Catalytic Hydride Transfer to CO Using Ru-NAD-Type Complexes under Electrochemical Conditions.

The catalytic performance of Ru-NAD-type complexes [Ru(tpy)(pbn)(CO)] ([1]; tpy = 2,2';6',2″-terpyridine; pbn = 2-(pyridin-2-yl)benzo[b][1,5]naphthyridine) and the Ru-CO-bridged metallacycle [2] was investigated in the context of the electrochemical reduction of CO in HO/CHCN at room temperature. A controlled-potential electrolysis of [1] and [2] afforded formate (HCOO) as the main product, under concomitant formation of minor amounts of CO and H. Metallacycle [2] showed a higher selectivity toward the formation of HCOO than [1] (HCOO/CO for [1], 2.7; HCOO/CO for [2], 7). The generation of HCOO via a catalytic hydride transfer from the NADH-type ligands of [1] and [2] to CO was supported by the experimental results and a comparison with the reduction of CO catalyzed by [Ru(tpy)(bpy)(CO)] under similar conditions. A mechanism for the catalytic reduction of CO by [1] and [2] was proposed based on the experimental evidence. The thus-obtained results may help to expand the field of NADH-assisted reduction reactions.