Vanadocene
Vanadocene, bis(η-cyclopentadienyl) vanadium, is the organometallic compound with the formula V(CH), commonly abbreviated CpV. It is a violet crystalline, paramagnetic solid. Vanadocene has relatively limited practical use, but it has been extensively studied. Structure and bonding. V(CH) 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 D 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 [VCl(THF)][ZnCl] with cyclopentadienylsodium. Properties. Vanadocene is a reactive molecule. As it only has 15 valence electrons available, it readily reacts with many ligands. With alkynes, for example, it reacts to yield the corresponding vanadium-cyclopropene complexes. One reaction involves carbon  monoxide, leading to an ionic vanadocene derivative when performed in inert atmosphere: Vanadocene is readily oxidized to the monocation when treated with a ferrocenium salt in toluene. These monocations are extremely air-sensitive and have a redox potential of -1.10 V. Vanadocene reacts with high pressures of carbon monoxide to give CpV(CO).