Mechanistic Insights into the Alternating Copolymerization of Epoxides and Cyclic Anhydrides Using a (Salph)AICI and Iminium Salt Catalytic System
Mechanistic Insights into the Alternating Copolymerization of Epoxides and Cyclic Anhydrides Using a (Salph)AICI and Iminium Salt Catalytic System
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DOI：
10.1021/jacs.7b09079
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发表时间：
2017-10-25
影响因子：
15
通讯作者：
Tolman, William B.
中科院分区：
文献类型：
--
作者：
Fieser, Megan E.;Sanford, Maria J.;Tolman, William B.
对（Salph）AlCl/[PPN]Cl催化体系中1-丁烯氧化物与碳酸酐完全交替共聚合的机理进行了协同实验和理论研究。这些研究表明，一阶依赖的环氧化物上的聚合速率，零阶依赖的环酐，和LLI的一阶依赖的催化剂，只有当催化对的两个成员被视为一个单一的单元。模型配合物的研究表明，混合的醇盐/羧酸铝中间体优先打开环酐环氧化物。此外，发现通过包含多个羧酸酯的中间体开环环氧化物是速率决定性的。在实验结果和DFT计算分析的基础上，提出了一种涉及两个催化循环的机制，其中交替共聚通过具有羧酸酯连接的中间体进行，避免了涉及双烷氧基物种的第二循环，从而解释了直到聚合完成为止没有副反应。
Mechanistic studies involving synergistic experiment and theory were performed on the perfectly alternating copolymerization of 1-butene oxide and carbic anhydride using a (salph)AlCl/[PPN]Cl catalytic pair. These studies showed a first-order dependence of the polymerization rate on the epoxide, a zero-order dependence on the cyclic anhydride, and a LLI first-order dependence on the catalyst only if the two members of the catalytic pair are treated as a single unit. Studies of model complexes showed that a mixed alkoxide/carboxylate aluminum intermediate preferentially opens cyclic anhydride over epoxide. In addition, ring-opening of epoxide by an intermediate comprising multiple carboxylates was found to be rate determining. On the basis of the experimental results and analysis by DFT calculations, a mechanism involving two catalytic cycles is proposed wherein the alternating copolymerization proceeds via intermediates that have carboxylate ligation in common, and a secondary cycle involving a bis-alkoxide species is avoided, thus explaining the lack of side reactions until the polymerization is complete.