Difference between revisions 6001646 and 6001647 on simplewiki

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'''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}}</ref> The rapid growth of [[organometallic chemistry]] is often attributed to the excitement arising from the discovery of ferrocene and its many [[Analog (chemistry)Structural analog|analogues]]s.

==History==
[[File:Ferrocene kealy.svg|thumb|left|Pauson and Kealy's original (incorrect) notion of ferrocene's molecular structure<ref name = "Pauson_Kealy" />]]
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==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 [[
aAromaticity|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-eElectron rule|18-electron]], [[noble gas]] 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 fe(contracted; show full)

: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 (ph
ysicsase 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}}</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 dichloro[[phosphine]],<ref>{{cite journal |title = Ferrocene derivatives. 27. Ferrocenyldimethylphosphine | author = G.R. Knox, P.L. Pauson and D. Willison |journal = Organometallics |volume = 11 |issue = 8 |pages = 2930–2933 |year = 1992 |doi = 10.1021/om00044a038 }}</ref> 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 }}</ref> In common with [[anisole]] the reaction of ferrocene w(contracted; show full) W. E. Geiger| title=Chemical Redox Agents for Organometallic Chemistry|journal=[[Chemical Reviews]]|year= 1996| volume= 96| pages= 877–910| doi=10.1021/cr940053x}}</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 not interconvertible. Ferrocenes that are asymetrically 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==
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===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 [[diphosphine
 ligands|diphosphine]] [[1,1'-bBis(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 bis[[fluorenyl]]iron.<ref name=Stepnicka/>

[[Image:FcVarietyPack.png|400px|center|Various ferrocene derivatives where cyclopentadienyl has been replaced by related ligands]]

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