Zirconium Complexes with Bulkier Amine Bis(phenolate) Ligands and Their Catalytic Properties for Ethylene (Co)polymerization

Abstract

A series of new zirconium complexes bearing bulkier amine bis(phenolate) tetradentate ligands, Me₂NCH₂CH₂N{CH₂(2-O-3-R-5-^tBu-C₆H₂)}₂ZrCl₂ [R = CPhMe₂ (1); CMePh₂ (2); CPh₃ (3); Ph (4); 3,5-Me₂C₆H₃ (5); 3,5-^tBu₂C₆H₃ (6); 4-^tBuC₆H₄ (7)], were synthesized and characterized by ¹H nuclear magnetic resonance (NMR), ¹³C NMR, and elemental analyses. The molecular structures of complexes 1 and 3 were determined by single-crystal X-ray diffraction analysis. The X-ray crystallography analysis reveals that these complexes display a slightly distorted octahedral geometry around their metal centers. Upon activation with methylaluminoxane (MAO), dry-MAO, MAO/butylated hydroxytoluene (BHT), or AlⁱBu₃/CPh₃B(C₆F₅)₄, these zirconium complexes exhibit high catalytic activity for ethylene polymerization [up to 1.07 × 10⁷ g PE (mol Zr)^-1 h^-1] and ethylene/1-hexene copolymerization [up to 2.78 × 10⁷ g polymer (mol Zr)^-1 h^-1], affording (co)polymers with moderate to high molecular weights and good comonomer incorporations. The zirconium complexes with bulkier R groups show higher catalytic activities and longer lifetimes and produce polymers with higher molecular weights, while the zirconium complexes with aryls as R groups demonstrate relatively good comonomer incorporation ability for the copolymerization reactions. These catalytic systems also show moderate catalytic activities for the polymerization reactions of propylene, 1-hexene, and 1-decene. Upon activation with MAO, the zirconium complexes also show moderate catalytic activities for the copolymerization reaction of ethylene with 3-buten-1-ol (treated with 1 equiv of AlⁱBu₃), affording copolymers with the incorporation of 3-buten-1-ol up to 1.05%.