Hydrogen generation from the dehydrogenation of ammonia–borane in the presence of ruthenium(III) acetylacetonate forming a homogeneous catalyst

Abstract

Starting with ruthenium(III) acetylacetonate a homogeneous catalyst is formed which catalyzes the release of 1 equivalent of hydrogen gas from the dehydrogenation of ammonia–borane in toluene solution at low temperature in the range 50–65 °C. Mercury poisoning experiments showed that the catalytic dehydrogenation of ammonia–borane starting with ruthenium(III) acetylacetonate is a homogeneous catalysis. The final product obtained after the catalytic dehydrogenation of ammonia borane was thoroughly characterized by using 11B Nuclear Magnetic Resonance and Infrared spectroscopies. The homogeneous catalyst formed from the reduction of ruthenium(III) acetylacetonate provides 950 turnovers (TTO) over 58 h and 27 (mol H2)(mol Ru)−1(h)−1 value of initial turnover frequency (TOF) in hydrogen generation from the dehydrogenation of ammonia–borane at 60 °C before deactivation. Kinetics of this homogenous catalytic dehydrogenation of ammonia–borane was studied depending on the catalyst concentration, substrate concentration, and temperature. The hydrogen generation was found to be first order with respect to both the substrate concentration and catalyst concentration. The activation parameters of this reaction were also determined from the evaluation of the kinetic data: activation energy; Ea = 48 ± 2 kJ mol−1, the enthalpy of activation; ΔH# = 45 ± 2 kJ mol−1 and the entropy of activation ΔS# = −152 ± 5 J mol−1 K−1.