Fast pirouetting motion in a pyridine bisamine-containing copper-complexed rotaxane.

The present work reports the introduction of pyridine bisamine terdentate ligands in the structure of a pirouetting copper rotaxane. Rotaxane 2[PF6] constitutes the first example of the incorporation of imine-based dynamic covalent chemistry in the synthesis of switchable copper-complexed interlocked systems. In this rotaxane, the substitution of the classical terpyridine terdentate unit by a pyridine bisamine moiety has led to a significant stabilization of the pentacoordinated site. That fact has been evidenced by EPR spectroscopy and cyclic voltammetry. Regarding the tetracoordinated site, the congestion around the coordination sphere has been reduced to accelerate the typically slow reorganization of the Cu(II). Ethynyl-3,8-substitution on the axis phenanthroline along with the 2,9-diphenyl-1,10-phenanthroline (dpp) present in the macrocycle afforded a very stable coordination environment for Cu(I), which is at the same time labile upon oxidation. In summary, the incorporation of a pyridine bisamine unit as a terdentate ligand and the optimization of the bidentate ligand of the axle not only has led to a simplification of the synthetic procedures, but it has also given rise to a bistable systems with an enhanced energetic separation between states and an acceleration of the reorganization processes. Thus far, rotaxane 2[PF6] presents the fastest switching cycle reported to date in copper-interlocked dynamic systems.