Modulating Thermostability and Productivity of Benzhydryl‐Substituted Bis(imino)pyridine‐Iron C2H4 Polymerization Catalysts through ortho‐CnH2n−1 (n=5, 6, 8, 12) Ring Size Adjustment

Abstract

AbstractFour types of benzhydryl‐containing bis(arylimino)pyridine‐iron(II) chloride complex, [2‐{CMeN(2,4,6‐Me3C6H2)}‐6‐{CMeN(Ar)}C5H3N]FeCl2 (Ar=2,4‐(CHPh2)2‐6‐(C5H9)C6H2 Fe1, 2,4‐(CHPh2)2‐6‐(C6H11)C6H2 Fe2, 2,4‐(CHPh2)2‐6‐(C8H15)C6H2 Fe3 and 2,4‐(CHPh2)2‐6‐(C12H23)C6H2 Fe4), discriminable by the ring size of the ortho‐CnH2n−1 (n=5, 6, 8, 12) group, have been prepared in good yield (>85 %) via the reaction of the corresponding N,N,N′‐ligand, L1–L4, with ferrous chloride tetrahydrate. All new complexes were characterized by FT‐IR spectroscopy and elemental analysis. The molecular structure of Fe3 emphasizes the distorted pseudo‐square pyramidal geometry bestowed to the metal center and the steric unevenness provided by the inequivalent N‐mesityl and N‐2,4‐dibenzyhydryl‐6‐cyclooctylphenyl groups. Extremely high activities for ethylene polymerization were achieved at temperatures between 60 °C and 70 °C following pre‐treatment of the iron(II) precatalyst with either MMAO or MAO, with the relative performance being: Fe2>Fe1>Fe3>Fe4. Notably, ortho‐cyclohexyl Fe2, under activation with MMAO, afforded the highest level of performance of this study reaching 2.82×107 g PE per mol (Fe) per h at 70 °C forming strictly linear and narrowly dispersed polyethylene (Mw/Mn=2.0) with moderate molecular weight (11.3 kg per mol). Furthermore, runs performed using Fe1/MMAO at 90 °C saw the catalytic activity drop by around only 40 % highlighting the remarkable thermostability of these catalysts. By comparison, polymerizations performed using MAO as co‐catalyst were less controlled with broader dispersities (Mw/Mn range: 4.8–10.1), while the molecular weights were generally higher (55.7–150.9 kg per mol).