The butadienediyl-bridged complexes [(η 5 -C 5 R 5 )Fe(dppe)] 2 (µ-CHdCHCHdCH) (R ) H, Me) and their radical cationic and dicationic forms have been prepared and characterized by cyclic voltammetry, electronic spectroscopy (UV-vis and near-IR), EPR, and X-ray crystallography (R ) Me). Comparisons with each other and with the literature complexes [(η 5 -C 5 H 5 )Fe(dppm)] 2 (µ-CHdCHCHdCH), [(η 5 -C 5 Me 5 )Fe(dppe)] 2 (µ-CtCCtC), and [(η 5 -C 5 Me 5 )-Fe(dppe)] 2 (µ-C(OMe)dCHCHdC(OMe)) have allowed for systematic evaluation of several structural variations (C 5 H 5 vs C 5 Me 5 , dppm vs dppe, µ-CHdCHCHdCH vs µ-CtCCtC, and µ-CHdCHCHdCH vs µ-C(OMe)dCHCHdC(OMe)) and their effects on spectra and electronic intermetal coupling. Some of the structural changes have opposite effects on H ab , the effective coupling parameter, and K c , the comproportionation constant. The data for the mixed-valence cations are most consistent with electronic delocalization.Many recent examples of transition metals linked with conjugated bridges have shown that such bridges can promote electronic coupling between metal centers. 1 Studies of mixed-valence (MV) ions in comparison with fully oxidized and fully reduced states have provided much insight concerning delocalization and/or intramolecular electron transfer 2 and have allowed more accurate predictions concerning potential use as molecular wires. 3 Through systematic evaluation of trends related to isolated structural variations, the role of different structural aspects has sometimes been discerned. 4 For complexes linked by conjugated hydrocarbon bridges, such systematic studies are rare. 5 We have previously described the preparation of several butadienediyl-bridged diiron complexes, [CpFeLL′] 2 (µ-CHdCHCHdCH) (1-4, Cp ) η 5 -C 5 H 5 ; Scheme 1), and the oxidation of these neutral species to dicationic and MV radical cationic species. 6 Lapinte and co-workers have reported the closely related butadiynediyl-bridged complex [Cp*Fe(dppe)] 2 (µ-CtCCtC) (7, Cp* ) η 5 -C 5 Me 5 , dppe ) Ph 2 PCH 2 CH 2 PPh 2 ) 7 and the butadienediyl-bridged complex [Cp*Fe(dppe)] 2 -(µ-C(OMe)dCHCHdC(OMe)) ( 8), 8 each also prepared in three oxidation levels. Though the MV cation forms of all of these species were found to be delocalized, class III 9 complexes, several interesting differences were

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