Water-soluble rhodium(I)- and ruthenium(II)tertiary phosphine complexes with meta-mono-sulphonated triphenylphosphine (TPPMS) and 1,3,5-triaza-7-phosphaadamantane (PTA) as ligands catalyze the hydrogenation of aqueous HCO3- to HCO2- under mild conditions. No amine additive is needed for good turnovers. CO2 accelerates the reactions with [RhCl(TPPMS)(3)] catalyst; however, it slightly inhibits the reductions catalyzed by [RuCl2(TPPMS)(2)]. Bicarbonate formed in the reaction of limestone with aqueous CO2 can also be used as starting material for formate production. Copyright (C) 2000 John Wiley & Sons, Ltd.