A series of xanthene-bridged dinucleating ligands bearing imino- and aminopyridyl moieties and their nickel complexes were synthesized and characterized. The properties of these dinuclear complexes in ethylene polymerization were studied in comparison with the corresponding mononuclear nickel complexes. The iminopyridyl dinuclear nickel complexes activated by methylaluminoxane (MAO) showed higher catalytic activities (up to 2.2 × 10⁶ g of PE (mol Ni)⁻¹ h^–1), higher molecular weights, and produced polyethylene with much lower branching density (27/1000C) than their mononuclear analogues. Similar trends were observed for the aminopyridyl dinuclear complexes. A metal–metal cooperativity effect was proposed to be able to slow down the β-hydride elimination and the corresponding chain-walking process. These results clearly demonstrated the great potentials of dinuclear nickel catalysts with the xanthene-bridged coordination modes in controlling the ethylene polymerization process as well as the microstructures of the resulting polyethylene products.

中文翻译：

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双核X吨桥联的氨基和氨基吡啶基镍配合物的乙烯聚合

合成并表征了一系列带有亚氨基和氨基吡啶基部分的x吨桥联的双核配体及其镍配合物。与相应的单核镍配合物相比，研究了这些双核配合物在乙烯聚合反应中的性能。由甲基铝氧烷（MAO）活化的亚氨基吡啶基双核镍配合物显示出更高的催化活性（高达2.2×10 ⁶ g的PE（mol Ni）^-1 h ^–1），分子量更高，并且产生的聚乙烯的支化密度低得多（27 / 1000C）。对于氨基吡啶基双核复合物观察到类似的趋势。金属-金属协同效应，提出要能够在β放缓-氢化物消除和相应的链走过程。这些结果清楚地证明了具有the吨桥联配位模式的双核镍催化剂在控制乙烯聚合过程以及所得聚乙烯产物的微观结构方面的巨大潜力。