Treatment of Cp(CO)2Fe-CO2-K+ with R3SnCl (R = Me, Ph) in THF (-78-degrees-C) gave Cp(CO)2Fe-SnR3, which was attributed to preferred dissociation of the starting metallocarboxylate to Cp(CO)2Fe-K+. (Abbreviations : Cp = eta5-C5H5;Cp* = eta5-C5Me5.) The more nucleophilic Cp*(CO)2Fe-CO2-K+ was trapped by Ph3SnCl as the thermally stable iron-tin carboxylate Cp*(CO)2Fe-CO2SnPh3 (8). C-13-labeled product (Cp*(CO)2Fe-CO2SnPh3)-C-13 also was obtained in excess of 90% yield. Similar trapping experiments using Me3SnCl gave Cp*(CO)2Fe-CO2SnMe3 (9) and (using (CO2)-C-13) (Cp*(CO)2Fe-CO2SnMe3)-C-13. Both slowly decarboxylated at room temperature to Cp*(CO)2Fe-SnMe3. A competing (slower) carboxylate-carbonyl label exchange also was documented for (Cp*(CO)2Fe-CO2SnMe3)-C-13 transforming to (Cp*(CO)(CO)Fe-CO2SnMe3)-C-13 and then to (Cp*(CO)(CO)Fe-SnMe3)-C-13. IR upsilon(CO2) bands for 8 and 9 were assigned only after comparing spectra for Cp*(CO)2Fe-CO2SnR3, (Cp*(CO)2Fe-CO2SnR3)-C-13, and Cp*(CO)2Fe-SnR3. This data was consistent with a chelating mu(eta1-C:eta2-O,O’) structure for 8 and an unsymmetric or metalloester mu(eta1-C:eta1-O) bonding for the more reactive/labile 9.