Preparation of carbonyl, halogeno, and alkyl niobocene complexes and their reactions with oxygen. Crystal structures of [Nb(η-C5H4SiMe3)2Cl2], [Nb(η-C5H4SiMe3)2(O)Me], and [Nb(η-C5H4SiMe3)2(C6F5)(CO)]
Abstract
The complexes [Nb(cp)2Cl2][cp =η-C5H5, η-C5H4SiMe3, or η-C5H3(SiMe3)2-1,3] are reduced with Na–Hg in the presence of CO to give the carbonylniobium(III) complexes [Nb(cp)2Cl(CO)]. The alkylation of these compounds using LiR, MgRX, or MgR2 leads to the alkyl derivatives [Nb(cp)2R(CO)](cp =η-C5H5 or η-C5H4SiMe3; R = Me, CH2CMe3, CH2SiMe3, CH2Ph, or C6F5). These alkyl carbonyl niobium(III) complexes react with oxygen to produce an unresolved mixture of compounds when cp =η-C5H5 whereas the complex [Nb(cp)2(O2)Me] is obtained in the reaction of [Nb(cp)2Me(PMe3)](cp =η-C5H4SiMe3) with oxygen. Similar reactions of [Nb(cp)2Cl(CO)] with O2 lead to the oxo-halogenoniobium(V) derivatives [Nb(cp)2(O)Cl][cp =η-C5H5, η-C5H4SiMe3, or η-C5H3(SiMe3)2-1,3]. However, the corresponding peroxo-chloro complex [Nb(cp)2(O2)Cl](cp =η-C5H4SiMe3) results from the reaction with oxygen of the chloro(alkyl isocyanide) niobium(III) complex and can be preparated alternatively by reaction of the dichloride with H2O2. The oxo-chloro niobium(V) complex [Nb(η-C5H4SiMe3)2(O)Cl] can be easily alkylated in reactions with LiR (R = Me, Bun, CH2CMe3, or CH2SiMe3). All these complexes were characterised by i.r., 1H and 13C n.m.r. spectroscopy and the chloro-carbonyl niobium(III) and oxo niobium(V) complexes were studied by cyclic voltammetry. The crystal structures of [Nb(η-C5H4SiMe3)2Cl2](2), [Nb(η-C5H4SiMe3)2(C6F5)(CO)](2f), and [Nb(η-C5H4SiMe3)2(O)Me](2h) have been determined by X-ray diffraction methods. Compound (2) crystallizes in the triclinic space group P1, with a= 12.680(5), b= 12.923(5), c= 6.806(3)Å, α= 97.82(2), β= 104.18(3), γ= 67.79(2)°, and Z= 2; (2h) crystallizes in the monoclinic space group P21/n, with a= 8.842(4), b= 37.108(10), c= 6.331(3)Å, β= 108.03(4)°, and Z= 4; (2f) crystallizes in the triclinic space group P, with a= 9.781(4), b= 14.440(6), c= 8.765(4)Å, α= 90.84(2), β= 85.86(2), γ= 93.90(2)°, and Z= 2. All the structures were solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least-squares methods to R= 0.0377 for 2 889 observed reflections [(2)], R= 0.0441 for 2 269 observed reflections [(2f)], and R= 0.0385 for 1 466 observed reflections [(2h)]. All structures contain a niobium atom bonded to two cyclopentadienyl rings in a η5 fashion; the co-ordination of the metal is completed by two Cl atoms in (2), by a terminal carbonyl group and a carbon atom from the C6F5 ligand in (2f), and by an oxygen atom and a carbon atom from a methyl group in (2h).