Unexpected Bisboronic Dicationic Acid Obtained from One‐Pot Condensation Reaction of 3‐Aminophenylboronic Acid and 2,6‐Pyridincarboxyaldehyde
Résumé
A one-pot double condensation reaction between 3-aminophenylboronic acid monohydrate and 2,6-pyridincarboxyaldehyde forms the very interesting building block bisboronic dicationic acid (1), the reaction was carried out in methanol with the presence of sulfuric acid as catalyst. The product contains a central core consisting of five delocalized fused heterocycles being a dicationic moiety and including methylsulfate (CH3OSO3−) as anion (1a). Treatment with CaCl2 under heating produces the anion interchange leading the chloride as anion (1b). Both salts were crystallized by slow solvent evaporation and the X-ray diffraction analysis reveals the presence of O−H⋅⋅⋅O hydrogen bonds favoring the 2D supramolecular arrangements. Three different motives were formed for 1a with the participation of water molecules, the methylsulfate anion and the boronic acid groups; by the way for 1b, the chloride anion interacts with a BOH group as well as a methanol molecule trough hydrogen bonds, additionally an electrostatic interactions were found with the cationic five membered rings. The possibility for syn-anti isomerization at room temperature is confirmed by computations with a weak energy barrier of 17.7 kcal mol−1.
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