Deciphering Asymmetric Induction in Photoredox Catalysis by Chiral Counteranions

Area of Science:

• Organic Chemistry
• Photocatalysis
• Stereoselective Synthesis

Background:

• Asymmetric counteranion-directed photoredox catalysis (ACPC) is a powerful tool for creating chiral molecules.
• Understanding the origin of stereocontrol in ACPC is crucial for designing efficient catalytic systems.

Purpose of the Study:

• To elucidate the mechanism and origin of stereocontrol in a representative [2 + 2] cycloaddition catalyzed by a chiral imidodiphosphorimidate (IDPi) counteranion.
• To investigate how the chiral counteranion influences both enantioselectivity and diastereoselectivity.

Main Methods:

• Extensive conformational sampling
• High-level density functional theory (DFT) calculations
• Multiscale modeling
• Atomic decomposition of London dispersion (ADLD) and molecular dispersion potential (MDP) analyses

Main Results:

• Stereoselectivity is established in the initial C-C bond formation.
• Diastereoselectivity originates from aryl-aryl interactions; enantioselectivity is dictated by the chiral IDPi counteranion.
• The counteranion, though electronically silent in electron transfer, organizes the radical cation and styrene for cycloaddition via van der Waals forces.

Conclusions:

• The chiral counteranion's architecture dictates substrate prealignment and transition state stabilization, leading to high stereoselectivity.
• Substituent effects on styrenes modulate noncovalent interactions, altering selectivity.
• Provides a unified framework for stereocontrol in chiral ion-pair radical catalysis and guides the design of new asymmetric photoredox transformations.