A copper-based shuttling [2]rotaxane with two bidentate chelates in the axis: Steric control of the motion

Contrary to most of the other molecular machines based on copper-complexed catenanes or rotaxanes made and investigated in Strasbourg, the present report is dealing with a molecular shuttle for which the copper centre is complexed to two bidentate chelates, regardless of the state of the shuttle. In other words, the axis contains a sterically hindering bidentate chelate, namely a 2,9-diphenyl-1,10-phenanthroline (dpp) derivative, and another but less hindering bidentate chelate, 2,2′-bipyridine (bipy). The synthesis of the [2]rotaxane involves 15 individual chemical steps, excluding the preparation of the macrocyclic component of the [2]rotaxane. The threaded macrocycle is a 39-membered ring which incorporates an endocyclic but non sterically hindering chelate of the 8,8′-diphenyl-3,3′-biisoquinoline family (dpbiiq). The electrochemically-induced gliding motion of the copper-complexed ring from the dpp "station" to the bipy "station" and vice versa is fast on the cyclic voltammetry timescale (milliseconds). The copper(i) state is preferably located on the dpp unit whereas, by oxidising the copper(i) centre to its divalent state, the translation motion takes place to afford the thermodynamically most stable state now involving the bipy chelate.