Efficient production of [n]rotaxanes by using template-directed clipping reactions

In this article, we report on the efficient synthesis of well defined, homogeneous [n]rotaxanes (n up to 11) by a template-directed thermodynamic clipping approach. By employing dynamic covalent chemistry in the form of reversible imine bond formation, [n]rotaxanes with dialkylammonium ion (-CH2NH2+CH2-) recognition sites, encircled by [24]crown-8 rings, were prepared by a thermodynamically controlled, template-directed clipping procedure, that is, by mixing together a dumbbell compound containing a discrete number of -CH2NH2+CH2- ion centers with appropriate amounts of a dialclehyde and a diamine to facilitate the [n]rotaxane formation. A 21-component self-assembly process is operative during the formation of the [11]rotaxane. The oligomeric dumbbells containing -CH2NH2+CH2- ion recognition sites were prepared by a stepwise protocol. Several of the dynamic [n]rotaxanes were converted into their kinetically stable counterparts, first by reduction ("fixing") of imine bonds with the BH3 center dot THF complex, then by protonation of the complex by addition of acid.