Advancing Polymerization Catalysis by Cooperativity: Dual Catalysis as a Tool to Achieve High Performance at Maximum Simplicity

由一种有机催化剂和一种未改性金属盐组成的双催化对将被用于o杂环单体开环聚合。这些组合的协同效应将在一项全面的研究中进行调查，以便统一和合理化到目前为止只有零散但非常有希望的报告存在的领域。为了实现这一目标，需要使用一系列经过精细调整的有机组分，从活性较低的n基催化剂（吡啶，4-二甲氨基吡啶（DMAP））到典型的有机催化剂，如1,8-重氮杂环十一-7-烯（DBU），还包括更强的n杂环碳烯（NHCs）和n杂环烯烃（NHOs），后者的部分阴离子性质。这些将应用于催化装置中，与现成的路易斯酸，如MgCl2， MgI2, CaCl2, ZnCl2, FeCl3， BiCl3或YCl3，聚合不同的内酯（即大内酯戊内酯，中等大小的三角戊内酯和高度应变的-丁内酯）。从这种筛选中获得的数据不仅可以确定竞争内酯均聚的合适组合（双催化可以导致聚合速率大幅提高，特别是不需要人工合成），而且还可以方便地操作相应的共聚物组成，正如最近的结果所揭示的那样。这种效应是基于给定Lewis酸对单体的特异性激活，也将用于通过选择性激活非活性/休眠有机催化剂来生成嵌段共聚聚酯，目的是实现具有挑战性或不寻常的嵌段序列。总体目标是建立参数，允许操作简单地合成所需的内酯基（co）聚酯，方便地利用市售的路易斯酸和易于获取的有机化合物。有了这些有机催化剂（大约20种化合物）和路易斯酸（大约10种不同的金属卤化物），这项研究还将扩展到包括其他杂环单体，即环氧化物和碳酸盐，目标是特别具有挑战性的单体。一方面，这将被取代的环氧化合物（环氧丙烷，环氧环己烯，苯乙烯氧化物），其中有机催化剂单独仍然遭受相对低的周转和缓慢的反应；双催化很好地解决了这个问题。其次，将重点关注碳酸乙烯。众所周知，这种单体需要苛刻的反应条件，并且容易损失二氧化碳，导致混合碳酸盐/环氧乙烷骨架。因此，Lewis酸活化与强亲核试剂的结合是产生可变碳酸盐/环氧乙烷含量聚合物的一个有吸引力的选择。

Dual catalytic pairs consisting of an organocatalyst and a non-modified metal salt will be employed for ring-opening polymerization of O-heterocyclic monomers. The synergistic effects of such combinations will be investigated in a comprehensive study, in an effort to unify and rationalize a field where so far only scattered, yet highly promising reports exist. To achieve this, a finely tuned array of organic components is to be used, ranging from less reactive N-based catalysts (pyridine, 4-dimethylaminopyridine (DMAP)) to typical organocatalysts such as 1,8-diazabicyclo-undec-7-ene (DBU) and including also the more powerful N-heterocyclic carbenes (NHCs) and N-heterocyclic olefins (NHOs), the latter partially anionic in character. Those are to be applied in a catalytic setup with readily available Lewis acids, such as MgCl2, MgI2, CaCl2, ZnCl2, FeCl3, BiCl3 or YCl3, to polymerize different lactones (i.e. the macrolactone pentadecalactone, the medium size delta-valerolactone and the highly strained beta-butyrolactone). The data derived from such a screening will not only identify suitable combinations for competitive lactone homopolymerization (where dual catalysis can result in massively increased polymerization rates, notably without synthetic efforts), but also for convenient manipulation of the corresponding copolymer composition, as very recent results have revealed. This effect is based on the monomer specific activation by a given Lewis acid and will also be used to generate block-copolyesters by selective activation of inactive/dormant organocatalysts with the aim to realize challenging or unusual block sequences. The overall goal is to establish parameters which allow for an operationally simple synthesis of the desired lactone-based (co)polyester at will, conveniently by employing commercially available Lewis acids and well accessible organic compounds. With this collection of organocatalysts (ca. 20 compounds) and Lewis acids (ca. 10 different metal halides) at hand, the study will also be extended to include other heterocyclic monomers, namely epoxides and carbonates, targeting specifically challenging monomers. On the one hand this will be substituted epoxides (propylene oxide, cyclohexene oxide, styrene oxide) for which organocatalysts alone still suffer from relatively low turnover and slow reactions; a situation where dual catalysis is well positioned to resolve the issue. Secondly, ethylene carbonate will be focused on. This monomer notoriously requires harsh reaction conditions and is prone to CO2-loss, resulting in a mixed carbonate/ethylene oxide backbone. Lewis acid activation in combination with strong nucleophiles is therefore an attractive option to generate polymer with variable carbonate/ethylene oxide content.