Vanadocene

{{Chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 425546122 | ImageFile = Vanadocen.svg | ImageSize = 130px | ImageAlt = | IUPACName = Vanadocene | OtherNames = | SystematicName = Bis(η5-cyclopentadienyl)vanadium | Section1 = {{Chembox Identifiers | CASNo_Ref = {{cascite|correct|??}} | CASNo = 1277-47-0 | ChemSpiderID = 21188623 | EINECS = 620-850-1 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = GZ5K54AP9L | PubChem = 18667909 | StdInChI=1S/2C5H5.V/c2*1-2-4-5-3-1;/h2*1-5H;/q2*-1;+2 | StdInChIKey = YXQWGVLNDXNSJJ-UHFFFAOYSA-N | SMILES = c1ccc[cH-]1.c2ccc[cH-]2.[V+2] }} | Section2 = {{Chembox Properties | Formula = V(C5H5)2 | MolarMass = 181.128 g/mol | Appearance = Violet crystals | Density = | MeltingPtC = 167 | BoilingPt = | Solubility = }} | Section3 = {{Chembox Hazards | GHS_ref=[https://echa.europa.eu/substance-information/-/substanceinfo/100.149.756] | GHSPictograms = {{GHS02}}{{GHS06}} | GHSSignalWord = Danger | HPhrases = {{H-phrases|}} | PPhrases = {{P-phrases|}} | MainHazards = | FlashPt = | AutoignitionPt = }} }} '''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.<ref>{{cite journal |author1=Robin D. Rogers |author2=Jerry L. Atwood |author3=Don Foust |author4=Marvin D. Rausch |name-list-style=amp | title = Crystal Structure of Vanadocene | journal = Journal of Crystal and Molecular Structure | volume = 11 | year = 1981 | pages = 183–188 | doi = 10.1007/BF01210393 | issue = 5–6|s2cid=93048446 }}</ref> 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.<ref>{{cite journal | author1 = Birmingham, J. M. | author2 = A. K. Fischer | author3 = G. Wilkinson | title = The Reduction of Bis-cyclopentadienyl Compounds | journal = Naturwissenschaften | volume = 42 | issue = 4 | year = 1955 | pages = 96 | doi = 10.1007/BF00617242| bibcode = 1955NW.....42Q..96B | s2cid = 44523847 }}</ref> A modern synthesis of vanadocene that allows production in higher quantities requires treating [V2Cl3(THF)6]2[Zn2Cl6] with cyclopentadienylsodium.<ref>Lorber, C. "Vanadium Organometallics." Chapter 5.01. Comprehensive Organometallic Chemistry III. Elsevier, 2007. 1-60.</ref> : 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.<ref>{{Cite thesis|title=Azine in der Koordinationssphäre von Vanadocenderivaten unterschiedlicher Oxidationsstufen|url=https://oops.uni-oldenburg.de/828/|publisher=Universität Oldenburg|date=2009|degree=PhD|first=Markus|last=Jordan}}</ref> :289x289px Likewise, high carbon monoxide pressures give CpV(CO)4.<ref name = RBK>{{cite book |author1= King, R. B. |author2=Stone, F. G. A. |chapter=Cyclopentadienyl Metal Carbonyls and Some Derivatives |title=Inorganic Syntheses | volume = 7 | year = 1963 | page = 99|doi=10.1002/9780470132388.ch31 }}</ref> That piano-stool complex can rearrange to an ionic, mixed-valence, vanadium hexacarbonyl derivative:{{cn|date=April 2025}} :Cp2V + V(CO)6 → [Cp2V(CO)2]+[V(CO)6]−

Vanadocene is extremely air-sensitive, and either 12% (by mass) hydrochloric acid<ref>{{cite book|doi=10.1016/S0065-3055(08)60082-9|title=Synthesis of cyclopentadienyl metal compounds|first=John M.|last=Birmingham|series=Advances in Organometallic Chemistry |date=1965 |volume=2 |page=384 |isbn=978-0-12-031102-6 }}</ref> or ferrocenium in toluene will easily oxidize an electron from the complex:<ref name="five">{{cite journal | author1 = Calderazzo, Fausto | author2 = Isabella Ferri | author3 = Guido Pampaloni | author4 = Ulli Englert | title = Oxidation Products of Vanadocene and of Its Permethylated Analogue, Including the Isolation and the Reactivity of the Unsolvated [VCp]Cation | journal = Organometallics | doi = 10.1021/om9809320 | year = 1999 | volume = 18 | issue = 13 | pages = 2452–2458}}</ref> :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.<ref name="five" />

Halocarbons oxidize vanadocene to the corresponding monohalide, e.g.:<ref>{{cite journal|doi=10.1002/recl.19610800805|journal=Recueil des Travaux Chimiques des Pays-Bas|title=Studies in transition metal chemistry, part II: The addition of organic halides to bis-cyclopentadienyl vanadium(II)|first1=H. J.|last1=de Liefde Meijer|first2=M. J.|last2=Janssen|first3=G. J. M.|last3=van der Kerk|volume=80|issue=8|pp=831–845}}</ref> :VCp2 + MeI → VCp2I + Me2

==Related compounds== *(Cycloheptatrienyl)(cyclopentadienyl)vanadium ({{chem2|V(C5H5)(C7H7)}}) *Vanadocene dichloride

== References == {{Reflist}} {{Vanadium compounds}} {{Cyclopentadienide complexes}} Category:Metallocenes Category:Organovanadium compounds Category:Cyclopentadienyl complexes