Metal-driven ligand assembly in the synthesis of cyclodextrin [2] and [3]rotaxanes

Cyclodextrin [ 2] and [ 3] rotaxanes have been synthesised by use of a metal-driven ligand formation methodology. The kinetically stable cobalt(III) complexes formed act as either linking or capping groups, the function being selected by manipulation of the reaction conditions to promote the formation of either 2 : 1 or 1 : 1 complexes, respectively. In all cases, mixtures of isomers containing different alpha-cyclodextrin orientations were observed. All three orientational isomers of the [ 3] rotaxane were isolated and structurally characterized by 2D NMR.