Syntheses and Ethylene Polymerization Behavior of Supported Salicylaldimine-Based Neutral Nickel(II) Catalysts

Two novel salicylaldimine-based neutral nickel(II) complexes, [(2,6-iPr2C6H3)NCH(2-ArC6H3O)]Ni(PPh3)Ph (6, Ar = 2-(OH)C6H4; 8, Ar = 2-OH-3-(2,6-iPr2C6H3NCH)C6H3), have been synthesized, and their structures have also been confirmed by X-ray crystallography, elemental analysis, and 1H and 13C NMR spectra. An important structural feature of the two complexes is the free hydroxyl group, which allows them to react with silica pretreated with trimethylaluminum under immobilization by the formation of a covalent bond between the neutral nickel(II) complex and the pretreated silica. As active single-component catalysts, the two complexes exhibited high catalytic activities up to 1.14 and 1.47 × 106 g PE/molNi·h for ethylene polymerization, respectively, and yielded branched polymers. Requiring no cocatalyst, the two supported catalysts also showed relatively high activities up to 4.0 × 105 g PE/molNi·h and produced polyethylenes with high weight-average molecular weights of up to 120 kg/mol and a moderate degree of branching (ca. 13−26 branches per 1000 carbon atoms).