ETHYLENE AND PROPYLENE POLYMERIZATION OVER CHIRAL ANSA-DICHLORO[O-PHENYLENEDIMETHYLENEBIS(ETA(5)-L-INDENYL)]ZIRCONIUM [ZR(C6H4(CH2-1-C9H6)(2)-1,2)CL-2]

Abstract

ansa-Dichloro[o-phenylenedimethylenebis(eta(5)-1-indenyl)zirconium (1) has been prepared from the reaction of dilithiated bis(1-indenyl)-o-xylene with ZrCl4 in tetrahydrofuran. A rac-1/meso-1 ratio close to 1 is obtained, and the diastereomeric complexes have been separated by fractional crystallization. Polymerizations of both ethylene and propylene with rac-1 and meso-1 in the presence of methylaluminoxane (MAO) as cocatalyst have been examined. In ethylene polymerization, meso-1 is more active than rac-1, while in propylene polymerization, the latter is much more active than the former. The polymerization data and the stereochemical analysis of the obtained polypropylene (PP) by C-13 NMR spectroscopy reveal that both the activity of the rac-1/MAO catalyst and the stereoregularity of PP are low due to the distortion of catalyst rac-1 from the C-2 symmetry and the fluxionality of the ansa-ligand, which is caused by the four carbon atoms of the rigid o-phenylenedimethylene bridge.