Ruthenium polypyridyl complexes have been shown to catalyze ammonia oxidation to dinitrogen at room temperature and ambient pressure with ca. 300 mV lower overpotential compared to the uncatalyzed oxidation at a glassy carbon electorde.1 Substituting the 4,4'-hydrogens in bipyridine with electron-donating NMe2substituents significantly lowered E1/2 for the RuII/III couple for [(trpy)({NMe2}2bpy)Ru(NH3)][PF6]2 relative to the value for [(trpy)(bpy)Ru(NH3)][PF6]2 (trpy = terpyridine), which was key to reducing the overpotential of the Ru-catalyzed oxidation. Reducing the net charge of a metal complex is an alternative approach to adding donating substituents for lowering E1/2 values, as well as influencing ligand substitution rates. We have synthesized [(trpy)(phpy)Ru(NH3)][PF6] (phpy = 2-phenylpyridine), where the RuII monocation is isoelectronic to the RuII dication in [(trpy)(bpy)Ru(NH3)][PF6]2. The influence of charge reduction as compared to adding electron donating substituents to the bipyridine ligands on E1/2 values and substitution rates of plausible intermediates is under investigation. Results from this study, in addition to effects of molecular design on electrocatalytic ammonia oxidation, will be presented.

Electrocatalytic ammonia oxidation with monocationic ruthenium complexes

ACS Spring 2022

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