Highly efficient and selective epoxidation of alkenes by photochemical oxygenation sensitized by a ruthenium(II) porphyrin with water as both electron and oxygen donor
Highly efficient and selective epoxidation of alkenes by photochemical oxygenation sensitized by a ruthenium(II) porphyrin with water as both electron and oxygen donor
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DOI：
10.1021/ja0295218
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发表时间：
2003-05-14
影响因子：
15
通讯作者：
Inoue, H
中科院分区：
文献类型：
--
作者：
Funyu, S;Isobe, T;Inoue, H
羰基配位四元反应混合物的可见光照射在碱性乙腈水溶液中，以（2，4，6-三甲基）苯基卟啉合钌（II）（（RuTMP）-T-II（CO））作为光敏剂，六氯铂酸盐（IV）作为电子受体，诱导烯烃的选择性环氧化，具有高量子产率（Phi = 0.6，对于环己烯的选择性= 94.4%和Phi = 0.4，对于异戊烯的选择性= 99.7%）。通过（H2O）-O-18的实验证实环氧化物的氧原子来自水分子。顺式二苯乙烯被转化成其环氧化物，顺式氧化二苯乙烯，而不形成反式氧化二苯乙烯。然而，反式二苯乙烯没有表现出任何反应性。在中性条件下，（RuTMP）-T-II（CO）的阳离子自由基在光反应的早期就能有效地积累，而氢氧化物离子的加入则使其与阳离子自由基迅速反应，促进反应，并使反应回复到起始产物（RuTMP）-T-II（CO）。通过使用（RuTMP）-T-VI（O）（2）的实验排除了Ru的较高氧化态如Ru-IV、Ru-V、Ru-VI通过Ru-III物质的歧化的可能参与。Ru络合物的脱羰基作用也被证明是无效的。反应机理包括电子从三重激发态的（RuTMP）-T-II（CO）转移到六氯铂酸盐（IV）和随后形成OH-配位的Ru-III物种，导致氧合钌络合物作为光化学环氧化的关键中间体，被假定。
Visible light irradiation of a reaction mixture of carbonyl-coordinated tetra(2,4,6-trimethyl)phenylporphyrinatoruthenium(II) ((RuTMP)-T-II(CO)) as a photosensitizer, hexachloroplatinate(IV) as an electron acceptor, and an alkene in alkaline aqueous acetonitrile induces selective epoxidation of the alkene with high quantum yield (Phi = 0.6, selectivity = 94.4% for cyclohexene and Phi = 0.4, selectivity = 99.7% for norbornene) under degassed conditions. The oxygen atom of the epoxide was confirmed to come from a water molecule by an experiment with (H2O)-O-18. cis-Stilbene was converted into its epoxide, cis-stilbeneoxide, without forming trans-stilbeneoxide. trans-Stilbene, however, did not exhibit any reactivity. Under neutral conditions, an efficient buildup of the cation radical of (RuTMP)-T-II(CO) was observed at the early stage of the photoreaction, while an addition of hydroxide ion caused a rapid reaction with the cation radical to promote the reaction with reversion to the starting (RuTMP)-T-II(CO). A possible involvement of a higher oxidized state of Ru such as Ru-IV, Ru-V, Ru-VI through a dismutation of the Ru-III species was excluded by an experiment with (RuTMP)-T-VI(O)(2). Decarbonylation of the Ru complex was also proven to be invalid. A reaction mechanism involving an electron transfer from the excited triplet state of (RuTMP)-T-II(CO) to hexachloroplatinate(IV) and subsequent formation of OH--coordinated Ru-III species, leading to an oxo-ruthenium complex as the key intermediate of the photochemical epoxidation, was postulated.