Decamethylcobaltocene

Decamethylcobaltocene
IUPAC name Bis(η5-pentamethylcyclopentadienyl)cobalt(II)
Other names bis(η5- pentamethylcyclopentadienyl)cobalt
Identifiers
CAS number	74507-62-3
Properties
Molecular formula	C20H30Co
Molar mass	329.39 g mol−1
Appearance	dark brown
Melting point	>210 °C
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Decamethylcobaltocene is an organocobalt compound with the formula Co(C₅(CH₃)₅)₂, abbreviated CoCp*₂. It is 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:

2 LiCp* + CoCl₂ → 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 easily undergoes vacuum sublimation.

Bonding

Co(C₅Me₅)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 [CoCp₂]^+/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.^[1]

Structure

Decamethylcobaltocene and decamethylferrocene have very similar structures.^[2] 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.^[3]

An illustrative redox reaction of decamethylcobaltocene is:

2 CoCp*₂ + C₆₀ → [CoCp*₂]⁺ + [C₆₀]^2-

References

1. ^ Connelly, Neil G., Geiger, Willam E. Chemical Redox Agents for Organometallic Chemistry. Chemistry Reviews. 1996. P. 877-910.DOI.
2. ^ Clark, Meghan M., Brennessel, William W., Holland, Patrick L. "Bis(η5-pentamethylcyclopentadienyl)cobalt(II)" Acta Crystallographica Structures Online Reports. 2009, Vol.65, . DOI.
3. ^ Antipin, Yu M., Augart, N., Boese, R., Schmid, G. Redetermination of the cobaltocene crystal structure at 100K and 297K. Structural Chemistry. Volume 4, No. 2. 1993. P. 91-101.