The water-soluble iridium(III) complexes [Cp*Ir(PTA)Cl2] (1) and [Cp*Ir(PTA)2Cl]Cl (2) (PTA = 1,3,5-triaza-7-phosphaadamantane) have been synthesised and characterised by spectroscopy and X-ray crystallography. The complexes were evaluated as catalyst precursors for the hydrogenation of CO2 and hydrogen carbonate in aqueous solutions, in the absence of amines or other additives, under relatively mild conditions. Complex 1 performed poorly while 2 catalyses the hydrogenation with moderate activity. The catalytically active monohydride [Cp*Ir(PTA)2H]+ was identified by multinuclear NMR spectroscopy and its nature confirmed by independent synthesis.