Probing Intramolecular B-N Interactions in Ortho-Aminomethyl Arylboronic Acids

This work investigates the interplay between the intramolecular B-N dative bonding and solvent insertion in various ortho-methylamino arylboronic acids in protic media. B-11 NMR experiments were conducted to study the effect that the degree of substitution of the amine group has on B-N bonding versus solvent insertion. It was found that there is a slight increase in the amount of B-N dative bonding on going from a tertiary to a secondary to a primary amine group, but that solvent insertion dominates in all cases of the boronate esters. A X-ray crystal structure gives further insight into the structure of the solvent-inserted boronate esters, showing that the inserted solvent has its hydrogen primarily on the amine. Lastly, studies of the use of boronate esters as receptors for simple alcohols and carboxylic acids are described.