Decamethylcobaltocene
{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 428353788
| ImageFile = Decamethylcobaltocene.svg
| ImageSize = 120px
| IUPACName = Bis(η5-pentamethylcyclopentadienyl)cobalt(II)
| OtherNames = bis(η5- pentamethylcyclopentadienyl)cobalt
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|??}}
| CASNo = 74507-62-3
| PubChem = 5148110
| ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}}
| ChemSpiderID = 4321575
| SMILES = C[c-]1c(c(c(c1C)C)C)C.C[c-]1c(c(c(c1C)C)C)C.[Co+2]
| InChI = 1/2C10H15.Co/c2*1-6-7(2)9(4)10(5)8(6)3;/h2*1-5H3;/q2*-1;+2
| InChIKey = NGJVBICXQZVNEF-UHFFFAOYAU
| StdInChI_Ref = {{stdinchicite|changed|chemspider}}
| StdInChI = 1S/2C10H15.Co/c2*1-6-7(2)9(4)10(5)8(6)3;/h2*1-5H3;/q2*-1;+2
| StdInChIKey_Ref = {{stdinchicite|changed|chemspider}}
| StdInChIKey = NGJVBICXQZVNEF-UHFFFAOYSA-N }}
|Section2={{Chembox Properties
| C=20 | H=30 | Co=1
| Appearance = dark brown
| MeltingPt = >
| MeltingPtC = 210
| BoilingPt =
| Solubility = }}
}}
Decamethylcobaltocene is an organocobalt compound with the formula Co(C5(CH3)5)2, abbreviated CoCp{{su|p=∗|b=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 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).Connelly, Neil G., Geiger, Willam E. Chemical Redox Agents for Organometallic Chemistry. Chemistry Reviews. 1996. P. 877-910.DOI: 10.1021/cr940053x.
Structure
Decamethylcobaltocene and decamethylferrocene have very similar structures.Clark, Meghan M., Brennessel, William W., Holland, Patrick L. "Bis(η5-pentamethylcyclopentadienyl)cobalt(II)" Acta Crystallographica Structures Online Reports. 2009, Vol.65, . DOI. 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.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.
An illustrative redox reaction of decamethylcobaltocene is:
:2 CoCp*2 + C60 → 2 [CoCp*2]+ + [C60]2−