What is "methylcyclopentadiene"

n. (context organic compound English) Any of three isomeric cyclic diolefins, (methyl derivatives of cyclopentadiene), the organic precursor to the methylcyclopentadienyl-ligand commonly found in organometallic chemistry.

Methylcyclopentadiene describes three isomeric cyclic di alkenes with the formula CMeH (Me = CH). These isomers are the organic precursor to the methylcyclopentadienyl ligand (CHMe, often denoted as Cp′), commonly found in organometallic chemistry. CMeH is prepared by thermal cracking its Diels–Alder dimer, followed by distillation to remove cyclopentadiene CH, a common impurity.

Relative to the corresponding Cp complexes, complexes of Cp′ exhibit enhanced solubility in organic solvents. Furthermore, Cp′ is often employed to probe the structure of organometallic complexes. For example, Cp'Fe(PPh3)(CO)I exhibits four MeCH resonances in its H NMR spectrum and five MeCH resonances in the C NMR spectrum. Free rotation of the Cp′ ligand does not equivalence the diastereopic protons and carbon centers. The achiral precursor complex Cp'Fe(CO)2I exhibits only two MeCH resonances in the H NMR spectrum and three MeCH resonances in the C NMR spectrum.