Porphyrin-stoppered [3]- and [5]-rotaxanes

A dicopper(I)-complexed [3]-rotaxane was prepared in 34% yield by a transition-metal-templated strategy involving a bis-chelating molecular thread, macrocycles incorporating the complementary chelating unit, and porphyrin stoppers as key components. A tetracopper(I)-complexed [5]-rotaxane was obtained as a byproduct in 8% yield. Coordination chemistry was performed either at the 2,9-diphenyl-1, 10-phenanthroline (dpp) chelates or at the porphyrin stoppers. The latter were metalated by either Zn(II), Au(III), or Zn(II) and Au(III). Both Cu(I) template cations could be removed by competitive complexation with CN- when at least one porphyrin stopper was complexed with Au(III), the other one being metalated with either Au(III) or Zn(II). This provided two strictly defined [3]-rotaxanes, in which the macrocycle and the molecular thread are not held together by metal coordination. Rather, dethreading is prevented by the bulky metalloporphyrin stoppers. Unexpectedly, when both stoppers were complexed with Zn(II), removal of the metal template in the same conditions as above yielded, very selectively, a copper(I)-complexed [3]-rotaxane containing only one metal-free macrocycle. The demetalated bis-dpp site could be remetalated with Ag(I), affording, in good yield, a dinuclear (Ag(I), Cu(I))-complexed [3]-rotaxane, ended by Zn(II)-porphyrin blocking groups.