H-Bond Assistance and Electronic Effects Accelerate the Cleavage of the N–O Bond in the Electrochemical Reduction of N2O Catalyzed by Rhenium Bipyridine Tricarbonyl Complexes

Abstract

The development of molecular catalysts for the electrochemical activation of small molecules focuses on understanding the factors that reduce the overpotential and increase the catalytic rate constants. Key factors include the electronic effects of substituents on ligands and the role of cofactors, such as proton donors. In this study, we demonstrate that the reductive deoxygenation of nitrous oxide (N₂O), catalyzed by rhenium bipyridine tricarbonyl complexes, is accelerated in the presence of water due to hydrogen bonding, which assists the cleavage of the N–O bond. Moreover, water decreases the overpotential by accelerating the decoordination of the hydroxo ligand, facilitating the regeneration of the active species after the first turnover. We also find that modifying the bipyridine ligand with electron-donating groups (CH₃, tBu, and OCH₃) has only a modest effect on the catalysis, suggesting that the electrons stored on the bipyridine ligand do not significantly influence the reaction unless they are strongly trapped, as evidenced by the lack of reactivity in the complex bearing strongly electron-withdrawing groups (CO(O)CH₃).