Theoretical Study of Photoinduced Epoxidation of Olefins Catalyzed by Ruthenium Porphyrin
Theoretical Study of Photoinduced Epoxidation of Olefins Catalyzed by Ruthenium Porphyrin
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DOI：
10.1021/jp200650q
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发表时间：
2011-05-12
影响因子：
2.9
通讯作者：
Sakaki, Shigeyoshi
中科院分区：
文献类型：
--
作者：
Ishikawa, Atsushi;Sakaki, Shigeyoshi
【摘要】：[Ru(TMP)(CO)(O)](-)(TMP=四均甲苯)对烯烃的环氧化反应是[Ru(TMP)(CO)]光催化烯烃环氧化反应的关键步骤,主要采用密度泛函理论(DFT)方法,以[Ru(Por)(CO)]为模型配合物(Por=未取代的卟啉)进行研究。 CASSCF 方法还用于研究催化循环中重要物质的电子结构。在参与催化循环的所有钌卟啉物种中，CASSCF波函数的主构型权重均大于85%，表明静态相关性不是很大。此外，此处无限制 DFT 计算的自然轨道与 CASSCF 计算的自然轨道基本相同。基于这些结果，我们在这项工作中采用了 DFT 方法。目前的计算结果显示了该反应的特征如下：（i）环氧化反应通过碳自由基型过渡态发生。在过渡态中既没有观察到碳正离子型特征，也没有观察到协同氧烯插入型特征。 (ii)在C-O键形成步骤中，电子和自旋群体从烯烃部分转移到卟啉环。 (iii) 烯烃和卟啉部分的电子和自旋种群在过渡态附近发生显着变化。 (iv) Ru的原子和自旋布居在反应中变化很小，表明Ru中心在整个催化循环中保持+II氧化态。 (v)烯烃加合物[Ru(Por)(CO)(O)(烯烃)](-)的稳定性很大程度上取决于烯烃的种类，例如乙烯、正己烯和苯乙烯。特别地，苯乙烯形成稳定的烯烃加合物。并且，(vi)有趣的是，这些烯烃之间的活化势垒在定量水平上的差异很小（在5 kcal/mol以内），这表明该催化剂可以应用于各种基材。这是因为烯烃加合物和过渡态的稳定性和电子结构类似地受到烯烃取代基的影响。
Epoxidation of olefin by [Ru(TMP)(CO)(O)](-) (TMP = tetramesitylporphine), which is a key step of photocatalyzed epoxidation of olefin by [Ru(TMP)(CO)], is studied mainly with the density functional theory (DFT) method, where [Ru(Por)(CO)] is employed as a model complex (Por = unsubstituted porphyrin). The CASSCF method was also used to investigate the electronic structure of important species in the catalytic cycle. In all of the ruthenium porphyrin species involved in the catalytic cycle, the weight of the main configuration of the CASSCF wave function is larger than 85%, suggesting that the static correlation is not very large. Also, unrestricted-DFT-calculated natural orbitals are essentially the same as CASSCF-calculated ones, here. On the basis of these results, we employed the DFT method in this work. Present computational results show characteristic features of this reaction, as follows: (i) The epoxidation reaction occurs via carboradical-type transition state. Neither carbocation-type nor concerted oxene-insertion-type character is observed in the transition state. (ii) Electron and spin populations transfer from the olefin moiety to the porphyrin ring in the step of the C-O bond formation. (iii) Electron and spin populations of the olefin and porphyrin moieties considerably change around the transition state. (iv) The atomic and spin populations of Ru change little in the reaction, indicating that the Ru center keeps the +II oxidation state in the whole catalytic cycle. (v) The stability of the olefin adduct [Ru(Por)(CO)(O)(olefin)](-) considerably depends on the kind of olefin, such as ethylene, n-hexene, and styrene. In particular, styrene forms a stable olefin adduct. And, (vi) interestingly, the difference in the activation barrier among these olefins is small in the quantitative level (within 5 kcal/mol), indicating that this catalyst can be applied to various substrates. This is because the stabilities and electronic structures of both the olefin adduct and the transition state are similarly influenced by the substituent of olefin.