Bis(cyclooctatetraene)iron is an organoiron compound with the formula Fe(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>, abbreviated Fe(COT)<sub>2</sub>. It is an air-sensitive black solid that is soluble in diethyl ether and aromatic solvents. The compound decomposes in solution after a few days even under inert atmosphere. It has no known practical applications but has been studied as a soluble source of Fe(0).
The laboratory synthesis of Fe(COT)<sub>2</sub>, using Schlenk techniques, involves reduction of ferric acetylacetonate by triethylaluminium in the presence of 1,3,5,7-cyclooctatetraene:
According to analysis by single crystal X-ray crystallography, the two cyclooctatetraene rings bind differently to the Fe center, leading to the description Fe(÷<sup>4</sup>-C<sub>8</sub>H<sub>8</sub>)(÷<sup>6</sup>-C<sub>8</sub>H<sub>8</sub>). One cyclooctatetraene ring binds to Fe with two adjacent double bonds. This interaction is similar to that in (÷<sup>4</sup>-C<sub>8</sub>H<sub>8</sub>)Fe(CO)<sub>3</sub>. The two planar groups formed by carbon atoms 1,2,7,8 and carbon atoms 3,4,5,6,7 form a dihedral angle of 33ð. The second cyclooctatetraene ring binds through three double bonds. The shape and coordination of the lower ring is similar to that in (÷<sup>6</sup>-C<sub>8</sub>H<sub>8</sub>)Mo(CO)<sub>3</sub>. The non-coordinated double bond has a similar bond length as an ordinary double bond.
In solution, Fe(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub> is a fluxional molecule such that its <sup>1</sup>H NMR spectrum consists of a singlet at room-temperature.