Editing Ferrocene (section)

===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>