Four-coordinated bipyridine complexes of nickel for ethene polymerization — the role of ligand structure

Four-coordinated bipyridine complexes of nickel, (2,2′-bipyridine)NiBr2 (1), (6,6′-dimethoxycarbonyl-2,2′-bipyridine)NiBr2 (2), (2,2′-biquinoline)NiBr2 (3) and (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline)NiBr2 (4), were synthesized. Single crystal X-ray structures were determined for compounds 2 and 4. Both structures were monoclinic with space group P21/c. For 2a=8.4289(7), b=13.5013(14), c=14.7341(15) Å, Z=4. For complex 4a=12.8143(4), b=22.5687(8), c=7.8172(2) Å, Z=4, respectively. Catalytic activities of complexes were studied in ethene polymerization using MAO as a cocatalyst. Complexes 2 and 3 showed a modest activity producing high-density polyethene. Polymerization temperature had a clear effect on the activities of the complexes. Reactions carried at 50°C yielded more polyethene than reactions at 30 or 70°. The effect of ligand structure on catalytic activity was also observed, the bulky substituents increased activity.