Synthesis and characterization of novel titanium complexes bearing [ONX]-type β-enaminoketonato ligands and their application to ethylene (co)polymerization

Abstract

A series of novel titanium complexes bearing tridentate β-enaminoketonato chelating ligands of type, [R²NC(CF₃)C(H)CR¹O]TiCl₃ (2a: R¹ = Ph, R² = −C₆H₄OMe(o); 2b: R¹ = Ph, R² = −C₉H₆N; 2c: R¹ = Ph, R² = −C₆H₄SMe(o); 2d: R¹ = Ph, R² = −C₆H₄SPh(o); 2e: R¹ = ^tBu, R² = −C₆H₄SPh(o)) and [R²NC(R¹)C(H)C(CF₃)O]TiCl₃ (2f: R¹ = Ph, R² = −C₆H₄PPh₂(o)) were prepared from TiCl₄ by treating with one equiv of deprotonated ligands in toluene. The reaction of 1a with equivalent of TiCl₄ in THF afforded another complex, C₆H₄OMeNC(CF₃)C(H)CPhO]TiCl₃(thf) (3a), in addition to formation of the dichloride complex 4a, [C₆H₄(OMe)NC(CF₃)C(H)CPhO]₂TiCl₂. After deprotonation by alkali-metal hydride at −78 °C in diethyl ether, ligand 1a could react with 0.5 equiv of TiCl₄ to form the exclusive and clean dichloride complex 4a in high yield. These complexes were identified by NMR and mass spectra as well as elemental analyses. X-ray diffraction studies on these new trichloride complexes revealed a distorted octahedral coordination of the central metal with three chlorine atoms in a mer disposition. Dichloride complex 4a also adopted a distorted octahedral geometry around the titanium center. Two chlorine atoms are situated in the cis position, as seen in the bond angles for Cl(1)–Ti–Cl(2) (92.64(7)°). The O atom on the heterocyclic group was not coordinated with Ti. When activated by modified methylaluminoxane (MMAO), complexes 2a–e exhibited moderate to high activity towards ethylene (co)polymerization, giving relatively high molecular weight polymers with unimodal molecular weight distribution.