Photochemical Reductive Regeneration of Benzimidazoline Accelerated by OH or NH Bonds Adjacent to the Reaction Center

ABSTRACT 1,3‐Dimethylbenzimidazoline (BIH) is an organic hydride with a strong hydride‐donating capacity. Photochemical regeneration of BIH derivatives from their oxidized form, 1,3‐benzimidazolium, using inexpensive reductants is crucial for their practical application as catalysts. We observed that 2‐aryl‐BIH compounds, bearing a heteroatom–hydrogen bond at the ortho‐position of the phenyl substituent attached to the C2 position of the benzimidazoline ring, underwent rapid regeneration by ascorbate under visible‐light irradiation. Computational analyses revealed that the heteroatom–hydrogen bond facilitated BIH regeneration by forming a hydrogen bond with ascorbate and/or by mediating inter‐ and intramolecular transfer of a proton and an electron. This paper presents an environmentally sustainable strategy for utilizing BIH‐based systems as reductive catalysts.