Vanadocene

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.

Vanadocene

Names
IUPAC name Vanadocene
Systematic IUPAC name Bis(η5-cyclopentadienyl)vanadium
Identifiers
CAS Number	1277-47-0 Y
3D model (JSmol)	Interactive image
ECHA InfoCard	100.149.756
PubChem CID	18667909
UNII	GZ5K54AP9L Y
CompTox Dashboard (EPA)	DTXSID10925957
SMILES c1ccc[cH-]1.c2ccc[cH-]2.[V+2]
Properties
Chemical formula	V(C5H5)2
Molar mass	181.128 g/mol
Appearance	Violet Crystal
Melting point	167 °C (333 °F; 440 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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 D_5d 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)