It was first prepared from tiglaldehyde and 2-butenyllithium, via 2,3,4,5-tetramethylcyclopent-2-enone, with a Nazarov cyclization reaction as a key step.
[7] Some representative reactions leading to such Cp*–metal complexes follow:[8] Deprotonation with n-butyllithium: Synthesis of (pentamethylcyclopentadienyl)titanium trichloride: Synthesis of (pentamethylcyclopentadienyl)iron dicarbonyl dimer from iron pentacarbonyl: This method is analogous to the route to the related Cp complex, see cyclopentadienyliron dicarbonyl dimer.
This method was traditionally used for preparation of the chloro-bridged dimers [Cp*IrCl2]2 and [Cp*RhCl2]2, but has been discontinued with the increased commercial availability of Cp*H. Such syntheses rely on a hydrohalic acid induced rearrangement of hexamethyl Dewar benzene[9][10] to a substituted pentamethylcyclopentadiene prior to reaction with the hydrate of either iridium(III) chloride[11] or rhodium(III) chloride.
[12] Complexes of pentamethylcyclopentadienyl differ in several ways from the more common cyclopentadienyl (Cp) derivatives.
Its bulk also attenuates intermolecular interactions, decreasing the tendency to form polymeric structures.