Nickel(II) complexes bearing pyrazolylimine ligand: synthesis, structure, and catalytic properties for vinyl-type polymerization of norbornene

摘要

Two nickel(II) complexes of {2-[C3HN2(R1)2-3,5]}tC(R2)=N(C6H3~iPr2-2/6)]NiBr2 (complex 1: R1 = CH3, R2 = 2,4,6-trimethylphenyl; complex 2: R1 = R2 = Ph) were synthesized and characterized. The solid-state structure of complex 1 has been confirmed by X-ray single-crystal analysis. Activated by methylaluminoxane (MAO), complexes 1 and 2 are capable of catalyzing the polymerization of norbornene with moderate activities [up to 10.56 x 10~5 gPNBE (mol Ni h)~(-1)] with high molecular weights (M_w ≤ 13.56 x 10~5 g mol~(-1)) and molecular weight distributions were around 2. The influences of polymerization parameters such as reaction temperature and Al-Ni molar ratio on catalytic activity and molecular weight of the polynorbornene were investigated in detail. The obtained polynorbornenes were characterized by means of ~1H-NMR and FTIR techniques. The analytical results of polymer structures indicated that the norbornene polymerization is vinyl-type polymerization rather than ROMP.