Trimethylsilyl cyclopentadiene explained

Trimethylsilyl cyclopentadiene is an organosilicon compound with the chemical formula C₅H₅Si(CH₃)₃. It exists as a colorless liquid. It is used in the synthesis of some metal cyclopentadienyl complexes and has attracted interest for its fluxional structure.

Trimethylsilyl cyclopentadiene is an example of a molecule that undergoes rapid sigmatropic rearrangement. Observations of trimethylsilyl cyclopentadiene using gas phase NMR spectroscopy show that the protons on the ring are chemically equivalent, indicated by a single peak. This phenomenon, an example of fluxionality, is explained by the migration of the silyl group from carbon-to-carbon, thereby giving the appearance of equivalent CH signals.^[1]

Properties:^[2]

refractive index n20/D 1.471(lit.)

bp 138-140 °C(lit.)

density 0.833 g/mL at 25 °C(lit.)

storage temp. −20 °C

Synthesis

Trimethylsilyl cyclopentadiene is prepared by the reaction trimethylsilyl chloride (Me₃SiCl) with sodium cyclopentadienide (NaC₅H₅):^{[3] [4]}

(CH₃)₃SiCl + NaC₅H₅ → C₅H₅Si(CH₃)₃ + NaCl

Notes and References

1. 10.1016/S0022-2860(00)00549-4 . 1H NMR observation of trimethylsilyl migration in gas phase 5-trimethylsilylcyclopentadiene . 2000 . Taha . A.N. . Moreno . P.O. . Lemaster . C.B. . Lemaster . C.L. . True . N.S. . Journal of Molecular Structure . 553 . 1–3 . 37–42. 2000JMoSt.553...37T .
2. Web site: Trimethylsilyl cyclopentadiene, mixture of isomers 257885. Sigma-Aldrich. 2018-12-05.
3. Seki, R. . Komatsu, S. . 2011 . Preparation of (trialkylsilyl)cyclopentadienes containing almost no bis(trialkylsilyl)cyclopentadienes . Jpn. Kokai Tokkyo Koh. .
4. Encyclopedia: 5-(Trimethylsilyl)-1,3-cyclopentadiene. Francisco Palacios . Jesús M. de los Santos . 2014. 10.1002/047084289X.rn01739. e-EROS Encyclopedia of Reagents for Organic Synthesis. 1–8. 978-0-470-84289-8.