Syntheses of Polysiloxane-Bridged Dinuclear Metallocenes and Their Catalytic Activities

The polysiloxane-bridged dinuclear metallocenes [(SiMe₂O)_n-SiMe₂(C₅H ₄)₂][(C₉H₇)ZrCl₂] ₂ (n=1 (7), 2 (8), 3 (9)) have been generated as a model complex for the immobilized metallocene at silica surface by treating the respective disodium salts of the ligands with 2 equivalents of (C₉H₇)ZrCl₃ in THF. All three complexes are characterized by ¹H NMR and measurement of metal content through ICP-MS. It turned out that the values of Δδ=[δ_d-δ_d], the chemical shift difference between the distal (δ_d) and proximal (δ_d) protons, for the produced dinuclear compounds (0.47 for 7, 0.49 for 8, and 0.5 for 9) were larger than the Δδ value of the known ansa-type complex holding the same ligand as a chelating one, that is just the opposite to the normal trend. In order to compare polymerization behavior of the dinuclear metallocene with the corresponding mononuclear metallocene, (Cp)(C₉H₇)ZrCl₂ was separately prepared. To investigate the catalytic properties of the dinuclear complexes and mononuclear metallocenes ethylene polymerization has been conducted in the presence of MMAO. The polymerization results display the typical activity dependence on polymerization temperature for all complexes. The most important feature is that the polymers from the dinuclear metallocenes represent enormously improved molecular weight compared with the polymer from the corresponding mononuclear metallocene. In addition, the influence of the nature of the bridging ligand upon the reactivities of the dinuclear metallocenes has also been observed.