Synthesis of zirconocene silsesquioxane complexes and their ethene polymerization activity in systems with methylaluminoxane

Abstract

Protocols for obtaining defined zirconocene complexes with polyhedral oligomeric silsesquioxanes with mono-, di-, and trisilanol functionality (SIPOSS, DIPOSS, and TRIPOSS) were established. The TRIPOSS silanolates binding one zirconocene and one chlorozirconocene moiety, [{(c-C5H9)7Si7O9O3}Zr2Cl(η5-C5H4R)4] (1, R = Bu; 2, R = H), were obtained by reacting the silanol with the respective zirconocene dichloride and triethylamine in CH2Cl2 in a 1.0:3.0:3.0 molar ratio, an excess of the zirconocene dichloride being required to suppress intramolecular dehydration of TRIPOSS. The related SIPOSS complex, [{(c-C5H9)7Si8O12O}2Zr(η5-C5H4Bu)2] (3), was prepared similarly at the stoichiometric ratio of [ZrCl2(η5-C5H4Bu)2]/ SIPOSS/NEt3 equal to 1.0:2.0:2.0. When employed in the 1.0:1.0:1.0 ratio, the same reagents afforded only the impure complex [{(c-C5H9)7Si8O12O}ZrCl(η5-C5H4Bu)2] (4), contaminated with 3 and unreacted [ZrCl2(η5-C5H4Bu)2]. Finally, the zirconocene complexes with SIPOSS and DIPOSS moiety, [{(c-C5H9)7Si8O12O}2Zr(η5-C5H5)2] (5) and [(c-C5H9)7Si7O9(OSiMe3)O2}- Zr(η5-C5H5)2] (6), respectively, were obtained by reacting [ZrMe2(η5-C5H5)2] with stoichiometric amounts of the appropriate silanols. All complexes were characterized by 1H, 13C, 29Si NMR and IR spectra, and by elemental analysis from XPS spectra. Preliminary ethene polymerization experiments showed that compounds 5 or 6 when combined with an excess of methylaluminoxane were nearly as active as [ZrCl2(η5-C5H5)2] whereas compound 2 was by about one order of magnitude less active.