Thermal Dehydrogenation and Hydrolysis of BH3NH3 Catalyzed by Cyclic (Alkyl)(amino)carbene Iridium Complexes under Mild Conditions

Though ammonia–borane (AB) is recognized as an excellent hydrogen storage material, efficient dehydrogenation of AB still remains a challenge. Herein, we report that cyclic (alkyl)­(amino)­carbene iridium complexes are highly efficient for both the thermal dehydrogenation and hydrolysis of AB under mild conditions. At 30 °C, the two processes are completed within 15 and 5 min, releasing 2.1 and 2.8 equiv of H2 per AB, respectively. Moreover, 2.8 equiv of H2 can be released within 10 min by thermal dehydrogenation at 60 °C. Kinetic studies revealed that the activation energies for thermal dehydrogenation and hydrolysis of AB are 10.7 and 8.5 kcal/mol, respectively. The catalyst can be recycled without significant loss of activity at least six times for both processes. The reaction mechanisms were further explored by theoretical calculations, stoichiometric reactions, and kinetic isotope effect experiments.