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(Ndouble bond; length as m-dashCPh2)

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[Ndouble bond; length as m-dashC(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[Ndouble bond; length as m-dashC(tBu)Ph] (1b) CpTiCl2(Ndouble bond; length as m-dashCPh2) (1c), and Cp∗TiCl2(Ndouble bond; length as m-dashCPh2) (2c) were prepared and identified; the structure of Cp∗TiCl2(Ndouble bond; length as m-dashCPh2) (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(Ndouble bond; length as m-dashCtBu2) (1a) exhibited both remarkable catalytic activity and efficient NBE incorporation for ethylene/NBE copolymerization.