Two Axles Threaded Using a Single Template Site: Active Metal Template Macrobicyclic Rotaxanes
2010-01-13T00:00:00Z (GMT) by
Template approaches to rotaxanes normally require at least <i>n</i> − 1 template sites to interlock <i>n</i> components. Here we describe the one-pot synthesis of rotaxanes in which a single metal template site induces formation of axles through each cavity of a bicyclic macrocycle. Central to the approach is that a portion of the bicyclic molecule acts as a ligand for a transition metal ion that mediates covalent bond formation through one or other macrocyclic cavity, depending on the ligand’s orientation, making a mechanical bond. The ligand can then rotate so that the transition metal can catalyze the formation of a second axle through the other macrocycle. Using this strategy with the Cu(I)-catalyzed azide−alkyne cycloaddition (the CuAAC reaction) generates a rotaxane with two identical axles in up to 86% yield. Rotaxanes with two different axles threaded through the macrobicyclic rings can also be created using a single template site, either by having copper(I) sequentially form both mechanical bonds (via the CuAAC reaction) using different sets of building blocks for each axle or by using two different reactions catalyzed by two different metal ions: a palladium(II)-mediated alkyne homocoupling to assemble the first thread through one cavity, followed by a copper(I)-mediated CuAAC reaction to form the second axle through the other ring.