Chiral Epoxides as Building Blocks for Ethylene-Bridgedansa-Metallocene Complexes – Synthesis ofC1-Symmetrical Zirconocene Dichlorides with Two Different Cyclopentadienyl Units
✍ Scribed by Rieger, Bernhard ;Steimann, Manfred ;Fawzi, Riad
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1992
- Tongue
- English
- Weight
- 497 KB
- Volume
- 125
- Category
- Article
- ISSN
- 0009-2940
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✦ Synopsis
Dicyclopentadienyl ligands / ansa-Zirconocenes, Cl-symmetrical / Epoxides Epoxystyrene undergoes ring opening on treatment with tetraphenylcyclopentadienyl-and fluorenyllithium to give the corresponding chiral alcohols 3 and 4 in high yield. Their trifluoromethanesulfonate derivatives 5 react with one equivalent of cyclopentadienylsodium to form the ligand precursors l-cyclopentadienyl-l-phenyl-2-(tetraphenylcyclopentadien-y1)ethane (L' H,) and l-cyclopentadienyl-2-(9-fluorenyl)-l-phenylethane (L'H,). The zirconocenes L'ZrClz (?a) and LZZrClz
(?b) are prepared from the dilithio salts L'Li, and L2Liz, respectively. A low-temperature X-ray structure investigation of complex ?a demonstrates the chiral arrangement of the four phenyl substituents of the tetraphenylcyclopentadienyl (C5Ph4) unit. A 'H-NMR study shows that the phenyl groups rotate rapidly on the NMR time scale at room temperature. The dependence of phenyl rotation on temperature is discussed.