Cyclobutadieneiron tricarbonyl

Cyclobutadieneiron tricarbonyl or (C₄H₄)Fe(CO)₃ is an organometallic complex of cyclobutadiene and an iron metal carbonyl. The chemical compound is used in organic chemistry as a precursor for cyclobutadiene.

Preparation

It was first prepared in 1965 by Rowland Pettit starting from cyclooctatetraene ^{[1] [2] [3]} :

Cyclooctatetraene is chlorinated to the [4.2.0]-bicyclic compound which reacts further with the alkyne dimethyl acetylenedicarboxylate in a Diels-Alder reaction followed by a reverse-DA reaction by pyrolysis at 200°C releasing cis-dichlorocyclobutene.

This compound reacts with di-iron nonacarbonyl (obtained from photolysis of iron pentacarbonyl) to Cyclobutadieneiron tricarbonyl.

Properties

Cyclobutadieneiron tricarbonyl displays aromaticity as evidenced by some of its reactions which can be classified as electrophilic aromatic substitution ^[4] :

It reacts in Friedel-Crafts acylation with acetyl chloride and aluminium chloride to 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 4

The reaction mechanism is identical to that of EAS:

References

Further reading

• 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.