DINUCLEAR AND TETRANUCLEAR SILYL-BRIDGED FERROCENES - SYNTHESIS, CYCLOVOLTAMMETRY AND CHEMICAL OXIDATION

The reaction of 4,4,8,8-tetramethyltetrahydro-4,8-disila-s-indacenediyl dianion (L, 1) and cyclopentadienyl anion (Cp) with solvated FeCl2 gave the bridged dinuclear ferrocenes anti- and syn-CpFeLFeCp (2a and 2b), the trinuclear ferrocenes anti, anti- and anti,syn-CpFeLFeLFeCp (3a and 3b), and the tetranuclear ferrocenes anti,anti,anti- and anti,syn,anti-CpFeLFeLFeLFeCp (4a and 4b) together with four ferrocene-type side products which were partly unknown before. The molecules were characterized by mass spectroscopy and H-1, C-13, and Si-29 NMR including stereochemical details. The anti/syn-isomer ratio did not change significantly with the temperature and showed that the anti-arrangement is preferred. 2a/b, 3a/b, 4a, and CpFe(C5H4SiMe2C5H4)FeCp (7) gave cyclovoltammograms (CV) which proved that all ferrocene units could be oxidized as reversibly as ferrocene itself. The resolution of the CV waves was better in propionitrile than in THF and changed with the temperature. The redox potentials were mainly influenced by the substitution of the ferrocene units and by their distance from each other. It could be shown that proper choice of the bridges allows to predetermine whether a molecule with three and more ferrocene units is first oxidized in the center or the periphery. Intermolecular electron transfer was observed in THF at higher concentrations. Reaction of 2a with HBF4 gave [(FMe2Si)2Cp]2Fe among others, whereas with I2 an oligoiodide of [2a]+, and with AgPF6.2MeCN paramagnetic [2a]PF6 was obtained. The latter gave Si-29, C-13, and H-1 spectra showing electron exchange between ferrocene and ferricenium units.