Photoinduced Cobalt(III)−Trifluoromethyl Bond Activation Enables Arene C−H Trifluoromethylation

Visible‐light capture activates a thermodynamically inert Co III −CF 3 bond for direct C−H trifluoromethylation of arenes and heteroarenes. New trifluoromethylcobalt(III) complexes supported by a redox‐active [OCO] pincer ligand were prepared. Coordinating solvents, such as MeCN, afford green, quasi‐octahedral [( S OCO)Co III (CF 3 )(MeCN) 2 ] ( 2 ), but in non‐coordinating solvents the complex is red, square pyramidal [( S OCO)Co III (CF 3 )(MeCN)] ( 3 ). Both are thermally stable, and 2 is stable in light. But exposure of 3 to low‐energy light results in facile homolysis of the Co III −CF 3 bond, releasing . CF 3 radical, which is efficiently trapped by TEMPO . or (hetero)arenes. The homolytic aromatic substitution reactions do not require a sacrificial or substrate‐derived oxidant because the Co II by‐product of Co III −CF 3 homolysis produces H 2 . The photophysical properties of 2 and 3 provide a rationale for the disparate light stability.