Outer-sphere reductive elimination as the enantio-determining step in IrIII/NiII metallaphotoredox-catalyzed α-(hetero)aryl amination: a DFT study

Abstract

The Ir^III/Ni^II metallaphotoredox-catalyzed enantioselective cross-coupling of chiral α-(hetero)aryl amines was systematically investigated using density functional theory (DFT) calculations. Both oxidative-quenching (Ir^III–*Ir^III–Ir^IV–Ir^III) and reductive-quenching (Ir^III–*Ir^III–Ir^II–Ir^III) photoredox cycles were found to be compatible with the nickel catalytic cycle (Ni^II–Ni^I–Ni^III–Ni^II). Mechanistic analysis indicates that the overall transformation proceeds through three fundamental steps: single-electron transfer, oxidative addition, and stepwise outer-sphere reductive elimination, with oxidative addition identified as the rate-determining step. Notably, the enantio-determining C–C bond-forming event occurs via an ion-pair intermediate embedded within the outer-sphere reductive-elimination pathway. Furthermore, the high enantioselectivity of the process originates predominantly from steric interactions between the substrate and the chiral ligand. These insights clarify the mechanistic basis of this photoredox-mediated dual-catalytic asymmetric transformation and may guide the design of next-generation metallaphotoredox asymmetric methodologies.