Electronic Effects Modulated Hemilabile Carboxylate Coordination of Ruthenium Complexes for Electrocatalytic Ammonia Oxidation

Abstract Efficient ammonia oxidation reaction (AOR) catalysts are key to advancing low-temperature ammonia fuel technology, yet this progress is constrained by a limited understanding of the structure-activity relationships. Here, we report the significant roles of electronic effects in modulating hemilabile carboxylate coordination during ruthenium-catalyzed ammonia oxidation. The coordination substitution of ammonia and the AOR were studied using a series of complex [Ru(bpc-κ-N2O1)(tpy-R)](PF6) (R = NMe2, H, CF3) (Ru(bpc)(t-R); Hbpc = 2,2-bipyridine-6-carboxylic acid; tpy-R = 4′-Dimethylamino/trifluoromethyl-terpyridine). The NH3 coordination is favored by stronger electron donation and a larger Ru–O1–C1–C2 torsion angle, with equilibrium constants following the order NMe2 > H > CF3. Electrochemical data show that the electron-donating NMe2 derivative offers the lowest overpotential at the cost of the smallest catalytic current, suggesting that electron donation promotes the initial oxidation but impedes N–H cleavage, and vice versa. Kinetic analysis supports an EC’ mechanism for the Ru(bpc)(t-R)(NH3) series, with N–N bond formation proceeding through nucleophilic attack of ammonia. This work reveals the mechanism by which electronic effects and hemilabile coordination synergistically regulate the performance of AOR catalysts, inspiring the design of new catalysts.