Efficient epoxidation of electron-deficient alkenes with hydrogen peroxide catalyzed by [γ-PW10O38V2(μ-OH)2]3-

Keigo Kamata; Kosei Sugahara; Kazuhiro Yonehara; Ryo Ishimoto; Noritaka Mizuno

doi:10.1002/chem.201101001

Efficient epoxidation of electron-deficient alkenes with hydrogen peroxide catalyzed by [γ-PW10O38V2(μ-OH)2]3-

Chemistry. 2011 Jun 27;17(27):7549-59. doi: 10.1002/chem.201101001. Epub 2011 Jun 6.

Authors

Keigo Kamata¹, Kosei Sugahara, Kazuhiro Yonehara, Ryo Ishimoto, Noritaka Mizuno

Affiliation

¹ Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.

PMID: 21647994
DOI: 10.1002/chem.201101001

Abstract

A divanadium-substituted phosphotungstate, [γ-PW(10)O(38)V(2)(μ-OH)(2)](3-) (I), showed the highest catalytic activity for the H(2)O(2)-based epoxidation of allyl acetate among vanadium and tungsten complexes with a turnover number of 210. In the presence of I, various kinds of electron-deficient alkenes with acetate, ether, carbonyl, and chloro groups at the allylic positions could chemoselectively be oxidized to the corresponding epoxides in high yields with only an equimolar amount of H(2)O(2) with respect to the substrates. Even acrylonitrile and methacrylonitrile could be epoxidized without formation of the corresponding amides. In addition, I could rapidly (≤10 min) catalyze epoxidation of various kinds of terminal, internal, and cyclic alkenes with H(2)O(2) under the stoichiometric conditions. The mechanistic, spectroscopic, and kinetic studies showed that the I-catalyzed epoxidation consists of the following three steps: 1) The reaction of I with H(2)O(2) leads to reversible formation of a hydroperoxo species [γ-PW(10)O(38)V(2)(μ-OH)(μ-OOH)](3-) (II), 2) the successive dehydration of II forms an active oxygen species with a peroxo group [γ-PW(10)O(38)V(2)(μ-η(2):η(2)-O(2))](3-) (III), and 3) III reacts with alkene to form the corresponding epoxide. The kinetic studies showed that the present epoxidation proceeds via III. Catalytic activities of divanadium-substituted polyoxotungstates for epoxidation with H(2)O(2) were dependent on the different kinds of the heteroatoms (i.e., Si or P) in the catalyst and I was more active than [γ-SiW(10)O(38)V(2)(μ-OH)(2)](4-). On the basis of the kinetic, spectroscopic, and computational results, including those of [γ-SiW(10)O(38)V(2)(μ-OH)(2)](4-), the acidity of the hydroperoxo species in II would play an important role in the dehydration reactivity (i.e., k(3)). The largest k(3) value of I leads to a significant increase in the catalytic activity of I under the more concentrated conditions.