Fluorinated cobalt catalysts and their use in forming narrowly dispersed polyethylene waxes of high linearity and incorporating vinyl functionality

Abstract

A family of six bis(arylimino)pyridine-cobalt(II) chloride complexes, [2-{CMeN(2-F-4,6-((4-FC₆H₄)₂CH)₂C₆H₂)}-6-(CMeNAr)C₅H₃N]CoCl₂ (Ar = 2,6-Me₂C₆H₃Co1, 2,6-Et₂C₆H₃Co2, 2,6-i-Pr₂C₆H₃Co3, 2,4,6-Me₃C₆H₂Co4, 2,6-Et-4-MeC₆H₂Co5) and [2-[CMeN{2-{(4-FC₆H₄)₂CH}-4-{CH(C₆H₅)Ar^F}-6-F}]-6-(CMeN(2,6-i-Pr₂C₆H₃))C₅H₃N]CoCl₂ (Ar^F = (3-(4-FC₆H₄)₂CH-4-NH₂-5-F)C₆H₂) (Co6), each incorporating one ortho-fluoride and one ortho-bis(4-fluorophenyl)methyl group, has been synthesized in good yield from the corresponding unsymmetrical N,N,N′-ligands, L1–L6. All complexes have been well characterized including by ¹⁹F NMR spectroscopy; a variable temperature ¹⁹F NMR study has also been performed on Co6 to investigate a dynamic isomerization process. The molecular structures of Co1 and Co5 emphasize the variation in steric protection of the metal center imparted by the inequivalent N-aryl groups. In the presence of methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), Co1–Co5 exhibited high activities of up to 11.7 × 10⁶ g of polyethylene (PE) (mol of Co)⁻¹ h⁻¹ at 70 °C, delivering strictly linear, low molecular weight PE waxes (between 924 and 5550 g mol⁻¹) of narrow dispersity and terminated with vinyl functionality. By comparison, Co6, possessing a more extended fluorinated para-CH(C₆H₅)Ar^F group, was the least active but afforded the highest molecular weight polyethylene (up to 10 027 mol⁻¹). In addition, DFT studies of the model Co(I)-propyl species, Co1′, Co3′ and Co6′, have been performed in an attempt to explain the favorable formation of the low molecular weight polymers.