Silylene-Bridged Dinuclear Iron Complexes [Cp(OC)2Fe]2SiX2 (X = H, F, Cl, Br, I). Synthesis, Molecular Structure, Vibrational Spectroscopy, and Theoretical Studies

The 2-silylene-bridged iron complexes [Cp(OC)2Fe]2SiX2 (X = F (2), Br (4), 1 (5)) have been prepared from the 2-SiH2 functional precursor [Cp(OC)2Fe]2SiH2 (1) by hydrogen/halogen exchange, using HBF4, CBr4, and CH2l2, respectively. The fluoro- and bromo-substituted derivatives 2 and 4 are converted upon UV irradiation to the carbonyland dihalosilylene-bridged dinuclear complexes [Cp(OC)Fe]2(2-CO)(2-SiX2) (X = F (6), Br (7)) via CO elimination. All new compounds have been characterized spectroscopically, and, in addition, the molecular structure of 2, 4, and the previously reported chloro derivative [Cp(OC)2Fe]2SiCl2 (3) has been determined by single-crystal X-ray diffraction methods. For 1-5, the Fourier transform infrared and Raman spectra have been recorded and discussed, together with density functional theory calculations, which support the experimental results of the structural and vibrational analysis. The computed geometries, harmonic vibrational wavenumbers, and their corresponding Raman scattering activities are in good agreement with the experimental data. A significant dependence of the CO and Fe-Si stretching modes on the X substituents of the -silylene bridge has been observed and discussed.