Synthesis of Novel Structure Based Low Generation Branched Salicylaldimine Nickel Complexes and Their Catalysis of Ethylene Oligomerization

Abstract A series of salicylaldimine nickel complexes bearing low generation branched molecules with naphthenic, straight and branched chain as cores have been synthesized by one‐pot method in high yield and were characterized by NMR spectroscopy, infrared spectroscopy, mass spectrometry and elemental analysis. The complexes C1‐C3 could form active catalysts in ethylene oligomerization reactions upon activation with co‐catalyst methylaluminoxane (MAO), triethylaluminium (AlMe 3 ), ethylaluminum sesquichloride (EASC), AlEtCl 2 or AlEt 2 Cl. The catalytic performance was affected by reaction conditions such as reaction temperature, ethylene pressure, Al/Ni molar ration and reaction time. The catalytic activity could reach up to 10 5 oligomer mol −1 (Ni) h −1 and the products were C 4 , C 6 , C 8 and trace higher carbon olefins (C 10 ‐C 18 ) under the optimum reaction conditions. When AlEt 3 was used as co‐catalyst, the major product was C 4 olefin. However the tandem reaction of ethylene oligomerization and Friedel‐Crafts occurred as chlorinated alkylaluminum reagents were used as co‐catalyst. In addition, the catalytic result showed that the kind of substituent groups in cores of branched salicylaldimine nickel complexes had a significant effect on the catalytic activity, and the distribution of ethylene oligomerization products was affected by co‐catalyst and solvent.