Supramolecular nanocapsules as platforms for molecular recognition and reactivity in confined spaces

The use of self-assembly to bring simple building blocks together into complex product, has led to the preparation of an increasing number of sophisticated and functional 3D supramolecular nanocapsules. By understanding the selectivity of these different coordinative bond-forming reactions and interactions between the subcomponents, complex supramolecular scaffolds by design are cleanly generated from simple building blocks. Important prospective applications of metal-organic capsules are the development of low-energy methodologies for chemical separations and purification of target molecules, and the reactivity modulation of confined guests for the efficient and selective production of valuable compounds. In the first part, this thesis builds upon expanding the capabilities of 1a·(BArF)8 (Pd(II)-based tetragonal prismatic nanocapsule) as a supramolecular mask, to gain full regio-functionalization control and modulate the reactivity of Bingel cyclopropanation reactions on confined fullerene C60. The confinement effect not only allows a very precise control of the regiochemistry in the synthesis of poly-functionalized C60 adducts, but also, completely precludes the over-reactivity commonly observed without mask. In this manner, fully equatorial bis-, tris- and tetrakis- homo and heteroadducts have been synthesized for the first time, as well as hekakis-heteroadducts. Afterwards, the Cu(II)-based tetragonal prismatic nanocapsule 5·(OTf)8, analogue of the 1a·(BArF)8, was prepared and fully characterized. As a consequence of the inherent lability of the Cu(II)-carboxylate coordinative bonds present in the metal nodes of 5·(OTf)8, this nanocapsule is able to reversibly encapsulate large fullerenes and EMFs in homogeneous and heterogeneous (host in solid and guest in solution) systems. The different affinities displayed by 5·(OTf)8 towards the species present in a Sc3N-based soot, allows for the straightforward purification of Sc3N@C80 in a single step. Then, 5·(OTf)8 nanocapsule was derivatized by exchanging its OTf counter-anions by BArF- , yielding 1b·(BArF)8. We investigated the ability of 1b·(BArF)8 as a selective host in the purification of U/Sc-based EMF soots. The very precise and divergent selectivity shown by 1b·(BArF)8 towards U2@C80 and unprecedented Sc2CU@C80 guests allows their sequential and selective uptake in a single and operationally simple step. The obtained results demonstrate that 1b·(BArF)8 is able to discriminate EMFs bearing exactly the same carbon cage and differing exclusively in the endohedral clusters. In the final part of this thesis, the ability of 1b·(BArF)8 to purify challenging EMFs directly from complex mixtures has been further exemplified by the selective encapsulation and purification of U-based C78 EMFs in the presence of U-based C80 ones. The molecular recognition events observed in the heterogeneous (host in solid and guest in solution) host-guest systems, were dictated by the enhanced electrostatic interactions between the host and the EMFs guests possessing ellipsoidal fullerene cages, such as U-based C78 EMFs, compared to spherical C80 species. Moreover, further host-guest experiments demonstrate that 1b·(BArF)8 is able to distinguish among EMF with very similar endohedral clusters, i.e. U2@D3h-C78 versus U2C@D3h C7 ​
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