Rotaxanes Incorporating Two Different Coordinating Units in Their Thread: Synthesis and Electrochemically and Photochemically Induced Molecular Motions

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Abstract

Three different multicomponent molecular systems have been synthesized by means of the three-dimensional template effect of copper(I). These systems incorporate both a coordinating ring (2,9-diphenyl-1,10-phenanthroline-containing 30-membered ring) and a molecular string which consists of two different coordination sites (2,9-disubstituted-1,10-phenanthroline and 5,5‘ ‘-disubstituted-2,2‘:6‘,2‘ ‘-terpyridine unit). Each end of the string could be functionnalyzed by a small group or by a bulky stopper (tris(p-tert-butylphenyl)(4-hydroxyphenyl)methane), leading to an unstoppered compound, to a semi-rotaxane, or to a real rotaxane. As in the case of a disymmetrical copper [2]-catenane, large reversible molecular motions have been induced both electrochemically and photochemically. The driving force of the rearrangement processes is the high stability of two markedly different coordination environments for the copper(I) and copper(II) ions. In the copper(I) state, two phenanthroline units (one of the ring, one of the string) interact with the metal ion in a tetrahedral geometry (CuI(4)), whereas in the copper(II) state, one phenanthroline belonging to the ring and the terpyridine of the string afford a five-coordinate geometry (CuII(5)). The rates of the molecular motion processes (from CuII(4) to CuII(5) and from CuI(5) to CuI(4)) are respectively faster and slower (minutes time scale) as compared to those for the catenane species. This result could be interpreted on the basis of structural differences between the rotaxane and catenane systems.

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