Halder Supriya, Mandal Sourav, Kundu Abhishek, Mandal Baishanal, Adhikari Debashis
Department of Chemical Sciences, Indian Institute of Science Education and Research Mohali, SAS Nagar 140306, India.
J Am Chem Soc. 2023 Oct 18;145(41):22403-22412. doi: 10.1021/jacs.3c05787. Epub 2023 Oct 3.
Herein we describe the anion of benzo[]phenothiazine as a super reductant species upon excitation by visible light. In contrary to N-substituted phenothiazines or benzophenothiazines, this molecule holds extreme reducing power to promote single electron transfer-based reductive cleavage at a potential of -3.51 V vs SCE. As a proof, a plethora of aryl chloride substrates have been reductively cleaved to fabricate molecules of the class isoindolinone and oxindole. Moreover, an aryl-chloride bond has been homolytically cleaved to generate aryl radicals that have been utilized for C-C cross-coupling or C-P bond formation reactions. To prove its extreme reducing ability, some of the aryl fluoride bonds have been cleaved to generate aryl radicals. A detailed photophysical study including steady-state and time-resolved spectroscopic techniques explain the molecule's behavior upon light excitation, and that correlates with its reactivity pattern. Theoretical calculations disclose the benzophenothiazine anion to be slightly puckered at the ground state as the molecule is antiaromatic in nature. In contrast, the excited-state geometry is planar, which is also close to that of the intermediate after one electron transfer. Abating the antiaromaticity of the anionic species is partially responsible for its highly reducing behavior.
在此，我们描述了苯并[]吩噻嗪阴离子在可见光激发下作为一种超强还原剂。与N-取代吩噻嗪或二苯并吩噻嗪不同，该分子具有极强的还原能力，能在相对于标准甘汞电极（SCE）为 -3.51 V的电位下促进基于单电子转移的还原裂解。作为例证，大量芳基氯底物已被还原裂解以制备异吲哚啉酮和羟吲哚类分子。此外，芳基 - 氯键已发生均裂以生成芳基自由基，这些自由基已被用于碳 - 碳交叉偶联或碳 - 磷键形成反应。为证明其极强的还原能力，一些芳基氟键已被裂解以生成芳基自由基。一项包括稳态和时间分辨光谱技术的详细光物理研究解释了该分子在光激发时的行为，且这与其反应模式相关。理论计算表明，由于该分子本质上是反芳香性的，二苯并吩噻嗪阴离子在基态时略有褶皱。相比之下，激发态几何结构是平面的，这也与单电子转移后的中间体几何结构相近。减弱阴离子物种的反芳香性是其具有高还原行为的部分原因。
