Remote dibenzocycloheptyl-substitution of an iminotrihydroquinoline-nickel catalyst as a route to narrowly dispersed branched polyethylene waxes with alkene functionality

The 8-(arylimino)-5,6,7-trihydroquinoline-nickel(II) chlorides, [8-N{2,6-R2-4-(C15H13)C6H2}C9H8N]NiCl2 (R = Me Ni1, Et Ni2, i-Pr Ni3, F Ni4, Cl Ni5), each appended with a remote para-dibenzocycloheptyl group, have been synthesized from either the pre-formed ligand (Ni1–Ni3) or by generating the ligand in-situ during complexation (Ni4, Ni5). The molecular structures of Ni2 and Ni3 adopt dimeric or trimeric forms in the solid state, in which the chlorides can act as doubly or triply bridging ligands. On treatment with either MMAO or Et2AlCl, Ni1–Ni5 showed low (Ni4, Ni5) to high activities (Ni1–Ni3: up to 4.58 × 106 g PE mol−1 (Ni) h−1) for ethylene polymerization producing unsaturated polyethylenes of low molecular weight (1.4–2.7 kg·mol−1) and narrow dispersity (< 2.0). In the main, these polyethylene waxes are highly branched and contain relatively high levels of internal vinylenes (eCH]CHe) with respect to terminal vinyls (eCH]CH2). The ortho-substituents of the precatalyst were found to not only affect the catalytic activity but also the vinylene:vinyl ratio and the branching content. Notably, the materials generated using ortho-fluoro Ni4/Et2AlCl possessed the least number of branches and an increased vinyl contribution. Furthermore, these unsaturated polyethylenes can be readily functionalized by epoxidation with almost quantitative conversion.