# Redox-Switchable Halogen Bonding in Haloanthracene Mediators Enables Efficient Electrocatalytic C–N Coupling

## TL;DR

This paper introduces redox-switchable halogen bonding in haloanthracene mediators to improve electrocatalytic C–N bond formation.

## Contribution

The novel use of redox-switchable halogen bonding to control reactivity and selectivity in electrocatalysis is presented.

## Key findings

- Iodoanthracene derivative 1a showed superior catalytic performance in C–N coupling.
- Mediator 1h, with a 3,5-bis(trifluoromethyl)phenyl group, achieved high yields in short reaction times.
- Computational studies confirmed that halogen bonding in the radical cation state enhances N–H acidity and PCET.

## Abstract

We report the development of redox mediators based on
9-halo-10-arylanthracenes
that engage in halogen bonding only upon one-electron oxidation. This
redox-switchable interaction enables an effective substrate preorganization
and promotes intramolecular C–N bond formation via electrocatalysis.
Systematic evaluation of halogenated mediators (1a–1c) across various N-protected 2-aminobiphenyl substrates
revealed that the iodoanthracene derivative 1a exhibited
superior catalytic performance. Building on this, we synthesized a
series of 10-aryl-substituted iodoanthracenes (1d–1h) to further optimize the mediator structure. Kinetic analysis by
foot-of-the-wave analysis identified 1h, bearing a 3,5-bis­(trifluoromethyl)­phenyl
group, as a highly active mediator with an apparent rate constant
over an order of magnitude higher than that of its counterparts. Bulk
electrolysis experiments confirmed its remarkable performance, achieving
high yields in short reaction times. Computational studies demonstrated
that halogen bonding is markedly strengthened in the radical cation
state, and that this interaction significantly enhances the acidity
of the N–H bond in the substrates, enabling proton-coupled
electron transfer (PCET) even with a weak base. Energy diagrams constructed
from density functional theory calculations supported a mechanism
in which the mediator not only facilitates PCET but also stabilizes
cationic intermediates throughout the catalytic cycle. This work establishes
a new design paradigm for redox mediators, where redox-induced noncovalent
interactions can be harnessed to control both reactivity and selectivity.
The concept of halogen-bonding-assisted PCET provides a powerful platform
for advancing molecular electrocatalysis.