Pentamethylcyclopentadiene

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 as 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.