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

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