Advancing polyethylene properties by incorporating NO2 moiety in 1,2-bis(arylimino)acenaphthylnickel precatalysts: synthesis, characterization and ethylene polymerization

Abstract

A new family of nickel halides (bromides Ni1–Ni5 and chlorides Ni6–Ni10) ligated by 1-(2,6-dibenzhydryl-4-nitrophenylimino)-2-(arylimino)acenaphthylene (Aryl = 2,6-Me₂C₆H₃L1, 2,6-Et₂C₆H₃L2, 2,6-ⁱPr₂C₆H₃L3, 2,4,6-Me₃C₆H₂L4, and 2,6-Et₂-4-MeC₆H₂L5) have been prepared and well characterized, and the scope of their catalytic properties toward the polymerization of ethylene has been investigated. Upon activation with either Et₂AlCl or EASC, the nickel bromide complexes displayed better activities than their nickel chloride counterparts and produced higher-molecular-weight polyethylene in the range of 10⁶ g mol⁻¹ with a very narrow range of molecular weight distributions. In comparison with reference precatalysts with non-nitro substituents (CH₃, F or Cl), the title complexes experienced a modest negative effect on catalytic activity upon replacement with a NO₂ moiety (activity up to 4.61 × 10⁶ g PE (mol Ni)⁻¹ h⁻¹ at 20 °C). Conversely, the NO₂ moiety exerted a positive effect to increase the molecular weight of the resulting polyethylene, and Ni4/Et₂AlCl gave polyethylene with a maximum molecular weight of as high as 32.8 × 10⁵ g mol⁻¹, which is not only the highest among the title complexes but also higher than any literature values reported with 1,2-diiminoacenaphthylnickel halides.