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(contracted; show full)'Ferrocene''' is an [[organometallic compound]] with the formula Fe(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>. It is the prototypical [[metallocene]], a type of [[organometallic chemistry|organometallic]] [[chemistry|chemical]] compound consisting of two [[cyclopentadienyl complex|cyclopentadienyl]] rings bound on opposite sides of a central [[metal]] atom. Such organometallic compounds are also known as [[sandwich compound]]s.<ref>{{cite journal|
author=R. Dagani |url=http://pubs.acs.org/isubscribe/journals/cen/79/i49/html/7949sci1.html|title=Fifty Years of Ferrocene Chemistry| journal=[[Chemical and Engineering News]] |date=3 December 2001|volume= 79 |issue= 49|pages = 37–38 |format=Subscription requireddoi = 10.1002/chin.200443242}}</ref> The rapid growth of [[organometallic chemistry]] is often attributed to the excitement arising from the discovery of ferrocene and its many [[Analog (chemistry)|analogues]].

==History==
[[File:Ferrocene kealy.svg|thumb|left|Pauson and Kealy's original (incorrect) notion of ferrocene's molecular structure]]
Ferrocene was first prepared unintentionally. In 1951, Pauson and Kealy at [[Duquesne University]] reported the reaction of cyclopentadienyl magnesium bromide and [[iron(III) chloride|ferric chloride]] with the goal of oxidatively coupling the diene to prepare [[fulvalene]]. Instead, they obtained a light orange powder of "remarkable stability."<ref>{{cite journal⏎
⏎
  |author = T. J. Kealy, P. L. Pauson⏎
⏎
  |title = A New Type of Organo-Iron Compound⏎
⏎
  |journal = Nature⏎
⏎
  |year = 1951 ⏎
⏎
|volume = 168 ⏎
⏎
|pages = 1039⏎
⏎
  |doi = 10.1038/1681039b0}}</ref> This stability was accorded to the aromatic character of the negative charged cyclopentadienyls, but the sandwich structure of the η<sup>5</sup> (pentahapto) compound was not recognized by them.

[[Robert Burns Woodward]] and [[Geoffrey Wilkinson]] deduced the structure based on its reactivity.<ref>{{cite journal⏎
⏎
  |author = G. Wilkinson, M. Rosenblum, M. C. Whiting, R. B. Woodward⏎
⏎
  |title = The Structure of Iron Bis-Cyclopentadienyl⏎
⏎
  |journal = [[Journal of the American Chemical Society]]⏎
⏎
  |year = 1952⏎
⏎
|volume = 74⏎
⏎
  |pages = 2125–2126⏎
⏎
  |doi = 10.1021/ja01128a527}}</ref> Independently [[Ernst Otto Fischer]] also came to the conclusion of the sandwich structure and started to synthesize other metallocenes such as [[nickelocene]] and [[cobaltocene]].<ref>{{cite journal⏎
⏎
  |author = E. O. Fischer, W. Pfab⏎
⏎
  |title = Zur Kristallstruktur der Di-Cyclopentadienyl-Verbindungen des zweiwertigen Eisens, Kobalts und Nickels ⏎
⏎
|journal = Z.eitschrift für Naturforsch.ung B⏎
⏎
  |year = 1952⏎
⏎
  |volume = 7⏎
⏎
  |pages = 377–379⏎
⏎
  |doi =}}</ref> Ferrocene's structure was confirmed by [[Nuclear magnetic resonance|NMR]] spectroscopy and [[X-ray crystallography]].<ref>{{cite journal⏎
⏎
  |author = J. Dunitz, L. Orgel, A. Rich⏎
⏎
  |title = The crystal structure of ferrocene⏎
⏎
  |journal = [[Acta Crystallographica]]⏎
⏎
  |year = 1956⏎
⏎
  |volume = 9⏎
⏎
  |pages = 373–5⏎
375 |doi = 10.1107/S0365110X56001091}}</ref><ref>{{cite journal⏎
⏎
|author = Pierre Laszlo, Roald Hoffmann,⏎
⏎
|title = Ferrocene: Ironclad History or Rashomon Tale?⏎
⏎
  |journal = Angewandte Chemie International Edition⏎
⏎
  |year = 2000⏎
⏎
  |volume = 39⏎
⏎
  |pages = 123–124⏎
⏎
  |doi = 10.1002/(SICI)1521-3773(20000103)39:1<123::AID-ANIE123>3.0.CO;2-Z}}</ref> Its distinctive "sandwich" structure led to an explosion of interest in compounds of [[d-block]] metals with hydrocarbons, and invigorated the development of the flourishing study of organometallic chemistry. In 1973 [[Ernst Otto Fischer|Fischer]] of the [[Technische Universität München]] and [[Geoffrey Wilkinson|Wilkinson]] of [[Imperial College London]] shared a Nobel Prize for their work on metallocenes(contracted; show full)

The lack of individual bonds between the carbon atoms of the Cp ring and the Fe<sup>2+</sup> ion results in the Cp rings to freely rotate about the Cp<sub>(centroid)</sub>-Fe-Cp<sub>(centroid)</sub> axis, as observed by [[nuclear magnetic resonance]]<ref>{{cite journal
⏎
⏎
  |author = E. W. Abel, N. J. Long, K. G. Orrell, A. G. Osborne, V. Sik⏎
⏎
  |title = Dynamic NMR studies of ring rotation in substituted ferrocenes and ruthenocenes⏎
⏎
  |journal = [[Journal of Organometallic Chemistry]]⏎
⏎
  |year = 1991⏎
⏎
  |volume = 403⏎
⏎
  |pages = 195–208⏎
⏎
  |doi = 10.1016/0022-328X(91)83100-I}}</ref> and [[scanning tunneling microscopy]].<ref>{{cite journal⏎
⏎
  |author = L. F. N. Ah Qune, K. Tamada, M. Hara⏎
⏎
  |title = Self-Assembling Properties of 11-Ferrocenyl-1-Undecanethiol on Highly Oriented Pyrolitic   Graphite Characterized by Scanning Tunneling Microscopy⏎
⏎
  |journal = E-Journal of Surface Science and Nanotechnology⏎
⏎
  |year = 2008⏎
⏎
  |volume = 6⏎
⏎
  |pages = 119–123⏎
⏎
  |doi = 10.1380/ejssnt.2008.119}}</ref><ref>[http://www.jstage.jst.go.jp/article/ejssnt/6/0/119/_pdf Self-Assembling Properties of 11-Ferrocenyl-1-Undecanethiol on Highly Oriented Pyrolitic Graphite Characterized by Scanning Tunneling Microscopy]</ref>

The carbon-carbon bond distances are 1.40 Å within the five membered rings, and the Fe-C bond distances are 2.04 Å.

==Synthesis and handling properties==
(contracted; show full)ne is an [[air]]-stable orange solid that readily [[Sublimation (physics)|sublime]]s, especially upon heating in a vacuum. It is stable to temperatures as high as 400 °C.<ref>Solomons, Graham, and Craig Fryhle. Organic Chemistry. 9th ed. USA: John Wiley & Sons, Inc., 2006.</ref> The following table gives typical values of vapor pressure of ferrocene at different temperatures:<ref>{{cite journal|doi=10.1021/je050502y|title=New Static Apparatus and Vapor Pressure of Reference Materials:
     Naphthalene, Benzoic Acid, Benzophenone, and Ferrocene|year=2006|last1=Monte|first1=Manuel J. S.|last2=Santos|first2=Luís M. N. B. F.|last3=Fulem|first3=Michal|last4=Fonseca|first4=José M. S.|last5=Sousa|first5=Carlos A. D.|journal=Journal of Chemical & Engineering Data|volume=51|pages=757}}</ref>

{| class="wikitable"
|-
! pressure(Pa)
! 1
! 10
! 100
(contracted; show full)
Many phosphine derivatives of ferrocenes are known and some are used in commercialized processes. Simplest and best known is [[1,1'-Bis(diphenylphosphino)ferrocene|1,1'-bis(diphenylphosphino)ferrocene]] (dppf) prepared from dilithioferrocene. Other routes to such ligands are known. For example, in the presence of [[aluminium chloride]] Me<sub>2</sub>NPCl<sub>2</sub> and ferrocene react to give ferrocenyl dichloro[[phosphine]],<ref>{{cite journal
⏎
⏎
  |title = Ferrocene derivatives. 27. Ferrocenyldimethylphosphine⏎
| | author = G.R. Knox, P.L. Pauson and D. Willison⏎
⏎
  |journal = Organometallics⏎
⏎
  |volume = 11⏎
⏎
  |issue = 8⏎
⏎
  |pages = 2930–2933⏎
⏎
  |year = 1992⏎
⏎
  |doi = 10.1021/om00044a038⏎
⏎
  }}</ref>
while treatment with [[phenyldichlorophosphine]] under similar conditions forms ''P,P''-diferrocenyl-''P''-phenyl phosphine.<ref>{{cite journal⏎
⏎
  |author = G.P. Sollott, H.E. Mertwoy, S. Portnoy and J.L. Snead⏎
⏎
  |title = Unsymmetrical Tertiary Phosphines of Ferrocene by Friedel-Crafts Reactions. I. Ferrocenylphenylphosphines ⏎
⏎
|journal = J. Org. Chem.⏎
⏎
  |year = 1963 ⏎
⏎
|volume = 28 ⏎
⏎
|pages = 1090–1092⏎
⏎
  |doi = 10.1021/jo01039a055⏎
⏎
  }}</ref> In common with [[anisole]] the reaction of ferrocene with P<sub>4</sub>S<sub>10</sub> forms a dithiadiphosphetane disulfide.<ref>{{cite journal⏎
⏎
  |title = 2,4-Diferrocenyl-1,3-dithiadiphosphetane 2,4-disulfide; structure and reactions with catechols and [PtCl<sub>2</sub>(PR<sub>3</sub>)<sub>2</sub>](R = Et or Bun)⏎
⏎
  |author = Mark R. St. J. Foreman, Alexandra M. Z. Slawin and J. Derek Woollins⏎
⏎
  |journal = J. Chem. Soc., Dalton Trans., ⏎
⏎
|year = 1996⏎
⏎
  |pages = 3653 – 3657⏎
⏎
  |doi = 10.1039/DT9960003653⏎
⏎
}}</ref>

===Redox chemistry===
{{main|Ferrocenium}}
Unlike the majority of hydrocarbons, ferrocene undergoes a one-electron oxidation at a low potential, around 0.5 V ''vs''. a [[saturated calomel electrode]] (SCE). It is also been used as standard in electrochemistry as Fc+/Fc = 0.64 V vs. NHE. Some [[electron]] rich hydrocarbons (e.g., [[aniline]]) also are oxidized at low potentials, but only irreversibly. Oxidation of ferrocene gives a stable cation called ferrocenium. On a pr(contracted; show full)Effect of Hydroxyferrocifens on both Hormone-Dependent and Hormone-Independent Breast Cancer Cell Lines| journal=Chemistry, a European Journal| year=2003| volume=9| pages=5223–36|pmid=14613131|doi=10.1002/chem.200305024|issue=21}}</ref><ref>{{cite journal|journal=[[Chemical and Engineering News]]|date=16 September 2002| title= The Bio Side of Organometallics|author= Ron Dagani| volume = 80| issue= 37| pages = 23–29| url=http://pubs.acs.org/cen/science/8037/8037sci1.html}}</ref><ref>
⏎
⏎
{{cite journal  |author=S. Top, B. Dauer, J. Vaissermann and G. Jaouen| journal=[[Journal of Organometallic Chemistry]]| title= Facile route to ferrocifen, 1-[4-(2-dimethylaminoethoxy)]-1-(phenyl-2-ferrocenyl-but-1-ene), first organometallic analogue of tamoxifen, by the McMurry reaction|doi=10.1016/S0022-328X(97)00086-7 |year=1997| volume=541| pages= 355–361}}</ref>

===Materials chemistry===
(contracted; show full)[[ru:Ферроцен]]
[[fi:Ferroseeni]]
[[sv:Ferrocen]]
[[th:เฟอร์โรซีน]]
[[tr:Ferrosen]]
[[uk:Фероцен]]
[[ur:Ferrocene]]
[[zh:二茂铁]]