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
Bis(cyclopentadienyl)vanadium
Other names
Vanadocene
Identifiers
3D model (JSmol)
ECHA InfoCard 100.149.756
UNII
Properties
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).
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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 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

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.[4]

One reaction involves carbon monoxide, leading to an ionic vanadocene derivative when performed in inert atmosphere:

Cp2V + V(CO)6 → [Cp2V(CO)2][V(CO)6]

Vanadocene is readily oxidized to the monocation when treated with a ferrocenium salt in toluene.[5]

VCp2 + [FeCp2]BR4 → [VCp2]BR4 + FeCp2 (R = Ph or 4-C6H4F)

These monocations are extremely air-sensitive and have a redox potential of -1.10 V.[5]

Vanadocene reacts with high pressures of carbon monoxide to give CpV(CO)4.[6]

References
  1. Robin D. Rogers; Jerry L. Atwood; Don Foust & Marvin D. Rausch (1981). "Crystal Structure of Vanadocene". Journal of Crystal and Molecular Structure. 11 (5–6): 183–188. doi:10.1007/BF01210393.
  2. Birmingham, J. M., A. K. Fischer, and G. Wilkinson (1955). "The Reduction of Bis-cyclopentadienyl Compounds". Naturwissenschaften. 42 (4): 96. doi:10.1007/BF00617242.CS1 maint: multiple names: authors list (link)
  3. Lorber, C. "Vanadium Organometallics." Chapter 5.01. Comprehensive Organometallic Chemistry III. Elsevier, 2007. 1-60.
  4. Jordan, Markus (2009). Azine in der Koordinationssphäre von Vanadocenderivaten unterschiedlicher Oxidationsstufen (PhD thesis). Universität Oldenburg.
  5. Calderazzo, Fausto, Isabella Ferri, Guido Pampaloni, and Ulli Englert (1999). "Oxidation Products of Vanadocene and of Its Permethylated Analogue, Including the Isolation and the Reactivity of the Unsolvated [VCp]Cation". Organometallics. 18 (13): 2452–2458. doi:10.1021/om9809320.CS1 maint: multiple names: authors list (link)
  6. King, R.B.; Stone, F.G.A. (1963). "Cyclopentadienyl Metal Carbonyls and Some Derivatives". Inorg. Synth. 7: 99. doi:10.1002/9780470132388.ch31.
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