Syntheses, Characterization, and Ethylene (Co-)Polymerization Screening of Amidate Half-Titanocene Dichlorides

A series of amidate half-titanocene dichlorides, Cp′TiLCl2 [Cp′ = Cp (as η5-C5H5) or Cp* (as η5-C5Me5), L = N-(2-methylquinolin-8-yl)-p-R-benzamides; C1: Cp′ = Cp, R = OMe; C2: Cp′ = Cp, R = Me; C3: Cp′ = Cp, R = H; C4: Cp′ = Cp, R = F; C5: Cp′ = Cp, R = Cl; C6: Cp′ = Cp*, R = OMe; C7: Cp′ = Cp*, R = Me], have been synthesized by the stoichiometric reaction of Cp′TiCl3 with the corresponding potassium amidates. All complexes are fully characterized by elemental and NMR analyses. The molecular structures of complexes C2 and C4 are confirmed by single-crystal X-ray diffraction, and the amidate moieties coordinate the titanium center by imino and alkoxide groups. The systems C1−C7/MAO show much higher activities toward ethylene polymerization than CpTiCl3/MAO or Cp*TiCl3/MAO systems. The procatalysts (C6 and C7) bearing a Cp* ligand exhibit higher activities than their analogues (C1−C5) containing a Cp ligand, while the amidate ligands containing electron-donating groups positively affect the catalytic behavior. Both increasing the ratio of MAO to titanium and reducing reaction temperature enhance the productivities; however, the molecular weights of the resultant polymers decrease with higher activities. Moreover, the C6/MAO system performs with high activity in the copolymerization of ethylene and 1-hexene or 1-octene.