As macrocyclic polyethers, crown ethers have attracted remarkable attention. Crown ether moieties are well-known host compounds in host–guest chemistry. They have shown a significant ability to form strong complexes with organic and inorganic anions or cations, selectively. Among the crown ethers, the cavity size of the 18-crown-6 and Kþ diameter are well matched. Thus, 18-crown-6 forms a very stable complex with Kþ.1,2 Designing catalysts based on crown ethers, which work well under mild conditions, is an attractive and desirable area of research.
