Vanadocene
Vanadocene, bis vanadium, is the organometallic compound with the formula V2, commonly abbreviated Cp2V. It is a violet crystalline, paramagnetic solid. Vanadocene has relatively limited practical use, but it has been extensively studied.
Structure and bonding
V2 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 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 2 with cyclopentadienylsodium.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:
Vanadocene is extremely air-sensitive, and either 12% hydrochloric acid or ferrocenium in toluene will easily oxidize an electron from the complex:
The monocations themselves oxidize in air, having a redox potential of -1.10 V.