C-1-symmetric heterocyclic zirconocenes as catalysts for propylene polymerization, 2 - ansa-Zirconocenes with linked dithienocyclopentadienyl-substituted indenyl ligands

Abstract

The synthesis of C 1 symmetric zirconocene complexes bearing the 2,5-dimethyl-7H-cyclopenta]1,2-b:4,3-b']dithiophene ligand (S 2 -3) linked to substituted cyclopentadienes is described. Different syntheses of S 2 -3, the common intermediate for the preparation of these complexes, are discussed. Many of these complexes have been found to be highly active in propylene polymerization, to require very low amounts of methylalumoxane to be actived, and to produce poly(propylene)s of low isotacticity and melting points? 13 C NMR analysis shows that the poly(propylene)s are fully regioregular and that the stereoerrors are randomly distributed, as shown by the enantiomorphic-site triad test E ≃ 1. The experimental pentad distribution was fitted using a two-site model with different probability parameters for each site. The probability of chain back-skip was also taken into account. The molecular weight and crystallinity of the poly(propylene)s are dependent upon the type of substituents on the cyclopentadienyl ring, and the correlation between mmmm and melting point of the PP confirms the random distribution of stereoerrors.