Improved Catalytic Capabilities of Vanadium Complexes bearing Tridentate Constrained Cyclic β-Enaminoketonato Ligands towards Ethylene (Co)polymerization

A series of vanadium complexes bearing tridentate constrained cyclic β-enaminoketonato ligands, [RC₆H₃-(O)C=C(CH₂)_nCH=NC₆H₄SPh]VC_l2(THF) (2a, n =1, R = H; 2b, n =1, R = C₆H₅; 2c, n = 2, R = C₆H₅; 2d, n = 3, R = C₆H₅), were synthesized and characterized, and the molecular structures of complexes 2b and 2c were further confirmed by X-ray crystal analysis. In the presence of ethyl trichloroacetate as reactivating agent, Et₂AlCl activated vanadium complexes produced polyethylenes with unimodal distribution (PDI = 1.4-1.8) in high activities (10⁷-10⁸ g_PE/mol_V•h). Complex 2b bearing phenyl at R position showed higher catalytic activity than complex 2a without bulky R group, and the catalytic properties of these catalysts could be easily tuned by varying the ligand structure and polymerization conditions. These tridentate vanadium complexes showed promising thermal stabilities and did not deactivate in 30 minutes. The copolymerization of ethylene with norbornene (NBE) and exo-1,4,4a,9,9a,10-hexahy-dro-9,10(1′,2′)-benzeno-1,4-methanoanthracene (HBM) were also efficiently catalyzed by these vanadium catalysts, and copolymers possessing high comonomer incorporations (NBE: 45.2 mol%; HBM: 25.2 mol%) and high glass transition temperature (NBE: 113°C; HBM: 191 °C) were obtained.