Metal-Free Ammonia-Borane Dehydrogenation Catalyzed by a Bis(borane) Lewis Acid

The storage of energy in a safe and environmentally benign way is one of the main challenges of today’s society. Ammonia–borane (AB=NH3BH3) has been proposed as a possible candidate for the chemical storage of hydrogen. However, the efficient release of hydrogen is still an active field of research. Herein, we present a metal‐free bis(borane) Lewis acid catalyst that promotes the evolution of up to 2.5 equivalents of H2 per AB molecule. The catalyst can be reused multiple times without loss of activity. The moderate temperature of 60 °C allows for controlling the supply of H2 on demand simply by heating and cooling. Mechanistic studies give preliminary insights into the kinetics and mechanism of the catalytic reaction. Two boron atoms collaborate: A highly efficient bis(borane) Lewis acid catalyst, which can be reused multiple times without loss of activity, catalyzes the release of 2.46 equivalents of H2 per H3N–BH3 molecule. The dehydrogenation can be initiated and stopped on demand simply be heating to 60 °C or cooling to room temperature. Mechanistic studies provide insight into the mode of action of the catalyst.