We have developed a novel polyoxometalate catalyst ([?-H2SiV2W10O40]4?, denoted as I) with the multi-nuclear active site of V-(?-OH)2-V that can act as an efficient homogeneous catalyst for the epoxidation of various terminal olefins with only one equiv. of hydrogen peroxide (?87% yield, ?99% selectivity). Further, polyoxometalate I showed high stereospecificity, diastereoselectivity, regioselectivity. The 51V NMR, 183W NMR, and CSI-MS spectroscopy show that the reaction of I with hydrogen peroxide leads to the reversible formation of a hydroperoxo species [?-HSiV2W10O39(OOH)]4? (II). The successive dehydration of II forms III, which possibly has an active oxygen species of a ??-?2:?2-peroxo group ([?-SiV2W10O38(O2)]4?). Furthermore, we synthesized the organic-inorganic hybrid support by covalently anchoring N-octyldihydroimidazolium cation fragment onto SiO2 and I could be immobilized onto the support with the strong anion-cation interaction. The supported catalyst also showed high stereospecificity, diastereoselectivity, regioselectivity, and the high efficiency of hydrogen peroxide utilization for the oxidation of various olefins without the loss of the intrinsic catalytic nature of the corresponding homogeneous analogue of I. The observed catalysis was truly heterogeneous and the catalyst was reusable without the loss of the high catalytic performance.
Polyoxometalate, Epoxidation, Olefins, Hydrogen Peroxide, Vanadium