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 alpha-olefin coordination and insertion, thereby providing comonomer-rich polyethylenes. Hafnium-based metallocenes incorporate alpha-olefins better than their zirconium congeners. The sterically encumbered bis(3',5'-di-tert-butyl-2-phenylindenyl)hafnium dichloride incorporates alpha-olefins with an ability comparable to the cyclopentadienylamido metallocene {eta(1):eta(5)-[(tert-butylamido)dimethylsilyl]-(2,3,4,5-tetramethyl-1-cyclopentadienyl)}titanium dichloride (Me2Si(Me4Cp)(BuNTiCl2)-Bu-t).