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

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journal contribution
posted on 18.03.2020, 12:46 by Zheng Wang, Gregory A. Solan, Yanping Ma, Qingbin Liu, Tongling Liang, Wen-Hua Sun
The 4,6-bis(arylimino)-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-iron(II) chlorides (aryl = 2,6-Me2C6H3Fe1; 2,6-Et2C6H3Fe2; 2,6-i-Pr2C6H3Fe3; 2,4,6-Me3C6H2Fe4; and 2,6-Et2-4-Me2C6H2Fe5) 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, FeCl2·4H2O, 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 Fe3 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 seven-membered carbocycles to be cis-configured. In combination with either MAO or MMAO, Fe1–Fe5 exhibited exceptionally high activities for ethylene polymerization (up to 15.86×106 gPE mol−1 Fe h−1 at 40°C (MMAO) and 9.60×106 gPE mol−1 Fe h−1 at 60°C (MAO)) and produced highly linear polyethylene (HLPE, Tm≥128°C) with a wide range in molecular weights; in general, the MMAO-promoted polymerizations were more active. Irrespective of the cocatalyst employed, the 2,6-Me2-substituted Fe1 and Fe4 proved the most active while the more sterically hindered 2,6-i-Pr2Fe3 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°C 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°C 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.


National Natural Science Foundation of China (No. 21871275)



AAAS Research, Volume 2019, Article ID 9426063

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Department of Chemistry


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