Remote electron effects and π-π interactions of α-diimine nickel complexes

The seminal report of α-diimine palladium and nickel catalysts in 1995 represented a major breakthrough in the preparation of functionalized polyolefin materials. Owing to the high abundance and low cost of nickel, nickel-based catalysts have great application prospects in the industrialization process of olefin coordination polymerization. In this work, various N-aryl substituents with different electronic effects were synthesized and introduced into α-diimine ligands. The as-prepared α-diimine nickel catalysts showed high polymerization activity (0.9×10⁷–3.0×10⁷ g·mol⁻¹·h⁻¹) in ethylene polymerization, generating polyethylene products with adjustable molecular weights (M_n values: 7.4×10⁴–146.9×10⁴ g·mol⁻¹) and branching densities (31/1000 C–68/1000 C). The resulting polyethylene products showed excellent mechanical properties, with high tensile strength (up to 25.0 MPa) and high strain at break values (up to 3890%). The copolymerization of ethylene and polar monomers can also be achieved by these nicekel complexes, ultimately preparing functionalized polyolefins.