Decamethylcobaltocene is an
organocobalt compound with the formula Co(C
5(CH
3)
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 CoCl
2:
:2 LiCp* + CoCl
2 → 2 LiCl + CoCp*
2
The permethylated form is more air-sensitive than the parent
cobaltocene
Cobaltocene, known also as bis(cyclopentadienyl)cobalt(II) or even "bis Cp cobalt", is an organocobalt compound with the formula Co(C5H5)2. It is a dark purple solid that sublimes readily slightly above room temperature. Cobaltocene was discovere ...
, owing to the inductive effects of methyl groups. It is a thermally stable compound and undergoes vacuum
sublimation.
Bonding
Co(C
5Me
5)
2 is a
metallocene
A metallocene is a compound typically consisting of two cyclopentadienyl anions (, abbreviated Cp) bound to a metal center (M) in the oxidation state II, with the resulting general formula Closely related to the metallocenes are the metallocene d ...
, 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
In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ).
Examples of substances that are commonly reducing agents include the Earth me ...
. Relative to the
ferrocene/
ferrocenium
Ferrocenium tetrafluoroborate is an organometallic compound with the formula e(C5H5)2F4. This salt is composed of the cation e(C5H5)2sup>+ and the tetrafluoroborate anion (). The related hexafluorophosphate is also a popular reagent with simi ...
couple, the redox potential for the
oCp*2sup>+/0 couple is -1.94 V compared to the
oCp2sup>+/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).
Structure
Decamethylcobaltocene and
decamethylferrocene
Decamethylferrocene or bis(pentamethylcyclopentadienyl)iron(II) is a chemical compound with formula or . It is a sandwich compound, whose molecule has an iron(II) cation attached by coordination bonds between two pentamethylcyclopentadienyl a ...
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 Cp
2Co 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 + C
60 → 2
oCp*2sup>+ +
60sup>2−
References
Organocobalt compounds
Metallocenes
Pentamethylcyclopentadienyl complexes
One-electron reducing agents