S-Cylindrophanes: From Metal Tweezers to Metal Sandwiches

Inclusion of Ag^I and Cu^I ions by the preorganized cylindrophane cage compound 1 provides the first examples of bis(η⁶) sandwich complexes of these metals. Locked in a trigonal-planar heteroatom ligand field, the guest ions are shown by NMR spectroscopy to withdraw electron density from the aromatic rings. A statistical study of η⁶ coordination in the solid state supports the description of arene-metal contacts between 2.5 and 3.5 Å as bonds.