A pentagonal cyanostar macrocycle with cyanostilbene CH donors binds anions and forms dialkylphosphate [3]rotaxanes

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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 C 5 -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 β 2 ≈ 12 and ΔG ≈ -70 kJ mol -1, of large anions (BF 4 -, ClO 4 - and PF 6 -) usually considered weakly coordinating. The cyanostar's size preference allowed formation of an unprecedented [3]rotaxane templated around a dialkylphosphate. © 2013 Macmillan Publishers Limited. All rights reserved.

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Nature Chemistry

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