Homogeneous catalysts for the hydrolysis of Sodium Borohydride : synthesis, characterization and catalytic use

Download
2010
Masjedi, Mehdi
Recent study has shown that ruthenium(III) acetylacetonate acts as a homogeneous catalyst in the hydrolysis of sodium borohydride. When two equivalents of trimethylphosphite per ruthenium is added to the reaction solution containing sodium borohydride and ruthenium(III) acetylacetonate in the mixture of water and tetrahydrofuran, the rate of hydrogen generation is practically stopped (or reduced to the level of self hydrolysis). However, the catalytic hydrogen evolution of sodium borohydride restarts at an unexpectedly high rate in a certain period of time (induction time) after addition of trimethylphosphite. Consequently, trimethylphosphite known to be a poison in the hydrolysis, is involved in the formation of a new active catalyst (ruthenium species containing trimethylphosphite ligands) which has much higher catalytic activity in comparison with sole ruthenium(III) acetylacetonate. The same rate enhancement is observed by addition of two equivalents of triphenylphosphite per ruthenium into the medium. Varying the phosphorus compound affects not only the life time of catalyst but also the kinetic and activation parameters of the hydrolysis of sodium borohydride. However, varying the mole ratio of phosphorus compound to ruthenium does not affect the rate of hydrolysis or in other words, the rate of hydrogen generation is independent of phosphite concentration. Trans- and cis-[Ru(acac)2{P(OMe)3}2] complexes do not show significant catalytic activity in hydrogen generation of sodium borohydride. However, catalytic activity of cis-isomer is highly increased in the presence of two equivalents of trimethylphosphite, showing that the active catalyst formed during hydrolysis of sodium borohydride starting with Ru(acac)3 or cis-[Ru(acac)2{P(OMe)3}2], has more than two phosphine ligands. For the first time, a ruthenium(I) complex was isolated from aqueous solution after finishing the catalytic hydrolysis of sodium borohydride starting with ruthenium(III) acetylacetonate and trimethylphosphite. Hydridotetrakis(trimethylphosphite)ruthenium(I), [Ru{P(OMe)3}4H] was isolated and characterized by single crystal X-ray diffraction, Mass, UV-visible, FTIR, 1H, 13C and 31PNMR spectroscopy. Following the catalytic reaction by UV-Visible spectroscopy shows in-situ formation of a Ru(II) species which is mostly converted back to ruthenium(III) acetylacetonate after hydrolysis reaction along with formation of [Ru{P(OMe)3}4H] complex as a minor product. Although Ru(II) species could not be isolated, adding 1 equivalent of 2,2'-bipyridine yielded [Ru(acac)(bipy){P(OMe)3}H] complex which could be isolated and characterized by Mass, UV-Visible, FTIR, 1H, 13C and 31PNMR spectroscopy. In-situ generated Ru(II) species has much higher catalytic activity in comparison with its stabilized form [Ru(acac)(bipy){P(OMe)3}H] or [Ru{P(OMe)3}4H] complex. Conclusively, the fac-[Ru(acac){P(OMe)3}3H] complex is believed to be the in-situ generated Ru(II) species and the active catalyst in the hydrolysis of sodium borohydride.

Suggestions

Novel homogeneous catalyst comprising ruthenium and trimethylphosphite for the hydrolysis of sodium borohydride
Masjedi, Mehdi; Yildirim, Leyla Tatar; Özkar, Saim (2012-03-01)
Homogeneous catalytic hydrolysis of sodium borohydride starting with Ru(acac)(3) (acac = acetylacetonate) and P(OMe)(3) was followed by monitoring the hydrogen evolution and the UV-vis electronic absorption spectra which shows the conversion of all ruthenium(III) to a ruthenium(II) species, most likely acting as catalyst. This active catalyst is alive only under reducing conditions and converted mainly to Ru(acac)(3) along with other minor complexes when the catalytic reaction is over. A ruthenium(II) compl...
Hydroxyapatite-supported cobalt(0) nanoclusters as efficient and cost-effective catalyst for hydrogen generation from the hydrolysis of both sodium borohydride and ammonia-borane
Rakap, Murat; Özkar, Saim (2012-03-20)
Herein, we report the preparation, characterization, and catalytic use of cobalt(0) nanoclusters supported on hydroxyapatite in the hydrolysis of both basic sodium borohydride and ammonia-borane solutions. They were prepared in situ from the reduction of cobalt(II) ions adsorbed on hydroxyapatite with sodium borohydride. Hydroxyapatite-supported cobalt(0) nanoclusters were stable enough to be isolated as solid material and characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES), ...
Water soluble polymer stabilized iron(0) nanoclusters: A cost-effective and magnetically recoverable catalyst in hydrogen generation from the hydrolysis of sodium borohydride and ammonia borane
Dinç, Melek; Metin, Önder; Özkar, Saim (Elsevier BV, 2012-3)
Water soluble polymer stabilized iron(0) nanoclusters were prepared from the reduction of iron(III) chloride by sodium borohydride (SB) and ammonia borane (AB) mixture in the presence of polyethylene glycol (PEG) as stabilizer and ethylene glycol as solvent at 80 degrees C under nitrogen atmosphere. PEG stabilized iron(0) nanoclusters were isolated from the reaction solution by centrifugation and characterized by UV-Vis, TEM, HRTEM, XRD, ICP-OES and FT-IR methods. The particle size of PEG stabilized iron(0)...
Testing the ruthenium(iii) acetylacetonate and 1,2-bis(diphenylphosphino)ethane system as homogeneous catalyst in the hydrolysis of sodium borohydride
Demiralp, Tülin; Özkar, Saim; Department of Chemistry (2008)
Recent studies have shown that ruthenium(III) acetylacetonate is acting as homogeneous catalyst in the hydrolysis of sodium borohydride. Although trimethlyphosphite is found to be a poison for the catalytic hydrolysis of sodium borohydride, a longer observation of the reaction in the presence of ruthenium(III) acetylacetonate and 2 equivalent trimethylphosphite shows an unexpected enhancement in the catalytic activity after an induction period. The same rate enhancement is observed when 2 equivalent triphen...
Trace level determination of beryllium in natural and flavored mineral waters after pre-concentration using activated carbon
KILINÇ, ERSİN; Bakirdere, Sezgin; YAMAN, MEHMET (Informa UK Limited, 2011-01-01)
The concentrations of beryllium (Be) in natural and flavored mineral water samples were determined by flame atomic absorption spectrophotometer (FAAS) after pre-concentration based on the complexation of Be(+2) with a mixture of acetylacetone (pentane-2,4-dione) plus morin (3,5,7,2',4'-pentaoxyflavone) and adsorption on activated carbon. The adsorbed complex was eluted with 1.5 ml of 2.0 M HNO(3) and evaporated to dryness. After adding 1.5 ml of 2 M HNO(3) and centrifuging, Be in acid solution was determine...
Citation Formats
M. Masjedi, “Homogeneous catalysts for the hydrolysis of Sodium Borohydride : synthesis, characterization and catalytic use,” Ph.D. - Doctoral Program, Middle East Technical University, 2010.