Synthesis, structure, and chemistry of hydride and alkyl niobocene ketene and ketenimine derivatives. X-ray crystal structure of [Nb(eta(5)-C5H4SiMe3)(2)(CH3)(eta(2)-(C,O)O=C=CPh2)]

[Nb(eta(5)-C5H4SiMe3)(2)Cl(eta(2)-(C,Z)-ZCCRPh)] (1a, Z = NPh, R = Ph; 1b, Z = NPh, R = Me; 1c, Z = NPh, R = Et; 1d, Z = NPh, R = H; 2, Z = O, R = Ph) reacts with Li(BEt3H) and with Grignard (RMgI) or dialkyl magnesium (R2Mg) reagents to give the hydride niobocene complexes [Nb(eta(5)-C5H4SiMe3)(2) H(eta(2)-(C,Z)-ZCCRPh)] (3a, Z = NPh, R = Ph; 3b, Z = NPh, R = Me; 3c, Z = NPh, R = Et; 3d, Z = NPh, R = H, 4, Z = O, R = Ph) and the alkyl niobocene complexes [Nb(eta(5)-C5H4SiMe3)(2)R(eta(2)-(C,Z)-ZCCR'Ph) (5a, Z = NPh, R = Me, R' = Ph; 5b, Z = NPh, R = R' = Me; 5c, Z = NPh, R = Me, R' = Et; 5d, Z = NPh, R = Me, R' = H; 6a, Z = O, R = Me, R' = Ph; 6b, Z = O, R = Et, R' = Ph) respectively. The molecular structure of 6a was determined by single-crystal diffractometry. It shows a typical bent-metallocene geometry around the niobium atom with the eta(2)(C,O) ketene and methyl groups arrayed in the plane between the two cyclopentadienyl rings. Finally, some hydride and alkyl niobocene ketenimine and ketene complexes were easily protonated with 1 equiv. of HBF4 . OEt2 giving rise, in one step, to the corresponding eta(2)-iminoacyl and eta(2)-acyl complexes [Nb(eta(5)-C5H4SiMe3)(2)Y(eta(2)-(C,Z)-ZCCRHPh)](+) +[BF4-] (7a, Y = H, Z = NPh, R = Ph; 7b, Y = H, Z = NPh, R = Me; 8a, Y = Me, Z = NPh, R = Ph; 8b, Y = Me, Z = NPh, R = Et; 9, Y = Me, Z = O, R = Ph). H-1 NMR studies on several unsymmetrical ketenimine-bearing chloro, hydride and methyl niobocene complexes containing E-Z isomeric mixtures were carried out, and it was found that intermolecular isomerization of the E and Z isomers may govern the different observed E-Z ratios. The structures of the different families of complexes were determined by spectroscopic methods.