2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridylcobalt(ii) dichlorides: Synthesis, characterization and ethylenepolymerization behavior

Abstract

A series of unsymmetrical 2,6-bis(imino)pyridylcobalt(II) complexes, {2-[2,6-(CH(C₆H₅)₂)₂-4-Me–C₆H₂NC(CH₃)]-6-(2,6-R¹₂-4-R²–C₆H₂NCCH₃)–C₅H₃NCoCl₂} where R¹ = Me, Et or ⁱPr, R² = H or Me, together with the new symmetrical complex 2,6-[2,6-(CH(C₆H₅)₂)₂-4-Me–C₆H₂NC(CH₃)]₂–C₅H₃NCoCl₂, were synthesized. All of the compounds were fully characterized by ¹H NMR and IR spectroscopy, as well as by elemental analysis. The molecular structures of Co1 (R¹ = Me, R² = H) and Co5 (R¹ = Et, R² = Me) were further confirmed by single crystal X-ray diffraction, which indicated that the cobalt centres were penta-coordinate with a pseudo square-pyramidal geometry. Upon treatment with MAO or MMAO, these cobalt pre-catalysts exhibited higher activities than any previously reported cobalt pre-catalysts, with values as high as 4.64 × 10⁶ g PE mol⁻¹(Co) h⁻¹ for ethylene polymerization at atmospheric pressure. The polyethylenes obtained were of high molecular weight and narrow molecular weight distribution.