Titanium complexes with β-ketoiminate chelate ligands for ethylene polymerization: The significant influence of substituents on structures and catalytic activities

Four titanium complexes having β-ketoiminate chelate ligands with fluorine or alkyl groups [(Ar)NC(CH3)C(H)C(CH3)O]2TiCl2 (3a: Ar = 2.6-F2C6H3; 3b: Ar = C6F5; 3c: Ar = 2.6-Me2C6H3; 3d: Ar = 2.6-iPr2C6H3) have been synthesized and characterized by 1H NMR and EA. Complexes 3a, 3c and 3d were further characterized by X-ray diffraction analysis and demonstrated distorted octahedral coordination structure around the titanium center. The substituents in ligands greatly affect the coordination mode, resulting in three different isomeric structures. These complexes are active catalysts for polymerization of ethylene with MMAO as cocatalyst. The substituents in ligands have also great influences on catalytic activity. The complexes with alkyl groups have lower activity, while the complexes with fluorine atoms have middle or high catalytic activity.

Graphical abstractFour novel titanium complexes with two β-ketoiminate ligands containing fluorine or alkyl substituent groups have been synthesized, in which the substituents have significant influences upon molecular structures and catalytic activities. Three different isomeric structures have been found as different substituents in ligands. The catalytic activity for ethylene polymerization can be enhanced greatly by introduction fluorine atoms into ligands, owing to electron withdrawing effect.Figure optionsDownload full-size imageDownload as PowerPoint slide