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(NCPh2)

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[NC(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[NC(tBu)Ph] (1b) CpTiCl2(NCPh2) (1c), and Cp∗TiCl2(NCPh2) (2c) were prepared and identified; the structure of Cp∗TiCl2(NCPh2) (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(NCtBu2) (1a) exhibited both remarkable catalytic activity and efficient NBE incorporation for ethylene/NBE copolymerization.

Graphical abstractEffects of the ketimide substituents for ethylene polymerization and ethylene/norbornene (NBE) copolymerization by Cp′TiCl2(NCR1R2) [Cp′ = Cp (1), Cp∗ (2); R1,R2 = tBu,tBu (a), tBu,Ph (b), Ph,Ph (c)]–MAO catalysts were investigated, and the structure of 2c was determined by X-ray crystallography.Figure optionsDownload full-size imageDownload as PowerPoint slide