Albano Galán, PhD student under the supervision of Prof. Pau Ballester, has defended his PhD Thesis entitled ‘Molecular Containers Based on calixpyrrole Scaffolds’ (assigned to the Organic and Analytical Chemistry Department of the Universitat Rovira i Virgili) publicly on January 29th at the ICIQ auditorium.
The members of his evaluation committee were: Prof. Christopher Hunter (University of Cambridge), Prof. Pere Deyà (Universitat de les Illes Balears) and Prof. Laura Rodríguez (Universitat de Barcelona).
This thesis comprises the synthesis and study of different molecular containers based on calixpyrrole scaffolds. The molecular containers possess polar functionalized cavities ideal for the recognition of anions or N-oxides. The preparation of containers with enforced cavities (cavitands) results in the formation of highly stable (both thermodynamic and kinetically) complexes. The conformations adopted in solution by the host and the solid-state geometry are discussed in detail. Furthermore, we also explore the host-guest chemistry of self-assembled molecular containers. We describe the formation of ordered co-encapsulation complexes of chloride with neutral guests within self-assembled hydrogen-bonded molecular capsules having a calixpyrrole core. In a great synthetic effort, a biscatenane molecular container was prepared by the mechanical link of a calixpyrrole and a calixarene hemisphere. The anisotropic cavity of the biscatenane allowed for the co-encapsulation of small N-oxides along with a solvent molecule. The high kinetic stability of the host-guest complexes allowed for the stabilization of a reactive propargylic N-oxide. The observed kinetic stability was related to the thermodynamics of the host-guest complex by a kinetic model. Finally, we studied the synthesis and properties of covalent molecular containers. The preparation of carcerand-like compounds by the Hay coupling of a tetra-alkynyl calixpyrrole afforded the unexpected formation of a figure-of-eight-like structure. The assembly of dynamic covalent capsules bearing reversible imine bonds was also explored using a tetra-aldehyde calixpyrrole as scaffold. In both cases, it was found that the role of the template was vital in the efficient synthesis of the containers.