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Hydrogenase enzyme reactivity modeling with transition-metal hydride and dihydrogen complexes
Abstract
This dissertation is an investigation into hydride transfer reactions of metal hydrides with the intent of developing catalytic systems utilizing dihydrogen and demonstrating reactivity patterns that mimic those of hydrogenase enzymes. Stoichiometric hydride transfer reactions between Cp*(dppm)RuH (1-H) and Cp*(dppf)RuH (2-H) and NADH model compounds, trityl cation and one-electron substrates has been investigated. The mode of reaction of 1-H has been demonstrated to be single-step hydride transfer for the reduction of NADH model compounds while 2-H has demonstrated one-electron reducing capabilities. Both hydrides coordinate dihydrogen at ambient conditions and function competantly as catalysts for the reduction of NADH models, trityl cation and ferrocinium cation utilizing dihydrogen as the terminal reductant. Product isotope reactions have been measured for both hydride transfer to and from 1-H with NADH model compounds. A novel dinitrogen complex (Cp*Ru(dppm)(N$\sb2)$) PF$\sb6\{$(N$\sb2)$) PF$\sb6\}$ has been isolated and demonstrated to be a useful synthon in the formation of analogous compounds with ligands such as CO, H$\sb2$O, ethylene, THF and acetonitrile. Isotope exchange between D$\sb2$ and water or alcohols has been observed, catalyzed by either 1(N$\sb2$)) PF$\sb6$ or 1-H. A method for bracketing transition metal hydride affinity has been developed and demonstrated with the reactions of 1-H with (BNAH) PF$\sb6$ and (MAH) PF$\sb6,$ in which the relative hydride affinity of 1-H has been ascertained. Other investigations into the nature of hydride transfer have dealt with the effect of ligands on the hydridicity of various metal hydrides and the role of ligand coordination to the resulting metal cation. The heterobimetallic hydride 2-H demonstrates catalytic one-electron reductions of trityl, (MAH) PF$\sb6$ and methyl viologen with hydrogen at ambient conditions. One- and two-electron oxidations of 2-H show rare reversible behavior. Mechanistic studies involving electron and atom transfers have been performed on 2-H as well as the isolable radical cation hydride (2-H) PF$\sb6$ which optical spectral analysis has indicated to be the first weakly delocalized mixed-valent metal hydride isolated.
Subject Area
Chemistry|Organic chemistry|Biochemistry
Recommended Citation
McQueen, James Scott, "Hydrogenase enzyme reactivity modeling with transition-metal hydride and dihydrogen complexes" (1995). ETD collection for University of Nebraska-Lincoln. AAI9611060.
https://digitalcommons.unl.edu/dissertations/AAI9611060