Over-Oxidation as the Key Step in the Mechanism of the MoCl5-Mediated Dehydrogenative Coupling of Arenes.
Over-Oxidation as the Key Step in the Mechanism of the MoCl5-Mediated Dehydrogenative Coupling of Arenes.
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DOI：
10.1002/anie.201508035
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发表时间：
2016-01
影响因子：
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通讯作者：
M. Schubert;P. Franzmann;Anica Wünsche von Leupoldt;K. Koszinowski;K. Heinze;S. Waldvogel
中科院分区：
文献类型：
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作者：
M. Schubert;P. Franzmann;Anica Wünsche von Leupoldt;K. Koszinowski;K. Heinze;S. Waldvogel
五氯化钼是芳烃脱氢偶联的强力试剂。由于MoCl5的高反应速率，一些不稳定的部分在这种转化中是耐受的。尽管最近发现了单电子转移作为初始步骤的迹象，但对反应的机理过程的讨论仍有争议。在此，基于综合研究、电化学测量、EPR光谱、DFT计算和质谱分析，我们推断出一个高度一致的机制场景：MoCl5在没有TiCl4的情况下作为单电子氧化剂，在有TiCl4的情况下作为双电子氧化剂，但在两种情况下都会导致过度氧化的中间体，从而保护其免受副反应的影响。在水处理过程中，试剂废物（Mo（III/IV）种）作为还原剂产生所需的有机C-C偶联产物。
Molybdenum pentachloride is an unusually powerful reagent for the dehydrogenative coupling of arenes. Owing to the high reaction rate using MoCl5, several labile moieties are tolerated in this transformation. The mechanistic course of the reaction was controversially discussed although indications for a single electron transfer as the initial step were found recently. Herein, based on a combined study including synthetic investigations, electrochemical measurements, EPR spectroscopy, DFT calculations, and mass spectrometry, we deduct a highly consistent mechanistic scenario: MoCl5 acts as a one-electron oxidant in the absence of TiCl4 and as two-electron oxidant in the presence of TiCl4, but leads to an over-oxidized intermediate in both cases, which protects it from side reactions. In the course of aqueous work-up the reagent waste (Mo(III/IV) species) acts as reducing agent generating the desired organic C-C coupling product.