Density functional theory along with a dielectric continuum solvation model has been applied to identify possible reaction intermediates for the catalytic hydrogenation of HCO3- anion into HCO2- that occurs in aqueous solutions in the presence of water-soluble ruthenium complexes. Bicarbonate ion is shown to coordinate to a Ru-dihydfide species, which then undergoes a protonation process that yields a CO2 complex. The C-H bond formation is found to take place via CO, insertion into a Ru-H bond and the direct elimination of the formate product is shown to be an energetically favored step, which is assisted by the water medium. We find that water is directly involved in the reaction as a protonating/ deprotonating agent and also acts as a coordinating ligand. (c) 2006 Elsevier B.V. All rights reserved.