Synthesis, characterization and reactivity of tetracyclopentadienylniobium(IV), a precursor to organometallic derivatives of niobium(IV)

In toluene as medium, tetra(cyclopentadienyl)niobium(IV), NbCp4, has been prepared in satisfactory yields from the reaction of NaCp with: (a) Nb2C110, (b) NbCl4(THF)2, or (c) NbCp2Cl2. Tetracyclopentadienylniobium(IV) has been characterized by X-ray diffraction. Crystal data: C20H20Nb, M=353.29 g mol−1, hexagonal, space group P65 (no. 170), a=b=9.396(2), c=31.23(3) Å, V=2388(2) Å3, Z=6, dcalc=1.48 g cm−3, λ(Cu–Kα)=1.54184 Å, T=291 K, μ=62.04 cm−1, F(000)=1686. Two of the four cyclopentadienyl ligands are bonded to niobium in a pentahapto fashion, the other two being monohapto. NbCp4 undergoes cyclopentadiene elimination in the presence of species containing active protons such as Ph3SiOH or strong acids, the products being tris- or biscyclopentadienyl compounds depending on the molar ratio of the reagents.