Moderately branched ultra-high molecular weight polyethylene by using N,N′-nickel catalysts adorned with sterically hindered dibenzocycloheptyl groups

Five examples of unsymmetrical 1,2-bis (arylimino) acenaphthene (L1 – L5), each containing one N-2,4-bis (dibenzocycloheptyl)-6-methylphenyl group and one sterically and electronically variable N-aryl group, have been used to prepare the N,N′-nickel (II) halide complexes, [1-[2,4-{(C 15 H 13 } 2 –6-MeC 6 H 2 N]-2-(ArN)C 2 C 10 H 6 ]NiX 2 (X = Br: 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) and (X = Cl: Ar = 2,6-Me 2 C 6 H 3 Ni6, 2,6-Et 2 C 6 H 3 Ni7, 2,6-i-Pr 2 C 6 H 3 Ni8, 2,4,6-Me 3 C 6 H 2 Ni9, 2,6-Et 2 –4-MeC 6 H 2 Ni10), in high yield. The molecular structures Ni3 and Ni7 highlight the extensive steric protection imparted by the ortho-dibenzocycloheptyl group and the distorted tetrahedral geometry conferred to the nickel center. On activation with either Et 2 AlCl or MAO, Ni1 – Ni10 exhibited very high activities for ethylene polymerization with the least bulky Ni1 the most active (up to 1.06 × 10 7  g PE mol −1 (Ni) h −1 with MAO). Notably, these sterically bulky catalysts have a propensity towards generating very high molecular weight polyethylene with moderate levels of branching and narrow dispersities with the most hindered Ni3 and Ni8 affording ultra-high molecular weight material (up to 1.5 × 10 6  g mol −1 ). Indeed, both the activity and molecular weights of the resulting polyethylene are among the highest to be reported for this class of unsymmetrical 1,2-bis (imino)acenaphthene-nickel catalyst.