Catalytic C–H Trifluoromethylation of Arenes and Heteroarenes via Visible Light Photoexcitation of a Co(III)–CF(3) Complex

[Image: see text] A cobalt photocatalyst for direct trifluoromethylation of (hetero)arene C(sp(2))–H bonds is described and shown to operate via visible light activation of a Co–CF(3) intermediate, which functions as a combined chromophore and organometallic reaction center. Chemical oxidations of previously reported (OCO)Co complexes containing a redox-active [OCO] pincer ligand afford a Co–CF(3) complex two oxidation states above Co(II). Computational and spectroscopic studies are consistent with formulation of the product as [(OCO(•))Co(III)(CF(3))(THF)(OTf)] (II) containing an open-shell [OCO(•)](1–) radical ligand bound to a S = 0 Co(III) center. II is thermodynamically stable, but exposure to blue (440 nm) light induces Co–CF(3) bond homolysis and release of (•)CF(3), which is trapped by radical acceptors including TEMPO(•), (hetero)arenes, or the radical [OCO(•)] ligand in II. The latter comprises a competitive degradation pathway, which is overcome under catalytic conditions by using excess substrate. Accordingly, generation of II from the reaction of [(OCO)Co(II)L] (III) (L = THF, MeCN) with Umemoto’s dibenzothiophenium trifluoromethylating reagent (1) followed by photolytic Co–CF(3) bond activation completes a photoredox catalytic cycle for C–H (hetero)arene trifluoromethylation utilizing visible light. Electronic structure and photophysical studies, including time-dependent density functional theory (TDDFT) calculations, suggest that Co–CF(3) bond homolysis at II occurs via an ligand-to-metal charge-transfer (LMCT) (OCO(0))Co(II)(CF(3)) state, revealing ligand redox activity as a critical design feature and establishing design principles for the use of base metal chromophores for selectivity in photoredox bond activations occurring via free radical intermediates.