Premium
Efficient Epoxidation of Electron‐Deficient Alkenes with Hydrogen Peroxide Catalyzed by [γ‐PW 10 O 38 V 2 (μ‐OH) 2 ] 3−
Author(s) -
Kamata Keigo,
Sugahara Kosei,
Yonehara Kazuhiro,
Ishimoto Ryo,
Mizuno Noritaka
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201101001
Subject(s) - chemistry , catalysis , allylic rearrangement , acrylonitrile , epoxide , alkene , medicinal chemistry , hydrogen peroxide , ether , polymer chemistry , organic chemistry , copolymer , polymer
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.