Norbornene-bridged zirconium metallocenes as self-immobilizing precatalysts for olefin polymerization.

Metallocene complexes are well established highly active precatalysts1 for the polymerization of ?-olefins. Their single-centre nature and the availability of a large variety of ?-ligands structures has allowed the preparation of polymers with a wide range of microstructures and properties. But, despite the interesting results achieved in the last twenty five years, they are still seldom applied in industrial processes since their homogeneous nature prevents a continuous process like the Ziegler-Natta heterogeneous catalysts. In order to be able to be used in the conventional gas phase or slurry reactors they must be heterogenized, possibly without losing their activity and/or stereoselectivity. The common approach to this problem is the use of organic (usually polystyrene) and inorganic (silica, alumina, and MgCl2) support materials. The main drawback of all these methods is the loss of activity and stereocontrol of the catalysts due to the reduced accessibility of the metal centers. One of the most elegant approaches to this problem is the development of self-immobilizing catalysts,2 i.e. catalysts with an unsaturated function that can be used as a comonomer in the polymerization. In the framework of this kind of research, we report here the synthesis, characterization, immobilization and ethylene polymerization experiments for several new norbornene-bridged zirconium catalysts.