| Popis: |
We report the novel host–guest chemistry of highly substituted [3 + 3] Schiff-base macrocycle 1 with secondary ammonium-based guest molecules. Complexation of host 1 with dibenzylammonium (DBA+) or dipropylammonium (DPA+) led to the formation of both internal (1⊃DBA+ or 1⊃DPA+) and external complexes (1·DBA+ or 1·DPA+), whereas binding with di(xylyl methylene)ammonium (DXA+) resulted in only an external analogue (1·DXA+). For 1 + DPA+, the internal complex is more stable than the external complex, whereas in 1+DBA+, the internal and external complexes are very close in energy and interchange very slowly, allowing both to be observed at room temperature. Although 1⊃DXA+ and 1·DXA+ are close in energy, steric interactions inhibit formation of 1⊃DXA+ and only 1·DXA+ can be detected at room temperature. Based on computational analysis, the complexes all exist in a mixed tautomeric state with two keto-enamine and four enol–imine functionalities. That is, introduction of the ammonium-based guests results in a tautomeric change within the macrocyclic host, where the enol–imine form is converted to the keto-enamine. Finally, it was also shown that when DBA·PF6 is used in the synthesis of 1, higher yields are obtained than when no additive is used, indicating the potential for ammonium-cation templation of Schiff-base macrocycles. |
