The Crystal and Molecular Structure of Hydridobis(trichlorosilyl)carbonyl-pi-cyclopentadienyliron, (pi-C5H5)FeH(SiCl3)(2)(CO)

The crystal structure of hydridobis(trichlorosilyl)carbonyl-r-cyclopentadienyliron, (,r-051-13)FeH(SiCl3)(2)(CO), has been determined by X-ray diffraction methods. A monoclinic unit cell of dimensions a = 7.493 (5) angstrom, b = 11.867 (9) angstrom, c = 8.651 (5) angstrom, and beta = 99.73 (2)degrees contains two monomeric molecules; the observed and calculated densities are, respectively, 1.88 (2) and 1.835 g cm(-3), and the space group is C-2-P2(1). The structure has been refined by least-squares methods to a conventional R factor of 0.041 over 1245 counter-diffractometric data. The absolute configuration of the molecules in the crystal used in the analysis has been determined by least-squares methods and Bijvoet ratio tests. The coordination polyhedron around the Fe atom can be regarded as a distorted tetragonal pyramid, with the centroid of the cyclopentadienyl ring at the apex and the remaining ligands in the basal plane. The Fe atom is displaced from the basal plane toward the ring. The two Fe-Si distances are equal at 2.252 (3) angstrom. This is the first determination of the length of such a bond. Structural data on transition metal-silicon bonds are summarized and arguments are presented in favor of some d(pi)-d(pi) back-bonding being involved in these bonds.