ELECTROCHEMICALLY AND PHOTOCHEMICALLY DRIVEN RING MOTIONS IN A DISYMMETRICAL COPPER [2]-CATENATE

By applying the three-dimensional template effect of copper(I), previo usly used far making various interlocking ring systems, a new disymmet rical [2]-catenate has been made which consists of two different inter locking rings. One ring contains a 2,9-diphenyl-1,10-phenanthroline (d pp) unit whereas the other cycle incorporates both a dpp motif and a 2 ,2',6',2''-terpyridine (terpy) fragment, the coordination: site of the se two chelates pointing toward the inside of the ring. Depending on t he oxidation state of the central metal (Cu(I)) or Cu(II)), and thus o n its preferred coordination number, two distinct situations have been observed. With monovalent copper, the two dpp units interact with the metal and the terpy fragment remains free, at the outside of the mole cule. By contrast, when the catenate is complexed to divalent copper,t he terpy motif is bonded to the metal and it is now a dpp ligand which lies at the periphery of the complex. This dual coordination mode lea ds to dramatically different molecular shapes and properties for both forms. The molecular motion which interconverts the four-and the five- coordinate complexes can be triggered chemically, electrochemically, o r photochemically by changing the oxidation state of the copper center (II/I). The process has been studied by electrochemistry and by UV-vis spectroscopy. Interestingly, once the stable 4-coordinate copper(I) c omplex has been oxidized to a thermodynamically unstable pseudo-tetrah edral copper(II) species,the rate of the gliding motion of the rings w hich will afford the stable 5-coordinate species (copper(II) coordinat ed to dpp and terpy) can be controlled at:will. Under certain experime ntal conditions, the changeover process is extremely slow (weeks), and the 4-coordinate complex is more or less frozen. By contrast, additio n of a coordinating counterion to the medium (Cl-) enormously speeds u p the rearrangement and leads to the thermodynamically stable 5-coordi nate complex within minutes.