Trefoil knot TK

The structure of the trefoil knot was demonstrated by a combination of high resolution mass spectrometry, NMR experiments, and computational modeling. Interestingly, the synthesis of the trefoil knot was accomplished with a consequent 56% yield, but it was shown to be accompanied by the formation of a [2]catenane species isolated in 22% yield as well as by the larger Solomon link structure detected only in minor amounts by mass spectrometry during the course of the reaction. 

SCH EME 17.6 Synthesis of molecular trefoil knot by dynamic covalent chemistry of imine bond formation.  

Based on the x-ray crystal structure of the [2]catenane and the DFT-calculated structure of the trefoil knot, the formation of the knotted structures resulted from a strong zinc templated chelation combined with the formation of dynamic covalent imine bonds catalyzed by Zn(II) acting as a Lewis acid and templated by strong tt-tt stacking interactions between the bipyridine of one strand and the phenoxy rings of another—an organization that predisposes the amine functions close to the formyl groups. 

In summary, metal templation and tt-tt stacking interactions were employed cooperatively along with the formation of reversible covalent imine bonds to template the three different links obtained when the two ligands were mixed with zinc. 

---