Crown-Ether-Based Cryptands with Rarely Strong Affinities for Binding Neutral Organic Molecules

Herein, we present the syntheses of two new crown-ether-based cryptands and their complexation behaviors with neutral organic molecules. The interactions between 4/5 and G1/G2 were fast exchange systems forming pseudorotaxane-like complexes with a 1 : 1 stoichiometric ratio. The association constant (K-a) of long-armed cryptand 5 with G2 was even up to 2.5x10(5) M-1, which is 10 to 10(3) times higher than the previously reported host-neutral guest system to the best of our knowledge. Such a large K-a is even comparable to that of reported cryptands with secondary ammonium salts and paraquat derivatives. Thorough studies demonstrated that excellent spatial fitting and multi non-covalent interactions (H-bonding and pi-pi stacking) are essential for such a large K-a.

Automated summary

Here, we report the syntheses of two new crown-ether-based cryptands and their complexation behaviors with neutral organic molecules. We found that one of the cryptands showed excellent complexation ability with G2, with a high association constant of 2.5x10(5) M-1.