The formation and polymerization behavior of Ni(II) α-diimine complexes using various aluminum activators

Several Ni(II) α-diimine complexes have been synthesized and examined for ethylene and propylene polymerization in combination with different aluminum co-catalysts. The precatalysts used in the study were [ArNC(Nap)C(Nap)NAr]NiBr2 (Nap=1,8-naphthdiyl) (1, Ar=2,4,6-trimethylphenyl; 2, Ar=2-tBu phenyl; 3, Ar=2-iPr phenyl). These complexes were synthesized via a one-pot reaction where the ligand is formed via an acid catalyzed condensation followed by direct addition of nickel(II) bromide. The complexes were also prepared by a two-step procedure where the ligand was first formed by condensation between the appropriate aniline and acenaphthoquinone, and the resulting ligand was then allowed to react with (1,2-dimethoxyethane) nickel(II) dibromide. X-ray structural studies of complexes 1 and 2 have been carried out. Diethylaluminum chloride (DEAC), and 1,3-dichloro-1,3-diisobutyldialuminoxane (DCDAO) show higher activities for ethylene and propylene polymerizations in combination with these Ni(II) α-diimine complexes than does polymethylaluminoxane (MAO). The molecular weight of the resulting polymers as well as their respective polydispersities and Tms are also presented. The polypropylenes obtained with 1/DEAC and 2/DEAC at 0 °C show similar rr triad percentage as previously reported for polypropylenes generated by MAO activated Ni(II) α-diimine complexes.