4,4′-Difluorobenzhydryl-modified bis(imino)-pyridyliron(ii) chlorides as thermally stable precatalysts for strictly linear polyethylenes with narrow dispersities

Abstract

The 4,4′-difluorobenzhydryl-modified bis(imino)pyridylferrous chlorides, [2-{CMeN(2,6-(4-FC₆H₄)₂CH₂-4-t-BuC₆H₂)}-6-(CMeNAr)C₅H₃N] FeCl₂ (Ar = 2,6-Me₂C₆H₃Fe1, 2,6-Et₂C₆H₃Fe2, 2,6-i-Pr₂C₆H₃Fe3, 2,4,6-Me₃C₆H₂Fe4, 2,6-Et-4-MeC₆H₂Fe5 and 2,6-(4-FC₆H₄)₂CH₂-4-t-BuC₆H₂Fe6), were synthesized in good yields. All iron complexes were characterized by ¹H/¹⁹F NMR and elemental analysis, and the molecular structures of representative complexes Fe1 and Fe6 were determined by single crystal X-ray diffraction, which revealed a slightly distorted square pyramid around the iron center. Activated with either MAO or MMAO, Fe1–Fe5 exhibited very high activities (up to 17.2 × 10⁶ g (PE) mol⁻¹ (Fe) h⁻¹ for Fe1/MMAO) toward ethylene polymerization, producing highly linear polyethylenes with narrow dispersities as required by industry and value added PEs. Importantly, the Fe1/MAO maintained an activity of 9.5 × 10⁶ g (PE) mol⁻¹ (Fe) h⁻¹ at 100 °C of operating temperature, making the catalytic system suitable for practical application. Simulation quantitatively revealed the mechanism of the enhanced catalytic performance from the electronic and steric point of view.