Decamethylcobaltocene is an organocobalt compound with the formula Co(C<sub>5</sub>(CH<sub>3</sub>)<sub>5</sub>)<sub>2</sub>, abbreviated CoCp. It is a dark brown solid. This compound is used as a strong reducing agent in organometallic chemistry.
Decamethylcobaltocene is prepared by treatment of LiCp* with CoCl<sub>2</sub>:
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.
Co(C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub> is a metallocene, having idealized D<sub>5d</sub> 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*<sub>2</sub>]<sup>+/0</sup> couple is -1.94 V compared to the [CoCp<sub>2</sub>]<sup>+/0</sup> couple of -1.33 V (in dichloromethane). For comparison, the difference between the redox ferrocene and its permethylated derivative FeCp*<sub>2</sub><sup>+/0</sup> couple is -0.59 V (also in dichloromethane).
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 ÃÂ 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 ÃÂ at room temperature (in the gas-phase, the Co-C distances in Cp<sub>2</sub>Co is 2.119 ÃÂ , closely resembling the Co-C bond lengths of decamethylcobaltocene.
An illustrative redox reaction of decamethylcobaltocene is: