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Mechanism of the Polymerization of rac-Lactide by Fast Zinc Alkoxide Catalysts
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2017-11-08 00:00:00 , DOI: 10.1021/acs.inorgchem.7b02544 Daniel E. Stasiw 1 , Anna M. Luke 1 , Tomer Rosen 2 , Aaron B. League 1 , Mukunda Mandal 1 , Benjamin D. Neisen 1 , Christopher J. Cramer 1 , Moshe Kol 2 , William B. Tolman 1
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2017-11-08 00:00:00 , DOI: 10.1021/acs.inorgchem.7b02544 Daniel E. Stasiw 1 , Anna M. Luke 1 , Tomer Rosen 2 , Aaron B. League 1 , Mukunda Mandal 1 , Benjamin D. Neisen 1 , Christopher J. Cramer 1 , Moshe Kol 2 , William B. Tolman 1
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The ring-opening transesterification polymerization (ROTEP) of rac-lactide (rac-LA) using LXZn catalysts (LX = ligand having phenolate, amine, and pyridine donors with variable para substituents X on the bound phenolate donor; X = NO2, Br, t-Bu, OMe) was evaluated through kinetics experiments and density functional theory, with the aim of determining how electronic modulation of the ligand framework influences polymerization rate, selectivity, and control. After determination that zinc-ethyl precatalysts required 24 h of reaction with benzyl alcohol to convert to active alkoxide complexes, the subsequently formed species proved to be active and fairly selective, polymerizing up to 300 equiv of rac-LA in 6–10 min while yielding isotactic (Pm = 0.72–0.78) polylactide (PLA) with low dispersities: Đ = 1.06–1.17. In contrast to previous work with aluminum catalysts for which electronic effects of ligand substituents were significant (Hammett ρ = +1.2–1.4), the LXZn systems exhibited much less of an effect (ρ = +0.3). Density functional calculations revealed details of the initiation and propagation steps, enabling insights into the high isotacticity and the insensitivity of the rate on the identity of X.
中文翻译：
快速烷氧基氧化锌催化rac-丙交酯聚合的机理
使用L X Zn催化剂（L X =在结合的酚盐供体上具有可变对位取代基X的酚盐，胺和吡啶供体的配体）进行rac-丙交酯（rac -LA）的开环酯交换聚合（ROTEP）2，Br，t-Bu，OMe）是通过动力学实验和密度泛函理论进行评估的，目的是确定配体骨架的电子调节如何影响聚合速率，选择性和控制力。在确定锌-乙基预催化剂需要与苄醇反应24小时才能转化为活性醇盐络合物后，随后形成的物质被证明具有活性和相当的选择性，可在6-10分钟内聚合多达300当量的rac- LA，同时产生低分散度的等规（P m = 0.72-0.78）聚丙交酯（PLA）：Đ = 1.06-1.17。与以前的铝催化剂工作相比，铝催化剂的配体取代基的电子效应显着（Hammettρ= + 1.2-1.4），与之相反，L X锌系统表现出的影响要小得多（ρ= +0.3）。密度泛函计算揭示了引发和传播步骤的细节，从而使人们能够深入了解X的同一性和速率的不敏感性。
更新日期：2017-11-08
中文翻译：
快速烷氧基氧化锌催化rac-丙交酯聚合的机理
使用L X Zn催化剂（L X =在结合的酚盐供体上具有可变对位取代基X的酚盐，胺和吡啶供体的配体）进行rac-丙交酯（rac -LA）的开环酯交换聚合（ROTEP）2，Br，t-Bu，OMe）是通过动力学实验和密度泛函理论进行评估的，目的是确定配体骨架的电子调节如何影响聚合速率，选择性和控制力。在确定锌-乙基预催化剂需要与苄醇反应24小时才能转化为活性醇盐络合物后，随后形成的物质被证明具有活性和相当的选择性，可在6-10分钟内聚合多达300当量的rac- LA，同时产生低分散度的等规（P m = 0.72-0.78）聚丙交酯（PLA）：Đ = 1.06-1.17。与以前的铝催化剂工作相比，铝催化剂的配体取代基的电子效应显着（Hammettρ= + 1.2-1.4），与之相反，L X锌系统表现出的影响要小得多（ρ= +0.3）。密度泛函计算揭示了引发和传播步骤的细节，从而使人们能够深入了解X的同一性和速率的不敏感性。
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