Synthesis and Characterization of Coordination Cages Based on Clathrochelate Metalloligands

The work presented in this thesis focused on the synthesis and characterization of new metalloligands based on iron(II) clathrochelate complexes. Clathrochelates can be functionalized peripherally with donor groups capable of coordinating metal ions. The synthetic accessibility of clathrochelate complexes, along with their excellent stability, and the broad structural and functional modifications possible, make this class of compound suitable to be used as building blocks in supramolecular chemistry. In chapter 1, a general introduction on supramolecular chemistry will be given. The chapter is focussing on the different approaches towards the process of self-assembly, and in particular on the use and properties of metalloligands. In chapter 2, clathrochelate complexes with terminal 3-pyridyl capping group are presented. These complexes were prepared by one-pot syntheses from commercially available or readily accessible starting materials. The resulting metalloligands were then incorporated in supramolecular coordination cages. Moreover, the influence of subtle changes in the structure of the ligands, and in particular in the aspect ratio of the ligands, was investigated as decisive factors which drive self-assembly processes towards different assemblies. In chapter 3, tetratopic clathrochelate-based metalloligands with appended 4-pyridyl functions are presented. These complexes were obtained by high-yield coupling reactions of brominated clathrochelate complexes. The metalloligands were used for the construction of novel supramolecular cages with gyrobifastigium geometry. The unusual geometry that arises from the combination of the new metalloligands and cis-blocked PtII and PdII complexes was explained on the base of steric interactions. In chapter 4, three novel tetratopic ligands with an extended range of aspect ratios are discussed. The ligands were tested in combination with cis-blocked PtII complexes. The results of these experiments confirmed that in the rational design of supramolecular assemblies, there is still ample room for surprises. The influence of the aspect ratio of ligands is not to be underestimated, and structurally very different assemblies were characterised. The characterization includes X-ray single crystal analyses. Thanks to the latter, we were able to confirm the formation of a sizable M8L16 molecular square orthobicupola, that is one of the biggest discrete assemblies reported to date. In order to give new functions to molecular cages based on clathrochelates, we move a first step towards the synthesis of redox-active molecular cages. This work is presented in chapter 5. The library of tetratopic ligands in our hands was enlarged with the synthesis of new iron(II) clathrochelate complexes based on redox non-innocent dioximes. The syntheses and characterisations of these new compounds and their precursors are reported. A preliminary electrochemical study of the ligands is also described. The ligands were then used for the synthesis of new supramolecular cages. The assemblies did not show reversible redox events. Nevertheless, the structural characterization can serve as a starting point to further investigations. In chapter 6, the syntheses of new metalloligands are discussed along with their precursors. An extensive characterization of the new complexes is given. Some of the building blocks were tested in combination with metal complexes or salts to investigate their behaviour as supramolecular subunits.