Synthesis of C7,C7‘-Ethylene- and C7,C7‘-Methylene-Bridged C₂-Symmetric Bis(indenyl)zirconium and -titanium Dichlorides

We have prepared several novel metallocenes bridged at the 7,7‘-positions of the indenyl moiety. The new metallocenes include the methylene-bridged [dl-bis(4,6-dimethylinden-7-yl)methylidene]titanium dichloride (20) and [dl-bis(4,6-dimethylinden-7-yl)methylidene]zirconium dichloride (21), which were prepared from m-xylene. In addition, [dl-1,2-bis(4-methylinden-7-yl)ethylidene]- and [dl-1,2-bis(4-isopropylinden-7-yl)ethylidene]zirconium dichlorides (dl-12a and dl-12b) and [dl-1,2-bis(4-isopropylinden-7-yl)ethylidene]titanium dichloride (dl-13) were synthesized from p-cymene and p-xylene, respectively. The structures of metallocene dichlorides dl-12a, dl-12b, and dl-13 were determined by X-ray crystallography and found to have C₁ symmetry in the solid state but in solution exhibit C₂ symmetry, as seen in the ¹H NMR spectra at room temperature.