Symbiotic Control in Mechanical Bond Formation

Since the advent of mechanically interlocked molecules (MIMs), many approaches to templating their formation using various different noncovalent bonding interactions have been introduced and explored. In particular, employing radical-pairing interactions between BIPY^.+units, the radical cationic state of 4,4′-bipyridinium (BIPY²⁺) units, in syntheses is not only a convenient but also an attractive source of templation because of the unique properties residing in the resulting catenanes and rotaxanes. Herein, we report a copper-mediated procedure that enables the generation, in the MIM-precursors, of BIPY^.+radical cations, while the metal itself, which is oxidized to Cu^I, catalyzes the azide–alkyne cycloaddition reactions that result in the efficient syntheses of two catenanes and one rotaxane, assisted by radical-pairing interactions between the BIPY^.+radical cations. This procedure not only provides a fillip for making and investigating the properties of Coulombically challenged catenanes and rotaxanes, but it also opens up the possibility of synthesizing artificial molecular machines which operate away from equilibrium.