1,4-Dimethoxybutadienediyl-Bridged Diiron Compounds in Three Oxidation States: Evaluation of Delocalization Effects

Abstract

The binuclear iron complexes [Cp*(PMe3)(CO)Fe–C(OCH3)═CH–CH═C(OCH3)–Fe(PMe3)(CO)Cp*] (1meso and 1dl) were prepared by double deprotonation of their known parents [Cp*(PMe3)(CO)Fe═C(OCH3)CH2–CH2–C(OCH3)═Fe(PMe3)(CO)Cp*](PF6)2 (5meso and 5dl) and were isolated in good yield (90%). These complexes were characterized by ESI-mass spectrometry, IR and multinuclear NMR spectroscopy, and cyclic voltammetry. The singly and doubly oxidized forms 1meso(PF6)n and 1dl(PF6)n (n = 1, 2) were prepared by oxidation of the parent neutral complexes with 1 and 2 equiv of ferrocenium salt (93–100% yield). The related complex [Cp*(dppe)Fe–C(OCH3)═CH–CH═C(OCH3)–Fe(dppe)Cp*](PF6) (2(PF6)) was obtained by reduction of the known dicationic derivative [Cp*(dppe)Fe–C(OCH3)═CH–CH═C(OCH3)–Fe(dppe)Cp*](PF6) (2(PF6)2) with 1 equiv of cobaltocene (100% yield). Multinuclear NMR spectroscopy allowed us to establish the diiron(II) conjugated μ-bis(carbene) structure for 1meso(PF6)2 and 1dl(PF6)2. In the case of the meso derivative, 1H NMR r...