Cationic Main Group Compounds as Water Compatible Small Anion Receptors

Abstract

The fluoride anion plays an important role in dental health and as a result is added to drinking water at low concentrations. If the concentration of fluoride is too high however, skeletal fluorosis can occur. Because of this, there has been significant interest in the development of water compatible anion sensors that can sense fluoride at the ppm level. This is made difficult by the high hydration enthalpy of fluoride (ΔH0 = -504 KJ/mol) which significantly lowers the reactivity of this anion in water. For this reason it has become the goal of the Gabbaï group, as well as other research groups to develop fluoride sensing small molecules. Such molecules should possess sufficient Lewis acidity to overcome the hydration enthalpy of the fluoride anion. A significant amount of research has been conducted on triarylboranes containing cationic moieties such as ammonium, phosphonium, and sulfonium groups. This thesis will describe additional examples of such species, including a series of ammonium boranes of the general formula [p-(Mes2B)C6H4(NMe2R)]+. As indicated by anion complexation studies, the R group present in these molecules has a notable effect on the anion affinity of the somewhat distant boron center. Another component of this thesis deals with the chemistry of newly synthesized stiboranes that are also decorated by peripheral ammonium groups. As observed for the ammonium boranes mentioned above, the ammonium groups present in these stiboranes drives anion capture, leading to zwitterionic ammonium antimonite formation.