Revision 6001668 of "User:Barras/Ferrocene" on simplewiki

{{chembox
| verifiedrevid = 396489042
| ImageFileL1 = Ferrocene.svg
| ImageSizeL1 = 80 px
| ImageFileR1 = Ferrocene-from-xtal-3D-balls.png
| ImageSizeR1 = 120 px
| ImageFile2 = Photo of Ferrocene (powdered).JPG
| ImageSize2 = 220 px
| ImageName2 = Powdered Ferrocene
| IUPACName = ferrocene, bis(η<sup>5</sup>-cyclopentadienyl)iron
| OtherNames = dicyclopentadienyl iron 
| Section1 = {{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 7329
| InChIKey = KTWOOEGAPBSYNW-UHFFFAOYAZ
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/2C5H5.Fe/c2*1-2-4-5-3-1;/h2*1-5H;/q2*-1;+2
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = KTWOOEGAPBSYNW-UHFFFAOYSA-N
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 102-54-5
| PubChem = 11985121
| ChEBI = 30672
| SMILES = [cH-]1cccc1.[cH-]1cccc1.[Fe+2]
| InChI = 1/2C5H5.Fe/c2*1-2-4-5-3-1;/h2*1-5H;/q2*-1;+2
}}
| Section2 = {{Chembox Properties
| Formula = C<sub>10</sub>H<sub>10</sub>Fe
| MolarMass = 186.04 g/mol
| Appearance = light orange powder
| Density = 1.107 g/cm<sup>3</sup> (0°C), 1.490 g/cm<sup>3</sup> (20 °C)<ref>{{cite web|url=http://www.chemicalbook.com/ProductMSDSDetailCB1414721_EN.htm|title=Ferrocene(102-54-5)|accessdate=3 February 2010}}</ref>
| MeltingPt = 174 °C
| BoilingPt = 249 °C
| Solubility = Insoluble in water, soluble in most organic solvents
 }}
| Section3 = {{Chembox Hazards
| MainHazards = 
| FlashPt = 
| Autoignition = 
 }}
| Section8 = {{Chembox Related
| OtherCpds = [[cobaltocene]], [[nickelocene]], [[chromacene]], [[bis(benzene)chromium]]}}
}}

'''Ferrocene''' is an [[Organometallic chemistry|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|doi = 10.1002/chin.200443242|title = Ferrocene: 50 Years of Transition Metal Organometallic Chemistry — From Organic and Inorganic to Supramolecular Chemistry|year = 2004|last1 = Federman Neto|first1 = Alberto|last2 = Pelegrino|first2 = Alessandra Caramori|last3 = Darin|first3 = Vitor Andre|journal = ChemInform|volume = 35|issue = 43}}</ref> The rapid growth of [[organometallic chemistry]] is often attributed to the excitement arising from the discovery of ferrocene and its many [[Structural analog|analogue]]s.

==History==
[[File:Ferrocene kealy.svg|thumb|left|Pauson and Kealy's original (incorrect) notion of ferrocene's molecular structure<ref name = "Pauson_Kealy" />]]
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 name = "Pauson_Kealy">{{cite journal |author = T. J. Kealy, P. L. Pauson |title = A New Type of Organo-Iron Compound |journal = [[Nature (journal)|Nature]] |year = 1951 |volume = 168 |pages = 1039 |doi = 10.1038/1681039b0 |issue=4285}}</ref><ref>A second group independently discovered ferrocene.  See:  S. A. Miller, J. A. Tebboth, and J. F. Tremaine (1952) "Dicyclopentadienyliron," ''Journal of the Chemical Society'' (London) , pages 632-635.  See also:  Pierre Laszlo and Roald Hoffmann (2000) "[http://www.roaldhoffmann.com/pn/modules/Downloads/docs/Ferrocene.pdf Ferrocene:  Ironclad History of Rashomon Tale?]," ''Angewandte Chemie'' (International Edition), vol. 39, no. 1, pages 123-124.</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 |issue = 8}}</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 = Zeitschrift für Naturforschung B |year = 1952 |volume = 7 |pages = 377–379 |doi =}}</ref><ref>A third group independently determined the structure of ferrocene.  See:  P. F. Eiland and R. Pepinsky (1952) "X-ray examination of iron biscyclopentadienyl," ''Journal of the American Chemical Society'', vol. 74, page 4971.  See also:  Pierre Laszlo and Roald Hoffmann (2000) "[http://www.roaldhoffmann.com/pn/modules/Downloads/docs/Ferrocene.pdf Ferrocene:  Ironclad History of Rashomon Tale?]," ''Angewandte Chemie'' (International Edition), vol. 39, no. 1, pages 123-124.</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 = 373–375 |doi = 10.1107/S0365110X56001091 |issue = 4}}</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 and other aspects of organometallic chemistry.<ref>{{cite web |url=http://nobelprize.org/nobel_prizes/chemistry/laureates/1973/press.html |title= Press Release: The Nobel Prize in Chemistry 1973 |year= 1973 |publisher= The Royal Swedish Academy of Sciences}}</ref>

==Structure and bonding==
The iron atom in ferrocene is normally assigned to the +2 oxidation state, as can be shown using [[Mössbauer spectroscopy]]. Each cyclopentadienyl (Cp) ring is then allocated a single negative charge, bringing the number of π-electrons on each ring to six, and thus making them [[Aromaticity|aromatic]]. These twelve electrons (six from each ring) are then shared with the metal via [[hapticity|haptic]] covalent bonding, which, when combined with the six ''d''-electrons on Fe<sup>2+</sup>, results in the complex having an [[18-Electron rule|18-electron]] configuration.

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 microscope|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==
The first reported<ref>{{cite journal|year=1951|last1=Kealy|first1=T. J.|last2=Pauson|first2=P. L.|journal=[[Nature (journal)|Nature]]|volume=168|pages=1039}}</ref> synthesis of ferrocene used the [[Grignard reaction|Grignard reagent]] cyclopentadienyl magnesium bromide, which can be prepared by reacting [[cyclopentadiene]] with magnesium and [[bromoethane]] in [[anhydrous]] [[benzene]]. [[Iron(II) chloride]] is then suspended in anhydrous [[diethyl ether]] and added to the Grignard reagent.  The reaction sequence is:

:2 C<sub>5</sub>H<sub>5</sub>MgBr + FeCl<sub>2</sub> &rarr; Fe(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub> + MgCl<sub>2</sub> + MgBr<sub>2</sub>

Numerous other syntheses have been reported, including the direct reaction of [[gas]]-phase cyclopentadiene with metallic iron<ref>{{cite journal|doi=10.1021/ja01636a080|year=1954|last1=Wilkinson|first1=G.|authorlink1=Geoffrey Wilkinson|last2=Pauson|first2=P. L.|last3=Cotton|first3=F. A.|journal=[[J. Am. Chem. Soc.]]|volume=76|pages=1970|issue=7}}</ref> at 350 °C or with [[iron pentacarbonyl]].<ref>{{cite journal|doi=10.1002/9780470166024.ch1|year=1959|last1=Wilkinson|first1=G.|authorlink1=Geoffrey Wilkinson|last2=Cotton|first2=F. A.|title=Cyclopentadienyl and Arene Metal Compounds|journal=Progress in Inorganic Chemistry|volume=1|pages=1–124}}</ref>
[[Image:Ferrocene 3d model 2.png|thumb|right|A space-filling model of the [[staggered conformation]] of ferrocene.]]

:Fe + 2 C<sub>5</sub>H<sub>6</sub>(g) &rarr; Fe(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub> + H<sub>2</sub>(g)

:Fe(CO)<sub>5</sub> + 2 C<sub>5</sub>H<sub>6</sub>(g) &rarr; Fe(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub> + 5 CO(g) + H<sub>2</sub>(g)

More efficient preparative methods are generally a modification of the original [[transmetalation]] sequence using either commercially available [[sodium cyclopentadienide]]<ref>{{OrgSynth|title = Ferrocene|author = [[Geoffrey Wilkinson]]|collvol = 4|collvolpages = 473|year = 1963|prep = cv4p0473}}</ref> or freshly [[dicyclopentadiene|cracked]] cyclopentadiene and [[potassium hydroxide]]<ref>Jolly, W. L., The Synthesis and Characterization of Inorganic Compounds, Prentice-Hall: New Jersey, 1970.</ref> with anhydrous iron(II) chloride in ethereal solvents:

:2 NaC<sub>5</sub>H<sub>5</sub> + FeCl<sub>2</sub> → Fe(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub> + 2 NaCl

:FeCl<sub>2</sub>.4H<sub>2</sub>O + 2 C<sub>5</sub>H<sub>6</sub> + 2 KOH &rarr; Fe(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub> + 2 KCl + 6 H<sub>2</sub>O

Direct transmetalation can also be used to prepare ferrocene from other metallocenes, such as [[manganocene]]:<ref>{{cite journal |last1= Wilkinson|first1= G.|authorlink1= Geoffrey Wilkinson|last2= Cotton|first2= F. A.|last3= Birmingham|first3= J. M.|year= 1956|title= On manganese cyclopentadienide and some chemical reactions of neutral bis-cyclopentadienyl metal compounds|journal= J. Inorg. Nucl. Chem.|volume= 2|issue= 2|pages= 95|url= |doi=10.1016/0022-1902(56)80004-3 }}</ref>

:FeCl<sub>2</sub> + Mn(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub> &rarr; MnCl<sub>2</sub> + Fe(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>

As expected for a symmetric and uncharged species, ferrocene is soluble in normal organic solvents, such as benzene, but is insoluble in water. Ferrocene is an [[air]]-stable orange solid that readily [[Sublimation (phase transition)|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|issue=2}}</ref>

{| class="wikitable"
|-
! pressure(Pa)
! 1
! 10
! 100
|-
| temperature(K)
| 298
| 323
| 353
|}

==Reactions==
===With electrophiles===
Ferrocene undergoes many reactions characteristic of aromatic compounds, enabling the preparation of substituted derivatives. A common undergraduate experiment is the [[Friedel-Crafts reaction]] of ferrocene with [[acetic anhydride]] (or [[acetyl chloride]]) in the presence of [[phosphoric acid]] as a catalyst.
[[Image:FcGen'l.png|400px|thumb|center|Important reactions of ferrocene with electrophiles and other reagents.]]

===Lithiation===
Ferrocene reacts readily with [[Butyllithium|butyl lithium]] to give 1,1'-dilithioferrocene, which in turn is a versatile [[nucleophile]]. But reaction of Ferrocene with [[Tert-Butyllithium|t-BuLi]] produces monolithioferrocene only.<ref>F Rebierea, O Samuela and H.B Kagan "A convenient method for the preparation of monolithioferrocene" Tetrahedron Letters Volume 31, Issue 22, 1990, Pages 3121-3124. {{DOI|10.1016/S0040-4039(00)94710-5}}</ref> These approaches are especially useful methods to introduce main group functionality, e.g. using S8, chlorophosphines, chlorosilanes. The strained compounds undergo [[ring-opening polymerization]].<ref>David E. Herbert, Ulrich F. J. Mayer, Ian Manners “Strained Metallocenophanes and Related Organometallic Rings Containing pi-Hydrocarbon Ligands and Transition-Metal Centers” Angew. Chem. Int. Ed. 2007, volume 46, 5060 - 5081. {{DOI|10.1002/anie.200604409}}</ref>

[[Image:FcLi2chem.png|450px|thumb|center|Some transformations of dilithioferrocene.]]

===Phosphorus derivatives===
Many phosphine derivatives of ferrocenes are known and some are used in commercialized processes.<ref name=Stepnicka>Petr Stepnicka "Ferrocenes: Ligands, Materials and Biomolecules" J. Wiley, Hoboken, 2008. ISBN 0470035854</ref> Simplest and best known is [[1,1'-Bis(diphenylphosphino)ferrocene|1,1'-bis(diphenylphosphino)ferrocene]] (dppf) prepared from dilithioferrocene.  For example, in the presence of [[aluminium chloride]] Me<sub>2</sub>NPCl<sub>2</sub> and ferrocene react to give ferrocenyl dichlorophosphine,<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> whereas treatment with [[dichlorophenylphosphine|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 |issue = 4 }}</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 |issue = 18}}</ref>

===Redox chemistry===
{{main|Ferrocenium}}
Unlike the majority of organic compounds, 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. SHE. Some [[electron]]-rich organic compounds (e.g., [[aniline]]) also are oxidized at low potentials, but only irreversibly. Oxidation of ferrocene gives a stable cation called ferrocenium. On a preparative scale, the oxidation is conveniently effected with FeCl<sub>3</sub> to give the blue-colored ion, [Fe(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>]<sup>+</sup>, which is often isolated as its [[hexafluorophosphate|PF<sub>6</sub><sup>−</sup>]] salt. Alternatively, [[silver nitrate]] may be used as the oxidizer.

Ferrocenium salts are sometimes used as oxidizing agents, in part because the product ferrocene is fairly inert and readily separated from ionic products.<ref>{{cite journal|author=N. G. Connelly, W. E. Geiger| title=Chemical Redox Agents for Organometallic Chemistry|journal=[[Chemical Reviews]]|year= 1996| volume= 96| pages= 877–910| doi=10.1021/cr940053x| pmid=11848774|issue=2}}</ref> Substituents on the cyclopentadienyl ligands alters the redox potential in the expected way: electron withdrawing group such as a carboxylic acid shift the potential in the [[anodic]] direction (''i.e.'' made more positive), whereas electron releasing groups such as [[methyl]] groups shift the potential in the [[Cathode|cathodic]] direction (more negative). Thus, [[decamethylferrocene]] is much more easily oxidised than ferrocene. Ferrocene is often used as an [[internal standard]] for calibrating redox potentials in non-aqeous [[electrochemistry]].

==Stereochemistry==
[[Image:Planar chiral ferrocene derivative.PNG|thumb|right|A planar chiral ferrocene derivative]]
A variety of substitution patterns are possible with ferrocene including substition at one or both of the rings. The most common substitution patterns are 1-substituted (one substituent on one ring) and 1,1'-disubstituted (one substituent on each ring). Usually the rings rotate freely, which simplifies the isomerism. Disubstituted ferrocenes can exist as either 1,2-, 1.3- or 1,1'- isomers, none of which are interconvertible. Ferrocenes that are asymmetrically disubstituted on one ring are chiral - for example [CpFe(EtC<sub>5</sub>H<sub>3</sub>Me)] is chiral but [CpFe(C<sub>5</sub>H<sub>3</sub>Me<sub>2</sub>)] is achiral.  This [[planar chirality]] arises despite no single atom being a [[stereocenter|stereogenic centre]].  The substituted ferrocene shown at right (a 4-(dimethylamino)pyridine derivative) has been shown to be effective when used for the [[kinetic resolution]] of [[racemic]] secondary [[alcohol]]s.<ref>{{cite journal |last1= Ruble|first1= J. C.|last2= Latham|first2= H. A.|last3= Fu|first3= G. C.|year= 1997|title= Effective Kinetic Resolution of Secondary Alcohols with a Planar-Chiral Analogue of 4-(dimethylamino)pyridine. Use of the Fe(C<sub>5</sub>Ph<sub>5</sub>) Group in Asymmetric Catalysis|journal= [[J. Am. Chem. Soc.]]|volume= 119|issue= 6|pages= 1492–1493|url= |doi= 10.1021/ja963835b}}</ref>

==Applications of ferrocene and its derivatives==
Ferrocene and its numerous derivatives have no large-scale applications, but have many niche uses that exploit the unusual structure (ligand scaffolds, pharmaceutical candidates), robustness (anti-knock formulations, precursors to materials), and redox (reagents and redox standards).

===Fuel additives===
Ferrocene and its derivatives are [[antiknock agent]]s used in the fuel for [[petrol engine]]s; they are safer than [[tetraethyllead]], previously used.<ref>[http://www.osd.org.tr/14.pdf Application of fuel additives]</ref> It is possible to buy at [[Halfords]] in the UK, a petrol additive solution which contains ferrocene which can be added to [[unleaded petrol]] to enable it to be used in [[vintage car]]s which were designed to run on leaded petrol.<ref>{{US patent|4104036}}</ref> The [[iron]] containing deposits formed from ferrocene can form a [[conductive]] coating on the [[spark plug]] surfaces.

===Pharmaceutical===
Some ferrocenium salts exhibit anticancer activity, and an experimental drug has been reported which is a ferrocenyl version of [[tamoxifen]].<ref name = top2003 /> The idea is that the tamoxifen will bind to the [[estrogen]] binding sites, resulting in a cytotoxicity effect.<ref name=top2003>{{cite journal|author=S. Top, A. Vessières, G. Leclercq, J. Quivy, J. Tang, J. Vaissermann, M. Huché and G. Jaouen| title=Synthesis, Biochemical Properties and Molecular Modelling Studies of Organometallic Specific Estrogen Receptor Modulators (SERMs), the Ferrocifens and Hydroxyferrocifens: Evidence for an Antiproliferative 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===
Ferrocene, being readily decomposed to iron nanoparticles, can be used as a catalyst for the production of carbon nanotubes.<ref>Devin Conroya, Anna Moisalab, Silvana Cardosoa, Alan Windleb and John Davidson,''Chemical Engineering Science'',2010,'''65''',2965-2977</ref> Due to the fact that many organic reactions can be used to modify ferrocenes, it is the case that [[vinyl]] ferrocene can be made. The vinyl ferrocene can be made by a [[Wittig reaction]] of the [[aldehyde]], a [[phosphonium salt]] and [[sodium hydroxide]].<ref>Liu, Wan-yi; Xu, Qi-hai; Ma, Yong-xiang; Liang, Yong-min; Dong, Ning-li; Guan, De-peng,''J. Organomet. Chem.'', 2001, '''625''', 128 - 132</ref> The vinyl ferrocene can be converted into a polymer which can be thought of as a ferrocenyl version of [[polystyrene]] (the phenyl groups are replaced with ferrocenyl groups).

===As a ligand scaffold===
Chiral ferrocenyl [[phosphine]]s are employed as ligands for transition-metal catalyzed reactions. Some of them have found industrial applications in the synthesis of pharmaceuticals and agrochemicals. For example, the [[diphosphines|diphosphine]] [[1,1'-Bis(diphenylphosphino)ferrocene]] (dppf) is a valuable ligand for [[palladium]]-[[coupling reaction]]s.

==Derivatives and variations==
Ferrocene analogues can be prepared with variants of cyclopentadienyl. For example, bis[[indene|indenyl]]iron and bisfluorenyliron.<ref name=Stepnicka/>

[[Image:FcVarietyPack.png|400px|center|Various ferrocene derivatives where cyclopentadienyl has been replaced by related ligands]]

Carbon atoms can be replaced by heteroatoms as illustrated by Fe(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(η<sup>5</sup>-P<sub>5</sub>) and Fe(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)(η<sup>5</sup>-C<sub>4</sub>H<sub>4</sub>N) ("[[azaferrocene]]"). Azaferrocene arises from decarbonylation of Fe(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)(CO)<sub>2</sub>(η<sup>1</sup>-pyrrole) in [[cyclohexane]].<ref>{{cite journal|doi=10.1016/0022-328X(90)85359-7|title=An improved photochemical synthesis of azaferrocene|year=1990|last1=Zakrzewski|first1=J|journal=Journal of Organometallic Chemistry|volume=388|pages=175}}</ref> This compound on boiling under [[reflux]] in [[benzene]] is converted to ferrocene.<ref>{{cite journal|doi=10.1021/ic00133a006|title=Chemistry of some .eta.5-pyrrolyl- and .eta.1-N-pyrrolyliron complexes |year=1982 |last1=Efraty |first1=Avi. |last2=Jubran |first2=Nusrallah |last3=Goldman |first3=Alexander |journal=Inorganic Chemistry|volume=21|pages=868|issue=3}}</ref>

Because of the ease of substitution, many structurally unusual ferrocene derivatives have been prepared. For example, the penta(ferrocenyl)cyclopentadienyl ligand,<ref>{{cite journal|author=Y. Yu, A.D. Bond, P. W. Leonard, K. P. C. Vollhardt, G. D. Whitener| title=Syntheses, Structures, and Reactivity of Radial Oligocyclopentadienyl Metal Complexes: Penta(ferrocenyl)cyclopentadienyl and Congeners| journal= [[Angewandte Chemie International Edition]]| volume =45|issue=11| pages= 1794–1799|year=2006|pmid=16470902| doi=10.1002/anie.200504047}}</ref> features a cyclopentadienyl anion derivatised with five ferrocene substituents.
[[Image:Penta(ferrocenyl)cyclopentadienyl.png|500px|center|Penta(ferrocenyl)cyclopentadienyl ligand]]

[[Image:Hexaferrocenylbenzene-3D-sticks.png|200px|thumb|right|Structure of hexaferrocenylbenzene]]

In '''hexaferrocenylbenzene''', C<sub>6</sub>[(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)Fe(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)]<sub>6</sub>, all six positions on a [[benzene]] molecule have ferrocenyl substituents ('''R''').<ref name = "hexaferrocenylbenzene">{{cite journal|title=Hexaferrocenylbenzene|author= Yong Yu, Andrew D. Bond, Philip W. Leonard, Ulrich J. Lorenz, Tatiana V. Timofeeva, K. Peter C. Vollhardt, Glenn D. Whitener and Andrey A. Yakovenko| journal=[[Chemical Communications|Chem. Commun.]]|issue=24| year=2006| pages= 2572–2574|pmid=16779481 |doi=10.1039/b604844g}}</ref> [[X-ray diffraction]] analysis of this compound confirms that the cyclopentadienyl ligands are not co-planar with the benzene core but have alternating [[dihedral angle]]s of +30° and −80°. Due to steric crowding the ferrocenyls are slightly bent with angles of 177° and have elongated C-Fe bonds. The quaternary cyclopentadienyl carbon atoms are also [[pyramidalization|pyramidalized]].<ref>Also, the benzene core has a [[chair conformation]] with dihedral angles of 14° and displays [[bond length]] alternation between 142.7 [[picometer|pm]] and 141.1 pm, both indications of steric crowding of the substituents.</ref>

The synthesis of hexaferrocenylbenzene has been reported using [[Negishi coupling]] of hexaiodidobenzene and diferrocenylzinc, using [[tris(dibenzylideneacetone)dipalladium(0)]] as [[catalyst]], in [[tetrahydrofuran]]:<ref name = "hexaferrocenylbenzene" />
:[[Image:Hexaferrocenylbenzene.png|400px|Hexaferrocenylbenzene synthesis by Negishi coupling]]
The [[yield (chemistry)|yield]] is only 4%, which is further evidence consistent with substantial [[steric strain|steric]] crowding around the arene core.
{{clear}}

==References==
{{reflist|2}}

{{commons category|ferrocene}}

==Further reading==
*{{cite journal| author=Miller, S. A., Tebboth, J. A., Tremaine, J. F.|journal= [[Journal of the Chemical Society|J. Chem. Soc.]]|year=1952| pages= 632–635| title=114. Dicyclopentadienyliron |doi=10.1039/JR9520000632}}
;Announcement of the correct 'sandwich' structure
*{{cite journal|author=[[Geoffrey Wilkinson|Wilkinson, G.]], Rosenblum, M., Whiting, M. C., [[Robert Burns Woodward|Woodward, R. B.]]|title= The Structure of Iron Bis-Cyclopentadienyl| journal=[[J. Am. Chem. Soc.]]|year= 1952| volume=74|pages=2125–2126|doi = 10.1021/ja01128a527|issue=8}}
*{{cite journal |author=[[Ernst Otto Fischer|Fischer, E. O.]], Pfab, W.|title=Cyclopentadien-Metallkomplexe, ein neuer typ metallorganischer Verbindungen |journal=Z. Naturforsch. B|year=1952| volume=7 |pages=377–379}}
;Others
*{{cite journal|author=Dunitz, J. D., Orgel, L. E.|title=Bis-Cyclopentadienyl - A Molecular Sandwich|journal= [[Nature (journal)|Nature]] |year=1953| volume=171 |pages= 121–122|doi = 10.1038/171121a0|issue=4342}}
*{{cite journal|author=Pauson, P. L.|title=Ferrocene-how it all began|journal=[[Journal of Organometallic Chemistry|J. Organomet. Chem.]]|year=2001|pages=637–639|volume = 637-639|doi = 10.1016/S0022-328X(01)01126-3}}
*{{cite book|author= Gerard Jaouen (ed.)| title=Bioorganometallics: Biomolecules, Labeling, Medicine| publisher=Wiley-VCH| location= Weinheim| year= 2006|isbn=978-3-527-30990-0}} (discussion of biological role of ferrocene and related compounds)
*University of Nottingham Molecular Videos, [http://www.periodicvideos.com/videos/mv_ferrocene.htm "Ferrocene"]

[[Category:Organoiron compounds]]
[[Category:Metallocenes]]
[[Category:Antiknock agents]]
[[Category:Sandwich compounds]]
[[Category:Cyclopentadienyl complexes]]

[[cs:Ferrocen]]
[[de:Ferrocen]]
[[es:Ferroceno]]
[[fr:Ferrocène]]
[[it:Ferrocene]]
[[nl:Ferroceen]]
[[ja:フェロセン]]
[[pl:Ferrocen]]
[[pt:Ferroceno]]
[[ru:Ферроцен]]
[[fi:Ferroseeni]]
[[sv:Ferrocen]]
[[th:เฟอร์โรซีน]]
[[tr:Ferrosen]]
[[uk:Фероцен]]
[[ur:Ferrocene]]
[[zh:二茂铁]]