Chiral Epoxides as Building Blocks for Ethylene‐Bridged ansa‐Metallocene Complexes – Synthesis of C₁‐Symmetrical Zirconocene Dichlorides with Two Different Cyclopentadienyl Units

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 1‐cyclopentadienyl‐1‐phenyl‐2‐(tetraphenylcyclopentadienyl)ethane (L¹H₂) and 1‐cyclopentadienyl‐2‐(9‐fluorenyl)‐1‐phenylethane (L²H₂). The zirconocenes L¹ZrCl₂ (7a) and L²ZrCl₂ (7b) are prepared from the dilithio salts L¹Li₂ and L²Li₂, respectively. A low‐temperature X‐ray structure investigation of complex 7a demonstrates the chiral arrangement of the four phenyl substituents of the tetraphenylcyclopentadienyl (C₅Ph₄) unit. A ¹H‐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.