Difference between revisions 6001785 and 6001786 on simplewiki

< previous diff
next diff >
User:Barras/Ferrocene
{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 457631192
| ImageFileL1 = Ferrocene.svg
| ImageSizeL1 = 80 px
| ImageFileR1 = Ferrocene-from-xtal-3D-balls.png
| ImageSizeR1 = 80 px
| ImageFileL2 = Ferrocene 3d model 2.png
| ImageFileR2 = Photo of Ferrocene (powdered).JPG
| 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]
| Jmol   = [cH-]1cccc1.[Fe+2].[cH-]1cccc1<!-- altered from SMILES to show correct -->
| 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
| Odor = [[camphor]]-like
| 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>
| MeltingPtC = 172.5
| MeltingPt_ref = <ref>{{RubberBible86th|page=3.258}}</ref>
| BoilingPtC = 249
| Solubility = Insoluble in water, soluble in most organic solvents
 }}
|Section3={{Chembox Hazards
| EUClass = [[Image:GHS-pictogram-skull.svg|60px]][[Image:GHS-pictogram-pollu.svg|60px]]
<ref>{{cite web|title=Material Safety Data Sheet. Ferrocene. MSDS# 03388. Section|url=https://www.nwmissouri.edu/naturalsciences/sds/f/Ferrocene.pdf|website=[[Northwest Missouri State University]]}}</ref>| MainHazards =Very hazardous in case of ingestion. Hazardous in case of skin contact (irritant), of eye contact (irritant), of inhalation<ref>{{cite web|title=Ferrocene MSDS |website=ScienceLab|url=http://www.sciencelab.com/msds.php?msdsId=9924047}}</ref>
| FlashPt =
| AutoignitionPt = 
| PEL = TWA 15 mg/m<sup>3</sup> (total) TWA 5 mg/m<sup>3</sup> (resp)<ref name=PGCH>{{PGCH|0205}}</ref>
| IDLH = N.D.<ref name=PGCH/>
| REL = TWA 10 mg/m<sup>3</sup> (total) TWA 5 mg/m<sup>3</sup> (resp)<ref name=PGCH/>
 }}
|Section8={{Chembox Related
| OtherCompounds = [[cobaltocene]], [[nickelocene]], [[chromocene]], [[ruthenocene]], [[osmocene]], [[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|analogues]].

==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 name = Miller>{{cite journal| last1=Miller|first1= S. A.|last2=Tebboth|first2= J. A.|last3= Tremaine|first3= 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|first1= Pierre|last1= Laszlo|first2= Roald |last2=Hoffmann|title = Ferrocene: Ironclad History or Rashomon Tale? |journal = [[Angewandte Chemie|Angew. Chem. Int. Ed.]] |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>{{cite journal | last1 = Werner | first1 = H | year = 2012 | title = At Least 60 Years of Ferrocene: The Discovery and Rediscovery of the Sandwich Complexes | url = | journal = [[Angew. Chem. Int. Ed.]] | volume = 51 | issue = | pages = 6052–6058 | doi = 10.1002/anie.201201598 }}</ref> The stability of the new organoiron compound was accorded to the aromatic character of the negatively 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 |first1= G. |last1=Wilkinson|author1-link=Geoffrey Wilkinson |first2=M.|last2= Rosenblum |first3=M. C.|last3= Whiting|first4= R. B. |last4=Woodward|author4-link=Robert Burns Woodward |title = The Structure of Iron Bis-Cyclopentadienyl |journal = [[Journal of the American Chemical Society|J. Am. Chem. Soc.]] |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 |author1-link=Ernst Otto Fischer|first1 = E. O.|last1= Fischer|first2= W. |last2=Pfab |title = Zur Kristallstruktur der Di-Cyclopentadienyl-Verbindungen des zweiwertigen Eisens, Kobalts und Nickels|trans-title=On the crystal structure of the bis-cyclopentadienyl compounds of divalent iron, cobalt and nickel |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|last1=Dunitz|first1= J. D.|last2= Orgel|first2= 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|bibcode = 1953Natur.171..121D }}</ref><ref>{{cite journal |first1= J.|last1= Dunitz|first2= L.|last2= Orgel|first3= A.|last3= Rich |title = The crystal structure of ferrocene |journal = [[Acta Crystallographica|Acta Crystallogr.]] |year = 1956 |volume = 9 |pages = 373–375 |doi = 10.1107/S0365110X56001091 |issue = 4}}</ref><ref>{{cite journal|first1=P. F. |last1=Eiland |first2= R.|last2= Pepinsky |year=1952|title=X-ray examination of iron biscyclopentadienyl|journal=[[Journal of the American Chemical Society|J. Am. Chem. Soc.]]|volume=74|page =4971|doi=10.1021/ja01139a527|issue=19}}</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&nbsp;Å within the five-membered rings, and the Fe–C bond distances are 2.04&nbsp;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>{{cite journal | last1 = Haaland | first1 = A. | last2 = Nilsson | first2 = J. E. | year = 1968 | title = The Determination of Barriers to Internal Rotation by Means of Electron Diffraction. Ferrocene and Ruthenocene | url = | journal = [[Acta Chemica Scandinavica|Acta Chem. Scand.]] | volume = 22 | issue = | pages = 2653–2670 | doi = 10.3891/acta.chem.scand.22-2653 }}</ref> and computational studies<ref>{{cite journal | last1 = Coriani | first1 = Sonia | last2 = Haaland | first2 = Arne | last3 = Helgaker | first3 = Trygve | last4 = Jørgensen | first4 = Poul | year = 2006 | title = The Equilibrium Structure of Ferrocene | url = | journal = [[ChemPhysChem]] | volume = 7 | issue = | 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 point group of the staggered conformation is D<sub>5d</sub> and the point group of the eclipsed conformation is D<sub>5h</sub>.

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 |first1= E. W. |last1=Abel |first2=N. J.|last2= Long |first3=K. G. |last3=Orrell |first4=A. G. |last4=Osborne|first5=V.|last5= Sik |title = Dynamic NMR studies of ring rotation in substituted ferrocenes and ruthenocenes |journal = [[Journal of Organometallic Chemistry|J. Org. Chem.]] |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 syntheses of ferrocene were nearly simultaneous.  Pauson and Kealy synthesised ferrocene using [[iron(III) chloride]] and a [[Grignard reaction|Grignard reagent]], cyclopentadienyl magnesium bromide.  Iron(III) chloride is suspended in [[anhydrous]] [[diethyl ether]] and added to the Grignard reagent, which is prepared by reacting [[cyclopentadiene]] with magnesium and [[bromoethane]] in anhydrous [[benzene]].<ref name = "Pauson_Kealy" />  An iron(III) salt was chosen as they sought to couple the cyclopentadienyl [[moiety (chemistry)|moieties]] to form dihydrofulvalene and then fullvalene, but ferrocene was formed instead as the oxidative formation of dihydrofulvalene also produced iron(II) by reduction, which in turn reacts with the Grignard.

:[[File:Kealy_Ferrocen_Synthese.svg|800px]]

[[File:Miller Ferrocen Synthese.svg|thumb|right|300px|The Miller ''et al.''<ref name = Miller /> approach to ferrocene]]
The other early synthesis of ferrocene was by Miller ''et al.'',<ref name = Miller /> who reacted metallic iron directly with [[gas]]-phase cyclopentadiene at elevated temperature.<ref>{{cite journal|doi=10.1021/ja01636a080|title=Bis-cyclopentadienyl Compounds of Nickel and Cobalt|year=1954|last1=Wilkinson|first1=G.|authorlink1=Geoffrey Wilkinson|last2=Pauson|first2=P. L.|last3=Cotton|first3=F. A.|authorlink3=F. Albert Cotton|journal=[[J. Am. Chem. Soc.]]|volume=76|pages=1970|issue=7}}</ref>  An approach using [[iron pentacarbonyl]] was also reported.<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.|authorlink2=F. Albert Cotton|title=Cyclopentadienyl and Arene Metal Compounds|journal=Prog. Inorg. Chem.|volume=1|pages=1–124|isbn=978-0-470-16602-4}}</ref>

:Fe(CO)<sub>5</sub> + 2&nbsp;C<sub>5</sub>H<sub>6</sub>(g) → Fe(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub> + 5&nbsp;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 name=orgsyn>{{OrgSynth|title = Ferrocene|author = [[Geoffrey Wilkinson]]|collvol = 4|collvolpages = 473|year = 1963|prep = cv4p0473}}</ref> or freshly [[dicyclopentadiene|cracked]] cyclopentadiene deprotonated with [[potassium hydroxide]]<ref>{{cite book|last=Jolly|first= W. L.|title= The Synthesis and Characterization of Inorganic Compounds |publisher=Prentice-Hall |location=New Jersey |date=1970}}</ref> and reacted with anhydrous iron(II) chloride in ethereal solvents.  A modern modification of the Grignard approach is also known:

:2&nbsp;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&nbsp;NaCl

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

:2&nbsp;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> + 2&nbsp;MgBrCl

Even some [[amine]] bases can be used for the deprotonation, though the reaction proceeds more slowly than when using stronger bases:<ref name=orgsyn/>

:2&nbsp;C<sub>5</sub>H<sub>6</sub> + 2&nbsp;(CH<sub>3</sub>CH<sub>2</sub>)<sub>2</sub>NH + FeCl<sub>2</sub> → Fe(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub> + 2&nbsp;(CH<sub>3</sub>CH<sub>2</sub>)<sub>2</sub>NH<sub>2</sub>Cl

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.|authorlink2= F. Albert Cotton|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>

[[File:Ferrocen.jpg|thumb|right|Crystals of ferrocene after purification by vacuum sublimation]]
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)|sublimes]], especially upon heating in a vacuum. It is stable to temperatures as high as 400&nbsp;°C.<ref>{{cite book|last1=Solomons|first1= Graham|first2= Craig|last2= Fryhle |title=Organic Chemistry |edition=9th |location=USA |publisher=John Wiley & Sons|date=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=J. Chem. Eng. 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]] 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 Lett.|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 [[octasulfur|S<sub>8</sub>]], [[chlorophosphine]]s or [[chlorosilane]]s. The strained compounds undergo [[ring-opening polymerization]].<ref>{{cite journal|first1=David E.|last1= Herbert |first2=Ulrich F. J.|last2= Mayer |first3=Ian |last3=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|380px|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>{{cite book|first=Petr |last=Stepnicka |title=Ferrocenes: Ligands, Materials and Biomolecules|publisher=J. Wiley |location=Hoboken, NJ|date=2008 |ISBN=0-470-03585-4}}</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 | first1= G. R. |last1=Knox |first2=P. L. |last2=Pauson |first3=D. |last3=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 |first1= G. P. |last1=Sollott |first2=H. E.|last2= Mertwoy |first3=S.|last3= Portnoy |first4=J. L. |last4=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 = [[Dalton Transactions|J. Chem. Soc., Dalton Trans.]] |year = 1996 |pages = 3653–3657 |doi = 10.1039/DT9960003653 |issue = 18}}</ref>

===Redox chemistry – the ferrocenium ion===
{{main article|Ferrocenium}}
Unlike the majority of organic compounds, ferrocene undergoes a one-electron oxidation at a low potential, around 0.5&nbsp;V versus a [[saturated calomel electrode]] (SCE). This reversible oxidation has itself been used as standard in electrochemistry as Fc<sup>+</sup>/Fc&nbsp;= 0.64&nbsp;V versus the [[standard hydrogen electrode]]. Some [[electron]]-rich organic compounds (e.g., [[aniline]]) also are oxidized at low potentials, but only irreversibly. Oxidation of ferrocene gives the stable blue-colored iron(III) cation {{chem|Fe(C|5|H|5|)|2|+}} originally called ferricinium, but now more commonly ferrocenium (these terms denote the ''same'' ion, contrary to what one would expect from the fact that [[ferric]] and [[ferrous]] denote different ions of a single iron atom).  On a preparative scale, the oxidation is conveniently effected with FeCl<sub>3</sub>, to give the ion, which is often isolated as its [[hexafluorophosphate|{{chem|PF|6|−}}]] 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|first1=N. G. |last1=Connelly |first2=W. E. |last2=Geiger| title=Chemical Redox Agents for Organometallic Chemistry|journal=[[Chemical Reviews|Chem. Rev.]]|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 and can even be oxidised to the corresponding dication.<ref>{{Cite journal|last=Malischewski|first=M.|last2=Adelhardt|first2=M.|last3=Sutter|first3=J.|last4=Meyer|first4=K.|last5=Seppelt|first5=K.|date=2016-08-12|title=Isolation and structural and electronic characterization of salts of the decamethylferrocene dication|url=http://science.sciencemag.org/content/353/6300/678|journal=Science|language=en|volume=353|issue=6300|pages=678–682|doi=10.1126/science.aaf6362|issn=0036-8075|pmid=27516596}}</ref> Ferrocene is often used as an [[internal standard]] for calibrating redox potentials in non-aqueous [[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>{{cite web|url=http://www.osd.org.tr/14.pdf |title=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>{{citation|country-code=US|patent-number=4104036|title=Iron-containing motor fuel compositions and method for using same|inventor-first= Tai S.|inventor-last= Chao |display-inventors=etal |issue-date= 1978-08-01}}</ref> The [[iron]]-containing deposits formed from ferrocene can form a [[conductive]] coating on the [[spark plug]] surfaces.

===Pharmaceutical===
Ferrocene derivatives have been investigated as drugs.<ref>{{cite journal|first1=Dave R. |last1=Van Staveren |first2=Nils |last2=Metzler-Nolte |title=Bioorganometallic Chemistry of Ferrocene |journal=[[Chemical Reviews|Chem. Rev.]]|date= 2004 |volume=104 |pages=5931–5986
|DOI=10.1021/cr0101510}}</ref> Only one drug has entered the clinic, fFerrocenerone, used to treat some cases of iron-deficiency. Though no evidence of the existance of this drug can be found in the lituraturequine, an [[antimalarial]].

[[Image:Ferroquine.png|thumb|220 px|Ferroquine is a commercial antimalarial drug containing a ferrocene group.]]
The anticancer activity of ferrocene derivatives was first investigted in the late 1970s, when derivatives bearing [[amine]] or [[amide]] groups were tested against lymphocytic [[leukemia]].<ref name=":0">{{Cite journal|last=Ornelas|first=Catia|title=Application of ferrocene and its derivatives in cancer research|journal=New Journal of Chemistry|volume=35|doi=10.1039/c1nj20172g}}</ref> Some ferrocenium salts exhibit anticancer activity, but no compound has seen evaluation in the clinic.<ref name="Babin">[No evidence in literature] >Babin, V. N., et al., "Ferrocenes as potential anticancer drugs. Facts and hypotheses", Russ. Chem. Bull. 2014, volume 63, 2405-2422. {{DOI|10.1007/s11172-014-0756-7}}</ref>  An experimental drug was 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 cytotoxicity.<ref name=top2003>{{cite journal|first1=S. |last1=Top |first2=A. |last2=Vessières |first3=G. |last3=Leclercq |first4=J. |last4=Quivy |first5=J. |last5=Tang |first6=J. |last6=Vaissermann|first7= M. |last7=Huché |first8=G. |last8=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=[[Chem. Eur. J.]]| 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|doi=10.1021/cen-v080n037.p023}}</ref>
7-chloro-N-(2-((dimethylamino)methyl)ferrocenyl)quinolin-4-amine
Particular success has been seen for [[antimalarial]] activity.<ref name="BiotNosten2011">{{cite journal|last1=Biot|first1=C.|last2=Nosten|first2=F.|last3=Fraisse|first3=L.|last4=Ter-Minassian|first4=D.|last5=Khalife|first5=J.|last6=Dive|first6=D.|title=The antimalarial ferroquine: from bench to clinic|journal=Parasite|volume=18|issue=3|year=2011|pages=207–214|issn=1252-607X|doi=10.1051/parasite/2011183207|url=http://www.parasite-journal.org/articles/parasite/full_html/2011/03/parasite2011183p207/parasite2011183p207.html|PMID=21894260|PMC=3671469}} {{open access}}</ref><ref>Roux, C.; Biot, C., "Ferrocene-based antimalarials", Future Med. Chem. 2012, 4, 783-797. {{DOI|10.4155/fmc.12.26}}</ref> 

===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|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|indenyliron]] 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|J. Organomet. Chem.]]|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 ''η''<sup>5</sup>-pyrrolyl- and ''η''<sup>1</sup>-''N''-pyrrolyliron complexes |year=1982 |last1=Efraty |first1=Avi |last2=Jubran |first2=Nusrallah |last3=Goldman |first3=Alexander |journal=Inorg. Chem.|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|first1=Y. |last1=Yu |first2=A. D. |last2=Bond |first3=P. W. |last3=Leonard |first4=K. P. C. |last4=Vollhardt |first5=G. D. |last5=Whitener| title=Syntheses, Structures, and Reactivity of Radial Oligocyclopentadienyl Metal Complexes: Penta(ferrocenyl)cyclopentadienyl and Congeners| journal= [[Angewandte Chemie International Edition|Angew. Chem. Int. Ed.]]| volume =45|issue=11| pages= 1794–1799|year=2006|pmid=16470902| doi=10.1002/anie.200504047}}</ref> features a cyclopentadienyl anion derivatized 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|first1= Yong|last1= Yu|first2= Andrew D. |last2=Bond |first3=Philip W. |last3=Leonard |first4=Ulrich J.|last4= Lorenz |first5=Tatiana V.|last5= Timofeeva |first6=K. Peter C. |last6=Vollhardt |first7=Glenn D.|last7= Whitener |first8=Andrey A. |last8=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]]. Also, the benzene core has a [[chair conformation]] with dihedral angles of 14° and displays [[bond length]] alternation between 142.7&nbsp;[[picometer|pm]] and 141.1&nbsp;pm, both indications of steric crowding of the substituents.

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}}


===Materials chemistry===
[[File:Wettability of a silica surface with a bound ferrocene-substituted polymer.jpg|left|thumb|500px|Strands of an uncharged ferrocene-substituted polymer are tethered to a [[hydrophobic]] [[silica]] surface.  Oxidation of the ferrocenyl groups produces a [[hydrophilic]] surface due to electrostatic attractions between the resulting charges and the polar solvent.<ref name = Pietschnig />]] 
Ferrocene, a precursor to iron nanoparticles, can be used as a catalyst for the production of carbon nanotubes.<ref>{{cite journal|first1=Devin |last1=Conroya |first2=Anna |last2=Moisalab|first3= Silvana |last3=Cardosoa |first4=Alan |last4=Windleb |first5=John |last5=Davidson|journal=[[Chemical Engineering Science|Chem. Eng. Sci.]]|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]]<nowiki></nowiki>ferrocene from ferrocene can be made by a [[Wittig reaction]] of the [[aldehyde]], a [[phosphonium salt]] and [[sodium hydroxide]].<ref>{{cite journal|last1=Liu |first1=Wan-yi |last2=Xu |first2=Qi-hai|last3= Ma|first3= Yong-xiang|last4= Liang|first4= Yong-min|last5= Dong|first5= Ning-li|last6= Guan|first6= De-peng|journal=[[Journal of Organometallic Chemistry|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 (polyvinylferrocene, PVFc), a ferrocenyl version of [[polystyrene]] (the phenyl groups are replaced with ferrocenyl groups). Another polymer which can be formed is poly(2-(methacryloyloxy)ethyl ferrocenecarboxylate), PFcMA.  In addition to using organic polymer backbones, these pendant ferrocene units have been attached to inorganic backbones such as [[polysiloxane]]s, [[polyphosphazene]]s, and poly[[phosphinoborane]]s, (&ndash;PH(R)&ndash;BH<sub>2</sub>&ndash;)<sub>''n''</sub>, and the resulting materials exhibit unusual physical and electronic properties relating to the ferrocene / ferrocinium redox couple.<ref name = Pietschnig>{{cite journal|first = Rudolf|last = Pietschnig|title = Polymers with pendant ferrocenes|journal = [[Chemical Society Reviews|Chem. Soc. Rev.]]|year = 2016|volume = 45|pages = 5216-5231|doi = 10.1039/C6CS00196C}}</ref>  Both PVFc and PFcMA have been tethered onto [[silica]] wafers and the [[wettability]] measured when the polymer chains are uncharged and when the ferrocene moieties are oxidised to produce positively charged groups.  The [[contact angle]] with water on the PFcMA-coated wafers was 70&deg; smaller following oxidation, while in the case of PVFc the decrease was 30&deg;, and the switching of wettability is reversible.  In the PFcMA case, the effect of lengthening the chains and hence introducing more ferrocene groups is significantly larger reductions in the contact angle upon oxidation.<ref name = Pietschnig /><ref>{{cite journal|first1 = J.|last1 = Elbert|first2 = M.|last2 = Gallei|first3 = C.|last3 = Rüttiger|first4 = A.|last4 = Brunsen|first5 = H.|last5 = Didzoleit|first6 = B.|last6 = Stühn|first7 = M.|last7 = Rehahn|journal = [[Organometallics]]|year = 2013|volume = 32|issue = 20|pages = 5873–5878|title = Ferrocene Polymers for Switchable Surface Wettability|doi = 10.1021/om400468p}}</ref>
==See also==
* [[Josiphos ligands]]

==References==
{{reflist|30em}}

==External links==
* [http://www.periodicvideos.com/videos/mv_ferrocene.htm Ferrocene] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
* [http://www.cdc.gov/niosh/npg/npgd0205.html NIOSH Pocket Guide to Chemical Hazards] (Centers for Disease Control and Prevention)

{{commons category|ferrocene}}

{{Authority control}}

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