Theoretical Studies of Lewis Acid-activated Oxidation of Hydrocarbons by Oxo and Peroxo Species of Ruthenium, Chromium, Vanadium and Osmium

The selective C-H bond activation of hydrocarbons is a key step in the oxidation of petroleum to useful organic chemicals. The search for highly efficient and selective oxidation catalysts that would save energy and raw materials and reduce polluting wastes remains a challenging task for chemists. There have been numerous studies on using metal oxo species for alkane/alkene oxidations and we have been interested in making use of Lewis acids to activate stable metal-oxo species as oxidants. In this project, we propose to study theoretical aspects of the activation of oxo and peroxo species of ruthenium, chromium, vanadium and osmium by Lewis acids towards the oxidation of alkanes, alkenes and arenes using density functional theory and polarization continuum model. Ruthenium forms an extensive series of oxo complexes from +VIII to +IV. It would be interesting to compare the activation of these oxo species by Lewis acids. Chromium oxo species have been used as an oxidant in organic chemistry for decades; an understanding of the activation of these species is of fundamental interest. In particular, a study of the methane oxidation by dichromate may provide insight on the oxidation mechanism of methane monooxygenase, which is believed to make use of an analogous diiron(IV)m-oxo species to oxidize methane. Vanadium forms various oxo and peroxo species. Our preliminary studies show that these species may be activated by Lewis acids to oxidize hydrocarbons. Relevant DFT calculations would provide information on whether the Lewis acid binds to an oxo or peroxo ligand.We plan to explore the potential energy surfaces, determine the activation barriers, and elucidate the reaction mechanisms for the alkanes/alkenes/arenes oxidation by Lewis acid?activated metal oxo/peroxo species. We are also interested in studying the steric and electronic effects of the Lewis acid on the reactivity of metal oxo/peroxo species. The Lewis acid catalyzes the oxidation by enhancing the ability of metal oxo/peroxo species to accept electrons from hydrocarbons. We propose to study the correlation of the barrier heights of oxidation with the energy of molecular orbital responsible for accepting electrons. We will examine the dynamic changes of electron density en route from reactants to transition state structure to products. Our proposed studies should contribute to the understanding of the interaction of Lewis acids with oxo/peroxo species of ruthenium, chromium, vanadium and osmium at molecular level and the role of Lewis acid on the catalytic activity of these complexes.