Sandrine Stanislas

Oxidations by the reagent `O2–H2O2 – vanadate anion – pyrazine-2-carboxylic acid'.: Part 10. Oxygenation of methane in acetonitrile and water

Abstract The oxidation of methane by a combination of air and hydrogen peroxide is effectively catalyzed in solution by a system composed of vanadate and pyrazine-2-carboxylic acid (PCA). In acetonitrile solution, containing the vanadate anion as tetrabutylammonium salt, the reaction gives, over a temperature range of 25 to 50°C, methanol, carbon monoxide, formaldehyde, formic acid and carbon dioxide, the latter three compounds, however, being partially due to the oxidation of the acetonitrile used as the solvent, especially at higher temperatures. In aqueous solution, containing the vanadate anion in the form of the sodium salt, the reaction affords, over a temperature range of 40 to 70°C, selectively methyl hydroperoxide within 4 h. The yield of CH3OOH attains 24%, based on H2O2, after 24 h at 50°C, the catalytic turnover number being 480. The process seems to involve hydroxyl radicals, generated by the catalyst from H2O2 even at low temperatures. At 120°C, methane is oxidized by O2 and H2O2 to give formaldehyde and formic acid, even in the absence of the catalyst, presumably due to the formation of HO· radicals from H2O2 in the presence of very low concentrations of metal ions from the autoclave under high temperature conditions.

Amphiphilic organoruthenium oxomolybdenum and oxovanadium clusters

Abstract Para-cymene ruthenium dichloride dimer reacts in aqueous solution with sodium molybdate or sodium vanadate to give the amphiphilic clusters [ (η6-p-MeC6H4i Pr) 4Ru4Mo4O16] (1) and [ (η6-p-MeC6H4i Pr) 4 Ru4V6O19] (4) respectively. The analogous reaction of hexamethylbenzene ruthenium dichloride dimer with sodium vanadate gives [ (η6-C6Me6) 4Ru4V6O19] (5) . The mixed-metal clusters [ (η6-p-MeC6H4i Pr) Ru (η5-C5Me5) 3Rh3Mo4O16] (2) and [ (η6-p-MeC6H4i Pr) 2Ru2 (η5-C5Me5) 2Rh2Mo4O16] (3) are accessible from a mixture of para-cymene ruthenium dichloride dimer and pentamethylcyclopentadienyl rhodium dichloride dimer with sodium molybdate in aqueous solution. The crystal structure analyses of 1 and 4 reveal different framework geometries of the metal oxygen skeletons. 17O NMR spectroscopy and partial charge calculations confirm the presence of three different types of oxygen atoms in 1.

Catalytic functionalization of methane

A mixture of sodium vanadate and pyrazine-2carboxylic acid (pcaH) efficiently catalyses the reaction of methane with molecular oxygen (from air) and hydrogen peroxide to give methyl hydroperoxide and, as consecutive products, methanol and formaldehyde. The reaction takes place under mild conditions (25‐75 °C) either in aqueous or in acetonitrile solution. The complexes formed from the catalyst precursor and the co-catalyst (under the reaction conditions) have been isolated and characterized as the derivatives [VO2(pca)2] ˇ (1) and [VO(O2) (pca)2] ˇ (3). The implications of these species in the catalytic process are discussed. Copyright # 2000 John Wiley & Sons, Ltd.

Carboxylation of methane with CO or CO2 in aqueous solution catalysed by vanadium complexes

Reaction of methane with CO or CO2 in aqueous solution in the presence of O2 (catalysed by NaVO3) or H2O2 (catalysed by NaVO3–pyrazine-2-carboxylic acid) at 25–100 °C affords acetic acid and in some cases also methanol, methyl hydroperoxide and formaldehyde.

OXYGENATION OF METHANE WITH ATMOSPHERIC OXYGEN IN AQUEOUS SOLUTION PROMOTED BY H2O2 AND CATALYZED BY A VANADATE ION-PYRAZINE-2-CARBOXYLIC ACID SYSTEM

Methane is oxidized in aqueous solution with atmospheric oxygen and hydrogen peroxide in a reaction catalyzed by a NaVO3-pyrazine-2-carboxylic acid system. Methyl hydroperoxide is selectively formed at 50°C. The turnover number of the catalyst after 24 h amounts to 480, and the yield of methyl hydroperoxide is 24% with respect to H2O2. Formaldehyde and formic acid are mainly formed at 120°C.

Large variation of the luminescence energy from rhenium(V) complexes with oxo and nitrido ligands

We observe visible and near-IR luminescence from oxo and nitrido compounds of rhenium(V) with chelating ligands combining soft (P) and hard (O) donors and show that the emitting state energy of the nitrido complexes is higher in energy by a factor of ca. two (8300 cm–1) than for the oxo compounds, an unusually large difference.

Bis­(tetra­butyl­ammonium) bis­(malonato)­oxovanadate(IV)

The synthesis, EPR (electron paramagnetic resonance) characterization, and crystal structure of (C16H36N)2[VO(C3H2O4)2] are described. The V atom is pentacoordinated by an oxo and two bidentate malonate ligands. The geometry around the metal is square-pyramidal and the two bidentate malonate ligands form the base of the pyramid. The V=O bond length is 1.556 (3) A and the range of V—O bond lengths is 1.960 (3)–1.968 (3) A. The EPR spectrum (giso = 1.965 and Aiso = 0.00965 cm−1) is typical of a VIV system.