Decamethylcobaltocene


Decamethylcobaltocene is an organocobalt compound with the formula Co2, abbreviated CoCp. 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 CoCl2:
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

Co2 is a metallocene, having idealized D5d 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 +/0 couple is -1.94 V compared to the +/0 couple of -1.33 V. For comparison, the difference between the redox ferrocene and its permethylated derivative FeCp*2+/0 couple is -0.59 V.

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 Cp2Co is 2.119 Å, closely resembling the Co-C bond lengths of decamethylcobaltocene.
An illustrative redox reaction of decamethylcobaltocene is: