Methylcyclopentadiene

Methylcyclopentadiene is any of three isomeric cyclic dialkenes 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.

Methylcyclopentadiene

Left to right: 2-methyl-1,3-cyclopentadiene; 1-methyl-1,3-cyclopentadiene; 5-methyl-1,3-cyclopentadiene
Names
Other names Cp′; MeCp
Identifiers
3D model (JSmol)	: Interactive image
ChemSpider	60141
ECHA InfoCard	100.043.400
PubChem CID	66775
InChI InChI=1S/C6H8/c1-6-4-2-3-5-6/h2-4H,5H2,1H3 Key: NFWSQSCIDYBUOU-UHFFFAOYSA-N InChI=1/C6H8/c1-6-4-2-3-5-6/h2-4H,5H2,1H3 Key: NFWSQSCIDYBUOU-UHFFFAOYAV
SMILES : C\1=C\C=C(\C)C/1
Properties
Chemical formula	C6H8
Molar mass	80.130 g·mol^−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

As with cyclopentadiene, methylcyclopentadiene is prepared by thermal cracking of its Diels–Alder dimer, followed by distillation for removal of cyclopentadiene, a common impurity.[1]

Methylcyclopentadienyl anion

Structure of Cp′Fe(PPh₃)(CO)I, with labels for the four diastereotopic ring protons.

Deprotonation of methylcyclopentadiene gives the aromatic methylcyclopentadienyl anion.[2] This ion is useful as a ligand for organometallic complexes. Relative to the corresponding cyclopentadienyl (Cp) complexes, complexes of Cp′ exhibit enhanced solubility in organic solvents.

Cp′ can be used to probe the structure of organometallic complexes. For example, Cp′Fe(PPh₃)(CO)I has four different signals in the ¹H NMR spectrum for the ring hydrogens and five different signals in the ¹³C NMR spectrum for the ring carbons. There is therefore no symmetry within the ring even accounting for rotation around the ring–metal axis, but instead there is a diastereotopic relationship as a result of being part of a chiral complex. The achiral precursor complex Cp′Fe(CO)₂I has only two signals for those hydrogens and three for those carbons, indicating a symmetric structure.[3]

References

1. Darkwa, James; Giolando, Dean M.; Murphy, Catherine Jones; Rauchfuss, Thomas B. (1990). "Bis(η⁵-Methylcyclopentadienyl)Titanium Pentasulfide, Bis(η-Methylcyclopentadienyl)-Divanadium Pentasulfide, and Bis(η⁵-Methylcyclopentadienyl)Divanadium Tetrasulfide". Inorg. Synth. 27: 51. doi:10.1002/9780470132586.ch10.
2. Wilkinson, G. (1956). "Ferrocene". Organic Syntheses. 36: 31. doi:10.15227/orgsyn.036.0031.
3. Carlton, L.; Johnston, P.; Coville, N. J. (1988). "Substituted cyclopentadienyl complexes. II. ¹³C NMR spectra of some [(η⁵-C₅H₄Me)Fe(CO)(L)I] complexes". J. Organomet. Chem. 339 (3): 339–343. doi:10.1016/S0022-328X(00)99395-1.

See also

• Pentamethylcyclopentadiene