Green solvent as electron source and reactant: Dual catalysis by cobalt didehydrocorrin complex and WO3 under visible-light irradiation

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%.