { "family_name": "Despagnet-Ayoub", "given_name": "Emmanuelle", "orcid": "0000-0002-9013-7574", "clpid": "Despagnet-Ayoub-E" }, { "family_name": "Miqueu", "given_name": "Karinne", "clpid": "Miqueu-K" }, { "family_name": "Sotiropoulos", "given_name": "Jean-Marc", "clpid": "Sotiropoulos-J-M" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Starting from the same ethylenediamine species, three valuable carbene precursors were synthesized under differing conditions: a tridentate dianionic N-heterocyclic carbene bearing an aniline, a phenol and a central dihydroimidazolium salt, its benzimidazolium isomer by intramolecular rearrangement and a dicationic benzimidazolium-benzoxazolium salt by changing the Br\u00f8nsted acid from HCl to HBF_4. A DFT study was performed to understand the rearrangement pathway. The structure of a bis[(NCO)carbene] zirconium complex was determined.", "doi": "10.1039/c3sc22171g", "issn": "2041-6520", "publisher": "Royal Society of Chemistry", "publication": "Chemical Science", "publication_date": "2013-02-26", "series_number": "5", "volume": "4", "issue": "5", "pages": "2117-2121" }, { "id": "authors:49fac-wdc91", "collection": "authors", "collection_id": "49fac-wdc91", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130118-153026625", "type": "article", "title": "Synthesis of a Bis(thiophenolate)pyridine Ligand and Its Titanium, Zirconium, and Tantalum Complexes", "author": [ { "family_name": "Lenton", "given_name": "Taylor N.", "clpid": "Lenton-T-N" }, { "family_name": "VanderVelde", "given_name": "David G.", "orcid": "0000-0002-2907-0366", "clpid": "VanderVelde-D-G" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A precursor to a new tridentate LX_2 type ligand, bis(thiophenol)pyridine ((SNS)H_2 = (2-C_6H_4SH)_2-2,6-C_5H_3N), was prepared. Bis(thiophenolate)pyridine complexes of Ti, Zr, and Ta having dialkylamido coligands were synthesized and structurally characterized. The zirconium complex (SNS)Zr(NMe_2)_2 (4) displays C_2 symmetry in the solid state, unlike a related bis(phenolate)pyridine compound, C_s-symmetric (ONO)Ti(NMe_2)_2. This change is likely the result of strain about the sulfur atom in the six-membered chelate with longer metal\u2013sulfur and carbon\u2013sulfur bonds. Solid-state structures of tantalum complexes (SNS)Ta(NMe_2)_3 (5) and (SNS)TaCl(NEt_2)_2 (6) also display pronounced C_2 twisting of the SNS ligand. 1D and 2D NMR experiments show that 5 is fluxional, with rotation about the Ta\u2013N(amide) bonds occurring on the NMR time scale that interchange the equatorial amide methyl groups (\u0394G^\u2021_(393) = 25.0(3) kcal/mol). The fluxional behavior of 6 in solution was also studied by variable-temperature ^1H NMR. Observation of separate signals for the diastereotopic protons of the methylene unit of the diethylamide indicates that the complex remains locked on the NMR time scale in one diastereomeric conformation at temperatures below \u221250 \u00b0C, fast rotation about the equatorial amide Ta\u2013N bonds occurs at higher temperature (\u0394G^\u2021_(393) = 13.4(3) kcal/mol), and exchange of diastereomeric methylene protons occurs via inversion at Ta that interconverts antipodes (\u0394G^\u2021_(393) \u2248 14(1) kcal/mol).", "doi": "10.1021/om300789h", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2012-11-12", "series_number": "21", "volume": "31", "issue": "21", "pages": "7492-7499" }, { "id": "authors:bxfq4-jra89", "collection": "authors", "collection_id": "bxfq4-jra89", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121107-102235374", "type": "article", "title": "Activator-Free Olefin Oligomerization and Isomerization Reactions Catalyzed by an Air- and Water-Tolerant Wacker Oxidation Intermediate", "author": [ { "family_name": "Winston", "given_name": "Matthew S.", "clpid": "Winston-M-S" }, { "family_name": "Oblad", "given_name": "Paul F.", "clpid": "Oblad-P-F" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A bench-stable, hydroxy-bridged \u03b1-diimine-Pd dimer can self-activate to an olefin oligomerization and isomerization catalyst in the presence of substrate (see scheme). A cationic Pd-hydride is generated principally through a Wacker oxidation of olefin to ketone, and with C_(4+) olefins, lesser amounts of allylic C-H activation, \u03b2-H transfer, and release of diene products are observed.", "doi": "10.1002/anie.201206215", "issn": "1433-7851", "publisher": "Wiley", "publication": "Angewandte Chemie International Edition", "publication_date": "2012-09-24", "series_number": "39", "volume": "51", "issue": "39", "pages": "9822-9824" }, { "id": "authors:mk4s5-mq548", "collection": "authors", "collection_id": "mk4s5-mq548", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121114-105428991", "type": "article", "title": "Diverse C\u2212C Bond-Forming Reactions of Bis(carbene)platinum(II)\n Complexes", "author": [ { "family_name": "Klet", "given_name": "Rachel C.", "clpid": "Klet-R-C" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The platinum(0) complex Pt(PPh_3)_4 catalyzes coupling of the carbene ligands of (CO)_5Cr{C(OMe)(p-MeOC_6H_4)} (1). The stable bis(carbene)platinum(II) complexes Cl_2Pt{C(OMe)(Me)}_2 (3), Br_2Pt{C(OMe)(Me)}_2 (4), and Cl_2Pt{C(O^iPr)(Me)}_2 (5) can be induced to undergo C\u2013C coupling reactions by several means. Reduction of 3\u20135 to platinum(0) with cobaltocene results in formation of internal olefins, (E/Z)-2,3-dimethoxybut-2-ene (6) or (E/Z)-2,3-diisopropoxybut-2-ene (7). Reaction of 3\u20135 with PPh3 yields terminal olefins, 2,3-dimethoxybut-1-ene (13) or 2,3-diisopropoxybut-1-ene (15), along with Cl_2Pt(PPh_3)_2 (12) or Br_2Pt(PPh_3)_2 (14). In contrast, addition of pyridine to 3\u20135 does not effect C\u2013C coupling; instead, the acyl complexes cis-Cl(py)Pt(COMe){C(OMe)(Me)} (8), cis-Br(py)Pt(COMe){C(OMe)(Me)} (9), and cis-Cl(py)Pt(COMe){C(O^iPr)(Me)} (10) are obtained, with concomitant formation of alkyl halide. Possible mechanistic pathways for C\u2013C bond formation are discussed, as well as explanations for the different reactivities observed for pyridine and PPh_3.", "doi": "10.1021/om300733h", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2012-09-24", "series_number": "18", "volume": "31", "issue": "18", "pages": "6652-6657" }, { "id": "authors:9ghse-tc645", "collection": "authors", "collection_id": "9ghse-tc645", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120925-115241978", "type": "article", "title": "A Versatile Ligand Platform that Supports Lewis Acid Promoted Migratory Insertion", "author": [ { "family_name": "Hazari", "given_name": "Amaruka", "clpid": "Hazari-A" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A helping hand: Incorporation of Group\u20052 Lewis acids into a macrocycle appended to a phosphine ligand attached to a rhenium carbonyl complex promotes otherwise unfavorable transformations of coordinated CO (see scheme; M=Ca, Sr). These Lewis acids form relatively weak M-O bonds, thereby enabling release of organic products from the metal center.", "doi": "10.1002/anie.201203264", "issn": "1433-7851", "publisher": "Wiley", "publication": "Angewandte Chemie International Edition", "publication_date": "2012-08-13", "series_number": "33", "volume": "51", "issue": "33", "pages": "8268-8271" }, { "id": "authors:ptwdf-rkb39", "collection": "authors", "collection_id": "ptwdf-rkb39", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120824-141138297", "type": "article", "title": "Mechanistic Studies of Ethylene and \u03b1-Olefin Co-Oligomerization Catalyzed by Chromium\u2212PNP Complexes", "author": [ { "family_name": "Do", "given_name": "Loi H.", "clpid": "Do-Loi-H" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "To explore the possibility of producing a narrow distribution of mid- to long-chain hydrocarbons from\nethylene as a chemical feedstock, co-oligomerization of\nethylene and linear \u03b1-olefins (LAOs) was investigated, using\na previously reported chromium complex, [CrCl_3(PNP^(OMe))]\n(1, where PNP^(OMe) = N,N-bis(bis(o-methoxyphenyl)-\nphosphino)methylamine). Activation of 1 by treatment with\nmodified methylaluminoxane (MMAO) in the presence of\nethylene and 1-hexene afforded mostly C_6 and C_(10) alkene\nproducts. The identities of the C_(10) isomers, assigned by\ndetailed gas chromatographic and mass spectrometric analyses, strongly support a mechanism that involves five- and seven-membered metallacyclic intermediates comprised of ethylene and LAO units. Using 1-heptene as a mechanistic probe, it was established that 1-hexene formation from ethylene is competitive with formation of ethylene/LAO cotrimers and that cotrimers derived from one ethylene and two LAO molecules are also generated. Complex 1/MMAO is also capable of converting 1-hexene to C_(12) dimers and C_(18) trimers, albeit with poor efficiency. The mechanistic implications of these studies are discussed and\ncompared to previous reports of olefin cotrimerization.", "doi": "10.1021/om300492r", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2012-07-23", "series_number": "14", "volume": "31", "issue": "14", "pages": "5143-5149" }, { "id": "authors:hrsrc-0m027", "collection": "authors", "collection_id": "hrsrc-0m027", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120621-134405616", "type": "article", "title": "Highly regioirregular polypropylene from asymmetric group 4 anilide(pyridine)phenoxide complexes", "author": [ { "family_name": "Klet", "given_name": "Rachel C.", "clpid": "Klet-R-C" }, { "family_name": "VanderVelde", "given_name": "David G.", "orcid": "0000-0002-2907-0366", "clpid": "VanderVelde-D-G" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Group 4 complexes containing an anilide(pyridine)phenoxide ligand and activated with methylaluminoxane (MAO) catalyze the formation of highly regioirregular polypropylene.", "doi": "10.1039/C2CC32806B", "issn": "1359-7345", "publisher": "Royal Society of Chemistry", "publication": "Chemical Communications", "publication_date": "2012-07-07", "series_number": "53", "volume": "48", "issue": "53", "pages": "6657-6659" }, { "id": "authors:an5tf-kca87", "collection": "authors", "collection_id": "an5tf-kca87", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120813-093717652", "type": "article", "title": "Effects of a vanadium post-metallocene catalyst-induced polymer backbone inhomogeneity on UV oxidative degradation of the resulting polyethylene film", "author": [ { "family_name": "Atiqullah", "given_name": "M.", "clpid": "Atiqullah-M" }, { "family_name": "Winston", "given_name": "M. S.", "clpid": "Winston-M-S" }, { "family_name": "Bercaw", "given_name": "J. E.", "clpid": "Bercaw-J-E" }, { "family_name": "Hussain", "given_name": "I.", "clpid": "Hussain-I" }, { "family_name": "Fazal", "given_name": "A.", "clpid": "Fazal-A" }, { "family_name": "Al-Harthi", "given_name": "M. A.", "clpid": "Al-Harthi-M-A" }, { "family_name": "Emwas", "given_name": "A.-H. M.", "clpid": "Emwas-A-H-M" }, { "family_name": "Khan", "given_name": "M. J.", "clpid": "Khan-M-J" }, { "family_name": "Hossaen", "given_name": "A.", "clpid": "Hossaen-A" } ], "abstract": "A Group 5 post-metallocene precatalyst,(ONO)VCl(THF)_2 (ONO = a bis(phenolate)pyridine LX_2 pincer ligand), activated with modified methylaluminoxane(MMAO-3A) produced a linear ethylene homopolymer (nm-HomoPE) and an unusual inhomogeneous copolymer (nm-CopolyPE) with 1-hexene having very low backbone unsaturation. The nm-CopolyPE inhomogeneity was reflected in the distributions of short chain branches, 1-hexene composition, and methylene sequence length. The 1-hexene incorporation into the\npolyethylene backbone strongly depended on the molecular weight of the growing polymer chain. (ONO)VCl(THF)_2, because of site diversity and easier removal of a tertiary (vs. a secondary) hydrogen, produced a skewed short chain branching (SCB) profile, incorporating 1-hexene more efficiently in the low molecular weight region than in the high molecular weight region. The significant decrease in molecular weight by 1-hexene showed that the (ONO)VCl(THF)_2 catalytic sites were also highly responsive to chain-transfer directly to 1-hexene itself, producing vinyl and trans-vinylene termini. Subsequently, the effect of backbone inhomogeneity on the UV oxidative degradation of films made from both polyethylenes was investigated. The\nmajor functional group accumulated in the branched nm-CopolyPE film was carbonyl followed by carboxyl,\nthen vinyl/ester, whereas that in the linear nm-HomoPE film was carboxyl. However, (carbonyl, carboxyl,\nvinyl, and ester)_(nm-CopolyPE film) >> (carboxyl)_(nm-HomoPE film). The distributions of the tertiary \u2261 C-H sites and methylene sequence length in the branched nm-CopolyPE film enhanced abstraction of H, decomposition of\nhydroperoxide group ROOH, and generation of carbonyl compounds as compared with those in the linear\nnm-HomoPE film. This clearly establishes the role played by the backbone inhomogeneity. The effect of short chain branches and sequence length distributions on peak melting temperature T_(pm), and most probably lamellar thickness L_0, was modeled from a nanoscopic viewpoint. The accumulation of the above oxygenated functionalities and its effect on % crystallinity are explained considering polyethylene UV autooxidation mechanism, and Norrish I and Norrish II chain scissions.", "doi": "10.1016/j.polymdegradstab.2012.03.042", "issn": "0141-3910", "publisher": "Elsevier Ltd.", "publication": "Polymer Degradation and Stability", "publication_date": "2012-07", "series_number": "7", "volume": "97", "issue": "7", "pages": "1164-1177" }, { "id": "authors:6xnxw-s3c84", "collection": "authors", "collection_id": "6xnxw-s3c84", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120530-084227048", "type": "article", "title": "Groups 5 and 6 Terminal Hydrazido(2\u2212) Complexes: N_\u03b2 Substituent Effects on Ligand-to-Metal Charge-Transfer Energies and Oxidation States", "author": [ { "family_name": "Tonks", "given_name": "Ian A.", "clpid": "Tonks-I-A" }, { "family_name": "Durrell", "given_name": "Alec C.", "clpid": "Durrell-A-C" }, { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Brightly colored terminal hydrazido(2\u2212) (dme)MCl_3(NNR_2) (dme = 1,2-dimethoxyethane; M = Nb, Ta; R = alkyl, aryl) or (MeCN)WCl_4(NNR_2) complexes have been synthesized and characterized. Perturbing the electronic environment of the \u03b2 (NR_2) nitrogen affects the energy of the lowest-energy charge-transfer (CT) transition in these complexes. For group 5 complexes, increasing the energy of the N_\u03b2 lone pair decreases the ligand-to-metal CT (LMCT) energy, except for electron-rich niobium dialkylhydrazides, which pyramidalize N_\u03b2 in order to reduce the overlap between the Nb\u2550N\u03b1 \u03c0 bond and the N\u03b2 lone pair. For W complexes, increasing the energy of N_\u03b2 eventually leads to reduction from formally [W^(VI)\u2261N\u2013NR_2] with a hydrazido(2\u2212) ligand to [W^(IV)\u2550N\u2550NR_2] with a neutral 1,1-diazene ligand. The photophysical properties of these complexes highlight the potential redox noninnocence of hydrazido ligands, which could lead to ligand- and/or metal-based redox chemistry in early transition metal derivatives.", "doi": "10.1021/ja302275j", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2012-05-02", "series_number": "17", "volume": "134", "issue": "17", "pages": "7301-7304" }, { "id": "authors:peacn-at859", "collection": "authors", "collection_id": "peacn-at859", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120418-111611466", "type": "article", "title": "Zirconium and Titanium Propylene Polymerization Precatalysts Supported by a Fluxional C_2-Symmetric Bis(anilide)pyridine Ligand", "author": [ { "family_name": "Tonks", "given_name": "Ian A.", "clpid": "Tonks-I-A" }, { "family_name": "Tofan", "given_name": "Daniel", "clpid": "Tofan-D" }, { "family_name": "Weintrob", "given_name": "Edward C.", "clpid": "Weintrob-E-C" }, { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Titanium and zirconium complexes supported by a bis(anilide)pyridine ligand (NNN = pyridine-2,6-bis(N-mesitylanilide)) have been synthesized and crystallographically characterized. C_2-symmetric bis(dimethylamide) complexes were generated from aminolysis of M(NMe_2)_4 with the neutral, diprotonated NNN ligand or by salt metathesis of the dipotassium salt of NNN with M(NMe_2)_2Cl_2. In contrast to the case for previously reported pyridine bis(phenoxide) complexes, the ligand geometry of these complexes appears to be dictated by chelate ring strain rather than metal\u2013ligand \u03c0 bonding. The crystal structures of the five-coordinate dihalide complexes (NNN)MCl_2 (M = Ti, Zr) display a C_1-symmetric geometry with a stabilizing ipso interaction between the metal and the anilido ligand. Coordination of THF to (NNN)ZrCl_2 generates a six-coordinate C_2-symmetric complex. Facile antipode interconversion of the C_2 complexes, possibly via flat C_(2v) intermediates, has been investigated by variable-temperature ^1H NMR spectroscopy for (NNN)MX_2(THF)_n (M = Ti, Zr; X = NMe_2, Cl) and (NNN)Zr(CH_2Ph)_2. These complexes were tested as propylene polymerization precatalysts, with most complexes giving low to moderate activities (10^2\u201310^4 g/(mol h)) for the formation of stereoirregular polypropylene.", "doi": "10.1021/om201262h", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2012-03-12", "series_number": "5", "volume": "31", "issue": "5", "pages": "1965-1974" }, { "id": "authors:nm5dp-5q269", "collection": "authors", "collection_id": "nm5dp-5q269", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120124-091855514", "type": "article", "title": "Intra- and Intermolecular C\u2212H Activation by Bis(phenolate)pyridineiridium(III) Complexes", "author": [ { "family_name": "Fu", "given_name": "Ross", "clpid": "Fu-Ross" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" } ], "abstract": "A bis(phenolate)pyridine pincer ligand (henceforth abbreviated as ONO) has been employed to support a variety of iridium complexes in oxidation states I, III, and IV. Complexes (ONO)IrL_2Me (L = PPh_3, PEt_3) react with I_2 to cleave the Ir\u2013C bond and liberate MeI, apparently via a mechanism beginning with electron transfer to generate an intermediate Ir(IV) complex, which can be isolated and characterized for the case L = PEt_3. The PPh_3 complex is transformed in benzene at 65 \u00b0C to the corresponding phenyl complex, with loss of methane, and subsequently to a species resulting from metalation of a PPh_3 ligand. Labeling and kinetics studies indicate that PPh_3 is the initial site of C\u2013H activation, even though the first observed product is that resulting from intermolecular benzene activation. C\u2013H activation of acetonitrile has also been observed.", "doi": "10.1021/om201069k", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2011-12-26", "series_number": "24", "volume": "30", "issue": "24", "pages": "6751-6765" }, { "id": "authors:19zy9-dbc54", "collection": "authors", "collection_id": "19zy9-dbc54", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110912-113950538", "type": "article", "title": "Trialkylborane-Assisted CO_2 Reduction by Late Transition\n Metal Hydrides", "author": [ { "family_name": "Miller", "given_name": "Alexander J. M.", "clpid": "Miller-A-J-M" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Trialkylborane additives promote reduction of CO_2 to formate by bis(diphosphine) Ni(II) and Rh(III) hydride complexes. The late transition metal hydrides, which can be formed from dihydrogen, transfer hydride to CO_2 to give a formateborane adduct. The borane must be of appropriate Lewis acidity: weaker acids do not show significant hydride transfer enhancement, while stronger acids abstract hydride without CO_2 reduction. The mechanism likely involves a pre-equilibrium hydride transfer followed by formation of a stabilizing formateborane adduct.", "doi": "10.1021/om200364w", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2011-08-22", "series_number": "16", "volume": "30", "issue": "16", "pages": "4308-4314" }, { "id": "authors:j77by-q0259", "collection": "authors", "collection_id": "j77by-q0259", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110912-114655621", "type": "article", "title": "Large Kinetic Isotope Effects for the Protonolysis of Metal-Methyl Complexes Are Not Reliable Mechanistic Indicators", "author": [ { "family_name": "Scott", "given_name": "Valerie J.", "clpid": "Scott-V-J" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Earlier work on protonolyses of several palladium and platinum methyl complexes (with release of methane) had suggested the possibility that observation of an unusually large kinetic isotope effect, consistent with significant contributions from quantum mechanical tunneling, might be diagnostic of a mechanism involving direct protonation of the metal\u2013methyl bond, as opposed to one proceeding via a metal hydride intermediate. By extension of these measurements to a wider set of complexes, we find no support for the proposed correlation.", "doi": "10.1021/om200432b", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2011-08-22", "series_number": "16", "volume": "30", "issue": "16", "pages": "4374-4378" }, { "id": "authors:d5b23-7v378", "collection": "authors", "collection_id": "d5b23-7v378", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110824-090934345", "type": "article", "title": "Heterobimetallic Complexes of Rhenium and Zinc: Potential Catalysts for Homogeneous Syngas Conversion", "author": [ { "family_name": "West", "given_name": "Nathan M.", "clpid": "West-N-M" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "6-(Diphenylphosphino)-2,2\u2032-bipyridine (PNN) coordinates to rhenium carbonyls in both \u03ba^1(P) and \u03ba^2(N,N) modes; in the former, the free bpy moiety readily binds to zinc alkyls and halides. [Re(\u03ba^1(P)-PNN)(CO)_5][OTf] reacts with dialkylzinc reagents to form [Re(\u03ba^1(P)-PNN\u00b7ZnR)(CO)_4(\u03bc_(2-)C(O)R)][OTf] (R = Me, Et, Bn), in which an alkyl group has been transferred to a carbonyl carbon and the resulting monoalkyl Zn is bound both to the bpy nitrogens and the acyl oxygen. ZnCl_2 binds readily to the bpy group in Re(\u03ba^1(P)-PNN)(CO)_4Me, and the resulting adduct undergoes facile migratory insertion, assisted by the Lewis acidic pendent Zn, to yield Re(\u03ba^1(P)-PNN\u00b7ZnCl)(\u03bc_(2-)Cl)(CO)_3(\u03bc_(2-)C(O)Me), in which one of the chlorides occupies the sixth coordination site on Re. Migratory insertion is inhibited by THF or other ethers that can coordinate to ZnCl_2. Migratory insertion is also observed for Re(\u03ba1(P)-PNN)(CO)_4(CH_2Ph) but not for Re(\u03ba^1(P)-PNN)(CO)_4(CH_2OCH_3); coordination of the methoxy oxygen to Zn appears to block its ability to coordinate to the carbonyl oxygen and facilitate migratory insertion. Intramolecular Lewis acid promoted hydride transfer from [(dmpe)_2PtH][PF_6] to a carbonyl in [Re(\u03ba^1(P)-PNN)(CO)_5][OTf] results in formation of a Re\u2013formyl species; additional hydride transfer leads to a novel Re\u2013Zn-bonded product along with some formal dehyde.", "doi": "10.1021/om200051u", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2011-05-23", "series_number": "10", "volume": "30", "issue": "10", "pages": "2690-2700" }, { "id": "authors:44qw3-0kz41", "collection": "authors", "collection_id": "44qw3-0kz41", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110506-093035142", "type": "article", "title": "Homogeneous syngas conversion", "author": [ { "family_name": "West", "given_name": "Nathan M.", "clpid": "West-N-M" }, { "family_name": "Miller", "given_name": "Alexander J. M.", "clpid": "Miller-A-J-M" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Recent approaches to the homogeneous conversion of synthesis gas to organic chemicals and fuels are reviewed. Progress in this field is placed in the context of important industrially practiced transformations, such as the Fischer\u2013Tropsch process for conversion of synthesis gas to higher alkanes, as well as previous attempts to produce a viable homogeneous alternative. Approaches to homogeneous syngas conversion discussed in some detail include the reduction of transition metal carbonyl complexes by main group hydrides or transition metal hydrides; unusual routes to formyls including radical-based late transition metal chemistry; early metal and lanthanide reductive couplings; cluster chemistry; and Lewis acid-assisted transformations. Our current research combines a number of these concepts in an attempt to convert syngas selectively to multicarbon organic fragments.", "doi": "10.1016/j.ccr.2010.08.019", "issn": "0010-8545", "publisher": "Elsevier", "publication": "Coordination Chemistry Reviews", "publication_date": "2011-04", "series_number": "7-8", "volume": "255", "issue": "7-8", "pages": "881-898" }, { "id": "authors:2jgt9-v7628", "collection": "authors", "collection_id": "2jgt9-v7628", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110506-141702379", "type": "article", "title": "Cationic Alkylaluminum-Complexed Zirconocene Hydrides: NMR-Spectroscopic Identification, Crystallographic Structure\n Determination, and Interconversion with Other Zirconocene Cations", "author": [ { "family_name": "Baldwin", "given_name": "Steven M.", "clpid": "Baldwin-S-M" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Brintzinger", "given_name": "Hans H.", "clpid": "Brintzinger-H-H" } ], "abstract": "The ansa-zirconocene complex rac-Me_2Si(1-indenyl)_2ZrCl_2 ((SBI)ZrCl_2) reacts with diisobutylaluminum hydride and trityl tetrakis(perfluorophenyl)borate in hydrocarbon solutions to give the cation [(SBI)Zr(\u03bc-H)_3(Al^iBu_2)_2]^+, the identity of which is derived from NMR data and supported by a crystallographic structure determination. Analogous reactions proceed with many other zirconocene dichloride complexes. [(SBI)Zr(\u03bc-H)_3(Al^iBu2)_2]^+ reacts reversibly with ClAl^iBu_2 to give the dichloro-bridged cation [(SBI)Zr(\u03bc-Cl)_2Al^iBu_2]^+. Reaction with AlMe_3 first leads to mixed-alkyl species [(SBI)Zr(\u03bc-H)_3(AlMe_x^iBu_(2\u2212x))_2^]+ by exchange of alkyl groups between aluminum centers. At higher AlMe_3/Zr ratios, [(SBI)Zr(\u03bc-Me)_2AlMe_2]^+, a constituent of methylalumoxane-activated catalyst systems, is formed in an equilibrium, in which the hydride cation [(SBI)Zr(\u03bc-H)_3(AlR_2)_2]^+ strongly predominates at comparable HAl^iBu_2 and AlMe_3 concentrations, thus implicating the presence of this hydride cation in olefin polymerization catalyst systems.", "doi": "10.1021/ja1050428", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2011-02-16", "series_number": "6", "volume": "133", "issue": "6", "pages": "1805-1813" }, { "id": "authors:ypk2h-00s25", "collection": "authors", "collection_id": "ypk2h-00s25", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110105-145137929", "type": "article", "title": "A Novel Bis(phosphido)pyridine [PNP]^(2\u2212) Pincer Ligand and Its Potassium and Bis(dimethylamido)zirconium(IV) Complexes", "author": [ { "family_name": "Winston", "given_name": "Matthew S.", "clpid": "Winston-M-S" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A novel PNP bis(secondary phosphine)pyridine pincer ligand, 2,6-bis(2-(phenylphosphino)phenyl)pyridine, has been prepared in high yield, and the properties of the doubly deprotonated form as a ligand in K_4(PNP)_2(THF)_6 and (PNP)Zr(NMe_2)_2 have been investigated. The neutral PNP ligand has been isolated as a mixture of noninterconverting diastereomers, due to the presence of two chirogenic phosphorus atoms of the secondary phopshines, but coordination of the dianionic form to potassium and zirconium allows for isolation of a single diastereomer in near-quantitative yield. The structure of a bis(dimethylamido)zirconium(IV) derivative of the bis(phosphido)pyridine ligand and DFT calculations suggest that the phosphides do not \u03c0-bond to early transition metals, likely due to geometric strain and possibly orbital size mismatch between phosphorus and zirconium. As a result, the soft phosphides are prone to formation of insoluble oligomers with substantial bridging of the phosphido lone pairs to other zirconium centers.", "doi": "10.1021/om100775g", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2010-12-13", "series_number": "23", "volume": "29", "issue": "23", "pages": "6408-6416" }, { "id": "authors:5vvrb-0ek05", "collection": "authors", "collection_id": "5vvrb-0ek05", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20101206-102302404", "type": "article", "title": "Intramolecular C\u2212H Activation of a Bisphenolate(benzene)-Ligated Titanium Dibenzyl Complex. Competing Pathways Involving \u03b1-Hydrogen Abstraction and \u03c3-Bond Metathesis", "author": [ { "family_name": "Golisz", "given_name": "Suzanne R.", "clpid": "Golisz-S-R" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A titanium dibenzyl complex featuring a ligand with two phenolates linked by a benzene-1,3-diyl group was found to undergo thermal decomposition to give toluene and a cyclometalated dimeric complex. The thermal decomposition followed first-order kinetics and was studied at a number of temperatures to determine the activation parameters (\u0394H\u2021 = 27.2(5) kcal/mol and \u0394S\u2021 = \u22126.2(14) cal/(mol K)). Deuterated isotopologues were synthesized to measure the kinetic isotope effects. The complexes with deuterium in the benzyl methylene positions decomposed more slowly than the protio analogues. Isotopologues of toluene with multiple deuteration positions were observed in the product mixtures. These data are consistent with competing \u03b1-abstraction and \u03c3-bond metathesis.", "doi": "10.1021/om100253u", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2010-11-08", "series_number": "21", "volume": "29", "issue": "21", "pages": "5026-5032" }, { "id": "authors:s3v9q-11q86", "collection": "authors", "collection_id": "s3v9q-11q86", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20101103-110627454", "type": "article", "title": "Homogeneous CO Hydrogenation: Ligand Effects on the Lewis Acid-Assisted Reductive Coupling of Carbon Monoxide", "author": [ { "family_name": "Miller", "given_name": "Alexander J. M.", "clpid": "Miller-A-J-M" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Structure-function studies on the role of pendent Lewis acids in the reductive coupling of CO are reported. Cationic rhenium carbonyl complexes containing zero, one, or two phosphinoborane ligands (Ph_2P(CH_2)_nB(C_8H_(14)), n=1-3) react with the nucleophilic hydride [HPt(dmpe)_2]^+\nto reduce [M-CO]^+ to M-CHO; this step is relatively insensitive to the Lewis acid, as both pendent\n(internal) and external boranes of appropriate acid strength can be used. In contrast, whether a\nsecond hydride transfer and C-C bond forming steps occur depends strongly on the number of carbon atoms between P and B in the phosphinoborane ligands, as well as the number of pendent acids in the complex: shorter linker chain lengths favor such reductive coupling, whereas longer\nchains and external boranes are ineffective. A number of different species containing partially reduced CO groups, whose exact structures vary considerably with the nature and\nnumber of phosphinoborane ligands, have been crystallographically characterized. The reaction of [(Ph -2P(CH_2)_2B(C_8H_(14)))_2Re(CO)4]^+ with [HPt(dmpe)_2]^+\ntakes place via a \"hydride shuttle\" mechanism, in which hydride is transferred from Pt to a pendent borane and thence to CO, rather than by direct hydride attack at CO. Addition of a second hydride in C_6D_5Cl at -40 \u00baC affords an unusual anionic bis(carbene) complex, which converts to a C-C bonded product on warming. These results support a working model for Lewis acid-assisted reductive coupling of CO, in which B (pendent or external) shuttles hydride from Pt to coordinated CO, followed by formation of an\nintramolecular B-O bond, which facilitates reductive coupling.", "doi": "10.1021/om100638d", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2010-10-25", "series_number": "20", "volume": "29", "issue": "20", "pages": "4499-4516" }, { "id": "authors:bc340-31j38", "collection": "authors", "collection_id": "bc340-31j38", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20101101-101358476", "type": "article", "title": "Cationic Alkylaluminum-Complexed Zirconocene Hydrides as Participants in Olefin Polymerization Catalysis", "author": [ { "family_name": "Baldwin", "given_name": "Steven M.", "clpid": "Baldwin-S-M" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Brintzinger", "given_name": "Hans H.", "clpid": "Brintzinger-H-H" } ], "abstract": "The alkylaluminum-complexed zirconocene trihydride\ncation [(SBI)Zr(\u03bc-H)_3(AliBu_2)_2]^+, which is obtained by reaction of (SBI)ZrCl_2 with [Ph_3C][B(C_6F_5)_4] and excess HAl^iBu_2 in toluene solution, catalyzes the formation of isotactic polypropene when exposed to propene at -30 \u00b0C. This cation remains the sole observable species in catalyst systems free of AlMe compounds. In the presence of AlMe_3, however, exposure to propene causes the trihydride cation to be completely converted, under concurrent consumption of all hydride species by propene hydroalumination, to the doubly Me-bridged cation [(SBI)Zr(\u03bc-Me)_2AlMe_2]^+. The latter then becomes the resting state for further propene polymerization, which produces, by chain transfer to Al, mainly AlMe_2-capped isotactic polypropene.", "doi": "10.1021/ja105040r", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2010-10-13", "series_number": "40", "volume": "132", "issue": "40", "pages": "13969-13971" }, { "id": "authors:tq7kw-0t887", "collection": "authors", "collection_id": "tq7kw-0t887", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20101021-145837882", "type": "article", "title": "Protonolysis of Platinum(II) and Palladium(II) Methyl Complexes: A Combined Experimental and Theoretical Investigation", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Chen", "given_name": "George S.", "clpid": "Chen-George-S" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Lin", "given_name": "Bo-Lin", "clpid": "Lin-Bo-Lin" } ], "abstract": "The protonolysis of platinum(II) and palladium(II) methyl complexes has been investigated by both experiment and computation. Previously the protonolysis of (COD)Pt^(II)(CH_3)_2 by CF_3COOY or (dppe)Pd^(II)(CH_3)_2 by CF_3CY_2OY (Y = H, D) was found to be accompanied by abnormally large and highly temperature-dependent kinetic isotope effects (KIEs), suggesting the involvement of tunneling. Here we find normal KIEs and no evidence of tunneling for protonolysis of (tmeda)Pt^(II)(CH_3)Cl by CF_3COOY (Y = H, D). Density functional theory (DFT) calculations indicate that protonation at the metal center followed by reductive coupling to the methane \u03c3 adduct (stepwise pathway) is favored for Pt complexes with good electron donor ligands, whereas direct protonation of the M\u2212CH_3 bond to generate the methane \u03c3 adduct (concerted pathway) is favored for Pt with electron-withdrawing ligands as well as for Pd. We suggest that KIE behavior consistent with tunneling may be an experimental indicator of the concerted pathway.", "doi": "10.1021/om100655w", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2010-10-11", "series_number": "19", "volume": "29", "issue": "19", "pages": "4354-4359" }, { "id": "authors:mm7n6-k4s79", "collection": "authors", "collection_id": "mm7n6-k4s79", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20101028-110659972", "type": "article", "title": "Mechanism of Reductive Elimination of Methyl Iodide from a Novel Gold(III)\u2212Monomethyl Complex", "author": [ { "family_name": "Scott", "given_name": "Valerie J.", "clpid": "Scott-V-J" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Oxidation of (Idipp)AuMe (Idipp = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with I_2 gives a monomethyl Au(III) complex, (Idipp)AuI_2Me, which decomposes cleanly to MeI and (Idipp)AuI. Kinetics experiments show that this transformation occurs primarily via three-coordinate, cationic [(Idipp)AuIMe]^+, which undergoes intramolecular reductive elimination rather than nucleophilic attack by external I^\u2212.", "doi": "10.1021/om1006566", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2010-09-27", "series_number": "18", "volume": "29", "issue": "18", "pages": "4090-4096" }, { "id": "authors:f23by-4p724", "collection": "authors", "collection_id": "f23by-4p724", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100604-110437467", "type": "article", "title": "(dme)MCl_3(NNPh_2) (dme= dimethoxyethane; M= Nb, Ta): A Versatile Synthon for [Ta\u2550NNPh_2] Hydrazido(2-) Complexes", "author": [ { "family_name": "Tonks", "given_name": "Ian A.", "clpid": "Tonks-I-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Complexes (dme)TaCl_3(NNPh_2) (1) and (dme)NbCl_3(NNPh_2) (2) (dme =1,2-dimethoxyethane) were synthesized from MCl5 and diphenylhydrazine via a Lewis-acid assisted dehydrohalogenation reaction. Monomeric 1 has been characterized by X-ray, IR, UV\u2212vis, ^(1)H NMR, and ^(13)C NMR spectroscopy and contains a \u03ba^(1)-bound hydrazido(2-) moiety. Unlike the corresponding imido derivatives, 1 is dark blue because of an LMCT that has been lowered in energy as a result of an N_(\u03b1)\u2212N_(\u03b2) antibonding interaction that raises the highest occupied molecular orbital (HOMO). Reaction of 1 with a variety of neutral, mono- and dianionic ligands generates the corresponding ligated complexes retaining the \u03ba^(1)-bound [Ta\u2212NNPh_2] moiety.", "doi": "10.1021/ic1004193", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2010-05-17", "series_number": "10", "volume": "49", "issue": "10", "pages": "4648-4656" }, { "id": "authors:q3m5b-fec90", "collection": "authors", "collection_id": "q3m5b-fec90", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100527-094834306", "type": "article", "title": "NMR Chemical Shifts of Trace Impurities: Common\n Laboratory Solvents, Organics, and Gases in Deuterated\n Solvents Relevant to the Organometallic\n Chemist", "author": [ { "family_name": "Fulmer", "given_name": "Gregory R.", "clpid": "Fulmer-G-R" }, { "family_name": "Miller", "given_name": "Alexander J. M.", "clpid": "Miller-A-J-M" }, { "family_name": "Sherden", "given_name": "Nathaniel H.", "clpid": "Sherden-N-H" }, { "family_name": "Gottlieb", "given_name": "Hugo E.", "clpid": "Gottlieb-H-E" }, { "family_name": "Nudelman", "given_name": "Abraham", "clpid": "Nudelman-A" }, { "family_name": "Stoltz", "given_name": "Brian M.", "orcid": "0000-0001-9837-1528", "clpid": "Stoltz-B-M" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Goldberg", "given_name": "Karen I.", "clpid": "Goldberg-K-I" } ], "abstract": "Tables of ^1H and ^(13)C NMR chemical shifts have been compiled for common organic compounds often used as reagents or found as products or contaminants in deuterated organic solvents. Building upon the work of Gottlieb, Kotlyar, and Nudelman in the Journal of Organic Chemistry, signals for common impurities are now reported in additional NMR solvents (tetrahydrofuran-d_8, toluene-d_8, dichloromethane-d_2, chlorobenzene-d_5, and 2,2,2-trifluoroethanol-d_3) which are frequently used in organometallic laboratories. Chemical shifts for other organics which are often used as reagents or internal standards or are found as products in organometallic chemistry are also reported for all the listed solvents.", "doi": "10.1021/om100106e", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2010-05-10", "series_number": "9", "volume": "29", "issue": "9", "pages": "2176-2179" }, { "id": "authors:zj3x4-axh28", "collection": "authors", "collection_id": "zj3x4-axh28", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100520-112818210", "type": "article", "title": "Thermodynamic Studies of [H_(2)Rh(diphosphine)_2]^+ and [HRh(diphosphine)_(2)(CH_(3)CN)]^(2+) Complexes in Acetonitrile", "author": [ { "family_name": "Wilson", "given_name": "Aaron D.", "clpid": "Wilson-A-D" }, { "family_name": "Miller", "given_name": "Alexander J. M.", "clpid": "Miller-A-J-M" }, { "family_name": "DuBois", "given_name": "Daniel L.", "clpid": "DuBois-D-L" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Thermodynamic studies of a series of [H_(2)Rh(PP)_2]^+ and [HRh(PP)_(2)(CH_(3)CN)]^(2+) complexes have been carried out in acetonitrile. Seven different diphosphine (PP) ligands were selected to allow variation of the electronic properties of the ligand substituents, the cone angles, and the natural bite angles (NBAs). Oxidative addition of H_2 to [Rh(PP)_2]^+ complexes is favored by diphosphine ligands with large NBAs, small cone angles, and electron donating substituents, with the NBA being the dominant factor. Large pK_a values for [HRh(PP)_(2)(CH_(3)CN)]^(2+) complexes are favored by small ligand cone angles, small NBAs, and electron donating substituents with the cone angles playing a major role. The hydride donor abilities of [H_(2)Rh(PP)_2]^+ complexes increase as the NBAs decrease, the cone angles decrease, and the electron donor abilities of the substituents increase. These results indicate that if solvent coordination is involved in hydride transfer or proton transfer reactions, the observed trends can be understood in terms of a combination of two different steric effects, NBAs and cone angles, and electron-donor effects of the ligand substituents.", "doi": "10.1021/ic100117y", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2010-04-19", "series_number": "8", "volume": "49", "issue": "8", "pages": "3918-3926" }, { "id": "authors:s7ceh-hsh31", "collection": "authors", "collection_id": "s7ceh-hsh31", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100408-095738244", "type": "article", "title": "Homogeneous CO Hydrogenation: Dihydrogen Activation Involves a Frustrated Lewis Pair Instead of a Platinum Complex", "author": [ { "family_name": "Miller", "given_name": "Alexander J. M.", "clpid": "Miller-A-J-M" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "During a search for conditions appropriate for Pt-catalyzed CO reduction using dihydrogen directly, metal-free conditions were discovered instead. A bulky, strong phosphazene base forms a \"frustrated\" Lewis pair (FLP) with a trialkylborane in the secondary coordination sphere of a rhenium carbonyl. Treatment of the FLP with dihydrogen cleanly affords multiple hydride transfers and C\u2212C bond formation.", "doi": "10.1021/ja100574n", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2010-03-17", "series_number": "10", "volume": "132", "issue": "10", "pages": "3301-3303" }, { "id": "authors:j1wgs-yft04", "collection": "authors", "collection_id": "j1wgs-yft04", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100308-111005616", "type": "article", "title": "Oxidation of Organometallic Platinum and Palladium Complexes Obtained from C\u2212H Activation", "author": [ { "family_name": "Oblad", "given_name": "Paul F.", "clpid": "Oblad-P-F" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Hazari", "given_name": "Nilay", "clpid": "Hazari-N" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" } ], "abstract": "\u03b7^3-Cyclohexenyl and -indenyl Pt(II) and Pd(II) diimine complexes, which are generated via C\u2212H activation of cyclohexene and indene by Pt and Pd hydroxy dimers, are selectively oxidized by Br_2, Na_2PtCl_6, and CuCl_2 to give halogenated organic products along with well-defined Pd(II) and Pt(II) species.", "doi": "10.1021/om900678z", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2010-02-22", "series_number": "4", "volume": "29", "issue": "4", "pages": "789-794" }, { "id": "authors:ny03t-byq66", "collection": "authors", "collection_id": "ny03t-byq66", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100305-091958620", "type": "article", "title": "Electronic Structures of Pd^(II) Dimers", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Durrell", "given_name": "Alec C.", "clpid": "Durrell-A-C" }, { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" }, { "family_name": "Green", "given_name": "Jennifer C.", "clpid": "Green-J-C" }, { "family_name": "Hazari", "given_name": "Nilay", "clpid": "Hazari-N" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Winkler", "given_name": "Jay R.", "orcid": "0000-0002-4453-9716", "clpid": "Winkler-J-R" } ], "abstract": "The Pd^(II) dimers [(2-phenylpyridine)Pd(\u03bc-X)]_2 and [(2-p-tolylpyridine)Pd(\u03bc-X)]_2 (X = OAc or TFA) do not exhibit the expected planar geometry (of approximate D_(2h) symmetry) but instead resemble an open \"clamshell\" in which the acetate ligands are perpendicular to the plane containing the Pd atoms and 2-arylpyridine ligands, with the Pd atoms brought quite close to one another (approximate distance 2.85 \u00c5). The molecules adopt this unusual geometry in part because of a d^8\u2212d^8 bonding interaction between the two Pd centers. The Pd\u2212Pd dimers exhibit two successive one-electron oxidations: Pd^(II)\u2212Pd^(II) to Pd^(II)\u2212Pd^(III) to Pd^(III)\u2212Pd^(III). Photophysical measurements reveal clear differences in the UV\u2212visible and low-temperature fluorescence spectra between the clamshell dimers and related planar dimeric [(2-phenylpyridine)Pd(\u03bc-Cl)]_2 and monomeric [(2-phenylpyridine)Pd(en)][Cl] (en = ethylenediamine) complexes that do not have any close Pd\u2212Pd contacts. Density functional theory and atoms in molecules analyses confirm the presence of a Pd\u2212Pd bonding interaction in [(2-phenylpyridine)Pd(\u03bc-X)]_2 and show that the highest occupied molecular orbital is a d_(z2) \u03c3* Pd\u2212Pd antibonding orbital, while the lowest unoccupied molecular orbital and close-lying empty orbitals are mainly located on the 2-phenylpyridine rings. Computational analyses of other Pd^(II)\u2212Pd^(II) dimers that have short Pd\u2212Pd distances yield an orbital ordering similar to that of [(2-phenylpyridine)Pd(\u03bc-X)]_2, but quite different from that found for d^8\u2212d^8 dimers of Rh, Ir, and Pt. This difference in orbital ordering arises because of the unusually large energy gap between the 4d and 5p orbitals in Pd and may explain why Pd d^8\u2212d^8 dimers do not exhibit the distinctive photophysical properties of related Rh, Ir, and Pt species.", "doi": "10.1021/ic902189g", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2010-02-15", "series_number": "4", "volume": "49", "issue": "4", "pages": "1801-1810" }, { "id": "authors:w8k9b-6t606", "collection": "authors", "collection_id": "w8k9b-6t606", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100128-135110571", "type": "article", "title": "Iridium(I) and Iridium(III) Complexes Supported by a Diphenolate Imidazolyl-Carbene Ligand", "author": [ { "family_name": "Weinberg", "given_name": "David R.", "clpid": "Weinberg-D-R" }, { "family_name": "Hazari", "given_name": "Nilay", "clpid": "Hazari-N" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Deprotonation of 1,3-di(2-hydroxy-5-tert-butylphenyl)imidazolium chloride (1a) followed by reaction with chloro-1,5-cyclooctadiene Ir(I) dimer affords the anionic Ir(I) complex [K][{OCO}Ir(cod)] (2: OCO = 1,3-di(2-hydroxy-5-tert-butylphenyl)imidazolyl; cod = 1,5-cyclooctadiene), the first Ir complex stabilized by a diphenolate imidazolyl-carbene ligand. In the solid state 2 exhibits square-planar geometry, with only one of the phenoxides bound to the metal center. Oxidation of 2 with 2 equiv of [FeCp_2][PF_6] generates the Ir(III) complex [{OCO}Ir(cod)(MeCN)][PF_6] (3). Reaction of 3 with H_2 results in the liberation of cyclooctane and a species capable of catalyzing the hydrogenation of cyclohexene to cyclohexane. Displacement of cyclooctadiene from 3 can be achieved by heating in acetonitrile to form [{OCO}Ir(MeCN)3][PF_6] (4) or by reaction with either PMe_3 or PCy_3 to generate [{OCO}Ir(PMe_3)_3][PF_6] (5) or [{OCO}Ir(PCy_3)_2(MeCN)][PF_6] (6), respectively. 6 reacts with CO in acetonitrile to give an equilibrium mixture of 6 and [{OCO}Ir(PCy_3)_2(CO)][PF_6] (7) and with chloride to generate [{OCO}Ir(PCy_3)_(2)Cl] (8). The solid-state structure of 8 shows that the diphenolate imidazolyl-carbene ligand is distorted from planarity; DFT calculations suggest this is due to an antibonding interaction between the phenolates and the metal center in the highest occupied molecular orbital (HOMO) of the complex. 8 undergoes two successive reversible one-electron oxidations in CH_(2)Cl_2 at \u22120.22 and at 0.58 V (vs ferrocene/ferrocenium); EPR spectra, mass spectroscopy, and DFT calculations suggest that the product of the first oxidation is [{OCO}Ir(PCy_3)_(2)Cl]+ (8+), with the unpaired electron occupying a molecular orbital that is delocalized over both the metal center and the diphenolate imidazolyl-carbene ligand.", "doi": "10.1021/om900803r", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2010-01-11", "series_number": "1", "volume": "29", "issue": "1", "pages": "89-100" }, { "id": "authors:342hm-jjs39", "collection": "authors", "collection_id": "342hm-jjs39", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100316-085446199", "type": "article", "title": "Dehydrogenation of amine\u2013boranes with a frustrated Lewis pair", "author": [ { "family_name": "Miller", "given_name": "Alexander J. M.", "clpid": "Miller-A-J-M" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Bulky tertiary phosphine/borane Lewis pairs P^tBu_3/B(C_6F_5)_3 react with amine\u2013boranes to afford dehydrocoupling products and phosphonium borohydride salts", "doi": "10.1039/b925659h", "issn": "1359-7345", "publisher": "Royal Society of Chemistry", "publication": "Chemical Communications", "publication_date": "2010", "series_number": "10", "volume": "46", "issue": "10", "pages": "1709-1711" }, { "id": "authors:c89c0-ep204", "collection": "authors", "collection_id": "c89c0-ep204", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091210-110907814", "type": "article", "title": "Synthesis of Early Transition Metal Bisphenolate Complexes and Their Use as Olefin Polymerization Catalysts", "author": [ { "family_name": "Golisz", "given_name": "Suzanne R.", "clpid": "Golisz-S-R" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Bisphenolate ligands with pyridine- and benzene-diyl linkers have been synthesized and metalated with group 4 and 5 transition metals. The solid-state structures of some of the group 4 complexes have been solved. The titanium, zirconium, hafnium, and vanadium complexes were tested for propylene polymerization and ethylene/1-octene copolymerization activities with methylaluminoxane as cocatalyst. The vanadium(III) precatalyst is the most active for propylene polymerization and shows the highest 1-octene incorporation for ethylene/1-octene copolymerization. The zirconium(IV) precatalyst was the most active for propylene polymerization of the group 4 precatalysts. Titanium(IV) and zirconium(IV) precatalysts with pyridine-diyl linkers provided mixtures of isotactic and atactic polypropylene while titanium(IV) precatalysts with benzene-diyl linkers gave atactic polypropylene only. The hafnium(IV) precatalyst with a pyridine-diyl linker generated moderately isotactic polypropylene.", "doi": "10.1021/ma901659q", "issn": "0024-9297", "publisher": "American Chemical Society", "publication": "Macromolecules", "publication_date": "2009-11-24", "series_number": "22", "volume": "42", "issue": "22", "pages": "8751-8762" }, { "id": "authors:cq3xg-eck47", "collection": "authors", "collection_id": "cq3xg-eck47", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091112-091620649", "type": "article", "title": "Activation of the C\u2212N Bond in Nitromethane by Palladium \u03b1-Diimine Complexes", "author": [ { "family_name": "Golisz", "given_name": "Suzanne R.", "clpid": "Golisz-S-R" }, { "family_name": "Hazari", "given_name": "Nilay", "clpid": "Hazari-N" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The reaction of glyoxal-derived \u03b1-diimines with palladium acetates in nitromethane leads to cleavage of the C\u2212N bond in nitromethane, to give palladium nitro complexes in which the \u03b1-diimine ligand has been methylated.", "doi": "10.1021/jo901635g", "issn": "0022-3263", "publisher": "American Chemical Society", "publication": "Journal of Organic Chemistry", "publication_date": "2009-11-06", "series_number": "21", "volume": "74", "issue": "21", "pages": "8441-8443" }, { "id": "authors:3p3wb-kdz13", "collection": "authors", "collection_id": "3p3wb-kdz13", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091130-142516834", "type": "article", "title": "Transformations of Group 7 Carbonyl Complexes: Possible Intermediates in a Homogeneous Syngas Conversion Scheme", "author": [ { "family_name": "Elowe", "given_name": "Paul R.", "clpid": "Elowe-P-R" }, { "family_name": "West", "given_name": "Nathan M.", "clpid": "West-N-M" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A variety of C\u2212H and C\u2212C bond forming reactions of group 7 carbonyl complexes have been studied as potential steps in a homogeneously catalyzed conversion of syngas to C_(2+) compounds. The metal formyl complexes M(CO)_3(PPh_3)_2(CHO) (M = Mn, Re) are substantially stabilized by coordination of boranes BX_3 (X = F, C_6F_5) in the form of novel boroxycarbene complexes M(CO)_3(PPh_3)_2(CHOBX_3), but these boron-stabilized carbenes do not react with hydride sources to undergo further reduction to metal alkyls. The related manganese methoxycarbene cations [Mn(CO)_(5\u2212x)(PPh_3)_x(CHOMe)]+ (x = 1 or 2), obtained by methylation of the formyls, do react with hydrides to form methoxymethyl complexes, which undergo further migratory insertion under an atmosphere of CO. The resulting acyls, cis- and trans-Mn(PPh_3)(CO)_4(C(O)CH_2OMe), can be alkylated to form the cationic carbene complex [Mn(PPh_3)(CO)_4(C(OR)CH_2OMe)]^+, which undergoes a 1,2 hydride shift to form 1,2-dialkoxyethylene, which is displaced from the metal, releasing triflate or diethyl ether adducts of [Mn(PPh_3)(CO)_4]^+. The acyl can also be protonated with HOTf to form a hydroxycarbene complex, which rearranges to Mn(PPh_3)(CO)_4(CH_2COOMe) and is protonolyzed to yield methyl acetate and [Mn(PPh_3)(CO)_4]^+; addition of L (L = PPh_3, CO) to the manganese cation regenerates [Mn(PPh_3)(CO)_4(L)]^+. Since the original formyl complex can be obtained by the reaction of [Mn(PPh_3)(CO)_5]^+ with [PtH(dmpe)_2]^+, which in turn can be generated from H_2, this set of transformations amounts to a stoichiometric cycle for selectively converting H_2 and CO into a C_2 compound under mild conditions.", "doi": "10.1021/om900804j", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2009-10-12", "series_number": "21", "volume": "28", "issue": "21", "pages": "6218-6227" }, { "id": "authors:q28qa-05m02", "collection": "authors", "collection_id": "q28qa-05m02", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091012-110516923", "type": "article", "title": "Activation of a C\u2212H Bond in Indene by [(COD)Rh(\u03bc_2-OH)]_2", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Hazari", "given_name": "Nilay", "clpid": "Hazari-N" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" } ], "abstract": "The air- and water-tolerant hydroxy-bridged rhodium dimer [(COD)Rh(\u03bc_2-OH)]_2 cleanly activates the aliphatic C\u2212H bond in indene to generate [(COD)Rh(\u03b7^3-indenyl)]. The mechanism involves direct coordination of indene to the dimer followed by rate-determining C\u2212H bond cleavage, in contrast to the previously reported analogous reactions of [(diimine)M(\u03bc_2-OH)]_2^(2+) (M = Pd, Pt), for which the dimer must be cleaved before rate-determining displacement of solvent by indene. Another difference is observed in the reactions with indene in the presence of acid: the Rh system generates a stable \u03b7^6-indene 18-electron cation, [(COD)Rh(\u03b7^6-indene)]+, that is not available for Pd and Pt, which instead form the \u03b7^3-indenyl C\u2212H activation products. The crystal structure of [(COD)Rh(\u03b7^6-indene)] is reported.", "doi": "10.1021/om9004498", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2009-09-28", "series_number": "18", "volume": "28", "issue": "18", "pages": "5489-5492" }, { "id": "authors:e9a5p-5f420", "collection": "authors", "collection_id": "e9a5p-5f420", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090911-153559302", "type": "article", "title": "Selective Oxidation of sp^3 C-H Bonds in Water Catalyzed by a Glycinate-Platinum(II) Complex", "author": [ { "family_name": "Chen", "given_name": "George S.", "clpid": "Chen-George-S" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "In aqueous solution, [Pt^(II)(glycinato)Cl_2]^\u2212 catalyzes oxidation by [Pt^(IV)Cl_6]^(2\u2212) of the methyl group of p-toluenesulfonate to the corresponding alcohol and aldehyde, with no further oxidation to the carboxylic acid. Both rate and selectivity are improved in comparison to the original Shilov system that employs [Pt^(II)Cl_n(H_2O)_(4\u2212n)]^(2\u2212n) as the catalyst.", "doi": "10.1021/om900267w", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2009-09-14", "series_number": "17", "volume": "28", "issue": "17", "pages": "4899-4901" }, { "id": "authors:cgw1e-t9463", "collection": "authors", "collection_id": "cgw1e-t9463", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090911-153559461", "type": "article", "title": "Robotic Lepidoptery: Structural Characterization of (mostly) Unexpected Palladium Complexes Obtained from High-Throughput Catalyst Screening", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Golisz", "given_name": "Suzanne R.", "clpid": "Golisz-S-R" }, { "family_name": "Hazari", "given_name": "Nilay", "clpid": "Hazari-N" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Schofer", "given_name": "Susan J.", "clpid": "Schofer-S-J" }, { "family_name": "Virgil", "given_name": "Scott", "orcid": "0000-0001-8586-5641", "clpid": "Virgil-S-C" } ], "abstract": "In the course of a high-throughput search for optimal combinations of bidentate ligands with Pd(II) carboxylates to generate oxidation catalysts, we obtained and crystallographically characterized a number of crystalline products. While some combinations afforded the anticipated (L-L)Pd(OC(O)R)_2 structures (L-L = bipyridine, tmeda; R = CH_3, CF_3), many gave unusual oligometallic complexes resulting from reactions such as C\u2212H activation (L-L = sparteine), P\u2212C bond cleavage (L-L = 1,2-bis(diphenylphosphino)ethane, and C\u2212C bond formation between solvent (acetone) and ligand (L-L = 1,4-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene). These findings illustrate potential pitfalls of screening procedures based on assuming uniform, in situ catalyst self-assembly.", "doi": "10.1021/om900240a", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2009-09-14", "series_number": "17", "volume": "28", "issue": "17", "pages": "5017-5024" }, { "id": "authors:67mt7-qy496", "collection": "authors", "collection_id": "67mt7-qy496", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090817-144813701", "type": "article", "title": "Competitive Benzene C\u2212H Bond Activation versus Olefin Insertion in a (Monomethyl)palladium(II) \u03b2-Diketiminate Complex", "author": [ { "family_name": "Lin", "given_name": "Bo-Lin", "clpid": "Lin-Bo-Lin" }, { "family_name": "Bhattacharyya", "given_name": "Koyel X.", "clpid": "Bhattacharyya-K-X" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The monomethylpalladium(II) complex (COD)Pd(CH_3)Cl (COD = 1,5-cyclooctadiene) is found to undergo both benzene C\u2212H activation and migratory insertion of olefin, with the former faster than the latter, at room temperature in the presence of an anionic \u03b2-diketiminate ligand, to yield \u03b7^3-(6-R-cyclooctenyl)palladium(II) \u03b2-diketiminate (R = methyl or phenyl). The reaction is proposed to take place via the formation of a (monomethyl)palladium(II) \u03b2-diketiminate with COD as the fourth ligand, followed by competitive benzene C\u2212H activation and migratory insertion of olefin. The proposed mechanism is supported by density functional theory calculations upon a simplified model system.", "doi": "10.1021/om900171d", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2009-08-10", "series_number": "15", "volume": "28", "issue": "15", "pages": "4400-4405" }, { "id": "authors:bstwy-dy965", "collection": "authors", "collection_id": "bstwy-dy965", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090808-142500065", "type": "article", "title": "Competitive Activation of a Methyl C\u2212H Bond of Dimethylformamide at an Iridium Center", "author": [ { "family_name": "Scott", "given_name": "Valerie J.", "clpid": "Scott-V-J" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" } ], "abstract": "During the synthesis of [AsPh_4][Ir(CO)_2I_3Me] by refluxing IrCl_3\u00b73H_2O in DMF (DMF = dimethylformamide) in the presence of aqueous HCl, followed by sequential treatment with [AsPh_4]Cl, NaI, and methyl iodide and finally recrystallization from methylene chloride/pentane, three crystalline byproducts were obtained: [AsPh4]_2[Ir(CO)I_5], [AsPh_4]_2[trans-Ir(CO)I_4Cl], and [AsPh_4][Ir(CO)(\u03ba^2O,C-CH_2NMeCHO)Cl_2I]. The last of these, whose structure (along with the others) was determined by X-ray diffraction, results from activation of a methyl C\u2212H bond of dimethylformamide, rather than the normally much more reactive aldehydic C\u2212H bond.", "doi": "10.1021/om9002413", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2009-07-27", "series_number": "14", "volume": "28", "issue": "14", "pages": "4229-4230" }, { "id": "authors:kzrd0-kpz43", "collection": "authors", "collection_id": "kzrd0-kpz43", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090904-133218609", "type": "article", "title": "Amine, Amido, and Imido Complexes of Tantalum Supported by a Pyridine-Linked Bis(phenolate) Pincer Ligand: Ta\u2212N \u03c0-Bonding Influences Pincer Ligand Geometry", "author": [ { "family_name": "Tonks", "given_name": "Ian A.", "clpid": "Tonks-I-A" }, { "family_name": "Henling", "given_name": "Larry M.", "clpid": "Henling-L-M" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A series of tantalum imido and amido complexes supported by a pyridine-linked bis(phenolate) ligand has been synthesized. Characterization of these complexes via X-ray crystallography reveals both C_s and C_2 binding modes of the bis(phenolate)pyridine ligand, with complexes containing two or fewer strong \u03c0-donor interactions from ancillary ligands giving C_s symmetry, whereas three strong \u03c0-donor interactions (e.g., three amido ligands or one amido ligand and one imido ligand) give C_2-symmetric binding of the bis(phenolate)pyridine ligand. DFT calculations and molecular orbital analyses of the complexes have revealed that the preference for C_s-symmetric ligand binding is a result of tantalum\u2212phenolate \u03c0-bonding, whereas in cases where tantalum\u2212phenolate \u03c0-bonding is overridden by stronger Ta\u2212N \u03c0-bonding, C_2-symmetric ligand binding is preferred, likely because conformationally this is the lowest-energy arrangement. This electronically driven change in geometry indicates that, unlike analogous metallocene systems, the bis(phenolate)pyridine pincer ligand is not a strong enough \u03c0-donor to exert dominant control over the electronic and geometric properties of the complex.", "doi": "10.1021/ic802234x", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2009-06-15", "series_number": "12", "volume": "48", "issue": "12", "pages": "5096-5105" }, { "id": "authors:jks4d-pwz36", "collection": "authors", "collection_id": "jks4d-pwz36", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090908-090227281", "type": "article", "title": "Synthesis and Characterization of Iron Derivatives Having a Pyridine-Linked Bis(anilide) Pincer Ligand", "author": [ { "family_name": "Weintrob", "given_name": "Edward C.", "clpid": "Weintrob-E-C" }, { "family_name": "Tofan", "given_name": "Daniel", "clpid": "Tofan-D" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A pyridine-linked bis(aniline) pincer ligand, [2]H_2 ([2]H_2 = (2,6-NC_5H_3(2-(2,4,6-Me_3C_6H_2)-NHC6H4)2), has been synthesized in two steps. Deprotonation with Me_3SiCH_2Li followed by metalation with FeCl_2 yielded a LiCl adduct of [2]Fe. The complex is freed of LiCl with excess TlPF_6 or by crystallization from toluene/petroleum ether, giving [2]Fe(THF). [2]Fe(THF) reacts with I_2 and O_2 to generate [2]FeI and ([2]Fe)_2O, respectively. The complexes have been characterized by ^1H NMR spectroscopy, elemental analysis, X-ray crystallography, and UV\u2212vis spectroscopy. [2]Fe(THF) has been examined using cyclic voltammetry.", "doi": "10.1021/ic900083s", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2009-04-20", "series_number": "8", "volume": "48", "issue": "8", "pages": "3808-3813" }, { "id": "authors:zw6wp-78x87", "collection": "authors", "collection_id": "zw6wp-78x87", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:LINcjc08", "type": "article", "title": "Mechanistic investigations of bipyrimidine-promoted palladium-catalyzed allylic acetoxylation of olefins", "author": [ { "family_name": "Lin", "given_name": "Bo-Lin", "clpid": "Lin-Bo-Lin" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Several pyridine-like ligands were found to improve Pd(OAc)2-catalyzed allylic oxidation of allylbenzene to cinnamyl acetate by p-benzoquinone in acetic acid. The best ligand examined, bipyrimidine, was used to identify the catalyst precursor for this system, (bipyrimidine)Pd(OAc)2, which was fully characterized. Mechanistic studies suggest the reaction takes place through disproportionation of (bipyrimidine)Pd(OAc)2 to form a bipyrimidine-bridged dimer, which reacts with olefin to form a Pd^II-olefin adduct, followed by allylic C\u2013H activation to produce (\u03b7^3-allyl)Pd^II species. The (\u03b7^3-allyl)Pd^II intermediate undergoes a reversible acetate attack to generate a Pd^0-(allyl acetate) adduct, which subsequently reacts with p-benzoquinone to release allyl acetate and regenerate (bipyrimidine)Pd(OAc)2. No KIE is observed for the competition experiment between allylbenzene-d0 and allylbenzene-d5 (CD2=CDCD2C6H5), suggesting that allylic C\u2013H activation is not rate-determining. Catalytic allylic acetoxylations of other terminal olefins as well as cyclohexene were also effected by (bipyrimidine)Pd(OAc)2.", "doi": "10.1139/V08-133", "issn": "0008-4042", "publisher": "National Research Council Canada", "publication": "Canadian Journal of Chemistry", "publication_date": "2009-01", "series_number": "1", "volume": "87", "issue": "1", "pages": "264-271" }, { "id": "authors:0xpcq-hyw39", "collection": "authors", "collection_id": "0xpcq-hyw39", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:AGAo08", "type": "article", "title": "Zirconium and titanium complexes supported by tridentate LX2 ligands having two phenolates linked to furan, thiophene, and pyridine donors: precatalysts for propylene polymerization and oligomerization", "author": [ { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "DiPasquale", "given_name": "Antonio G.", "clpid": "DiPasquale-A-G" }, { "family_name": "Rheingold", "given_name": "Arnold L.", "orcid": "0000-0003-4472-8127", "clpid": "Rheingold-A-L" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Zirconium and titanium complexes with tridentate bis(phenolate)-donor (donor = pyridine, furan and thiophene) ligands have been prepared and investigated for applications in propylene polymerization. The ligand framework has two X-type phenolates connected to the flat heterocyclic L-type donor at the 2,6- or 2.5- positions via direct ring-ring (sp^2-sp^2)linkages. The zirconium and titanium dibenzyl complexes have been prepared by treatment of the neutral bis(phenol)-donor ligands with M(CH_2Ph)_4 (M = Ti, Zr) with loss of 2 equiv of toluene. Titanium complexes with bis(phenolate)pyridine and -furan ligands and zirconium complexes with bis(phenolate)pyridine and -thiophene ligands have been characterized by single-crystal X-ray diffraction. The solid-state structures of the bis(benzyl)titanium complexes are roughly C_2 symmetric, while the zirconium derivatives display C_s and C^1 symmetry. The bis(phenolate)pyridine titanium complexes are structurally affected by the size of the substituents substituents (CMe_3 or CEt_3) ortho to the oxygens, the larger group leading to a larger C_2 distortion. Both titanium and zirconium dibenzyl complexes were found to be catalyst precursors for the polymerization of propylene upon activation with methylaluminoxane (MAO). The activities observed for the zirconium complexes are particularly notable, exceeding 10^6 g polypropylene/mol Zr center dot h in some cases. The bis(phenolate)pyridine titanium analogues are about 10^3 times less active, but generate polymers of higher molecular weight. When activated with MAO, the titanium bis(phenolate)furan and bis(phenolate)thiophene systems were found to promote propylene oligomerization.", "doi": "10.1021/om800136y", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2008-12-08", "series_number": "23", "volume": "27", "issue": "23", "pages": "6245-6256" }, { "id": "authors:sevze-ky535", "collection": "authors", "collection_id": "sevze-ky535", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:BERacie08", "type": "article", "title": "C-H Bond Activation by [{(Diimine)Pd(\u03bc-OH)}2]2+ Dimers: Mechanism-Guided Catalytic Improvement", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Hazari", "given_name": "Nilay", "clpid": "Hazari-N" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Oblad", "given_name": "Paul E.", "clpid": "Oblad-P-E" } ], "abstract": "These conclusions\u2014that the hydroxy-bridged dimer 1b is the most reactive species in the Pd system, considerably more reactive than either 2a or 2b towards C-H bond activation, and that there is an important solvent-assisted component in the rate law\u2014suggest a way to substantially improve the catalytic conversion of cyclohexene into benzene [Eq. (3)]. Our previous studies involved 2b (or mixtures of 1b and 2b) in the noncoordinating solvent dichloroethane. In a typical experiment, after 24 h under 1 atm of O2 with 5 mol% of 2b as the catalyst, 8% of the cyclohexene had been converted into benzene; furthermore, there was an initiation period before any reaction occurred, and competing disproportionation of cyclohexene to benzene and cyclohexane was a major side reaction.[3] In contrast, under the same conditions but using only 1 mol% of pure 1b as the catalyst and TFE as solvent, conversion was 25% after 24 h, with no induction period or competing isomerization.[7]", "doi": "10.1002/anie.200804455", "issn": "1433-7851", "publisher": "Wiley", "publication": "Angewandte Chemie International Edition", "publication_date": "2008-12-08", "series_number": "51", "volume": "47", "issue": "51", "pages": "9941-9943" }, { "id": "authors:j75qf-7jk28", "collection": "authors", "collection_id": "j75qf-7jk28", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:AGAo08a", "type": "article", "title": "Synthesis and reactivity of tantalum complexes supported by bidentate X2 and tridentate LX2 ligands with two phenolates linked to pyridine, thiophene, furan, and benzene connectors: mechanistic studies of the formation of a tantalum benzylidene and insertion chemistry for tantalum-carbon bonds", "author": [ { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Using either alkane elimination or salt metathesis methods, tantalum complexes have been prepared with new ligand systems with tridentate bis(phenolate)donor (donor = pyridine, furan, and thiophene) or bidentate bis(phenolate)benzene arrangements. The ligand framework has two X-type phenolates connected to the flat heterocyclic L-type donor at the 2,6- or 2,5- positions or to the 2,6- positions of benzene via direct ring\u2212ring (sp_2\u2212sp_2) linkages. Solid-state structures of these complexes show that in all cases the ligands bind in a mer fashion, but with different geometries of the LX_2 frameworks. The pyridine-linked system binds in a Cs-fashion, the furan-linked system in a C2_v-fashion, and the thiophene-linked system in a C_1-fashion. A bis(phenolate)pyridine tantalum tribenzyl species (7), upon heating in the presence of dimethylphenylphosphine, generates a stable benzylidene complex by \u03b1-hydrogen abstraction with loss of toluene and PMe_2Ph trapping. This process was found to be independent of PMe_2Ph concentration with \u0394H = 31.3 \u00b1 0.6 kcal\u00b7mol\u22121 and \u0394S = 3 \u00b1 2 cal\u00b7mol\u22121\u00b7K\u22121, and the kinetic isotope effect kH/kD = 4.9 \u00b1 0.4, consistent with a mechanism involving rate determining \u03b1-hydrogen abstraction with loss of toluene, followed by fast phosphine coordination to the resulting benzylidene species. An X-ray structure determination reveals that the benzylidene \u03c0-bond is oriented perpendicular to the oxygen\u2212oxygen vector, in accord with the prediction of DFT calculations. Tantalum alkyl complexes with the benzene-linked bis(phenolate) ligand (Ta(CH_3)2[(OC_6H_2-tBu_2)2C_6H_3] (16), Ta(CH_2Ph)2[(OC_6H_2-tBu_2)2C_6H_3] (17), and TaCl_2CH_3[(OC_6H_2-tBu_2)2C_6H_4] (18)) are obtained with (to afford pincer complexes) or without cyclometalation at the ipso-position. Deuterium labeling of the phenol hydrogens and of the linking 1,3-benzene-diyl ring reveals an unexpected mechanism for the metalation of bis(phenol)benzene with TaC_l2(CH_3)3 to generate 18. This process involves protonolysis of a methyl group, followed by C-H/Ta-CH_3 \u03c3 bond metathesis leading to cyclometalation of the linking ring, and finally protonation of the cyclometallated group by the pendant phenol. TaCl_2CH_3[(OC_6H_2-tBu_2)2C_6H_4] was found to undergo \u03c3 bond metathesis at temperatures over 90 \u00b0C to give the pincer complex TaCl_2[(OC_6H_2-tBu_2)2C_6H_3] (1_9) and methane (\u0394H = 27.1 \u00b1 0.9 kcal\u00b7mol\u22121; \u0394S\u2260 = \u22122 \u00b1 2 cal\u00b7mol^1\u00b7K^1; k_H/k_D = 1.6 \u00b1 0.2 at 125 \u00b0C). Ta(CH_3)_2[(OC_6H_2-tBu_2)_2C_6H_3] (16) was found to react with tBuNC to insert into the Ta-CH_3 bonds and generate an imino-acyl species (23). Reaction of 16 with Ph_2CO or PhCN leads to insertion into the Ta-Ph bond to give 21 and 22. Complexes 6, 7, 10, 11-P, 12, 13, 17, 18, 19-OEt_2, 21, 22, and 23 have been structurally characterized by single crystal X-ray diffraction, and all show a mer binding mode of the diphenolate ligands, but the ligand geometry varies leading to C_2v-, pseudo-C_s-, pseudo-C_2-, and C_1-symmetric structures.", "doi": "10.1021/om8002653", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2008-12-08", "series_number": "23", "volume": "27", "issue": "23", "pages": "6123-6142" }, { "id": "authors:css0e-29453", "collection": "authors", "collection_id": "css0e-29453", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090724-092407360", "type": "article", "title": "Hydrogen tunneling in protonolysis of platinum(II) and palladium(II) methyl complexes: mechanistic implications", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Chen", "given_name": "George S.", "clpid": "Chen-George-S" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Lin", "given_name": "Bo-Lin", "clpid": "Lin-Bo-Lin" } ], "abstract": "The selective transformation of C-H bonds is an important area\nof current research; over the past several decades, numerous examples\nof C-H activation by transition metals have appeared in the literature.1\nOf particular significance is the development of a number of\nhomogeneous catalytic systems based on late transition metals,\nespecially platinum2 and palladium.3 Several general mechanisms for\nC-H activation by transition metal complexes have been identified,\nincluding (1) electrophilic activation, (2) oxidative addition, (3) \u03c3-bond\nmetathesis, (4) 1,2-addition to metal-ligand multiple bonds, (5) H-atom\nabstraction by metal-oxo complexes, and (6) metalloradical activation.4\nKinetic hydrogen/deuterium isotope effects (KIEs) have been used\nextensively by many groups to probe the nature of these reactions and\nto gain key mechanistic insights.5", "doi": "10.1021/ja807427d", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2008-12-04", "series_number": "52", "volume": "130", "issue": "52", "pages": "17654-17655" }, { "id": "authors:wsm6n-ak614", "collection": "authors", "collection_id": "wsm6n-ak614", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090720-141909224", "type": "article", "title": "Alkylaluminum-complexed zirconocene hydrides: identification of hydride-bridged species by NMR spectroscopy", "author": [ { "family_name": "Baldwin", "given_name": "Steven M.", "clpid": "Baldwin-S-M" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Brintzinger", "given_name": "Hans H.", "clpid": "Brintzinger-H-H" } ], "abstract": "Reactions of unbridged zirconocene dichlorides, (R_nC_5H_5\u2212n)_2ZrCl_2 (n = 0, 1, or 2), with diisobutylaluminum hydride (HAl^iBu_2) result in the formation of tetranuclear trihydride clusters of the type (R_nC_5H_5\u2212n)_2Zr(\u03bc-H)_3(Al^iBu_2)_3(\u03bc-Cl)_2, which contain three [Al^iBu_2] units. Ring-bridged ansa-zirconocene dichlorides, Me_2E(R_nC_5H_4\u2212n)_2ZrCl_2 with E = C or Si, on the other hand, are found to form binuclear dihydride complexes of the type Me_2E(R_nC_5H_4\u2212n)_2Zr(Cl)(\u03bc-H)_2Al^iBu_2 with only one [Al^iBu_2] unit. The dichotomy between unbridged and bridged zirconocene derivatives with regard to tetranuclear versus binuclear product formation is proposed to be connected to different degrees of rotational freedom of their C_5-ring ligands. Alkylaluminum-complexed zirconocene dihydrides, previously observed in zirconocene-based precatalyst systems activated by methylalumoxane (MAO) upon addition of HAl^iBu_2 or Al^iBu_3, are proposed to be species of the type Me_2Si(ind)_2Zr(Me)(\u03bc-H)_2Al^iBu_2, stabilized by interaction of their terminal Me group with a Lewis acidic site of MAO.", "doi": "10.1021/ja8054723", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2008-11-25", "series_number": "51", "volume": "130", "issue": "51", "pages": "17423-17433" }, { "id": "authors:3zmyy-73f62", "collection": "authors", "collection_id": "3zmyy-73f62", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:BERjoc08", "type": "article", "title": "Oxidative aromatization of olefins with dioxygen catalyzed by palladium trifluoroacetate", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Hazari", "given_name": "Nilay", "clpid": "Hazari-N" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" } ], "abstract": "Molecular oxygen can replace sacrificial olefins as the hydrogen acceptor in the palladium trifluoroacetate catalyzed dehydrogenation of cyclohexene and related cyclic olefins into aromatics. One of the major drawbacks of the homogeneous system is the tendency of the palladium trifluoroacetate to precipitate as palladium(0) at elevated temperatures. The use of better ligands affords catalysts that can operate at higher temperatures, although they are less reactive than palladium trifluoroacetate.", "doi": "10.1021/jo8016296", "issn": "0022-3263", "publisher": "American Chemical Society", "publication": "Journal of Organic Chemistry", "publication_date": "2008-11-07", "series_number": "21", "volume": "73", "issue": "21", "pages": "8654-8657" }, { "id": "authors:jc78m-40707", "collection": "authors", "collection_id": "jc78m-40707", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:BERjacs08", "type": "article", "title": "Selective Methylative Homologation: An Alternate Route to Alkane Upgrading", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Hazari", "given_name": "Nilay", "clpid": "Hazari-N" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Scott", "given_name": "Valerie J.", "clpid": "Scott-V-J" }, { "family_name": "Sunley", "given_name": "Glenn J.", "clpid": "Sunley-G-J" } ], "abstract": "InI3 catalyzes the reaction of branched alkanes with methanol to produce heavier and more highly branched alkanes, which are more valuable fuels. The reaction of 2,3-dimethylbutane with methanol in the presence of InI3 at 180\u2212200 \u00b0C affords the maximally branched C7 alkane, 2,2,3-trimethylbutane (triptane). With the addition of catalytic amounts of adamantane the selectivity of this transformation can be increased up to 60%. The lighter branched alkanes isobutane and isopentane also react with methanol to generate triptane, while 2-methylpentane is converted into 2,3-dimethylpentane and other more highly branched species. Observations implicate a chain mechanism in which InI3 activates branched alkanes to produce tertiary carbocations which are in equilibrium with olefins. The latter react with a methylating species generated from methanol and InI3 to give the next-higher carbocation, which accepts a hydride from the starting alkane to form the homologated alkane and regenerate the original carbocation. Adamantane functions as a hydride transfer agent and thus helps to minimize competing side reactions, such as isomerization and cracking, that are detrimental to selectivity.", "doi": "10.1021/ja803029s", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2008-09-10", "series_number": "36", "volume": "130", "issue": "36", "pages": "11988-11995" }, { "id": "authors:aq9ey-g5b57", "collection": "authors", "collection_id": "aq9ey-g5b57", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:MILjacs08", "type": "article", "title": "Reductive Coupling of Carbon Monoxide in a Rhenium Carbonyl Complex with Pendant Lewis Acids", "author": [ { "family_name": "Miller", "given_name": "Alexander J. M.", "clpid": "Miller-A-J-M" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Phosphinoborane ligands impart unique reactivity to a rhenium carbonyl cation relative to simple phosphine complexes. Addition of either triethylborohydride or a platinum hydride (that can be formed from H2) forms a rhenium boroxycarbene. This carbene, which crystallizes as a dimer, disproportionates over a period of days to afford the starting cation and a structurally unprecedented boroxy(boroxymethyl)carbene, in which a new C\u2212C bond has been formed between two reduced CO ligands. This product of C\u2212C bond formation can be independently synthesized by addition of 2 equiv of hydride to the rhenium carbonyl cation.", "doi": "10.1021/ja805108z", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2008-09-10", "series_number": "36", "volume": "130", "issue": "36", "pages": "11874-11875" }, { "id": "authors:xeqem-hd028", "collection": "authors", "collection_id": "xeqem-hd028", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170308-131107147", "type": "article", "title": "Catalyst Site Epimerization during the Kinetic Resolution of Chiral \u03b1-Olefins by Polymerization", "author": [ { "family_name": "Min", "given_name": "Endy Y.-J.", "clpid": "Min-Endy-Y-J" }, { "family_name": "Byers", "given_name": "Jeffery A.", "clpid": "Byers-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A new enantiopure C1-symmetric olefin polymerization precatalyst, (1,2-SiMe_2)_2{\u03b7^5-C_5H_2-4-((S)-CHEtCMe_3)}{\u03b7^5-C_5H-3,5-(CHMe_2)_2}ZrCl_2, (S)-2, was synthesized, and its use for the kinetic resolution of 3-methyl-substituted racemic \u03b1-olefins was investigated. Upon activation with methyl aluminoxane (MAO), selectivity factors for most olefins were greater when (S)-2 was used as the catalyst as compared to its previously reported methylneopentyl analogue, (1,2-SiMe_2)_2{\u03b7^5-C_5H_2-4-((S)-CHMeCCMe_3)}{\u03b7^5-C_5H-3,5-(CHMe_2)_2}ZrCl_2, (S)-1. Pentad analysis of polypropylene produced by the two catalysts at various propylene concentrations indicates that (S)-2 undergoes more efficient site epimerization (polymeryl chain swinging prior to subsequent monomer enchainment) at intermediate propylene concentrations compared to (S)-1. At high and low propylene concentrations, however, the two catalysts behave similarly. On the other hand, polymerization of 3,5,5-trimethyl-1-hexene at different olefin concentrations and temperatures illustrated that selectivity differences between the two catalysts are likely not a consequence of inefficient site epimerization for (S)-1.", "doi": "10.1021/om700778e", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2008-05-26", "series_number": "10", "volume": "27", "issue": "10", "pages": "2179-2188" }, { "id": "authors:38ecn-q9d46", "collection": "authors", "collection_id": "38ecn-q9d46", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170515-144435435", "type": "article", "title": "C\u2212H Bond Activation by Air-Stable [(Diimine)M^(II)(\u03bc_2-OH)]_2^(2+)Dimers (M = Pd, Pt)", "author": [ { "family_name": "Williams", "given_name": "Travis J.", "clpid": "Williams-T-J" }, { "family_name": "Caffyn", "given_name": "Andrew J. M.", "clpid": "Caffyn-A-J-M" }, { "family_name": "Hazari", "given_name": "Nilay", "clpid": "Hazari-N" }, { "family_name": "Oblad", "given_name": "Paul F.", "clpid": "Oblad-P-F" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Air- and water-tolerant C\u2212H activation is observed in reactions of [(diimine)Pt(\u03bc_2-OH)]_2^(2+) dimers with allylic and benzylic C\u2212H groups. The reactions proceed in good yields under mild conditions. Mechanistic studies indicate that the active species is the monomeric [(diimine)Pt(OH_2)]^(2+) dication. The related palladium species, [(diimine)Pd(\u03bc_2-OH)_2]^(2+), exhibit similar stoichiometric activations and also effect catalytic oxidation of cyclohexene to benzene with molecular oxygen as the terminal oxidant.", "doi": "10.1021/ja076740q", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2008-02-27", "series_number": "8", "volume": "130", "issue": "8", "pages": "2418-2419" }, { "id": "authors:2rv13-8p409", "collection": "authors", "collection_id": "2rv13-8p409", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170419-150139603", "type": "article", "title": "Conversion of Methanol to 2,2,3-Trimethylbutane (Triptane) over Indium(III) Iodide", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Diaconescu", "given_name": "Paula L.", "orcid": "0000-0003-2732-4155", "clpid": "Diaconescu-P-L" }, { "family_name": "Grubbs", "given_name": "Robert H.", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" }, { "family_name": "Hazari", "given_name": "Nilay", "clpid": "Hazari-N" }, { "family_name": "Kay", "given_name": "Richard D.", "clpid": "Kay-R-D" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Mehrkhodavandi", "given_name": "Parisa", "clpid": "Mehrkhodavandi-P" }, { "family_name": "Morris", "given_name": "George E.", "clpid": "Morris-G-E" }, { "family_name": "Sunley", "given_name": "Glenn J.", "clpid": "Sunley-G-J" }, { "family_name": "Vagner", "given_name": "Patrick", "clpid": "Vagner-P" } ], "abstract": "InI_3 is able to catalyze the conversion of methanol to a mixture of hydrocarbons at 200 \u00b0C with one highly branched alkane, 2,2,3-trimethylbutane (triptane), being obtained in high selectivity. The mechanism for InI_3-catalyzed reactions appears to be basically the same as that proposed for the previously studied ZnI_2-catalyzed system in which sequential methylation of olefins is followed by competing reactions of the resulting carbocation:\u2009 proton loss to give the next olefin vs hydride transfer to give the corresponding alkane. Although the reaction conditions and typical triptane yields achievable with ZnI_2 and InI_3 are quite similar, the two systems behave rather differently in a number of important particulars, including significant differences between the detailed product distributions. Most of the differences in behavior can be ascribed to the stronger Lewis acidity of InI_3, including the ability to activate some alkanes, the higher activity for methylation of arenes, and the fact that methanol conversion can be observed at somewhat lower temperatures with InI_3 than with ZnI_2.", "doi": "10.1021/ic7014447", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2007-12-24", "series_number": "26", "volume": "46", "issue": "26", "pages": "11371-11380" }, { "id": "authors:avt5e-r1c86", "collection": "authors", "collection_id": "avt5e-r1c86", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170515-111025629", "type": "article", "title": "Mechanistic Studies of Olefin and Alkyne Trimerization with Chromium Catalysts: Deuterium Labeling and Studies of Regiochemistry Using a Model Chromacyclopentane Complex", "author": [ { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A system for catalytic trimerization of ethylene utilizing chromium(III) precursors supported by diphosphine ligand PNP^(O4) = (o-MeO\u2212C_6H_4)_2PN(Me)P(o-MeO\u2212C_6H_4)_2 has been investigated. The mechanism of the olefin trimerization reaction was examined using deuterium labeling and studies of reactions with \u03b1-olefins and internal olefins. A well-defined chromium precursor utilized in this studies is Cr(PNP^(O4))(o,o'-biphenyldiyl)Br. A cationic species, obtained by halide abstraction with NaB[C_6H_3(CF_3)_2]_4, is required for catalytic turnover to generate 1-hexene from ethylene. The initiation byproduct is vinylbiphenyl; this is formed even without activation by halide abstraction. Trimerization of 2-butyne is accomplished by the same cationic system but not by the neutral species. Catalytic trimerization, with various (PNP^(O4))Cr precursors, of a 1:1 mixture of C_2D_4 and C_2H_4 gives isotopologs of 1-hexene without H/D scrambling (C_6D_(12), C_6D_8H_4, C_6D_4H_8, and C_6H_(12) in a 1:3:3:1 ratio). The lack of crossover supports a mechanism involving metallacyclic intermediates. Using a SHOP catalyst to perform the oligomerization of a 1:1 mixture of C_2D_4 and C_2H_4 leads to the generation of a broader distribution of 1-hexene isotopologs, consistent with a Cossee-type mechanism for 1-hexene formation. The ethylene trimerization reaction was further studied by the reaction of trans-, cis-, and gem-ethylene-d_2 upon activation of Cr(PNP^(O4))(o,o'-biphenyldiyl)Br with NaB[C_6H_3(CF_3)_2]_4. The trimerization of cis- and trans-ethylene-d_2 generates 1-hexene isotopomers having terminal CDH groups, with an isotope effect of 3.1(1) and 4.1(1), respectively. These results are consistent with reductive elimination of 1-hexene from a putative Cr(H)[(CH_2)_4CH\u2550CH_2] occurring much faster than a hydride 2,1-insertion or with concerted 1-hexene formation from a chromacycloheptane via a 3,7-H shift. The trimerization of gem-ethylene-d2 has an isotope effect of 1.3(1), consistent with irreversible formation of a chromacycloheptane intermediate on route to 1-hexene formation. Reactions of olefins with a model of a chromacyclopentane were investigated starting from Cr(PNP^(O4))(o,o'-biphenyldiyl)Br. \u03b1-Olefins react with cationic biphenyldiyl chromium species to generate products from 1,2-insertion. A study of the reaction of 2-butenes indicated that \u03b2-H elimination occurs preferentially from the ring CH rather than exo-CH bond in the metallacycloheptane intermediates. A study of cotrimerization of ethylene with propylene correlates with these findings of regioselectivity. Competition experiments with mixtures of two olefins indicate that the relative insertion rates generally decrease with increasing size of the olefins.", "doi": "10.1021/ja073493h", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2007-11-21", "series_number": "46", "volume": "129", "issue": "46", "pages": "14281-14295" }, { "id": "authors:64q6d-18g42", "collection": "authors", "collection_id": "64q6d-18g42", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:BERcc07", "type": "article", "title": "Enhanced selectivity in the conversion of methanol to 2,2,3-trimethylbutane (triptane) over zinc iodide by added phosphorous or hypophosphorous acid", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Grubbs", "given_name": "Robert H.", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" }, { "family_name": "Hazari", "given_name": "Nilay", "clpid": "Hazari-N" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Li", "given_name": "Xingwei", "clpid": "Li-Xingwei" } ], "abstract": "The yield of triptane from the reaction of methanol with zinc iodide is dramatically increased by addition of phosphorous or hypophosphorous acid, via transfer of hydride from a P\u2013H bond to carbocationic intermediates.", "doi": "10.1039/b705470j", "issn": "1359-7345", "publisher": "Royal Society of Chemistry", "publication": "Chemical Communications", "publication_date": "2007-06-20", "series_number": "28", "volume": "2007", "issue": "28", "pages": "2974-2976" }, { "id": "authors:c7z28-gea06", "collection": "authors", "collection_id": "c7z28-gea06", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170309-085914464", "type": "article", "title": "Cyclometalated Tantalum Diphenolate Pincer Complexes: Intramolecular C\u2212H/M\u2212CH_3\u03c3-Bond Metathesis May Be Faster than O\u2212H/M\u2212CH_3 Protonolysis", "author": [ { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A diphenol linked at the ortho positions to a benzene ring was metalated with TaCl_2(CH_3)_3. Deuterium labeling of the phenol hydrogens and of the linking 1,3-benzenediyl ring reveals an unexpected mechanism involving protonolysis of a methyl group, followed by C\u2212H/Ta\u2212CH_3 \u03c3-bond metathesis, leading to cyclometalation of the linking ring and finally protonation of the cyclometalated group by the pendant phenol.", "doi": "10.1021/om700284c", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2007-06-04", "series_number": "12", "volume": "26", "issue": "12", "pages": "2957-2959" }, { "id": "authors:wcy2g-a6t23", "collection": "authors", "collection_id": "wcy2g-a6t23", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170308-152527539", "type": "article", "title": "Dialkyl and Methyl-Alkyl Zirconocenes: Synthesis and Characterization of Zirconocene-Alkyls That Model the Polymeryl Chain in Alkene Polymerizations", "author": [ { "family_name": "Klamo", "given_name": "Sara B.", "clpid": "Klamo-S-B" }, { "family_name": "Wendt", "given_name": "Ola F.", "clpid": "Wendt-O-F" }, { "family_name": "Henling", "given_name": "Larry M.", "clpid": "Henling-L-M" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Zirconocene precatalysts with sterically bulky alkyl groups were designed as model systems for the propagating species in zirconocene-catalyzed alkene polymerization. Specialty alkyllithium reagents Li(CH_2CEt_3) and Li(CH_2CMe_2CH_2Ph) were prepared and utilized in the synthesis of dialkyl and methyl-alkyl zirconocenes of the form CpCp^*ZrR_2, Cp_2Zr(CH_3)(R), and CpCp^*Zr(CH_3)(R) (Cp = (\u03b7^5-C_5H_5); Cp^* = (\u03b7^5-C_5Me_5); R = CH_2CMe_3, CH_2SiMe_3, CH_2CEt_3, CH_2CMe_2CH_2Ph). These new zirconocene alkyls were isolated and fully characterized by NMR spectroscopy and in some cases by X-ray diffraction. The molecular structures determined display the bent-sandwich coordination mode common for zirconocenes. The steric influence of the alkyl group on the observed structural parameters is reflected in slightly expanded C\u2212Zr\u2212C or C\u2212Zr\u2212Cl angles in the equatorial plane and long zirconium\u2212alkyl bond distances.", "doi": "10.1021/om0601302", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2007-06-04", "series_number": "12", "volume": "26", "issue": "12", "pages": "3018-3030" }, { "id": "authors:6pg08-skg96", "collection": "authors", "collection_id": "6pg08-skg96", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:BERpnas07", "type": "article", "title": "The coordination chemistry of saturated molecules", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" } ], "abstract": "Our understanding of bonding in transition metal complexes, as well as our ability to use that understanding in the synthesis and application of new species, has evolved over the last 100 years; and in some sense this special feature on the coordination chemistry of saturated molecules may be considered to represent its culmination. The nature of complexes between transition metal ions and neutral molecules such as ammonia was first correctly described by Werner around the beginning of the 20th century. Interpretations in terms of electronic bonding theories followed soon after. The key feature, of course, is the availability of a low-energy filled \"lone pair\" orbital available for donation to a vacant orbital on the electron-accepting metal ion.", "doi": "10.1073/pnas.0700902104", "pmcid": "PMC1855396", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "2007-04-24", "series_number": "17", "volume": "104", "issue": "17", "pages": "6899-6900" }, { "id": "authors:1f9q3-d8z40", "collection": "authors", "collection_id": "1f9q3-d8z40", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:CHEpnas07a", "type": "article", "title": "The role of alkane coordination in C\u2013H bond cleavage at a Pt(II) center", "author": [ { "family_name": "Chen", "given_name": "George S.", "clpid": "Chen-George-S" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The rates of CFormula H bond activation for various alkanes by [(N\u2013N)Pt(Me)(TFEd3)]+ (N Formula N = ArFormula NFormula C(Me)Formula C(Me)Formula NFormula Ar; Ar = 3,5-di-tert-butylphenyl; TFE-d3 = CF3CD2OD) were studied. Both linear and cyclic alkanes give the corresponding alkene-hydride cation [(N\u2013N)Pt(H)(alkene)]+ via (i) rate determining alkane coordination to form a CFormula H {sigma} complex, (ii) oxidative cleavage of the coordinated CFormula H bond to give a platinum(IV) alkyl-methyl-hydride intermediate, (iii) reductive coupling to generate a methane {sigma} complex, (iv) dissociation of methane, and (v) beta-H elimination to form the observed product. Second-order rate constants for cycloalkane activation (CnH2n), are proportional to the size of the ring (k ~ n). For cyclohexane, the deuterium kinetic isotope effect (kH/kD) of 1.28 (5) is consistent with the proposed rate determining alkane coordination to form a CFormula H {sigma} complex. Statistical scrambling of the five hydrogens of the Pt-methyl and the coordinated methylene unit, via rapid, reversible steps ii and iii, and interchange of geminal CFormula H bonds of the methane and cyclohexane CFormula H {sigma} adducts, is observed before loss of methane.", "doi": "10.1073/pnas.0610981104", "pmcid": "PMC1855376", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "2007-04-24", "series_number": "17", "volume": "104", "issue": "17", "pages": "6915-6920" }, { "id": "authors:nzxe6-kv737", "collection": "authors", "collection_id": "nzxe6-kv737", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170309-082713121", "type": "article", "title": "Group 3 Dialkyl Complexes with Tetradentate (L, L, N, O; L = N, O, S) Monoanionic Ligands: Synthesis and Reactivity", "author": [ { "family_name": "Marinescu", "given_name": "Smaranda C.", "orcid": "0000-0003-2106-8971", "clpid": "Marinescu-S-C" }, { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Tripodal, tetradentate phenols, (LCH_2)_2NCH_2-C_6H_2-3,5-(CMe_3)_2-2-OH (L = CH_2OCH_3 (1), CH_2NEt_2 (2), 2-C_5H_4N (3), CH_2SCMe_3 (5), CH_2NMe_2 (6)), were synthesized, and metalations were performed via alkane elimination from yttrium and scandium trialkyl complexes to generate the corresponding dialkyl complexes [(LCH_2CH_2)_2NCH_2-C_6H_2-3,5-(CMe_3)_2-2-O]MR_2 (M = Y, L = OCH_3, R = CH_2SiMe_2Ph (7a); M = Y, L = NEt_2, R = CH_2SiMe_2Ph (7b); M = Sc, L = OCH_3, R = CH_2SiMe_2Ph (8a); M = Sc, L = SCMe_3, R = CH_2SiMe_2Ph (8b); M = Y, L = OCH_3, R = CH_2SiMe_3 (9); M = Sc, L = OCH_3, R = CH_2SiMe_3 (10)). X-ray crystallographic studies show that 7a,b and 8a adopt, in the solid state, mononuclear structures of C_1 symmetry. The ^1H NMR spectra of these dialkyl complexes in benzene-d_6 at high temperatures reveal exchange processes involving the ether groups and the alkyl groups. The dynamic behavior of species 7a, 8a, and 10 in toluene-d8 was investigated by variable-temperature ^1H NMR spectroscopy. The activation parameters of the fluxional processes for 7a, 8a, and 10 were determined by line-shape and Eyring analyses (for 7a, \u0394H^\u29e7 = 7.3 \u00b1 0.3 kcal/mol and \u0394S^\u29e7 = \u221216 \u00b1 1.4 cal/(mol K); for 8a, \u0394H^\u29e7 = 9.9 \u00b1 0.5 kcal/mol and \u0394S^\u29e7 = \u221215.3 \u00b1 1.8 cal/ (mol K); for 10, \u0394H^\u29e7 = 10.8 \u00b1 0.6 kcal/mol and \u0394S^\u29e7 = \u221211.4 \u00b1 1.9 cal/(mol K)). These data establish that the dialkyl complexes 7a, 8a, and 10 undergo a nondissociative exchange process. The scandium dialkyl complex [(C_5H_4N-2-CH_2)_2NCH_2-C_6H_2-3,5-(CMe_3)_2-2-O]Sc(CH_2SiMe_2Ph)_2 (11) was found to undergo clean activation of a C\u2212H bond of a methylene linking a pyridine to the central nitrogen donor. This process follows first-order kinetics (k = [2.8(3)] \u00d7 10^(-4) s^(-1) at 0 \u00b0C). The yttrium dialkyl complexes 7a and 9 react with 1 equiv of [PhNHMe_2]+[B(C_6F_5)_4]- in chlorobenzene-d_5, to generate a solution that slowly polymerizes ethylene. Compounds 7\u221210 also polymerize ethylene with low activity upon activation with MAO.", "doi": "10.1021/om0608612", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2007-02-26", "series_number": "5", "volume": "26", "issue": "5", "pages": "1178-1190" }, { "id": "authors:3whma-k6e25", "collection": "authors", "collection_id": "3whma-k6e25", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161031-110459657", "type": "article", "title": "Reactions of Indene and Indoles with Platinum Methyl Cations: Indene C\u2212H Activation, Indole \u03c0 versus Nitrogen Lone-Pair Coordination", "author": [ { "family_name": "Williams", "given_name": "Travis J.", "clpid": "Williams-T-J" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Reactions of indene and various substituted indoles with [(diimine)Pt^(II)(Me)(TFE)]^+ cations have been studied (diimine = ArNC(Me)\u2212C(Me)NAr; TFE = 2,2,2-trifluoroethanol). Indene displaces the TFE ligand from platinum to form a stable \u03c0 coordination complex that, upon heating, undergoes C\u2212H activation with first-order kinetics, \u0394H^\u29e7 = 29 kcal/mol, \u0394S^\u29e7 = 10 eu, and a kinetic isotope effect of 1.1 at 60 \u00b0C. Indoles also initially form coordination complexes through the C_2=C_3 olefin, but these undergo rearrangement to the corresponding N-bound complexes. The relative rates of initial coordination and rearrangement are affected by excess acid or methyl substitution on indole.", "doi": "10.1021/om0606643", "pmcid": "PMC4833004", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2007-01-15", "series_number": "2", "volume": "26", "issue": "2", "pages": "281-287" }, { "id": "authors:hhm4y-yes88", "collection": "authors", "collection_id": "hhm4y-yes88", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170725-130119305", "type": "article", "title": "C\u2212H Bond Activation by Dicationic Platinum(II) Complexes", "author": [ { "family_name": "Driver", "given_name": "Tom G.", "clpid": "Driver-T-G" }, { "family_name": "Williams", "given_name": "Travis J.", "clpid": "Williams-T-J" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Double protonolysis of diimine platinum dimethyls [(N-N)PtMe_2] (N-N \u2550 ArNC(Me)C(Me) \u2550 NAr) generates dicationic Pt(II) complexes that can activate a variety of C\u2212H bonds, liberating 1 equiv of acid and forming organoplatinum species that are moderately stable to the resulting acidic conditions. Ethylbenzenes lead to \u03b7^3-benzyl complexes; mechanistic experiments suggest that \u03b7^3-benzyl product formation proceeds via C\u2212H bond activation at the benzylic methylene position. In some cases \u03c0-arene complexes can be observed, but their role in the C\u2212H activation process is not clear. Cyclohexane and 1-pentene react to give \u03b7^3-allyl complexes; allylbenzene gives a chelated phenyl-\u03b7^2-olefin structure, as determined by X-ray diffraction. No stable C\u2212H activation products are obtained from methylbenzenes, benzene itself, or alkanes.", "doi": "10.1021/om060792r", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2007-01-15", "series_number": "2", "volume": "26", "issue": "2", "pages": "294-301" }, { "id": "authors:bg42q-r4j49", "collection": "authors", "collection_id": "bg42q-r4j49", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170725-104220151", "type": "article", "title": "Competitive Oxidation and Protonation of Aqueous Monomethylplatinum(II) Complexes: A Comparison of Oxidants", "author": [ { "family_name": "Weinberg", "given_name": "David R.", "clpid": "Weinberg-D-R" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "[Pt^(II)(CH_3)Cl_3]^(2-) (1), generated at 95 \u00b0C in situ from Cs_2[Pt^(IV)(CH_3)_2Cl_4] in an aqueous solution of high chloride concentration and [H^+] = 0.2 M, undergoes competitive oxidation versus protonation (k_(ox)/k_(H+)) with several oxidants. A first-order dependence on oxidant concentration was determined for both CuCl_2 and FeCl_3 oxidations of 1, and k_(ox)/k_(H+) was determined to be 191 \u00b1 24 and 14 \u00b1 3. CuCl_2 was shown to catalyze the oxidation of 1 by dioxygen; however, [Pt^(II)Cl_4]^(2-) was also oxidized under these conditions. Anion 1, generated in a mixture of platinum(II) salts, [Cp_2Co^(III)]_2{[Pt^(II)Cl_4] + 1 + [Pt^(II)(CH_3)_2Cl_2] (4)}\u00b7xNaCl (5), also undergoes competitive oxidation and protonation at room temperature in D_2O when in the presence of oxidants. Increasing chloride decreases the ratio k_(ox)/k_(H+) for 1 when Na_2[Pt^(IV)Cl_6] is used as the oxidant, but when CuCl_2 is used as the oxidant, added chloride increases k_(ox)/k_(H+). The one-electron oxidants, Na_2[IrCl_6] and (NH_4)_2[Ce(NO_3)_6], were also shown to oxidize 1.", "doi": "10.1021/om060763g", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2007-01-01", "series_number": "1", "volume": "26", "issue": "1", "pages": "167-172" }, { "id": "authors:245w8-1ja37", "collection": "authors", "collection_id": "245w8-1ja37", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170427-090114775", "type": "article", "title": "On the Mechanism of the Conversion of Methanol to 2,2,3-Trimethylbutane (Triptane) over Zinc Iodide", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Diaconescu", "given_name": "Paula L.", "orcid": "0000-0003-2732-4155", "clpid": "Diaconescu-P-L" }, { "family_name": "Grubbs", "given_name": "Robert H.", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" }, { "family_name": "Kay", "given_name": "Richard D.", "clpid": "Kay-R-D" }, { "family_name": "Kitching", "given_name": "Sarah", "clpid": "Kitching-S" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Li", "given_name": "Xingwei", "clpid": "Li-Xingwei" }, { "family_name": "Mehrkhodavandi", "given_name": "Parisa", "clpid": "Mehrkhodavandi-P" }, { "family_name": "Morris", "given_name": "George E.", "clpid": "Morris-G-E" }, { "family_name": "Sunley", "given_name": "Glenn J.", "clpid": "Sunley-G-J" }, { "family_name": "Vagner", "given_name": "Patrick", "clpid": "Vagner-P" } ], "abstract": "Methanol is converted to a mixture of hydrocarbons by reaction with zinc iodide at 200 \u00b0C with one highly branched alkane, 2,2,3-trimethylbutane (triptane), being obtained in surprisingly high selectivity. Mechanistic studies implicate a two-stage process, the first involving heterogeneously catalyzed formation of a carbon\u2212carbon-bonded species, probably ethylene, that undergoes homogeneously catalyzed sequential cationic methylation to higher hydrocarbons. The first stage can be bypassed by addition of olefins, higher alcohols, or arenes, which act as initiators. Rationales for the particular activity of zinc iodide and for the selectivity to triptane are proposed.", "doi": "10.1021/jo0617823", "issn": "0022-3263", "publisher": "American Chemical Society", "publication": "Journal of Organic Chemistry", "publication_date": "2006-11-10", "series_number": "23", "volume": "71", "issue": "23", "pages": "8907-8917" }, { "id": "authors:2mzr8-ke350", "collection": "authors", "collection_id": "2mzr8-ke350", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170309-075631633", "type": "article", "title": "Nitrogen-Linked Diphosphine Ligands with Ethers Attached to Nitrogen for Chromium-Catalyzed Ethylene Tri- and Tetramerizations", "author": [ { "family_name": "Elowe", "given_name": "Paul R.", "clpid": "Elowe-P-R" }, { "family_name": "McCann", "given_name": "Cassandra", "clpid": "McCann-C" }, { "family_name": "McCann", "given_name": "Paul G.", "clpid": "McCann-P-G" }, { "family_name": "Spitzmesser", "given_name": "Stefan K.", "clpid": "Spitzmesser-S-K" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A series of bis(diphenylphosphino)amine ligands with a donor group attached to the nitrogen linker have been prepared. Metalation of these ligands with chromium trichloride provides precursors to highly active, relatively stable, and selective catalysts for trimerization and tetramerization of ethylene. It has been demonstrated in oligomerization reactions performed at 1 and 4 atm of ethylene that these new systems increase total productivity by enhancing catalyst stability, as compared with those lacking a donor group on the diphosphine ligand. Furthermore, the use of chlorobenzene solvent (rather than toluene) significantly improves productivity, stability, and selectitvity. The product distributions and minor byproducts provide information relevant to mechanistic issues surrounding these types of reactions.", "doi": "10.1021/om0601596", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2006-10-23", "series_number": "22", "volume": "25", "issue": "22", "pages": "5255-5260" }, { "id": "authors:0tg65-t0m09", "collection": "authors", "collection_id": "0tg65-t0m09", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:BYEpnas06", "type": "article", "title": "Kinetic resolution of racemic {alpha}-olefins with ansa-zirconocene polymerization catalysts: Enantiomorphic site vs. chain end control", "author": [ { "family_name": "Byers", "given_name": "Jeffery A.", "clpid": "Byers-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Copolymerization of racemic {alpha}-olefins with ethylene and propylene was carried out in the presence of enantiopure C1-symmetric ansa metallocene, {1,2-(SiMe2)2({eta}5-C5H-3,5-(CHMe2)2)({eta}5-C5H3)}ZrCl2 to probe the effect of the polymer chain end on enantioselection for the R- or S-{alpha}-olefin during the kinetic resolution by polymerization catalysis. Copolymerizations with ethylene revealed that the polymer chain end is an important factor in the enantioselection of the reaction and that for homopolymerization, chain end control generally works cooperatively with enantiomorphic site control. Results from propylene copolymerizations suggested that chain end control arising from a methyl group at the beta carbon along the main chain can drastically affect selectivity, but its importance as a stereo-directing element depends on the identity of the olefin.", "doi": "10.1073/pnas.0603071103", "pmcid": "PMC1622822", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "2006-10-17", "series_number": "42", "volume": "103", "issue": "42", "pages": "15303-15308" }, { "id": "authors:k38r1-rt019", "collection": "authors", "collection_id": "k38r1-rt019", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170607-133944016", "type": "article", "title": "Mechanism of Isotactic Polypropylene Formation with C_1-Symmetric Metallocene Catalysts", "author": [ { "family_name": "Miller", "given_name": "Stephen A.", "orcid": "0000-0002-3181-1426", "clpid": "Miller-S-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The mechanism for isotactic polypropylene formation by the C_1-symmetric catalyst system [Me_2C(3-tert-butyl-C_5H_3)(C_(13)H_8)]ZrCl_2/MAO (MAO = methylaluminoxane, C13H8 = fluorenylidene) has been examined. Evidence supports an alternating mechanism, where both sites of the metallocene wedge are utilized for monomer insertion, rather than the previously proposed site epimerization (inversion at Zr) following each monomer insertion. As the polymerization temperature increases (0 to 60 \u00b0C) with lower concentrations of propylene, the site epimerization mechanism begins to compete, as evidenced by an increase in isotacticity. The alternating mechanism also accounts for polypropylene microstructures obtained with Me_2C(3-R-C_5H_3)(Oct)ZrCl_2/MAO, where Oct = octamethyloctahydrodibenzofluorenylidene and R = methyl, cyclohexyl, diphenylmethyl, and with Me_2C(3-tert-butyl-4-Me-C_5H_2)(Oct)ZrCl_2/MAO. For an Oct-containing catalyst system with R = 2-methyl-2-adamantyl, unprecedentedly high (for a fluorenyl-based metallocene catalyst) isotacticity ([mmmm] > 99%) is obtained; the polymer prepared at 0 \u00b0C has T_m = 167 \u00b0C and M_w = 370\u2009000.", "doi": "10.1021/om050841k", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2006-07-17", "series_number": "15", "volume": "25", "issue": "15", "pages": "3576-3592" }, { "id": "authors:tfa16-jjv59", "collection": "authors", "collection_id": "tfa16-jjv59", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170308-143404019", "type": "article", "title": "Ethylene Trimerization Catalysts Based on Chromium Complexes with a Nitrogen-Bridged Diphosphine Ligand Having ortho-Methoxyaryl or ortho-Thiomethoxy Substituents: Well-Defined Catalyst Precursors and Investigations of the Mechanism", "author": [ { "family_name": "Schofer", "given_name": "Susan J.", "clpid": "Schofer-S-J" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Chromium-based ethylene trimerization catalyst precursors ((PNP^(OMe)_(-d)_(12))CrPh_3 (4) and (PNP^(OMe)_(-d)_(12))CrPh_2Cl (7)) having a bis(diphenylphosphino)amine ligand (o-CD_3OC_6H_4)_2PN(CH_3)P(o-CD_3OC_6H_4)_2 ((PNP^(OMe)_(-d)_(12)) = 1) have been prepared and characterized. A thioether analogue (o-CD_3SC_6H_4)_2PN(CH_3)P(o-CD_3SC_6H_4)_2 ((PNP^(SMe)_(-d)_(12)) = 2) and its triphenylchromium complex (PNP^(SMe))CrPh_3 (5) have also been synthesized. The solid-state structures of 4 and 7 display octahedral geometries with a \u03ba^3-(P,P,O) coordination of PNP^(OMe) ligands having chromium\u2212oxygen bond lengths of 2.29\u22122.44 \u00c5. Compound 5 differs, exhibiting (S,P,S)-\u03ba^3 coordination of the PNP^(SMe) ligand. The deuteromethyl groups allow for ^2H NMR characterization of these paramagnetic complexes in solution. Dynamic exchange processes occur in solution at room temperature to render all four of the methoxy or thioether groups equivalent on the ^2H NMR time scale; two distinct coalescence processes are observed by variable-temperature ^2H NMR spectroscopy for all compounds. The neutral species 4 and 7 react with ethylene (1 atm) by insertion into chromium\u2212phenyl bonds with the release of styrene and ethylbenzene, but 1-hexene is not observed under these conditions. Activation of 4 by protonation and activation of 7 by halide abstraction in the presence of ethylene provide active trimerization catalysts that give turnover numbers for 1-hexene as high as 3000 mol 1-hexene\u00b7mol^(-1) Cr. These catalysts display comparable activity and selectivity for 1-hexene compared to the original BP system, where the catalyst is generated in situ from CrCl_3(THF)_3, 1, and MAO. Both the well-defined systems and the CrCl_3(THF)_3/PNP^(OMe)/MAO system provide catalysts that undergo an initiation period followed by an apparent first-order decomposition process. Activated complexes 4 and 7 initiate trimerization primarily through ethylene insertion into the chromium\u2212phenyl bond, followed by \u03b2-hydrogen elimination and reductive elimination to give the active species, rather than via reductive elimination of biphenyl.", "doi": "10.1021/om0506062", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2006-05-22", "series_number": "11", "volume": "25", "issue": "11", "pages": "2743-2749" }, { "id": "authors:jkw07-jkd10", "collection": "authors", "collection_id": "jkw07-jkd10", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170726-082000200", "type": "article", "title": "A Chromium-Diphosphine System for Catalytic Ethylene Trimerization: Synthetic and Structural Studies of Chromium Complexes with a Nitrogen-Bridged Diphosphine Ligand with ortho-Methoxyaryl Substituents", "author": [ { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "To gain molecular-level insight into the important features of a chromium-diphosphine catalytic system for ethylene trimerization, the coordination chemistry of chromium with \"PNP\" ligands (PNP^(OMe) = (o-MeOC_6H_4)_2PN(CH_3)P(o-MeOC_6H_4)_2, P^(t-Bu)N^(i-amyl)P_(OMe)) = (2-MeO-4-t-BuC_6H_3)_2PN(i-amyl)P(2-MeO-4-t-BuC_6H_3)_2) has been explored. Chromium(0) carbonyl complexes have been synthesized by CO displacement with diphosphine. Oxidation of Cr(CO)_4{\u03ba^2-(P,P)-(PNP^(OMe))} with I_2, Br_2, and PhICl_2 generates the corresponding chromium(III) halide complexes. Chromium(III) complexes CrCl_3{(\u03ba^3-(P,P,O)-(PNP^(OMe))}, CrCl_3{\u03ba^3-(P,P,O)-(P^(t-)^(Bu)N^(i-amyl)P^(OMe))}, and CrCl_2(CH_3){\u03ba^3-(P,P,O)-(PNP^(OMe))} can be synthesized by metalation with CrCl_3(THF)_3 or CrCl_2(CH_3)(THF)_3. Reaction of CrCl_3{\u03ba^3-(P,P,O)-(PNP^(OMe))} with o,o'-biphenyldiyl diGrignard affords CrBr(o,o'-biphenyldiyl){\u03ba^3-(P,P,O)-(PNP^(OMe))}. Single-crystal X-ray diffraction studies show that the Cr\u2212O and Cr\u2212P distances can vary significantly as a function of metal oxidation state and the other ligands bound to chromium. Variable-temperature ^2H NMR spectroscopy studies of chromium(III) complexes supported by PNP ligands indicate fluxional behavior with the ether groups interchanging at higher temperatures. Low-temperature ^2H NMR spectra are consistent with solution structures similar to the ones determined in the solid state.", "doi": "10.1021/om050605+", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2006-05-22", "series_number": "11", "volume": "25", "issue": "11", "pages": "2733-2742" }, { "id": "authors:s84bf-fwz18", "collection": "authors", "collection_id": "s84bf-fwz18", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170512-144736275", "type": "article", "title": "Kinetics and Mechanism of Methane, Methanol, and Dimethyl Ether C\u2212H Activation with Electrophilic Platinum Complexes", "author": [ { "family_name": "Owen", "given_name": "Jonathan S.", "clpid": "Owen-J-S" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The relative rates of C\u2212H activation of methane, methanol, and dimethyl ether by [(N-N)PtMe(TFE-d_3)]+ ((N-N) = ArN\u2550C(Me)\u2212C(Me)\u2550NAr; Ar = 3,5-di-tert-butylphenyl, TFE-d_3 = CF_3CD_2OD) (2(TFE)) were determined. Methane activation kinetics were conducted by reacting 2(TFE)-^(13)C with 300\u22121000 psi of methane in single-crystal sapphire NMR tubes; clean second-order behavior was obtained (k = 1.6 \u00b1 0.4 \u00d7 10^(-3) M^(-1) s^(-1) at 330 K; k = 2.7 \u00b1 0.2 \u00d7 10^(-4) M^(-1) s^(-1) at 313 K). Addition of methanol to solutions of 2(TFE) rapidly establishes equilibrium between methanol (2(MeOD)) and trifluoroethanol (2(TFE)) adducts, with methanol binding preferentially (K_(eq) = 0.0042 \u00b1 0.0006). C\u2212H activation gives [(N-N)Pt(CH_2OD)(MeOD)]^+ (4), which is unstable and reacts with [(RO)B(C_6F_5)_3]^- to generate a pentafluorophenyl platinum complex. Analysis of kinetics data for reaction of 2 with methanol yields k = 2.0 \u00b1 0.2 \u00d7 10^(-3) M^(-1) s^(-1) at 330 K, with a small kinetic isotope effect (k_H/k_D = 1.4 \u00b1 0.1). Reaction of dimethyl ether with 2(TFE) proceeds similarly (K_(eq) = 0.023 \u00b1 0.002, 313 K; k = 5.5 \u00b1 0.5 \u00d7 10^(-4) M^(-1) s^(-1), k_H/k_D = 1.5 \u00b1 0.1); the product obtained is a novel bis(alkylidene)-bridged platinum dimer, [(diimine)Pt(\u03bc-CH_2)(\u03bc-(CH(OCH_3))Pt(diimine)]^(2+) (5). Displacement of TFE by a C\u2212H bond appears to be the rate-determining step for all three substrates; comparison of the second-order rate constants (k(_(methane))/k(_(methanol)) = 1/1.3, 330 K; k(_(methane))/k(_(dimethyl ether)) = 1/2.0, 313 K) shows that this step is relatively unselective for the C\u2212H bonds of methane, methanol, or dimethyl ether. This low selectivity agrees with previous estimates for oxidations with aqueous tetrachloroplatinate(II)/hexachloroplatinate(IV), suggesting a similar rate-determining step for those reactions.", "doi": "10.1021/ja056387t", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2006-02-15", "series_number": "6", "volume": "128", "issue": "6", "pages": "2005-2016" }, { "id": "authors:j15rx-gv065", "collection": "authors", "collection_id": "j15rx-gv065", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170725-135756147", "type": "article", "title": "Improved One-Pot Synthesis of Mixed Methyl\u2212Aryl Platinum(II) Diimine Complexes", "author": [ { "family_name": "Lersch", "given_name": "Martin", "clpid": "Lersch-M" }, { "family_name": "Dalhus", "given_name": "Bj\u00f8rn", "clpid": "Dalhus-B" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Labinger", "given_name": "Jay", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Tilset", "given_name": "Mats", "clpid": "Tilset-M" } ], "abstract": "A general one-pot synthetic route for mixed methyl\u2212aryl Pt(II) diimine complexes is described. Performing the alkylation in neat Me_2S instead of ether or THF greatly reduces the amount of comproportionation products otherwise formed, diminishes separation problems, and improves yields. Treatment of the intermediate methyl\u2212aryl complexes (Me_2S)_2Pt(Me)(Ar) with diimines (N\u2212N) furnishes the methyl\u2212aryl Pt(II) diimine complexes (N\u2212N)Pt(Me)(Ar) in 76\u221284% yields. The Pt methyl\u2212phenyl complex [p-Tol-N \u2550 VC(Me)C(Me) \u2550 N-p-Tol]Pt(Me)(Ph) has been characterized by X-ray diffraction.", "doi": "10.1021/om050899z", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2006-02-13", "series_number": "4", "volume": "25", "issue": "4", "pages": "1055-1058" }, { "id": "authors:8g86k-z0c21", "collection": "authors", "collection_id": "8g86k-z0c21", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170308-145705982", "type": "article", "title": "Cyclopentadienyl and Olefin Substituent Effects on Insertion and \u03b2-Hydrogen Elimination with Group 4 Metallocenes. Kinetics, Mechanism, and Thermodynamics for Zirconocene and Hafnocene Alkyl Hydride Derivatives", "author": [ { "family_name": "Chirik", "given_name": "Paul J.", "clpid": "Chirik-P-J" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Reactions of group 4 metallocene dihydrides, (R_nCp)_2MH_2 (R_nCp = alkyl-substituted cyclopentadienyl; M = Zr, Hf), with olefins afford stable metallocene alkyl hydride complexes of the general formula (R_nCp)_2M(CH_2CHR'_2)(H) (R' = H, alkyl). For sterically crowded, monomeric dihydrides, Cp^*_2ZrH_2 (Cp^* = \u03b7^5-C_5Me_5), Cp^*(\u03b7^5-C_5Me_4H)ZrH_2, Cp^*(\u03b7^5-C_5Me_4Et)ZrH_2, Cp^*_2HfH_2, and Cp^*(\u03b7^5-C_5H_3-1,3-(CMe_3)_2)HfH_2, second-order rate constants for olefin insertion have been measured. For Cp^*_2HfH_2, the relative rates of olefin insertion have been found to be 1-pentene > styrene \u226b cis-2-butene > cyclopentene > trans-2-butene > isobutene. The rate of isobutene insertion into Cp^*(\u03b7^5-C_5Me_4H)ZrH_2 is 3.8 \u00d7 10^3 times greater than that for Cp^*_2ZrH_2 at \u221263 \u00b0C, demonstrating the striking steric effect for isobutene insertion imposed by a tenth methyl substituent on the two cyclopentadienyl ligands. A primary k_H/kD of 2.4(3) at 23 \u00b0C and a linear free energy correlation to \u03c3 (\u03c1 = \u22120.46(1)) for para-substituted styrene insertion indicate that insertion into a Zr\u2212H bond proceeds via rate-determining hydride transfer to coordinated olefin, with small positive charge buildup at the \u03b2-carbon of the inserting styrene. The rates of \u03b2-H elimination for the series (R_nCp)_2Zr(CH_2CHR')(H) have been measured via rapid trapping of the intermediate zirconocene dihydride with 4,4-dimethyl-2-pentyne. Key observations for \u03b2-H elimination are (a) primary kinetic deuterium isotope effects (k_H/k_D = 3.9\u22124.5) and (b) a linear free relationship for the phenethyl hydride series Cp^*(\u03b7^5-C_5Me_4H)Zr(CH_2CH_2-p-C_6H_4-X)(H) (X = H, CH_3, CF_3, OCH_3), which correlates better to \u03c3 than \u03c3^+; \u03c1 = \u22121.80(5). The rate of \u03b2-H elimination slows with more substituted, hence more sterically crowded, cyclopentadienyl ligands. Equilibration of a series of Cp^*(CpR_n)Zr(CH_2CHMe_2)(H) and Cp^*(CpR_n)Zr(CH_2CH_2CH_2CH_3)(H) with free isobutene and 1-butene has established the relative ground-state energies of isobutyl and n-butyl complexes. These data, in combination with the free energies of activation for \u03b2-H elimination, allow free energy profiles to be constructed for insertion and \u03b2-H elimination for each olefin.", "doi": "10.1021/om0580351", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2005-10-24", "series_number": "22", "volume": "24", "issue": "22", "pages": "5407-5423" }, { "id": "authors:nxdyt-ad165", "collection": "authors", "collection_id": "nxdyt-ad165", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170725-152201084", "type": "article", "title": "Mechanism of C\u2212H Bond Activation of Alkyl-Substituted Benzenes by Cationic Platinum(II) Complexes", "author": [ { "family_name": "Driver", "given_name": "Tom G.", "clpid": "Driver-T-G" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "While all methyl- and ethyl-substituted benzenes react with diimine Pt(II) methyl cations to give \u03b7^3-benzyl products, they do not all get there by the same pathway. For toluene and p-xylene, isotopic labeling shows that initial activation occurs at aryl positions with subsequent intermolecular conversion to the benzyl product. For ethylbenzene and 1,4-diethylbenzene, initial activation takes place exclusively at aryl C\u2212H bonds, and conversion to the \u03b7^3-benzyl product takes place via intramolecular isomerization. Only in the most extreme case of steric crowding the reaction of a bulky diimine platinum methyl cation (Ar = Mes) with triethylbenzene does direct activation of the ethyl group become preferred to aryl activation.", "doi": "10.1021/om050251m", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2005-07-17", "series_number": "15", "volume": "24", "issue": "15", "pages": "3644-3654" }, { "id": "authors:0xt9s-fsq74", "collection": "authors", "collection_id": "0xt9s-fsq74", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150622-144456252", "type": "article", "title": "Experimental Evidence for \u03b3-Agostic Assistance in \u03b2-Methyl Elimination, the Microscopic Reverse of \u03b1-Agostic Assistance in the Chain Propagation Step of Olefin Polymerization", "author": [ { "family_name": "Chirik", "given_name": "Paul J.", "clpid": "Chirik-P-J" }, { "family_name": "Dalleska", "given_name": "Nathan F.", "orcid": "0000-0002-2059-1587", "clpid": "Dalleska-N-F" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Isotopically labeled zirconocene methyl neopentyl complexes of the formula (CpR_n)_2Zr(CH_3)(CH_2C(CH_3)2CD_3) are obtained via reaction of LiCH_2C(CH_3)_2CD_3 with (CpR_n)_2Zr(CH_3)(Cl). Addition of B(C_6F_5)_3 to (CpR_n)_2Zr(CH_3)(CH_2C(CH_3)_2CD_3) results in \u03b2-methyl elimination, forming the ion-paired species [(CpR_n)_2Zr(CH_3)][CH_3B(C_6F_5)_3] along with isotopologs of isobutene. The relative amounts of d_3- and d_0-isobutene afford the isotope effect for \u03b2-methyl elimination. For Cp_2Zr(CH_3)(CH_2C(CH_3)_2CD_3) (Cp = (\u03b7^5-C_5H_5)), a kinetic deuterium isotope effect of 1.40(2) has been measured at 23 \u00b0C. Comparable deuterium kinetic isotope effects have been observed for four other zirconocene methyl neopentyl compounds:\u2009 [Cp^*(C_5Me_4H)Zr] (Cp^* = (\u03b7^5-C_5Me_5)), [Cp^*_2Zr], [rac-(EBI)Zr] (EBI = ethylenebis(indenyl)), and [(THP)Zr] (THP = 1,2-(SiMe_2)_2(\u03b7^5-3,5-C_5H(CHMe_2)_2)(\u03b7^5-C_5H_3)). The direction and magnitude of these effects are consistent with \u03b3-agostic assistance in the transition state for \u03b2-methyl elimination, the microscopic reverse of \u03b1-agostic assistance in the transition state for olefin insertion into the Zr\u2212methyl bond.", "doi": "10.1021/om058002l", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2005-05-23", "series_number": "11", "volume": "24", "issue": "11", "pages": "2789-2794" }, { "id": "authors:rgbd0-6ya09", "collection": "authors", "collection_id": "rgbd0-6ya09", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170420-084321419", "type": "article", "title": "Kinetic and Thermodynamic Preferences in Aryl vs Benzylic C\u2212H Bond Activation with Cationic Pt(II) Complexes", "author": [ { "family_name": "Heyduk", "given_name": "Alan F.", "clpid": "Heyduk-A-F" }, { "family_name": "Driver", "given_name": "Tom G.", "clpid": "Driver-T-G" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Anhydrous cationic Pt(II) complexes [(NN)Pt(CH_3)(CF_3CD_2OD)]+ (1, NN = ArNC(Me)\u2212C(Me)NAr), which are obtained by reaction of (NN)Pt(CH_3)_2 with B(C_6F_5)_3 in CF_3CD_2OD, activate C\u2212H bonds of benzene and methylbenzenes, with enhanced reactivity compared to the previously prepared equilibrium mixtures with the (thermodynamically favored) aquo complexes. For methylbenzenes (toluene, p-xylene, mesitylene), activation at the aromatic and benzylic positions are kinetically competitive, but the product of the latter is strongly favored thermodynamically. This unusual trend is attributed to formation of \u03b7^3-benzyl structures, which can be observed spectroscopically for 1,4-diethylbenzene activation.", "doi": "10.1021/ja045078k", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2004-11-24", "series_number": "46", "volume": "126", "issue": "46", "pages": "15034-15035" }, { "id": "authors:qgkck-1gx61", "collection": "authors", "collection_id": "qgkck-1gx61", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170420-063815176", "type": "article", "title": "Pyridinium-Derived N-Heterocyclic Carbene Complexes of Platinum: Synthesis, Structure and Ligand Substitution Kinetics", "author": [ { "family_name": "Owen", "given_name": "Jonathan S.", "clpid": "Owen-J-S" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A series of [(R-iso-BIPY)Pt(CH_3)L]^+X^- complexes [R-iso-BIPY = N-(2-pyridyl)-R-pyridine-2-ylidene; (R = 4-H, 1; 4-tert-butyl, 2; 4-dimethylamino, 3; 5-dimethylamino, 4); L = SMe_2, b; dimethyl sulfoxide (DMSO), c; carbon monoxide (CO), d; X = OTf- = trifluoromethanesulfonate and/or [BPh_4]-] were synthesized by cyclometalation of the [R-iso-BIPY\u2212H]^+[OTF]- salts 1a\u22124a ([R-iso-BIPY\u2212H]^+ = N-(2-pyridyl)-R-pyridinium) with dimethylplatinum-\u03bc-dimethyl sulfide dimer. X-ray crystal structures for 1b, 2c\u22124c as well as complexes having bipyridyl and cyclometalated phenylpyridine ligands, [(bipy)Pt(CH_3)(DMSO)]^+ (5c) and (C_(11)H_8N)Pt(CH_3)(DMSO) (6c), have been determined. The pyridinium-derived N-heterocyclic carbene complexes display localized C\u2212C and C\u2212N bonds within the pyridinium ligand that are indicative of carbene \u03c0-acidity. The significantly shortened platinum\u2212carbon distance, for \"parent\" complex 1b, together with NMR parameters and the \u03bd(CO) values for carbonyl cations 1d\u22124d support a degree of Pt\u2212C10 multiple bonding, increasing in the order 3 < 4 < 2 < 1. Degenerate DMSO exchange kinetics have been determined to establish the nature and magnitude of the trans-labilizing ability of these new N-heterocyclic carbene ligands. Exceptionally large second-order rate constants (k_2 = 6.5 \u00b1 0.4 M^(-1)\u00b7s^(-1) (3c) to 2300 \u00b1 500 M^(-1)\u00b7s^(-1) (1c)) were measured at 25 \u00b0C using ^1H NMR magnetization transfer kinetics and variable temperature line shape analysis. These rate constants are as much as 4 orders of magnitude greater than those of a series of structurally similar cationic bis(nitrogen)-donor complexes [(N\u2212N)Pt(CH_3)(DMSO)]^+ reported earlier, and a factor of 32 to 1800 faster than an analogous charge neutral complex derived from cyclometalated 2-phenylpyridine, (C_(11)H_8N)Pt(CH_3)(DMSO) (k_2 = 0.21 \u00b1 0.02 M^(-1)\u00b7s^(-1) (6c)). The differences in rate constant are discussed in terms of ground state versus transition state energies. Comparison of the platinum\u2212sulfur distances with second order rate constants suggests that differences in the transition-state energy are largely responsible for the range of rate constants measured. The \u03c0-accepting ability and trans-influence of the carbene donor are proposed as the origin of the large acceleration in associative ligand substitution rate.", "doi": "10.1021/ja040075t", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2004-07-07", "series_number": "26", "volume": "126", "issue": "26", "pages": "8247-8255" }, { "id": "authors:8e8jn-4xv07", "collection": "authors", "collection_id": "8e8jn-4xv07", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170420-063814924", "type": "article", "title": "Kinetic Resolution of Chiral \u03b1-Olefins Using Optically Active ansa-Zirconocene Polymerization Catalysts", "author": [ { "family_name": "Baar", "given_name": "Cliff R.", "clpid": "Baar-C-R" }, { "family_name": "Levy", "given_name": "Christopher J.", "clpid": "Levy-C-J" }, { "family_name": "Min", "given_name": "Endy Y.-J.", "clpid": "Min-Endy-Y-J" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A series of enantiopure C_1-symmetric metallocenes, {(SiMe_2)_2[\u03b7^5-C_5H(CHMe_2)_2][\u03b7^5-C_5H_2((S)-CHMeCMe_3)]}ZrCl_2, (S)-2, {(SiMe_2)_2[\u03b7^5-C_5H(CHEt_2)_2][\u03b7^5-C_5H_2((S)-CHMeCMe_3)]}ZrCl_2, (S)-6, and {(SiMe_2)_2[\u03b7^5-C_5HCy_2][\u03b7^5-C_5H_2((S)-CHMeCMe_3)]}ZrCl_2, (S)-7 (Cy = cyclohexyl), zirconocene dichlorides that have an enantiopure methylneopentyl substituent on the \"upper\" cyclopentadienyl ligand, and diastereomerically pure precatalysts, {(SiMe_2)_2[\u03b7^5-C_5H((S)-CHMeCy)(CHMe_2)][\u03b7^5-C_5H_3]}ZrCl_2, (S)-8a and (S)-8b, which have an enantiopure, 1-cyclohexylethyl substituent on the \"lower\" cyclopentadienyl ligand, has been synthesized for use in the polymerization of chiral \u03b1-olefins. When activated with methylaluminoxane, these metallocenes show unprecedented activity for the polymerization of bulky racemic monomers bearing substitution at the 3- and/or 4-positions. Due to the optically pure nature of these single site catalysts, they effect kinetic resolution of racemic monomers:\u2009 the polymeric product is enriched with the faster reacting enantiomer, while recovered monomer is enriched with the slower reacting enantiomer. The two components are easily separated. For most olefins surveyed, a partial kinetic resolution was achieved (s = k_(faster)/k_(slower) \u2248 2), but, in one case, the polymerization of 3,4-dimethyl-1-pentene, high levels of separation were obtained (s > 15). ^(13)C NMR spectroscopy of poly(3-methyl-1-pentene) produced with (S)-2 indicates that the polymers are highly isotactic materials. X-ray crystal structure determinations for (S)-2, {(SiMe_2)_2[\u03b7^5-C_5H(CHMe_2)_2][\u03b7^5-C_5H_2((S)-CHMeCMe_3)]}Zr(SC_6H_5)_2, (S)-6, and (S)-7 have been used in combination with molecular mechanics calculations to examine the prevailing steric interactions expected in the diastereomeric transition states for propagation during polymerization. Precatalysts (S)-8a and (S)-8b are less selective polymerization catalysts for the kinetic resolution of 3-methyl-1-pentene than are (S)-2, (S)-6, and (S)-7.", "doi": "10.1021/ja040021j", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2004-07-07", "series_number": "26", "volume": "126", "issue": "26", "pages": "8216-8231" }, { "id": "authors:3wnnz-9fh69", "collection": "authors", "collection_id": "3wnnz-9fh69", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170807-155218146", "type": "article", "title": "Highly Stereoregular Syndiotactic Polypropylene Formation with Metallocene Catalysts via Influence of Distal Ligand Substituents", "author": [ { "family_name": "Miller", "given_name": "Stephen A.", "orcid": "0000-0002-3181-1426", "clpid": "Miller-S-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Highly stereoregular syndiotactic polypropylene is obtained with the catalyst systems Ph_2C(Oct)(C_5H_4)ZrCl_2/MAO (8/MAO) (Oct = octamethyloctahydrodibenzofluorenyl; MAO = methylaluminoxane) and Me_2C(Oct)(C_5H_4)ZrCl_2/MAO (12/MAO). The syndiotactic polypropylenes obtained are largely devoid of stereoerrors by ^(13)C NMR analysis ([r] > 98%), and melting temperatures as high as 153 or 154 \u00b0C (from 8 and 12, respectively) are found for the thermally quenched polymers (without annealing). A related hafnium catalytic system, Ph_2C(Tet)(C_5H_4)HfCl_2/MAO (11/MAO) (Tet = tetramethyltetrahydrobenzofluorenyl), was found to be the most syndioselective of the hafnocenes tested (T_m = 141 \u00b0C). The metallocene dichloride precatalysts represent the first examples of transition metal complexes containing the Oct or Tet ligands. Reported are the solid state crystal structures of 8, the diprotio ligand precursor of 8(Ph_2C(OctH)(C_5H_5)), and the zirconium analogue of 11, Ph_2C(Tet)(C_5H_4)ZrCl_2 (10). Distal ligand influences are thus demonstrated to have a dramatic effect on polymer stereochemistry.", "doi": "10.1021/om030333f", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2004-04-12", "series_number": "8", "volume": "23", "issue": "8", "pages": "1777-1789" }, { "id": "authors:af9b5-ybv56", "collection": "authors", "collection_id": "af9b5-ybv56", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170419-145525386", "type": "article", "title": "Mechanistic Studies of the Ethylene Trimerization Reaction with Chromium\u2212Diphosphine Catalysts: Experimental Evidence for a Mechanism Involving Metallacyclic Intermediates", "author": [ { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" }, { "family_name": "Schofer", "given_name": "Susan J.", "clpid": "Schofer-S-J" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A system for catalytic trimerization of ethylene utilizing CrCl_3(THF)_3 and a diphosphine ligand PNP^(OMe) [=\u2009(o-MeO-C_6H_4)_2PN(Me)P(o-MeO-C_6H_4)_2] has been investigated. The coordination chemistry of chromium with PNP^(OMe) has been explored, and (PNP^(OMe))CrCl_3 and (PNP^(OMe))CrPh_3 (3) have been synthesized by ether displacement from chromium(III) precursors. Salt metathesis of (PNP^(OMe))CrCl_3 with o,o'-biphenyldiyl Grignard affords (PNP^(OMe))Cr(o,o'-biphenyldiyl)Br (4). Activation of 3 with H(Et_2O)_2B[C_6H_3(CF_3)_2]_4 or 4 with NaB[C_6H_3(CF_3)_2]_4 generates a catalytic system and trimerizes a 1:1 mixture of C_2D_4 and C_2H_4 to give isotopomers of 1-hexene without H/D scrambling (C_6D_(12), C_6D_8H_4, C_6D_4H_8, and C_6H_(12) in a 1:3:3:1 ratio). The lack of crossover supports a mechanism involving metallacyclic intermediates. The mechanism of the ethylene trimerization reaction has also been studied by the reaction of trans-, cis-, and gem-ethylene-d_2 with 4 upon activation with NaB[C_6H_3(CF_3)_2]_4.", "doi": "10.1021/ja038968t", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2004-02-11", "series_number": "5", "volume": "126", "issue": "5", "pages": "1304-1305" }, { "id": "authors:6kc0p-2p343", "collection": "authors", "collection_id": "6kc0p-2p343", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170405-141647841", "type": "article", "title": "C\u2212H Bond Activation by Unsymmetrical 2-(N-Arylimino)pyrrolide Pt Complexes: Geometric Effects on Reactivity", "author": [ { "family_name": "Iverson", "given_name": "Carl N.", "clpid": "Iverson-Carl-N" }, { "family_name": "Carter", "given_name": "Charles A. G.", "clpid": "Carter-Charles-A-G" }, { "family_name": "Baker", "given_name": "R. Tom", "clpid": "Baker-R-Tom" }, { "family_name": "Scollard", "given_name": "John D.", "clpid": "Scollard-John-D" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-Jay-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Reactions of chloroplatinum methyl complexes with N-(arylimino)pyrrolide anions afford cis and trans neutral platinum methyl complexes. Isomers with methyl trans to the pyrrolide nitrogen activate benzene C\u2212H bonds at 85 \u00b0C more than 80 times faster than the corresponding cis isomer. In addition, reactions of platinum dimethyl complexes with N-(arylimino)pyrroles (Ar = 4-substituted phenyl) in C_6D_6 at ambient temperature give unlabeled methane and cis methyl complex containing heavily deuterated Pt\u2212Me. In contrast, bulky aryl substituents give methane isotopomers and trans-Pt\u2212Ph product. The origins of these observations are discussed.", "doi": "10.1021/ja036511d", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2003-10-22", "series_number": "42", "volume": "125", "issue": "42", "pages": "12674-12675" }, { "id": "authors:b9vre-fx662", "collection": "authors", "collection_id": "b9vre-fx662", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170310-073002998", "type": "article", "title": "Arene C\u2212H Bond Activation and Arene Oxidative Coupling by Cationic Palladium(II) Complexes", "author": [ { "family_name": "Ackerman", "given_name": "Lily J.", "clpid": "Ackerman-L-J" }, { "family_name": "Sadighi", "given_name": "Joseph P.", "clpid": "Sadighi-J-P" }, { "family_name": "Kurtz", "given_name": "David M.", "orcid": "0000-0002-6382-4651", "clpid": "Kurtz-D-M" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "N,N'-Diaryl-\u03b1-diimine-ligated Pd(II) dimethyl complexes (^(tBu)2^(Ar)DAB^(Me))PdMe_2 and {(CF_3)_2^(Ar)DAB^(Me)}PdMe_2 {^(tBu)2^(Ar)DAB^(Me):\u2009ArNC\u2550(CH_3)\u2212C(CH_3\u2550NAr, Ar=3,5-di-tert-butylphenyl; (CF_3)_2^(Ar)DAB^(Me):Ar = 3,5-bis(trifluoromethyl)phenyl} undergo protonolysis with HBF_4(aq) in trifluoroethanol (TFE) to form cationic complexes [(\u03b1-diimine)Pd(CH_3)(H_2O)][BF_4]. The cations activate benzene C\u2212H bonds at room temperature. Kinetic analyses reveal trends similar to those observed for the analogous platinum complexes:\u2009 the C\u2212H activation step is rate-determining (KIE = 4.1 \u00b1 0.5) and is inhibited by H_2O. The kinetic data are consistent with a mechanism in which benzene substitution proceeds by a solvent- (TFE-) assisted associative pathway. Following benzene C\u2212H activation under 1 atm O_2, the products of the reaction are biphenyl and a dimeric \u03bc-hydroxide complex, [(\u03b1-diimine)Pd(OH)]_2[BF_4]_2. The Pd(0) formed in the reaction is reoxidized by O_2 to the dimeric \u03bc-hydroxide complex after the oxidative C\u2212C bond formation. The regioselectivity of arene coupling was investigated with toluene and \u03b1,\u03b1,\u03b1-trifluorotoluene as substrates.", "doi": "10.1021/om0303294", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2003-09-15", "series_number": "19", "volume": "22", "issue": "19", "pages": "3884-3890" }, { "id": "authors:raj5x-5qn52", "collection": "authors", "collection_id": "raj5x-5qn52", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170417-065654691", "type": "article", "title": "Catalytic Alcoholysis of Tetramethylsilane via Pt-Mediated C\u2212H Bond Activation", "author": [ { "family_name": "Heyduk", "given_name": "Alan F.", "clpid": "Heyduk-A-F" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Tetramethylsilane reacts with 2,2,2-trifluoroethanol (TFE) in the presence of a cationic platinum(II) catalyst [(NN)PtMe(TFE)]+ (NN = 1,2-bis(3,5-dimethylphenylimino)butane). Catalytic Si\u2212C bond heterolysis results in the formation of the trimethylsilyl ether, Me_3SiOCH_2CF_3, accompanied by liberation of one equivalent of methane. Preliminary experiments suggest that a rate-determining C\u2212H bond activation precedes rapid attack by solvent at silicon to yield the silyl ether product and regenerate the active platinum methyl cation.", "doi": "10.1021/ja029099v", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2003-05-28", "series_number": "21", "volume": "125", "issue": "21", "pages": "6366-6367" }, { "id": "authors:31c9t-1e973", "collection": "authors", "collection_id": "31c9t-1e973", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170310-064611489", "type": "article", "title": "Experimental and Theoretical Studies of Olefin Insertion foransa-Niobocene andansa-Tantalocene Ethylene Hydride Complexes", "author": [ { "family_name": "Ackerman", "given_name": "Lily J.", "clpid": "Ackerman-L-J" }, { "family_name": "Green", "given_name": "Malcolm L. H.", "clpid": "Green-M-L-H" }, { "family_name": "Green", "given_name": "Jennifer C.", "clpid": "Green-J-C" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Using dynamic NMR methods the rates of hydrogen exchange following intramolecular ethylene insertion into the metal\u2212hydride bond have been measured for the following group 5 ansa-metallocene complexes:\u2009 [Me_2Si(\u03b7^5-C_5H_4)(\u03b7^5-C_5H_3-3-R)]Nb(CH_2CH_2)H (R = CHMe_2, CMe_3), rac- and meso-[Me_2Si(\u03b7^5-C_5H_3-3-CMe_3)_2]Nb(CH_2CH_2)H, and [(1,2-SiMe_2)_2(\u03b7^5-C_5H-3,5-(CHMe_2)_2)(\u03b7^5-C_5H_2-4-CMe_3)]Ta(CH_2CH_2)H. The singly bridged ansa-niobocenes exchange up to 3 orders of magnitude faster than unbridged complexes. However, the doubly bridged ansa-tantalocene complex exchanges at a rate comparable to that previously reported for (\u03b7^5-C_5Me_5)_2Ta(CH_2CH_2)H and much slower than a singly bridged complex, [Me_2Si(\u03b7^5-C_5Me_4)_2]Ta(CH_2CH_2)H. These \"ansa-effects\" were investigated by DFT calculations on model complexes. The computed exchange pathway showed the presence of an agostic ethyl intermediate. The calculated barriers for hydrogen exchange of model unbridged, singly bridged, and doubly bridged niobocenes correlate with the experimental results.", "doi": "10.1021/om0206296", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2003-01-06", "series_number": "1", "volume": "22", "issue": "1", "pages": "188-194" }, { "id": "authors:pke8d-xa911", "collection": "authors", "collection_id": "pke8d-xa911", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170808-142319435", "type": "article", "title": "Preparation of ansa-Niobocene and ansa-Tantalocene Olefin Hydride Complexes as Transition State Analogues in Metallocene-Catalyzed Olefin Polymerization", "author": [ { "family_name": "Chirik", "given_name": "Paul J.", "clpid": "Chirik-P-J" }, { "family_name": "Zubris", "given_name": "Deanna L.", "clpid": "Zubris-D-L" }, { "family_name": "Ackerman", "given_name": "Lily J.", "clpid": "Ackerman-L-J" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "o examine the effects of cyclopentadienyl and olefin substitution on preferred stereochemistry, a series of singly [SiMe_2]-bridged ansa-niobocene and -tantalocene olefin hydride complexes has been prepared via reduction and alkylation of the corresponding dichloride complexes. In this manner, [Me_2Si(\u03b7^5-C_5H_4)(\u03b7^5-C_5H_3-3-R)]M(CH_2\u268cCHR')H (M = Nb, Ta; R = CHMe_2, CMe_3; R' = H, C6H5; M = Ta; R = CHMe2, CMe3; R' = Me), rac- and meso-[Me_2Si(\u03b7^5-C_5H_3-3-R)(\u03b7^5-C_5H^3-3-R)]Nb(CH_2\u268cCH_2)H (R = CMe_3), and [Me_2Si(\u03b7^5-C_5H_4)(\u03b7^5-C_5H^2-2,4-(CHMe_2)_2)]Ta(CH_2\u268cCHR')H (R' = H, C_6H_5) have been prepared and characterized by NMR spectroscopy and, in some cases, X-ray diffraction. The doubly [SiMe_2]-bridged ansa-tantalocene ethylene hydride complex [(1,2-SiMe_2)_2(\u03b7^5-C_5H-3,5-(CHMe_2)_2)(\u03b7^5-C_5H_2-4-CMe_3)]Ta(CH_2\u268cCH_2)H has been prepared from thermolysis of the methylidene methyl complex [(1,2-SiMe_2)_2(\u03b7^5-C_5H-3,5-(CHMe_2)_2)(\u03b7^5-C_5H_2-4-CMe_3)]Ta(CH_2)CH_3. Addition of an excess of propylene or styrene to the tantalocene ethylene hydride results in olefin exchange and formation of the olefin hydride complexes [(1,2-SiMe_2)_2(\u03b7^5-C_5H-3,5-(CHMe_2)_2)(\u03b7^5-C_5H_2-4-CMe_3)]Ta(CH_2\u268cCHR')H (R' = CH_3, C_6H_5). These compounds serve as stable transition state analogues for the much more kinetically labile group 4 metallocenium cationic intermediates in metallocene-catalyzed olefin polymerization. Characterization of the thermodynamically preferred isomers of metallocene olefin hydride complexes reveals that alkyl substitution on the cyclopentadienyl ligand array may have a significant effect on the stereochemistry of olefin coordination.", "doi": "10.1021/om020628d", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2003-01-06", "series_number": "1", "volume": "22", "issue": "1", "pages": "172-187" }, { "id": "authors:fc96x-jr256", "collection": "authors", "collection_id": "fc96x-jr256", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170414-073636496", "type": "article", "title": "The Electronic Influence of Ring Substituents and Ansa Bridges in Zirconocene Complexes as Probed by Infrared Spectroscopic, Electrochemical, and Computational Studies", "author": [ { "family_name": "Zachmanoglou", "given_name": "Cary E.", "clpid": "Zachmanoglou-C-E" }, { "family_name": "Docrat", "given_name": "Arefa", "clpid": "Docrat-A" }, { "family_name": "Bridgewater", "given_name": "Brian M.", "clpid": "Bridgewater-B-M" }, { "family_name": "Parkin", "given_name": "Gerard", "clpid": "Parkin-G" }, { "family_name": "Brandow", "given_name": "Christopher G.", "clpid": "Brandow-C-G" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Jardine", "given_name": "Christian N.", "clpid": "Jardine-C-N" }, { "family_name": "Lyall", "given_name": "Mark", "clpid": "Lyall-M" }, { "family_name": "Green", "given_name": "Jennifer C.", "clpid": "Green-J-C" }, { "family_name": "Keister", "given_name": "Jerome B.", "clpid": "Keister-J-B" } ], "abstract": "The electronic influence of unbridged and ansa-bridged ring substituents on a zirconocene center has been studied by means of IR spectroscopic, electrochemical, and computational methods. With respect to IR spectroscopy, the average of the symmetric and asymmetric stretches (\u03bd_(CO(av))) of a large series of dicarbonyl complexes (Cp^R)_2Zr(CO)_2 has been used as a probe of the electronic influence of a cyclopentadienyl ring substituent. For unbridged substituents (Me, Et, Pri, But, SiMe_3), \u03bd_(CO(av)) on a per substituent basis correlates well with Hammett \u03c3_(meta) parameters, thereby indicating that the influence of these substituents is via a simple inductive effect. In contrast, the reduction potentials (E\u00b0) of the corresponding dichloride complexes (Cp^R)_2ZrCl_2 do not correlate well with Hammett \u03c3_(meta) parameters, thereby suggesting that factors other than the substituent inductive effect also influence E\u00b0. Ansa bridges with single-atom linkers, for example [Me_2C] and [Me_2Si], exert a net electron-withdrawing effect, but the effect is diminished upon increasing the length of the bridge. Indeed, with a linker comprising a three-carbon chain, the [CH_2CH_2CH_2] ansa bridge becomes electron-donating. In contrast to the electron-withdrawing effect observed for a single [Me_2Si] ansa bridge, a pair of vicinal [Me_2Si] ansa bridges exerts an electron-donating effect relative to that from the single bridge. DFT calculations demonstrate that the electron-withdrawing effect of the [Me_2C] and [Me_2Si] ansa-bridges is due to stabilization of the cyclopentadienyl ligand acceptor orbital, which subsequently enhances back-donation from the metal. The calculations also indicate that the electron-donating effect of two vicinal [Me_2Si] ansa bridges, relative to that of a single bridge, is a result of it enforcing a ligand conformation that reduces back-donation from the metal.", "doi": "10.1021/ja020236y", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2002-08-14", "series_number": "32", "volume": "124", "issue": "32", "pages": "9525-9546" }, { "id": "authors:90phk-tcn88", "collection": "authors", "collection_id": "90phk-tcn88", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170321-100112771", "type": "article", "title": "Structural and Mechanistic Investigations of the Oxidation of Dimethylplatinum(II) Complexes by Dioxygen", "author": [ { "family_name": "Rostovtsev", "given_name": "Vsevolod V.", "clpid": "Rostovtsev-V-V" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The oxidation of (tmeda)Pt^(II)(CH_3)_2 (1, tmeda = N,N,N',N'-tetramethylethylenediamine) to (tmeda)Pt^(IV)(OH)(OCH_3)(CH_3)_2 (3) by dioxygen in methanol proceeds via a two-step mechanism. The initial reaction between (tmeda)Pt(CH_3)_2 and dioxygen yields a hydroperoxoplatinum(IV) intermediate, (tmeda)Pt(OOH)(OCH_3)(CH_3)_2 (2), which reacts with a second equivalent of (tmeda)Pt(CH_3)_2 to afford the final product 3. Both 2 and 3 have been fully characterized, including X-ray crystallographic structure determinations. The effect of ligand variation on the oxidation of several dimethylplatinum(II) complexes by 2 as well as by dioxygen has been examined.", "doi": "10.1021/ic0112903", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2002-07-15", "series_number": "14", "volume": "41", "issue": "14", "pages": "3608-3619" }, { "id": "authors:f0qzc-81593", "collection": "authors", "collection_id": "f0qzc-81593", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150327-084003977", "type": "article", "title": "Understanding and exploiting C\u2013H bond activation", "author": [ { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The selective transformation of ubiquitous but inert C\u2013H bonds to other functional groups has far-reaching practical implications, ranging from more efficient strategies for fine chemical synthesis to the replacement of current petrochemical feedstocks by less expensive and more readily available alkanes. The past twenty years have seen many examples of C\u2013H bond activation at transition-metal centres, often under remarkably mild conditions and with high selectivity. Although profitable practical applications have not yet been developed, our understanding of how these organometallic reactions occur, and what their inherent advantages and limitations for practical alkane conversion are, has progressed considerably. In fact, the recent development of promising catalytic systems highlights the potential of organometallic chemistry for useful C\u2013H bond activation strategies that will ultimately allow us to exploit Earth's alkane resources more efficiently and cleanly.", "doi": "10.1038/417507a", "issn": "0028-0836", "publisher": "Nature Publishing Group", "publication": "Nature", "publication_date": "2002-05-30", "series_number": "6888", "volume": "417", "issue": "6888", "pages": "507-514" }, { "id": "authors:1whfa-4cz09", "collection": "authors", "collection_id": "1whfa-4cz09", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170515-152616804", "type": "article", "title": "Chain Epimerization during Propylene Polymerization with Metallocene Catalysts: Mechanistic Studies Using a Doubly Labeled Propylene", "author": [ { "family_name": "Yoder", "given_name": "Jeffrey C.", "clpid": "Yoder-J-C" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The mechanisms of chain epimerization during propylene polymerization with methylaluminoxane-activated rac-(EBTHI)ZrCl_2 and rac-(EBI)ZrCl_2 catalysts (EBTHI = ethylenebis(\u03b7^5-tetrahydroindenyl); EBI = ethylenebis(\u03b7^5-indenyl)) have been studied using specifically isotopically labeled propylene: CH_2\u2550CD^(13)CH_3. These isospecific catalysts provide predominantly the expected [mmmm] pentads with [\u2212CH_2CD^(13)CH_3-] repeating units (^(13)C NMR). Under relatively low propylene concentrations at 50 and 75 \u00b0C, where stereoerrors attributable to chain epimerization are prevalent, ^(13)C NMR spectra reveal ^(13)C-labeled methylene groups along the polymer main chain, together with [CD^(13)CH_3] units in [mmmr], [mmrr], and [mrrm] pentads and [CH^(13)CH_3] units in [mmmmmm] and [mmmmmr] heptads, as well as [mrrm] pentads. The isotopomeric regiomisplacements and stereoerrors are consistent with a mechanism involving \u03b2-D elimination, olefin rotation and enantiofacial interconversions, and insertion to a tertiary alkyl intermediate [Zr\u2212C(CH_2D)(^(13)CH_3)P] (P = polymer chain), followed by the reverse steps to yield two stereoisomers of [Zr\u2212CHDCH(^(13)CH_3)P] and [Zr\u2212^(13)CH_2CH(CH_2D)P], as well as unrearranged [Zr\u2212CH_2CD(^(13)CH_3)P]. The absence of observable [\u2212CH2CH13CH2D\u2212] in the [mrrm] pentad region of the ^(13)C NMR spectra provides evidence that an allyl/dihydrogen complex does not mediate chain epimerization.", "doi": "10.1021/ja0123296", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2002-03-20", "series_number": "11", "volume": "124", "issue": "11", "pages": "2548-2555" }, { "id": "authors:9yetf-ydk28", "collection": "authors", "collection_id": "9yetf-ydk28", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170808-092203789", "type": "article", "title": "Isotactic\u2212Hemiisotactic Polypropylene from C_1-Symmetric ansa-Metallocene Catalysts: A New Strategy for the Synthesis of Elastomeric Polypropylene", "author": [ { "family_name": "Miller", "given_name": "Stephen A.", "orcid": "0000-0002-3181-1426", "clpid": "Miller-S-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Control of \"isotactic\u2212hemiisotactic\" alignment, a polypropylene microstructure in which every other stereocenter is of the same configuration and the intervening stereocenters tend to align with their neighbors, has been achieved by R substituent selection in the ansa-metallocene catalyst system R'_2C(\u03b7^5-3-R-C_5H_3)(\u03b7^5-C_(13)H_8)MCl_2\u2212MAO (M = Zr, Hf; \u03b7^5-C_(13)H_8 = fluorenyl; MAO = methylaluminoxane). For R = 2-adamantyl, R' = Ph, and M = Zr (4), \u03b1, a parameter equal to the m diad fraction, is approximately 0.58, with M_n = 204\u2009000\u2212463\u2009000, and the isotactic\u2212hemiisotactic polypropylene obtained is elastomeric. Typical elongations are between 7 and 14 times the original length, and the residual elongation following a 200% strain is between 1.5% and 9.3%. The elastomeric properties are rationalized by the statistical existence of isotactic stereoblocks among otherwise amorphous hemiisotactic connecting segments. A two-parameter (\u03b1 and M_n) statistical model has been derived which calculates the isotactic block length distribution and the percent crystallinity, assuming isotactic blocks of 21 monomer units and longer participate in crystallites. The best elastomers are found to have a calculated percent crystallinity in the range of 1.50\u22124.45% (\u03b1 = 0.557\u22120.630).", "doi": "10.1021/om010788+", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2002-03-04", "series_number": "5", "volume": "21", "issue": "5", "pages": "934-945" }, { "id": "authors:b88dx-64x91", "collection": "authors", "collection_id": "b88dx-64x91", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170321-104910356", "type": "article", "title": "C\u2212H Bond Activation by Cationic Platinum(II) Complexes: Ligand Electronic and Steric Effects", "author": [ { "family_name": "Zhong", "given_name": "H. Annita", "clpid": "Zhong-H-Annita" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A series of bis(aryl)diimine-ligated methyl complexes of Pt(II) with various substituted aryl groups has been prepared. The cationic complexes [(ArN CR\u2212CR NAr)PtMe(L)]^+[BF_4]- (Ar = aryl; R = H, CH_3; L = water, trifluoroethanol) react smoothly with benzene at approximately room temperature in trifluoroethanol solvent to yield methane and the corresponding phenyl Pt(II) cations, via Pt(IV)-methyl-phenyl-hydrido intermediates. The reaction products of methyl-substituted benzenes suggest an inherent reactivity preference for aromatic over benzylic C\u2212H bond activation, which can however be overridden by steric effects. For the reaction of benzene with cationic Pt(II) complexes bearing 3,5-disubstituted aryl diimine ligands, the rate-determining step is C\u2212H bond activation, whereas for the more sterically crowded analogues with 2,6-dimethyl-substituted aryl groups, benzene coordination becomes rate-determining. This switch is manifested in distinctly different isotope scrambling and kinetic deuterium isotope effect patterns. The more electron-rich the ligand is, as assayed by the CO stretching frequency of the corresponding carbonyl cationic complex, the faster the rate of C\u2212H bond activation. Although at first sight this trend appears to be at odds with the common description of this class of reaction as electrophilic, the fact that the same trend is observed for the two different series of complexes, which have different rate-determining steps, suggests that this finding does not reflect the actual C\u2212H bond activation process, but rather reflects only the relative ease of benzene displacing a ligand to initiate the reaction; that is, the change in rates is mostly due to a ground-state effect. The stability of the aquo complex ground state in equilibrium with the solvento complex increases as the diimine ligand is made more electron-withdrawing. Several lines of evidence, including the mechanism of degenerate acetonitrile exchange for the methyl-acetonitrile Pt(II) cations in alcohol solvents, suggest that associative substitution pathways operate to get the hydrocarbon substrate into, and out of, the coordination sphere; that is, the mechanism of benzene substitution proceeds by a solvent (TFE)-assisted associative pathway.", "doi": "10.1021/ja011189x", "issn": "0002-7863", "publisher": "Journal of the American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2002-02-20", "series_number": "7", "volume": "124", "issue": "7", "pages": "1378-1399" }, { "id": "authors:dazff-k8d64", "collection": "authors", "collection_id": "dazff-k8d64", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170808-082527490", "type": "article", "title": "Ancillary Ligand and Olefin Substituent Effects on Olefin Dissociation for Cationic Zirconocene Complexes Bearing a Coordinated Pendant Olefin", "author": [ { "family_name": "Brandow", "given_name": "Christopher G.", "clpid": "Brandow-C-G" }, { "family_name": "Mendiratta", "given_name": "Arjun", "clpid": "Mendiratta-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A series of zirconocene complexes bearing 2,2-dimethyl-2-sila-4-pentenyl substituents (and methyl-substituted olefin variants) ((\u03b7^5-C_5H_5)_2Zr(CH_3)(CH_2SiMe_2CH_2CR^1\u2550CR^2R^3) (R^1, R^2, R^3 = H, CH_3, 1, 5\u22127), (\u03b7^5-C_5H_4CMe_3)_2Zr(CH_3)(CH_2SiMe_2CH_2CH\u2550CH_2) (2), {Me_2Si(\u03b7^5-C_5H_4)_2}Zr(CH_3)(CH_2SiMe_2CH_2CH\u2550CH_2) (3), and {1,2-(SiMe_2)_2(\u03b7^5-C_5H_3)_2Zr(CH_3)(CH_2SiMe_2CH_2CH\u2550CH_2) (4)) have been prepared. Methide abstraction with B(C_6F_5)_3 results in reversible coordination of the tethered olefin to the cationic zirconium center. The kinetics of olefin dissociation have been examined using NMR methods, and the effects of ligand variation for unlinked, singly [SiMe_2]-linked, and doubly [SiMe_2]-linked bis(cyclopentadienyl) arrangements have been compared (\u0394G^\u29e7 values for olefin dissociation vary from 11.4 to 15.6 kcal\u00b7mol^(-1) measured over the temperature range 223\u2212283 K). For the cation derived from 4 the kinetics for olefin dissociation and site epimerization (inversion at zirconium) can be distinguished. Additionally, with this ligand system competitive binding of the olefin and the [CH_3B(C_6F_5)_3] anion is observed. Methide abstraction from {1,2-(SiMe_2)_2(\u03b7^5-C_5H_3)_2}Zr(CH_3)(CH_2CMe_2CH_2CH\u2550CH_2) results in rapid \u03b2-allyl elimination with loss of isobutene to cleanly afford the allyl cation [{1,2-(SiMe_2)_2(\u03b7^5-C_5H_3)_2}Zr(\u03b7^3-CH_2CH\u2550CH_2)]^+.", "doi": "10.1021/om010363n", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2001-10-01", "series_number": "20", "volume": "20", "issue": "20", "pages": "4253-4261" }, { "id": "authors:r3es2-emn61", "collection": "authors", "collection_id": "r3es2-emn61", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170725-102245085", "type": "article", "title": "Thermally Stable Dialkylzirconocenes with \u03b2-Hydrogens. Synthesis and Diastereoselectivity", "author": [ { "family_name": "Wendt", "given_name": "Ola F.", "clpid": "Wendt-O-F" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Alkylation of Cp^r_2ZrCl_2 (Cpr = Cp (\u03b7^5-C_5H_5), Cp' (\u03b7^5-C_5H_4Me), Cp^* (\u03b7^5-C_5Me_5)) and CpCp^*Zr(CH_3)Cl with 1-lithio-2-methylpentane (R^1Li) gives the corresponding dialkylzirconocenes Cp^r_2ZrR^1_2 and CpCp^*Zr(CH_3)R^1, in high yields. Such alkyls have unprecedented thermal stabilities, especially for the CpCp^* ligand framework. The diastereomers of the Cp^r_2ZrR^1_2 complexes are formed in a statistical distribution, whereas the diastereomers of CpCp^*Zr(CH_3)R^1 form in a 2:3 ratio.", "doi": "10.1021/om0102910", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2001-09-03", "series_number": "18", "volume": "20", "issue": "18", "pages": "3891-3895" }, { "id": "authors:y2fk4-86534", "collection": "authors", "collection_id": "y2fk4-86534", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140723-153427748", "type": "article", "title": "Chemistry of water-soluble Pt-diimine complexes relevant to C-H bond activation", "author": [ { "family_name": "Balzarek", "given_name": "Christoph", "clpid": "Balzarek-C" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Detailed mechanistic studies of selective catalytic alkane oxidation with Pt\ncomplexes have revealed that the reaction pathway includes the following steps:\nInitial C-H bond activation at a Pt(ll) center leads to formation of a Pt(ll) alkyl\ncomplex which in turn is oxidized in the second step to a hexacoordinate Pt(IV)\nspecies. Most mechanistic studies have been carried out with Pt-complex\nbearing bidentate N-ligands (diamines, diimines) in non-aqueous solvents, while\nthe early work by Shilov et al. on Pt-catalyzed hydrocarbon functionalization was\ncarried out in aqueous solution. To relate the diaminel diimine model chemistry\nto the Shilov chemistry in water, the water-soluble Pt-complex 1 was prepared.\nThe results of synthetic and mechanistic studies of 1 in water will be presented.", "issn": "0065-7727", "publisher": "American Chemical Society", "publication": "Abstracts of Papers of the American Chemical Society", "publication_date": "2001-04-01", "volume": "221", "pages": "INOR 201" }, { "id": "authors:188e6-7d666", "collection": "authors", "collection_id": "188e6-7d666", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140723-073829527", "type": "article", "title": "Carbon-hydrogen bond activation mediated by cationic platinum(II) complexes", "author": [ { "family_name": "Zhong", "given_name": "Hong Annita", "clpid": "Zhong-H-Annita" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Transition metal catalyzed hydrocarbon functionalization is of current interest to\nchemical and petroleum industries. The so-called \"Shilov System\", comprised of\naqueous solutions of Pt(II) and Pt(IV) chlorides. converts simple alkanes,\nincluding methane, to alcohols and alkyl chlorides. The C-H activation step\nappears to dictate both the selectivity and the overall reaction rates of these\ntransformations. Consequently, we have been trying to gain more insights\nthrough studying model systems. A series of diaryldiimine-ligated cationic Pt(II)\nmethyl complexes are synthesized. These compounds show high reactivity\ntowards hydrocarbons, and the reactions are accelerated by both increased\nelectron density and decreased steric bulk on metal centers. The reactions\nappear to proceed through a solvent-assisted associative pathway. The substrate\nregioselectivity depends on the steric bulk of both the substrates and the metal\ncenters.", "issn": "0065-7727", "publisher": "American Chemical Society", "publication": "Abstracts of Papers of the American Chemical Society", "publication_date": "2001-04-01", "volume": "221", "pages": "INOR 83" }, { "id": "authors:a06jm-23s48", "collection": "authors", "collection_id": "a06jm-23s48", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140723-074041789", "type": "article", "title": "Studies towards the functionalization of light alkanes: Facile C-H bond activation by a neutral Pt(II) alkyl complex", "author": [ { "family_name": "Scollard", "given_name": "John D.", "clpid": "Scollard-J-D" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Recently our group and the Tilset group reported the activation of R-H bonds by\nelectrophilic platinum cations of the type [(N-N)PtMe]+ (N-N= \u03b1-diimine) to\ngenerate [(N-N)PtR]+ and methane, a model for the initial step in the so-called\nShilov system. The next step involves the oxidation of the resulting Pt(II) alkyl\ncomplex. Unfortunately, cationic Pt(II) alkyls are incompatible with the mild\noxidizing agents necessary for catalytic turnover. Therefore, a neutral Pt(II)\ncomplex which could activate C-H bonds was desirable. The activation of C-H\nbonds by a neutral Pt(II) complex was achieved by replacing the a-diimine\nancillary ligands with mono-anionic X-L type ligands. The addition of pyrrole-2-\nimines to [(SMe_2)PtMe_2]_2 in benzene results in the formation of a Pt(II) phenyl\ncomplex concomitant with evolution of methane (eq. 1). The scope and\nlimitations of the C-H activation step and the subsequent oxidation chemistry\nwill be discussed.", "issn": "0065-7727", "publisher": "American Chemical Society", "publication": "Abstracts of Papers of the American Chemical Society", "publication_date": "2001-04-01", "volume": "221", "pages": "INOR 85" }, { "id": "authors:04zwx-w3491", "collection": "authors", "collection_id": "04zwx-w3491", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170203-140332613", "type": "article", "title": "Catalysis Research of Relevance to Carbon Management: Progress, Challenges, and Opportunities", "author": [ { "family_name": "Arakawa", "given_name": "Hironori", "clpid": "Arakawa-Hironori" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "abstract": "There is increased recognition by the world's scientific, industrial, and political communities that the concentrations of greenhouse gases in the earth's\natmosphere, particularly CO_2, are increasing. For\nexample, recent studies of Antarctic ice cores to\ndepths of over 3600 m, spanning over 420 000 years,\nindicate an 80 ppm increase in atmospheric CO_2 in\nthe past 200 years (with most of this increase\noccurring in the past 50 years) compared to the\nprevious 80 ppm increase that required 10 000 years.2\nThe 160 nation Framework Convention for Climate\nChange (FCCC) in Kyoto focused world attention on\npossible links between CO2 and future climate change\nand active discussion of these issues continues.3 In\nthe United States, the PCAST report4 \"Federal\nEnergy Research and Development for the Challenges\nof the Twenty First Century\" focused attention\non the growing worldwide demand for energy and the\nneed to move away from current fossil fuel utilization.\nAccording to the U.S. DOE Energy Information\nAdministration,5 carbon emission from the transportation\n(air, ground, sea), industrial (heavy manufacturing,\nagriculture, construction, mining, chemicals,\npetroleum), buildings (internal heating, cooling, lighting),\nand electrical (power generation) sectors of the\nWorld economy amounted to ca. 1823 million metric\ntons (MMT) in 1990, with an estimated increase to\n2466 MMT in 2008-2012 (Table 1).", "doi": "10.1021/cr000018s", "issn": "0009-2665", "publisher": "American Chemical Society", "publication": "Chemical Reviews", "publication_date": "2001-04", "series_number": "4", "volume": "101", "issue": "4", "pages": "953-996" }, { "id": "authors:1k58h-h4281", "collection": "authors", "collection_id": "1k58h-h4281", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170808-074543551", "type": "article", "title": "Synthesis of Singly and Doubly Bridgedansa-Zirconocene Hydrides. Formation of an Unusual Mixed Valence Trimeric Hydride by Reaction of H_2 with {(Me_2Si)_2(\u03b7^5-C_5H_3)_2}Zr(CH_3)_2and Generation of a Dinitrogen Complex by Reaction of N_2 with a Zirconocene Dihydride", "author": [ { "family_name": "Chirik", "given_name": "Paul J.", "clpid": "Chirik-P-J" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "A series of singly and doubly bridged ansa-zirconocene dihydride complexes has been prepared from hydrogenation of the corresponding dimethyl complexes. For the singly [SiMe_2]-bridged species, the hydrogenation reaction is facile at 25 \u00b0C, whereas for the doubly [SiMe_2]-bridged complexes hydrogenation occurs over the course of days at 87 \u00b0C. Hydrogenation of {meso-Me_2Si(\u03b7^5-C_5H_3-3-CMe_3)_2}ZrMe_2 affords the isomeric dimeric dihydrides [{meso-Me_2Si(\u03b7^5-C_5H_3-3-CMe_3)_2}ZrH]_2(\u03bc_2-H)_2, one of which has been characterized by X-ray diffraction. The racemo isomer of Me_2Si(\u03b7^5-C_5H_2-2-SiMe_3-4-CMe_3)_2ZrMe_2 (BpZrMe_2) reacts with dihydrogen, affording the first example of a monomeric ansa-zirconocene dihydride, {rac-Me_2Si(\u03b7^5-C_5H_2-2-SiMe_3-4-CMe_3)_2}ZrH_2 (rac-BpZrH_2). In the presence of dinitrogen, rac-BpZrH_2 undergoes thermal reductive elimination of H_2 and reaction with N_2, yielding the dinitrogen complex BpZr(\u03bc_2,\u03b7^2,\u03b7^2-N_2)ZrBp, for which the dinitrogen ligand is coordinated in a side-on fashion to both zirconiums with a N\u2212N bond distance of 1.241(3) \u00c5. The doubly [SiMe_2]-bridged zirconium dimethyl complex {(Me_2Si)_2(\u03b7^5-C_5H_3)_2}ZrMe_2 (RpZrMe_2) undergoes hydrogenation under forcing conditions, affording the mixed valent (Zr(IV)/Zr(IV)/Zr(III)) hydride trimer [RpZr]_3(\u03bc_3-H)_2(\u03bc_2-H)_3, which has been characterized by X-ray diffraction. More substituted doubly [SiMe_2]-bridged zirconocene dihydrides such as [{(Me_2Si)_2(\u03b7^5-C_5H-3,5-(CHMe_2)_2)(\u03b7^5-C_5H_2-4-CHMeEt}ZrH]_2(\u03bc_2-H)_2 ([sec-BuThpZrH]_2(\u03bc_2-H)_2) and [(Me_2Si)_2(\u03b7^5-C_5H-2,4-(CHMe_2)_2)(\u03b7^5-C_5H_2-4-CHMe_2)ZrH]_2(\u03bc_2-H)_2 ([^iPrThpZrH]_2(\u03bc_2-H)_2) have been prepared and shown to be robust dimers in solution.", "doi": "10.1021/om000739h", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2001-02-05", "series_number": "3", "volume": "20", "issue": "3", "pages": "534-544" }, { "id": "authors:akff8-7m013", "collection": "authors", "collection_id": "akff8-7m013", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170524-154233004", "type": "article", "title": "Aminofluorenyl\u2212Pentamethylcyclopentadienyl and Bis(aminofluorenyl) Derivatives of Group 4 Metals", "author": [ { "family_name": "Miller", "given_name": "Stephen A.", "orcid": "0000-0002-3181-1426", "clpid": "Miller-S-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "New group 4 compounds containing a 9-(dialkylamino)fluorenyl ligand have been prepared, and their properties and reactivities have been briefly investigated. Single-crystal X-ray analysis of {9-(N,N-dimethylamino)fluorenyl}_2ZrCl_2 (4) reveals strong zirconium\u2212nitrogen dative bonds. The asymmetric unit contains two molecules with an unusual coordination of aminofluorenyl ligands, best described as comprised of a strong Zr\u2212N dative interaction and essentially an \u03b7^1-fluorenyl coordination, supplemented by a weak additional C C dative interaction of one double bond of one of the benzo units. The barrier to rotation around the C\u2212N bond of {9-(N,N-diisopropylamino)fluorenyl}(pentamethylcyclopentadienyl)ZrCl_2 (9) has been determined:\u2009 \u0394G\u29e7(\u221225 \u00b0C) = 11.1 kcal\u00b7mol^(-1). Unlike related aminoborollide complexes, aminofluorenyl complexes resist quaternization by alkyl halides. Several aminofluorenyl complexes have been tested for propylene polymerization behavior in the presence of methylaluminoxane (MAO); atactic polypropylene is obtained with very low activities. The syntheses of 9-(dialkylamino)fluorene compounds are described, as are the syntheses of group 4 compounds via the corresponding 9-(dialkylamino)fluorenide lithium salts.", "doi": "10.1021/om000723r", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2000-12-25", "series_number": "26", "volume": "19", "issue": "26", "pages": "5608-5613" }, { "id": "authors:bn02z-y6f68", "collection": "authors", "collection_id": "bn02z-y6f68", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180413-134041553", "type": "article", "title": "Alkyl Rearrangement Processes in Organozirconium Complexes. Observation of Internal Alkyl Complexes during Hydrozirconation", "author": [ { "family_name": "Chirik", "given_name": "Paul J.", "clpid": "Chirik-P-J" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Isotopically labeled alkyl zirconocene complexes of the form (CpR_n)_2Zr(CH_2CDR'_2)(X) (CpR_n = alkyl-substituted cyclopentadienyl; R' = H, alkyl group; X = H, D, Me) undergo isomerization of the alkyl ligand as well as exchange with free olefin in solution under ambient conditions. Increasing the substitution on the Cp ring results in slower isomerization reactions, but these steric effects are small. In contrast, changing X has a very large effect on the rate of isomerization. Pure \u03c3-bonding ligands such as methyl and hydride promote rapid isomerization, whereas \u03c0-donor ligands inhibit \u03b2-H elimination and hence alkyl isomerization. For (\u03b7^5-C_5H_5)2Zr(R)(Cl), internal alkyl complexes have been observed for the first time. The rate of isomerization depends on the length of the alkyl group:\u2009 longer alkyl chains (heptyl, hexyl) isomerize faster than shorter chains (butyl). The transient intermediate species have been identified by a combination of isotopic labeling and ^1H, ^2H, and ^(13)C NMR experiments. The solid-state structure of the zirconocene cyclopentyl chloride complex, Cp_2Zr(cyclo-C_5H_9)(Cl), has been determined by X-ray diffraction.", "doi": "10.1021/ja9912022", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "1999-11-10", "series_number": "44", "volume": "121", "issue": "44", "pages": "10308-10317" }, { "id": "authors:3nsv2-80b53", "collection": "authors", "collection_id": "3nsv2-80b53", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180518-145758180", "type": "article", "title": "Fluxional \u03b7^3-Allyl Derivatives of ansa-Scandocenes and an ansa-Yttrocene. Measurements of the Barriers for the \u03b7^3 to \u03b7^1 Process as an Indicator of Olefin Binding Energy to d^0 Metallocenes", "author": [ { "family_name": "Abrams", "given_name": "Michael B.", "clpid": "Abrams-M-B" }, { "family_name": "Yoder", "given_name": "Jeffrey C.", "clpid": "Yoder-J-C" }, { "family_name": "Loeber", "given_name": "Cyrille", "clpid": "Loeber-C" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Variable-temperature ^1H NMR spectroscopy indicates fluxional behavior for a number of group 3 metallocene allyl complexes. Spectral simulations and line shape analyses for the variable-temperature spectra indicate an allyl rearrangement mechanism involving rate-determining carbon\u2212carbon double-bond dissociation from the metal center, i.e. an \u03b7^3 to \u03b7^1 change in coordination. Activation barriers to olefin dissociation have been determined for (\u03b7^5-C_5Me_5)_2Sc(\u03b7^3-C^3H^5), meso-Me^2Si(\u03b7^5-3-CMe^3-C_5H_3)_2Sc(\u03b7^3-C_3H_5), meso-Me_2Si[\u03b7^5-2,4-(CHMe_2)_2-C_5H_2]_2Sc(\u03b7^3-C_3H_5), meso-Me_2Si{\u03b7^5-3-[2-(2-Me)-adamantyl]-C_5H_3}_2Sc(\u03b7^3-C_3H_5), meso-Me_2Si{\u03b7^5-3-[2-(2-Me)-adamantyl]-C_5H_3}_2Y(\u03b7^3-C_3H_5), rac-Me_2Si[\u03b7^5-2,4-(CHMe_2)_2-C_5H_2]_2Sc(\u03b7^3-C_3H_5)), and R-(C_(20)H_(12)O_2)Si(\u03b7^5-2-SiMe_3-4-CMe_3-C_5H_2)_2Sc(\u03b7^3-C_3H_5):\u2009 \u0394G^\u29e7 = 11\u221216 kcal mol^(-1) at ca. 300\u2212350 K. Donor solvents do not significantly affect the rate of olefin dissociation. A second rearrangement mechanism that involves 180\u00b0 rotation of the \u03b7^3-C_3H_5 moiety has been found to operate in those metallocenes whose ancillary ligand arrays adopt rigid meso geometries. Line shape analysis indicates that the rate of \u03b7^3-C_3H_5 rotation is generally more than 1 order of magnitude faster than olefin dissociation for a given meso metallocene. The data do not allow unambiguous assessments of the mechanism(s) for the fluxional behavior for the allyl derivatives of the racemic metallocenes. An X-ray structure determination for rac-Me_2Si[\u03b7^5-C_5H_2-2,4-(CHMe_2)_2]_2Sc(\u03b7^3-C_3H_5) has been carried out.", "doi": "10.1021/om980893s", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "1999-04-12", "series_number": "8", "volume": "18", "issue": "8", "pages": "1389-1401" }, { "id": "authors:8xjrt-he390", "collection": "authors", "collection_id": "8xjrt-he390", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180518-154132453", "type": "article", "title": "Synthesis, Molecular Structure, and Racemate\u2212Meso Interconversion for rac-(Me_2Si)_2{\u03b7^5-C_5H-3-(CHMe_2)-5-Me}_2MCl_2 (M = Ti and Zr)", "author": [ { "family_name": "Miyake", "given_name": "Shigenobu", "clpid": "Miyake-Shigenobu" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Doubly [SiMe_2]-bridged group IV metallocenes, rac-(Me_2Si)_2{\u03b7^5-C_5H-3-(CHMe_2)-5-Me}_2MCl_2 (M = Ti, Zr), have been synthesized, and a crystal structure of rac-(Me_2Si)_2{\u03b7^5-C_5H-3-(CHMe_2)-5-Me}_2TiCl_2 has been determined by X-ray diffraction methods. Racemate\u2212meso interchange occurs in benzene solution just above room temperature, affording an approximately 1:1 mixture of rac-(Me_2Si)_2{\u03b7^5-C_5H-3-(CHMe_2)-5-Me}_2TiCl_2 and meso-(Me_2Si)_2{\u03b7^5-C_5H-3-(CHMe_2)-5-Me}_2TiCl_2. Measurements of the kinetics of the approach to equilibrium reveal \u0394H^\u29e7 = 18(1) kcal\u00b7mol^(-1) and \u0394S^\u29e7 = \u22127(2) eu. The corresponding zirconium compound is configurationally stable.", "doi": "10.1021/om980505m", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "1998-12-07", "series_number": "25", "volume": "17", "issue": "25", "pages": "5528-5533" }, { "id": "authors:ts0c3-k8789", "collection": "authors", "collection_id": "ts0c3-k8789", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180518-154959101", "type": "article", "title": "Racemic\u2212Meso Interconversion for ansa-Scandocene and ansa-Yttrocene Derivatives. Molecular Structures of rac-{Me_2Si[\u03b7^5-C_5H_2-2,4-(CHMe_2)_2]_2}ScCl\u00b7LiCl(THF)_2, [meso-{Me_2Si[\u03b7^5-C_5H_2-2,4-(CHMe_2)_2]_2}Y(\u03bc_2-Cl)]_2, and meso-{Me_2Si[\u03b7^5-C_5H_2-2,4-(CHMe_2)_2]_2}Zr(NMe_2)_2", "author": [ { "family_name": "Yoder", "given_name": "Jeffrey C.", "clpid": "Yoder-J-C" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The dilithium bis(cyclopentadienide) species Li_2{Me_2Si[C_5H_2-2,4-(CHMe_2)_2]_2} (Li_2Ip) reacts with ScCl_3(THF)_3 to afford rac-IpScCl\u00b7LiCl(THF)_2 (1) and [meso-IpSc(\u03bc_2-Cl)]_2 (2) and with YCl_3(THF)_(3.5) to afford rac-IpYCl\u00b7LiCl(THF)_2 (3) and [meso-IpY(\u03bc_2-Cl)]_2 (4). Metalation with both scandium and yttrium chlorides yields the metallocene chlorides in approximately 3:1 racemic:meso ratios. Reaction of IpH_2 with Zr(NMe_2)_4 yields exclusively meso-IpZr(NMe_2)_2 (9). Treatment of 1 or 2 with allylmagnesium bromide affords the allyl complexes rac-IpSc(\u03b7^3-C_3H_5) (5) and meso-IpSc(\u03b7^3-C_3H_5) (6) and with crotylmagnesium chloride affords rac-IpSc(\u03b7^3-C_3H_4Me) (7) and meso-IpSc(\u03b7^3-C_3H_4Me) (8). Diastereomerically pure rac dichlorometalate compounds (1 or 3) or pure meso chloro dimers (2 or 4) undergo spontaneous isomerization upon dissolution in THF-d_8 with reversion back to a 3:1 racemic:meso ratio. Isomerization of 5 and 6 is observed in THF-d_8, above 55 \u00b0C, affording an equilibrium ratio of \u223c2:1 racemic:meso isomers. While spontaneous isomerization of 5, 6, 7, or 8 is very slow at room temperature, various salts and Grignard reagents promote isomerization even at room temperature; the isomerizations are not accelerated by light. The proposed mechanism for racemic\u2212meso isomerization involves heterolytic dissociation of one cyclopentadienide ligand from the metal, rotation around that Si\u2212Cp- bond, and recoordination on the opposite face, effecting net epimerization. X-ray diffraction studies have been performed on rac-IpScCl\u00b7LiCl(THF)_2 (1), [meso-IpY(\u03bc_2-Cl)]_2 (4), and meso-IpZr(NMe_2)_2 (9).", "doi": "10.1021/om980349j", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "1998-11-09", "series_number": "23", "volume": "17", "issue": "23", "pages": "4946-4958" }, { "id": "authors:8pt6z-7k537", "collection": "authors", "collection_id": "8pt6z-7k537", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180518-153456930", "type": "article", "title": "Oxidation of Dimethylplatinum(II) Complexes with Dioxygen", "author": [ { "family_name": "Rostovtsev", "given_name": "Vsevolod V.", "clpid": "Rostovtsev-V-V" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Lasseter", "given_name": "Tami L.", "clpid": "Lasseter-T-L" }, { "family_name": "Goldberg", "given_name": "Karen I.", "clpid": "Goldberg-K-I" } ], "abstract": "Dimethylplatinum(II) complexes (L\u2212L)Pt(CH_3)_2 (L\u2212L = bpy, phen, tmeda) are oxidized by dioxygen in methanol to the corresponding alkoxoplatinum(IV) complexes (L\u2212L)Pt(CH_3)_2(OH)(OCH_3).", "doi": "10.1021/om980541l", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "1998-10-12", "series_number": "21", "volume": "17", "issue": "21", "pages": "4530-4531" }, { "id": "authors:0g2a7-75602", "collection": "authors", "collection_id": "0g2a7-75602", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180507-113416915", "type": "article", "title": "Homogeneous Oxidation of Alkanes by Electrophilic Late Transition Metals", "author": [ { "family_name": "Stahl", "given_name": "Shannon S.", "orcid": "0000-0002-9000-7665", "clpid": "Stahl-S-S" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The selective oxidation of alkanes is a topic of considerable interest to both industrial and academic chemists. While the initial discovery occurred more than 25 years ago, new developments in alkane oxidation catalyzed by electrophilic late transition metals have provided important mechanistic insights as well as potentially practical methods for alkane transformations.", "doi": "10.1002/(SICI)1521-3773(19980904)37:16<2180::AID-ANIE2180>3.0.CO;2-A", "issn": "1433-7851", "publisher": "Wiley", "publication": "Angewandte Chemie International Edition", "publication_date": "1998-09-04", "series_number": "16", "volume": "37", "issue": "16", "pages": "2180-2192" }, { "id": "authors:tsbz9-k7y67", "collection": "authors", "collection_id": "tsbz9-k7y67", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180525-141337304", "type": "article", "title": "Investigations of the Factors Affecting the Stability of Dihydrogen Adducts of Platinum(II)", "author": [ { "family_name": "Stahl", "given_name": "Shannon S.", "orcid": "0000-0002-9000-7665", "clpid": "Stahl-S-S" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The preparation and study of Pt(II) H_2 adducts and Pt(IV) dihydride complexes are described. The species of interest are generated by protonation of hydridoplatinum(II) complexes of the type trans-(PCy_3)_2Pt(H)X [X = SiH_3, H, CH_3, Ph, Cl, Br, I, CN, CF_3SO_3] and [trans-(PCy_3)_2Pt(H)L][BArf_4] [L = CO, 4-picoline; BArf_4 = B(3,5-C_6H_3(CF_3)_2)_4]. The proton attacks one of three different sites on these complexes (hydride, platinum, or the trans ligand), depending on which ligand is trans to hydride. These studies reveal several factors affecting the stability and reactivity of Pt(II) \u03c3 adducts, which thus have implications for C\u2212H activation by Pt(II).", "doi": "10.1021/ic970944y", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "1998-05-18", "series_number": "10", "volume": "37", "issue": "10", "pages": "2422-2431" }, { "id": "authors:af8hj-ahh40", "collection": "authors", "collection_id": "af8hj-ahh40", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180518-141650830", "type": "article", "title": "Heterolysis of H\u2212X Bonds by Pentamethylcyclopentadienyl\u2212Aminoborole Complexes of Zirconium and Hafnium", "author": [ { "family_name": "Kiely", "given_name": "Andrew F.", "clpid": "Kiely-A-F" }, { "family_name": "Nelson", "given_name": "Cory M.", "clpid": "Nelson-C-M" }, { "family_name": "Pastor", "given_name": "Antonio", "clpid": "Pastor-A" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Day", "given_name": "Michael W.", "clpid": "Day-M-W" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The pentamethylcyclopentadienyl\u2212aminoborole chloro complexes Cp*{\u03b7^5-C_4H_4BN(CHMe_2)_2}MCl\u00b7LiCl (Cp* = (\u03b7^5-C_5Me_5); M = Zr, Hf) heterolytically cleave H\u2212X bonds to form Cp*{\u03b7^5-C_4H_4BNH(CHMe_2)_2}MCl(X) (X = OR, SR, C\u22eeCR). Control experiments using deuterium-labeled substrates show heterolysis occurs with no incorporation of deuterium into the 2,5 positions of the borole heterocycle. Cp*{\u03b7^5-C_4H_4BNH(CHMe_2)_2}Hf(C\u22eeCSiMe_3)_2 is prepared from Cp*{\u03b7^^5-C_4H_4BN(CHMe_2)_2}Hf(\u03b7^3-C_3H_5) and 2 equiv of (trimethylsilyl)acetylene. Treatment of Cp*{\u03b7^5-C_4H_4BN(CHMe_2)_2}MCl\u00b7LiCl (M = Zr, Hf) with donor ligands L yields the LiCl-free complexes Cp*{\u03b7^5-C_4H_4BN(CHMe_2)_2}MCl(L) (M = Zr, L = NMe2H; M = Hf, L = PMe_3). Cp*{\u03b7^5-C_4H_4BN(CHMe_2)_2}HfCl(PMe_3) reacts with (trimethylsilyl)acetylene with loss of HN(CHMe_2)_2 to form Cp*{\u03b7^5-C_4H_4B(C\u22eeCSiMe_3)}HfCl(PMe_3), resulting from formal migration of acetylide from hafnium to boron. X-ray structure determinations of Cp*{\u03b7^5-C_4H_4BNH(CHMe_2)_2}HfCl(C\u22eeCSiMe_3), Cp*{\u03b7^5-C_4H_4BN(CHMe_2)_2}HfCl(PMe_3), and Cp*{\u03b7^5-C_4H_4B(C\u22eeCSiMe_3)}HfCl(PMe_3) are reported.", "doi": "10.1021/om9709345", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "1998-03-30", "series_number": "7", "volume": "17", "issue": "7", "pages": "1324-1332" }, { "id": "authors:aqx9h-ex334", "collection": "authors", "collection_id": "aqx9h-ex334", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180518-161116349", "type": "article", "title": "A Cationic Imido Complex of Permethyltantalocene:\u2009 H_2 and Carbon\u2212Hydrogen Bond Activation, [2 + 2] Cycloaddition Reactions, and an Unusual Reaction with Carbon Dioxide That Affords Coordinated Isocyanate", "author": [ { "family_name": "Blake", "given_name": "Robert E., Jr.", "clpid": "Blake-R-E-Jr" }, { "family_name": "Antonelli", "given_name": "David M.", "clpid": "Antonelli-D-M" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" }, { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" }, { "family_name": "Hardcastle", "given_name": "Kenneth I.", "clpid": "Hardcastle-K-I" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The cationic imido complex [Cp*2Ta(=NCMe_3)(THF)][B(C_6F_5)_4] (1) (Cp* = (\u03b7^5-C_5Me_5)) reacts with \u03c3 bonds H\u2212X to afford [Cp*_2Ta(NHCMe_3)X][B(C_6F_5)_4] (X = Cl, OH, C\u22eeCR). Intramolecular activation of a carbon\u2212hydrogen bond of a Cp* methyl group ultimately yields [Cp*Ta(\u03b7^5-C_5Me_4CH_2NCMe_3)H][B(C_6F_5)_4]. Reaction with carbon dioxide leads to dealkylation of the imido group, liberating isobutylene and yielding the isocyanate complex [Cp*_2Ta(OH)(NCO)][B(C_6F_5)_4].", "doi": "10.1021/om970815p", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "1998-02-16", "series_number": "4", "volume": "17", "issue": "4", "pages": "718-725" }, { "id": "authors:t7dr7-xbe20", "collection": "authors", "collection_id": "t7dr7-xbe20", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180530-134833370", "type": "article", "title": "Model Ziegler-Natta \u03b1-Olefin Polymerization Catalysts Derived from [{(\u03b7^5-C_5Me_4)SiMe_2(\u03b7^1-NCMe_3)}(PMe_3)Sc(\u00b5_2-H)]_2 and [{(\u03b7^5-C_5Me_4)SiMe_2(\u03b7^1-NCMe_3)}Sc(\u00b5_2-CH_2CH_2CH_3)]_2. Synthesis, Structures, and Kinetic and Equilibrium Investigations of the Catalytically Active Species in Solution", "author": [ { "family_name": "Shapiro", "given_name": "Pamela J.", "clpid": "Shapior-P-J" }, { "family_name": "Cotter", "given_name": "W. Donald", "clpid": "Cotter-W-D" }, { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The scandium hydride complex [(Cp*SiNR)(PMe_3)Sc(\u00b5-H)]_2 (1), ((Cp*SiNR) = ((\u03b7^5-C_5Me_4)SiMe_2(\u03b7^1-NCMe_3)}) is prepared by hydrogenation of (Cp*SiNR)ScCH(SiMe_3)_2 in the presence of trimethylphosphine. The hydride complex is a catalyst precursor for the polymerization of \u03b1-olefins, yielding atactic products of low molecular weight (M, = 3000-7000). GC/MS analysis of volatile, oligomeric products revealed that all scandium centers are active during the polymerization. Selectivity for head-to-tail insertion is high (>99%) and for the tetramer, pentamer, and hexamer formed during propene polymerization, the maximum theoretical numbers of head-to-tail stereoisomers are observed by capillary GC. The stoichiometric reaction between 1 and 2 equiv of ethylene produces the unusual ethylene-bridged dimer [(Cp*SiNR)(PMe_3)Sc]_2(\u00b5,\u03b7^2,\u03b7^2-C_2H_4) (2) and an equivalent of ethane, whereas the same reaction with propene affords the phosphine-free, alkyl-bridged scandium dimer [(Cp*S~NR)Sc]_2(\u00b5-CH_2CH_2CH_3)_2 (3). The absence of coordinating phosphine allows the latter complex to function as a more active olefin polymerization catalyst precursor. 1 reacts with styrene to form a unique double-insertion product arising from sequential 1,2- and 2,1-styrene insertion. The structure of the catalytic intermediate in solution was determined by low-temperature ^(13)C-NMR studies of the model complexes (Cp*SiNR)(P(^(13)CH_3)_3]ScCH_2CH(CH_3)CHCH_2CH_2CH_3 and (Cp*SiNR)(PMe_3)Sc^(13)CH_2CHCH(^(13)CH_3)_2. One phosphine-bound species is observed in equilibrium with only one phosphine-free species. The symmetry properties of the latter indicate that it is a monomeric, hence 12-electron, scandium alkyl complex. Semiquantitative treatment of equilibrium concentration data supports this conclusion.", "doi": "10.1021/ja00090a011", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "1994-06-01", "series_number": "11", "volume": "116", "issue": "11", "pages": "4623-4640" }, { "id": "authors:y3e16-x4c40", "collection": "authors", "collection_id": "y3e16-x4c40", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180529-162411954", "type": "article", "title": "Pentamethylcyclopentadienyl Aminoborollide Derivatives of Zirconium and Hafnium: A New Class of Amphoteric Molecule Having Both Lewis Acidic and Lewis Basic Sites", "author": [ { "family_name": "Quan", "given_name": "Roger W.", "clpid": "Quan-Roger-W" }, { "family_name": "Bazan", "given_name": "Guillermo C.", "clpid": "Bazan-G-C" }, { "family_name": "Kiely", "given_name": "Andrew F.", "clpid": "Kiely-A-F" }, { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "[no abstract]", "doi": "10.1021/ja00089a053", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "1994-05-18", "series_number": "10", "volume": "116", "issue": "10", "pages": "4489-4490" }, { "id": "authors:9k1yx-84p31", "collection": "authors", "collection_id": "9k1yx-84p31", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180521-131822953", "type": "article", "title": "Competitive Chain Transfer by \u03b2-Hydrogen and \u03b2-Methyl Elimination for a Model Ziegler-Natta Olefin Polymerization System [Me_2Si(\u03b7^5-C_5Me_4)_2]Sc{CH_2CH(CH_3)_2}(PMe_3)", "author": [ { "family_name": "Hajela", "given_name": "Sharad", "clpid": "Hajela-S" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The reaction of OpSc(H) (PMe_3) (Op = {(\u03b7^5-C_5Me_4)_2SiMe_2}) with isobutene produces OpSc(CH_3)(PMe_3) along with isobutene, 2-methylpentane, isobutene, 2-methyl-l-pentene, propane, and n-pentane. These products arise from a series of reactions involving olefin insertion, \u03b2-CH_3 and (faster) \u03b2-H elimination which proceed until only the 2-methyl-1-alkenes (C_4H_8, C_6H_(12), etc.) and the predominant organoscandium product OpSc(CH_3)(PMe_3) remain. A transient observed in the reaction sequence has been unambiguously characterized as OpSc(CH_2CH_2CH_3) (PMe_3). Slower u bond metathesis involving the methyl C-H bonds of PMe_3 and the Sc-C bonds of the scandium alkyls accounts for the observation of saturated alkanes (2-methylalkanes (C_4H_(10), C_6H_(14), etc.), normal alkanes (C_3H_8, C_5H_(12), etc.), and a minor organoscandium product OpScCH_2-PMe_2 in the product mixture. b-Ethyl migration is not observed for the closely related 2-ethylbutyl derivative, OpSC{CH_2CH(C_2H_5)CH_2CH_3}(PMe_3), obtained from reaction of 2-ethyl-1-butene with OpSc(H)(PMe_3).", "doi": "10.1021/om00016a018", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "1994-04", "series_number": "4", "volume": "13", "issue": "4", "pages": "1147-1154" }, { "id": "authors:37hpc-can92", "collection": "authors", "collection_id": "37hpc-can92", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180413-142737272", "type": "article", "title": "Oxidation of Zeise's Salt by [PtCl_6]^(2-): A Mechanistic Model for Hydrocarbon Oxidation", "author": [ { "family_name": "Luinstra", "given_name": "Gerrit A.", "clpid": "Luinstra-G-A" }, { "family_name": "Wang", "given_name": "Lin", "clpid": "Wang-Lin" }, { "family_name": "Stahl", "given_name": "Shannon S.", "orcid": "0000-0002-9000-7665", "clpid": "Stahl-S-S" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Among a variety of organometallic approaches to C-H bond activation, reactions with electrophilic metal centers such as Pt(II), Pd(II), and Hg(Il) currently appear to offer the best prospects for productive alkane functionalization. Our working mechanistic scheme for conversion of alkanes to alcohols and alkyl chlorides by aqueous solutions of [PtCl_4]^(2-) and [PtCl_6]^(2-) (eq 1) consists of electrophilic C-H activation to generate a platinum(II) alkyl, transformation to a platinum(IV) alkyl, and nucleophilic attack by water or chloride, displacing platinum(II) and generating the product alcohol or alkyl chloride.", "doi": "10.1021/om00015a005", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "1994-03", "series_number": "3", "volume": "13", "issue": "3", "pages": "755-756" }, { "id": "authors:dmwh6-g0506", "collection": "authors", "collection_id": "dmwh6-g0506", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180529-145628341", "type": "article", "title": "Theoretical Studies of Ziegler-Natta Catalysis: Structural Variations and Tacticity Control", "author": [ { "family_name": "Bierwagen", "given_name": "Erik P.", "clpid": "Bierwagen-E-P" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Goddard", "given_name": "W. A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "abstract": "Models for the likely active catalysts in homogeneous Ziegler-Natta systems have been studied using ab initio quantum chemical methods. We investigated the geometries of the isoelectronic model complexes, X_2M-R where X = Cl or Cp = (\u03b7^5-C_5H_5); where M = Sc and Ti^+ (and also Ti); and where R = H, CH_3, or SiH_3. The general trend is that the M = Sc compounds strongly prefer a planar configuration, whereas the M = Ti^+ cases generally prefer pyramidal geometries. This difference in geometry can be related to the differing ground-state electronic configurations for the metals: Sc is (4s)^2(3d)^1, whereas Ti^+ is (4s)^1(3d)^2. The nonplanar geometry for [Cp_2Ti-R]^+ suggests an explanation for the origin of stereospecificity in the syndiotactic polymerization by unsymmetric metallocene catalysts. These results suggest that {(\u03b7^5-C_5H_4)CMe_2(\u03b7^5-fluorenyl)}Sc-R would not catalyze syndiotactic polymerization under these conditions.", "doi": "10.1021/ja00083a037", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "1994-02-23", "series_number": "4", "volume": "116", "issue": "4", "pages": "1481-1489" }, { "id": "authors:9mj34-g9564", "collection": "authors", "collection_id": "9mj34-g9564", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230419-953279000.13", "type": "article", "title": "Electrocatalytic functionalization of alkanes using aqueous platinum salts", "author": [ { "family_name": "Freund", "given_name": "Michael S.", "orcid": "0000-0003-1104-2292", "clpid": "Freund-Michael-S" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-Jay-A" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "p-Toluenesulfonic acid is electrocatalytically hydroxylated to the alcohol,p-HO\u2083SC\u2086H\u2084CH\u2082OH, by a system consisting of aqueous PtCl\u2084\u00b2\u207b as C-H activation catalyst, phosphomolybdic acid as redox mediator, in an electrochemical cell containing a carbon cloth anode.", "doi": "10.1016/0304-5102(93)e0230-e", "issn": "0304-5102", "publisher": "Elsevier", "publication": "Journal of Molecular Catalysis", "publication_date": "1994-01-19", "series_number": "1", "volume": "87", "issue": "1", "pages": "L11-L15" }, { "id": "authors:svmqp-zd828", "collection": "authors", "collection_id": "svmqp-zd828", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160914-160016927", "type": "article", "title": "The monopotassium salt of the ligand of a Ziegler\u2013Natta catalyst", "author": [ { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" }, { "family_name": "Cotter", "given_name": "W. Donald", "clpid": "Cotter-W-D" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The anion of dipotassium (tert-butylamino)-dimethyl(tetramethylcyclopentadienyl)silanediide can coordinate to transition metals to form precursors for single-component Ziegler-Natta polymerization catalysts. The related monoanion derivative potassium (tert-butylamino )dimethyl( tetramethyl-cyclopentadienyl) silanide tetrahydrofuran solvate has been isolated as the first crystalline salt of this important ligand family. The tetramethylcyclopentadienyl group in the crystal has a potassium ion on each face, 2.8 \u00c5 from the center of the five-membered ring; each K atom is bonded to two rings and one tetrahydrofuran solvent molecule.", "doi": "10.1107/S0108270193001842", "issn": "0108-2701", "publisher": "International Union of Crystallography", "publication": "Acta Crystallographica Section C", "publication_date": "1993-08", "series_number": "8", "volume": "49", "issue": "8", "pages": "1489-1492" }, { "id": "authors:j8dxc-tr960", "collection": "authors", "collection_id": "j8dxc-tr960", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180521-113254660", "type": "article", "title": "Pentamethylcyclopentadienyl-dicarbollide derivatives of scandium", "author": [ { "family_name": "Bazan", "given_name": "Guillermo C.", "clpid": "Bazan-G-C" }, { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The reactions of [Cp*ScCl_2]_x (Cp* = (\u03b7^5-C_5Me_5)) with Na_2[C_2B_9H_(11) or [Cp*ScMe_2]_x, with C_2B_9H_(13), followed by treatment with THF yield Cp*(C_2B_9H_(11))Sc(THF)_3. Alkylation of Cp*-(C_2 B_9 H_(11)) with LiCH(SiMe_3)_2 yields Cp(C_2B_9H_(11))ScCH(SiMe_3)_2Li(THF)_3, and {[Cp*(C_2B_9H_(11))ScCH(SiMe_3)_2]_2Li}-Li(THF)_3, which is obtained by its recrystallization from pentane/toluene, has been characterized structurally. This alkyl derivative reacts slowly with H_2 to yield [Cp*(C_2B_9H_(11))SCH]_2[LiTHF)_n]_2, a surprisingly reactive scandium hydride dimer. Once again, recrystallization from toluene affords a crystalline form with less coordinated THF, [Cp*(C_2B_9H_(11))ScH]_2[Li(THF)_2\u2022(3/2)(C_6H_5CH_)3, whose structure reveals that the two anionic [Cp*(C_2B_9H_(11))ScH]^- fragments are held together by reciprocal B-H dative bonding from the dicarbollide ligand to the electron deficient scandium. The potential of pentamethylcyclopentadienyl-dicarbollide derivatives of scandium to serve as efficient a olefin polymerization catalysts is discussed.", "doi": "10.1021/om00030a024", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "1993-06", "series_number": "6", "volume": "12", "issue": "6", "pages": "2126-2130" }, { "id": "authors:64ggd-1sn16", "collection": "authors", "collection_id": "64ggd-1sn16", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160914-141704518", "type": "article", "title": "Structure of Hydroxo(methyl)bis(\u03b7^5-pentamethylcyclopentadienyl)tantalum(V) Hydroxotris(pentafluorophenyl)borate", "author": [ { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" }, { "family_name": "Quan", "given_name": "Roger W.", "clpid": "Quan-Roger-W" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "[Ta(C_(10)H_(15))i(OH)(CH_3)][B(OH)(C_6F_5)_3], M_r = 1001.63, monoclinic, P2_1/n, \u0251 = 12.217 (2), b = 16.848 (6), c = 18.834 (3) \u00c5, \u03b2 = 100.37 (2)\u00b0, V = 3813.l (15) \u00c5^3, Z = 4, D_x = 1.75 g cm^(-3), \u03bb{Mo K\u0251) = 0.71073 \u00c5, \u03bc = 29.52 cm^(-1), F(000) = 1972, room temperature, R = 0.031 for 3534 reflections with F_o^2 > 3\u03c3(F_o^2). The Ta cation has the expected geometry, with Ta-C and Ta-O distances 2.211 (6) and 1.865 (5) \u00c5, respectively. The anion has not been characterized previously; its geometry is irregular\nwith tetrahedral angles at boron ranging from 103.6 (6) to 113.8 (6)\u00ba, and systematic angular distortions in the C_6F_5 rings.", "doi": "10.1107/S0108270192001628", "issn": "0108-2701", "publisher": "International Union of Crystallography", "publication": "Acta Crystallographica Section C", "publication_date": "1993-05-15", "series_number": "5", "volume": "49", "issue": "5", "pages": "878-881" }, { "id": "authors:6d9xv-fbt24", "collection": "authors", "collection_id": "6d9xv-fbt24", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180501-151530831", "type": "article", "title": "Mechanism and stereochemistry for nucleophilic attack at carbon of platinum(IV) alkyls: model reactions for hydrocarbon oxidation with aqueous platinum chlorides", "author": [ { "family_name": "Luinstra", "given_name": "Gerrit A.", "clpid": "Luinstra-G-A" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "We and others have recently confirmed the original reports by Shilov that aqueous solutions of a mixture of [PtCl_4]^(2-) and [PtCl_6]^(2-) are capable of functionalizing the C-H bonds of substrates including methane, initially producing a mixture of alcohols and alkyl chlorides. The working mechanistic scheme invokes the following general features: (1) electrophilic C-H activation to generate a platinum(I1) alkyl, (2) oxidation to a platinum(1V) alkyl, and (3) nucleophilic attack by water or chloride, displacing platinum(II) and generating the product alcohol or alkyl chloride. In this article we report the preparation, isolation, and characterization of methyl and \u03b2-hydroxyethyl derivatives of chloroplatinum(IV) along with the results of our investigations of the mechanism for nucleophilic attack by water or chloride. The rates and stereochemistry provide some of the first firm support for the latter stages of this working mechanistic scheme.", "doi": "10.1021/ja00060a070", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "1993-04-07", "series_number": "7", "volume": "115", "issue": "7", "pages": "3004-3005" }, { "id": "authors:f536p-rwj95", "collection": "authors", "collection_id": "f536p-rwj95", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180501-151528266", "type": "article", "title": "Oxidation of hydrocarbons by aqueous platinum salts: mechanism and selectivity", "author": [ { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Herring", "given_name": "Andrew M.", "clpid": "Herring-A-M" }, { "family_name": "Lyon", "given_name": "David K.", "clpid": "Lyon-D-K" }, { "family_name": "Luinstra", "given_name": "Gerrit A.", "clpid": "Luinstra-G-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Horvath", "given_name": "Istvan T.", "clpid": "Horvath-I-T" }, { "family_name": "Eller", "given_name": "Karsten", "clpid": "Eller-K" } ], "abstract": "Water-soluble organic compounds are selectively oxidized by aqueous solutions of chloroplatinum(II) and chloroplatinum(IV) salts. p-Toluenesulfonic acid undergoes stepwise hydroxylation to the corresponding alcohol and aldehyde, with no further oxidation to the carboxylic acid; p-ethylbenzenesulfonic acid is functionalized at both the benzylic and methyl positions. Ethanol is converted to a spectrum of C_2 (chloro)oxygenates, including ethylene glycol and 2-chloroethanol, products resulting from methyl fundionalization. n-Propanol is also significantly attacked at the methyl position. ^(13)C labeling and kinetics studies were used to elucidate mechanistic pathways. The reactivity of a methyl group C-H bond is at least as high as that of a C-H bond CY to oxygen, in contrast to most alkane conversion systems.", "doi": "10.1021/om00027a045", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "1993-03", "series_number": "3", "volume": "12", "issue": "3", "pages": "895-905" }, { "id": "authors:1wa7v-9aw32", "collection": "authors", "collection_id": "1wa7v-9aw32", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160914-141706345", "type": "article", "title": "Structure of a Permethylcyclopentadienyl-\u03bc-tetramethylcyclopentadienylmethylene Scandium Dimer", "author": [ { "family_name": "Hajela", "given_name": "Sharad", "clpid": "Hajela-S" }, { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Bis(\u03b7^5-pentamethylcyclopentadienyl)-bis[\u03bc-2,3,4,5-tetramethyl-1-methylene-ScC^1:Sc'(\u03b7^5)-cyclopentadienyl]-discandium(III), [Sc_2(C_(10)H_(15))_2-(C_(10)H_(14)_2], M_r = 628.90, triclinic, Pl, \u0251 = 8.641 (5), b= 9.478 (2), c = 12.338 (5) \u00c5, \u0251 = 75.58 (3), \u03b2 = 80.39 (4), y = 63.75 (3)\u00ba, V = 875.8 (7) \u00c5^3, Z = 1, D_x\n= 1.19 g cm^(-3), \u03bb(Mo K\u0251}=0.71073 \u00c5, \u03bc = 4.11 cm^(-1), F(000) = 340, room temperature, R (on F) = 0.046 for 2241 reflections with F_o^2 > 3\u03c3(F_o^2). Two bis(pentamethylcyclopentadienyl)scandium molecules are joined across a center of symmetry. One of the Cp^* methyl groups has lost an H atom and that methylene group bonds to the symmetry-related Sc atom: Sc-C6' = 2.282 (5) \u00c5. Other aspects of the bis-Cp^*Sc geometry are normal.", "doi": "10.1107/S0108270192002038", "issn": "0108-2701", "publisher": "International Union of Crystallography", "publication": "Acta Crystallographica Section C", "publication_date": "1992-10-15", "series_number": "10", "volume": "48", "issue": "10", "pages": "1771-1773" }, { "id": "authors:8cv0r-pkx07", "collection": "authors", "collection_id": "8cv0r-pkx07", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160914-141706830", "type": "article", "title": "A Silicon-Bridged Bis(substituted Cp) Yttrium Complex", "author": [ { "family_name": "Marsh", "given_name": "Richard E.", "clpid": "Marsh-R-E" }, { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" }, { "family_name": "Coughlin", "given_name": "E. Bryan", "clpid": "Coughlin-E-B" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "rac-Bis(tetrahydrofuran)lithium [bis(2-trimethylsilyl-4-tert-butyl-\u03b7^5-cyclopentadienyl)dimethylsilane] dichloroyttrate, [Li(C_4H_80)_2][Y(C_(26)H_(48)-Si_3)Cl_2], M_r= 755.87, triclinic, Pl, \u0251 = 13.110 (8), b = 17.163 (15), c = 20.623 (14) \u00c5, \u0251= 104.02 (7), \u03b2 = 99.38 (5), y = 100.24 (6)\u00ba, V = 4326 (6) \u00c5^3, z = 4,\nD_x = 1.16 g cm^(-3), \u03bb(Mo K\u0251)= 0.71073 \u00c5, \u03bc = 15.86 cm^(-1), F(000) = 1608, room temperature, R = 0.056 for 6136 reflections with F_o^2 > 3\u03c3(F_o^2). There are two virtually identical molecules in the asymmetric unit. In each, the Y atom is tetrahedrally\ncoordinated to a substituted Si-bridged bis(cyclopentadienyl)\nligand and to two Cl ions in the cleft. The Li atom is 2.35 \u00c5 from each Cl ion, and two molecules of tetrahydrofuran are connected to the Li, completing its tetrahedral coordination.", "doi": "10.1107/S0108270192001987", "issn": "0108-2701", "publisher": "International Union of Crystallography", "publication": "Acta Crystallographica Section C", "publication_date": "1992-10-15", "series_number": "10", "volume": "48", "issue": "10", "pages": "1773-1776" }, { "id": "authors:2mk5n-0xv66", "collection": "authors", "collection_id": "2mk5n-0xv66", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170118-144405649", "type": "article", "title": "Structure of trimethylplatinum(IV) with a tripod ligand", "author": [ { "family_name": "Marsh", "given_name": "Richard E.", "clpid": "Marsh-R-E" }, { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" }, { "family_name": "Lyon", "given_name": "David K.", "clpid": "Lyon-D-K" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "[1(\u03b7^5)-Cyclopentadienyl]-tris-\u00b5-(dimethyl-phosphito-1\u03baP:2\u03baO)(trimethyl-2\u03ba^3C)cobaltplatinum, [CoPt(C_2H_6O_3P)_3(C_5H_5)(CH_3)_3], M_r = 691.35, triclinic, P1, a = 9.106(3), b = 14.803(3), c = 15.147(3) \u00c5, \u03b1 = 112.95(2), \u03b2 = 103.68(2), \u03b3 = 95.10(2)\u00b0, V = 1788.9(9) \u00c5^3, Z = 3, D_x = 1.93 g cm^(-3), \u03bb(Mo K\u03b1) = 0.71073 \u00c5, \u00b5 = 68.69 cm^(-1), F(000) = 1014, room temperature, R = 0.038 for 4620 reflections with F_o^2 > 3\u03c3(F_o^2). The trimethylplatinum(IV) completes octahedral coordination by bonding to three O atoms of the tripod-shaped methoxy Kl\u00e4ui ligand. There are two independent molecules in the cell, one disordered about a center of symmetry. The ordered molecule has normal bond distances and angles; Pt-C = 2.001 (11) and Pt-O = 2.173(5) \u00c5. Many distances in the disordered molecule are uncertain, particularly in the areas of the Cp C atoms and the CH_3 groups, which overlap in the two orientations.", "doi": "10.1107/S010827019200163X", "issn": "0108-2701", "publisher": "International Union of Crystallography", "publication": "Acta Crystallographica Section C", "publication_date": "1992-09-15", "series_number": "9", "volume": "48", "issue": "9", "pages": "1603-1606" }, { "id": "authors:7gt3m-9pw56", "collection": "authors", "collection_id": "7gt3m-9pw56", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160914-100611088", "type": "article", "title": "A platinum chloro (fluoroaryl)phosphine complex", "author": [ { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" }, { "family_name": "Lyon", "given_name": "David K.", "clpid": "Lyon-D-K" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "trans-Dichloro bis[ tris(peritafluorophenyl)phosphine\n]platinum(II), [PtCl_2{P(C_6F_5)_3}_2], M_r = 1330.29, triclinic, Pl, \u0251 = 9.536 (4), b = 11.221 (2), c = 11.613 (1)\u00c5, \u0251 = 62.55 (1), \u03b2 = 65.81 (2), y = 73.05 (2)\u00ba, V = 997.8 (4) \u00c5^3, Z = 1, D_x = 2.21 g cm^(-3), \u03bb(Mo K\u0251)= 0.71073 A, \u03bc = 39.27 cm^(-1), F(000) = 628, room temperature, R = 0.034 for 3497 reflections with F_o^2 > 0. The molecule is centrosymmetric, with Pt-Cl distance 2.304 (2) and Pt-P 2.280 (1) \u00c5, and P-Pt-Cl angle 94.8 (1)\u00b0. The C-P distances average 1.824 (4)\u00c5, slightly longer than normal, and the pentafluoro-phenyl groups all have small [116.3 (3)\u00ba] angles at the c atom bonded to P.", "doi": "10.1107/S0108270192001008", "issn": "0108-2701", "publisher": "International Union of Crystallography", "publication": "Acta Crystallographica Section C", "publication_date": "1992-09-15", "series_number": "9", "volume": "48", "issue": "9", "pages": "1582-1584" }, { "id": "authors:5d0y8-06232", "collection": "authors", "collection_id": "5d0y8-06232", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160914-141706592", "type": "article", "title": "Cp,Cp*-Dimethyltantalum Triflate", "author": [ { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" }, { "family_name": "Quan", "given_name": "Roger W.", "clpid": "Quan-Roger-W" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "(\u03b7^5-Cyclopentadienyl)(dimethyl)(\u03b7^5-pentamethylcyclopentadienyl)tantalum trifluoromethylsulfonate, [Ta(C_5H_5)(C_(10)H_(15)CH_3)_2]CF_3S0_3, M_r = 560.41, orthorhombic, Pbca, \u0251 = 14.230 (4), b = 19.283 (4), c = 14.628 (4) \u00c5, v = 4014 (2) \u00c5^3, z = 8, D_x = 1.855 g cm^(-3), \u03bb(Mo K\u0251)= 0.71073 \u00c5, \u03bc = 55.3 cm^(-1), F(000) = 2192, room temperature, R(F) = 0.038 for 1882 reflections with F_o^2 > 3\u03c3(F_o^2). The Ta-C(methyl)\u00c5 distances are virtually equal at 2.171 (12) \u00c5, with a C-Ta-C angle of 95.8 (5)\u00ba. The coordination of the two \u03b7^5 ligands is normal; the Cp(centroid}-Ta-Cp^*(centroid) angle is 136.2\u00b0. Intermolecular contacts are all approximately at van der Waals distances, with indications of CH\u00b7\u00b7\u00b7O hydrogen bonding between methyl groups and the triflate anion.", "doi": "10.1107/S0108270192001628", "issn": "0108-2701", "publisher": "International Union of Crystallography", "publication": "Acta Crystallographica Section C", "publication_date": "1992-09-15", "series_number": "9", "volume": "48", "issue": "9", "pages": "1610-1612" }, { "id": "authors:zaz6a-ttb22", "collection": "authors", "collection_id": "zaz6a-ttb22", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170408-143105320", "type": "article", "title": "Structure of trimethylplatinum(IV) with a tripod ligand", "author": [ { "family_name": "Marsh", "given_name": "Richard E.", "clpid": "Marsh-R-E" }, { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" }, { "family_name": "Lyon", "given_name": "David K.", "clpid": "Lyon-D-K" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "[1(\u03b7^5)-Cyclopentradienyl]-tris-\u00b5-(dimethyl-phosphino-1\u03ba\u03a1:2\u03baO)(trimethyl-2\u03ba^3C)cobaltplatinum, [CoPt(c_2H_6O_3P)_3(C_5H_5(CH_3)_3], M_r = 691.36, triclinic, P1[bar], a= 9.106 (3), b= 14.803 (3), c= 15.147 (3) \u00c5, \u03b1 = 112.95 (2), \u03b2 = 103.68 (2), \u03b3 = 95.10 (2)\u00b0, V = 1788.9 (9) \u00c5^3, Z = 3, D_x = 1.93 g cm^3, \u03bb(Mo K\u03b1) = 0.71073 \u00c5, \u00b5 = 68.69 cm^(-1) F(000) = 1014, room temperature, R = 0.038 for 4620 reflections with F^2_0 > 3\u03c3(F^2_0). The trimethlyplatinum(IV) completes octahedral coordination by bonding to three O atoms of the tripod-shaped methoxy Kl\u00e4ui ligand. There are two independent molecules in the cell, one disordered about a center of symmetry. The ordered molecule has normal bond distances and angles; Pt-C = 2.001 (!!) and Pt-O = 2.173 (5) \u00c5. Many distances in the disordered molecule are uncertain, particularly in the areas of the Cp C atoms andf the CH_3 groups, which overpla in the two orientations.", "doi": "10.1107/S010827019200163X", "issn": "0108-2701", "publisher": "International Union of Crystallography", "publication": "Acta Crystallographica Section C", "publication_date": "1992-09", "series_number": "9", "volume": "48", "issue": "9", "pages": "1603-1606" }, { "id": "authors:705mq-qg635", "collection": "authors", "collection_id": "705mq-qg635", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160914-100611327", "type": "article", "title": "A permethylcyclopentadienyl carbollide scandium complex, Sc_2Si_4O_3C_(50)B_(18)Li_2H_(114)", "author": [ { "family_name": "Marsh", "given_name": "Richard E.", "clpid": "Marsh-R-E" }, { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" }, { "family_name": "Bazan", "given_name": "Guillermo C.", "clpid": "Bazan-G-C" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Tris(tetrahydrofuran)lithium lithium bis[3-bis\n(trimethylsilyl)methyl-3-(\u03b7^5-pentamethylcyclopentadienyl)-1,2-dicarba-3-scanda-closo-dodecaborate- (l-)], [Li(C_4H_80)_3].Li[Sc(C_2B_9H_(11))(C_(10)H_(15))CH {Si(\nCH_3)_3)]_2]_2, M_r = 1174.16, triclinic, Pl, \u0251 = 8.924 (4),\nb = 18.467 (5), c = 22.165 (3)\u00c5, \u0251 = 91.42 (2), \u03b2 = 92.36 (2), y = 92.21 (3)\u00ba, v = 3645.6 (18) A^3, Z = 2, D_x = 1.07 g cm^(-3), \u03bb(Mo K\u0251)= 0.71073 \u00c5, \u03bc = 2.84 cm^(-1), F(000) = 1264, room temperature, 294 K, R = 0.064 for 3069 reflections. Each Sc atom is bonded to one Cp^* in an 175 fashion, to one carbollide ligand in an \u03b7^5 fashion (completing a distorted icosahedron), and to one -CH(SiMe_3)_2 group in the cleft; the angle at Sc subtended by the centers of the two \u03b7^5 groups is 137.8\u00b0. Two of these complexes share an Li atom which is loosely bonded to three B atoms of each carbollide, creating a dimeric monoanion. The counterion, a second Li atom, is coordinated\nto three tetrahydrofuran molecules.", "doi": "10.1107/S0108270192000714", "issn": "0108-2701", "publisher": "International Union of Crystallography", "publication": "Acta Crystallographica Section C", "publication_date": "1992-08-15", "series_number": "8", "volume": "48", "issue": "8", "pages": "1416-1419" }, { "id": "authors:91yte-nv396", "collection": "authors", "collection_id": "91yte-nv396", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160914-100610561", "type": "article", "title": "Structure of permethyltantalocenephenylmethanecarbothialdehyde hydride, (\u03b7^5-C_5Me_5)_2Ta(\u03b7^2-SCHCH_2C_6H_5)H", "author": [ { "family_name": "Nelson", "given_name": "Janet E.", "clpid": "Nelson-Janet-Elizabeth" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Marsh", "given_name": "Richard E.", "clpid": "Marsh-R-E" }, { "family_name": "Henling", "given_name": "Lawrence M.", "clpid": "Henling-L-M" } ], "abstract": "Hydridobis( 7] 5-pentamethylcyclopentadienyl)\n(phenylmethanecarbothialdehyde-kC,kS)tantalum C_(28)H_(39)STa, Mr= 588.63, monoclinic, P2_1 c, \u0251 = 15.729 (5), b = 10.203 (2), c = 17.599 (5) \u00c5, \u03b2 = 116.18 (2)\u00ba , v = 2535 (1) \u00c5^3, z = 4, D_x = 1.54 g cm^(-3), \u03bb(Mo K\u0251) = 0.71073 A, \u03bc = 46.6 cm^(-1), F(000) = 1184, room temperature (297 K), R = 0.068 for 2333 reflections with F_o^2 > 0, R = 0.054 for 2179 with F_o^2 > 3\u03c3(F_o^2). The structure is disordered, with two enantiomeric molecules\noccupying the same crystallographic site. For the major component, the thioaldehyde ligand has an S-C bond length of 1.86 (2) \u00c5. The ligand is bonded to the Ta center with a Ta-S bond distance of 2.418 (9) \u00c5 and a Ta-C bond distance of 2.28 (2) \u00c5.", "doi": "10.1107/S0108270191011927", "issn": "0108-2701", "publisher": "International Union of Crystallography", "publication": "Acta Crystallographica Section C", "publication_date": "1992-06-15", "series_number": "6", "volume": "48", "issue": "6", "pages": "1023-1025" }, { "id": "authors:s9zym-mnz65", "collection": "authors", "collection_id": "s9zym-mnz65", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180521-111433261", "type": "article", "title": "Synthesis and characterization of thioaldehyde hydride derivatives of permethyltantalocene. Investigations of their equilibration with thiolates and the stereochemistry of alkyl migrations from sulfur to tantalum", "author": [ { "family_name": "Nelson", "given_name": "Janet E.", "clpid": "Nelson-Janet-Elizabeth" }, { "family_name": "Parkin", "given_name": "Gerard", "clpid": "Parkin-G" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Permethyltantalocene thioaldehyde hydride complexes, Cp*_2Ta(\u03b7^2-S-CHR)H (Cp* = \u03b7^5-C_5Me_5; R = H, C_6H_5, CH_2C_6H_5, CH_2CMe_3), have been prepared by treating precursors to [Cp*_2Ta-R'] (e.g. Cp*_2Ta(=C=CH_2)H for R' = CH=CH_22) with the appropriate thiol RCH_2SH. Oxidative addition of the S-H bond leads to the unstable Ta(V) derivatives Cp*_2Ta(R'(H)(SCH_2R). Reductive elimination of R'H is facile, forming [Cp*_2Ta-ScH_2R], which subsequently undergoes \u03b2-He limination to yield the thiddehyde hydrides Cp*_2Ta( \u03b7^2-S-CHR)H. The results of an X-ray structure determination for Cp*_2Ta( \u03b7_2-SC-HCH_2C_6H_5)H are summarized. These permethyltantalocene thioaldehyde hydride complexes are shown to be in rapid equilibrium with the corresponding 16-electron thiolate species [CP*_2Ta-SCH_3R] through a \u03b2-H migratory inaertion/elimination process. When they are heated, the permethyltantalocene thiddehyde hydride complexes undergo rearrangement to the thermodynamically favored tautomer, the permethyltantalocene sulfido alkyl Cp*_2Ta(=S)CH_2R. An inverse kinetic deuterium isotope effect observed for Cp*_2Ta(\u03b7^2-S-CY_2)Y (Y = H, D) ((k_H)/(k_D) = 0.72 (3) at 138 \u00b0C) is indicative of a stepwise process involving to Cp*_2Ta(=S)CY_3. Derivatives of the permethyltantalocene phenylthioacetaldehyde hydride have been prepared from the erythro- and threo-phenethyl-d_2 mercaptan, C_6H_5CHDCHDSH, to elucidate the mechanism of alkyl transfer. The migration has been found to proceed with \u2273 85% retention of stereochemistry at carbon for the migrating phenethyl-d_2 group. The sulfido methyl complex Cp*_2Ta(=S)CH_3 is hydrogenated under forcing conditions to yield methane and CP*~T~(=S)bHu,t this product resists final hydrogenation to Cp*_2TaH_3 and H_2S.", "doi": "10.1021/om00042a036", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "1992-06", "series_number": "6", "volume": "11", "issue": "6", "pages": "2181-2189" }, { "id": "authors:w5yn1-xrj20", "collection": "authors", "collection_id": "w5yn1-xrj20", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160914-100610290", "type": "article", "title": "Structure of a scandium-(silicon-bridged Cp, Cp^*) complex", "author": [ { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" }, { "family_name": "K\u00f6hn", "given_name": "Randolf D.", "clpid": "K\u00f6hn-R-D" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "({\u03b7^5-3-[2-(Di-tert-butylphosphino)ethyl]-cyclopentadienyl} (dimethyl)(\u03b7^5-tetramethylcyclopentadienyl)silane)bis(trimethylsilyl)methylscandium, C_(33)H_(62)PScSi_3, M_r = 595.04, monoclinic, P2_1/n, \u0251 = 14.449 (3), b = 12.807 (5), c = 20.848 (5) \u00c5, \u03b2 =\n99.52 (2)\u00ba, V = 3804.8 (18) \u00c5^3, Z = 4, D_x = 1.04 g cm^(-3), \u03bb(Mo K\u0251)= 0.71073 \u00c5,\u03bc = 3.18 cm^(-1)F(000) = 1352, T = 296 K, final R = 0.108 for 3100 reflections with F_o^2 > 0, 0.054 for 1766 reflections with F_o^2 > 3\u03c3(F_o^2). The Sc-C(l) bond [2.253 (8) \u00c5] is insignificantly shorter than the 2.271 (7) \u00c5 found in a similar compound; the geometry about C(l) is nearly trigonal, with angles 118.5 (5), 116.0 (5) and 119.4(6)\u00ba.", "doi": "10.1107/S0108270191008375", "issn": "0108-2701", "publisher": "International Union of Crystallography", "publication": "Acta Crystallographica Section C", "publication_date": "1992-02-15", "series_number": "2", "volume": "48", "issue": "2", "pages": "251-253" }, { "id": "authors:6j1g6-6w425", "collection": "authors", "collection_id": "6j1g6-6w425", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160914-085914313", "type": "article", "title": "Structures of chlorohydroxobis(pentamethylcyclopentadienyl)tantalum(V) trifluoromethanesulfonate (triflate) and dihydroxobis(pentamethylcyclopentadienyl)tantalum(V) triflate", "author": [ { "family_name": "Quan", "given_name": "Roger W.", "clpid": "Quan-Roger-W" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" } ], "abstract": "[Ta(C_(10)H_(15))2(C1)(OH)][CF_3SO_3] (I), Mr = 652.94, monoclinic, P2_1/n, a = 9.965(7), b = 18.796 (5), c = 13.269 (3)\u00c5, \u03b2 = 94.02 (3)\u00b0, V = 2479-2 (19)\u00c5^3, Z = 4, D_x = 1.75 g cm^(-3), \u03bb(Mo Kce) = 0.71073 \u00c5, \u00b5 = 46 cm^(-1), F(000) = 1288, room temperature, R = 0.107 for 3702 reflections with F_o^2 > 0 [R=0.053 for 2094 reflections with F_o^2 > 3\u03c3(F_o^2)]. [Ta(C_(10)H_(15))_2(OH)_2][CF_3SO_3] (II), M_r = 634.49, triclinic, P1, a = 10\u22c5052 (2), b = 10\u22c5111 (2), c = 12\u22c5739(2) \u00c5, \u0251 = 71\u22c538(2), \u03b2 = 78\u22c521 (1), y = 77\u22c540 (2)\u00b0, V = 1184\u22c57 (4)\u00c5^3, Z = 2, D_x =\n1\u22c578 g cm^(-3), \u03bb(Mo K\u0251) = 0\u22c571073 \u00c5, \u00b5 = 47 cm^(-1) F(000) = 628, room temperature, R = 0\u22c5032 for 4046\nreflections with Fo g > 0 [R = 0\u22c5026 for 3664 reflections\nwith F_o^2 > 3\u03c3(F_o^2)]. Severe disorder of the triflate\nanion in (I) led to a less satisfactory structure, but\ncations in both compounds are well defined, with\nnormal Ta\u2500Cp^* geometry. Ta\u2500C1 2\u22c5343 (4), Ta\u2500O 1\u22c5853 (8)\u00c5 and C1\u2500Ta\u2500O 96\u22c54 (3)\u00b0 in (I); Ta\u2500O 1\u22c5907(6)A and O\u2500Ta\u2500O 100\u22c54(2)\u00b0 in (II). Tantalum-bound OH groups are hydrogen bonded to triflate O atoms.", "doi": "10.1107/S0108270191003323", "issn": "0108-2701", "publisher": "International Union of Crystallography", "publication": "Acta Crystallographica Section C", "publication_date": "1991-10-15", "series_number": "10", "volume": "47", "issue": "10", "pages": "2057-2060" }, { "id": "authors:f9k8g-wre56", "collection": "authors", "collection_id": "f9k8g-wre56", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180521-105844972", "type": "article", "title": "Reactivity of permethylscandocene derivatives with acetylene. Structure of acetylenediylbis(permethylscandocene), (\u03b7^5-C_5Me_5)_2Sc-C\u2261C-Sc(\u03b7^5-C_5Me_5)_2", "author": [ { "family_name": "St. Clair", "given_name": "Martin", "clpid": "St-Clair-M" }, { "family_name": "Schaefer", "given_name": "William P.", "clpid": "Schaefer-W-P" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Excess acetylene reacts with Cp*_2Sc-R (Cp* = \u03b7-C5Me_5; R = H, alkyl, aryl, alkenyl, alkynyl, amide) below -78 \u00b0C to yield R-H and Cp*_2Sc-C\u2261CH; the latter then reacts with excess C_2H_2 to form polyacetylene. Cp*_2Sc-C\u2261CH cleanly decomposes to Cp*_2Sc-C\u2261C-ScCp*_2, most likely via u bond metathesis involving the Sc-acetylide and terminal C-H bonds for two molecules of Cp*_2Sc-C\u2261CH. The structure of this unusual acetylenediyl-bridged dimer has been determined by X-ray diffraction methods. It crystallizes with a half-molecule of toluene per scandium dimer in the tetragonal system, space group P42_1c (No. 114), with a = 15.057 (3) \u00c5, c = 18.617 (6) \u00c5, V = 4220.7 (18) \u00c5^3, and z = 4.", "doi": "10.1021/om00049a001", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "1991-03", "series_number": "3", "volume": "10", "issue": "3", "pages": "525-527" }, { "id": "authors:svfe3-phb05", "collection": "authors", "collection_id": "svfe3-phb05", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180809-152106699", "type": "article", "title": "Carbon-hydrogen and carbon-carbon bond activation with highly electrophilic transition metal complexes", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Highly electron deficient scandocene derivatives of the types (\u03b7^5-C_5Me_5)_2ScR, {(\u03b7^5-C_5Me_4)_2SiMe_2}ScR and {(\u03b7^5-C_5H_3CMe_3)_2SiMe_2}ScR catalyze the polymerization of ethylene, the head-to-tail dimerization of \u03b1 olefins, the cyclization of \u03b1,\u03c9 dienes to methylene cycloalkanes, and the branching of 1,4 pentadienes to isoprenes. The mechanisms of the individual steps have been studied. Key steps involve sequential and reversible olefin insertion/\u03b2 H elimination/\u03b2 alkyl elimination, the last of which is particularly facile in these systems. [((\u03b7^5-C_5Me_4)Me_2Si(\u03b7^1-NCMe_3)(PMe_3)Sc(\u00b5-H)]_2, catalyzes the polymerization of \u03b1 olefins. Evidence is presented in support of a well defined, one component catalyst system with all scandium centers functioning alike.", "doi": "10.1351/pac199062061151", "issn": "0033-4545", "publisher": "International Union of Pure and Applied Chemistry", "publication": "Pure and Applied Chemistry", "publication_date": "1990-06", "series_number": "6", "volume": "62", "issue": "6", "pages": "1151-1154" }, { "id": "authors:5fvpt-18w98", "collection": "authors", "collection_id": "5fvpt-18w98", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180430-145259868", "type": "article", "title": "Ethylene insertion and \u03b2-hydrogen elimination for permethylscandocene alkyl complexes. A study of the chain propagation and termination steps in Ziegler-Natta polymerization of ethylene", "author": [ { "family_name": "Burger", "given_name": "Barbara J.", "clpid": "Burger-B-J" }, { "family_name": "Thompson", "given_name": "Mark E.", "orcid": "0000-0002-7764-4096", "clpid": "Thompson-M-E" }, { "family_name": "Cotter", "given_name": "W. Donald", "clpid": "Cotter-W-D" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "The rates of ethylene insertion into the Sc-C bond for Cp*_2ScR (Cp* = (\u03b7^5-C_5Me_5), R = CH_3, CH_2CH_3, CH_2CH_2CH_3) have been measured at -80 \u00b0C by ^(13)C NMR; the second order rate constants (M^(-1) S^(-1)) are as follows: R = CH_3, 8.1 (2) X 10^(-4); R = CH_2CH_3,4.4 (2) X 10^(-4); R = CH_2CH_2CH_3, 6.1 (2) X 10^(-3). The slow rate for the ScCH_2CH_3 complex is attributed to a ground-state stabilization by a \u03b2-C-H \"agostic\" interaction. The distributions of molecular weights for ethylene oligomers (CH_3(CH_2)_nCH_3, n = 11-47) produced from known amounts of ethylene and Cp*_2ScCH_2CH_2CH_3 at -80 \u00b0C satisfactorily fit a Poisson distribution, indicative of a \"living\" Ziegler-Natta polymerization system. From the measured, slower initiation rates of insertion for Cp*ScCH_3 and Cp*_2ScCH_2CH_3 and propagation rates equal to that for Cp_2ScCH_2CH_2CH_3, the molecular weight distributions of ethylene oligomers are also accurately predicted. Cp*ScCH_3 undergoes a single insertion with 2-butyne with a moderate enthalpy of activation and a large, negative entropy of activation. The second-order rate constants for the insertion of 3-phenyl-2-propyne, 2-pentyne, and 4-methyl-2-pentyne have been measured. The rates for &hydrogen elimination for members of the series of permethylscandocene alkyl complexes Cp*_2ScCH_2CH_2R (R = H, CH_3, CH_2CH_3, C_6H_5, C_6H_4-p-CH_3, C_6H_4-p-CF_3, C_6H_4-p-NMe_2) have been obtained by rapidly trapping Cp*ScH with 2-butyne. A transition state for the \u03b2-hydrogen elimination is indicated with partial charge on the &carbon. Hydrogen is thus transferred to the scandium center as hydride in the \u03b2-H elimination process.", "doi": "10.1021/ja00160a041", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "1990-02-14", "series_number": "4", "volume": "112", "issue": "4", "pages": "1566-1577" }, { "id": "authors:48xe4-agb73", "collection": "authors", "collection_id": "48xe4-agb73", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120510-132916331", "type": "article", "title": "A new mechanism for exchange processes observed in the compounds [M(\u03b7-C_5H_5)_2(exo-\u03b7-RCH = CH_2)H], M = Nb and Ta", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Burger", "given_name": "Barbara J.", "clpid": "Burger-B-J" }, { "family_name": "Green", "given_name": "Malcolm L. H.", "clpid": "Green-M-L-H" }, { "family_name": "Santarsiero", "given_name": "Bernard D.", "clpid": "Santarsiero-B-D" }, { "family_name": "Sella", "given_name": "Andrea", "clpid": "Sella-A" }, { "family_name": "Trimmer", "given_name": "Mark S.", "clpid": "Trimmer-M-S" }, { "family_name": "Wong", "given_name": "Luet-Lok", "clpid": "Wong-Luet-Lok" } ], "abstract": "Dynamic n.m.r. studies of the exchange processes in the complexes [M(\u03b7-C_5H_5)(exo-\u03b7-RCH=CH_2)H], M = Nb, Ta, lead to the proposal of a new mechanism involving intermediates with agostic bonding.", "doi": "10.1039/c39890000734", "issn": "0022-4936", "publisher": "Royal Society of Chemistry", "publication": "Journal of the Chemical Society. Chemical Communications", "publication_date": "1989-06-01", "series_number": "11", "volume": "1989", "issue": "11", "pages": "734-736" }, { "id": "authors:2e1m7-ba037", "collection": "authors", "collection_id": "2e1m7-ba037", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120517-111723864", "type": "article", "title": "Direct protonation of the W\u2013H bonds of Bis(pentamethylcyclopentadienyl)tungsten dihydride", "author": [ { "family_name": "Parkin", "given_name": "Gerard", "clpid": "Parkin-G" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "abstract": "Protonation of (C_5Me_5)_2 WH_2 to give [(C_5Me_5)_2WH_3]+ is proposed to occur by attack at both W\u2013H bonds rather than by direct attack at the d^2 metal centre.", "doi": "10.1039/c39890000255", "issn": "0022-4936", "publisher": "Royal Society of Chemistry", "publication": "Journal of the Chemical Society. Chemical Communications", "publication_date": "1989-02-15", "series_number": "4", "volume": "1989", "issue": "4", "pages": "255-257" }, { "id": "authors:5ap9f-yp938", "collection": "authors", "collection_id": "5ap9f-yp938", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151008-153202191", "type": "article", "title": "^1H, ^(13)C, and ^(15)N Nuclear Magnetic Resonance Studies of a Dinitrogen Complex of Permethyltitanocene. Evidence for Molecular Nitrogen Coordinated \"Edge-on\" to a Transition Metal", "author": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Rosenberg", "given_name": "Edward", "clpid": "Rosenberg-E" }, { "family_name": "Roberts", "given_name": "John D.", "clpid": "Roberts-J-D" } ], "abstract": "In connection with the current interest in transition metal dinitrogen complexes and their possible roles in nitrogen-fixing reaction systems, we have obtained results which bear on the structure of a titanium dinitrogen\ncomplex in solution. We report here successful application of ^(15)N nmr spectroscopy to studies of a transition metal dinitrogen complex which provides a potentially powerful technique for elucidation of the structure of such complexes.", "doi": "10.1021/ja00809a063", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "1974-01", "series_number": "2", "volume": "96", "issue": "2", "pages": "612-614" }, { "id": "authors:k5k5y-1sq19", "collection": "authors", "collection_id": "k5k5y-1sq19", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120815-073948090", "type": "article", "title": "New cobalt(I) complexes derived from dicarbonyltricyanocobaltate(I)", "author": [ { "family_name": "Bercaw", "given_name": "John", "clpid": "Bercaw-J-E" }, { "family_name": "Guastalla", "given_name": "Giovanni", "clpid": "Guastalla-G" }, { "family_name": "Halpern", "given_name": "Jack", "clpid": "Halpern-J" } ], "abstract": "The preparation and characterization of several series of mixed ligand cobalt(I) complexes of the types [Co(CN)_2(CO)_2(PR_3)]\u2013, [Co(CN)_2(CO)(PR_3)_2]\u2013, and [Co(CN)(CO)_2(PR_3)_2], prepared by the reactions of tertiary phosphines (PR_3) with [Co(CN)_3(CO)_2]^(2\u2013), are described and some novel aspects of their chemistry are discussed.", "doi": "10.1039/C29710001594", "issn": "0577-6171", "publisher": "Royal Society of Chemistry", "publication": "Journal of the Chemical Society D: Chemical Communications", "publication_date": "1971", "series_number": "24", "volume": "1971", "issue": "24", "pages": "1594-1595" } ]