Ditopic binding of cyclodextrin-included ligands in trigonal silver(I) complexes

The X-ray crystal structures of trigonal silver(I) cyclodextrin complexes of introverted bidentate sulfur (1) and phosphorus (2) ligands give a clear indication on how a cyclodextrin-included ligand may bind in a ditopic fashion both the encapsulated metal ion and the cyclodextrin inner wall. In the solid state, the silver-coordinated water molecule of complex [Ag(H2O)(1)]BF4 induces a major distortion of the macrocyclic structure, along with dramatic conformational changes in the two opposite glucose units with which it is hydrogen bonded. In complex [AgBr(2)], the included bulky bromide anion, which lacks hydrogen bonding capability, does not affect the overall circular shape of the cyclodextrin receptor. A 1H–19F HOESY experiment conducted on the silver(I) complex of 1 in CDCl3 showed that in this solvent, the water molecule is displaced by the BF4 counterion at the metal coordination site, the cavity being here no longer distorted.

The ditopic binding of weakly coordinating ligands to cyclodextrin-based silver(I) complexes has been investigated by 2D NMR (1H–19F HOESY) in solution and X-ray diffraction studies in the solid state.Figure optionsDownload as PowerPoint slideResearch highlights
► Silver(I) chelate complexes of α-CD-based dithioether and diphosphine ligands.
► Evidence of ditopic binding for silver-coordinated ligands included in the CD cavity.
► A metal-coordinated water molecule induces a major deformation of the CD torus.
► Weakly binding ligands undergo exchange at the metal center within the CD cavity.