Development of Epoxidation of Alkenes with Molecular Oxygen Catalyzed by Metal-substituted Polyoxometalates

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(1) Lacunary POM as an efficient epoxidation catalyst with hydrogen peroxide.The lacunary Keggin-type silicodecatungstate has been used as a catalyst precursor for epoxidation of olefins with H_2O_2 at 305 K. The catalytic epoxidation proceeded with【greater than or equal】 99% selectivity to epoxide, 【greater than or equal】99% efficiency of H_2O_2 utilization, high stereospecificity, and the easy recovery of the catalyst.(2) Bis (μ-oxo) bridged di-Iron site on the lacunary POM as an efficient epoxidation catalyst with molecular oxygen.Bis (オ-oxo) bridged di-iron site on the lacunary POM has been used as catalysts for the oxygenation of alkenes in homogeneous reaction media using molecular oxygen as an oxygen donor. It is remarkable that selectivity to cyclooctene oxide and turnover number reached up to 98% and 10000, respectively, for the oxygenation of cyclooctene. Not only cyclooctene but also cyclododecene, 1-octene, 2-octene, 2-heptene and 2-hexene were catalytically oxygenated with high turnover numbers and high selectivity to the corresponding epoxides.(3) Microstructured POMs as a shape-selective catalyst.Keggin-type polyoxometalate, SiW_<12>O_<40>^<4->, and Cr(III) trinuclear cation, Cr_3O(OOOCH)_6(H_2O)_3^+, assembled in the presence of K^+ to create a channeled complex K_3[Cr_3O(OOCH)_6(H_2O)_3]SiW_<12>O_<40>・16H_2O with an opening of 0.5 x 0.8 nm. The complex reversibly absorbs water and polar organic molecules smaller than C2. The guest inclusion was highly selective and even a difference of one methylene group in the organic guest molecule was discriminated. Polar organic molecules with longer methylene chain and non-polar molecules were completely excluded. The distinctive guest inclusion was successfully applied to the oxidation of methanol from a mixture of alcohols.