Kiyotsuna TOYOHARA, Hirotaka NAGAO and Koji TANAKA
[Chem. Lett. 27 (1996)]
The CO2/CO conversion under protic conditions is explained by an acid-base equilibrium among (eta)1-CO2, -COOH and -CO metal complexes (eq 1). The molecular
structures of both [Ru(bpy)2(CO)2]2+ and [Ru(bpy)2(CO)(CO2)] were already demonstrated by X-ray analysis. The molecular structure of the remaining [Ru(bpy)2(CO)((COOH)]+ is specially of interest, since the amphoteric reactivity of [Ru(bpy)2(CO)((COOH)]+ plays the key role in the CO2/CO conversion in both CO2 reduction and water gas shift reaction. X-ray analysis of [Ru(bpy)2(CO)(C(O)OH)](PF6) revealed that the Ru-COOH bond distance of [Ru(bpy)2(CO)(C(O)OH)]+ (2.003 Å) is much shorter than the Ru-CO2 one of [Ru(bpy)2(CO)(CO2)] (2.064 Å). The shortening of the former is ascribed to an increase in a (pi)-acceptor ability of the COOH moiety, since the Ru-N bond (trans to Ru-C) also show the similar behavior (Figure 1). The smooth conversion of eq. 1 in H2O, therfore, is assited by synergic s-donor and p-acceptor chracteristics of bpy ligands.