研究领域

Inorganic Chemistry

The research covered in our group is highly varied and ranges from understanding the roles that zinc plays in biological systems to the influence that "ansa bridges" exert on the chemistry of metallocene complexes. The importance of the former topic is illustrated by the fact that zinc is a constituent of more than 300 enzymes. The active sites of these enzymes feature a zinc center attached to the protein backbone by three or four amino acid residues, the nature of which influences the specific function of the enzyme. In order to understand why different zinc enzymes utilize different amino acid residues at the active site, it is necessary to understand how and why the chemistry of zinc is modulated by its coordination environment. Answers to these questions are being provided by a study of synthetic analogues of zinc enzymes, i.e., small molecules that resemble the enzyme-active sites. Metallocene complexes presently play prominent roles as reagents in organic syntheses and as catalysts for olefin polymerization. Significantly, the incorporation of an ansa bridge (which links the two cyclopentadienyl groups together) modulates the chemistry of metallocene derivatives, and we are presently ascertaining the reasons for the profound differences. As an illustration of the reactivity differences, we have demonstrated that a [Me2Si] linker promotes C­H, C­C, and C­S cleavage reactions in molybdenocene chemistry. In each case, the problems are studied by a combined experimental approach that involves synthesis, structural characterization by X­ray diffraction, and a detailed study of reactivity and mechanism by using multinuclear NMR spectroscopy. In addition to experimental studies, further insight into the systems under investigation is provided by the use of computational methods. For example, we have used density functional theory calculations to explain why the W­H bond energies in W(PMe3)4Hs2X2 are influenced by the nature of X, increasing in the sequence I < Br < Cl < F. This observation is of particular interest because M­H bond energies are influenced in the opposite way in Ir(PPh3)2(CO)(X)H2 derivatives.

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"Synthetic Pathways in Binuclear Molybdenum Chemistry: μ-Acetato, Chloro, and Tertiary Phosphine Derivatives; X-ray Structure Determination of trans-[MoCl(PBun3)(μ-O2CMe)]2." Malcolm L. H. Green, Gerard Parkin, Jim Bashkin, John Fail and Keith Prout J. Chem. Soc., Dalton Trans. 1982, 2519-2525. "Trimethylphosphine-tungsten Chemistry: Hydrido, Silyl, Fluoro, Hydroxy and Aquo Derivatives; Crystal structure of [W(PMe3)4H2(OH2)F]F." Malcolm L. H. Green, Gerard Parkin, Chen Mingqin and Keith Prout J. Chem. Soc., Chem. Commun. 1984, 1400-1402. "Formation of (η‑Cyclopentadienyl)pentahydrido(trimethylphosphino)-tungsten from Cyclopentane, Trimethylphosphine and Tungsten atoms." Malcolm L. H. Green and Gerard Parkin J. Chem. Soc., Chem. Commun. 1984, 1467-1468. "Formation of an η2-Formaldehyde compound from Methanol and its Hydrogenation giving Methanol." Malcolm L. H. Green, Gerard Parkin, Kelly J. Moynihan and Keith Prout J. Chem. Soc., Chem. Commun. 1984, 1540. "Synthetic Use of Lithium Nitride, an Unusual Reducing agent. Formation of Ti4 and Ti6 Complexes." Melvyn Kilner, Gerard Parkin and Andrew G. Talbot J. Chem. Soc., Chem. Commun. 1985, 34-35. "Formation of (η-Benzene) or (η-Cyclohexa-1,3-diene) Compounds of Chromium, Tungsten and Rhenium from Cyclohexane and the Metal atoms." Malcolm L. H. Green, Dermot O'Hare and Gerard Parkin J. Chem. Soc., Chem. Commun. 1985, 356-357. "η-Arene and η-Cyclohexadiene Tungsten Chemistry: New Synthetic Routes to Tertiaryphosphine-Hydride Derivatives." Malcolm L. H. Green and Gerard Parkin J. Chem. Soc., Chem. Commun. 1985, 771-773. "The Synthesis of Electron-rich η-Cyclopentadienyl Trimethylphosphine Complexes of Tungsten." Malcolm L. H. Green and Gerard Parkin J. Chem. Soc., Chem. Commun. 1985, 1383-1384. "Tertiary Phosphine Complexes of Tungsten." Gerard Parkin Reviews in Inorganic Chemistry 1985, 7, 251-297. "Ethylene Insertion into the W-C bond of the η2-Formaldehyde Ligand System of W(PMe3)4(η2‑CH2O)H2 giving the Oxometallacyclopentane Derivative W(OCH2CH2CH2)(PMe3)2(C2H4)2 and Related Studies." Malcolm L. H. Green and Gerard Parkin J. Chem. Soc., Chem. Commun. 1986, 90-91. "The reaction of [W(PMe3)4(η2-CH2PMe2)H] with Carbon Dioxide and Dihydrogen: Characterization of [{W(PMe3)3H2(η1-PMe2CH2)}2(C3H2O6)] using Two-dimensional Nuclear Magnetic Resonance Spectroscopy." Malcolm L. H. Green, Gerard Parkin, Dermot O'Hare, Luet-Lok Wong and Andrew E. Derome J. Organomet. Chem. 1986, 317, 61-68. "Lithium Nitride Reduction of Cp2TiCl2 and CpTiCl3: The Synthesis of (Cp2TiCl)2, (CpTiCl2)n, Cp2Ti(CO)2 and Chloro-Ti4 and Nitrido-Ti6 Complexes." Melvyn Kilner and Gerard Parkin J. Organomet. Chem. 1986, 302, 181-191. "The Chemistry of [W(PMe3)4(η2-CH2PMe2)H]: Synthesis of Hydroxy-hydrido, Fluoro-hydrido and Silyl-hydrido complexes and the Dimerisation of Ethylene and Propylene giving η4-Diene Derivatives." Mingqin Chen, Malcolm L. H. Green, Gerard Parkin and Keith Prout J. Chem. Soc., Dalton Trans. 1986, 2227-2236. "Synthesis of (η-Cyclopentadienyl)(trimethylphosphine)tungsten Derivatives and Related Chemistry." Malcolm L. H. Green and Gerard Parkin J. Chem. Soc., Dalton Trans. 1987, 1611-1618. "Alpha-and Beta-Migratory Insertion and Elimination Processes for Alkyl Complexes of Permethylscandocene and Permethyltantalocene." Gerard Parkin, Emilio Bunel, Barbara J. Burger, Mark. S. Trimmer, Allan van Asselt and John E. Bercaw J. Mol. Catalysis 1987, 41, 21-39. "Structure of (Pentamethylcyclopentadienyl)(pentamethyl-cyclopentadienyloxy)dioxotungsten(VI), (η5‑C5Me5)W(=O)2(OC5Me5). Structural Evidence for the Strong trans influence of the Oxo Ligand." Gerard Parkin, Richard E. Marsh, William P. Schaefer and John E. Bercaw Inorg. Chem. 1988, 27, 3262-3264. "Halide, Hydride, Alkyl, Oxo and Related Derivatives of Bis(pentamethylcyclopentadienyl)tungsten(IV)." Gerard Parkin and John E. Bercaw Polyhedron 1988, 7, 2053-2082. "(h5-C5Me5)2W=O: An Exceptionally Reactive Organometallic Oxo Derivative. Reduction with H2 and Reaction with O2 Resulting in Insertion of Oxygen into a Tungsten-Carbon Bond." Gerard Parkin and John E. Bercaw J. Am. Chem. Soc. 1989, 111, 391-393. "Direct Protonation of the W-H Bonds of Bis(pentamethylcyclopentadienyl)tungsten Dihydride." Gerard Parkin and John E. Bercaw J. Chem. Soc., Chem. Commun. 1989, 255-257. "Elimination Processes for Alkyl, Hydride, and Hydroxy Derivatives of Permethyltungstenocene." Gerard Parkin and John E. Bercaw Organometallics 1989, 8, 1172-1179.