Molecular tweezers as synthetic receptors: molecular recognition of neutral and cationic aromatic substrates. A comparison between the supramolecular structures in crystal and in solution.
The synthesis of substituted naphthalene- and benzene-spaced tweezer mols. [(I; R1,R2 given: OAc,OAc; OMe,OMe) and (II; R1,R2 given: OCH2CO2Et,OCH2CO2Et; OCH2CO2-; OCH2CO2-(III); OAc,OH;OAc, OCH2CO2Et; OH,OCH2CO2H; OH,OCH2CO2-(IV))] is reported. They selectively bind electron-deficient neutral and cationic arom. substrates. The structural parameters of the substrate-receptor complexes derived from 1H NMR measurements in soln. are in good agreement with those obtained from single-crystal structure analyses. The tweezer III forms a stable complex with N,N-bis-(3,5-di-tert-butylbenzyl)-4,4'-bipyridinium 14, a substituted viologen dication, that exhibits the structure of a clipped rotaxane with a wheel opened on one side. The benzene-spaced tweezer IV shows complexation of the cesium cation Cs+ inside the cavity.
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