Interfacial Hydroxyl Chemistry and Electronic Modulation in Pd/In(OH)3 Promote Electrochemical Suzuki-Miyaura Coupling.

Electrochemical Suzuki-Miyaura coupling (eSMC) offers a sustainable alternative to thermally driven cross-coupling reactions; however, its development remains limited by inefficient catalytic systems and incomplete mechanistic understanding. Herein, we report In(OH)3-supported Pd nanoparticles (Pd/In(OH)3) as an efficient electrocatalyst for eSMC between aryl bromides and arylboronic acids under mild conditions. The catalyst delivers near-quantitative conversion (99%) with exclusive selectivity toward biaryl products at 30 °C in an ethanol/H2O mixed solvent, without the need for an inert atmosphere. A high turnover frequency of 1143 h-1 is achieved, significantly outperforming commercial Pd/C (by 20-fold) and comparable to many thermally driven catalytic systems. Comprehensive experimental and theoretical investigations reveal that hydroxyl-rich interfacial sites on In(OH)3 directly participate in the rate-determining transmetalation step by enabling geometric preorganization of reactants and reducing the entropic penalty. Meanwhile, electron-enriched Pd sites, generated via interfacial electron transfer from In(OH)3 to Pd, further stabilize key intermediates and transition states involved in transmetalation. This cooperative dual-site mechanism synergistically lowers the energy barrier for transmetalation, thereby accelerating overall reaction kinetics. This work provides both an efficient catalyst design strategy and mechanistic insights for advancing eSMC, offering guidance for future development of organic electrosynthesis.