Imino- and aminomethylphenylboronic acids: stabilizing effect of hydrogen bonds

ortho-Iminomethylphenylboronic acids were synthesized from the reaction of 2-formyl-phenylboronic acid with primary aromatic amines. Reduction of these compounds yielded the corresponding aminomethylphenylboronic acids. For both types of the compounds, the crystal structure was determined by single crystal X-ray diffraction method. Hydrogen-bonded dimers with an additional intramolecular B-O-H center dot center dot center dot N hydrogen bond have been observed. Calculations at MP2/6-31+G** level proved that the most stable form is that with the above-mentioned intramolecular hydrogen bond while the form with dative N -> B bond is less favoured. Since the calculated energy difference is small, the competition between possible forms was analyzed in terms of substituent effect stabilization energy (SESE). In the case of p-iminomethylphenylboronic acid, both hydroxyl groups are engaged in intermolecular O-H center dot center dot center dot O interactions resulting in a supramolecular ribbon motif. (C) 2012 Elsevier Ltd. All rights reserved.