18437-79-1Relevant articles and documents
Oxygen-transfer reactions of molybdenum- and tungstendioxo complexes containing η2-pyrazolate ligands
Most, Kerstin,Hossbach, Jens,Vidovic, Denis,Magull, Joerg,Moesch-Zanetti, Nadia C.
, p. 463 - 472 (2005)
Dioxomolybdenum and -tungsten compounds containing sterically demanding pyrazolate ligands have been synthesised by treatment of dioxometal halides with the potassium salts of 3,5-di-tert-butylpyrazole (t-Bu2pzH) and 3,5-di-terf-butyl-4-bromopyrazole (t-Bu2-4-BrpzH). The products [MoO2Cl(η2-t-Bu2pz)] (1), [MoO 2(η2-t-Bu2pz)2] (2), [MoO 2(η2-t-Bu2-4-Brpz)2] (3), [WO2(η2-t-Bu2pz)2] (4) and [WO2(η2-t-Bu2-4-Brpz)2] (5) were characterised by spectroscopic techniques. The X-ray structure of complex 3 reveals a distorted trigonal prismatic geometry with two η2-co- ordinated pyrazolate ligands. These high-valent compounds participate in oxygen-transfer reactions and catalyse the oxidation of PPh3 with dimethyl sulphoxide. UV/VIS measurements of the oxo-transfer reactions and the kinetics of the catalytic process are described. By the reaction of 2 with three equivalents of PEt3 or treatment of [MoOCl2-(PMe 3)2] with two equivalents of f-Bu2pzK mononuclear mono-oxo compounds of the type [MoO(t-Bu2-pz) 2(PR3)2] (R = Et 6, R = Me 7) were obtained and characterised by X-ray diffraction analyses. This points to biologically relevant mononuclear Mo(IV) intermediates in the catalytic process with this type of complex.
Kinetics, Mechanisms, and Catalysts of Oxygen Atom Transfer Reactions of S-Oxide and Pyridine N-Oxide Substrates with Molybdenum(IV,VI) Complexes: Relevance to Molybdoenzymes
Caradonna, John P.,Reddy, P. Rabindra,Holm, R. H.
, p. 2139 - 2144 (1988)
The kinetics and mechanism of the oxygen atom transfer reactions MoO2(L-NS2) + (RF)3P -> MoO(L-NS2)(DMF) + (RF)3PO (1) and MoO(L-NS2)(DMF + XO -> MoO2(L-NS2) + X, with X = (RF)2SO (2) and 3-fluoropyridine N-oxide (3), heve been investigated in DMF solutions (L-NS2 = 2,6-bis(2,2-diphenyl-2-mercaptoethyl)pyridine(2-), RF = p-C6H4F).The following rate constants (297.5 K) and activation parameters were obtained: reaction 1, k2 = 9.7 (4) X 10-3 M-1 s-1, ΔH(excit.) = 11.7 (6) kcal/mol, ΔS(excit.) = -28.4 (1.6) eu; reaction 2, k1 = 14.0 (7) X 10-4 s-1, ΔH(excit.) = 22.1 (1.3) kcal/mol, ΔS(excit.) = 2.6 (1.6) eu; reaction 3, k1 = 16.0 (8) X 10-4 s-1, ΔH(excit.) = 23.4 (1.4) kcal/mol, ΔS(excit.) = 7.2 (2.0) eu. reactions 2 and 3 exhibit saturation kinetics, under which the rate-determining step is intramolecular atom transfer.Mechanisms and transition states are proposed.The activation parameters are the first measured for oxo transfer from substrate; the small activation entropies suggest a transition state structurally similar to the complex MoO(L-NS2)(XO) formed in a labile equilibrium prior to oxo transfer to Mo.Coupling of reaction 1 with reaction 2 or 3 affords the catalytic reaction 4, (RF)3P + XO -> (RF)3PO + X; no reaction occurs in the absence of the Mo catalyst.The kinetics of catalysis were examined by monitoring the concentrations of reactants and products by 19F NMR spectroscopy.After 15 h, each system showed ca. 100 turnovers.Reaction 4 with XO = (RF)2SO has a catalytic rate constant of 7 X 10-3 M-1 s-1, close to the value for reaction 1.This and other considerations show that the catalytic rate is limited by the rate of oxo transfer from the Mo(VI) complex MoO2(L-NS2). An attempt to establish the catalytic mechanism led to detection of inhibition; the inhibitory species could not be identified.These results provide the most detailed information on the kinetics and mechanisms of Mo-mediated oxygen atom transfer and demonstrate the efficacy of 19F NMR for detecting and monitoring catalysis and determining catalytic velocities and rate constants.The relation of these results to the enzymatic reduction of N-oxides ans S-oxides is briefly discussed.
Air-stable phosphine organocatalysts for the hydroarsination reaction
Leung, Pak-Hing,Li, Yongxin,Pullarkat, Sumod A.,Tay, Wee Shan,Yang, Xiang-Yuan
supporting information, (2020/03/18)
Readily-available triarylphosphines are explored as organocatalysts for the hydroarsination reaction. When compared to transition metal catalysis, phosphine organocatalysis greatly improved solvent compatibility of the hydroarsination of nitrostyrenes. Upon complete conversion, arsine products were isolated in up to 99% yield while up to 48% of the phosphine catalyst was still active. A mechanism was proposed and structure-activity analysis regarding catalyst activity concluded that sterically-bulkier catalysts were effective at minimizing catalyst deactivation.
Photooxidation of triarylphosphines under aerobic conditions in the presence of a gold(iii) complex on cellulose extracted from Carthamus tinctorius immobilized on nanofibrous phosphosilicate
Sadeghzadeh, Seyed Mohsen,Zhiani, Rahele
, p. 1509 - 1516 (2019/01/24)
Triarylphosphines were converted to the corresponding oxides via photooxidation as a novel method. In this study, cellulose was extracted from the Carthamus tinctorius plant and then oxidized by sodium metaperiodate. A gold complex was supported on this natural cellulose. Then, a gold complex on natural cellulose supported on FPS (FPS/Au(iii)) was synthesized for the reduction of phosphine oxides to corresponding phosphines with remarkable chemoselectivity. The morphology of FPS led to higher catalytic activity. FPS/Au(iii) NPs were thoroughly characterized using TEM, FESEM, FTIR, TGA, and BET.
