Abstract Ligand steric bulk is of paramount importance in late transition-metal mediated olefin polymerization. In this contribution, we designed and prepared two structurally similar bis(imino)pyridyl iron(II) complexes bearing 2,6-bis(dibenzhydryl)phenyl N-aryl moiety (Ph-Fe) and pentiptycenyl N-aryl moiety (Ipty-Fe) to reveal the huge effect of steric bulk on ethylene polymerization. Two iron(II) complexes were confirmed by NMR spectroscopy, mass spectroscopy, elemental analysis, and vital X-ray diffraction analysis, which indicates that Ph-Fe has a larger buried volume around the metal center than Ipty-Fe (%Vbur: 55.5 vs. 52.7). As a result, in the presence of Al reagent, Ph-Fe showed extremely low activity for ethylene polymerization, but Ipty-Fe with a less steric blockage exhibited much higher (two orders of magnitude) activity (up to 25,500 kg mol−1 h−1). Reaction temperature, time, pressure, type and amount of Al reagents were comprehensively studied to evaluate and compare these two iron(II) complexes. More interestingly, chain-end-functionalization of these obtained polyethylenes bearing vinylic end-groups could be achieved in situ by the Friedel-Crafts addition to aromatic toluene as the reaction solvent at elevated temperature or high ratio of [Al]/[Fe].

中文翻译：

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高活性戊烯基取代双(亚氨基)吡啶基铁(II)介导乙烯聚合的综合研究

摘要 配体空间体积在后期过渡金属介导的烯烃聚合中至关重要。在这一贡献中，我们设计并制备了两种结构相似的双（亚氨基）吡啶基铁（II）配合物，它们带有 2,6-双（二苯甲基）苯基 N-芳基部分（Ph-Fe）和戊烯基 N-芳基部分（Ipty-Fe ）揭示空间体积对乙烯聚合的巨大影响。两种铁 (II) 配合物经核磁共振光谱、质谱、元素分析和重要 X 射线衍射分析证实，表明 Ph-Fe 在金属中心周围具有比 Ipty-Fe 更大的埋藏体积（%Vbur：55.5与 52.7）。因此，在 Al 试剂的存在下，Ph-Fe 对乙烯聚合表现出极低的活性，但具有较少空间位阻的 Ipty-Fe 表现出更高（两个数量级）的活性（高达 25，500 kg mol−1 h−1)。综合研究了反应温度、时间、压力、Al 试剂的类型和用量，以评估和比较这两种铁 (II) 配合物。更有趣的是，这些获得的带有乙烯基端基的聚乙烯的链端官能化可以通过在升高的温度或 [Al]/[Fe] 的高比例下将 Friedel-Crafts 添加到作为反应溶剂的芳族甲苯中来原位实现。