Hydrolysis of the Borohydride Anion BH(4)(−): A (11)B NMR Study Showing the Formation of Short-Living Reaction Intermediates including BH(3)OH(−)

In hydrolysis and electro-oxidation of the borohydride anion BH(4)(−), key reactions in the field of energy, one critical short-living intermediate is BH(3)OH(−). When water was used as both solvent and reactant, only BH(3)OH(−) is detected by (11)B NMR. By moving away from such conditions and using DMF as solvent and water as reactant in excess, four (11)B NMR quartets were observed. These signals were due to BH(3)-based intermediates as suggested by theoretical calculations; they were DMF·BH(3), BH(3)OH(−), and B(2)H(7)(−) (i.e., [H(3)B−H−BH(3)](−) or [H(4)B−BH(3)](−)). Our results shed light on the importance of BH(3) stemming from BH(4)(−) and on its capacity as Lewis acid to interact with Lewis bases such as DMF, OH(−), and BH(4)(−). These findings are important for a better understanding at the molecular level of hydrolysis of BH(4)(−) and production of impurities in boranes synthesis.