Lewis Acid-Activated Oxidation of Alkanes by Ruthenium, Chromium and Vanadium Oxo Species

The selective oxidation of alkanes is an important technology for the conversion of petroleum to useful organic chemicals. Existing technologies usually require high temperature and may not very selective. This project aims to generate highly reactive Lewis acid/metal oxo systems for oxidation of alkanes under mild conditions. The researchers have previously shown that certain metal oxo species that are normally unreactive, such as [Os(N)(O)3]-, can be activated by Lewis acids to become a very strong oxidant. The researchers have also developed a highly efficient catalytic system based on Lewis acid/[Os(N)Cl4]- that can oxidize alkanes at ambient conditions using peroxides as terminal oxidants. These results show that the use of a Lewis acid in combination with a metal oxo species (or a metal-oxo precursor) is a feasible strategy for the development of highly active catalytic systems for the oxidation of alkanes and other organic substrates using environmentally friendly oxidants such as H2O2. In this project, the researchers will focus on the activation of oxo complexes of ruthenium, chromium and manganese by Lewis acids. Ruthenium is much cheaper than osmium, and ruthenium oxo complexes are in general much more potent oxidants than the corresponding osmium oxo complexes, hence more active catalytic systems may be developed based on ruthenium oxo/Lewis acid. The researchers will attempt to oxidize methane using ruthenium oxo/Lewis acid systems in inert solvents. The activation of chromium oxo species by Lewis acids is of fundamental interest. The oxidation of alkanes, including methane, by dichromate/Lewis acid is of particular interest because the enzyme methane monooxygenase is believed to make use of a diiron(IV) μ-oxo species to oxidize methane and other alkanes. Vanadium is cheap, relatively less toxic and it forms very stable oxo complexes. If these oxo complexes can be activated by Lewis acids to oxidize organic substrates, then it may be possible to regenerate the oxo species by O2. The ruthenium and vanadium oxo species (and precursors) will also be adsorbed onto various materials such as silica, alumina and ionexchange resins. These materials could function both as a solid support to facilitate catalyst recycle and as a Lewis acid to activate the metal oxo species. This studies should provide a new approach for the selective catalytic oxidation of alkanes and other organic substrates under mild conditions.