Electrochemical CO₂ Reduction Using a New Ru‐NAD Type Bis Carbonyl Complex

Abstract A new ruthenium(II) NAD (NAD=Nicotinamide Adenine Dinucleotide) type bis‐carbonyl complex, [Ru(bpy)(pbn)(CO) 2 ] 2+ [pbn = 2‐(pyridin‐2‐yl)benzo[b]‐1,5‐naphthyridine; bpy = 2,2′‐bipyridine] [ 1 ] 2+ , was successfully synthesized and fully characterized by single‐crystal X‐ray structural analysis, ESI‐MS, IR and NMR spectroscopy. Complex [ 1 ] 2+ together with [Ru(bpy)(pbn)(CO)(COOH)] + and/or [Ru(bpy)(pbn)(CO)(CO 2 )] 0 complexes exist as equilibrium mixtures in aqueous solutions as evident from spectroscopic study. Chemical reduction of [ 1 ] 2+ resulted the formation corresponding NADH form i. e., [Ru(bpy)(pbn HH )(CO) 2 ] 2+ (pbn HH = 2‐(pyridin‐2‐yl)‐5,10‐dihydrobenzo[b][1,5]naphthyridine) [ 1.HH ] 2+ as a two‐electron‐reduced species. The electrochemical behavior of complex [ 1 ] 2+ in the presence of acid was investigated based on cyclic voltammetry analysis. A control potential electrolysis of [ 1 ] 2+ afforded formate (HCOO − ) as the major product with a lesser amount of CO and H 2 , whereas that of [Ru(bpy) 2 (CO) 2 ] 2+ complex produced CO as the main product with a lesser amount of HCOO − and H 2 . The experimental results suggest that the selectivity of HCOO − over CO should be due to catalytic hydride transfer from the NADH‐type ligands of [ 1 ] 2+ to CO 2 .