FERROCENYLSILATRANES - A SYNTHETIC, STRUCTURAL AND THEORETICAL INVESTIGATION

Ferrocene derivatives containing the silatranyl moiety were prepared a nd studied by NMR spectroscopy and cyclic voltammetry. Compared with t he corresponding triethoxysilanyl derivatives, the silatranes are much more easily oxidized (Delta E-1/2(ox) up to 0.26V). In order to under stand this result, theoretical calculations (extended Huckel (EH) and density functional theory (DFT)) were performed. The geometries of the four complexes were optimized using DFT calculations. The change in t he energy of the HOMO when exchanging Si(OMe)(3) for silatranyl as wel l as the transition state energy using the half-electron approach foll ow the oxidation potentials. This result can be rationalized from the Si-N anti-bonding character of the HOMO in the silatrane derivatives w hich leads to an increase in energy. Such a bond is absent in the othe r species. The prototype of this class of compounds, silatranylferroce ne, was characterized by crystal structure analysis. The Si-N distance is 2.181(2)Angstrom and thus lies in the range expected for an aromat ic substituent at silicon. The agreement between calculated and observ ed structure is quite good except for the Si-N distance, where a compa ratively large deviation was found which reflects the difference betwe en gas and solid state. A direct interaction between iron and silicon can be excluded for both structural and theoretical reasons. (C) 1997 Elsevier Science S.A.