Sensitizer-Free Photochemical Regeneration of Benzimidazoline Organohydride

Organohydridesare an important class of organic compounds thatcan provide hydride anions for chemical and biochemical reactions,as demonstrated by reduced nicotinamide adenine dinucleotides servingas important natural redox cofactors. The coupling of hydride transferfrom the organohydride to the substrate and subsequent regenerationof the organohydride from its oxidized form can realize organohydride-catalyzedreduction reactions. Depending on the structure of the organohydride,its hydridicity and ease of regeneration vary. Benzimidazoline (BIH)is one of the strongest synthetic C-H hydride donors; however,its reductive regeneration requires highly reducing conditions. Inthis study, we synthesized various oxidized and reduced forms of BIHderivatives with aryl groups at the 2-position and investigated theirphotophysical and electrochemical properties. 4-(Dimethylamino)phenyl-substitutedBIH exhibited salient red-shifted absorption compared with other synthesizedBIH derivatives, and visible-light-driven regeneration without usingan external photosensitizer was achieved. This knowledge has significantimplications for the future development of solar-energy-based catalyticphotoreduction technologies that utilize organohydride regenerationstrategies.

Automated summary

Organohydrides are important organic compounds that provide hydride anions for reactions, and their hydride transfer and regeneration play a crucial role in organohydride-catalyzed reduction reactions. In this study, different forms of BIH derivatives were synthesized and their photophysical and electrochemical properties were investigated. The 4-(dimethylamino)phenyl-substituted BIH showed red-shifted absorption and visible-light-driven regeneration without using an external photosensitizer. This has implications for the development of solar-energy-based catalytic photoreduction technologies.