Decamethylferrocene
# Decamethylferrocene

Decamethylferrocene or bis(pentamethylcyclopentadienyl)iron(II) is a chemical compound with formula $Fe(C_5(CH_3)_5)_2$ or $C_{20}H_{30}Fe.$ It is a sandwich compound, whose molecule has an iron(II) cation $Fe^{2+}$ attached by coordination bonds between two pentamethylcyclopentadienyl anions $(Cp*^−,$ $(CH_3)_5C−5).$ 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, $Me_{10}Fc$ 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 $Li(C_5Me_5)$ + $FeCl_2$ → $Fe(C_5Me_5)_2$ + 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 $[FeCp_2]^{0/+}$ reference (−0.48 V vs $Fc/Fc^+$ in $CH_2Cl_2).$ Oxygen is reduced to hydrogen peroxide by decamethylferrocene in acidic solution.

Using powerful oxidants (e.g. $SbF_5$ or $AsF_5$ in $SO_2,$ or $XeF^+/Sb_2F−11$ in $HF/SbF_5)$ decamethylferrocene is oxidized to a stable dication with an iron(IV) core. In the $Sb_2F−11$ 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 SbF−6 salt.

