Naphthalenyl-Substituted α,α′-Bisimino-2,3 : 5,6-Bis(pentamethylene)pyridines as Thermally Robust Supports for Iron Ethylene Polymerization Catalysts

Six examples of N,N,N-chelated iron(II) chloride complex, [2,3 : 5,6-{C4H8C(NAr)}2C5H3N]FeCl2 (Ar=1-C10H7 Fe1, 2-Me-1-C10H6 Fe2, 2-(CHMePh)-1-C10H6 Fe3, 2-Cl-1-C10H6 Fe4, 4-Br-1-C10H6 Fe5, 4-NO2-1-C10H6 Fe6), differing in the steric/electronic properties of the substituents appended to the N-naphthalen-1-yl groups, have been synthesized in reasonable yield via a facile one-pot route. The molecular structure of five-coordinate Fe3 emphasizes the steric hindrance imposed on the iron center by the CHMePh-substituted bicyclic aromatic groups. With either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO) as activator, the complexes displayed a wide range in catalytic activities for ethylene polymerization with the order for MMAO being: Fe3>Fe2≫Fe1>Fe4≫Fe5 while Fe6 was almost inactive. In particular, Fe3/MMAO exhibited exceptionally high activity at 70 °C (up to 15.7×106 g (PE) mol−1 (Fe) h−1) affording low molecular weight (2.97 kg mol−1) polyethylene of high linearity and narrow dispersity (Mw/Mn=1.38). Moreover, the same catalyst displayed excellent thermostability by maintaining high activity at 90 °C (up to 9.26×106 g (PE) mol−1 (Fe) h−1). Similar activity trends were observed with MAO though the catalysts were in general less active but formed distinctly higher molecular weight polyethylene.