Electrocatalytic properties of a novel ruthenium(ii) terpyridine-based complex towards CO₂ reduction

The electrocatalytic properties of Ru complexes are of great technological interest given their potential application in reactions such water splitting and CO2 reduction. In this work, a novel terpyridine-based Ru(ii) complex, [RuCl(trpy)(acpy)], trpy = 2,2 ':6 ',2 ''-terpyridine, acpy(-) = 2-pyridylacetate was synthesized and its spectroscopic, electrochemical and catalytic properties were explored in detail. In dry acetonitrile, the complex exhibits two reduction peaks at -1.95 V and -2.20 V vs. Fc/Fc(+), attributed to consecutive 1 e(-) reduction. Under CO2 atmosphere, a catalytic wave is observed (E-onset = 2.1 V vs. Fc/Fc(+)), with CO as the main reduction product. Bulk electrolysis reveals a turnover number (TON) of 12 (k(obs) = 1.5 s(-1)). In the presence of 1% water, an improvement in the catalytic activity is observed (TONCO = 21 and k(obs) = 2.0 s(-1)) and, additionally, formate was also detected (TONHCOO = 7). Spectroelectrochemical experiments allowed the identification of a metallocarboxylate (Ru-COO-) intermediate under anhydrous conditions, while in water, the partial labilization of the acpy(-) ligand was observed in the course of the catalytic cycle. The experimental data was combined with DFT calculations, allowing the proposal of a catalytic cycle. The results establish important relationships between selectivity, ligand structure and reaction conditions.