Enhancing the thermal stability of α-Diimine Ni(II) catalysts for ethylene polymerization via symmetrical axial shielding strategy

Targeting practical complex catalyst for ethylene polymerization, the catalytic system requires a good thermo-stability along with high activity as well as reasonable molecular weights of resultant polyethylene. Herein, a series of symmetrical alpha-diimine-nickel complexes bearing functionalized 2,6-dibenzhydryl-4-t-butylphenyl N-aryl were prepared and examined in detail for ethylene polymerization, and compared the catalytic performance with their unsymmetrical analogues. The sym-metrical catalysts displayed high activities in the level of 106 g mol-1 h-1, producing high molecular weight branched polyethylene (Mw: > 1.79 x 105 g mol-1) at all the reaction temperatures ranging from 30 degrees C to 100 degrees C, in comparison, both classical and unsymmetrical alpha-diimine-nickel analogues gave low activities and became completely inactive at 100 degrees C under similar conditions. It was proposed that 7C-7C interactions between the acenaphthylene and phenyl of benzahydral group suppress the N-aryl rotation and thereby generate a blockage around the metal center by interlocking the axial positions, which in result significantly improve the thermal stability of the nickel complex catalysts.

Automated summary

A series of symmetrical alpha-diimine-nickel complexes bearing functionalized 2,6-dibenzhydryl-4-t-butylphenyl N-aryl were synthesized and compared with their unsymmetrical analogues for ethylene polymerization. The symmetrical catalysts exhibited high activities and produced high molecular weight branched polyethylene at all reaction temperatures, while the unsymmetrical catalysts showed low activities and became completely inactive at 100 degrees C. The enhanced thermal stability of the nickel complexes was attributed to the 7C-7C interactions between the acenaphthylene and phenyl of benzhydryl group.