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 acety l groups [Ru(bpy)(2)(CO)L](+) (L = CH3, C(O)H and C(O)CH,) were examined fr om the view point of active species in multi-step reduction of CO, on Ru. T he methyl complex was prepared by the reaction of [Ru(bpy)(2)(OH2)(2)](2+) with trimethylsilyl acetylene and fully characterized by infrared, Raman, C -13-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 diff icult to determine the bond parameters of the two groups accurately, but th e molecular structure of the analogous acetyl complex, which was obtained b y 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 a nd acetyl complex with 174(1) and 175.5(5)degrees, respectively, are in the ranges of those of previously characterized [Ru(bpy)(2)(CO)L](n divided by ) (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 freq uency in the Raman spectra. (C) 2001 Elsevier Science B.V. All rights reser ved.