Effect of ketimide ligand for ethylene polymerization and ethylene/norbornene copolymerization catalyzed by (cyclopentadienyl)(ketimide)titanium complexes-MAO catalyst systems: Structural analysis for Cp*TiCl2(N{double bond, long}CPh2)

Article abstract of DOI:10.1016/j.jorganchem.2007.04.043

Ligand effects on the catalytic activity [and norbornene (NBE) incorporation] for both ethylene polymerization and ethylene/NBE copolymerization using half-titanocenes (titanium half-sandwich complexes) containing ketimide ligand of type Cp′TiCl₂[N{double bond, long}C(R¹)R²] [Cp′ = Cp (1), C⁵Me⁵ (Cp^*, 2); R¹,R² = ^tBu,^tBu (a), ^tBu,Ph (b), Ph,Ph (c)]-methylaluminoxane (MAO) catalyst systems have been investigated. CpTiCl₂[N{double bond, long}C(^tBu)Ph] (1b) CpTiCl₂(N{double bond, long}CPh₂) (1c), and Cp^*TiCl₂(N{double bond, long}CPh₂) (2c) were prepared and identified; the structure of Cp^*TiCl₂(N{double bond, long}CPh₂) (2c) was determined by X-ray crystallography. The catalytic activity for ethylene polymerization increased in the order: 1a > 1b > 1c, suggesting that an electronic nature of the ketimide ligand affects the activity. However, molecular weight distributions for resultant (co)polymers prepared by 1b,c and by 2c-MAO catalyst systems were bi- or multi-modal, suggesting that the ketimide substituent plays a key role in order for these (co)polymerizations to proceed with single catalytically-active species. CpTiCl₂(N{double bond, long}C^tBu₂) (1a) exhibited both remarkable catalytic activity and efficient NBE incorporation for ethylene/NBE copolymerization.