Recent advancements in α-diimine-nickel and -palladium catalysts for ethylene polymerization

The fascination of the well-defined metal catalysts for olefin polymerization is their capability to control the properties of the polymer such as topology (linear to highly branched), range of molecular weights and molecular weight distributions, stereochemistry, regio-chemistry, end group fidelity etc. Homogeneous α-diimine-nickel and palladium catalysts have a considerable track record for ethylene (co)polymerization. For ethylene polymerization, the catalyst structure-activity and polymer properties are continuously investigated from more than two decades. Herein, we have summarized the recent advancements made in the electronic and steric substituents of α-diimine-nickel and palladium catalysts for ethylene polymerization and how these modifications influence the catalyst activity, chain walking mechanism and thermal stability. The catalysts structure relationship with activity and properties of polymer are the most distinct features of these α-diimine metal catalysts. Most importantly, the steric substitution at axial sites of the catalysts are the main switches to obtain polymer with characteristics properties. In most of the cases, highly branched polyethylene are accessible which are in high demand for the production of thermoplastic elastomers, functional materials as well as lubricant application.