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

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.