Redox divergent conversion of a [2]rotaxane into two distinct degenerate partners with different shuttling dynamics

Abstract

The submolecular translational movement in novel hydrogen-bonded [2]rotaxanes containing benzylic amide macrocycles and two azo/hydrazodicarboxamide binding sites was analyzed by dynamic NMR spectroscopy. The results show that the activation free energies of the macrocycle shuttling in these systems depend on the oxidation level of both nitrogen-based binding sites embedded in the thread; the shuttling motion being more rapid in [2]rotaxanes at the lower oxidation level bis(hydrazo)-based rotaxanes. Moreover, by means of a fully controllable chemical switching, these two-station [2]rotaxanes are able to swap over three different dynamic states, which differ in macrocycle shuttling velocity: a) faster in a bis(hydrazo) [2]rotaxane, the lower oxidation state; b) moderate in a bis(azo) [2]rotaxane, the higher oxidation state; and c) practically stopped at the azodicarboxamide station of an azo/hydrazo [2]rotaxane, the intermediate oxidation state. Thus, from this latter resting state, two “fans” of different velocity can be turned on and off by simple chemical redox processes.