To enhance the performance of the bis(imino)acenaphthene-nickel precatalyst, an axial phenyl group was introduced on the acenaphthenyl backbone, and five analogues were formed: bis(aryl)imino-5-phenylacenaphthene nickel bromides (aryl: 2,6-dimethylphenyl, Ni1; 2,6-diethylphenyl, Ni2; 2,6-diisopropylphenyl, Ni3; 2,4,6-trimethylphenyl, Ni4; and 2,6-diethyl-4-methylphenyl, Ni5). The molecular structures of mononuclear Ni2 and dinuclear Ni3 were confirmed as distorted tetrahedron and square-pyramidal geometries around the nickel core, respectively. All five precatalysts achieved better activity as well as thermostability for ethylene polymerization and delivered polyethylene elastomer with higher molecular weight and more branches than the benchmark nickel precatalyst proposed by Brookhart. Specifically, Ni2/EASC maintained a catalytic activity of 4.52 × 10⁶ g PE per mol (Ni) per h even at 100 °C. More importantly, the resultant polyethylenes exhibited excellent mechanical properties with high strain (>1000%) and stress (>10 MPa) values observed during tensile stress–strain tests. Topographic steric maps showed that there is sufficient space around the nickel center for ethylene to conduct coordination and facilitate polymeric propagation. The introduction of an axial phenyl group into the backbone of nickel complexes not only elevates the catalytic performance, but also provides these polyethylene elastomers with attractive properties.

中文翻译：

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轴向苯基约束的双（亚氨基）苊镍预催化剂增强乙烯聚合


为了提高双（亚氨基）苊镍预催化剂的性能，在苊基主链上引入了一个轴向苯基，并形成了五种类似物：双（芳基）亚氨基-5-苯基乙酰萘溴化镍（芳基：2,6-二甲基苯基，Ni1;2,6-二乙基苯基，Ni2;2,6-二异丙基苯基，Ni3;2,4,6-三甲基苯基，Ni4;和2,6-二乙基-4-甲基苯基，Ni5）。单核 Ni2 和双核 Ni3 的分子结构分别被证实为围绕镍核的扭曲四面体和方形金字塔几何形状。与 Brookhart 提出的基准镍预催化剂相比，所有五种预催化剂都实现了更好的乙烯聚合活性和热稳定性，并提供了分子量更高、支链更多的聚乙烯弹性体。具体来说，即使在 100 °C 下，Ni2/EASC 也保持了 4.52 ×^{10 6} g PE/mol （Ni） /h 的催化活性。 更重要的是，所得聚乙烯表现出优异的机械性能，在拉伸应力-应变测试中观察到高应变 （>1000%） 和应力 （>10 MPa） 值。地形空间位图显示，镍中心周围有足够的空间供乙烯进行配位并促进聚合物传播。在镍配合物的主链中引入轴向苯基不仅提高了催化性能，还为这些聚乙烯弹性体提供了有吸引力的特性。