Molybdenum Peroxo Complexes Research Articles

Mo-modified Pt/C electrocatalyst prepared by the catalytic decomposition of molybdenum peroxo-complexes for the hydrogen oxidation reaction with enhanced CO tolerance

Commercial 20 % Pt/C catalyst was modified by molybdenum via catalytic decomposition of peroxocomplexes of molybdenum with the subsequent reduction of the Pt2Mo1/C precursor in H2 flow at 600 °C. The detailed HRTEM, EDX, XRD and XPS studies showed that amorphous molybdenum oxide was deposited on Pt particles surface and partially on carbon support. After reduction of the Pt2Mo1/C precursor, the substantial Mo fraction merges the structure of Pt particles thus forming PtMo alloy with reduced lattice parameter, while the rest of molybdenum covers the surface of PtMo particles as MoO3. The presented method of Mo-modification of Pt-based catalysts provides rather simple way to vary Pt:Mo molar ratio. Electrochemical study revealed that the amount of the surface MoO3 plays a key role in the CO tolerance of the PtMo/C catalyst. As prepared Pt2Mo1/C precursor is 15 times superior to the Pt/C catalyst in the CO-tolerance. After reduction, the Pt2Mo1/C electrocatalyst exhibits extremely high CO-tolerance, more than 100 times higher than that of the pristine commercial platinum catalyst.

Fe(II)-promoted activation of peroxymonosulfate by molybdenum disulfide for effective degradation of acetaminophen

In this study, it was demonstrated that the Fe ion was an effective promoter of bulk MoS2 for the activation of peroxymonosulfate (PMS) to degrade acetaminophen (ACT). ACT removal rate constant in the presence of 5 mg/L FeSO4·7H2O (0.1099 min−1) was approximately 20 times as that in the absence (0.0045 min−1) with 0.1 g/L MoS2 of FeSO4·7H2O at pH0 3. Both electron paramagnetic resonance (EPR) characterization and quenching experiment suggested the key role of singlet oxygen (1O2), acting as dominant reactive species responsible for ACT degradation in the Fe2+/MoS2/PMS system. Besides, the chemical state and composition of MoS2, the ion (Fe and Mo) concentrations and the speciation of Mo(VI) were investigated. Results suggested that the promoting effect of Fe(II) ion originated from the regeneration of Fe2+ mediated by MoS2, and the formation of molybdenum(VI) peroxo complex species in Fe2+/MoS2/PMS system. The present study not only provides an insight into PMS activation by MoS2 accelerated by Fe(II) ion, but also suggests an high-efficiency, easy-to-handle and environmentally friendly method to treat refractory wastewater.

Selective and Green Sulfoxidation in Water using a New Chitosan Supported Mo(VI) Complex as Heterogeneous Catalyst

AbstractImmobilization of oxo‐peroxo molybdenum(VI) species on natural biopolymer, chitosan led to the development of a new heterogeneous catalyst which displayed excellent activity, stability and chemoselectivity for the oxidation of a wide variety of sulfides to the respective sulfoxides by H2O2 in water, at ambient temperature. The catalyst has been comprehensively characterized by elemental analysis, spectral studies (FTIR, Raman, solid‐state 13C NMR and diffuse reflectance UV‐Vis), PXRD, Brunauer‐Emmett‐Teller (BET), SEM, EDX and TGA‐DTG analysis. The density functional theory (DFT) method has been employed to study the structure of the synthesized chitosan peroxomolybdenum complex (PMoCh). In addition to water, the catalyst is also highly compatible with a variety of safer organic solvents like methanol and acetonitrile. Apart from being high yielding and operationally simple, the developed catalytic protocol is environmentally clean and safe as it is absolutely free from halogenated organic solvent. Other significant green attributes of the methodology include its ready scalability, high H2O2 efficiency and easy recyclability of the catalyst for several catalytic cycles with consistent activity/selectivity profile.

Green synthesis of nanostructured SiCs by using natural biopolymers (guar, tragacanth, Arabic, and xanthan gums) for oxidative desulfurization of model fuel

Mesoporous SiC ceramics were prepared using different natural biopolymers (guar, tragacanth, Arabic, and xanthan gum) as both template and carbon sources. Natural biopolymers are safe, biocompatible, and inexpensive materials that can be green candidates for carbon sources. Low-temperature magnesiothermic technique was used to form porous silicon carbide. In this study, tetraethylorthosilicate was prepared by sol–gel method and used as silica precursor. The mixture of silica and carbon sources was carbonized under argon atmosphere at 750 °C, and then, the reaction continued by adding magnesium powder at 700 °C. Products were characterized using SEM, BET/BJH, XRD, FTIR, and Raman spectroscopy. The produced SiC materials showed mesoporous structures with high surface area and identical structures related to their carbon precursors. The results suggest that the natural gums can be potentially used as carbon templates in controlled formation of nanostructures. Also the synthesized silicon carbide nanostructures were used as catalyst supports in oxidative desulfurization of a model fuel. For this purpose, MoO3 was immobilized on the surface of SiC supports by using peroxo molybdenum complex. Such excellent catalytic performance was attributed in the presence of silicon carbide (99, 98, 94, and 93% conversion for SiCs produced from Arabic, xanthan, guar, and tragacanth, respectively).

ChemInform Abstract: Macromolecular Peroxo Complexes of Vanadium(V) and Molybdenum(VI): Catalytic Activities and Biochemical Relevance

AbstractReview: [155 refs.]

Macromolecular peroxo complexes of Vanadium(V) and Molybdenum(VI): Catalytic activities and biochemical relevance

Our recent achievements concerning the synthesis and characterization of water soluble peroxo complexes of V(V) and Mo(VI) in macroligand environment, as well as some key features of biological relevance of these compounds, such as their hydrolytic stability, activity with phosphohydrolase enzyme vis-à-vis free peroxovanadium (pV) or peroxomolybdenum (pMo) complexes, and their activity in biomimetic oxidative bromination are presented here. Immobilization of pMo species on insoluble polymer matrices viz., amino acid functionalized Merrifield resins and poly(acrylonitrile) on the other hand, afforded a set of heterogeneous catalysts highly effective in facile organic transformations such as selective oxidation of organic sulfides and oxidative bromination of aromatic substrates by H2O2, at ambient temperature. The methodologies are straightforward, high-yielding, halogen-free and the catalysts afford easy regeneration. Our findings illustrate the various features which make the procedures sustainable and synthetically useful. Series of macrocomplexes have been synthesized by immobilizing peroxo species of vanadium and molybdenum on water soluble, as well as insoluble polymer supports. The soluble complexes inhibit the activity of phosphatases non-competitively. The insoluble polymeric complexes served as efficient heterogeneous catalysts for selective organic oxidations under eco-compatible reaction conditions.

Fe2(MoO4)3 as a novel heterogeneous catalyst to activate persulfate for Rhodamine B degradation

Iron molybdate (Fe2(MoO4)3) was used as a novel heterogeneous catalyst to activate persulfate (S2O82-) for rhodamine B (RhB) degradation. Results indicated 10 mg/L RhB can be completely removed under the addition of 4mM S2O82- and 0.4 g/L Fe2(MoO4)3 within 240 min. Fe2(MoO4)3 can be repeatedly used for six cycles and showed high stability with Fe leaching amounts less than 2.9% in each run. Possible catalytic mechanism was proposed as follows: RhB degradation intermediate products such as hydroxybenzene, quinone compounds and organic compound radicals acted as electron transfer agents to reduce Fe3+ to Fe2+, which reacted with persulfate to form Fe3+ creating the redox cycling of iron, the RhB and those intermediate products are oxidized directly by the molybdenum peroxo complexes which forming probably with MoO42- and persulfate, and the synergy between Fe3+ and MoO42- occurring the catalytic effect on the persulfate. Additionally, the major intermediates of RhB were identified according to GC/MS and the possible degradation pathway was proposed.

Comparative Studies on the Metallurgical and Biological Activity of Peroxo Complexes of Molybdenum (VI) and Uranium (VI)

New peroxo complexes of molybdenum (VI) and uranium (IV) have been prepared. The complexes were characterized on the basis of elemental analyses, conductivity measurements, magnetic measurements, infrared spectral studies and by reactions with allyl alcohol, triphenylphosphine and triphenylarsine. The complexes of U (VI) showed strong activity against both the gram positive and gram negative bacteria than the other complexes indicating the higher zone of inhibition. The present findings of MIC experiment showed that the complex 3 of U (VI) was more potent against all the bacteria tested than the other complex. Results showed that the complex 2 of Mo (VI) exhibits more toxic to brine shrimp compared to other complexes of Mo (VI) and U (VI) indicating the lower values of LC50 and LC99 for both the exposure 16h and 36h.

Two novel compounds of vanadium and molybdenum with carnitine exhibiting potential pharmacological use

The reaction of sodium orthovanadate with carnitine hydrochloride molecule results in the precipitation of decavanadate compound of carnitine whereas the reaction of metallic molybdenum with hydrogen peroxide and carnitine results in the peroxo-molybdenum complex of carnitine. The decavanadate compound as well as the molybdenum complex of carnitine have been characterized by means of elemental analysis, IR, electronic spectra, 1H NMR, 2D-COSY-NMR (=correlation spectroscopy) and thermo-gravimetric analysis (TGA). In addition decavanadate compound of carnitine was fully characterized by X-ray crystallography. The analytical data were in good agreement with the empirical formulae of both, decavanadate compound and molybdenum complex. The two compounds were also evaluated for cell toxicity and their anticancer activity by the MTT(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)-based assay method, using primary cells and tumor cell lines of both human and murine origins and the results show that compound 1 shows an increased biological activity in comparison with compound 2. Moreover using confocal microscopy and antibodies against cleaved caspase 3 we further analyzed the cell toxicity and we conclude that the apoptotic pathway is triggered efficiently with tumor specificity by compound 1 and not by compound 2.

New insights into the mechanism of oxodiperoxomolybdenum catalysed olefin epoxidation and the crystal structures of several oxo–peroxo molybdenum complexes

[Mo(O)(O(2))(2)(L)(2)] compounds (L = pz, pyrazole; dmpz, 3,5-dimethylpyrazole) were reacted stoichiometrically, in the absence of an oxidant, with cis-cyclooctene in an ionic liquid medium where selective formation of the corresponding epoxide was observed. However, this oxo-transfer reaction was not observed for some other olefins, suggesting that alternative reaction pathways exist for these epoxidation processes. Subsequently, DFT studies investigating the oxodiperoxomolybdenum catalysed epoxidation model reaction for ethylene with hydrogen peroxide oxidant were performed. The well known Sharpless mechanism was first analysed for the [Mo(O)(O(2))(2)(dmpz)(2)] model catalyst and a low energy reaction pathway was found, which fits well with the observed experimental results for cis-cyclooctene. The structural parameters of the computed dioxoperoxo intermediate [Mo(O)(2)(O(2))(dmpz)(2)] in the Sharpless mechanism compare well with those found for the same moiety within the [Mo(4)O(16)(dmpz)(6)] complex, for which the full X-ray report is presented here. A second mechanism for the model epoxidation reaction was theoretically investigated in order to clarify why some olefins, which do not react stoichiometrically in the absence of an oxidant, showed low level conversions in catalytic conditions. A Thiel-type mechanism, in which the oxidant activation occurs prior to the oxo-transfer step, was considered. The olefin attack of the hydroperoxide ligand formed upon activation of hydrogen peroxide with the [Mo(O)(O(2))(2)(dmpz)(2)] model catalyst was not possible to model. The presence of two dmpz ligands coordinated to the molybdenum centre prevented the olefin attack for steric reasons. However, a low energy reaction pathway was identified for the [Mo(O)(O(2))(2)(dmpz)] catalyst, which can be formed from [Mo(O)(2)(O(2))(dmpz)(2)] by ligand dissociation. Both mechanisms, Sharpless- and Thiel-type, were found to display comparable energy barriers and both are accessible alternative pathways in the oxodiperoxomolybdenum catalysed olefin epoxidation. Additionally, the molecular structures of [Mo(O)(O(2))(2)(H(2)O)(pz)] and [Hdmpz](4)[Mo(8)O(22)(O(2))(4)(dmpz)(2)]·2H(2)O and the full X-ray report of [Mo(O)(O(2))(2)(pz)(2)] are also presented.

New molybdenum peroxocomplexes as a promising catalysts

New molybdenum peroxocomplexes as a promising catalysts

Molybdenum-Doped Anatase and Its Extraordinary Photocatalytic Activity in the Degradation of Orange II in the UV and vis Regions

Molybdenum-doped anatase was prepared by thermal hydrolysis of peroxotitanium complex aqueous solutions containing a molybdenum peroxo-complex. The synthesized samples were characterized by X-ray diffraction, high-resolution transmission electron microscopy, selected area electron diffraction, and surface area (BET) and porosity (BJH) determination. Molybdenum doping caused the increase of unit cell constants of anatase and changes in the morphology of particles from spindle-like shapes to the shapes with rectangular or square cross sections. The presence of Mo5+/Mo6+ ion doping in the TiO2 nanostructure has no significant effect on the transformation of anatase to rutile. In the visible region, the photocatalytic activity is substantially enhanced in the molybdenum concentration of about 1.38%. The photocatalytic activity of doped titania samples was determined by the decomposition of Orange II dye during irradiation at 365 and 400 nm. The titania sample with 1.38% Mo has the highest catalytic activity d...

ChemInform Abstract: On the Peroxomolybdate Complexes as Sources of Singlet Oxygen

AbstractReview: 40 refs.

Dinuclear peroxo complexes of molybdenum(VI) containing Mannich base ligands

Dinuclear molybdenum(VI) peroxo complexes containing Mannich base ligands having formulae [Mo2O4(O2)2L-L(H2O)2] · H2O [where L-L = N-[1-morpholinobenzyl] acetamide (MBA), N-[1-piperidinobenzyl] acetamide (PBA), N-[1-morpholino(-4-nitrobenzyl)] benzamide (MPNBB), N-[1-piperidino(-3-nitrobenzyl)] benzamide (PMNBB), N-[1-morpholino(-2-nitrobenzyl)] acetamide (MONBA), and N-[1-morpholino(-3-nitrobenzyl)] acetamide (MMNBA)] have been synthesized by stirring ammonium heptamolybdate with excess 30% aqueous hydrogen peroxide followed by treatment with ethanolic solution of corresponding ligands. The complexes have been characterized by elemental analysis, molar conductance, magnetic measurements, infrared (IR), electronic, TGA/DTA, mass spectral, and 1H NMR studies. The complexes are non-electrolytes and diamagnetic. The IR spectral studies suggest that the ligands are bidentate to metal through carbonyl oxygen and ring nitrogen. Thermal analyses provide conclusive evidence for the presence of coordinated, as well as lattice water in the complexes. Dinuclear complexes preserve the individuality of the molybdenum oxo peroxo core. The complexes exhibit higher antibacterial activity against bacterium Ralastonia solanacearum (Pseudomonas solanacearum) than the free ligands.

On the peroxomolybdate complexes as sources of singlet oxygen

Peroxidation of molybdenum(VI) demonstrates that mono-, di- and tetraperoxo complexes are formed only in low quantities, triperoxomolybdate predominanting. Triperoxomolybdate may react directly with reactive reductants, whereas less reactive reductants are oxidized by indirectly formed 1 O 2 . The successive formation of peroxomolybdenum(VI) complexes is discussed and it is shown that proton-consuming steps are followed by a proton-producing one; the pH maximum (=10) appears at a [H 2 O 2 ]/[MoO 4 ] 2− ratio of 2:1. The approximated formation constants are utilized to calculate the concentrations of peroxo complexes as a function of the ligand concentration. The mono-, di- and tetraperoxo complexes are formed in only negligible quantities, whereas the oxodiperoxohydroperoxo (simply, triperoxo) complex proves to be the predominant species. The triperoxo complex may react directly if a sufficiently reactive partner is present; if not, it oxidizes H 2 O 2 to 1 O 2 , which reacts further. The activation parameters of formation of O 2 are determined as a function of pH: the enthalpy minimum (50.45 kJ mol −1 ) is found at pH 10, where the negative activation entropy reaches its lowest value (−149.5 J K −1 mol −1 ). The possible functions of the peroxo ligands are considered.

Peroxo Complexes of Molybdenum(VI) Containing Mannich Base Ligands

AbstractThe molybdenum(VI)‐peroxo complexes containing Mannich base ligands having a formula as [MoO(O2)2(L‐L)] [where L‐L=morpholinobenzyl benzamide (MBB), piperidinobenzyl benzamide (PBB), morpholinobenzyl urea (MBU), piperidinobenzyl urea (PBU), morpholinobenzyl thiourea (MBTU), piperdinobenzyl thiourea (PBTU)] have been synthesized and characterized by physico‐chemical, electrochemical techniques and TGA/DTA studies. The complexes have been prepared by stirring ammonium molybdate and excess of 30% aqueous‐H2O2 and then treatment with ethanolic solution of the ligand. Studies revealed that these complexes were non‐electrolytes and diamagnetic in nature. The ligands are bound to metal in a bidentate mode through carbonyl oxygen/thiocarbonyl sulphur and the ring nitrogen. The cyclic voltammograms of the complexes show two quasi‐reversible steps involving complexes. The complexes have also been tested for antibacterial activity against Salmonella and Kleibsella. The antibacterial study of the ligands and complexes indicate that the complexes exhibit higher activity than the free ligands.

Oxidative Desulfurization of Fuels Catalyzed by Peroxotungsten and Peroxomolybdenum Complexes in Ionic Liquids

Peroxotungsten and peroxomolybdenum complexes such as [WO(O2)2·Phen·H2O] and [MoO(O2)2·Phen] (Phen: 1,10-phenanthroline) have been synthesized and characterized and were immobilized in 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4), 1-n-octyl-3-methylimidazolium tetrafluoroborate ([Omim]BF4), 1-butyl-3-methyl-imidazolium hexafluorophosphate ([Bmim]PF6), and 1-n-octyl-3-methylimidazolium hexafluorophosphate ([Omim]PF6) for extraction and catalytic oxidation of dibenzothiophene (DBT) remaining in n-octane. The results demonstrated that ionic liquid (IL) was only used as an extractant for DBT-containing model oil and the removal of sulfur was only about 12.2−22.0%. After addition of 30 wt % H2O2 in IL, model oil with 30.0−63.0% sulfur removal was given via chemical oxidation. While H2O2 and catalyst were introduced together, the removal of sulfur increased sharply. In the case of the system containing H2O2, WO(O2)2·Phen·H2O and [Bmim]BF4, extraction and catalytic oxidation increased the sulfur removal to 98.6%. However, the oxidative desulfurization systems containing WO(O2)2·Phen·H2O and H2O2 only led to 50.3% sulfur removal in the absence of IL. This experiment demonstrated that a combination of catalytic oxidation and extraction in IL can deeply remove DBT from model oil. This result also indicated the remarkable advantage of this process over the desulfurization by mere solvent extraction with IL or catalytic oxidation without IL.

Metallurgical and Biological Activity of Peroxo Complexes of Molybdenum (VI) Containing Organic Acid and Amine Bases

Metallurgical and Biological Activity of Peroxo Complexes of Molybdenum (VI) Containing Organic Acid and Amine Bases

Why Do Peroxomolybdenum Complexes Chemoselectively Oxidize the Sulfur Centers of Unsaturated Sulfides and Sulfoxides? A DFT Analysis

AbstractThe reasons why oxo‐peroxo molybdenum complexes chemoselectively oxidize unsaturated sulfides to the corresponding sulfoxides and these to sulfones without any epoxidation of the electron‐rich double bond were elucidated by transition state theory and density functional calculations at the B3LYP level. For the diperoxo model complex with the structure MoO(η2‐O2)2OPH3 and for allyl methyl sulfide as a model of unsaturated sulfides, the calculations show that the oxygen transfer process from the peroxomolybdenum complex to the sulfur center requires a lower free activation energy (ΔG‡ = 19.0 kcal mol–1) than the attack on the double bond moiety (ΔG‡ = 26.4 kcal mol–1) of the unsaturated sulfide. Subsequent oxidation of allyl methyl sulfoxide at the sulfinyl group to yield the corresponding sulfone also requires a lower activation energy (ΔG‡ = 21.5 kcal mol–1) thanthe corresponding epoxidation process (ΔG‡ = 27.7 kcal mol–1),yielding 2,3‐epoxypropyl methyl sulfoxide. These results unambiguously account for these complexes’ excellent chemoselectivity towards the sulfur groups in unsaturated sulfides and sulfoxides, as has been observed experimentally. On the basis of SCRF calculations, the level of chemoselectivity is predicted to diminish with increasing solvent polarity. Charge decomposition analysis and the orbital interaction model reveal that unsaturated sulfides with reaction sites carrying lone pair and π electrons behave as nucleophiles toward the electrophilic peroxo oxygen group. The origin of the chemoselectivity is ascribed to the fact that the electronic state related to the sulfur lone pair (HOMO) lies 1.2 eV above that associated with the π electrons (HOMO–1). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Synthesis and evaluation of the antitumor agent TMC-69-6H and a focused library of analogs

A concise, efficient and flexible total synthesis of the potent antitumor agent TMC-69-6H ( 2 ) is described. Key steps involve the palladium catalyzed regioselective addition of 4-hydroxy-2-pyridone 5 to pyranyl acetate 6 which is accompanied by a spontaneous 1,4-addition of the phenolic –OH group to the emerging enone to give the tricyclic product 7 in excellent yield. When this reaction is carried out with optically enriched ( S)- 6 (conveniently prepared by a lipase catalyzed kinetic dynamic resolution) in the presence of the chiral ligand ( S, S)- 12 and allylpalladium chloride dimer, the ensuing matched situation delivers the key building block (−)- 7 in 96% ee. Its further elaboration into 2 involves a Julia–Kocienski olefination with tetrazolylsulfone 19 and a final N-oxidation effected by the peroxomolybdenum complex [(pyridine)MoO 5(HMPA)] to form the hydroxamic acid motif. The flexibility inherent to this route allows for the preparation of a focused library of analogues for biochemical evaluation. The results obtained show that N-hydroxy-2-pyridone derivatives constitute a promising new class of selective phosphatase inhibitors. In contrast to previous reports in the literature, however, TMC-69-6H and congeners are found to exhibit pronounced activities against the tyrosine protein phosphatase PTB1B, the dual specific phosphatase VHR, and the serine/threonine phosphatase PP1, while being only weak inhibitors for the dual specific phosphatases Cdc25 A and B. Two key intermediates of the synthesis route have been characterized by X-ray crystallography.