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Selective Binding of Spherical and Linear Anions by Tetraphenyl(thio)urea-Based Dihomooxacalix[4]arene Receptors

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posted on 2017-10-09, 00:00 authored by Filipa A. Teixeira, Paula M. Marcos, José R. Ascenso, Giovanna Brancatelli, Neal Hickey, Silvano Geremia
Three novel tetra­(thio)­ureido dihomo­oxa­calix­[4]­arene anion receptors (phenylurea 4a, phenylthiourea 4b, and tert-butylurea 4c) were synthesized and obtained in the cone conformation in solution, as shown by NMR studies. The X-ray crystal structure of 4c is reported. The host–guest properties of these receptors toward several anions were investigated by 1H NMR titrations. Phenylurea 4a displayed a very efficient binding toward the spherical F and Cl anions, and the linear CN (log Kass = 3.46, 3.50, and 4.02, respectively). In comparison to related bidentate phenylurea dihomooxacalix[4]­arenes, tetraphenylurea 4a is more preorganized and the higher number of hydrogen bond donor sites provides a remarkable enhancement of its binding efficiency.

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