Treating alkly(η 5-indenyl) iron complexes In(CO) 2FeR (R CH 3, CH 2OCH 3) with either nucleophilic metalate Cp(CO) 2Fe −Na + (CP η 5-C 5H 5) or In(CO) 2Fe −Na + affords stable bimetallic complexes In(CO)Fe (η-CO) 2Fe(In)- (COCH 3) −Na + ( 3) and (In)(Cp)(CO) 3Fe 2(COR) −Na + ( 4, R CH 3; 9, R CH 2OCH 3). The fully characterized PPN + salts 3 and 4 (PPN Ph 3PNPPh 3) both retain cis-structures having terminal (η 1) acyl ligands. Compound 4 exists as a 1 1 mixture of isomers corresponding to the acetyl group at alternate iron centers: results of 1H NMR magnetization transfer experiments further established that these isomers slowly equilibrate at room temperature. X-ray structural determination of 4PPN + showed that it crystallizes as the isomer having the acetyl coordinated on the CpFe end. These binuclear acyl products readily fragment (1 atm CO, R′X) into mononuclear acyl products, Cp(CO) 2FeCOCH 3 and Cp(CO) 2FeCOCH 2-OCH 3 from 4 and 9, respectively, and In(CO) 2FeCOCH 3 from 3. By-products include In(CO) 2FeR′ (R′ CH 3, CH 3CH 2, Ph 3Sn) and, depending on the reaction conditions, binuclear vinylidene compounds. A reaction pathway is proposed that accounts (by invoking reversible η 5/η 3-In ligand shifts) for the regioselective cleavage and carbonylation of 4 and 9 to their mononuclear Cp(CO) 2Fe-acyl products.