820-10-0Relevant articles and documents
Peroxo-Cerium(IV)-Containing Polyoxometalates: [CeIV6(O2)9(GeW10O37)3]24-, a Recyclable Homogeneous Oxidation Catalyst
Qasim, Hafiz M.,Ayass, Wassim W.,Donfack, Patrice,Mougharbel, Ali S.,Bhattacharya, Saurav,Nisar, Talha,Balster, Torsten,Solé-Daura, Albert,R?mer, Isabella,Goura, Joydeb,Materny, Arnulf,Wagner, Veit,Poblet, Josep M.,Bassil, Bassem S.,Kortz, Ulrich
supporting information, p. 11300 - 11307 (2019/09/07)
The class of peroxo-cerium-containing polyoxometalates has been discovered via the synthesis of the 9-peroxo-6-cerium(IV)-containing 30-tungsto-3-germanate, [CeIV6(O2)9(GeW10O37)3]24- (1). Polyanion 1 consists of a cyclic [Ce6(O2)9]6+ assembly that is stabilized by three dilacunary [GeW10O37]10- Keggin fragments. The title polyanion 1 is solution-stable, on the basis of 183W nuclear magnetic resonance, and was shown to act as a recyclable homogeneous catalyst for the selective, microwave-activated sulfoxidation of the model substrate methionine to the sulfoxide in the absence and to the sulfone in the presence of hydrogen peroxide. Solution and solid-state Raman as well as solid-state infrared studies of 1 demonstrated the complete loss (and regain) of the nine peroxo groups in situ during the catalytic cycle, suggesting that the peroxo-free {Ce6(GeW10)3} skeleton remains most likely intact during the catalytic cycle. Solid-state X-ray photoelectron spectroscopy measurements showed that peroxo loss is accompanied by reduction of the cerium ions from +4 to +3, which is fully reversible. Density functional theory calculations are in complete agreement with all of these observations and furthermore suggest that the reduction of the six cerium(IV) ions is accompanied by the formation of molecular dioxygen.
Reactive ZrIV and HfIV butterfly peroxides on polyoxometalate surfaces: Bridging the gap between homogeneous and heterogeneous catalysis
Carraro, Mauro,Nsouli, Nadeen,Oelrich, Holger,Sartorel, Andrea,Soraru, Antonio,Mal, Sib Sankar,Scorrano, Gianfranco,Walder, Lorenz,Kortz, Ulrich,Bonchio, Marcella
supporting information; experimental part, p. 8371 - 8378 (2011/09/19)
At variance with previously known coordination compounds, the polyoxometalate (POM)-embedded ZrIV and HfIV peroxides with formula: [M2(O2)2(α-XW 11O39)2]12- (M=ZrIV, X=Si (1), Ge (2); M=HfIV, X=Si (3)) and [M6(O 2)6(OH)6(γ-SiW10O 36)3]18- (M=ZrIV (4) or Hf IV (5)) are capable of oxygen transfer to suitable acceptors including sulfides and sulfoxides in water. Combined 1HNMR and electrochemical studies allow monitoring of the reaction under both stoichiometric and catalytic conditions. The reactivity of peroxo-POMs 1-5 is compared on the basis of substrate conversion and kinetic. The results show that the reactivity of POMs 1-3 outperforms that of the trimeric derivatives 4 and 5 by two orders of magnitude. Reversible peroxidation of 1-3 occurs by H 2O2 addition to the spent catalysts, restoring oxidation rates and performance of the pristine system. The stability of 1-3 under catalytic regime has been confirmed by FT-IR, UV/Vis, and resonance Raman spectroscopy. The reaction scope has been extended to alcohols, leading to the corresponding carbonyl compounds with yields up to 99 % under microwave (MW) irradiation. DFT calculations revealed that polyanions 1-3 have high-energy peroxo HOMOs, and a remarkable electron density localized on the peroxo sites as indicated by the calculated map of the electrostatic potential (MEP). This evidence suggests that the overall description of the oxygen-transfer mechanism should include possible protonation equilibria in water, favored for peroxo-POMs 1-3. Copyright
L-Methionine related 1-amino acids by acylase cleavage of their corresponding N-acetyl-DL-derivatives
Bommarius, Andreas S.,Drauz, Karlheinz,Guenther, Kurt,Knaup, Guenter,Schwarm, Michael
, p. 3197 - 3200 (2007/10/03)
Acylase I from Aspergillus oryzae is an even more useful enzyme than suggested so far. Besides standard amino acids such as L-Met, L-Val and L-Phe, a number of additional sulfur- and selenium-containing amino acids can be obtained at useful reaction rates and in very high enantiomeric purity by kinetic resolution of the respective N-acetyl-DL-amino acids.
