Decamethylcobaltocene

Decamethylcobaltocene is an organocobalt compound with the formula Co(C5(CH3)5)2, abbreviated CoCp∗
2. It is a dark brown solid. This compound is used as a strong reducing agent in organometallic chemistry.

Decamethylcobaltocene
Names
IUPAC name
Bis(η5-pentamethylcyclopentadienyl)cobalt(II)
Other names
bis(η5- pentamethylcyclopentadienyl)cobalt
Identifiers
3D model (JSmol)
ChemSpider
Properties
C20H30Co
Molar mass 329.393 g·mol−1
Appearance dark brown
Melting point > 210 °C (410 °F; 483 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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 undergoes vacuum sublimation.

Bonding

Co(C5Me5)2 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 [CoCp*2]+/0 couple is -1.94 V compared to the [CoCp2]+/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).[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 → 2 [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: 10.1021/cr940053x.
  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.
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