This review article describes recent results obtained in the self-assembly of supramolecular capsules derived from calixpyrrole components. Due to their ease of synthesis, calixpyrroles are by far the most typically used units in these systems. A clear conformational and structural analogy exists between calixarenes and calixpyrroles. However, to date, the number of examples in the literature that use calixpyrrole scaffolds instead of calixarenes for the construction of supramolecular capsules is still meager. Four different approaches are considered for the use of calixpyrrole derivatives in the assembly of molecular capsules. Firstly, in an analogous manner to resorcinarenes and pyrogallolarenes, aryl-extended calixpyrroles with hydroxyl groups in their upper rim self-assemble through direct or mediated rim-to-rim interactions into capsular aggregates. Secondly, aryl-extended calixpyrroles having non-complementary hydrogen-bonding groups in their upper rim form dimeric templated capsules with suitable substrates. Thirdly, the elaboration of the upper rim of the calixpyrroles with urea groups affords dimeric capsules with polar functionalized interiors that closely resemble their tetraurea calixarene analogs. Finally, the chemical modification of the pyrrole units of octamethyl calixpyrrole into tetrathiafulvalene derivatives yields dimeric capsules induced by anion coordination that display interesting properties in the binding of electron-poor guests.
Supramolecular capsules derived from calixpyrrole scaffolds
Isr. J. Chem. 2011, 51, 710-724.