IrIII/NiII-Metallaphotoredox-Catalyzed Enantioselective Decarboxylative Arylation of α-Amino Acids: Theoretical Insight of Enantio-Determining Outer-Sphere Reductive Elimination.

Abstract

The IrIII/NiII-metallaphotoredox-catalyzed enantioselective decarboxylative arylation of α-amino acids has been systematically investigated using density functional theory calculations. The combination of oxidative quenching (IrIII-*IrIII-IrIV-IrIII) or reductive quenching (IrIII-*IrIII-IrII-IrIII) cycle with the nickel catalytic cycle (NiII-NiI-NiIII-NiII) is possible. The favorable reaction mechanism consists of three major processes: single-electron transfer, oxidative addition, and stepwise outer-sphere reductive elimination. The rate-determining step is the oxidative addition. Unexpectedly, the enantio-determining C-C bond formation occurs via an ion-pair intermediate involved in the stepwise outer-sphere reductive elimination process, which is unusual in the IrIII/NiII-metallaphotoredox catalysis. Furthermore, computational results reveal that the high enantioselectivity of this reaction is mainly dependent on the steric effect of substituents on substrates. This theoretical study provides useful knowledge for deep insights into the activity and selectivity of visible-light-mediated enantioselective metallaphotoredox dual catalysis at the molecular and atomic levels and benefits the development of asymmetric synthesis.