The pincer ligand dihydride complex [IrH2{(Bu-t(2))PCH2CH2CHCH2CH2P(Bu-t(2))}] interacts with carbon dioxide to give an isolable bicarbonate [IrH(kappa(2)-O2COH)}{(Bu-t(2))PCH2CH2CHCH2CH2P(Bu-t(2))}] derivative and a metal hydride carbonyl compound. An intermediate metallo-formate complex can be detected by NMR spectroscopy. The reaction described is a reverse water gas shift process, CO2 + H-2 <--(-->) CO + H2O.