Electrolyte-anion-controlled reactivity of aromatic radical cations

Electrolytes are indispensable in electrosynthesis, yet their function is generally confined to ionic conduction. Here we show that specific association of electrolyte anions provides a powerful means to regulate the reactivity of electrogenerated aromatic radical cations. Electrochemical oxidation of 2,5-diarylthiophenes in the presence of a coordinating anion, triflate (TfO^-), selectively triggers C-C bond formation, leading to dimerization followed by oxidative cyclization to afford thiophenium cations. In contrast, weakly coordinating anions such as B(C₆F₅)₄ ^- stabilize persistent and largely unreactive radical cations. Spectroscopic analyses confirm radical cation formation under weakly coordinating conditions, while the presence of a coordinating anion fundamentally alters the reaction pathway, selectively enabling productive C-C bond formation. These results establish electrolyte anion coordination as a general strategy to switch between reaction pathways, offering a new design principle for selective electrosynthetic transformations.