Mechanism of Excited-State Dissociation of Ni–C and Ni–Br Bonds in (bpy)NiII(alkyl)(Br) Complexes

Ni^IIRX (R = aryl, alkyl; X = halogen) complexes containing bipyridine (bpy)-type ligands play a crucial role in metallaphotoredox-catalyzed cross-coupling reactions. Despite the excited-state dissociation of Ni–C and Ni–halide bonds in the (bpy)Ni^II(aryl)(halide) complex being well understood, the corresponding (bpy)Ni^II(alkyl)(halide) complex remains largely unexplored. Experimentally, it is challenging due to its instability, making isolation and characterization difficult and necessitating computational investigations. This study employs high-level computational methods to investigate the excited-state dissociation of Ni–C and Ni–Br bonds in (bpy)Ni^II(alkyl)(Br) complexes. Additionally, we explored the influence of bpy substituents (OMe, t-Bu, Me, H, CO₂Me, CF₃, Cl, Ph) at the 4,4′ positions, along with other ligands, bi-imidazole (H₂bim) and phenanthroline (phen), revealing key electronic factors governing bond homolysis. Our findings provide fundamental insights into excited-state properties that impact catalytic performance, guiding the rational design of visible light-induced Ni-catalyzed alkylation reactions.