ansa-eta-Cyclopentadienylimide derivatives of niobium

Treatment of the ansa-bridged eta-cyclopentadienylimide compound [Nb{eta(5),kappa N-C5H4(CH2)(3)N}Cl-2] 1 with MgMeBr gave the binuclear ansa-bridged eta-cyclopentadienylimide derivative [MeNb{mu-C5H4(CH2)(3)N}-{mu-NCH(CH2)(2)C5H4}NbMe2] 2. The crystal structure of 2 has been determined. Detailed H-1 and C-13 NMR studies showed that 2 undergoes an interesting fluxional process involving interchange of two methyl groups under an ansa arch. Reaction of 1 with Na(C5H5) gave [Nb{eta(5),kappa N-C5H4(CH2)(3)N}(eta(5)-C5H5)(eta(1)-C5H5)] 3, which is also fluxional and undergoes diverse dynamic processes including exchange between eta(1)- and eta(5)-cyclopentadienyl rings. The compounds [Nb{eta(5),kappa N-C5H4(CH2)(3)N}(CH2Ph)(2)] and [Nb{eta(5),kappa N-C5H4(CH2)(3)N}{CH2C(Me)CH2}(2)] have also been prepared.