The reaction of cis-Fe(dmpe)2H2 (1) with 13C-labeled carbon dioxide (CO2) was investigated, and trans[Fe(dmpe)2(CO)H] · [HCO3] (5) was identified as a reaction byproduct. Both the carbonyl ligand and the bicarbonate anion are derived from CO2, and this effectively constitutes a disproportionation of CO2 to CO and CO32-. trans-[Fe(dmpe)2(CO)H].[HCO3] (5) was characterized by crystallography and by NMR spectroscopy. © 2008 American Chemical Society.