Electronic Tuning of Sterically Encumbered 2-(Arylimino)Pyridine-Nickel Ethylene Polymerization Catalysts by Para-Group Modification

A collection of five related 2-(arylimino)pyridines, 2-{(2,6-(CH(C6H4-p-F)2)2-4- RC6H2)N=CMe}C5H4N, each ortho-substituted with 4,4′-difluorobenzhydryl groups but distinct in the electronic properties para-R substituent (R = Me L1, Et L2, i-Pr L3, F L4, OCF3 L5), were prepared and combined (DME)NiBr2 to form their corresponding LNiBr2 complexes, Ni1–Ni5, high yields. All complexes characterized by FT-IR, 19F NMR spectroscopy elemental analysis, while Ni5 was additionally subject an X-ray determination, revealing a bromide-bridged dimer. The molecular structure bis-ligated (L4)2NiBr2 (Ni4’) also determined, result ligand reorganization having occurred during attempted crystallization Ni4. On activation either EtAlCl2 or MMAO, Ni1–Ni5 exhibited catalytic activities (up 4.28 × 106 g PE (mol Ni)−1 h−1 using EtAlCl2) produced highly branched polyethylene exhibiting low weight (Mw range: 2.50–6.18 kg·mol−1) narrow dispersity (Mw/Mn 2.21–2.90). Notably, it found that type group impacted on performance > Ni4 Ni3 Ni1 Ni2 for both co-catalysts, underlining positive influence electron withdrawing substituents. Analysis structural composition 1H 13C revealed existence vinyl-end (–CH=CH2) levels internal unsaturation (–CH=CH–) (ratio vinylene vinyl, 3.1:1–10.3:1) along various types branch (Me, Et, Pr, Bu, 1,4-paired Me, 1,6-paired LCBs). Furthermore, reaction temperature shown greatly affect end type, branching density, turn melting points resulting polyethylenes.