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首页> 外文期刊>Chemistry: A European journal >Oxidation of Ethers, Alcohols, and Unfunctionalized Hydrocarbons by the Methyltrioxorhenium/H2O2 System: A Computational Study on Catalytic C-H Bond Activation
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Oxidation of Ethers, Alcohols, and Unfunctionalized Hydrocarbons by the Methyltrioxorhenium/H2O2 System: A Computational Study on Catalytic C-H Bond Activation

机译：甲基三氧杂hen / H2O2系统氧化醚，醇和未官能化烃的氧化：催化C-H键活化的计算研究

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The potential-energy surfaces (PESs) of methyltrioxorhenium (MTO)-catalyzed C-H insertion reactions in the presence of hydrogen peroxide were studied by accurate DFT methods for a series of substrates including unsaturated hydrocarbons, an ether, and an alcohol. Based on the comprehensive analysis of transition states and intrinsic reaction coordinate (IRC) scans, C-H insertion was found to proceed by a concerted mechanism that does not require, as previously thought, a side-on or a butterfly-like transition state. We found that a typical transition state follows requirements of the S(N)2 reaction instead. Furthermore, by exploring the PESs of several C-H insertion reactions, we discovered that no ionic intermediate is formed even in a polar solvent. The latter was modeled within the self-consistent reaction field approach in a polarizable continuum model (PB-SCRF/PCM). According to our study, C-H insertion occurs by a concerted but highly asynchronous mechanism that first proceeds by hydride transfer and then turns into hydroxide transfer/rebound. For the oxidation of alcohols, C-H bond cleavage occurs without formation of alkoxide intermediates on the dominant pathway. The computed deuterium kinetic isotope effect of 2.9 for the hydride-transfer transition state for alcohol oxidation is in good agreement with the experimental k(H)/k(D) ration of 3.2 reported by Zauche and Espenson. As confirmed by IRC and PES scans in different solvents, the OH-rebound phase of the C-H insertion pathway demonstrates strong similarities with the rebound mechanism that was previously proposed for cytochrome P450 and metalloporphyrin-catalyzed oxidations.
机译：通过精确的DFT方法，对包括不饱和烃，醚和醇在内的一系列底物进行了精确的DFT研究，研究了在过氧化氢存在下，甲基三氧-（MTO）催化的C-H插入反应的势能表面（PES）。基于对过渡态和本征反应坐标（IRC）扫描的全面分析，发现C-H插入是通过一种协同机制进行的，该机制不需要像以前所认为的那样从侧面或蝴蝶状转变。我们发现典型的过渡态反而遵循S（N）2反应的要求。此外，通过探索几种C-H插入反应的PES，我们发现即使在极性溶剂中也不会形成离子中间体。后者是在可极化连续体模型（PB-SCRF / PCM）的自洽反应场方法中建模的。根据我们的研究，C-H插入是通过一种协调但高度异步的机制发生的，该机制首先通过氢化物转移进行，然后转变为氢氧化物转移/反弹。对于醇的氧化，发生C-H键裂解而在主要途径上没有形成醇盐中间体。对于醇氧化的氢化物转移过渡态，计算得出的氘动力学同位素效应为2.9，与Zauche和Espenson报告的实验k（H）/ k（D）配比为3.2很好地吻合。正如在不同溶剂中进行的IRC和PES扫描所证实的那样，C-H插入途径的OH反弹相与以前针对细胞色素P450和金属卟啉催化的氧化所提出的反弹机理表现出强烈的相似性。

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