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Pentamethylcyclopentadiene

Pentamethylcyclopentadiene
Skeletal formula of pentamethylcyclopentadiene
Ball-and-stick model of the pentamethylcyclopentadiene molecule
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.021.586
PubChem CID
Properties
C10H16
Molar mass 136.24 g/mol
Boiling point 55 to 60 °C (131 to 140 °F; 328 to 333 K) at 13 mmHg (1.7 kPa)
Sparingly soluble
Hazards
Flash point 114 °C (237 °F; 387 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

1,2,3,4,5-Pentamethylcyclopentadiene is a cyclic dialkene with the formula C5Me5H (Me = CH3). 1,2,3,4,5-Pentamethylcyclopentadiene is the precursor to the ligand 1,2,3,4,5-pentamethylcyclopentadienyl, which is often denoted Cp* (to signify the five methyl groups radiating from the periphery of this ligand as in a five-pointed star). In contrast to less-substituted cyclopentadiene derivatives, Cp*H is not prone to dimerization.

Pentamethylcyclopentadiene is commercially available. It was first prepared from tiglaldehyde via 2,3,4,5-tetramethylcyclopent-2-enone. Alternatively 2-butenyllithium adds to ethyl acetate followed by acid-catalyzed dehydrocyclization:

Cp*H is a precursor to organometallic compounds containing the C
5
Me
5
(Cp*) ligand.

Some representative reactions leading to such Cp*–metal complexes follow:

For the related Cp complex, see cyclopentadienyliron dicarbonyl dimer.

An instructive but obsolete route to Cp* complexes involves the use of hexamethyl Dewar benzene. This method was traditionally used for preparation of the chloro-bridged dimers [Cp*IrCl2]2 and [Cp*RhCl2]2. Such syntheses rely on a hydrohalic acid induced rearrangement of hexamethyl Dewar benzene to a substituted pentamethylcyclopentadiene prior to reaction with the hydrate of either iridium(III) chloride or rhodium(III) chloride.


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