Examples of biologically related reactivity of complexes of nickel, molybdenum and tungsten

This thesis examines the biomimetic inorganic chemistry of three metals: nickel, molybdenum and tungsten. Chapter 2 describes the synthesis, characterization and reactivity of several nickel complexes, which meet the requirements for a functional model for carbon monoxide dehydrogenase. These complexes, of the form Ni(bpy)Me(SR), are prepared via the reaction of Ni(bpy)Me{dollar}sb2{dollar} with the appropriate thiol. All display characteristic NMR resonances and bond distances expected for Ni-alkyl and Ni-thiolate compounds. The addition of one equivalent of CO to Ni(bpy)Me(S-2,6-{dollar}rm Csb6Hsb3Clsb2),{dollar} yields the acyl complex Ni(bpy)COMe(S-2,6-{dollar}rm Csb6Hsb3Clsb2).{dollar} Further addition of CO to Ni(bpy)COMe(S-2,6-{dollar}rm Csb6Hsb3Clsb2){dollar} or the addition of greater than 3 eq of CO to any Ni(bpy)Me(SR) compound induces reductive elimination of thioester, RSCOCH{dollar}sb3,{dollar} with concomitant formation of Ni(bpy)CO{dollar}sb2.{dollar} The in situ yields of these reactions imply that the Ni-mediated formation of thioester is an intramolecular process. This study demonstrates the biological precedence of the reaction sequence NiMe-SR + CO {dollar}to{dollar} NiCOMe {dollar}to{dollar} Ni + RSCOMe and viability for the species with the formulation Ni-acyl-thiolate. These experiments are relevant to the action of the nickel containing carbon monoxide dehydrogenases where several mechanistic details for an analogous thioester synthesis remain undefined.; Chapter 3 of this work explores the kinetics of the oxotransfer reactions between a congener pair of molybdenum and tungsten complexes and various phosphine substrates for insight into the reactivity differences between these two metals. Rate constants for the reaction (MO{dollar}rmsb2(mnt)sb2rbracksp{lcub}2-{rcub}+Rsb3Ptolbrack MO(mnt)sb2rbracksp{lcub}2-{rcub}+Rsb3PO{dollar} were measured at several temperatures using the phosphines (MeO){dollar}sb3{dollar}P and (MeO){dollar}sb2{dollar}PhP. From these data activation parameters have been calculated. A reaction profile, based on the recent work of Pietsch and Hall, is proposed for the oxygen atom transfer reactions. The reducibility of the metal and strength of the M-O appear to be two factors that contribute to the rate differences between Mo and W in these reactions. These results of this study are noted in the context of molybdenum and tungsten biochemistry.