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Abstract
Since the discovery of crown ethers, macrocycles have been recognized as powerful platforms for supramolecular chemistry. Although their numbers and variations are now legion, macrocycles that are simple to make using high-yielding reactions in one pot and on the multigram scale are rare. Here we present such a discovery obtained during the creation of a C5-symmetric cyanostilbene ‘campestarene’ macrocycle, cyanostar, that employs Knoevenagel condensations in the preparation of its cyanostilbene repeat unit. In the solid state, cyanostars form π-stacked dimers constituted of chiral P and M enantiomers. The electropositive central cavity stabilizes anions with CH hydrogen-bonding units that are activated by electron-withdrawing cyano groups. In solution, the cyanostar shows high-affinity binding as 2:1 sandwich complexes, log β2 ≈ 12 and ΔG ≈ −70 kJ mol−1, of large anions (BF4−, ClO4− and PF6−) usually considered weakly coordinating. The cyanostar's size preference allowed formation of an unprecedented [3]rotaxane templated around a dialkylphosphate. Macrocycles are key compounds in supramolecular chemistry, yet their efficient preparation is an ever present challenge. Now, it has been shown that a C5-symmetric macrocycle, termed ‘cyanostar’, can be formed in high yields on multigram scales in one pot. Cyanostars form unusually strong sandwich complexes with large and weakly coordinating anions and can template the formation of a dialkylphosphate [3]rotaxane. Cite this article
Lee, S., Chen, CH. & Flood, A. A pentagonal cyanostar macrocycle with cyanostilbene CH donors binds anions and forms dialkylphosphate [3]rotaxanes. Nature Chem 5, 704–710 (2013). https://doi.org/10.1038/nchem.1668 