Synthesis of bis-silylated cyclopentadienyl niobium(IV) and (V) neutral and cationic complexes

New niobium(IV) complexes, Nb(η-C5H3RR′)2X2, R = H, R′ = SiMe3, X = Br (1), X = I (3); R = R′= SiMe3, X = Br (2), X = I (4), have been isolated in high yields from the reactions of Nb(η-C5H3RR′)2H3 and Nb(η-C5H3RR′)2X with EtBr and MeI. Both chemical and electrochemical oxidation processes of these niobium(IV) complexes produce the cationic niobium(V) compounds, [Nb(η-C5H4SiMe3)2X2]+, X = Cl (5), Br (6), I (7), which exhibit an acidic character towards nucleophilic reagents, such as Me2SiOR, to give new niobium(V) alkoxo complexes, [Nb(η-C5H4SiMe3)2Cl(OR)]+, R = CH3 (8), CH2CH3(9), CH(CH3)2 (10). Spectroscopic IR, ESR and NMR data are available for these compounds.