The water soluble ruthenium(II) complex [RuCl₂(PTA)([9]aneS₃)] (PTA = 1,3,5-triaza-7-phosphadamantane, [9]aneS₃ = 1,4,7-trithiacyclononane) catalyzes the hydrogenation of CO₂ and bicarbonate in aqueous solution. While the catalytic activity is low, the formation of an intermediate involving coordination of both hydride and bicarbonate to the ruthenium centre has been unambiguously established by ¹H, ³¹P and ¹³C NMR spectroscopy. Such an intermediate has previously been proposed on the basis of theoretical studies and experimental findings.