Position Makes the Difference: Electronic Effects in Nickel-Catalyzed Ethylene Polymerizations and Copolymerizations

A series of phosphine-sulfonate ligands and the corresponding nickel complexes are prepared and characterized. These ligands are specifically designed to bear systematically varied electron-donating and -withdrawing substituents (H, OMe, NMe₂, CF₃, and Me). More importantly, these substituents are installed at different positions on the ligand framework, namely, the para-position of the phenylphosphino group (position X), and para to the arylsulfonate group of the main ligand (position Y). These nickel complexes are highly active single-component catalysts for the polymerization of ethylene. An electron-donating substituent at position X or an electron-withdrawing substituent at position Y is beneficial to the properties of these nickel catalysts. Specifically, the catalyst bearing the NMe₂ substituent at position X exhibits high stability and high activity (3.3 × 10⁶ g mol^–1 h^–1), and catalyzes the formation of polyethylene of high molecular weight (M_n 405 000) and high melting point (T_m 138.5 °C). This catalyst also mediates the efficient copolymerizations of ethylene with methyl 10-undecenoate, 6-chloro-1-hexene, and trimethoxyvinylsilane.