Pentamethylcyclopentadiene

Clear to yellowish liquid

Liquid

0.84 g · cm -3 ( 20 ° C)

58 ° C (17 hPa)

1.474 (20 ° C, 589 nm)

Attention

Template: Infobox chemical / molecular formula search available

1,2,3,4,5 -pentamethyl cyclopentadiene is a cyclic alkene, with the empirical formula C5Me5H (Me = CH3), which is a five- methylated derivative of cyclopentadiene ( Cp). 1,2,3,4,5 -pentamethyl cyclopentadiene is the precursor of the ligand 1,2,3,4,5 - pentamethylcyclopentadienyl ( C5Me5 ), which is often abbreviated as Cp *; the star represents the five strahlenförming arranged methyl groups. Cp * is an important reagent in organometallic chemistry. In contrast to the less substituted cyclopentadiene derivatives pentamethyl cyclopentadiene tends not to dimerization.

Synthesis

Pentamethyl cyclopentadiene is commercially available. It was first shown for trans-2- methyl-2- enal on 2,3,4,5- Tetramethylcyclopent -2- enones.

Alternatively, 2- butenyllithium be reacted with ethyl acetate, followed by acid-catalyzed dehydrocyclization:

Organometallic derivatives

Pentamethyl cyclopentadiene is an important precursor for metal- organic compounds. The anionic form pentamethylcyclopentadienyl is due to binding of the five permanent ring carbon atoms to the metal atom as a ligand.

Synthesis of Cp * complexes

Some exemplary reactions for the synthesis of Cp * common metal complexes (see table):

An in teaching used but outdated route for the synthesis of Cp * complexes used hexamethyl Dewar benzene. This method has been traditionally used for the production of chloro- bridged [Cp * IrCl2 ] 2 - and [Cp * RhCl2 ] 2 dimers used. Which synthesis is based on a hydrohalic acids -induced rearrangement of hexamethyl dewar benzene substituted pentamethyl cyclopentadiene, and the subsequent reaction with iridium (III) chloride hydrate and rhodium (III ) chloride hydrate.

Comparison between Cp * and Cp

Pentamethylcyclopentadienyl complexes differ in several respects from the more widely cyclopentadienyl derivatives. When electron-rich ligand Cp * is a stronger donor and less easy to remove from the central metal atom. This results in a higher thermal stability of Cp * complexes. Its steric bulk allows the isolation of complexes with ligands fragile, reduced intermolecular interactions and reduces the tendency to polymeric structures. Cp * complexes are highly soluble in general also in nonpolar solvents.