Pentamethylcyclopentadienyl
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3D model (Jmol)
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| ChemSpider | |
| ECHA InfoCard | 100.021.586 |
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PubChem CID
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| 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) |
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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 | |
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
5Me−
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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