Chemical Sciences Division, Lawrence Berkeley National Laboratory and Department of Chemistry, University of California-Berkeley, Berkeley, California 94720, United States.
Department of Chemistry, School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
J Am Chem Soc. 2020 Nov 11;142(45):19327-19338. doi: 10.1021/jacs.0c09556. Epub 2020 Nov 2.
Although most of the currently developed supramolecular catalysts that emulate enzymatic reactivity with unique selectivity and activity through specific host-guest interactions work under homogeneous conditions, enzymes in nature can operate under heterogeneous conditions as membrane-bound enzymes. In order to develop such a heterogeneous system, an immobilized chiral supramolecular cluster Ga () was introduced into cross-linked polymers with cationic functionalities. These heterogeneous supramolecular catalysts were used in aza-Prins and aza-Cope reactions and successfully applied to continuous-flow reactions. They showed high durability and maintained high turnovers for long periods of time. In sharp contrast to the majority of examples of heterogenized homogeneous catalysts, the newly developed catalysts showed enhanced activity and robustness compared to those exhibited by the corresponding soluble cluster catalyst. An enantioenriched cluster was also immobilized to enable asymmetric catalysis, and activity and enantioselectivity of the supported chiral catalyst were maintained during recovery and reuse experiments and under a continuous-flow process. Significantly, the structure of the ammonium cations in the polymers affected stability, reactivity, and enantioselectivity, which is consistent with the hypothesis that the cationic moieties in the polymer support interact with cluster as an exohedral protecting shell, thereby influencing their catalytic performance.
尽管目前大多数通过特定主客体相互作用模拟酶反应性的超分子催化剂具有独特的选择性和活性，且在均相条件下工作，但自然界中的酶可以作为膜结合酶在非均相条件下发挥作用。为了开发这种非均相体系，将手性超分子簇 Ga() 固定在具有阳离子官能团的交联聚合物中。这些非均相超分子催化剂在氮杂-Prins 和氮杂-Cope 反应中得到了应用，并成功应用于连续流反应。它们表现出高耐久性，并在长时间内保持高转化率。与大多数异相均相催化剂的例子形成鲜明对比的是，与相应的可溶性簇催化剂相比，新开发的催化剂表现出增强的活性和稳健性。此外，还固定了手性富集的簇以实现不对称催化，并且在回收和再利用实验以及连续流过程中，负载手性催化剂的活性和对映选择性得以保持。值得注意的是，聚合物中铵阳离子的结构影响稳定性、反应性和对映选择性，这与聚合物载体中的阳离子部分与簇作为外壳相互作用的假设一致，从而影响它们的催化性能。
