Revision 6001713 of "User:Barras/Ferrocene" on simplewiki

{{chembox
| Verifiedfields = changed
| verifiedrevid = 457631192
| ImageFileL1 = Ferrocene.svg
| ImageSizeL1 = 80 px
| ImageFileR1 = Ferrocene-from-xtal-3D-balls.png
| ImageSizeR1 = 120 px
| ImageFileL2 = Ferrocene 3d model 2.png
| ImageSizeL2 = 120 px
| ImageFileR2 = Photo of Ferrocene (powdered).JPG
| ImageSizeR2 = 120 px
| 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_Ref = {{ebicite|changed|EBI}}
| ChEBI = 30672
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = U96PKG90JQ
| 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 = 172.5 °C<ref>{{RubberBible86th|page=3.258}}</ref>
| BoilingPt = 249 °C
| Solubility = Insoluble in water, soluble in most organic solvents
 }}
| Section3 = {{Chembox Hazards
| MainHazards = 
| FlashPt = 
| Autoignition = 
 }}
| Section8 = {{Chembox Related
| OtherCpds = [[cobaltocene]], [[nickelocene]], [[chromocene]], [[ruthenocene]], [[plumbocene]]}}
}}

'''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&nbsp;— 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><ref>{{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}}</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|first1 = T. J.|last1 = Kealy|first2 = P. L.|last2 = 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|bibcode = 1951Natur.168.1039K}}</ref> 
A second group at [[British Oxygen]] also unknowingly discovered ferrocene. Miller, Tebboth and Tremaine were trying to synthesise amines from hydrocarbons such as cyclopentadiene and ammonia in a modification of the [[Haber process]]. They published this result in 1952 although the actual work was done three years earlier <ref>{{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}}</ref><ref name=r1>{{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 |pmid=10649350|issue = 1}}</ref><ref>Werner, H. (2012), At Least 60 Years of Ferrocene: The Discovery and Rediscovery of the Sandwich Complexes. Angew. Chem. Int. Ed., 51: 6052–6058. {{doi|10.1002/anie.201201598}}</ref> The stability of the new organoiron compound was accorded to the aromatic character of the negative charged cyclopentadienyls, but they were not the ones to recognize the η<sup>5</sup> (pentahapto) sandwich structure.

[[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>

The structure of ferrocene was confirmed by [[Nuclear magnetic resonance|NMR]] spectroscopy and [[X-ray crystallography]].<ref name=r1/><ref>{{cite journal|author=Dunitz, J. D., Orgel, L. E.|title=Bis-Cyclopentadienyl&nbsp;– A Molecular Sandwich|journal= [[Nature (journal)|Nature]] |year=1953| volume=171 |pages= 121–122|doi = 10.1038/171121a0|issue=4342}}</ref><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=P. F. Eiland and R. Pepinsky |year=1952|title=X-ray examination of iron biscyclopentadienyl|journal=Journal of the American Chemical Society|volume=74|page =4971}}</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 carbon-carbon bond distances are 1.40 Å within the five membered rings, and the Fe-C bond distances are 2.04 Å.  Although [[X-ray crystallography]] (in the monoclinic space group) points to the Cp rings being in a staggered conformation, it has been shown through gas phase electron diffraction<ref>Haaland, A.; Nilsson, J. E. "The Determination of Barriers to Internal Rotation by Means of Electron Diffraction. Ferrocene and Ruthenocene" Acta Chemica Scandinavica 1968, volume 22, pp. 2653-2670. {{DOI|10.3891/acta.chem.scand.22-2653}}</ref> and computational studies<ref>Sonia Coriani, Arne Haaland, Trygve Helgaker, Poul Jørgensen "The Equilibrium Structure of Ferrocene" ChemPhysChem 2006, Volume 7, pages 245–249. {{doi|10.1002/cphc.200500339}}</ref> that in the gas phase the Cp rings are eclipsed. The staggered conformation is believed to be most stable in the condensed phase due to crystal packing.

The Cp rings rotate with a low barrier about the Cp<sub>(centroid)</sub>-Fe-Cp<sub>(centroid)</sub> axis, as observed by measurements on substituted derivatives of ferrocene using <sup>1</sup>H and <sup>13</sup>C [[nuclear magnetic resonance]] spectroscopy.  For example methylferrocene (CH<sub>3</sub>C<sub>5</sub>H<sub>4</sub>FeC<sub>5</sub>H<sub>5</sub>) exhibits a singlet for the C<sub>5</sub>H<sub>5</sub> ring.<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>

In terms of bonding, the iron center in ferrocene is usually assigned to the +2 oxidation state, consistent with measurements 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 covalent bonding.  When combined with the six ''d''-electrons on Fe<sup>2+</sup>, the complex attains an [[18-Electron rule|18-electron]] configuration.

==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|doi=10.1038/1681039b0|issue=4285|title=A New Type of Organo-Iron Compound}}</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> → 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=10.1002/978-0-470-16602-4.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|series=Progress in Inorganic Chemistry|isbn=978-0-470-16602-4}}</ref>

:Fe + 2 C<sub>5</sub>H<sub>6</sub>(g) → 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) → 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 → 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|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> → 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|page=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>{{cite journal|title=A convenient method for the preparation of monolithioferrocene|journal= Tetrahedron Letters |volume =31|issue =22|year= 1990|pages =3121–3124|doi=10.1016/S0040-4039(00)94710-5|last1=Rebiere|first1=F|last2=Samuel|first2=O|last3=Kagan|first3=H.B}}</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>{{cite journal|author=David E. Herbert, Ulrich F. J. Mayer, Ian Manners |title=Strained Metallocenophanes and Related Organometallic Rings Containing pi-Hydrocarbon Ligands and Transition-Metal Centers|journal= Angew. Chem. Int. Ed. |year=2007|volume =46|pages= 5060–5081|doi=10.1002/anie.200604409|issue=27}}</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 0-470-03585-4</ref> Simplest and best known is [[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 [[diferrocenyl-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 groups 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.svg|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&nbsp;– 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|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}} "Iron-containing motor fuel compositions and method for using same" Tai S. Chao et al. Issue date: Aug 1, 1978</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>{{cite journal|author=Devin Conroya, Anna Moisalab, Silvana Cardosoa, Alan Windleb and John Davidson|journal=Chemical Engineering Science|year=2010|volume=65|pages=2965–2977|doi=10.1016/j.ces.2010.01.019|title=Carbon nanotube reactor: Ferrocene decomposition, iron particle growth, nanotube aggregation and scale-up|issue=10}}</ref> The [[vinyl]] ferrocene from ferrocene can be made by a [[Wittig reaction]] of the [[aldehyde]], a [[phosphonium salt]] and [[sodium hydroxide]].<ref>{{cite journal|author=Liu, Wan-yi; Xu, Qi-hai; Ma, Yong-xiang; Liang, Yong-min; Dong, Ning-li; Guan, De-peng|journal=J. Organomet. Chem.|year=2001|volume=625|pages=128–132|doi=10.1016/S0022-328X(00)00927-X|title=Solvent-free synthesis of ferrocenylethene derivatives}}</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|last2=Giannotti|first2=Charles}}</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}}

[[josiphos ligands]]

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

[[ca:Ferrocè]]
[[cs:Ferrocen]]
[[de:Ferrocen]]
[[es:Ferroceno]]
[[fa:فروسن]]
[[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]]