Fluoride Ion Complexation and Sensing Using Organoboron Compounds

A review of research work conducted toward the development of superior fluoride ion receptors and sensors using organoboron compounds is presented. Boranes are found to show a high selectivity for fluoride anions and this selectivity is assigned to the steric protection of the boron atom, which prevents coordination of larger anions for triarylboranes featuring at least two mesityl or anthryl groups. The rate at which individual aryltrifluoroborates undergo hydrolysis varies markedly, with rate constants varying by some 3 orders of magnitude, depending on the substitution pattern of the aryl substituent. Complex fluorinated boranes are found to form highly acidic water adducts, while lack of steric protection and the exceptional Lewis acidity of adducts preclude selectivity for fluoride and result in a tendency for it to bind various larger and less basic anions. The synthesis of isomeric imidazolium-functionalized phenylboronic acids show that the greater binding affinity of these acids allow it to function as a fluorescence-based sensor for fluoride in the presence of various anions.