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. It was first prepared in 1965 by Rowland Pettit starting from cyclooctatetraene  :


 * [[Image:CyclobutadieneirontricarbonylSynthesis.png|600px|Cyclobutadieneiron tricarbonyl Synthesis]]

Cyclooctatetraene is chlorinated to the [4.0.2]-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.

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


 * [[Image:CyclobutadieneirontricarbonylReactions.png|600px|Cyclobutadieneiron tricarbonyl Reactions]]

It reacts in Friedel-Crafts acylation with acetyl chloride and aluminum 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:


 * [[Image:Cyclobutadieneirontricarbonylreactionmechanism.png|400px|Cyclobutadieneiron tricarbonyl EAS reactionmechanism]]