Oxo and Imido Complexes of Rhenium and Molybdenum in Catalytic Reductions

High oxidation state transition metal oxo and imido complexes are ubiquitous in catalytic oxidations and oxygen atom transfer reactions. Recently these complexes, particularly those of rhenium and molybdenum, have been shown to catalyze reductions of organic compounds bearing C=O, C=N, C=C, and C≡C functional groups. High oxidation state catalysts are convenient because they are often air and moisture stable; they also provide a new paradigm for transition element chemistry that is attractive for in-depth mechanistic investigation. In this review, we summarize the latest development in the field with emphasis on the current understanding of the operative hydrosilylation mechanisms for oxo and imido catalysts.