Cyclobutadieneiron tricarbonyl: Difference between revisions

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|ImageFile = Cyclobutadienyl-iron-tricarbonyl-from-xtal-3D-balls.png

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|CASNo = 12078-17-0

|ChemSpiderID = 9096597

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|SMILES = c1ccc1.[Fe]([C]#[O])([C]#[O])[C]#[O]

|StdInChI=1S/C4H4.3CO.Fe/c1-2-4-3-1;3*1-2;/h1-4H;;;;

|StdInChIKey=PHCIVYPTULNGTJ-UHFFFAOYSA-N

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| C=7|H=4|Fe=1|O=3

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| Appearance = pale yellow oil

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'''Cyclobutadieneiron tricarbonyl''' is an [[organoiron compound]] with the formula Fe(C₄H₄)(CO)₃. It is a yellow oil that is soluble in organic solvents. It has been used in [[organic chemistry]] as a precursor for [[cyclobutadiene]], which is an elusive species in the free state.<ref>{{cite journal|doi=10.1021/om020946c |title=(Cyclobutadiene)iron Tricarbonyl. A Case of Theory before Experiment |date=2003 |last1=Seyferth |first1=Dietmar |journal=Organometallics |volume=22 |pages=2–20 }}</ref>

==Preparation and structure==

Cyclobutadieneiron tricarbonyl was first prepared in 1965 by Pettit from 3,4-dichlorocyclobutene and [[diiron nonacarbonyl]]:<ref>''Cyclobutadiene- and Benzocyclobutadiene-Iron Tricarbonyl Complexes'' G. F. Emerson, L. Watts, R. Pettit; [[J. Am. Chem. Soc.]]; '''1965'''; 87(1); 131-133. [http://pubs.acs.org/cgi-bin/abstract.cgi/jacsat/1965/87/i01/f-pdf/f_ja01079a032.pdf First Page]</ref><ref>{{cite journal |first1=R.|last1=Pettit|first2=J.|last2=Henery|doi=10.15227/orgsyn.050.0021|title=Cyclobutadieneiron Tricarbonyl|journal=Organic Syntheses|year=1970|volume=50|page=21}}</ref>

:C₄H₄Cl₂ + 2 Fe₂(CO)₉ → (C₄H₄)Fe(CO)₃ + 2 Fe(CO)₅ + 5 CO + FeCl₂

The compound is an example of a [[piano stool complex]]. The C-C distances are 1.426 Å.<ref>{{ cite journal | journal = [[Inorganic Chemistry (journal)|Inorg. Chem.]] | volume = 27 | issue = 1 | year = 1988 | pages = 57–59 | doi = 10.1021/ic00274a013 | title = Structure of tricarbonyl(η⁴-cyclobutadienyl)iron(0) at −45 °C |author1=P. D. Harvey |author2=W. P. Schaefer |author3=H. B. Gray |author4=D. F. R. Gilson |author5=I. S. Butler}}</ref>

==Properties==

[[Oxidative decomplexation]] of cyclobutadiene is achieved by treating the tricarbonyl complex with [[ceric ammonium nitrate]]. The released cyclobutadiene is trapped with a [[quinone]], which functions as a [[dienophile]].<ref>{{cite journal|title=Cyclobutadiene In Synthesis: ''endo''-Tricyclo[4.4.0.02,5]deca-3,8-diene-7,10-dione |author=L. Brener |author2=J. S. Mckennis |author3=R. Pettit|journal=Org. Synth.|year=1976|volume=55|page=43|doi=10.15227/orgsyn.055.0043}}</ref>

Cyclobutadieneiron tricarbonyl displays [[aromaticity]] as evidenced by some of its reactions, which can be classified as [[electrophilic aromatic substitution]]:<ref>Cyclobutadieneiron Tricarbonyl. A New Aromatic System J. D. Fitzpatrick, L. Watts, G. F. Emerson, R. Pettit [[J. Am. Chem. Soc.]]; '''1965''', vol. 87, 3254-3255 [http://pubs.acs.org/cgi-bin/abstract.cgi/jacsat/1965/87/i14/f-pdf/f_ja01092a050.pdf Abstract]</ref>

It undergoes [[Friedel-Crafts acylation]] with acetyl chloride and aluminium chloride to give the acyl derivative '''2''', with [[formaldehyde]] and [[hydrochloric acid]] to the chloromethyl derivative '''3''', in a [[Vilsmeier-Haack reaction]] with N-methylformanilide and phosphorus oxychloride to the [[formyl]] '''4''', and in a [[Mannich reaction]] to amine derivative '''5'''.

==Related compounds==

Several years before Petit's work, (C₄Ph₄)Fe(CO)₃ had been prepared from the reaction of [[iron carbonyl]] and [[diphenylacetylene]].<ref>R. P. Dodge, V. Schomaker, "Crystal Structure of Tetraphenylcyclobutadiene Iron Tricarbonyl", Nature 1960, vol. 186, 798-799.{{doi|10.1038/186798b0}}</ref>

[[(Butadiene)iron tricarbonyl]] is isoelectronic with cyclobutadieneiron tricarbonyl.

==History==

In 1956, Longuet-Higgins and Orgel<ref>{{Cite journal |last1=Longuet-Higgins |first1=H. C. |last2=Orgel |first2=L. E. |date=1956-01-01 |title=385. The possible existence of transition-metal complexes of cyclobutadiene |url=https://pubs.rsc.org/en/content/articlelanding/1956/jr/jr9560001969 |journal=Journal of the Chemical Society (Resumed) |language=en |pages=1969–1972 |doi=10.1039/JR9560001969 |issn=0368-1769}}</ref> predicted the existence of transition-metal cyclobutadiene complexes, in which the degenerate e_g orbital of cyclobutadiene has the correct symmetry for π interaction with the d_xz and d_yz orbitals of the proper metal. The compound was synthesized three years after the prediction<ref>{{Cite journal |last1=Criegee |first1=R. |last2=Schröder |first2=G. |date=1959-01-21 |title=Ein Nickel-Komplex des Tetramethyl-Cyclobutadiens |url=https://onlinelibrary.wiley.com/doi/10.1002/ange.19590710210 |journal=Angewandte Chemie |language=de |volume=71 |issue=2 |pages=70–71 |doi=10.1002/ange.19590710210}}</ref> This case of theory before experiment.<ref>{{Cite journal |last=Seyferth |first=Dietmar |date=2003-01-01 |title=(Cyclobutadiene)iron TricarbonylA Case of Theory before Experiment |url=https://pubs.acs.org/doi/10.1021/om020946c |journal=Organometallics |language=en |volume=22 |issue=1 |pages=2–20 |doi=10.1021/om020946c |issn=0276-7333}}</ref>

==References==

{{reflist}}

{{iron compounds}}

[[Category:Half sandwich compounds]]

[[Category:Iron(0) compounds]]

[[Category:Alkene complexes]]