Rotaxanes incorporating two different coordinating units in their thread: Synthesis and electrochemically and photochemically induced molecular motions

Three different multicomponent molecular systems have been synthesized by m eans of the three-dimensional template effect of copper(I). These systems i ncorporate both a coordinating ring (2,9-diphenyl-1,10-phenanthroline-conta ining 30-membered ring) and a molecular string which consists of two differ ent coordination sites (2,9-disubstituted-1,10-phenanthroline and 5,5 "-dis ubstituted-2,2':6',2 "-terpyridine unit). Each end of the string could be f unctionnalyzed by a small group or by a bulky stopper (tris(p-tert-butylphe nyl)(4-hydroxyphenyl)methane), leading to an unstoppered compound, to a sem i-rotaxane, or to a real rotaxane. As in the case of a disymmetrical copper [2]-catenane, large reversible molecular motions have been induced both el ectrochemically and photochemically. The driving force of the rearrangement processes is the high stability of two markedly different coordination env ironments for the copper(I) and copper(II) ions. In the copper(I) state, tw o phenanthroline units (one of the ring, one of the string) interact with t he metal ion in a tetrahedral geometry (Cu-(4)(I)), whereas in the copper(I I) state, one phenanthroline belonging to the ring and the terpyridine of t he string afford a five-coordinate geometry (Cu-(5)(II)). The rates of the molecular motion processes (from Cu-(4)(II) to Cu-(5)(II) and from Cu-(5)(I ) to Cu-(4)(I)) are respectively faster and slower (minutes time scale) as compared to those for the catenane species. This result could be interprete d on the basis of structural differences between the rotaxane and catenane systems.