SYNTHESIS AND CHARACTERIZATION OF NEW SILYL NIOBOCENE COMPLEXES - X-RAY MOLECULAR-STRUCTURE OF D(O) NB(ETA(5)-C(5)H(4)SIME(3))(2)(H)(2)(SIPH(2)H)

Thermal treatment of Nb(eta(5)-C(5)H(5)SiMe(3))(2)(H)(3) (1) with orga nosilicon, hydrides (HSiR(3)) affords bis((trimethylsilyl)cyclopentadi enyl)niobium dihydride silyl complexes, Nb(eta(5)-C(5)H(5)SiMe(3))(2)( H)(2)(SiR(3)), SiR(3) = SiMe(2)Ph (2), SiMePh(2) (3), SiPhH(2) (4), Si Ph(2)H (5), or SiPh(3) (6), in excellent yields. Spectroscopic data in dicate the presence of only one of two possible structural isomers in which the silyl substituent is central in the equatorial plane with a symmetrical structure. Compound 5 has been characterized by X-ray diff raction: monoclinic group P2(1)/n, with alpha = 13.233(4) Angstrom, b = 20.843(6) Angstrom, c = 11.043(7) Angstrom, beta = 99.17(2)degrees, V = 3007(2) Angstrom(3), Z = 4, D-calcd = 1.221 g/mL, R = 0.0543, and R(w) = 0.0570. The coordination polyhedron may be described as a disto rted tetrahedron with a centered edge. The complex adopts a ''bent san dwich'' coordination with the two hydrides flanking either side of the Nb-Si bond (2.616(3) Angstrom).