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Ruthenium(III) acetylacetonate: A homogeneous catalyst in the hydrolysis of sodium borohydride

2008-05-01
Keceli, Ezgi
Özkar, Saim
Ruthenium(ill) acetylacetonate was employed for the first time as homogeneous catalyst in the hydrolysis of sodium borohydride. Ruthenium(III) acetylacetonate was not reduced by sodium borohydride under the experimental conditions and remains unchanged after the catalysis. Poisoning experiments with mercury and trimethylphosphite provide compelling evidence for the fact that ruthenium(III) acetylacetonate is indeed a homogenous catalyst in the hydrolysis of sodium borohydride. Kinetics of the ruthenium(III) acetylacetonate catalyzed hydrolysis of sodium borohydride 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; E(d) = 58.2 +/- 2.6 kJ mol(-1), the enthalpy of activation: Delta H(#) = 55.7 +/- 2.5 kJ mol(-1) and the entropy of activation Delta S(#) = 118 +/- 5 J mol(-1) K(-1). Ruthenium(III) acetylacetonate was found to be highly active catalyst providing 1200 turnovers over 180 min in hydrogen generation from the hydrolysis of sodium borohydride before deactivation.