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.
“Carbon–Sulfur Bond Cleavage and Hydrodesulfurization of Thiophenes by Tungsten” Aaron Sattler and Gerard Parkin J. Am. Chem. Soc. 2011, in press.
“Modeling Aspects of Hydrodesulfurization by Molybdenum Hydride Compounds: Desulfurization of Thiophene and Benzothiophene and C–S Bond Cleavage of Dibenzothiophene.” Aaron Sattler, Kevin E. Janak and Gerard Parkin Inorg. Chim. Acta 2011, in press (special issue in honor of R. G. Bergman).
“Synthesis and Structural Characterization of Tris(2-oxo-1-t-butylimidazolyl) and Tris(2-oxo-1-methylbenzimidazolyl)hydroborato Complexes: A New Class of Tripodal Oxygen Donor Ligand.” Ahmed Al-Harbi, Wesley Sattler, Aaron Sattler and Gerard Parkin Chem. Commun. 2011, in press.
“Cleaving Carbon–Carbon Bonds by Inserting Tungsten into Unstrained Aromatic Rings” Aaron Sattler, Gerard Parkin, Nature 463, 523-526 (2010)
“On the Chalcogenophilicity of Mercury: Evidence for a Strong Hg–Se Bond in [TmBut]HgSePh and its Relevance to the Toxicity of Mercury” Jonathan G. Melnick, Kevin Yurkerwich, Gerard Parkin, J. Am. Chem. Soc. 132, 647-655 (2010)
“2-Mercapto-1-t-butylimidazolyl as a Bridging Ligand: Synthesis and Structural Characterization of Nickel and Palladium Paddlewheel Complexes” Keliang Pang, Joshua S. Figueroa, Ian A. Tonks, Wesley Sattler, Gerard Parkin, Inorg. Chim. Acta 362, 4609-4615 (2009) (special issue in memory of S. Trofimenko)
“p-tert-Butyltetrathiatetramercaptocalixarene as a Sulfur-Rich Platform for Molybdenum, Tungsten and Nickel” Daniela Buccella, Gerard Parkin, Chem. Commun 289-291 (2009)
“Molecular Structures of Protonated and Mercurated Derivatives of Thimerosal” Wesley Sattler, Kevin Yurkerwich, Gerard Parkin, Dalton Trans. 4327-4333 (2009)
“Multiple Modes for Coordination of Phenazine to Molybdenum: Ring Fusion Promotes Access to h4-Coordination, Oxidative Addition of Dihydrogen and Hydrogenation of Aromatic Nitrogen Compounds” Aaron Sattler, Guang Zhu, Gerard Parkin, J. Am. Chem. Soc. J. Am. Chem. Soc. 131, 7828-7838 (2009)
“Reactivity of Mo(PMe3)6 Towards Benzothiophene and Selenophenes: New Pathways Relevant to Hydrodesulfurization” Daniela Buccella, Kevin E. Janak, Gerard Parkin, J. Am. Chem. Soc. 130, 16187-16189 (2008)
“Synthesis of Transition Metal Isocyanide Compounds from Carbonyl Complexes via Reaction with Li[Me3SiNR]” Wesley Sattler and Gerard Parkin, Chem. Commun 7566-7568 (2009)
“Synthesis, Structure and Reactivity of Two–Coordinate Mercury Alkyl Compounds with Sulfur Ligands: Relevance to Mercury Detoxification” Jonathan G. Melnick, Kevin Yurkerwich, Gerard Parkin, Inorg. Chem. 48, 6763-6772 (2009)
“Temperature Dependent Transitions Between Normal and Inverse Isotope Effects Pertaining to the Interaction of H–H and C–H Bonds with Transition Metal Centers” Gerard Parkin, Acc. Chem. Res. 42, 315-325 (2009)