The stereoselective polymerization of polar vinyl monomers has recently received much attention due to their excellent physicochemical properties. Over the past decade, breakthroughs have been achieved in this field by rare-earth catalysts. However, the mechanistic origins of those stereoselective polymerizations still remain unclear. Herein, stereoselective polymerization of ortho-methoxystyrene (oMOS) by several representative rare-earth catalysts bearing different ligands (i.e., η⁵-C₅Me₅, pyridinyl-methylene-fluorenyl, quinolyl-anilido, β-diketiminato) were systematically investigated by density functional theory (DFT) calculations. After achieving agreement between the calculations and experiments, we focused on discussing the role of ligands in controlling stereoselectivity. Our results reveal that the stereoregularity of oMOS polymerization is mainly controlled by the steric effect of the catalyst–monomer structures. Specifically, the type of ligand influences the orientation and configuration of the inserting monomer, thereby affecting the tacticity of the polymers. In the cases of η⁵-C₅Me₅-, pyridinyl-methylene-fluorenyl, and quinolyl-anilido-ligated yttrium catalysts, we observe consistent insertion directions and alternating insertion sides of oMOS monomers, leading to syndiotactic selectivity. The opposite insertion directions and the alternating insertion sides of oMOS monomers were observed in the case of the β-diketiminato yttrium catalyst, leading to isotactic selectivity. These findings reported here offer valuable insights into the role of ligands in controlling stereoselectivity in rare-earth catalyzed coordination polymerization of polar vinyl monomers, thus providing guidance for the rational design of new ligands for stereospecific polymerization of polar monomers in the future.

中文翻译：

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稀土催化剂配体控制的邻甲氧基苯乙烯立体选择性聚合的起源：理论视角


极性乙烯基单体的立体选择性聚合由于其优异的物理化学性质近年来受到广泛关注。近十年来，稀土催化剂在这一领域取得了突破性进展。然而，这些立体选择性聚合的机制起源仍不清楚。本文通过几种具有不同配体的代表性稀土催化剂（即 η ⁵ -C ₅ Me ₅ 进行邻甲氧基苯乙烯（oMOS）的立体选择性聚合，通过密度泛函理论（DFT）计算系统地研究了吡啶基-亚甲基-芴基、喹啉基-苯胺基、β-二酮亚胺基）。在计算和实验达成一致后，我们重点讨论配体在控制立体选择性中的作用。我们的结果表明，oMOS 聚合的立构规整性主要受催化剂-单体结构的空间效应控制。具体而言，配体的类型影响插入单体的取向和构型，从而影响聚合物的立构规整度。在 η ⁵ -C ₅ Me ₅ -、吡啶基-亚甲基-芴基和喹啉基-苯胺基-配位钇催化剂的情况下，我们观察到一致的插入oMOS 单体的方向和交替插入侧，导致间规选择性。在β-二酮亚胺钇催化剂的情况下，观察到oMOS单体的相反插入方向和交替插入侧，从而导致全同立构选择性。 本文报道的这些发现为了解配体在控制极性乙烯基单体的稀土催化配位聚合中的立体选择性中的作用提供了有价值的见解，从而为未来极性单体立体定向聚合的新配体的合理设计提供了指导。