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

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.