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

A series of trans-(Cl)-[Ru(L)(CO)(2)Cl-2]-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 (E-p) of the ruthenium complex. The catalytic abilities for CO2 reduction are evaluated in photoreactions (>400nm) 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 E-p a negative value until it reaches the reduction potential of the photosensitizer.