Optimizing\nthe Cation Binding Pocket in Nickel Phenoxyimine\nCatalysts Improves Ethylene Polymerization Efficiency

Cation tuning is a simple yet powerful strategy to modulate\nthe\nreactivity of polymerization catalysts, but the design rules to achieve\nmaximum cation effects are not well understood. In the present work,\nit was demonstrated that inserting a methylene spacer between a nickel\nphenoxyimine complex and an M-polyethylene glycol (PEG) (where M =\nLi<sup>+</sup>, Na<sup>+</sup>, K<sup>+</sup>, or Cs<sup>+</sup>)\nunit led up to >70-fold increase in ethylene polymerization activity\nand 6-fold higher polymer molecular weight relative to that of the\nfirst-generation catalysts. It is hypothesized that these effects\nare due to the exclusive formation of 1:1 over 2:1 nickel:alkali species\nand closer proximity of the M-PEG moiety to the nickel center. These\nresults suggest that the successful creation of cation-responsive\ncatalysts requires an understanding of the cation binding stoichiometry\nas well as the structural and electronic changes associated with its\nhost–guest interactions.