Polar iso-Tellurazole N-Oxides and their Complexes

Abstract

This thesis describes the synthesis and chemistry of iso-tellurazole N-oxides that have been functionalized with polar groups to enhance their solubility in polar solvents such as alcohols and water. Albeit the heterocycles of this type are polar as individual molecules, they form very strong Te…O chalcogen bonds that assemble supramolecular macrocyclic aggregates which overall are nonpolar. Such property has limited the application of these supramolecular systems to nonpolar media. The derivatives with pendant primary alcohol groups were conveniently prepared by standard methods starting from a protected acetylene. Crystallization experiment identified two polymorphs, one featuring infinite spiral chains and the other contained macrocyclic tetramers. In this regard, the new compounds display the same self-assembly properties of other isotellurazole N-oxides. The ability of these molecules to coordinate to d-block metal ions in polar solvents was demonstrated with the preparation of their Fe(II) and Ni(II) complexes. However, these investigations unveiled an unusual hexameric macrocyclic structure in which Te…ON chalcogen bonds are formed trans to the Te-C bond instead of the Te-N bond, which is observed in all other previously characterized aggregates of iso-tellurazole N-oxides. Further derivatization of the new iso-tellurazole N-oxides was demonstrated with the synthesis of an ionic species featuring a OSO3- group.