Difference between revisions 6001622 and 6001623 on simplewiki

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The first reported<ref>{{cite journal|year=1951|last1=Kealy|first1=T. J.|last2=Pauson|first2=P. L.|journal=Nature|volume=168|pages=1039}}</ref> synthesis of ferrocene used the [[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:


:CH<sub>3</sub>CH<sub>2</sub>Br + Mg + C<sub>5</sub>H<sub>6</sub> &rarr; C<sub>5</sub>H<sub>5</sub>MgBr + CH<sub>3</sub>CH<sub>3</sub>⏎
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: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|year=1954|last1=Wilkinson|first1=G.|last2=Pauson|first2=P. L.|last3=Cotton|first3=F. A.|journal=Journal of the American Chemical Society|volume=76|pages=1970}}</ref> at 350 °C or with [[iron pentacarbonyl]].<ref>{{cite journal|year=1959|last1=Wilkinson|first1=G.|last2=Cotton|first2=F. A.|journal=Progress in Inorganic Chemistry|volume=1|pages=1-124}}</ref>

: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)

[[Image:Ferrocene 3d model 2.png|thumb|right|A space-filling model of ferrocene.]]
Modern and 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, 1(contracted; show full)
[[Image:FcGen'l.png|400px|thumb|center|Important reactions of ferrocene with electrophiles and other reagents.]]

===Lithiation===
Ferrocene reacts readily with [[butyl lithium]] to give 1,1'-dilithioferrocene, which in turn is a versatile [[nucleophile]]. But reaction of Ferrocene with [[t-BuLi]] produces monolithioferrocene only. <ref>F Rebierea, O Samuela and H.B Kagan "A convenient method for the preparation of monolithioferrocene" Tetrahedron Letters
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  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. Other routes to such ligands are known. For example, in the presence of [[aluminium chloride]] Me<sub>2</sub>NPCl<sub>2</sub> and ferrocene react to give ferrocenyl dichloro[[phosphine]],<ref>{{cite journal |title = Ferrocene derivatives. 27. Ferrocenyldimethylphosphine | author = G.R. Knox, P.L. Pauson and D. Willison |journal = Organometallics |volume = 11 |issue = 8 |pages = 2930–2933 |year = 1992 |doi = 10.1021/om00044a038 }}</ref>⏎
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  whileereas treatment with [[phenyldichlorophosphine]] under similar conditions forms ''P,P''-diferrocenyl-''P''-phenyl phosphine.<ref>{{cite journal |author = G.P. Sollott, H.E. Mertwoy, S. Portnoy and J.L. Snead |title = Unsymmetrical Tertiary Phosphines of Ferrocene by Friedel-Crafts Reactions. I. Ferrocenylphenylphosphines |journal = J. Org. Chem. |year = 1963 |volume = 28 |pages = 1090–1092 |doi = 10.1021/jo01039a055 }}</ref> In common with [[anisole]] the react(contracted; show full)[[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 [[cathodic]] direction (more negative). Thus, decamethylferrocene is much more eas
y toily oxidised than ferrocene itself. Ferrocene is often used as an [[internal standard]] for calibrating redox potentials in non-aqeous [[electrochemistry]].

==Stereochemistry==
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- and 1,1' isomers, which are not interconvertible. 1,2-Heterodisubstituted ferrocenes are chiralFerrocenes that are disubstituted on one ring are chiral, e.g. CpFe(EtC<sub>5</sub>H<sub>3</sub>Me).

==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.

In [[Diesel fuel|diesel]]-fuelled engines, ferrocene reduces the production of [[soot]].⏎
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  Ferrocene is available under multiple brand names, including [[Ferox (fuel additive)|Ferox]].

===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(contracted; show full)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).


Ferrocene is also used as a nano-sized "loom" in the manufacture of ultra-high molecular weight polyethylene's very long fibers, which are used to manufacture newer types of bulletproof vest fabric.{{Citation needed|date=March 2008}}⏎
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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 ligand|diphosphine]] [[1,1'-bis(diphenylphosphino)ferrocene]] (dppf) is a valuable ligand for [[palladium]]-[[coupling reaction]]s.

==Derivatives and variations==
Many other hydrocarbons can be used insteadFerrocene analogues can be prepared with variants of cyclopentadienyl. For example, bis[[indene|indenyl]] can be used in place of the cyclopentadienyl to form bisbenzoferrocene.<ref>{{cite journal|doi=10.1016/S0020-1693(99)00123-1|title=Novel organoiron compounds resulting from the attempted syntheses of dibenzofulvalene complexes|year=1999|last1=Waldbaum|first1=B|journal=Inorganica Chimica Acta|volume=291|pages=109}}</refiron and bis[[fluorenyl]]iron.<ref name=Stepnicka/>

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

The cCarbon 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}}</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| doi=10.1002/anie.200504047}}</ref> features a cyclopentadiene derivatised with five ferrocene substituents.
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[[Image:Penta(ferrocenyl)cyclopentadienyl.png|500px|center|Penta(ferrocenyl)cyclopentadienyl ligand]]

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

In '''hexaferrocenylbenzene''', all six positions on a [[benzene]] molecule have ferrocenyl substituents ('''R''').<ref>{{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]]| year=2006| pages= 2572–2574 |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>

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

{{commonscat|ferrocene}}

==Further reading==
;Announcement of the discovery of ferrocene, but with wrong structure
*{{cite journal|author=Kealy, T. J., Pauson, P. L.|title=A New Type of Organo-iron Compound|journal= [[Nature (journal)|Nature]]| year= 1951|volume= 168| pages =1039–40|doi = 10.1038/1681039b0}}⏎
*{{cite journal| author=Miller, S. A., Tebboth, J. A., Tremaine, J. F.|journal= [[Journal of the Chemical Society]]|year=1952| pages= 632–635| title=114. Dicyclopentadienyliron |doi=10.1039/JR9520000632}}
;Announcement of the correct 'sandwich' structure
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