Reversing the Role of the Metal−Oxygen π-Bond. Chemoselective Catalytic Reductions with a Rhenium(V)-Dioxo Complex

The metal-oxygen bond plays a critical role in some of the most important biological and synthetic reactions. However, the majority of these processes result in the oxidation of the target organic substrate; applications of this class of metal complexes to other organic transformations are extremely rare. In this paper, we report a new type of catalytic process in which complexes with metal-oxygen multiple bonds are used as reductants rather than oxidants. The overall reaction provides a highly chemoselective reduction/protection of carbonyl groups. In addition to providing a new way of catalyzing organic reactions, these catalysts can be used in the presence of a wide range of other functional groups such as amino, cyano, nitro, aryl halo, ester, and alkene; unlike many of their late metal relatives, they are inexpensive as well as air and moisture tolerant.