Boosting activity, thermostability, and lifetime of iron ethylene polymerization catalysts through gem‐dimethyl substitution and incorporation of ortho‐cycloalkyl substituents

Abstract

AbstractSix types of ferrous chloride complex, [2‐(ArN=CMe)‐8‐(ArN)‐7,7‐Me2C9H6N]FeCl2 (Ar=2‐(C5H9)‐6‐MeC6H3 Fe1, 2‐(C6H11)‐6‐MeC6H3 Fe2, 2‐(C8H15)‐6‐MeC6H3 Fe3, 2‐(C5H9)‐4,6‐Me2C6H2 Fe4, 2‐(C6H11)‐4,6‐Me2C6H2 Fe5, 2‐(C8H15)‐4,6‐Me2C6H2 Fe6), each bearing a gem‐dimethyl‐substituted N,N,N‐chelating ligand that differs in the ortho‐cycloalkyl ring size and para‐substituent of the N‐aryl groups, are disclosed. All complexes have been prepared by a straightforward one‐flask route and characterized by FT‐IR spectroscopy and elemental analysis. In the case of Fe1, oxidation to form the oxo‐bridged diferric species [2‐(2‐(C5H9)‐6‐MeC6H3N=CMe)‐8‐(2‐(C5H9)‐6‐MeC6H3N)‐7,7‐Me2C9H6N]FeCl(μ‐O)FeCl3 (Fe1') has been demonstrated and its structural identity confirmed by single crystal X‐ray diffraction. Following treatment with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), Fe1–Fe6 exhibited optimal catalytic activities at 60°C for ethylene polymerization [up to 2.35 × 107 g of PE (mol of Fe)−1 h−1 for Fe1/MMAO] producing linear polyethylene; even over prolonged run times, high activities were maintained. Moreover, this family of iron catalysts exhibited remarkable thermostability by displaying appreciable activity at temperatures as high as 100°C [activity up to 7.8 × 106 g of PE (mol of Fe)−1 h−1]. By varying the ring size of the ortho‐cycloalkyl and para‐R2 group (R2 = H, Me), excellent control over molecular weight of the polyethylenes could be achieved with values in the range 1.4–67.8 kg mol−1 obtainable. In addition, end‐group analysis of the polymers generated with Fe/MAO or Fe/MMAO revealed that both β‐H elimination and chain transfer to aluminum are competitive processes during chain termination.