The butadienediyl-bridged complexes [eta5-Cs Me5]Fe(CO)(PPh3)]2 (micro-CH=CH-CH=CH) have been prepared and characterized by cyclic voltammetry, NMR, and X-ray crystallography. Compound 3 diastereomers showed two reversible one-electron oxidations at -0.053 approximately -0.056 V and -0.02 approximately 0.03 V, respectively. The comproportionation constant, Kc, was calculated from these measurements. Kc values are very high, 1.0 approximately 3.0 x 10(9). These values are consistent with the Robin-Day Mixed-Valence Class III.