Graduate School of Natural Science and Technology , Kanazawa University , Kakuma-machi , Kanazawa 920-1192 , Japan.
WPI Nano Life Science Institute (WPI-NanoLSI) , Kanazawa University Kakuma-machi , Kanazawa 920-1192 , Japan.
J Am Chem Soc. 2019 Oct 2;141(39):15597-15604. doi: 10.1021/jacs.9b06926. Epub 2019 Sep 16.
Host-guest binding sometimes triggers the subsequent chemical reactions of the host framework as well as changes in the physical properties. Since the host-guest binding generally occurs very quickly, it is sometimes difficult to differentiate the mechanism from the alternative one in which the guest binding occurs after the reaction. However, it is important to differentiate the two mechanisms when we develop new molecules based on time-dependent functions. Thus, we propose two distinct mechanisms, and , in a slowly reacting host system. We designed and synthesized a new cobalt(III) metallohost, LCo(pip) (pip = piperidine), which can take up a guest cation into its 18-crown-6-like cavity causing concomitant exchange of the axial piperidine ligands under solvolytic conditions. We investigated the mechanism to elucidate whether the guest recognition or ligand exchange occurs first. When Na (5-10 equiv) was present, the guest recognition occurred by the mechanism; i.e., Na was initially taken up into the cavity, then the axial piperidine ligands were replaced with methoxo ligands. On the other hand, when 1 equiv of M (= K, Rb) was present, the guest recognition occurred by the mechanism; i.e., M was taken up after one of the piperidine ligands was replaced with a methoxo ligand. Therefore, the recognition pathway can be switched by changing the guest cations.
主体-客体结合有时会触发主体框架的后续化学反应以及物理性质的变化。由于主体-客体结合通常发生得非常快，因此有时很难将其与反应后客体结合的替代机制区分开来。然而，当我们基于时间相关的功能开发新分子时，区分这两种机制是很重要的。因此，我们在一个缓慢反应的主体体系中提出了两种截然不同的机制和。我们设计并合成了一种新的钴(III)金属主体[LCo(pip)] (OTf) (pip = 哌啶)，它可以在溶剂解条件下将客体阳离子纳入其 18-冠-6 样空腔中，同时交换轴向哌啶配体。我们研究了该机制，以阐明是客体识别还是配体交换首先发生。当存在 Na(5-10 当量)时，客体识别通过机制发生; 即，Na 首先被纳入空腔，然后轴向哌啶配体被甲氧基配体取代。另一方面，当存在 1 当量的 M(= K, Rb)时，客体识别通过机制发生; 即，M 在一个哌啶配体被甲氧基配体取代后被纳入。因此，通过改变客体阳离子可以切换识别途径。
