Bogie Paul M, Holloway Lauren R, Ngai Courtney, Miller Tabitha F, Grewal Divine K, Hooley Richard J
Department of Chemistry, University of California-Riverside, Riverside, CA, 92521, USA.
Chemistry. 2019 Aug 1;25(43):10232-10238. doi: 10.1002/chem.201902049. Epub 2019 Jul 1.
A self-assembled Fe L cage complex internally decorated with acid functions is capable of accelerating the thioetherification of activated alcohols, ethers and amines by up to 1000-fold. No product inhibition is seen, and effective supramolecular catalysis can occur with as little as 5 % cage. The substrates are bound in the host with up to micromolar affinities, whereas the products show binding that is an order of magnitude weaker. Most importantly, the cage host alters the molecularity of the reaction: whereas the reaction catalyzed by simple acids is a unimolecular, S 1-type substitution process, the rate of the host-mediated process is dependent on the concentration of nucleophile. The molecularity of the cage-catalyzed reaction is substrate-dependent, and can be up to bimolecular. In addition, the catalysis can be prevented by a large excess of nucleophile, where substrate inhibition dominates, and the use of tritylated anilines as substrates causes a negative feedback loop, whereby the liberated product destroys the catalyst and stops the reaction.
一种内部装饰有酸性官能团的自组装铁笼配合物能够将活性醇、醚和胺的硫醚化反应加速高达1000倍。未观察到产物抑制现象，并且仅使用5%的笼配合物就能实现有效的超分子催化。底物以高达微摩尔亲和力结合在主体中，而产物的结合力则弱一个数量级。最重要的是，笼状主体改变了反应的分子性：简单酸催化的反应是单分子的SN1型取代过程，而主体介导过程的速率取决于亲核试剂的浓度。笼催化反应的分子性取决于底物，最高可达双分子。此外，大量过量的亲核试剂会阻止催化作用，此时底物抑制起主导作用，并且使用三苯甲基化苯胺作为底物会导致负反馈循环，由此释放的产物会破坏催化剂并使反应停止。
