Molecular weight control of polyethylene waxes using a constrained imino-cyclopenta[b]pyridyl-nickel catalyst

Five examples of nickel(II) bromide complexes bearing N,N-imino-cyclopenta[b]pyridines, [7-(ArN)-6,6-Me 2 C 8 H 5 N]NiBr 2 (Ar=2,6-Me 2 C 6 H 3 (Ni1), 2,6-Et 2 C 6 H 3 (Ni2), 2,6-i-Pr 2 C 6 H 3 (Ni3), 2,4,6-Me 3 C 6 H 2 (Ni4), 2,6-Et 2 -4-MeC 6 H 2 (Ni5)), have been prepared by the reaction of the corresponding ligand, L1-L5, with NiBr 2 (DME) (DME=1,2-dimethoxyethane). On crystallization from bench dichloromethane, Ni1 underwent adventitious reaction with water to give the aqua salt, [L1NiBr(OH 2 ) 3 ][Br] (Ni1'). The molecular structures of Ni1' and Ni3 have been structurally characterized, the latter revealing a bromide-bridged dimer. On activation with either MMAO or Et 2 AlCl, Ni1, Ni2, Ni4, and Ni5, all exhibited high activities for ethylene polymerization (up to 3.88 × 10 6 g(PE) mol -1 (Ni) h -1 ); the most sterically bulky Ni3 gave only low activity. Polyethylene waxes are a feature of the materials obtained which typically display low molecular weights (M w s), narrow M w distributions and unsaturated vinyl and vinylene functionalities. Notably, the catalyst comprising Ni1/Et 2 AlCl produced polyethylene with the lowest M w , 0.67 kg mol -1 , which is less than any previously reported data for any class of cycloalkyl-fused pyridine-nickel catalyst.