We have successfully developed an environmentally friendly organic transformation method, where green alcohols were used as the solvent, electron source, and reactant simultaneously. The novel photocatalytic system, consisting of a Co-didehydrocorrin complex, pyrocob(III)6C 1 ester ( P -Co(III) ), and tungsten oxide (fine WO₃) efficiently generated the corresponding Co(I) species under visible light irradiation using methanol (CH₃OH) as the electron source. The formation of Co(I) species was confirmed by diffuse reflectance (DR)-UV-vis spectroscopy and electron spin resonance (ESR). The photo-induced Co(I) species reacted with methyl iodide (CH₃I) to afford the Co(III)–CH₃ complex, which underwent homolytic Co–C bond cleavage upon additional photoirradiation, as evidenced by DR-UV-vis spectroscopy and electrospray ionization-mass spectrometry (ESI-MS). This photocatalytic system was successfully applied to the esterification of trichloromethyl compounds. When fine WO 3 was added to a CH 3 OH solution including P -Co(III) and irradiated with visible light (λ > 420 nm), trichloromethylbenzene was converted to methyl benzoate in 82% yield. Thus, this reaction represents a sustainable organic transformation that uses visible-light energy and green solvents and operates without sacrificial reagents, providing an integrated strategy to design organic synthesis systems with reduced environmental impact. • A dual catalytic system comprising a Co-didehydrocorrin complex and fine WO 3 enables the use of green alcohol solvents as both an electron source and a reactant. • The dual catalytic system generates reactive Co(I) species under visible light irradiation, using CH 3 OH as an electron source. • The dual catalytic system facilitates visible light-driven ester formation from benzotrichlorides, in which CH 3 OH serves simultaneously as the solvent, electron source, and reactant. • Fifteen esters are produced using this dual system in yields of up to 99%.
Shichijo et al. (Sun,) studied this question.