A Two-Coordinate Copper Carbene/Acetylide Complex Exhibiting Intraligand Charge-Transfer Luminescence and Visible-Light-Driven Photocatalytic Activities

Two-coordinate, linear carbene-metal-amide (CMA) complexes featuring coinage metals have gained significant attention due to their ligand-to-ligand charge transfer (LLCT) luminescence properties and their wide range of applications in photochemistry. However, linear carbene-metal-acetylide (CMAc) complexes are underdeveloped. To date, research has primarily focused on CMAc complexes with Au(I), where ligand-to-ligand or intraligand charge transfer luminescence is rarely observed, and, instead, ligand-centered (LC) emissions have typically been detected. None of these complexes has been used in visible-light-driven photocatalysis. Herein, we report the synthesis and characterization of three new CMAc complexes ([Cu(AcenaphIPr)(CCPh)], [Ag(AcenaphIPr)(CCPh)], and [Au(AcenaphIPr)(CCPh)]) and their photophysical properties. All the complexes feature intraligand charge transfer (ILCT) absorptions and display ILCT luminescence in solution at room temperature. Interestingly, CMAc complexes feature ILCT absorptions in the visible region and have been used as photosensitizers in visible-light-driven energy-transfer photocatalysis. In particular, the Cu(I) complex [Cu(AcenaphIPr)(CCPh)] performed effectively in a variety of photocatalytic reactions, namely, (i) amine-to-imine formation, (ii) phosphine-to-phosphine oxide formation, and (iii) α-cyanation of N-aryl-tetrahydroisoquinolines under visible-light irradiation.