Models for Conformationally Dynamic Metallocenes. Copolymerization Behavior of the Unbridged Metallocene (1-Methyl-2-phenylindenyl)(2-phenylindenyl)zirconium Dichloride

Abstract

The metallocene (1-methyl-2-phenylindenyl)(2-phenylindenyl)zirconium dichloride (2) was synthesized and its propylene homopolymerization and ethylene/propylene (EP) copolymerization behavior investigated. This metallocene yields polypropylenes of lower tacticity than the unsubstituted bis(2-phenylindenyl)zirconium dichloride (1). Four bridged model compounds anti- and syn-dimethylsilylbis(2-phenylindenyl)zirconium dichloride (anti-3 and syn-3, respectively) and their 3-methyl-substituted analogues anti- and syn-dimethylsilyl(3-methyl-2-phenylindenyl)(2-phenylindenyl)zirconium dichloride (anti-4 and syn-4, respectively) were prepared to model the catalytic behavior of 2. These studies suggest that the conformational isomer modeled by metallocene syn-3 is the major contributor to the overall behavior of 2 in propylene homopolymerization. While the introduction of a methyl group onto one of the 2-phenylindenyl ligands strongly influences the structure of the resulting polypropylenes, the copolymers obtained from 2 and all four bridged metallocenes were quite similar, revealing similar copolymerization behavior for both the bridged and unbridged metallocenes.