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

A direct one-pot assembly has been utilized for the preparation of 2-imino-6,7-dihydroquinlin-8(5<i>H</i>)-imine-ferrous chloride complexes, [2-(ArN[double bond, length as m-dash]CCH₃)-8-(ArN)C₉H₈N]FeCl₂ (Ar = 2-Me-4-(CHPh₂)-6-(C₅H₉)C₆H₂Fe1, 2-Me-4-(C₅H₉)-6-(CHPh₂)C₆H₂Fe2, 2-(C₅H₉)-4-Me-6-(CHPh₂)C₆H₂Fe3, 2-(C₅H₉)-4,6-(CHPh₂)₂C₆H₂Fe4, 2-(C₆H₁₁)-4,6-(CHPh₂)₂C₆H₂Fe5, 2-(C₈H₁₅)-4,6-(CHPh₂)₂C₆H₂Fe6, 2-F-4,6-(CHPh₂)₂C₆H₂Fe7, 2-Cl-4,6-(CHPh₂)₂C₆H₂Fe8], disparate in the steric/electronic profile of their <i>N</i>-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 [<i>M</i> _w range: 1.36-62.41 kg mol^-1 (MMAO) <i>vs.</i> 13.07-210.56 kg mol^-1 (MAO)], with <i>ortho</i>-cycloalkyl-containing Fe4-Fe6 forming polymers at the lowest end of the <i>M</i> _w range and with the narrowest dispersity (<i>M</i> _w/<i>M</i> _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 <i>N</i>-aryl substitution pattern. Significantly, the molecular weights of many of these polyethylenes fall within the specification range for polyethylene waxes used in industrial applications.