Acid- and Base-Catalyzed Hydrolytic Hydrogen Evolution from Diboronic Acid

Graphical Metal-free H 2 or D 2 evolution is obtained in a few minutes from acid- or base-catalyzed hydrolysis of diboronic acid, respectively, under ambient conditions and is coupled to hydrogenation reactions. Kinetic studies allow proposing mechanisms by considering primary kinetic isotope effects observed for both acid- and based-catalyzed reactions with D 2 O. The efficient production of H 2 from hydrogen-rich sources, particularly from water, is a crucial task and a great challenge, both as a sustainable energy source and on the laboratory scale for hydrogenation reactions. Herein, a facile and effective synthesis of H 2 and D 2 from only acid- or base-catalyzed metal-free hydrolysis of B 2 (OH) 4 , a current borylation reagent, has been developed without any transition metal or ligand. Acid-catalyzed H 2 evolution was completed in 4 min, whereas the base-catalyzed process needed 6 min. The large kinetic isotopic effects for this reaction with D 2 O, deuteration experiments and mechanistic studies have confirmed that both H atoms of H 2 originate from water using either of these reactions. This new, metal-free catalytic system holds several advantages, such as high efficiency, simplicity of operation, sustainability, economy, and potential further use.