Electrochemical investigations of ruthenium-substituted heteropolytungstate anions : catalytic studies of an inorganic oxometalloporphyrin analog

Citation

Bart, John C. (1995) Electrochemical investigations of ruthenium-substituted heteropolytungstate anions : catalytic studies of an inorganic oxometalloporphyrin analog. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/wdkr-zr39. https://resolver.caltech.edu/CaltechETD:etd-09122007-081836

Abstract

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Ruthenium-substituted heteropolytungstate anions (Ru-HPAs), such as [...], are expected to be catalytically active for reactions such as the oxidation of alcohols. Since little is known about this compound, several studies were undertaken so as to better understand its chemical and electrochemical properties.

Ligand exchange of nitrogen bases like pyridine for the water molecule bound to the ruthenium center confirmed an earlier report that the polyoxotungstate cage acts as a weak [...]-electron acceptor. When this action is taken into account, the physical properties of the ruthenium-nitrogen base complexes and the rate constants for their formation are comparable to other [...] species such as [...].

Electron transfer studies between [...] and [...] are complicated by the fact that the cage species does not act as a point charge, and thus rate constant calculations based on simple ionic strength equations are not accurate. Switching the oxidant to a neutral compound like dioxygen greatly simplifies the reaction conditions, so that the Marcus equation for outer sphere electron transfer can be used to precisely predict the electron transfer rate constant.

Rate constants for the catalytic oxidation of various alcohols by [...] have been measured. The magnitude of these rate constants was much smaller than initial expectations, but not unusually so compared to other oxoruthenium (V) catalysts which have been described in the literature since this project began. Work in which Ru-HPA was used to catalyze the oxidation of non-alcoholic substrates is also discussed. Lessons learned from this project are analyzed in the context of general catalysis of oxidation reactions and thoughts on the next generation of catalysts are presented.

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