Mechanistic Investigations of an α-Aminoarylation Photoredox Reaction
Mechanistic Investigations of an α-Aminoarylation Photoredox Reaction
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DOI：
10.1021/jacs.1c03693
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发表时间：
2021-06-02
影响因子：
15
通讯作者：
Swierk, John R.
中科院分区：
文献类型：
--
作者：
Stevenson, Bernard G.;Spielvogel, Ethan H.;Swierk, John R.
虽然光氧化还原催化继续改变现代合成化学，但涉及直接观察反应中间体和速率常数的详细机理研究很少。通过使用稳态光化学测量，瞬态激光光谱和电化学方法的组合，α-氨基芳基化机制，这是大量的光氧化还原反应的灵感进行了严格的表征。尽管产物产率高，但反应的外量子产率（QY）仍然低（15-30%）。通过使用瞬态吸收光谱，生产性和非生产性的反应途径进行了鉴定和速率常数指定开发一个全面的反应机理图片。氰基芳烃，1，4-二氰基苯，的作用被发现是出乎意料的复杂，功能作为初始质子受体在反应中，并作为中性稳定剂的1，4-二氰基苯自由基阴离子。最后，动力学建模被用来分析在一个前所未有的理解水平的反应。该建模表明，反应不受单个步骤的动力学的限制，而是受光化学惰性供体-受体复合物的散射损失和寄生吸收的限制。
While photoredox catalysis continues to transform modern synthetic chemistry, detailed mechanistic studies involving direct observation of reaction intermediates and rate constants are rare. By use of a combination of steady state photochemical measurements, transient laser spectroscopy, and electrochemical methods, an alpha-aminoarylation mechanism that is the inspiration for a large number of photoredox reactions was rigorously characterized. Despite high product yields, the external quantum yield (QY) of the reaction remained low (15-30%). By use of transient absorption spectroscopy, productive and unproductive reaction pathways were identified and rate constants assigned to develop a comprehensive mechanistic picture of the reaction. The role of the cyanoarene, 1,4-dicyanobenzne, was found to be unexpectedly complex, functioning both as initial proton acceptor in the reaction and as a neutral stabilizer for the 1,4-dicyanobenzene radical anion. Finally, kinetic modeling was utilized to analyze the reaction at an unprecedented level of understanding. This modeling demonstrated that the reaction is limited not by the kinetics of the individual steps but instead by scattering losses and parasitic absorption by a photochemically inactive donor-acceptor complex.