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

Six 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.