Switching between Anion-Binding Catalysis and Aminocatalysis with a Rotaxane Dual-Function Catalyst

The off state for aminocatalysis by a switch able [2]rotaxane is shown to correspond to an on state for anion-binding catalysis. Conversely, the aminocatalysis on state of the dual-function rotaxane is inactive in anion-binding catalysis. Switching between the different states is achieved through the stimuli-induced change of position of the macrocycle on the rotaxane thread. The anion-binding catalysis results from a pair of triazolium groups that act together to CH-hydrogen-bond to halide anions when the macrocycle is located on an alternative (ammonium) binding site, stabilizing the in situ generation of benzhydryl cation and oxonium ion intermediates from activated alkyl halides. The aminocatalysis and anion-binding catalysis sites of the dual-function rotaxane catalyst can be sequentially concealed or revealed, enabling catalysis of both steps of a tandem reaction process.