Modulation of 2-imino-6,7-dihydroquinlin-8(5H)-imine-iron ethylene polymerization catalysts through (cyclo)alkyl, benzhydryl and halide substitution

Abstract

A direct one-pot assembly has been utilized for the preparation of 2-imino-6,7-dihydroquinlin-8(5H)-imine-ferrous chloride complexes, [2-(ArNCCH₃)-8-(ArN)C₉H₈N]FeCl₂ (Ar = 2-Me-4-(CHPh₂)-6-(C₅H₉)C₆H₂ Fe1, 2-Me-4-(C₅H₉)-6-(CHPh₂)C₆H₂ Fe2, 2-(C₅H₉)-4-Me-6-(CHPh₂)C₆H₂ Fe3, 2-(C₅H₉)-4,6-(CHPh₂)₂C₆H₂ Fe4, 2-(C₆H₁₁)-4,6-(CHPh₂)₂C₆H₂ Fe5, 2-(C₈H₁₅)-4,6-(CHPh₂)₂C₆H₂ Fe6, 2-F-4,6-(CHPh₂)₂C₆H₂ Fe7, 2-Cl-4,6-(CHPh₂)₂C₆H₂ Fe8], disparate in the steric/electronic profile of their N-aryl groups. In addition to spectroscopic characterization, the structural properties of representative Fe3 and Fe5 have been determined by single crystal XRD. Under activation with MAO or MMAO, Fe1–Fe8 displayed very high catalytic activities for ethylene polymerization at 60 °C [up to 25.20 × 10⁶ g (PE) per mol (Fe) per h for Fe2/MMAO]; even at temperatures as high as 100 °C the activity remained high [3.92 × 10⁶ g (PE) per mol (Fe) per h]. Notably, the polymers generated using MMAO as activator showed distinctly lower molecular weight than those with MAO [M_w range: 1.36–62.41 kg mol⁻¹ (MMAO) vs. 13.07–210.56 kg mol⁻¹ (MAO)], with ortho-cycloalkyl-containing Fe4–Fe6 forming polymers at the lowest end of the M_w range and with the narrowest dispersity (M_w/M_n range: 1.6–2.3). Microstructural analysis of selected polymers highlighted the presence of both vinyl-terminated polymers and fully saturated polymers, the ratio of which could be influenced by not only the type of aluminum-alkyl activator but also by the run temperature and the N-aryl substitution pattern. Significantly, the molecular weights of many of these polyethylenes fall within the specification range for polyethylene waxes used in industrial applications.