Assembly of [2]Rotaxanes in Water

Two [2]rotaxanes have been assembled in water from modular subunits through Cu-I-catalyzed azide-alkyne click chemistry. For this purpose, 2,6-disubstituted naphthalene axles with solubilizing oligo(ethylene glycol) (OEG) chains (n = 1-5) and propargyl terminal groups were synthesized and examined for their propensity to form inclusion complexes with a dicationic Diederich-type cyclophane host. The dependence of pseudorotaxane formation on the linkers between the naphthalene core and OEG chains, and in the case of ester linkers on different spacer lengths, was analyzed by titration experiments. In addition, the inclusion complexes of two [2]rotaxanes were trapped by using a water-soluble azide-functionalized stopper. Repetitive chromatography finally enabled the isolation of both mechanically interlocked [2]rotaxanes.