Heteroleptic copper(I) complexes [Cu(dmp)(N^P)]BF₄ for photoinduced atom-transfer radical addition reactions

Earth-abundant copper(I) coordination complexes of an imine-phosphine and a diimine have been developed as visible-light photocatalysts. Reaction of [Cu(MeCN)₄]BF₄ with hetero-bidentate phosphinopyrazole (phpz) ligand R¹R²C₃HN₂PPh₃ (R¹ = R² = H (1a); R¹ = H, R² = Me (1b); R¹ = H, R² = Ph (1c); R¹ = R² = Me (1d)) and 2,9-dimethyl-1,10-phenanthroline (dmp) gave four heteroleptic bis-chelate Cu(I) complexes [Cu(dmp)(R¹R²C₃HN₂PPh₃)]BF₄ (R¹ = R² = H (2a); R¹ = H, R² = Me (2b); R¹ = H, R² = Ph (2c); R¹ = R² = Me (2d)) with distorted tetrahedral geometries. Complexes 2a-2d exhibited broad absorption in the visible spectrum and could facilitate photochemical intermolecular atom-transfer radical addition reactions of CBr₄, or CCl₃Br, CHI₃ to styrenes in yields up to 91% and with a broad substrate scope. The absorption, emission, redox potential and photocatalytic activity were dependent on the substituents on the phpz ligand. Mechanistic studies supported an atom-transfer radical addition (ATRA) mechanism.