Reactivity and Coordination Chemistry of Pnictogen-Containing Complexes
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Only within the last decade has supramolecular chemistry begun to adopt the Group 15 elements into its field of research. This dissertation presents a supramolecular approach to the self-assembly and reactivity of Group 15 metalloids, specifically arsenic and antimony, with organothiolate ligands. Investigating the self-assembly of pnictogen-based coordination complexes allows for in-depth characterization of the chemical behavior of arsenic, antimony and other Group 15 elements. Currently, the infiltration of arsenic into global groundwater systems has developed into a worldwide health concern. There are no chelating agents available for public use in the treatment of arsenic poisoning which are capable of binding arsenic (III) in its preferred coordination geometry thereby hindering the selectivity for rapid chelation. Chapter I is a review covering two important characteristics observed in the Group 15 elements: 1) a stabilizing, non-covalent cation-π interaction aiding in the formation of pnictogen-aryl thiolates, and 2) an observed lack of selectivity in environments containing multiple pnictogen ions which enables transmetalation of the complexes to occur or the generation of heterometallic assemblies. Based on the discovery of this new transmetalation reactivity, the remainder of the dissertation explores the effects of external additives during self-assembly in order to understand how they may affect the reactivity of these self-assembled complexes and provide insight into formation mechanisms. Chapter II identifies a catalyst for the acceleration of a slow self-assembly reaction between AsCl3 and a dithiolate ligand to give an As2L3 cryptand. Chapter III examines the oxidation of the arsenic cryptand using iodine, which leads to the self-assembly of a series of differently sized, discrete disulfide-bridged macrocycles. In Chapter IV, the self-assembly of the first trinuclear arsenic- and antimony-based coordination complexes was studied, revealing interesting solvent dependent conformational isomerism in solution. Chapter V applies the pnictogen-enhanced iodine oxidation to the synthesis of known and new cyclophanes using supramolecular chemistry, including the self-assembly and covalent capture of an unprecedented tetrahedral thiacyclophane. Additionally, an unusual trithioorthoformate capped tricyclophane cage was also synthesized and isolated by pnictogen-activated oxidation. Chapter VI includes the conclusion and future directions for the project. This dissertation includes co-authored material and previously published results.