The reactions of cis- and trans-Fe(dmpe)2Me2 (1) [dmpe = 1,2-bis(dimethylphosphino)ethane] and cis/trans- Fe(depe) 2Me2 (6) [depe = 1,2-bis(diethylphosphino)ethane] with carbon dioxide (CO2) were investigated along with the isomerization properties of the starting materials 1 and 6. Irradiation with UV light cleanly isomerizes the dimethyl complexes from their cis configurations 1a and 6a to their trans configurations 1b and 6b. At 300 K, addition of CO2 (1 atm) to 1 or 6 forms a stable methyl acetate, Fe(dmpe)2(OCOCH 3)Me (2) or Fe(depe)2(OCOCH3)Me (7), respectively, by insertion of CO2 into one of the metal-carbon bonds. At 330 K, the addition of CO2 (5-6 atm) to 1 results in the initial formation of the methyl acetate (2) followed by the formation of an octahedral bis-acetate complex Fe(dmpe)2(OCOCH3)2 (3), which was also synthesized independently. Complex 3 rearranges to a salt containing a bidentate acetate and an acetate counterion, [Fe(dmpe) 2(OCOCH3)]+[OCOCH3]- (4). The depe analogue to 3, Fe(depe)2(OCOCH3)2 (8), was not observed in the reaction between 6 and CO2, and only the salt [Fe(depe)2(OCOCH3)]+[OCOCH 3]- (9) was isolated. In the reactions of either cis- or trans-Fe(dmpe)2Me2 (1) with CO2, a stable carbonate complex, Fe(dmpe)2(CO3) (5), with a bidentate carbonate ligand, was also observed. All complexes were characterized by multinuclear NMR spectroscopy, with IR spectroscopy and elemental analyses confirming structures of thermally stable complexes where possible. Complexes 1b, 3, 5, 6b, and 9 were characterized by X-ray crystallography. © 2008 American Chemical Society.