Organic photoredox catalysts for reductive transformations of organic molecules

Abstract

Photoinduced electron transfer (PET) is a fundamental photochemical process involving single electron transfer (SET) promoted reduction and oxidation (redox) of excited state materials. In nearly half a century, extensive investigations to elucidate the PET reaction mechanism and to discover a variety of organic redox reactions were conducted. Since the reaffirmation of the synthetic potential of PET reactions promoted by visible-light-absorbing transition metal photoredox catalysts, numerous synthetically useful reactions catalyzed by these metal complexes have been reported. From a green and sustainable perspective, the processes promoted by organic photoredox catalysts are often proposed to be more desirable. Although a variety of organic electron-acceptor photocatalysts have been utilized, their electron-donor counterparts have been less well explored. Brief history of organic electron-donor photocatalysts and recent developments of new photocatalysts and catalytic protocols for carrying out reduction reactions of organic molecules are described in this review.