Institution: | 1. Laboratoire de Chimie Organique, Université libre de Bruxelles (ULB), Avenue F.D. Roosevelt 50, CP160/06, 1050 Brussels, Belgium
These authors contributed equally to this work;2. Service de Chimie Générale, Université libre de Bruxelles (ULB), Route de Lennik 808, CP 609, 1070 Brussels, Belgium;3. Engineering of Molecular NanoSystems, Université libre de Bruxelles (ULB), Avenue F.D. Roosevelt 50, CP165/64, 1050 Brussels, Belgium;4. Laboratoire de Chimie et de Biochimie Pharmacologiques et Toxicologiques, Sorbonne Paris Cité, CNRS UMR 8601, Université Paris Descartes, 45 rue des Saints-Pères, 75006 Paris, France;5. Laboratoire de Résonance Magnétique Nucléaire Haute Résolution, Université libre de Bruxelles (ULB), Avenue F.D. Roosevelt 50, CP160/08, 1050 Brussels, Belgium;6. Laboratoire de Chimie Organique, Université libre de Bruxelles (ULB), Avenue F.D. Roosevelt 50, CP160/06, 1050 Brussels, Belgium |
Abstract: | The straightforward synthesis of a new hexahomotrioxacalix3]arene-based ligand capped by a tren subunit was developed and the binding properties of the corresponding zinc complex were explored by NMR spectroscopy. Similarly to the closely related calix6]tren-based systems, the homooxacalixarene core ensures the mononuclearity of the zinc complex and the metal center displays a labile coordination site for exogenous guests. However, very different host–guest properties were observed: i) in CDCl3, the zinc complex strongly binds a water molecule and is reluctant to recognize other neutral guests, ii) in CD3CN, the exo-coordination of anions prevails. Thus, in strong contrast to the calix6]tren-based systems, the coordination of neutral guests that thread through the small rim and fill the polyaromatic cavity was not observed. This unique behaviour is likely due to the fact that the 18-membered ethereal macrocycle is too small to let a molecule threading through it. This work illustrates the key role played by the second coordination sphere in the binding properties of metal complexes. |