A promoting effect of water on CO2 insertion into TpRu(PPh3) (CH3CN) H [Tp = Hydrotris(pyrazolyl) borate] is observed. In situ high-pressure 1H, 31P and 13C NMR monitoring shows that CO2 readily inserts into Ru- Hto form the hydrated metal formate TpRu (PPh3) (CH3CN) (-n'-OCHO) ? H2O in which the formate ligand is intermolecularly H-bonded to a water molecule. Theoretical calculations carried out at the B3LYP level show that electrophilicity of the carbon center of CO2 is enhanced by the formation of H-bonds between its oxygen atoms and H2O in the transition state of the process, and thus reaction barrier of the CO2 insertion is significantly reduced in the presence of water. The hydrated formate species TpRu(PPh3) (CH3CN) (η'-OCHO) ? H20 comes into equilibrium rapidly with another metal formate species TpRu(PPh3) (H2O) (η'-OCHO), in which the coordinated H2O is intramolecularly H- bonded with the formate ligand.

Key words: CARBON DIOXIDE, RUTHENIUM COMPLEX, FORMIC ACID P, HYDROGEN BONDS, ACTIVATION ENERGY