Vanadocene
Chemical compound
From Wikipedia, the free encyclopedia
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.
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| Names | |
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| IUPAC name
Vanadocene | |
| Systematic IUPAC name
Bis(η5-cyclopentadienyl)vanadium | |
| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.149.756 |
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CompTox Dashboard (EPA) |
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| Properties | |
| V(C5H5)2 | |
| Molar mass | 181.128 g/mol |
| Appearance | Violet crystals |
| Melting point | 167 °C (333 °F; 440 K) |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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.[1] 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.[2] A modern synthesis of vanadocene that allows production in higher quantities requires treating [V2Cl3(THF)6]2[Zn2Cl6] with cyclopentadienylsodium.[3]
- 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.[4]
Likewise, high carbon monoxide pressures give CpV(CO)4.[5] That piano-stool complex can rearrange to an ionic, mixed-valence, vanadium hexacarbonyl derivative:[citation needed]
- Cp2V + V(CO)6 → [Cp2V(CO)2]+[V(CO)6]−
Vanadocene is extremely air-sensitive, and either 12% (by mass) hydrochloric acid[6] or ferrocenium in toluene will easily oxidize an electron from the complex:[7]
- 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.[7]
Related compounds
- (Cycloheptatrienyl)(cyclopentadienyl)vanadium (V(C5H5)(C7H7)