Investigation of positively charged supramolecular cages towards guest-uptake and catalysis

Over the recent decades, interest in anion-$\pi$ interactions has grown rapidly. Naphthalene diimide (NDI) compounds were found to offer a useful $\pi$-acidic platform. While open, non-capsular systems with NDI moieties have been used as anion-$\pi$ catalysts for various reactions, they have not yet been incorporated into supramolecular cages for explicit anion-$\pi$ catalysis. This thesis investigated two strategies for the synthesis of positively charged, supramolecular cages with subcomponents featuring $\pi$-acidic surfaces offering multiple binding sites for anion-$\pi$ interactions, which could serve as potential catalysts for anionic reactions.
First, dynamic covalent chemistry was applied using reversible imine condensation between NDI dialdehyde 175, which was synthesized in four steps, and either TREN (128a), TRPN (128b) or the more rigid triamine 128c as subcomponents in a 3:2 ratio. Imine cages XXIIIa-c formed preferentially with Tri2Di3 topology in every case. TREN-based imine cage XXIIIa was reduced to its corresponding ammonium chloride cage XVIIa. Anion exchange gave access to its ammonium trifluoroactetate cage XXVa. Guest-uptake experiments were conducted with anionic guests showing rather moderate binding constants between 75 and 460 M-1. The cage was considered too small for our endeavours and the binding constants not convincing enough. Intriguingly, four more highly symmetric imine species formed with increasing TREN (128a) concentration during the first step. Driven by the desire to obtain cages with bigger cavities, such as those with Tri4Di6 topology, the imine species mixtures have been reduced to their corresponding ammonium species. Unfortunately, two were identified as ammonium species 204a and 205a of lower molecular weight after an extensive workup procedure. The other two remained unknown with evidence for decomposition being visible only after partial purification.
In the second part of this thesis, coordination driven self-assembly was used as a strategy for the construction of novel coordination cages. For this, NDI dialdehyde 176 was synthesized in two steps. The reaction between subcomponent 176 and TREN or TRPN with various metal precursors was investigated. Zn2L3(NTf2)4 helicate XXXII was obtained. Its crystal structure was elucidated, showing no cavity due to $\pi$-$\pi$ stacking between the NDI ligands. An edge-linked tetrahedral M4L6 cage could not be accessed with NDI dialdehyde 176. The literature known Fe4L6(NTf2)8 tetrahedron XXIX proved to be unstable against water and bases. Trialdehyde ligand 177, based on the $\pi$-acidic triphenylene triimide (TPTI) scaffold, was pursued next. Six steps were envisioned for the synthesis of ligand 177, but the TPTI scaffold was found to be unstable towards water during aqueous workups. The last step of its synthesis failed. Therefore, trialdehyde 178, bearing no $\pi$-acidic moiety, was synthesized in three steps instead. Subcomponent self-assembly between tritopic ligand 178 with TREN and Zn(NTf2)2 gave face-capped Zn4L4(NTf2)8 tetrahedron Zn-XLIII. No water-soluble derivative was accessible. However, the cage proved to be stable against water and various bases at elevated temperatures. It was able to bind anionic guests with binding constants between 40 and 850 M-1 in MeCN-d3/H2O = 9:1. Neutral guests were not bound by cage Zn-XLIII. Despite its net positive charge of +8, the cage was not able to accelerate reactions with anionic transition states. Deceleration occurred instead in every single case investigated and the exact reason for this remains unknown.