A Novel Photo-Driven Hydrogenation Reaction of an NAD-Type Complex Toward Artificial Photosynthesis.

The photocatalytic reduction of carbon dioxide (CO) to value-added chemicals is an attractive strategy to utilize CO as a feedstock for storing renewable energy, such as solar energy, in chemical bonds. Inspired by the biological function of the nicotinamide adenine dinucleotide redox couple (NAD/NADH), we have been developing transition-metal complexes containing NAD/NADH-functionalized ligands to create electro- and/or photochemically renewable hydride donors for the conversion of CO into value-added chemicals. Our previous findings have provided insights for the development of photocatalytic organic hydride reduction reactions for CO, however, further examples, as well as investigation, of these photo-driven NAD/NADH-type hydrogenation and organic hydride transfer reactions are required not only to explore the mechanism in detail but also to develop a highly efficient catalyst for artificial photosynthesis. In this paper, we report the synthesis, characterization, and photo-induced NAD/NADH conversion properties of a new ruthenium(II) complex, Ru(bpy)(Me-pn) (), which contains a new NAD-type ligand, Me-pn (2-methyl-6-(pyridin-2-yl)-1,5-naphthyridine). In addition, we have succeeded in the isolation of the corresponding two-electron reduced ruthenium(II) complex containing the NADH-type ligand Me-pnHH (2-methyl-6-(pyridin-2-yl)-1,4-dihydro-1,5-naphthyridine), i.e., Ru(bpy)(Me-pnHH) (), by the photo-induced hydrogenation reaction of . Thus, in this study, a new photo-driven NAD/NADH-type hydrogenation reaction for possible CO reduction using the NAD/NADH redox function has been constructed.