Homogeneous epoxidation polyoxometallates

Polyoxometalates have been used as homogenous catalysts for a wide variety of thermal organic substrate oxidations37. This involves the epoxidation of relatively electron poor terminal olefins by H2O2 and heteropoly acids, principally H3[PWi2C>4o], using PTC (equation 9). 

The vast majority of homogeneous catalysts are transition metal complexes and many systems have been reported, for example, Ru(III) [129], W(VI) [130], polyoxometallates [131], Re(V) [132], Fe(III) [133], and Pt(II) [134] with hydrogen peroxide, Mn(II) [135-137] with peracetic acid, and Ti-tartrate with alkyl hydroperoxides [75]. The subject of epoxidation by H2O2 has been reviewed [138-140]. 

Khenkin, A. and HiU, C. (1993). Selective Homogeneous Catalytic Epoxidation of AUcenes by Hydrogen Peroxide Catalysed by Oxidatively- and Solvolytically-Resistant Polyoxometalate Complexes, Mendeleev Commun., 3, pp. 140-141. 

Abstract The catalytic oxidation is an area of the key technologies for converting petroleum-based feedstocks to useful chemicals such as diols, epoxides, alcohols, and carbonyl compounds. Many efficient homogeneous and heterogeneous oxidation systems based on polyoxometalates (POMs) with green oxidants such as H2O2 and O2 have been developed. This chapter summarizes the remarkable oxidation catalyses by POMs with multimetallic active sites. The multifunctionality of multimetallic active sites in POMs such as cooperative activation of oxidants, simultaneous activation of oxidants and substrates, stabilization of reaction intermediates, and multielectron transfer leads to their remarkable activities and selec-tivities in comparison with the conventional monometallic complexes. Finally, the future opportunities for the development of shape- and stereoselective oxidation by POM-based catalysts are described. 

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