Effect of ketimide ligand for ethylene polymerization and ethylene/norbornene copolymerization catalyzed by (cyclopentadienyl)(ketimide)titanium complexes–MAO catalyst systems: Structural analysis for Cp ∗TiCl 2(N [dbnd]CPh 2)

Abstract

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′TiCl 2[N C(R 1)R 2] [Cp′ = Cp ( 1), C 5Me 5 (Cp ∗, 2); R 1,R 2 = t Bu, t Bu ( a), t Bu,Ph ( b), Ph,Ph ( c)]–methylaluminoxane (MAO) catalyst systems have been investigated. CpTiCl 2[N C( t Bu)Ph] ( 1b) CpTiCl 2(N CPh 2) ( 1c), and Cp ∗TiCl 2(N CPh 2) ( 2c) were prepared and identified; the structure of Cp ∗TiCl 2(N CPh 2) ( 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. CpTiCl 2(N C t Bu 2) ( 1a) exhibited both remarkable catalytic activity and efficient NBE incorporation for ethylene/NBE copolymerization.