Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 145, Issue 41, Pages 22403-22412Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.3c05787
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Here, we describe the highly reducing nature of the anion of benzo[b]phenothiazine upon excitation by visible light. This molecule shows extreme reducing power and can promote reductive cleavage reactions at a low potential. This property has been demonstrated by the successful synthesis of isoindolinone and oxindole molecules through the reductive cleavage of aryl chloride substrates.
Herein we describe the anion of benzo[b]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.
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