Rotaxanes and catenanes by click chemistry

Copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition between terminal alkynes and azides - also known as the copper (Cu)-catalyzed Azide-Alkyne Cycloaddition (CuAAC) - has been used in the syntheses of molecular compounds with diverse structures and functions, owing to its functional group tolerance, facile execution, and mild reaction conditions under which it can be promoted. Recently, rotaxanes of four different structural types, as well as donor/acceptor catenanes, have been prepared using CuAAC, attesting to its tolerance to supramolecular interactions as well. In one instance of a rotaxane synthesis, the catalytic role of copper has been combined successfully with its previously documented ability to preorganize rotaxane precursors, i.e., form pseudorotaxanes. The crystal structure of a donor/acceptor catenane formed using the CuAAC reaction indicates that any secondary [π⋯π] interactions between the 1,2,3-triazole ring and the bipyridinium π-acceptor are certainly not destabilizing. Finally, the preparation of robust rotaxane and catenane molecular monolayers onto metal and semiconductor surfaces is premeditated based upon recent advances in the use of the Huisgen reaction for surface functionalization.