trans-(Cl)-[Ru(5,5'-diamide-2,2'-bipyridine)(CO)2 Cl2 ]: Synthesis, Structure, and Photocatalytic CO2 Reduction Activity.

A series of trans-(Cl)-[Ru(L)(CO)2 Cl2 ]-type complexes, in which the ligands L are 2,2'-bipyridyl derivatives with amide groups at the 5,5'-positions, are synthesized. The C-connected amide group bound to the bipyridyl ligand through the carbonyl carbon atom is twisted with respect to the bipyridyl plane, whereas the N-connected amide group is in the plane. DFT calculations reveal that the twisted structure of the C-connected amide group raises the level of the LUMO, which results in a negative shift of the first reduction potential (Ep ) of the ruthenium complex. The catalytic abilities for CO2 reduction are evaluated in photoreactions (λ>400 nm) with the ruthenium complexes (the catalyst), [Ru(bpy)3 ](2+) (bpy=2,2'-bipyridine; the photosensitizer), and 1-benzyl-1,4-dihydronicotinamide (the electron donor) in CO2 -saturated N,N-dimethylacetamide/water. The logarithm of the turnover frequency increases by shifting Ep a negative value until it reaches the reduction potential of the photosensitizer.