Photodriven Sm(III)-to-Sm(II) Reduction for Catalytic Applications

The selectivity of SmI₂ as a one electron-reductant motivates the development of methods for reductive Sm-catalysis. Photochemical methods for SmI₂ regeneration are desired for catalytic transformations. In particular, returning Sm^III-alkoxides to Sm^II is a crucial step for Sm-turnover in many potential applications. To this end, photochemical conditions for reduction of both SmI₃ and a model Sm^III-alkoxide to SmI₂(THF)_n are described here. The Hantzsch ester can serve either as a direct photoreductant or as the reductive quencher for an Ir-based photoredox catalyst. In contrast to previous Sm^III reduction methodologies, no Lewis acidic additives or byproducts are involved, facilitating selective ligand coordination to Sm. Accordingly, Sm^II species can be generated photochemically from SmI₃ in the presence of protic, chiral, and/or Lewis basic additives. Both the photoreductant and photoredox methods for SmI₂ generation translate to intermolecular ketone-acrylate coupling as a proof-of-concept demonstration of a photodriven, Sm-catalyzed reductive cross-coupling reaction.