This metal carbonyl is an important reagent in organometallic chemistry and of occasional use in organic synthesis.

This micaceous orange solid is virtually insoluble in all common solvents.

Elucidation of the structure of Fe2(CO)9 proved to be challenging because its low solubility inhibits growth of crystals.

Oxidative addition of allyl bromide to diiron nonacarbonyl gives the allyl iron(II) derivative:[11] Cyclobutadieneiron tricarbonyl is prepared similarly using 3,4-dichlorocyclobutene perhaps according to the following idealized equation:[12] Fe2(CO)9 has also been employed in the synthesis of cyclopentadienones via a net [2+3]-cycloaddition from dibromoketones, known as the Noyori [3+2] reaction.

[13] Low temperature UV/vis photolysis of Fe2(CO)9 yields the Fe2(CO)8 unsaturated complex, producing both CO-bridged and unbridged isomers.