Cyclobutadieneiron tricarbonyl

Cyclobutadieneiron tricarbonyl
Identifiers
CAS Number	12078-17-0 ;
3D model (JSmol)	Interactive image;
ChemSpider	9096597;
	InChI InChI=1S/C4H4.3CO.Fe/c1-2-4-3-1;3*1-2;/h1-4H;;;; Key: PHCIVYPTULNGTJ-UHFFFAOYSA-N;
	SMILES c1ccc1.[Fe]([C]#[O])([C]#[O])[C]#[O];
Properties
Chemical formula	C7H4FeO3
Molar mass	191.951 g·mol−1
Appearance	pale yellow oil
Boiling point	47 °C (117 °F; 320 K) 3 mm
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

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.^[1]

Preparation and structure

Cyclobutadieneiron tricarbonyl was first prepared in 1965 by Pettit from 3,4-dichlorocyclobutene and diiron nonacarbonyl:^[2]^[3]

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.^[4]

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.^[5]

Cyclobutadieneiron tricarbonyl displays aromaticity as evidenced by some of its reactions, which can be classified as electrophilic aromatic substitution:^[6]

Cyclobutadieneiron tricarbonyl Reactions

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.

The reaction mechanism is identical to that of EAS:

Cyclobutadieneiron tricarbonyl EAS reactionmechanism

Related compounds

Several years before Petit's work, (C₄Ph₄)Fe(CO)₃ had been prepared from the reaction of iron carbonyl and diphenylacetylene.^[7]

(Butadiene)iron tricarbonyl is isoelectronic with cyclobutadieneiron tricarbonyl.

History

In 1956, Longuet-Higgins and Orgel^[8] 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^[9] This is a case of theory before experiment.^[10]

References

^ Seyferth, Dietmar (2003). "(Cyclobutadiene)iron Tricarbonyl. A Case of Theory before Experiment". Organometallics. 22: 2–20. doi:10.1021/om020946c.
^ Cyclobutadiene- and Benzocyclobutadiene-Iron Tricarbonyl Complexes G. F. Emerson, L. Watts, R. Pettit; J. Am. Chem. Soc.; 1965; 87(1); 131-133. First Page
^ Pettit, R.; Henery, J. (1970). "Cyclobutadieneiron Tricarbonyl". Organic Syntheses. 50: 21. doi:10.15227/orgsyn.050.0021.
^ P. D. Harvey; W. P. Schaefer; H. B. Gray; D. F. R. Gilson; I. S. Butler (1988). "Structure of tricarbonyl(η⁴-cyclobutadienyl)iron(0) at −45 °C". Inorg. Chem. 27 (1): 57–59. doi:10.1021/ic00274a013.
^ L. Brener; J. S. Mckennis; R. Pettit (1976). "Cyclobutadiene In Synthesis: endo-Tricyclo[4.4.0.02,5]deca-3,8-diene-7,10-dione". Org. Synth. 55: 43. doi:10.15227/orgsyn.055.0043.
^ 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 Abstract
^ R. P. Dodge, V. Schomaker, "Crystal Structure of Tetraphenylcyclobutadiene Iron Tricarbonyl", Nature 1960, vol. 186, 798-799.doi:10.1038/186798b0
^ Longuet-Higgins, H. C.; Orgel, L. E. (1956-01-01). "385. The possible existence of transition-metal complexes of cyclobutadiene". Journal of the Chemical Society (Resumed): 1969–1972. doi:10.1039/JR9560001969. ISSN 0368-1769.
^ Criegee, R.; Schröder, G. (1959-01-21). "Ein Nickel-Komplex des Tetramethyl-Cyclobutadiens". Angewandte Chemie (in German). 71 (2): 70–71. doi:10.1002/ange.19590710210.
^ Seyferth, Dietmar (2003-01-01). "(Cyclobutadiene)iron TricarbonylA Case of Theory before Experiment". Organometallics. 22 (1): 2–20. doi:10.1021/om020946c. ISSN 0276-7333.