Decamethylferrocene

Decamethylferrocene or bis(pentamethylcyclopentadienyl)iron(II) is a chemical compound with formula Fe(C5(CH3)5)2 or C20H30Fe. It is a sandwich compound, whose molecule has an iron(II) cation Fe(2+) attached by coordination bonds between two pentamethylcyclopentadienyl anions (Cp\*(-), (CH3)5C5(-)). It can also be viewed as a derivative of ferrocene, with a methyl group replacing each hydrogen atom of its cyclopentadienyl rings. The name and formula are often abbreviated to DmFc, Me10Fc or FeCp\*2.

This compound is a yellow crystalline solid that is used in chemical laboratories as a weak reductant. The iron(II) core is easily oxidized to iron(III), yielding the monovalent cation decamethylferrocenium, and even to higher oxidation states.

Preparation
Decamethylferrocene is prepared in the same manner as ferrocene from pentamethylcyclopentadiene. This method can be used to produce other decamethylcyclopentadienyl sandwich compounds.
 * 2 Li(C5Me5) + FeCl2 → Fe(C5Me5)2 + 2 LiCl

The product can be purified by sublimation. FeCp\*2 has staggered Cp\* rings. The average distance between iron and each carbon is approximately 2.050 Å. This structure has been confirmed by X-ray crystallography.

Redox reactions
Like ferrocene, decamethylferrocene forms a stable cation because Fe(II) is easily oxidized to Fe(III). Because of the electron donating methyl groups on the Cp\* groups, decamethylferrocene is more reducing than is ferrocene. In a solution of acetonitrile the reduction potential for the [FeCp\*2]^{+/0} couple is −0.59 V compared to a [FeCp2]^{0/+} reference (−0.48 V vs Fc/Fc(+) in CH2Cl2). Oxygen is reduced to hydrogen peroxide by decamethylferrocene in acidic solution.

Using powerful oxidants (e.g. SbF5 or AsF5 in SO2, or XeF(+)/Sb2F11(-) in HF/SbF5) decamethylferrocene is oxidized to a stable dication with an iron(IV) core. In the Sb2F11(-) salt, the Cp\* rings are parallel. In contrast, a tilt angle of 17° between the Cp\* rings is observed in the crystal structure of the SbF6(-) salt.