5-Methoxy-Substituted Zirconium Bis-indenyl <i>ansa</i>-Complexes: Synthesis, Structure, and Catalytic Activity in the Polymerization and Copolymerization of Alkenes

A number of 2-methyl-4-aryl-5-methoxy-6-alkylindenes and C2-symmetric Me2Si-bridged ansa-zirconocenes based on them were synthesized. Zirconocenes were obtained by means of highly effective and scalable racemo-selective synthetic approach based on the use of a Zr tert-butyl amide complex. The structure of μ-(bis-[η5-6-tert-butyl-5-methoxy-2-methyl-4-tert-butylphenyl-1H-inden-1-yl]­dimethylsilanediyl)­dichlorozirconium­(IV) (14) has been established with X-ray analysis. The introduction of a methoxy group into the indenyl fragment of zirconocene significantly improved its catalytic performance (i.e., its activity, stereoselectivity, molecular mass potential, and thermal stability) in the polymerization and copolymerization of propylene in comparison with the benchmark Spaleck-zirconocene. The role of the methoxy group is proposed to stabilize the cationic catalytic intermediates, which was confirmed using DFT calculations.本研究合成了一系列2-甲基-4-芳基-5-甲氧基-6-烷基茚，以及基于该类茚衍生物的C2对称二甲基硅桥联ansa-桥联茂锆配合物（ansa-zirconocene）。该类茂锆配合物可通过基于叔丁基酰胺锆（Zr tert-butyl amide complex）的高效、可规模化的外消旋选择性合成策略制备得到。通过X射线单晶衍射分析，确定了μ-（双-[η⁵-6-叔丁基-5-甲氧基-2-甲基-4-叔丁基苯基-1H-茚-1-基]二甲基硅二基）二氯化锆(IV)（化合物14）的晶体结构。与参比催化剂Spaleck茂锆（Spaleck-zirconocene）相比，在茂锆配合物的茚配体骨架中引入甲氧基，可显著提升其在丙烯均聚与共聚反应中的催化性能，具体涵盖催化活性、立体选择性、聚合物分子量上限及热稳定性。研究推测甲氧基的作用机制为稳定阳离子催化中间体，该推测通过密度泛函理论（DFT）计算得到了验证。