Synthesis, structures and electrochemical properties of ruthenium (II) complexes bearing bidentate 1,8-naphthyridine and terpyridine analogous (N,N,C)-tridentate ligands

1,8-Naphthyridine (napy) and terpyridine-analogous (N,N,C) tridentate ligands coordinated ruthenium (II) complexes, [RuL(napy-κ2N,N′) (dmso)](PF6)2 (1: L=L1=N″-methyl-4′-methylthio-2,2′:6′,4″-terpyridinium, 2: L = L2 = N″-methyl-4′-methylthio-2,2′:6′,3″-terpyridinium) were prepared and their chemical and electrochemical properties were characterized. The structure of complex 1 was determined by X-ray crystallographic study, showing that it has a distorted octahedral coordination style. The cyclic voltammogram of 1 in DMF exhibited two reversible ligand-localized redox couples. On the other hand, the CV of 2 shows two irreversible cathodic peaks, due to the Ru–C bond of 2 containing the carbenic character. The IR spectra of 1 in CO2-saturated CH3CN showed the formation of Ru-(η1-CO2) and Ru–CO complexes under the controlled potential electrolysis of the solution at −1.44 V (vs. Fc/Fc+). The electrochemical reduction of CO2 catalyzed by 1 at −1.54 V (vs. Fc/Fc+) in DMF-0.1 M Me4NBF4 produced CO with a small amount of HCO2H.