Synthesis and host-guest chemistry of molecular cages containing gold or zirconium

The kinetic inertness and low solubility of Au3(pyrazolate)3 complexes have made it difficult to integrate them into supramolecular assemblies. In this thesis, an investigation into the dynamic combinatorial chemistry of these complexes is presented, followed by strategies for their incorporation into molecular cages and a study of the host - guest chemistry of the resulting assemblies. The first research chapter, Chapter 2, describes the constitutional dynamic chemistry of Au3(pyrazolate)3 complexes. Ligand exchange reactions between"free" pyrazole ligands and Au3(pyrazolate)3 complexes were performed, and a pronounced autocatalytic behavior was observed. This led to the understanding that pyrazole ligands can act as catalysts for ligand scrambling between two Au3(pyrazolate)3 complexes. In addition, four crystal structures of heteroleptic Au3(pyrazolate)2(pyrazolate') are presented. Building on this foundation, Chapter 3 describes the synthesis of a dodecanuclear Au(I) cage. The cage consists of four Au3(pyrazolate)3 units, connected through an organic linker. The cage was first synthesized by a ligand exchange reaction, using an Au3(triazolate)3 complex as a gold source. Surprisingly, the same cage was also obtained in a direct synthesis from a reaction with AuCl(SMe2). The results highlight the importance of ligand design for the successful formation of Au3(pyrazolate)3-based cages. In Chapters 4 and 5, we demonstrate how the kinetic inertness of Au cyclic trinuclear complexes (CTCs) can be utilized in order to use them as pre-formed building blocks for cage synthesis. In Chapter 4, a stepwise approach, in which the use of metalloligands enabled the construction of a Fe24Au24Pd8 cage, is presented. With a molecular weight of 21 kDa and a diameter of approximately 4.1 nm, it is among the largest [Pd6L8]12+ cages reported. In addition, we demonstrate the use of a heteroleptic Au3(pyrazolate)2(pyrazolate') complex for the construction of a smaller Fe8Au12Pd2 cage. In Chapter 5, the preparation of three Au3(pyrazolate)3-based cages by combining coordination chemistry and dynamic covalent chemistry is described. First, two Au3(pyrazolate)3 complexes bearing peripheral aldehyde groups were synthesized. These complexes were used as building blocks for an imine condensation reaction, yielding one tetrahedral cage, containing four CTC units, and two prismatic cages, containing two CTC units each. The crystal structures of all three assemblies are reported. In addition, the host-guest chemistry with pi-acidic guests was studied: the tetrahedral cage was found to bind fullerenes with high affinity, while the prismatic cages encapsulate halogenated aromatic compounds. In Chapter 6, the combination of coordination chemistry and dynamic covalent chemistry for the synthesis of a new family of zirconium-based cages is presented. Pre-formed zirconium clusters were employed as rigid, preorganized building blocks, leading to the synthesis of four new cages