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 su bstituents in the 3 position of indene and a single carbon bridge is d isclosed: variation of the size of the substituent in C(3) has a stron g effect on the extent of chain transfer and isospecificity in propene polymerization. In fact, while rac-[Me2C(1-indenyl)(2)]ZrCl2 produces low molecular weight and moderately isotactic polypropene (iPP) also containing some regioirregularities ((M) over bar(n) = 6500, mmmm ca. 81% and 2,1(tot) = 0.4% at 50 degrees C in liquid monomer), rac-[Me2C( 3-tert-butyl-1-indenyl)(2)]ZrCl2 produces iPP with molecular weights b etween 25000 (T-p = 70 degrees C) and 410000 (T-p = 20 degrees C) and a fairly high isotacticity (mmmm ca. 95% at 50 degrees C), with no det ectable 2,1 units. The influence of polymerization temperature on the catalyst performance has been investigated by polymerizing liquid prop ene in the temperature range of 20-70 degrees C: the experimental Delt a Delta E(not subset of)values for enantioface selectivity have been e stimated for two members of the new class (rac-[Me2C(3-tert-butyl-1-in denyl)(2)]ZrCl2 Delta Delta E-enant(not subset of) = 4.6 kcal/mol; rac -[Me2C(3-(trimethylsilyl)1-indenyl)(2)]ZrCl2 Delta Delta E-enant(not s ubset of) = 2.6 kcal/mol). For comparison, Brintzinger's moderately is ospecific, benchmark catalyst rac-[ethylene(1-indenyl)(2)]ZrCl2 (Delta Delta E-enant(not subset of) = 3.3 kcal/mol), the single carbon bridg ed, unsubstituted rac-[Me2C(1-indenyl)(2)]ZrCl2 (Delta Delta E-enant(n ot subset of) = 2.8 kcal/mol), and the C-2-symmetric, practically aspe cific, rac-[ethylene(3-methyl-1-indenyl)(2)]ZrCl2 (Delta Delta E-enant (not subset of) = 1.9 kcal/mol) are also reported. The molecular struc tures of rac-[Me2C(3-tert-butyl-1-indenyl)(2)]ZrCl2 and rac-[Me2C(3-(t rimethylsilyl)-1-indenyl)(2)]ZrCl2 have been determined.