Structural and spectroscopic characterization of ruthenium(II) complexes with methyl, formyl, and acetyl groups as model species in multi-step CO2 reduction

The molecular structures of Ru(II) complexes with methyl, formyl, and acetyl groups [Ru(bpy)2(CO)L]+ (L=CH3, C(O)H and C(O)CH3) were examined from the view point of active species in multi-step reduction of CO2 on Ru. The methyl complex was prepared by the reaction of [Ru(bpy)2(OH2)2]2+ with trimethylsilyl acetylene and fully characterized by infrared, Raman, 13C-NMR and single-crystal X-ray crystallography. Disorder of the RuCO and RuC(O)H bonds in the crystal structure of the formyl complex made it difficult to determine the bond parameters of the two groups accurately, but the molecular structure of the analogous acetyl complex, which was obtained by the reaction of [Ru(bpy)2(CO3)] with propiolic acid, was determined by X-ray analysis. The ruthenium–carbonyl (RuCO) bond angles of the methyl and acetyl complex with 174(1) and 175.5(5)°, respectively, are in the ranges of those of previously characterized [Ru(bpy)2(CO)L]n+ (L=CO2, C(O)OH, CO and CH2OH). On the other hand, the RuCH3 and RuC(O)CH3 bond distances showed unusual relationship against the stretching frequency in the Raman spectra.