Oxygen effect in heterobimetallic catalysis: The Zr-O-Ti system as an excellent example for olefin polymerization

This paper describes the synthesis of a covalently linked oxygen-bridged heterobimetallic complex of zirconium and titanium (2) by using the precursors Cp*2ZrMe(OH) (1) and Cp*TiMe3. The crystal structural data show that complexes 1 and 2 crystallize in the orthorhombic and monoclinic system, respectively. Compound 2, when activated with methylaluminoxane (MAO), shows high activity in ethylene homopolymerization and produces LLDPE. A theoretical study on complex 2 reveals that the bridging oxygen enhances the Lewis acidity at the metal centers. Preliminary investigation of the catalytically active species shows that the initial attack of MAO occurs at the titanium center. Complex 2 exhibits good thermal stability in high-temperature polymerization reactions. The polymer products were characterized by C-13 NMR, DSC measurement, and GPC analysis.