Olefin epoxidation with hydrogen peroxide catalyzed by lacunary polyoxometalate [γ-SiW10O34(H2O)2]4-
Olefin epoxidation with hydrogen peroxide catalyzed by lacunary polyoxometalate [γ-SiW10O34(H2O)2]4-
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DOI：
10.1002/chem.200600384
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发表时间：
2007-01-01
影响因子：
4.3
通讯作者：
Mizuno, Noritaka
中科院分区：
文献类型：
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作者：
Kamata, Keigo;Kotani, Mirki;Mizuno, Noritaka
四正丁基铵盐[TBA](4)[γ-SiW10O34-(H2O)(2)](1)催化烯烃、烯丙醇和硫化物与30%过氧化氢的氧转移反应。对取代苯乙烯竞争氧化反应的负Hammett Rho(+)(-0.99)和I催化氧化5-硫杂菲(SSO)的低(亲核氧化)/(总氧化)值X-SO=0.04表明，在I上形成了强亲电的氧化剂物种。3-甲基-1-环己烯环氧化反应中反式环氧化物的优先生成表明I的活性中心受到空间位阻的限制。I催化的环氧化反应具有诱导期，而I用过氧化氢处理后诱导期消失。Si-29和W-183核磁共振谱和CSI质谱图表明，I与过量的过氧化氢反应可快速生成二过氧物种[TBA](4)[Gamma-SiW10O32(O-2)(2)](11)，并保留了Gamma-Keggin结构。虽然分离的化合物11对环辛烯的化学计量环氧化没有活性，但11在过氧化氢存在下进行环氧化。11与过氧化氢反应生成活性物种(111)，该步骤与催化环氧化反应的诱导期相对应。动力学、光谱和机理研究表明，催化环氧化反应是通过Ⅲ进行的。
ne tetra-n-butylammonium (TBA) salt of the divacant Keggin-type polyoxometalate [TBA](4)[gamma-SiW10O34-(H2O)(2)] (1) catalyzes the oxygen-transfer reactions of olefins, allylic alcohols, and sulfides with 30% aqueous hydrogen peroxide. The negative Hammett rho(+) (-0.99) for the competitive oxidation of p-substituted styrenes and the low value of (nucleophilic oxidation)/(total oxidation), X-SO = 0.04, for I-catalyzed oxidation of thianthrene 5-oxide (SSO) reveals that a strongly electrophilic oxidant species is formed on I. The preferential formation of trans-epoxide during epoxidation of 3-methyl-1-cyclohexene demonstrates the steric constraints of the active site of I. The I-catalyzed epoxidation proceeds with an induction period that disappears upon treatment of I with hydrogen peroxide. Si-29 and W-183 NMR spectroscopy and CSI mass spectrometry show that reaction of I with excess hydrogen peroxide leads to fast formation of a diperoxo species, [TBA](4)[gamma-SiW10O32(O-2)(2)] (11), with retention of a gamma-Keggin type structure. Whereas the isolated compound 11 is inactive for stoichiometric epoxidation of cyclooctene, epoxidation with 11 does proceed in the presence of hydrogen peroxide. The reaction of 11 with hydrogen peroxide would form a reactive species (111), and this step corresponds to the induction period observed in the catalytic epoxidation. The steric and electronic characters of III are the same as those for the catalytic epoxidation by I. Kinetic, spectroscopic, and mechanistic investigations show that the present epoxidation proceeds via III.