Testing catalytic activity of ruthenium(III) acetylacetonate in the presence of trialkylphosphite or trialkylphosphine in hydrogen generation from the hydrolysis of sodium borohydride

Abstract

Catalytic activity of Ru(acac) 3 in the presence of different phosphorus compounds (P(OMe) 3, P(OPh) 3, PPh 3 and dppe) was investigated for the first time in the hydrolysis of NaBH 4. Phosphorus compound, usually known as poison in catalysis, is involved in the formation of a species which has higher catalytic activity in comparison with Ru(acac) 3 alone. Varying the phosphorus compound affects the catalytic activity and lifetime of the catalyst as well as the kinetics and the activation parameters of the hydrolysis of NaBH 4. For all of the phosphorus compounds, the hydrogen generation was found to be zero-order with respect to the substrate concentration and first-order regarding the catalyst concentration. The catalyst system with P(OMe) 3 shows the highest catalytic activity and provides the largest total turnover number (TTON = 20,700 over 72 h) in the hydrolysis of NaBH 4. The highest activation energy and enthalpy values were obtained for the catalyst with dppe ( E a = 59 ± 2, Δ H # = 60 ± 2 kJ/mol) while the lowest values were found for the catalyst system with PPh 3 ( E a = 46 ± 2, Δ H # = 43 ± 1 kJ/mol).