Generation of Thioxanthone Hydrogen Anion by Double Photoreduction and Uses for Catalytic Photoreductions

Anions are the reduced form of precatalysts that are a special type of photoredox catalyst, unlike traditional iridium or ruthenium complexes. Among them, radical anions often have much shorter excited-state lifetimes because of fast nonradiative decay. Herein, we report the discovery of thioxanthone hydrogen anion ( 5 ), a super-reducing photocatalyst with a long excited-state lifetime ( E ox * = −2.74 V vs SCE, τ S = 4.1 ns). Using 5 as a catalytic reductant, we developed a series of photoreductions, including hydrogenation, reductive dehalogenation, deoxygenative hydrogenation, and deoxygenation, thereby demonstrating the feasibility of the 2e – consecutive photoinduced electron transfer (ConPET) strategy and the versatility of the catalyst.