# Deciphering Asymmetric Induction in Photoredox Catalysis by Chiral Counteranions

## TL;DR

This paper explains how chiral counteranions control the stereochemistry in a specific type of light-driven chemical reaction.

## Contribution

The study reveals the mechanism of stereocontrol in asymmetric photoredox catalysis using chiral counteranions.

## Key findings

- Diastereoselectivity arises from aryl−aryl interactions in the radical cation−styrene pair.
- Enantioselectivity is imposed by the chiral environment of the IDPi counteranion.
- Van der Waals forces stabilize the transition state and promote product formation.

## Abstract

We investigate the origin of stereocontrol in asymmetric
counteranion-directed
photoredox catalysis (ACPC) using a representative [2 + 2] cycloaddition
mediated by a chiral imidodiphosphorimidate (IDPi) counteranion (Science
2023, 379, 494−499). Combining extensive conformational sampling,
high-level DFT calculations, and multiscale modeling, we elucidate
the mechanism and stereochemical landscape of this transformation.
Both enantio- and diastereoselectivity are established in the first
C−C bond-forming step: diastereoselectivity arises from intrinsic
aryl−aryl interactions within the radical cation−styrene
pair, whereas enantioselectivity is imposed by the confined chiral
environment of the IDPi counteranion. Although electronically silent
during the initial photoinduced single-electron transfer, the counteranion
anchors the radical cation and organizes its cycloaddition with styrene.
Atomic decomposition of the London dispersion (ADLD) and molecular
dispersion potential (MDP) analyses reveal that attractive van der
Waals forces, shaped by the steric and electronic architecture of
the counteranion, promote reactive prealignment of the substrates
and selectively stabilize the transition state, leading to the major
product. Extension to substituted styrenes shows that ring substitution
reconfigures the noncovalent contact map within the catalyst pocket,
reshaping the energetic balance between competing pathways, in line
with experiment. These findings provide a unified framework for stereocontrol
in chiral ion-pair radical catalysis and offer general strategies
for designing asymmetric photoredox transformations.