Highly Regiospecific Zirconocene Catalysts for the Isospecific Polymerization of Propene

• Published in: Journal of the American Chemical Society 1998-03, Vol.120 (10), p.2308-2321
• Main Authors: Resconi, Luigi, Piemontesi, Fabrizio, Camurati, Isabella, Sudmeijer, Olof, Nifant'ev, Ilya E, Ivchenko, Pavel V, Kuz'mina, Lyudmila G
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja973160s

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-[Me2C(1-indenyl)2]ZrCl2 produces low molecular weight and moderately isotactic polypropene (iPP) also containing some regioirregularities (M̄ n = 6500, mmmm ca. 81% and 2,1tot = 0.4% at 50 °C in liquid monomer), rac-[Me2C(3-tert-butyl-1-indenyl)2]ZrCl2 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 ΔΔE ⧧ values for enantioface selectivity have been estimated for two members of the new class (rac-[Me2C(3-tert-butyl-1-indenyl)2]ZrCl2 ΔΔE ⧧ enant = 4.6 kcal/mol; rac-[Me2C(3-(trimethylsilyl)-1-indenyl)2]ZrCl2 ΔΔE ⧧ enant = 2.6 kcal/mol). For comparison, Brintzinger's moderately isospecific, benchmark catalyst rac-[ethylene(1-indenyl)2]ZrCl2 (ΔΔE ⧧ enant = 3.3 kcal/mol), the single carbon bridged, unsubstituted rac-[Me2C(1-indenyl)2]ZrCl2 (ΔΔE ⧧ enant = 2.8 kcal/mol), and the C 2-symmetric, practically aspecific, rac-[ethylene(3-methyl-1-indenyl)2]ZrCl2 (ΔΔE ⧧ enant = 1.9 kcal/mol) are also reported. The molecular structures of rac-[Me2C(3-tert-butyl-1-indenyl)2]ZrCl2 and rac-[Me2C(3-(trimethylsilyl)-1-indenyl)2]ZrCl2 have been determined.