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Research Summary
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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“67Zn Solid State NMR Spectroscopy of {[TpBut,Me]Zn(OH2)}[HOB(C6F5)3]. The Importance of the Anion, [HOB(C6F5)3]–” Andrew S. Lipton, Melissa M. Morlok, Gerard Parkin and Paul D. Ellis, Inorg. Chem., in press (2008)
“Coordination Chemistry of Molybdenum Relevant to Hydrodenitrogenation: Reactivity of Mo(PMe3)6 Towards 6–Membered Heterocyclic Aromatic Nitrogen Compounds involving C–H Bond Cleavage and h6–Coordination” Guang Zhu, Keliang Pang and Gerard Parkin, Inorg. Chim. Acta, in press, special issue in honor of R. J. Angelici (2008)
“New Modes for Coordination of Aromatic Heterocyclic Nitrogen Compounds to Molybdenum: Catalytic Hydrogenation of Quinoline, Isoquinoline, and Quinoxaline by Mo(PMe3)4H4” Guang Zhu, Keliang Pang and Gerard Parkin, J. Am. Chem. Soc. 130, 1564-1565 (2008)
“Reactivity of the Ni->B Dative s–Bond in the Nickel Boratrane Compounds [k4–B(mimBut)3]NiX (X = Cl, OAc, NCS, N3): Synthesis of a Series of B-Functionalized Tris(2-mercapto-1-t-butylimidazolyl)borato Complexes, [YTmBut]NiZ” Keliang Pang, Joseph M. Tanski, and Gerard Parkin, Chem. Commun. 1008-1010 (2008)
“Applications of Tripodal [S3] and [Se3] L2X Donor Ligands to Zinc, Cadmium and Mercury Chemistry: Organometallic and Bioinorganic Perspectives” Gerard Parkin New J. Chem. 31, 1996-2014 (2007)
“Applications of Deuterium Isotope Effects for Probing Aspects of Reactions Involving Oxidative Addition and Reductive Elimination of H–H and C–H Bonds” Gerard Parkin, J. Labelled Compounds and Radiopharmaceuticals 50, 1088-1114 (2007)
“Applications of Bis(1-R–imidazol-2-yl)disulfides and Diselenides as Ligands for Main Group and Transition Metals: k2–[N,N] Coordination, S–S Bond Cleavage and S–S/E–E (E = S, Se) Bond Metathesis Reactions” Joshua S. Figueroa, Kevin Yurkerwich, Jonathan Melnick, Daniela Buccella and Gerard Parkin, Inorg. Chem. 46, 9234-9244 (2007)
“Exo and Endo Isomerism of Subvalent Tin and Germanium Complexes Derived from 1,3–Diethers of p-tert-Butylcalix[4]arene” Tony Hascall, Keliang Pang and Gerard Parkin, Tetrahedron 63, 10826-10833, Special issue on New Trends in Calixarene Chemistry (2007)
“Synthesis and Structural Characterization of [BseMe]Ni(PPh3)(NO), a Nickel Complex with a Bent Nitrosyl Ligand” Victoria K. Landry and Gerard Parkin, Polyhedron 26, 4751-4757 (2007)
"Cleaving Mercury-Alkyl Bonds: A Functional Model for Mercury Detoxification by MerB" Jonathan G. Melnick and Gerard Parkin, Science 317, 225-227 (2007)
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