Intermetal Coupling in [(η⁵-C₅R₅)Fe(dppe)]₂(μ-CHCHCHCH) and in Their Dicationic and Monocationic Mixed-Valence Forms

Abstract

The butadienediyl-bridged complexes [(η5-C5R5)Fe(dppe)]2(μ-CHCHCHCH) (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 [(η5-C5H5)Fe(dppm)]2(μ-CHCHCHCH), [(η5-C5Me5)Fe(dppe)]2(μ-C⋮CC⋮C), and [(η5-C5Me5)Fe(dppe)]2(μ-C(OMe)CHCHC(OMe)) have allowed for systematic evaluation of several structural variations (C5H5 vs C5Me5, dppm vs dppe, μ-CHCHCHCH vs μ-C⋮CC⋮C, and μ-CHCHCHCH vs μ-C(OMe)CHCHC(OMe)) and their effects on spectra and electronic intermetal coupling. Some of the structural changes have opposite effects on Hab, the effective coupling parameter, and Kc, the comproportionation constant. The data for the mixed-valence cations are most consistent with electronic delocalization.