Heteroleptic copper(i) complexes [Cu(dmp)(N boolean AND 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 (RRC3HN2PPh3)-R-1-C-2 (R-1 = R-2 = H (1a); R-1 = H, R-2 = Me (1b); R-1 = H, R-2 = Ph (1c); R-1 = R-2 = Me (1d)) and 2,9-dimethyl-1,10-phenanthroline (dmp) gave four heteroleptic bis-chelate Cu(i) complexes [Cu(dmp)((RRC3HN2PPh3)-R-1-C-2)]BF4 (R-1 = R-2 = H (2a); R-1 = H, R-2 = Me (2b); R-1 = H, R-2 = Ph (2c); R-1 = R-2 = 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.