A New Homogeneous Catalyst for the Dehydrogenation of Dimethylamine Borane Starting with Ruthenium(III) Acetylacetonate

Abstract

The catalytic activity of ruthenium(III) acetylacetonate was investigated for the first time in the dehydrogenation of dimethylamine borane. During catalytic reaction, a new ruthenium(II) species is formed in situ from the reduction of ruthenium(III) and characterized using UV-Visible, Fourier transform infrared (FTIR), 1H NMR, and mass spectroscopy. The most likely structure suggested for the ruthenium(II) species is mer-[Ru(N2Me4)3(acac)H]. Mercury poisoning experiment indicates that the catalytic dehydrogenation of dimethylamine-borane is homogeneous catalysis. The kinetics of the catalytic dehydrogenation of dimethylamine borane starting with Ru(acac)3 were studied depending on the catalyst concentration, substrate concentration and temperature. The hydrogen generation was found to be first-order with respect to catalyst concentration and zero-order regarding the substrate concentration. Evaluation of the kinetic data provides the activation parameters for the dehydrogenation reaction: the activation energy Ea = 85 ± 2 kJ·mol−1, the enthalpy of activation ∆H# = 82 ± 2 kJ·mol−1 and the entropy of activation; ∆S# = −85 ± 5 J·mol−1·K−1. The ruthenium(II) catalyst formed from the reduction of ruthenium(III) acetylacetonate provides 1700 turnovers over 100 hours in hydrogen generation from the dehydrogenation of dimethylamine borane before deactivation at 60 °C.

Highly active and long lived homogeneous catalyst for the dehydrogenation of dimethylamine borane starting with ruthenium(III) acetylacetonate and oleylamine precatalyst

“…In summary, our study on the dehydrogenation of dimethylamine boranestarting with Ru(acac) 3 whereby the reaction is essentially independent of substrate concentration [31]. (vii) The activation energyof catalytic dehydrogenation of dimethylamine borane starting with Ru(acac) 3 and 3 equivalent oleylamine (E a = 58 ± 2 kJ·mol −1 )is much lower than that obtained for the same reaction by using the sole Ru(acac) 3 precursor (E a = 85 ±2 kJ·mol −1 ) [31].…”

“…(vii) The activation energyof catalytic dehydrogenation of dimethylamine borane starting with Ru(acac) 3 and 3 equivalent oleylamine (E a = 58 ± 2 kJ·mol −1 )is much lower than that obtained for the same reaction by using the sole Ru(acac) 3 precursor (E a = 85 ±2 kJ·mol −1 ) [31]. (viii)…”

“…Our report also includes the results of catalytic tests using Ru(acac) 3 plus oleylamine in the dehydrogenation of dimethylamine borane in toluene solution as well as the results of the kinetic study of the catalytic reaction depending on the catalyst concentration, substrate concentration and temperature. The results reported here clearlyshow the novelty of the present study.Of particular importance is that adding 3 equivalent oleylamine per mole of ruthenium into the precatalyst solution of Ru(acac) 3 increases the catalytic activity by a factor of 5 and the lifetime of the catalyst by a factor of >9 compared to the ones obtained by using soleRu(acac) 3 [31] in dehydrogenation of dimethylamine borane in toluene at 60.0 ± 0.1 °C.Another interesting feature of the present study is the simplicity of preparing the catalytic materials as the precatalyst system reported here is composed of a ruthenium compound and a stabilizer ligand, both of which are commercially available.…”

“…Prompted by the observation that ruthenium(III) acetylacetonate, Ru(acac) 3 acts as homogeneous catalyst in the hydrolysis of sodium borohydride at room temperature [30], we have very recently shown that dehydrogenation of dimethylamine borane can also be catalyzed starting with sole Ru(acac) 3 in toluene solution at temperature above 50°C [31].…”

“…However, there is no report concerning the use of oleylamine as stabilizing ligand for homogeneous catalysis resulting in coordination of oleylamine to metal. Since our recent paper [31] has reported the identification of a ruthenium(II) species bearing two N-ligands in the catalytic dehydrogenation of dimethylamine borane starting with Ru(acac) 3 we decided to add oleylamine as N-ligand for the stabilization of active catalyst in this reaction.…”