On the nature of arene η⁶ interactions in the solid state and the use of cylindrophanes as ligands for sandwich complexation of metals with longer- range interactions with the benzene ring

A novel mode of containment for metal ions which participate in longer- range interactions with aryl rings (≥ 2.5 Å) is demonstrated in the preorganized cylindrical host 1. Three equatorial sulfur atoms in 1 hold metals in a trigonal planar ligand field between two apical benzene centroids at an M-Ar distance of about 3 Å. Evidence of an interaction between the π electrons and the metals is gained by ¹H NMR spectroscopy of the complexes, and support for the general description of metal-arene contacts in the 2.5- 3.5 Å range as 'bonds' is derived from a statistical study of η⁶- coordination in the solid state. Crystal structures of [Ag(1)]BF₄ and [Cu(1)]BF₄ confirm the first examples of arene Ag(I) and Cu(I) sandwich complexation and indeed the only structurally characterized Cu(I)-aryl centroid interaction. The two isomeric tris-sulfoxides derived from 1 show less tendency to interact with metals ions.