Weak noncovalent interactions are an effective strategy for modulating catalytic olefin polymerization but have never been observed in bis(imino)pyridyl iron catalysts. In this paper, a series of “sandwich” bis(imino)pyridyl iron complexes with substituted 8-(p-R-phenyl)naphthylamine (R = OMe, Me, H, CF₃) were designed and synthesized for ethylene polymerization. The π–π interactions between the capping aryl groups and the pyridyl ring are clearly observed in “sandwich” bis(imino)pyridyl iron complexes by single crystal X-ray diffraction analysis, UV–vis, and photoluminescence (PL) spectra. The intramolecular π–π interactions make the naphthyl rings tilt away from the iron center in the horizontal direction, thereby causing a more open horizontal space within iron complexes for ethylene coordination. Ethylene polymerization results show that π–π interactions are a crucial driving force rather than the electronic effects of ligands. Unprecedentedly, bulky “sandwich” bis(imino)pyridyl iron catalysts produce low-molecular-weight PE with a bimodal distribution, which originates from β-H transfer to monomer modulated by the π–π interactions. Density functional theory (DFT) calculations mechanistically demonstrate that the coordination of ethylene to the iron center is a crucial step in ethylene polymerization.

中文翻译：

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使用“三明治”双（亚氨基）吡啶铁催化剂进行 π-π 相互作用驱动的乙烯聚合

弱非共价相互作用是调节催化烯烃聚合的有效策略，但从未在双（亚氨基）吡啶基铁催化剂中观察到。本文设计并合成了一系列带有取代8-(对-R-苯基)萘胺(R = OMe, Me, H, CF ₃ )的“三明治”双(亚氨基)吡啶铁配合物用于乙烯聚合。通过单晶 X 射线衍射分析、紫外可见光谱和光致发光 (PL) 光谱，在“三明治”双（亚氨基）吡啶基铁配合物中清楚地观察到封端芳基和吡啶环之间的 π-π 相互作用。分子内π-π相互作用使萘环在水平方向上远离铁中心倾斜，从而在铁配合物内产生更开放的水平空间以进行乙烯配位。乙烯聚合结果表明，π-π相互作用是关键的驱动力，而不是配体的电子效应。前所未有的是，庞大的“三明治”双(亚氨基)吡啶基铁催化剂产生了具有双峰分布的低分子量PE，其源自β-H转移到由π-π相互作用调节的单体。密度泛函理论（DFT）计算从机理上证明乙烯与铁中心的配位是乙烯聚合的关键步骤。