Fusing Carbocycles of Inequivalent Ring Size to a Bis(imino)pyridine-Iron Ethylene Polymerization Catalyst: Distinctive Effects on Activity, PE Molecular Weight, and Dispersity

The 4,6-bis(arylimino)-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-iron(II)chlorides(aryl=2,6-Me_(2)C_(6)H_(3) Fe1;2,6-Et_(2)C_(6)H_(3) Fe_(2);2,6-i-Pr_(2)C_(6)H_(3) Fe_(3);2,4,6-Me3C_(6)H_(2) Fe4;and 2,6-Et_(2)-4-Me_(2)C_(6)H_(2) Fe_(5))have been prepared in good yield by a straightforward one-pot reaction of 2,3,7,8,9,10-hexahydro-1H-cyclohepta[b]quinoline-4,6-dione,FeCl_(2)·4H_(2)O,and the appropriate aniline in acetic acid.All ferrous complexes have been characterized by elemental analysis and FT-IR spectroscopy.In addition,the structure of Fe_(3) has been determined by single crystal X-ray diffraction,which showed the iron center to adopt a distorted square pyramidal geometry with the saturated sections of the fused six-and sevenmembered carbocycles to be cis-configured.In combination with either MAO or MMAO,Fe1–Fe5 exhibited exceptionally high activities for ethylene polymerization(up to 15:86×10^(6) g(PE)mol^(−1)(Fe)h^(−1) at 40℃(MMAO)and 9:60×10^(6) g(PE)mol^(−1)(Fe)h^(−1) at 60℃(MAO))and produced highly linear polyethylene(HLPE,Tm≥128℃)with a wide range in molecular weights;in general,the MMAO-promoted polymerizations were more active.Irrespective of the cocatalyst employed,the 2,6-Me_(2)-substituted Fe1 and Fe4 proved the most active while the more sterically hindered 2,6-i-Pr_(2) Fe_(3) the least but afforded the highest molecular weight polyethylene(Mw:65.6–72.6 kg mol^(-1)).Multinuclear NMR spectroscopic analysis of the polymer formed using Fe4/MMAO at 40℃ showed a preference for fully saturated chain ends with a broad bimodal distribution a feature of the GPC trace(Mw/Mn=13:4).By contrast,using Fe4/MAO at 60℃ a vinyl-terminated polymer of lower molecular weight(Mw=14:2 kg mol^(−1))was identified that exhibited a unimodal distribution(Mw/Mn=3:8).Moreover,the amount of aluminoxane cocatalyst employed,temperature,and run time were also found to be influential on the modality of the polymer.