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Size- and Shape-Selective Catalysis with a Functionalized Self-Assembled Cage Host
The Journal of Organic Chemistry ( IF 3.6 ) Pub Date : 2021-09-07 , DOI: 10.1021/acs.joc.1c01511
Courtney Ngai 1 , Bryce da Camara 1 , Connor Z Woods 1 , Richard J Hooley 1
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A self-assembled Fe4L6 cage with internally oriented carboxylic acid functions was shown to catalyze a variety of dissociative nucleophilic substitution reactions that proceed via oxocarbenium ion or carbocation intermediates. The catalytic behavior of the cage was compared to that of other small acid catalysts, which illustrated large differences in reactivity of the cage-catalyzed reactions, dependent on the structure of the substrate. For example, only a 5% cage confers a 1000-fold rate acceleration of the thioetherification of vinyldiphenylmethanol when compared to the rate with free carboxylic acid surrogates but only a 52-fold acceleration in the formation of small thioacetals. Multiple factors control the variable reactivity in the host, including substrate inhibition, binding affinity, and accessibility of reactive groups once bound. Simple effective concentration increases or the overall charge of the cage does not explain the variations in reactivity shown by highly similar reactants in the host: small differences in structure can have large effects on reactivity. Reaction of large spherical guests is highly dependent on substitution, whereas flat guests are almost unaffected by size and shape differences. The cage is a promiscuous catalyst but has strong selectivity for particular substrate shapes, reminiscent of enzymatic activity.

中文翻译:

具有功能化自组装笼主体的尺寸和形状选择性催化

自组装 Fe 4 L 6具有内部取向羧酸官能团的笼被证明可以催化通过氧代碳正离子或碳正离子中间体进行的各种离解亲核取代反应。笼的催化行为与其他小型酸催化剂的催化行为进行了比较,这表明笼催化反应的反应性存在很大差异,这取决于底物的结构。例如,与使用游离羧酸替代物的速率相比,仅 5% 的笼子使乙烯基二苯基甲醇的硫醚化的速率加速了 1000 倍,但小硫缩醛的形成仅加速了 52 倍。多种因素控制着宿主的可变反应性,包括底物抑制、结合亲和力和反应基团一旦结合的可及性。简单的有效浓度增加或笼子的总电荷并不能解释宿主中高度相似的反应物所显示的反应性变化:结构上的微小差异会对反应性产生很大影响。大球形客体的反应高度依赖于替代,而扁平客体几乎不受大小和形状差异的影响。笼子是一种混杂的催化剂,但对特定底物形状具有很强的选择性,让人联想到酶活性。而扁平的客人几乎不受大小和形状差异的影响。笼子是一种混杂的催化剂,但对特定底物形状具有很强的选择性,让人联想到酶活性。而扁平的客人几乎不受大小和形状差异的影响。笼子是一种混杂的催化剂,但对特定底物形状具有很强的选择性,让人联想到酶活性。
更新日期:2021-09-17
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