A “Conjugal” Consanguineous Family of Butadiynediyl-Derived Complexes: Synthesis and Electronic Ground States of Neutral, Radical Cationic, and Dicationic Iron/Rhenium C₄Species

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Abstract

The reaction of (η5-C5Me5)Re(NO)(PPh3)(C⋮CC⋮CSiMe3) and (η5-C5Me5)Fe(η2-dppe)(Cl) with KF, KPF6, and 18-crown-6 in MeOH/THF gives the heterobimetallic butadiynediyl complex (η5-C5Me5)Re(NO)(PPh3)(C⋮CC⋮C)(η2-dppe)Fe(η5-C5Me5) (9, 65%). This can be oxidized with [(η5-C5H5)2Fe]+ PF6- to the isolable radical cation 9+ PF6- and dication 92+ 2PF6-, which constitute the first conjugal consanguineous family of Cx complexes. The crystal structure of 9 is determined, and 9n+ nPF6- are characterized in detail by cyclic voltammetry (CV) and IR, NMR, near-IR, ESR, and 57Fe Mössbauer spectroscopies. The bond lengths/angles suggest some bridge polarization in 9, and CV data show that the iron and rhenium endgroups communicate strongly. The odd electron in 9+ PF6- is delocalized between the endgroups. In 92+ 2PF6-, both electronic and magnetic interactions are found between remote unpaired spins on the rhenium and iron endgroups. This antiferromagnetic coupling stabilizes the singlet cumulenic over the triplet butadiynediyl state. At room temperature, however, both isomers of 92+ 2PF6- are simultaneously present. Data are carefully compared to those of the analogous consanguineous diiron and dirhenium complexes.

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