Vanadocene, bis(η5-cyclopentadienyl) vanadium, is the organometallic compound with the formula V(C5H5)2, 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
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..
Related compounds
- (Cycloheptatrienyl)(cyclopentadienyl)vanadium (V(C5H5)(C7H7)
References
