Aminoborate-Catalyzed\nReductive Counterreactions for\nOxidative Electrosynthetic Transformations

Electrooxidative transformations\nfrequently rely on proton reduction\nas the terminal electron sink. However, this cathodic counterreaction\ncan be slow in organic solvents and can operate at reducing potentials\nthat are incompatible with catalysts and reagents needed for oxidative\nreactions. We report aminoborate adducts as redox mediators for proton\nreduction that operate at mild reducing potentials. This reliable\ncathodic couple ultimately enables successful oxidative organic transformations,\nincluding chlorodeborylation, developed herein, and Cu-catalyzed Chan–Lam\ncoupling, reported previously by our group. Pyridinium borate adducts\nformed during electrooxidative chlorination of aryl trifluoroborates\nserve as easily reduced complexes (−1.1 V vs Fc/Fc<sup>+</sup>) to catalyze proton reduction. Reactions that promote the formation\nof borate adducts result in high yields, operate at low cell potentials,\nsuppress aryl trifluoroborate decomposition, and mitigate electrode\npassivation. These studies illustrate the utility of Lewis acid–base\ncomplexes in cathodic counterreactions and underscore the importance\nof developing both anodic and cathodic reactions in electrosynthesis.