Non-Symmetrically Fused Bis(arylimino)pyridines with para-Phenyl Substitution: Exploring Their Use as N′,N,N″-Supports in Iron Ethylene Polymerization Catalysis

Abstract

Through the implementation of a one-pot strategy, five examples of non-symmetrical [N,N-diaryl-11-phenyl-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-4,6-diimine]iron(II) chloride complexes (aryl = 2,6-Me2Ph Fe1, 2,6-Et2Ph Fe2, 2,6-i-Pr2Ph Fe3, 2,4,6-Me3Ph Fe4, and 2,6-Et2-4-MePh Fe5), incorporating fused six- and seven-membered carbocyclic rings and appended with a remote para-phenyl group, were readily prepared. The molecular structures of Fe2 and Fe3 emphasize the variation in fused ring size and the skewed disposition of the para-phenyl group present in the N′,N,N″-ligand support. Upon activation with MAO or MMAO, Fe1–Fe5 all showed high catalytic activity for ethylene polymerization, with an exceptional level of 35.92 × 106 g (PE) mol−1 (Fe) h−1 seen for mesityl-substituted Fe4/MMAO operating at 60 °C. All catalysts generated highly linear polyethylene with good control of the polymer molecular weight achievable via straightforward manipulation of run temperature. Typically, low molecular weight polymers with narrow dispersity (Mw/Mn = 1.5) were produced at 80 °C (MMAO: 3.7 kg mol−1 and MAO: 4.9 kg mol−1), while at temperatures between 40 °C and 50 °C, moderate molecular weight polymers were obtained (MMAO: 35.6–51.6 kg mol−1 and MAO: 72.4–95.5 kg mol−1). Moreover, analysis of these polyethylenes by 1H and 13C NMR spectroscopy highlighted the role played by both β-H elimination and chain transfer to aluminum during chain termination, with the highest rate of β-H elimination seen at 60 °C for the MMAO-activated system and 70 °C for the MAO system.