A series of shape-persistent bis-[C(sp³)-chelating] Ti₂ (plus Zr₂ and Hf₂) complexes with a rigid linker component (xanthene or dibenzofuran) are presented. These structurally diverse assemblies display limited yet different conformational flexibility, and crucially, such geometric constraints confer access to a range of intermetallic separations and orientations to potentially enhance catalytic activity and cooperative effects. For ethylene polymerizations, the Ti₂ catalysts (in conjunction with trityl borate) exhibit greater efficiencies and produced polymers with higher M_w than mononuclear controls, which is significant considering the more crowded environment for cofacial bimetallic sites. Proficient 1-hexene incorporations were observed for ethylene-(α-olefin) copolymerization reactions. The F-substituted m-aryl/dibenzofuran-linked catalyst (5), which is revealed by NMR analysis to be conformationally dissimilar to its F-absent congener, produced copolymers with higher M_w and elevated 1-hexene incorporation levels (up to 44%), when compared with its mono-Ti control (19%). These results suggest that catalyst frameworks with suitably adjustable conformations and Ti···Ti distances can facilitate bimetallic enchainment interactions with α-olefin substrates and their insertion.

中文翻译：

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几何约束的共面双钛烯烃聚合催化剂：调整和提高共聚单体掺入密度


提出了一系列具有刚性接头成分（氧杂蒽或二苯并呋喃）的形状持久性双 [C（sp³） -螯合] Ti₂（加上 Zr₂ 和 Hf₂）复合物。这些结构多样的组装体显示出有限但不同的构象灵活性，至关重要的是，这种几何约束赋予了一系列金属间分离和取向，从而可能增强催化活性和协同效应。对于乙烯聚合，Ti₂ 催化剂（与硼酸三酯结合）表现出比单核对照更高的效率并产生具有更高 M_w 的聚合物，考虑到共界面双金属位点更拥挤的环境，这一点非常重要。在乙烯-（α-烯烃）共聚反应中观察到熟练的 1-己烯掺入。FMR 分析显示，F 取代的间芳基/二苯并呋喃连接的催化剂 （5） 在构象上与其不存在 F 的同系物不同，与其单钛对照 （19%） 相比，产生的共聚物具有更高的 M_w 和更高的 1-己烯掺入水平（高达 44%）。这些结果表明，具有适当可调构象的催化剂框架和 Ti···Ti 距离可以促进双金属链与 α-烯烃衬底的相互作用及其插入。