High Comonomer Selectivity in Ethylene/Hexene Copolymerization by Unbridged Indenyl Metallocenes

Catalysts derived from unbridged 2-arylindene metallocenes of Hf and Zr are active for ethylene/hexene copolymerization and show a much higher selectivity toward hexene than unsubstituted bis(indenyl) metallocenes. The ligand substitution pattern and the nature of the metal ion have a strong influence on the ability of unbridged 2-arylindenyl metallocenes to incorporate 1-hexene comonomer in ethylene/hexene copolymerizations. Our data support the hypothesis that arene substituents near the active site promote the α-olefin coordination and insertion, thereby providing comonomer-rich polyethylenes. Hafnium-based metallocenes incorporate α-olefins better than their zirconium congeners. The sterically encumbered bis(3‘,5‘-di- tert -butyl-2-phenylindenyl)hafnium dichloride incorporates α-olefins with an ability comparable to the cyclopentadienylamido metallocene {η 1:η 5 -[( tert -butylamido)dimethylsilyl](2,3,4,5-tetramethyl-1-cyclopentadienyl)}titanium dichloride (Me 2 Si(Me 4 Cp) t BuNTiCl 2 ).