Difference between revisions 6793164 and 8085742 on simplewiki

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(contracted; show full)m 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
|s2cid = 4181383}}</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 = 25| pages = 6052–6058 | doi = 10.1002/anie.201201598 | pmid = 22573490 }}</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 =10.1515/znb-1952-0701|s2cid = 93978102}}</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 |s2cid= 4263761}}</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(contracted; show full)

==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. At room temperature down to 164K,  [[X-ray crystallography]] points to the Cp rings being in a staggered conformation due to imposed molecular centrosymmetric symmetry in the monoclinic space group.<ref>{{Cite journal|last
1=Eiland|first1=Philip Frank|last2=Pepinsky|first2=Ray|date=1952-10-01|title=X-RAY EXAMINATION OF IRON BISCYCLOPENTADIENYLtitle=X-Ray Examination of Iron Biscyclopentadienyl|date=1952-10-01|url=https://dx.doi.org/10.1021/ja01139a527|journal=Journal of the American Chemical Society|volume=74|issue=19|pages=4971–4971|doi=10.1021/ja01139a527|issn=0002-7863}}</ref> Below 110 K, ferrocene crystallizes in an orthorhombic crystal lattice in which the Cp rings are ordered and eclipsed.<ref>{{Cite journal|last1=Seiler|first1=P.|last2=Dunitz|first2=J. D.|date=1982-06-15|title=Low-temperature crystallization of orthorhombic ferrocene: structure analysis at 98 K|url=http://scripts.iucr.org/cgi-bin/paper?S0567740882007080|journal=Acta Crystallographica Section B|language=en|volume=38|issue=6|pages=1741–1745|doi=10.1107/s0567740882007080|issn=0567-7408}}</ref> 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 = 1| pages = 245–249 | doi = 10.1002/cphc.200500339 | pmid = 16404766 }}</ref> that in the gas phase the Cp rings are eclipsed. 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 |issue=1–2 |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 co(contracted; show full)eoffrey 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|
doi-broken-date=2022-03-03|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)

(contracted; show full)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
|pmid= 17587203 }}</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=isbn=978-0-470-03585-46}}</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 |journa(contracted; show full)nyl 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
1=Malischewski|first1=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|bibcode=2016Sci...353..678M|s2cid=43385610}}</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]]
(contracted; show full)pdf |title=Application of fuel additives |url-status=dead |archiveurl=https://web.archive.org/web/20060505193757/http://www.osd.org.tr/14.pdf |archivedate=2006-05-05 }}</ref> Petrol additive solutions containing ferrocene can be added to unleaded petrol to enable its use in vintage cars 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-
inveneditors=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 |issue=12 |pages=5931–5986
|DOIdoi=10.1021/cr0101510|pmid=15584693 }}</ref> Only one drug has entered the clinic, Ferroquine, 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 investigated 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=35year=2011|volume=35|issue=10|page=1973|doi=10.1039/c1nj20172g}}</ref> Some ferrocenium salts exhibit anticancer activity, but no compound has seen evaluation in the clinic.<ref name=Babin>Babin, V. N., et al., "Ferrocenes as potential anticancer drugs. Facts and hypotheses", Russ. Chem. Bull. 2014, volume 63, 2405-2422. {{DOIdoi|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(contracted; show full) 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|
PMIDpmid=21894260|PMCpmc=3671469}} {{open access}}</ref><ref>Roux, C.; Biot, C., "Ferrocene-based antimalarials", Future Med. Chem. 2012, 4, 783-797. {{DOIdoi|10.4155/fmc.12.26}}</ref>

==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=175–179|last2=Giannotti|first2=Charles|issue=1–2}}</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>

(contracted; show full)''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
|url= https://zenodo.org/record/896672}}</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]] (contracted; show full)ysiloxane]]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|
issue = 19|pages = 5216–5231|doi = 10.1039/C6CS00196C|pmid = 27156979}}</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° smaller following oxidation, while in the case of PVFc the decrease was 30°, 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==
{{Commonscat}}
*[http://www.periodicvideos.com/videos/mv_ferrocene.htm Ferrocene] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
*[https://www.cdc.gov/niosh/npg/npgd0205.html NIOSH Pocket Guide to Chemical Hazards] (Centers for Disease Control and Prevention)

{{Authority control}}

[[:Category:Ferrocenes| ]]
[[:Category:Antiknock agents]]
[[:Category:Sandwich compounds]]
[[:Category:Cyclopentadienyl complexes]]