Aerobic oxidations catalyzed by colloidal nanogold

Recently, dispersions of gold nanoclusters in liquid media (colloidal nanogold) have been extensively used as quasi-homogeneous catalysts for various aerobic oxidation reactions. This review describes recent progress in such reactions, with a focus on our comprehensive studies on gold clusters (<2 nm) stabilized by poly(N-vinyl-2-pyrrolidone) and their participation in oxidation reactions of alcohols, α-hydroxylation reactions of benzylic ketones, and homocoupling reactions of organoboronates, as well as formal Lewis acidic reactions, such as intramolecular hydroalkoxylation and hydroamination reactions of nonactivated alkenes. Mechanistic studies have shown that a partial electron transfer from the gold clusters to O(2) generates superoxide- or peroxide-like species and Lewis acidic centers, both of which play essential roles in the catalytic reactions.