Decamethylcobaltocene
# Decamethylcobaltocene

Decamethylcobaltocene is an organocobalt compound with the formula $Co(C_5(CH_3)_5)_2,$ abbreviated $CoCp^∗$ $_2.$ It is a dark brown solid. This compound is used as a strong reducing agent in organometallic chemistry.

## Synthesis

Decamethylcobaltocene is prepared by treatment of LiCp* with $CoCl_2:$

    2 LiCp* + $CoCl_2$ → 2 LiCl + $CoCp*_2$

The permethylated form is more air-sensitive than the parent cobaltocene, owing to the inductive effects of methyl groups. It is a thermally stable compound and undergoes vacuum sublimation.

## Bonding

$Co(C_5Me_5)_2$ is a metallocene, having idealized $D_{5d}$ symmetry. Like cobaltocene, decamethylcobaltocene has a 19 electron count in its valence shell and is paramagnetic.

It is used as a one-electron reducing agent. Relative to the ferrocene/ferrocenium couple, the redox potential for the $[CoCp*_2]^{+/0}$ couple is -1.94 V compared to the $[CoCp_2]^{+/0}$ couple of -1.33 V (in dichloromethane). For comparison, the difference between the redox ferrocene and its permethylated derivative $FeCp*_2^{+/0}$ couple is -0.59 V (also in dichloromethane).

## Structure

Decamethylcobaltocene and decamethylferrocene have very similar structures. The additional electron occupies an orbital that is anti-bonding with respect to the Co-C bonds. Co-C distances of 2.118 Å at room temperature are slightly longer than seen in other metallocenes such as the Fe-C bonds in ferrocene, and fairly longer than its parent cobaltocene at 2.096 Å at room temperature (in the gas-phase, the Co-C distances in $Cp_2Co$ is 2.119 Å, closely resembling the Co-C bond lengths of decamethylcobaltocene.

An illustrative redox reaction of decamethylcobaltocene is:

    2 $CoCp*_2$ + $C_{60}$ → 2 $[CoCp*_2]^+$ + $[C_{60}]^{2−}$
