Rotaxanes and Catenanes Derived from Tetra-Urea Calix[4]arenes

Summary: Calix4]arenes, substituted by four urea groups at their wide rim, form dimeric capsules in apolar solvents, which are held together by a seam of intermolecular hydrogen bonds. The heterodimerisation of tetra-aryl and tetratosyl ureas was used to synthesize various derivatives, in which adjacent urea residues are connected to form two, three or four loops. The aliphatic connections were tied by olefin metathesis between adjacent alkenyl residues followed by hydrogenation. Heterodimers of tetra-alkenyl substituted tetra-ureas and bis- or tetraloop derivatives were converted analogously to multiple catenanes. Tetra2]rotaxanes were obtained in a similar manner. In addition to the spectroscopic evidence (NMR, MS) several compounds were confirmed by crystal structures.