Vanadocene

V(C5H5)2 is a metallocene, a class of organometallic compounds that typically have a metal ion sandwiched between two cyclopentadienyl rings. In the solid state, the molecule has D5d symmetry. The vanadium(II) center resides equidistant between the center of the two cyclopentadienyl rings at a crystallographic center of inversion. The average V-C bond distance is 226 pm. The Cp rings of vanadocene are dynamically disordered at temperatures above 170 K and are only fully ordered at 108 K. == Preparation ==

Vanadocene was first prepared in 1954 by Birmingham, Fischer, and Wilkinson via a reduction of vanadocene dichloride with aluminum hydride, after which vanadocene was sublimed in vacuum at 100 ˚C. A modern synthesis of vanadocene that allows production in higher quantities requires treating [V2Cl3(THF)6]2[Zn2Cl6] with cyclopentadienylsodium. : 2 [V2Cl3(THF)6]2[Zn2Cl6] + 8 NaCp + THF → 4 Cp2V == Properties ==

With only 15 valence electrons, vanadocene is highly reactive. For example, it adds alkynes to yield the corresponding vanadium-cyclopropene complexes. : Likewise, high carbon monoxide pressures give CpV(CO)4. That piano-stool complex can rearrange to an ionic, mixed-valence, vanadium hexacarbonyl derivative: :Cp2V + V(CO)6 → [Cp2V(CO)2]+[V(CO)6]− Vanadocene is extremely air-sensitive, and either 12% (by mass) hydrochloric acid or ferrocenium in toluene will easily oxidize an electron from the complex: :VCp2 + [FeCp2]BR4 → [VCp2]BR4 + FeCp2 (R = Ph or 4-C6H4F) The monocations themselves oxidize in air, having a redox potential of -1.10 V. :VCp2 + MeI → VCp2I + Me2 ==Related compounds==

• (Cycloheptatrienyl)(cyclopentadienyl)vanadium () • Vanadocene dichloride == References ==