New molecular topologies by fourfold metathesis reactions within a hydrogen-bonded calix[4]arene dimer

A calix[4]arene tetrapentyl ether in the cone conformation substituted at its wide rim by four m-(omega-octenyloxy)phenyl urea groups forms hydrogen-bonded dimeric capsules in dichloromethane/benzene (95:5). Metathesis reaction with Grubbs' catalyst under high-dilution conditions (1.1 x 10(-4) M) followed by hydrogenation leads to a covalent connection of all the urea groups within a dimer. Three topologically different products may be expected in such a reaction: a bis[2]catenane, a doubly bridged monocatenane and a tetrabridged capsule. All three possible reaction products could be isolated in an overall yield up to 60 % for the separated and purified compounds. Their identification was based on the NMR patterns which reflect the characteristic symmetry properties of the isomeric products especially in the region of the hydrogen-bonded NH protons and were further confirmed by MALDI-TOF mass spectra. Further structural support for the bis[2]catenane comes from a single-crystal X-ray structure, although severe disorder prevents the localization of all atoms in the aliphatic chains connecting the two calix[4]arenes. Kinetic studies for the guest release/exchange (cyclohexane against the solvent [D(6)]benzene) do not show remarkable differences between the starting dimer and the additionally linked dimers, while the mobility of an included tetraethylammonium cation is obviously more restricted.