Chemistry: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.
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]
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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(C
5H
5)(C
7H
7)
References
- ↑ 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.
- ↑ Birmingham, J. M.; A. K. Fischer; G. Wilkinson (1955). "The Reduction of Bis-cyclopentadienyl Compounds". Naturwissenschaften 42 (4): 96. doi:10.1007/BF00617242. Bibcode: 1955NW.....42Q..96B.
- ↑ Lorber, C. "Vanadium Organometallics." Chapter 5.01. Comprehensive Organometallic Chemistry III. Elsevier, 2007. 1-60.
- ↑ Jordan, Markus (2009). Azine in der Koordinationssphäre von Vanadocenderivaten unterschiedlicher Oxidationsstufen (PhD thesis). Universität Oldenburg.
- ↑ King, R. B.; Stone, F. G. A. (1963). "Cyclopentadienyl Metal Carbonyls and Some Derivatives". Inorganic Syntheses. 7. p. 99. doi:10.1002/9780470132388.ch31.
- ↑ Birmingham, John M. (1965). Synthesis of cyclopentadienyl metal compounds. Advances in Organometallic Chemistry. 2. p. 384. doi:10.1016/S0065-3055(08)60082-9. ISBN 978-0-12-031102-6.
- ↑ 7.0 7.1 Calderazzo, Fausto; Isabella Ferri; Guido Pampaloni; 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.
Template:Cyclopentadienide complexes
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