The work presented in this dissertation describes the influence of structural modifications on supramolecular structure and function. Investigations focused on an M4L6 tetrahedral structure self-assembled in solution, which is known for its wide applicability in the stabilization of reactive species and enzyme-like microenvironment catalysis of reactions.
Chapter One offers context for this work, including an overview of the field of supramolecular chemistry, focusing on catalysis and on coordination frameworks such as the M4L6 tetrahedron discussed herein. A brief historical perspective of supramolecular chemistry, with emphasis on molecular machines, catalysts, and ion binders is discussed. Parallels to biological systems, from which supramolecular chemists often draw inspiration, are also emphasized throughout the introduction. Examples in which noncovalent forces are crucial to structure as well as function of a supramolecular system are highlighted.
In Chapter Two, the synthesis and reactivity of two pyrene-based supramolecular assemblies is reported. The modification of conditions resulted in the synthesis of an “empty,” or solvent-containing, supramolecular assembly with a modified polycyclic aromatic hydrocarbon core, allowing access to the use of a larger cavity for supramolecular catalysis and enabling size comparison experiments for the first time. In size comparison experiments, changing the aromatic core of the assembly significantly impacted the selectivity of two reactions, a Prins cyclization and a nucleophilic substitution with stereoretention. These results demonstrate the importance of substrate–host size matching in selective supramolecular catalysis, while reactivity was effected by peripheral changes to the supramolecular assembly. Further attempts to examine the nucleophilic substitution reaction using new substrates were explored within the context of supramolecular catalysis.
Chapter Three describes the impact of ligand modification on the process of self-assembly. The introduction discusses the design principles that govern the stoichiometry, shape, and size of metal–ligand coordination assemblies, with an emphasis on symmetry considerations. Secondary factors not accounted for in these design principles are also discussed, as well as examples in which those secondary factors alter the supramolecular architecture of a set of metal and ligand subcomponents. With these design principles in mind, modifications to an M4L6 supramolecular tetrahedron were explored. The periphery, core, and chirality of ligands that make up the tetrahedron were modified. Studies showed that extending the core of the ligand and adding sterically bulky groups to the periphery hinder tetrahedron formation, enabling formation of the entropically favored M2L3 helicate instead. Impacts of reaction conditions on the sensitive equilibria between these two species were explored, as well as attempts to circumvent this equilibrium through templation of a guest followed by its removal.
