Vanadoceen: verschil tussen versies
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Versie van 8 jan 2012 14:59
| Vanadoceen | ||||
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| Structuurformule en molecuulmodel | ||||
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| Algemeen | ||||
| Molecuulformule | (C5H5)2V V(C5H5)2 | |||
| IUPAC-naam | Bis(cyclopentadienyl)vanadium | |||
| Andere namen | Vanadoceen | |||
| Molmassa | 181,128 g/mol | |||
| CAS-nummer | 1277-47-0 | |||
| Wikidata | Q305472 | |||
| Beschrijving | Violette kristallen | |||
| Fysische eigenschappen | ||||
| Smeltpunt | 167 °C | |||
| Tenzij anders vermeld zijn standaardomstandigheden gebruikt (298,15 K of 25 °C, 1 bar). | ||||
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Vanadoceen, bis(η5-cyclopentadienyl)vanadium, is een organometaalverbinding met de formule V(C5H5)2, wat doorgaans afgekort wordt tot Cp2V. De stof vormt violette, paramagnetische kristallen. Praktisch, technische toepassingen van de stof zijn er weinig, wel is vanadoceen uitgebreid bestudeerd.
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. 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.[4]
- 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.[4]
References
- ↑ Robin D. Rogers, Jerry L. Atwood, Don Foust, and Marvin D. Rausch (1981). Crystal Stucture of Vanadocene. Journal of Crystal and Molecular Structure 11 (5–6): 183–188. DOI: 10.1007/BF01210393.
- ↑ Birmingham, J. M., A. K. Fischer, and G. Wilkinson (1955). The Reduction of Bis-cyclopentadienyl Compounds. Naturwissenschaften 42 (4): 96. DOI: 10.1007/BF00617242.
- ↑ Lorber, C. "Vanadium Organometallics." Chapter 5.01. Comprehensive Organometallic Chemistry III. Elsevier, 2007. 1-60.
- ↑ a b 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.