Bifunctional Polymer Architectures for Cooperative Catalysis: Tunable Acid-Base Polymers for Aldol Condensation
Bifunctional Polymer Architectures for Cooperative Catalysis: Tunable Acid-Base Polymers for Aldol Condensation
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DOI：
10.1002/cctc.201601104
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发表时间：
2017-01-01
期刊：
影响因子：
4.5
通讯作者：
Jones, Christopher W.
中科院分区：
文献类型：
--
作者：
Hoyt, Caroline B.;Lee, Li-Chen;Jones, Christopher W.
弱酸和碱性胺协同作用的催化剂在温和的条件下能够有效地催化羟醛及其相关的偶联反应。大多数用于Aldol反应的合作化学催化剂都是基于二氧化硅负载的胺。在这项工作中，展示了另一种方法，通过实施聚合物载体来定制协作胺/酸的相互作用。通过使用线性聚苯乙烯载体，这项工作表明，单体单元的设计和间距在羟醛缩合反应中酸碱中心的协同性中起着至关重要的作用。每种聚合物催化剂的单体顺序对催化活性有很大影响，其中无规共聚物表现出最佳的酸碱协同作用，嵌段共聚物则显著降低催化剂活性。在二氧化硅支撑的体系中确立的趋势，例如使用表现出活性降低的更强的酸性单体，得到了验证，并扩展到这些聚合物支撑的体系。总体而言，这种第一代聚合物支载体系不如过去十年开发的最佳二氧化硅支载催化剂有效，因为这里研究的聚合物溶解性很差，导致胺中心的利用效率低下。
Cooperative catalysts combining weak acids and basic amines have been utilized to effectively catalyze aldol and related coupling reactions under mild conditions. Most cooperative chemical catalysts for the aldol reaction have been based on silica-supported amines. In this work, an alternate approach is demonstrated whereby cooperative amine/acid interactions are tailored through the implementation of polymeric supports. By using linear poly(styrene) supports, this work demonstrates that the design and spacing of monomer units plays an essential role in the cooperativity of the acid-base sites in the aldol condensation. The monomer sequence of each polymer cata-lyst dramatically affects the catalytic activity, with a random copolymer displaying optimal cooperativity between the acid and base, and block copolymers drastically reducing catalyst activity. Trends established in the silica-supported systems, such as use of stronger acid monomers demonstrating reduced activity, are verified and extended to these polymer-supported systems. Overall, this first generation polymer-supported system is not as efficient as the optimal silica-supported catalysts developed over the last decade, with the polymers studied here being poorly soluble, leading to inefficient use of the amine sites.