Editing Ferrocene (section)

==Reactions==
[[Image:FcGen'l.png|upright=1.5|thumb|left|Important ferrocene reactions|alt=Formylation, acylation, mercuration, oxidation]]

===Aromatic substitution===
Ferrocene is an [[aromaticity|aromatic substance]].  [[Electrophiles]] typically [[substitution reaction|substitute onto]], rather than [[addition reaction|add to]], the cyclopentadienyl ligands. For example, a common undergraduate experiment performs [[Friedel-Crafts reaction#Friedel-Crafts acylation|Friedel-Crafts acylation]] with [[acetic anhydride]] and a [[phosphoric acid]] catalyst.  Just as this reagent mixture converts [[benzene]] to [[acetophenone]], it converts ferrocene to [[acetylferrocene]].<ref>{{cite journal| vauthors = Bozak RE |title = Acetylation of Ferrocene: A Chromatography Experiment for Elementary Organic Laboratory|journal = [[J. Chem. Educ.]]|year = 1966|volume = 43|issue = 2|page = 73|doi = 10.1021/ed043p73|bibcode = 1966JChEd..43...73B}}</ref> 

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 | vauthors = Knox GR, Pauson PL, Willison D |author-link2=Peter Pauson |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 | vauthors = Sollott GP, Mertwoy HE, Portnoy S, Snead JL |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>  [[Vilsmeier-Haack reaction|Vilsmeier-Haack formylation]] using [[formanilide|formylanilide]] and [[phosphorus oxychloride]] gives [[ferrocenecarboxaldehyde]].<ref name=Rausch/>  

Unsubstituted ferrocene undergoes aromatic substitution more easily than benzene, because electrophiles can attack the metal ion before rearranging to the [[Wheland intermediate]].<ref name=GE1287>{{Greenwood&Earnshaw1st|p=1287}}</ref>  Thus ferrocene reacts with the weak electrophile [[Phosphorus pentasulfide|P<sub>4</sub>S<sub>10</sub>]] to form 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) | vauthors = ((St J Foreman MR)), Alexandra MZ, Slawin AM, Woollins JD |journal = [[Dalton Transactions|J. Chem. Soc., Dalton Trans.]] |issue = 18 |year = 1996 |pages = 3653–3657 |doi = 10.1039/DT9960003653}}</ref> [[Mannich reaction|Mannich conditions]] suffice to iminylate ferrocene unto [[N,N-Dimethylaminomethylferrocene|N,N-dimethylaminomethylferrocene]].{{cn|date=May 2025}}  

Superacidic protonation does not complete aromatic substitution, but rather traps the unrearranged [[bent metallocene|bent]] intermediate [[hydrido]] salt, [Cp<sub>2</sub>FeH]PF<sub>6</sub>.<ref>{{cite journal | vauthors = Malischewski M, Seppelt K, Sutter J, Heinemann FW, Dittrich B, Meyer K | title = Protonation of Ferrocene: A Low-Temperature X-ray Diffraction Study of [Cp<sub>2</sub> FeH](PF<sub>6</sub> ) Reveals an Iron-Bound Hydrido Ligand | journal = Angewandte Chemie | volume = 56 | issue = 43 | pages = 13372–13376 | date = October 2017 | pmid = 28834022 | doi = 10.1002/anie.201704854}}</ref>  Strongly oxidizing electrophiles, such as [[halogen]]s and [[nitric acid]], neither rearrange to a Wheland intermediate nor coordinate to iron, instead generating ferrocenium salts (see {{slink||Redox chemistry}}).<ref name=GE1287/>  

In accordance with [[Jemmis mno rules|cluster compound theory]], ferrocene's rings behave as a single delocalized &pi; system.  Electronic perturbations to one ring propagate to the other.   For example, introduction of a [[Electrophilic aromatic directing groups|deactivating]] aldehyde group on one ring inhibits formylation of the other ring as well.<ref name=Rausch>{{cite journal |doi=10.1139/v63-182 |title=Metallocene Chemistry—A Decade of Progress |date=1963 |last1=Rausch |first1=M. D. |journal=Canadian Journal of Chemistry |volume=41 |issue=5 |pages=1289–1314 }}</ref>

===Metallation===
Ferrocene readily metallates.  Ferrocene reacts with [[butyllithium]] to give [[1,1'-Dilithioferrocene|1,1′-dilithioferrocene]], which is a versatile [[nucleophile]]. In combination with butyllithiium, [[Tert-Butyllithium|''tert''-butyllithium]] produces monolithioferrocene.<ref>{{cite journal |author=Busacca |first1=Carl A. |last2=Eriksson |first2=Magnus C. |last3=Haddad |first3=Nizar |last4=Han |first4=Z. Steve |last5=Lorenz |first5=Jon C. |last6=Qu |first6=Bo |last7=Zeng |first7=Xingzhong |last8=Senanayake |first8=Chris H. |year=2013 |title=Practical Synthesis of Di-tert-Butyl-Phosphinoferrocene |journal=Organic Syntheses |volume=90 |page=316 |doi=10.15227/orgsyn.090.0316 |doi-access=free}}</ref>  Likewise ferrocene [[mercuration|mercurates]] to give ferrocendiyl dimercuriacetate.<ref name=GE1288>{{Greenwood&Earnshaw1st|p=1288}}</ref>  

Further reaction gives the [[nitro compound|nitro]], halo-, and borono derivatives.<ref name=GE1288/>

=== Redox chemistry ===
[[File:Biferrocene.svg|thumb|left|132px|The one-electron oxidized derivative of [[biferrocene]] has attracted much research attention.]]
Ferrocene undergoes a one-electron oxidation at around 0.4&nbsp;V versus a [[saturated calomel electrode]] (SCE), becoming '''ferrocenium'''.<ref name=federman/> This reversible oxidation has been used as standard in electrochemistry as Fc<sup>+</sup>/Fc&nbsp;= 0.64&nbsp;V versus the [[standard hydrogen electrode]],<ref>{{cite journal | vauthors = Cardona CM, Li W, Kaifer AE, Stockdale D, Bazan GC | title = Electrochemical considerations for determining absolute frontier orbital energy levels of conjugated polymers for solar cell applications | journal = Advanced Materials | volume = 23 | issue = 20 | pages = 2367–2371 | date = May 2011 | pmid = 21462372 | doi = 10.1002/adma.201004554 | bibcode = 2011AdM....23.2367C | s2cid = 40766788 }}</ref> however other values have been reported.<ref>{{citation|surname1=Vitaly V Pavlishchuk, Anthony W Addison|periodical=Inorganica Chimica Acta|title=Conversion constants for redox potentials measured versus different reference electrodes in acetonitrile solutions at 25°C|volume=298|issue=1|at=pp.&nbsp;97–102|date=January 2000 |language=German |doi=10.1016/S0020-1693(99)00407-7|url=https://linkinghub.elsevier.com/retrieve/pii/S0020169399004077|access-date=2022-07-26
}}</ref><ref>{{cite journal | vauthors = Mygind JB, Deissler NH, Li S, Fu X, Kibsgaard J, Chorkendorff I | title = Hydrogen Oxidation Beyond Water: In Search of Proton Mediation Pathways | journal = ACS Electrochemistry | volume = X | issue = X | pages = X-X | date = 1 March 2025 | publisher = American Chemical Society | doi = 10.1021/acselectrochem.5c00009 | url = https://doi.org/10.1021/acselectrochem.5c00009 }}</ref> [[Ferrocenium tetrafluoroborate]] is a common reagent.<ref>{{cite journal | vauthors = Connelly NG, Geiger WE | title = Chemical Redox Agents for Organometallic Chemistry | journal = Chemical Reviews | volume = 96 | issue = 2 | pages = 877–910 | date = March 1996 | pmid = 11848774 | doi = 10.1021/cr940053x }}</ref> The remarkably reversible oxidation-reduction behaviour has been extensively used to control electron-transfer processes in electrochemical<ref>{{cite journal | vauthors = Sirbu D, Turta C, Gibson EA, Benniston AC | title = The ferrocene effect: enhanced electrocatalytic hydrogen production using meso-tetraferrocenyl porphyrin palladium(II) and copper(II) complexes | journal = Dalton Transactions | volume = 44 | issue = 33 | pages = 14646–14655 | date = September 2015 | pmid = 26213204 | doi = 10.1039/C5DT02191J | url = https://eprint.ncl.ac.uk/fulltext.aspx?url=214473/2DD72927-25BC-4809-8636-5FDB014D7CB0.pdf&pub_id=214473 }}</ref><ref>{{cite journal | vauthors = Lennox AJ, Nutting JE, Stahl SS | title = Selective electrochemical generation of benzylic radicals enabled by ferrocene-based electron-transfer mediators | journal = Chemical Science | volume = 9 | issue = 2 | pages = 356–361 | date = January 2018 | pmid = 29732109 | pmc = 5909123 | doi = 10.1039/C7SC04032F | doi-access = free }}</ref> and photochemical<ref>{{Cite journal| vauthors = Dannenberg JJ, Richards JH |date=1965-04-01|title=Photosensitization by Ferrocene. Photochemistry of Higher Electronic Excited States|journal=Journal of the American Chemical Society|volume=87|issue=7|pages=1626–1627|doi=10.1021/ja01085a048|issn=0002-7863}}</ref><ref>{{Cite journal| vauthors = Sirbu D, Turta C, Benniston AC, Abou-Chahine F, Lemmetyinen H, Tkachenko NV, Wood C, Gibson E | display-authors = 6 |date=2014-05-23|title=Synthesis and properties of a meso- tris–ferrocene appended zinc(II) porphyrin and a critical evaluation of its dye sensitised solar cell (DSSC) performance |journal=RSC Advances|language=en|volume=4|issue=43|pages=22733–22742|doi=10.1039/C4RA03105A|bibcode=2014RSCAd...422733S |issn=2046-2069| url = https://eprint.ncl.ac.uk/fulltext.aspx?url=199647/CED25CA5-111E-4500-8188-DCFC5D4D7190.pdf&pub_id=199647}}</ref> systems. 

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 | vauthors = Malischewski M, Adelhardt M, Sutter J, Meyer K, Seppelt K | title = Isolation and structural and electronic characterization of salts of the decamethylferrocene dication | journal = Science | volume = 353 | issue = 6300 | pages = 678–682 | date = August 2016 | pmid = 27516596 | doi = 10.1126/science.aaf6362 | s2cid = 43385610 | bibcode = 2016Sci...353..678M }}</ref> Ferrocene is often used as an [[internal standard]] for calibrating redox potentials in non-aqueous [[electrochemistry]].