Molecular tweezers as synthetic receptors: molecular recognition of neutral and cationic aromatic substrates. A comparison between the supramolecularstructures in crystal and in solution

The synthesis of substituted naphthalene- and benzene-spaced tweezer molecu les Ib and c and 2e-j is reported. They selectively bind electron-deficient neutral and cationic aromatic substrates. The structural parameters of the substrate-receptor complexes derived from H-1 NMR measurements in solution are in good agreement with those obtained from single-crystal structure an alyses. The tweezer 2f forms a stable complex with N,N-bis-(3,5-di-tert-but ylbenzyl)-4,4'-bipyridinium 14, a substituted viologen dication, that exhib its the structure of a clipped rotaxane with a wheel opened on one side. Th e benzene-spaced tweezer 2j shows complexation of the cesium cation Cri ins ide the cavity. Copyright (C) 2000 John Wiley & Sons, Ltd.