1,2-Diethynylbenzene-Bridged [Cp*(dppe)Fe]<sup><i>n</i>+</sup> Units: Effect of Steric Hindrance on the Chemical and Physical Properties
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The binuclear complex [{Cp*(dppe)Fe–CC−}2-μ-(1,2-C6H4)] (o-1) was prepared via the bis(vinylidene) [{(Cp*(dppe)FeCCH−}2-μ-(1,2-C6H4)](PF6)2 (o-1H2(PF6)2) in good yield. The new complex was characterized by ESI-mass spectrometry, IR, multinuclear NMR, and Mössbauer spectroscopies, X-ray diffraction on a single crystal, and cyclic voltammetry. The data are consistent with a strong steric interaction between the vicinal organoiron centers responsible for the very long time of reaction for the preparation of o-1. The singly and doubly oxidized forms o-1(PF6) and o-1(PF6)2 were prepared by oxidation of o-1 with 1 and 2 equiv of ferrocenium salt. These salts were characterized by high-resolution ESI-mass spectra, XRD analyses on single crystals, and IR, Mössbauer, ESR, UV–vis, and NIR spectroscopies. In addition, the magnetic properties of compound o-1(PF6)2 were investigated by 1H and 31P NMR. The data were analyzed with the support of quantum chemistry calculations at the DFT level of theory. The radical cation o-1(PF6) belongs to class IIB of the mixed-valence classification (Hab < 1500 cm–1). The narrowness of the IVCT bands is explained by the steric hindrance, which limits the number of conformers. The singlet/triplet states ratio is independent of the temperature for the doubly oxidized complex o-1(PF6)2.
