The electronic and steric properties of ligands are of great importance in late transition metal catalyst mediated ethylene polymerization to tune the catalytic performance. In this contribution, strong electron-withdrawing groups—fluoro and nitro—along with benzhydryl as a steric component, were incorporated into the parent bis(imino)pyridine ligand structure to prepare a series of iron (II) chloride complexes: 2-[MeC=N{2-(Ph2CH)-4-NO2-6-F}C6H2]-6-[MeC=N(Ar)C6H2]C5H3N–FeCl2 (Ar = 2,6-Me2C6H3Fe2Me, 2,6-Et2C6H3Fe2Et, 2,6-iPr2C6H3Fe2iPr, 2,4,6-Me3C6H2Fe3Me and 2,6-Et2-4-MeC6H2Fe2Et,Me). Apart from the structural characterization of all complexes executed via FTIR and elemental analysis, X-ray diffraction analysis unveiled distorted square pyramidal geometry for Fe2Me (τ5 = 0.21) and Fe2Et (τ5 = 0.28). Upon in situ activation with either MAO or MMAO cocatalysts, all iron complexes displayed distinguished polymerization performance, especially in terms of thermo-stability. In particular, the less hindered Fe2Me exhibited high activity: 20.4 × 106 g mol−1 h−1 at 70 °C, 1.5 × 106 g mol−1 h−1 at 110 °C, and 0.6 × 106 g mol−1 h−1 at 120 °C. Whereas, the sterically more hindered Fe2iPr proved to be more productive in generating high molecular weight polyethylene (Mw up to 410.7 kg mol−1 at 70 °C). Moreover, by adjusting the reaction temperature and ligand structure, the chain termination reaction could be modulated from a high proportion of vinyl-terminated polyethylene to saturated polyethylene rich product [CH2CH(CH2)nCH3/CH3(CH2)nCH3 = 0.7/0.3–0.39/0.61], as confirmed by high-temperature 1H/13C NMR spectra. Low molecular weight vinyl-terminated polyethylenes are of significant importance in the synthesis of functional polymers and can serve as valuable additives in lubricants.

中文翻译：

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掺有 NO2、F 和二苯甲基取代基的双(亚氨基)吡啶酮作为乙烯基封端聚乙烯的热稳定预催化剂


配体的电子和空间性质对于后过渡金属催化剂介导的乙烯聚合调节催化性能非常重要。在这项贡献中，强吸电子基团——氟和硝基——以及作为空间组分的二苯甲基，被纳入母体双(亚氨基)吡啶配体结构中，以制备一系列氯化铁(II)络合物：2-[MeC =N{2-(Ph2CH)-4-NO2-6-F}C6H2]-6-[MeC=N(Ar)C6H2]C5H3N–FeCl2 (Ar = 2,6-Me2C6H3Fe2Me, 2,6-Et2C6H3Fe2Et, 2 ,6-iPr2C6H3Fe2iPr、2,4,6-Me3C6H2Fe3Me 和 2,6-Et2-4-MeC6H2Fe2Et,Me)。除了通过 FTIR 和元素分析执行的所有配合物的结构表征之外，X 射线衍射分析还揭示了 Fe2Me (τ5 = 0.21) 和 Fe2Et (τ5 = 0.28) 的扭曲方锥几何形状。使用 MAO 或 MMAO 助催化剂进行原位活化后，所有铁配合物均表现出出色的聚合性能，特别是在热稳定性方面。特别是，受阻较小的 Fe2Me 表现出高活性：70 °C 时为 20.4 × 106 g mol−1 h−1，110 °C 时为 1.5 × 106 g mol−1 h−1，以及 0.6 × 106 g mol−1 h 120°C 时为-1。然而，空间位阻更大的 Fe2iPr 被证明在生成高分子量聚乙烯（70°C 下 Mw 高达 410.7 kg mol−1）方面更具生产力。此外，通过调节反应温度和配体结构，可以将链终止反应从高比例的乙烯基封端聚乙烯调节为富含饱和聚乙烯的产物[CH2CH(CH2)nCH3/CH3(CH2)nCH3 = 0.7/0.3–0.39 /0.61]，由高温 1H/13C NMR 谱证实。低分子量乙烯基封端聚乙烯在功能聚合物的合成中具有重要意义，并且可以作为润滑剂中有价值的添加剂。