Mechanistic Studies of ε-Caprolactone Polymerization by (salen)AlOR Complexes and a Predictive Model for Cyclic Ester Polymerizations.
Mechanistic Studies of ε-Caprolactone Polymerization by (salen)AlOR Complexes and a Predictive Model for Cyclic Ester Polymerizations.
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DOI：
10.1021/acscatal.5b02607
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发表时间：
2016-02-05
期刊：
影响因子：
12.9
通讯作者：
Tolman WB
中科院分区：
文献类型：
--
作者：
Marlier EE;Macaranas JA;Marell DJ;Dunbar CR;Johnson MA;DePorre Y;Miranda MO;Neisen BD;Cramer CJ;Hillmyer MA;Tolman WB
制备了具有三碳连接基和具有可变吸电子能力（X = NO2、Br、OMe）的对位取代基的 salen 配体的烷醇铝配合物 (2)，并研究了其 ε-己内酯 (CL) 开环聚合 (ROP) 的动力学随温度的变化，目的是与之前研究的具有二碳连接基的类似体系进行比较 (1)。虽然 1 和 2 表现出饱和动力学及其 ROP 速率对取代基 X 的类似依赖性（对于 k2，分别为不变的 Keq，类似的 Hammett ρ = +1.4(1) 和 1.2(1)），2 的 ROP 明显快于 1。理论计算证实，虽然反应物结构不同，但过渡态几何形状非常相似，并且通过分析伴随结构变化的所涉及的畸变的能量学，显着贡献确定了费率差异的基础。利用这些知识，提出了一种评估配体结构对环酯 ROP 速率影响的简化计算方法，该方法可能对未来的催化剂设计有用。
Aluminum alkoxide complexes (2) of salen ligands with a three-carbon linker and para substituents having variable electron-withdrawing capabilities (X = NO2, Br, OMe) were prepared, and the kinetics of their ring-opening polymerization (ROP) of ε-caprolactone (CL) were investigated as a function of temperature, with the aim of drawing comparisons to similar systems with two-carbon linkers investigated previously (1). While 1 and 2 exhibit saturation kinetics and similar dependences of their ROP rates on substituents X (invariant Keq, similar Hammett ρ = +1.4(1) and 1.2(1) for k2, respectively), ROP by 2 was significantly faster than for 1. Theoretical calculations confirm that, while the reactant structures differ, the transition state geometries are quite similar, and by analyzing the energetics of the involved distortions accompanying the structural changes, a significant contribution to the basis for the rate differences was identified. Using this knowledge, a simplified computational method for evaluating ligand structural influences on cyclic ester ROP rates is proposed that may have utility for future catalyst design.