Methylcyclopentadiene

  Methylcyclopentadiene describes three isomeric cyclic diolefins with the formula C₅MeH₅ (Me = CH₃). These isomers are the organic precursor to the methylcyclopentadienyl-ligand (C₅H₄Me, often denoted as Cp'), commonly found in organometallic chemistry. C₅MeH₅ is prepared by thermal cracking its Diels-Alder dimer, followed by distillation to remove cyclopentadiene C₅H₆, a common impurity.^[1]

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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, (MeC₅H₄)Fe(PPh₃)(CO)I, exhibitss four MeC₅H₄ resonances in its ¹H NMR spectrum and five MeC₅H₄ resonances in the ¹³C NMR spectrum. Free rotation of the Cp' ligand does not equivalence the diastereopic protons and carbon centers. The achiral precursor complex (MeC₅H₄)Fe(CO)₂)I exhibits only two MeC₅H₄ resonances in the ¹H NMR spectrum and three MeC₅H₄ resonances in the ¹³C NMR spectrum.^[2]  

References

1. ^ “Bis(methylcyclopentadienyl)titanium pentasulfide, Bis(methylcyclopentadienyl)divanadium pentasulfide, Bis(methylcyclopentadienyl)divanadium tetrasulfide", Darkwa, J.; Giolando, D. M.; Murphy, C. J.; Rauchfuss, T. B., Inorganic Syntheses 1990, volume 27, p 51ff.
2. ^ Carlton, L.; Johnston, P.; Coville, N. J. (1988). "Substituted cyclopentadienyl complexes. II. Carbon-13 NMR spectra of some [(η⁵-C₅H₄Me)Fe(CO)(L)I] complexes". Journal of Organometallic Chemistry 339: 339-43. doi:10.1016/S0022-328X(00)99395-1.

See also

• Cyclopentadiene
• Pentamethylcyclopentadiene