Highly Regiospecific Zirconocene Catalysts for the Isospecific Polymerization of Propene

A new class of isospecific and highly regiospecific C 2 - symmetric ansa -zirconocenes, characterized by a bisindenyl ansa ligand with bulky substituents in the 3 position of indene and a single carbon bridge is disclosed: variation of the size of the substituent in C(3) has a strong effect on the extent of chain transfer and isospecificity in propene polymerization. In fact, while rac -Me 2 C(1-indenyl) 2 ZrCl 2 produces low molecular weight and moderately isotactic polypropene (iPP) also containing some regioirregularities ( M̄ n = 6500, mmmm ca. 81% and 2,1 tot = 0.4% at 50 °C in liquid monomer), rac -Me 2 C(3- tert -butyl-1-indenyl) 2 ZrCl 2 produces iPP with molecular weights between 25 000 ( T p = 70 °C) and 410 000 ( T p = 20 °C) and a fairly high isotacticity ( mmmm ca. 95% at 50 °C), with no detectable 2,1 units. The influence of polymerization temperature on the catalyst performance has been investigated by polymerizing liquid propene in the temperature range of 20−70 °C: the experimental ΔΔ E ⧧ values for enantioface selectivity have been estimated for two members of the new class ( rac -Me 2 C(3- tert -butyl-1-indenyl) 2 ZrCl 2 ΔΔ E ⧧ enant = 4.6 kcal/mol; rac -Me 2 C(3-(trimethylsilyl)-1-indenyl) 2 ZrCl 2 ΔΔ E ⧧ enant = 2.6 kcal/mol). For comparison, Brintzinger's moderately isospecific, benchmark catalyst rac -ethylene(1-indenyl) 2 ZrCl 2 (ΔΔ E ⧧ enant = 3.3 kcal/mol), the single carbon bridged, unsubstituted rac -Me 2 C(1-indenyl) 2 ZrCl 2 (ΔΔ E ⧧ enant = 2.8 kcal/mol), and the C 2 -symmetric, practically aspecific, rac -ethylene(3-methyl-1-indenyl) 2 ZrCl 2 (ΔΔ E ⧧ enant = 1.9 kcal/mol) are also reported. The molecular structures of rac -Me 2 C(3- tert -butyl-1-indenyl) 2 ZrCl 2 and rac -Me 2 C(3-(trimethylsilyl)-1-indenyl) 2 ZrCl 2 have been determined.