Photoinduced Ligand-to-Metal Charge Transfer Enables Photocatalyst-Independent Light-Gated Activation of Co(II)

Photoredox catalysis can be used to manipulate the redox state of a transition metal complex leading to the desired reactivity. While powerful, obviating the role of the second catalyst would be attractive from the perspective of simplifying the protocol and using visible light to uncover unexpected, enabling reactivity. Herein we report that Co-acetylides, formed in situ, are photoactive complexes that undergo ligand-to-metal charge transfer using visible light. The net transformation uses air-stable Co(II) complexes as precatalysts and induces Co(I) chemistry. The acetylide is an electron reservoir forming the Co(I) but accepting the electron back at the end of the catalytic cycle. The electronic nature of the acetylide leads to either on-off behavior or simply initiates catalysis, depending on electronics.