A POSSIBLE MODEL FOR THE STEREOSPECIFICITY IN THE SYNDIOSPECIFIC POLYMERIZATION OF PROPENE WITH GROUP-4A METALLOCENES

The techniques of conformational analysis to investigate the factors that determine the stereospecificity, previously applied to stereorigid model sites for the homogeneous isospecific Ziegler-Natta catalysis, are now extended to other stereorigid cationic model sites. For a model site including an isopropyl(cyclopentadienyl-1-fluorenyl) ligand, a precise definition of the interactions that determine its enantioselectivity at the molecular level is presented. For other model sites including an isoprophyl(cyclopentadienyl-1-indenyl) or an isopropyl(1-fluorenyl-3-methylcyclopentadienyl) ligand, on the basis of energy calculations, predictions of their stereospecific behavior are presented, which are in a qualitative agreement with the available experimental information.