ELECTROCHEMICALLY INDUCED MOLECULAR MOTIONS IN COPPER-COMPLEXED THREADED SYSTEMS - FROM THE UNSTOPPERED COMPOUND TO THE SEMI-ROTAXANE AND THE FULLY BLOCKED ROTAXANE

A molecular assembly incorporating a coordinating ring (30-membered ma crocycle) and a molecular string with two chelating sites (bidentate a nd terdentate ligands) has been constructed by means of the template e ffect of copper(I). Electrochemical oxidation of tetracoordinate coppe r(I) to copper(ll) results in the motion of the ring and the metal ion from the bidentate to the terdentate site on the string due to the pr eference of copper(II) for a square base pyramidal-type geometry vs. t etrahedral, Electrochemical reduction of copper(ll) to copper(I) leads to the opposite movement. In order to avoid a dethreading process (es sentially due to the copper(ll) complexes) during the redox cycles, on e or two blocking groups [tris(p-tert-butylphenyl)(4-hydroxyphenyl)met hane] have been covalently attached to the ends of the thread to affor d a semi-rotaxane or a rotaxane, respectively. In the case of the rota xane, a perfect reversibility of the motions of the ring on the thread has been demonstrated by electrochemical techniques.