Epoxidation of olefins with hydrogen peroxide catalyzed by polyoxometalates

Epoxides are an important class of industrial chemicals that have been used as chemical intermediates. Catalytic epoxidation of olefins affords an interesting technology for their production. This review summarizes recent developments for the epoxidation of olefins with hydrogen peroxide catalyzed by polyoxometalates. The versatility, accessibility, and tunability of polyoxometalates open up the development of effective epoxidation systems. Polyoxometalates for H2O2-based epoxidation can be classified into two groups according to the structural and mechanistic aspects: (i) catalyst precursors of peroxotungstate or peroxomolybdate species and (ii) oxidatively and hydrolytically stable transition-metal-substituted polyoxometalates. In addition, we describe our recent studies on the silicotungstate compound, [gamma-SiW10O34(H2O)2](4-) (I*) synthesized by protonation of divacant lacunary Keggin-type [gamma-SiW10O36](8-). The tetra-n-butylammonium salt derivative of I* (TBAT) exhibits high catalytic activity in the epoxidation of various olefins including non-reactive terminal olefins such as propylene with hydrogen peroxide under mild conditions. (c) 2004 Elsevier B.V. All rights reserved.