Kamata Keigo, Kuzuya Shinjiro, Uehara Kazuhiro, Yamaguchi Syuhei, Mizuno Noritaka
Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Inorg Chem. 2007 Apr 30;46(9):3768-74. doi: 10.1021/ic0701211. Epub 2007 Mar 22.
The reaction of the dinuclear peroxotungstate, [(n-C4H9)4N]2[{WO(O2)2}2(mu-O)] (II), with H2O2 gives the novel mu-eta1:eta1-peroxo-bridging dinuclear tungsten species, [(n-C4H9)4N]2[{WO(O2)2}2(mu-O2)] (I), which has been characterized by X-ray crystallography, elemental analysis, IR, Raman, UV-vis, and 183W NMR. Only I is active for the epoxidation of cyclic, internal, and terminal olefins, whereas II is inactive for each. The low XSO (XSO=(nucleophilic oxidation)/(total oxidation)) value of I (0.18+/-0.02) in comparison with that of II (0.39+/-0.01) for the stoichiometric oxidation of thianthrene 5-oxide, which is a mechanistic probe for determining the electronic character of an oxidant, reveals that I is more electrophilic than II. On the basis of the kinetic and spectroscopic results, the catalytic epoxidation proceeds by the reaction of I with an olefin to form II and the corresponding epoxide followed by the regeneration of I by the reaction of II with H2O2.
双核过氧钨酸盐[(n-C4H9)4N]2[{WO(O2)2}2(μ-O)] (II) 与H2O2反应生成新型的μ-η1:η1-过氧桥连双核钨物种[(n-C4H9)4N]2[{WO(O2)2}2(μ-O2)] (I)，该物种已通过X射线晶体学、元素分析、红外光谱、拉曼光谱、紫外可见光谱和183W核磁共振进行了表征。只有I对环状、内烯烃和末端烯烃的环氧化反应具有活性，而II对每种烯烃的环氧化反应均无活性。对于作为确定氧化剂电子性质的机理探针的噻蒽5-氧化物的化学计量氧化反应，I的低XSO（XSO =（亲核氧化）/（总氧化））值（0.18±0.02）与II的值（0.39±0.01）相比，表明I比II更具亲电性。基于动力学和光谱结果，催化环氧化反应通过I与烯烃反应形成II和相应的环氧化物，然后II与H2O2反应使I再生来进行。
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