Exploiting the Reversible Dimerization of N-Heterocyclic Carbenes to Access Dynamic Polymer Networks with an Organocatalytic Activity,ACS Macro Letters

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Exploiting the Reversible Dimerization of N-Heterocyclic Carbenes to Access Dynamic Polymer Networks with an Organocatalytic Activity
ACS Macro Letters ( IF 5.1 ) Pub Date : 2024-07-25 , DOI: 10.1021/acsmacrolett.4c00390
Karine Abou-Ezze ₁ , Audrey Llevot ₁ , Daniel Taton ₁

Affiliation

The capability of some N-heterocyclic carbenes (NHCs) to reversibly dimerize is exploited to access dynamic polymer networks. Benzimidazolium motifs serving as NHC precursors have thus been supported onto copolymer chains by reversible addition–fragmentation chain transfer (RAFT) copolymerization of styrene and up to 20 mol % of 4-vinylbenzyl-ethyl-benzimidazolium chloride. Molecular versions of 1,3-dialkyl benzimidazolium salts have been synthesized as models, the deprotonation of which with a strong base yields the NHC dimers in the form of tetraaminoalkenes. The crossover reaction between two distinct NHC homodimers, forming heterodimers, is then evidenced. Applying this deprotonation method to the RAFT-derived copolymers leads to polymer networks with cross-links consisting of labile dimerized NHC motifs. These networks can be subsequently decross-linked using two distinct triggers, namely, a monofunctional NHC precursor as competitor and carbon dioxide (CO₂). In the latter case, regeneration of the network occurs by chemically fueling the linear copolymer bearing benzimidazolium motifs with tBuOK in the presence of trace amounts of water. The same networks can also be used as latent precursors of transient polyNHCs to catalyze the benzoin condensation upon heating. The polymer-supported organocatalysts can thus be used in successive catalytic cycles.

中文翻译：

利用 N-杂环卡宾的可逆二聚作用获得具有有机催化活性的动态聚合物网络

利用一些N-杂环卡宾 (NHC) 可逆二聚的能力来访问动态聚合物网络。因此，通过苯乙烯和高达 20 mol% 的 4-乙烯基苄基-乙基-苯并咪唑氯化物的可逆加成-断裂链转移 (RAFT) 共聚，将作为 NHC 前体的苯并咪唑鎓基序负载到共聚物链上。 1,3-二烷基苯并咪唑鎓盐的分子形式已被合成为模型，其用强碱去质子化产生四氨基烯烃形式的 NHC 二聚体。然后证明了两个不同的 NHC 同二聚体之间形成异二聚体的交叉反应。将这种去质子化方法应用于 RAFT 衍生的共聚物会产生具有由不稳定二聚 NHC 基序组成的交联的聚合物网络。这些网络随后可以使用两种不同的触发物解交联，即作为竞争剂的单功能 NHC 前体和二氧化碳 (CO ₂ )。在后一种情况下，网络的再生是通过在微量水存在下用t BuOK 以化学方式为带有苯并咪唑鎓基序的线性共聚物提供燃料来实现的。相同的网络也可以用作瞬态聚NHC的潜在前体，以在加热时催化安息香缩合。因此，聚合物负载的有机催化剂可以用于连续的催化循环。

更新日期：2024-07-25

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