Oxoperoxo Molybdenum Research Articles

Synthesis, characterization and DNA nuclease activity of oxo-peroxomolybdenum(VI) complexes

The synthesis and structural characterization of two oxo-peroxo molybdenum(VI) complexes, [Mo(O)(O)2(PAA)]− (1) and [Mo(O)(O)2(PAH)]− (2), with phenylacetic acid (PAA) and 2-phenylacetylhydroxamic acid (PAHH) ligands have been accomplished. The coordination geometry of the oxo-peroxo molybdenum(VI) complexes is found to be pentagonal bipyramidal where, in both cases, the ligands are coordinated in bidentate fashion through oxygen atoms. The binding affinities of 1 and 2 with calf-thymus DNA (CT DNA) are determined using absorption spectroscopic measurements. The spectroscopic as well as cyclic voltammetric (CV) studies and viscosity measurements indicate that both complexes interact with CT DNA in the groove. The intrinsic binding constants are 5.2 × 104 M−1 and 7.3 × 104 M−1 for 1 and 2, respectively, from UV–vis studies. Complexes 1 and 2 show nuclease activity with plasmid DNA in the presence of H2O2. Concentration-dependent nuclease study suggests that 2 possesses higher ability to cleave plasmid DNA compared to 1. The experimental results of the binding of 1 and 2 with DNA are further supported by molecular docking studies.

Heterogeneous SBA-15-supported Oxoperoxomolybdenum(VI) complex for enhanced olefin epoxidation

Heterogeneous nanoscale catalyst was successfully synthesized via anchoring of oxoperoxo molybdenum(VI) complex on the chloro-functionalized SBA-15. The mesoporous nanomaterials, MoO3(sal-phz)/SBA-15 (where sal-phz is salicylidene 2-picoloyl hydrazine) were identified by several characterization techniques. MoO3(sal-phz)/SBA-15 and MoO3(sal-phz) were also treated as catalysts in the olefins epoxidation reactions. Both homogenous and heterogeneous catalysts exhibit outstanding activity and selectivity for epoxide with tert-BuOOH in decane as oxidant at 95°C. In addition, the heterogeneous nanocatalyst was chemically stable and can be efficiently reused for at least six cycles without a significant loss in catalytic activity.

Dioxo and oxo-peroxo molybdenum(VI) complexes bearing salicylidene 2-picoloyl hydrazone: Structures and catalytic performances

Molybdenum complexes bearing a salicylidene 2-picoloyl hydrazone ligand have been synthesized and characterized. The salicylidene 2-picoloyl hydrazone ligand (H2sal-phz) was prepared by reaction of picoloyl hydrazine with salicylaldehyde. Reaction of H2sal-phz with MoO2(acac)2 generates the dioxo molybdenum complex MoO2(sal-phz)(CH3OH). Treatment of MoO3 in the presence of H2O2 with H2sal-phz produces the oxo-peroxo molybdenum(VI) complex MoO(O2)(sal-phz)(CH3OH). The new compounds were characterized by 1H NMR and IR spectroscopies, and elemental analysis. The complexes were also characterized by single crystal X-ray diffraction crystallography. The complexes were evaluated for epoxidation catalysis with tert-butyl hydroperoxide (tert-BuOOH). The MoO2(sal-phz)(CH3OH) complex exhibited high catalytic activity for the epoxidation of olefins, whereas the peroxo analogue is inert to reaction with olefins, thus ruling out the peroxide compound as the intermediate responsible in the [MoO2(sal-phz)(CH3OH)]-catalyzed epoxidation with tert-BuOOH.

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.

Catalytic efficiency of a novel complex of oxoperoxo molybdenum(VI): Synthesis, X-ray structure and alkane oxidation

A new mononuclear oxo–peroxo complex of molybdenum(VI) of the formula [MoO(O2)(phox)2] (where phox = 2-(2′-hydroxyphenyl)oxazoline) has been synthesized and characterized by X-ray structure analysis, elemental analysis, infrared, UV–visible and 1H, 13C NMR spectroscopy. A monoclinic space group P−1 was determined by X-ray crystallography from single-crystal data of this complex. Complex functions as facile alkane oxidation catalyst with hydrogen peroxide as terminal oxidant at room temperature. The catalyst shows very much efficient reactivity in the oxidation reactions giving high yield, turnover number (TON) and selectivity.

The Nuclease Activity of an Oxo-peroxo Molybdenum Complex

The nuclease activity of the oxo-peroxo molybdenum (VI) complex on DNA has been studied by UV-Vis, fluorescence, viscosity, and gel electrophoresis techniques whereby the complex has been found to promote cleavage of pUC19 DNA from the supercoiled form I (SC) to nicked circular relaxed form II (NC). The intrinsic binding constant of the complex with DNA was calculated and found to be (5.3 ± 0.02) × 105 M−1 from UV-Vis studies. Fluorimetric studies indicate that the complex competes with EB in binding to DNA. The relative viscosity of CT DNA increases with increasing Mo complex indicating intercalative binding. All the above results suggest that the complex binds to DNA intercalatively and imparts DNA cleavage.

Synthesis and Crystal Structure of Dichlorobis(dimethylsulfoxide)oxoperoxo Molybdenum(VI)

AbstractHydrogen peroxide reacts with [MoO2Cl2(dmso)2] to produce orange crystals of the title complex, [MoO(O2)Cl2(dmso)2]. The structure is orthorhombic with distorted pentagonal bipyramidal geometry around the molybdenum ion. A short O‐O bond length suggested the presence of a superoxide, but electron paramagnetic resonance measurements definitely supported the peroxo structure.

Oxoperoxo molybdenum(VI)- and tungsten(VI) complexes with 1-(2′-hydroxyphenyl) ethanone oxime: Synthesis, structure and catalytic uses in the oxidation of olefins, alcohols, sulfides and amines using H 2O 2 as a terminal oxidant

High yield synthesis of two new oxodiperoxo-molybdate, PPh 4[MoO(O 2) 2(HPEOH)] ( 1), and -tungstate, PPh 4[WO(O 2) 2(HPEOH)] ( 2), complexes with 1-(2′-hydroxyphenyl) ethanone oxime (HPEOH 2) as organic ligand has been achieved by adding methanol solution of the ligand to the pale-yellow solution obtained by dissolving molybdic-/tungstic-acid (freshly prepared) in hydrogen peroxide and precipitating the complexes using tetraphenylphosphonium chloride. The orange-yellow complexes have been characterized by elemental analysis, IR, 1H NMR, UV–Vis spectroscopy and finally by X-ray structure analysis. Both the complexes function as facile olefin epoxidation catalysts with hydrogen peroxide as terminal oxidant and bicarbonate as a co-catalyst at room temperature. Catalytic potentiality of 1 and 2 is also exhibited in the case of oxidation of alcohols, amines and sulfides. The catalysts are very much efficient especially in olefin epoxidation giving high yield, TON (turnover number) and TOF (turnover frequency). The method described is environmentally benign and cost-effective in all the cases.

Molybdenum(VI)-catalysed olefin epoxidation: Structure and reactivity study

Dioxo and oxoperoxo molybdenum(VI) complexes, I– III, containing the non-labile bidentated oxazolinyl-pyridine ligand 1, were used as catalytic precursors in the epoxidation of cyclooctene and ( R)-limonene, to explore the nature of the catalytic species. The high diastereoselectivity showed by I and II towards limonene epoxide formation ( trans/ cis- 8 = 4/1) could be justified by the kinetic resolution observed to give the double epoxide ( 9), but also by the olefin coordination to the metal centre due to the presence of a labile ligand (isothiocyanate). 95Mo NMR monitoring experiments of complex II in the presence of ( R)-limonene, together with conductivity measurements, showed the formation of an ionic metallic species (1:1 electrolyte). These results point to a bimetallic species where one of the metal atoms is coordinated to the olefin by the dissociation of the isothiocyanate group, remaining coordinated the spectator chiral ligand, which is the responsible of the selectivity observed.

The use of low-nuclearity oxoperoxo molybdenum species to achieve high dispersions on zirconia materials

Abstract Molybdenum(VI) species have been deposited on zirconia materials by adsorption equilibrium procedures using two precursors: (i) an isopolyanion salt: ammonium heptamolybdate and (ii) low-nuclearity oxoperoxo molybdenum complexes. Two zirconia supports have been considered: calcined zirconia (ZrO 2 ) and the parent zirconium oxyhydroxide (ZrO x (OH) 4−2 x ). After drying, the catalysts have been calcined and characterized by chemical analysis, powder X-ray diffraction, thermogravimetry, Raman and UV–vis diffuse reflectance spectroscopies, X-ray photoelectron spectroscopy, nitrogen physisorption experiments, and TEM and EDX analysis. In contrast to ZrO 2 , quantitative grafting of molybdenum species can be obtained when zirconium oxyhydroxide is used. With this material, the anchoring of low-nuclearity oxoperoxo species leads to higher specific surface areas than with ammonium heptamolybdate, and hence to lower molybdenum surface densities.

Oxoperoxo molybdenum(vi) and tungsten(vi) and oxodiperoxo molybdate(vi) and tungstate(vi) complexes with 8-quinolinol: synthesis, structure and catalytic activity

A solution obtained by dissolving MoO3 in a moderate excess of H2O2 reacts with 8-quinolinol (QOH) to give [MoO(O2)(QO)2] (1), but, when the same reaction is conducted with a large excess of H2O2, an anionic complex is formed, which reacts with PPh4Cl to give the corresponding salt [MoO(O2)2(QO)][PPh4] (2·PPh4). Freshly prepared WO3 behaves the same way and, depending on the amount of H2O2 used, as above, produces either [WO(O2)(QO)2] (3) or [WO(O2)2(QO)][PPh4] (4·PPh4), respectively. Crystallographic analyses reveal the coordination geometries around the metal center in these complexes to be distorted pentagonal bipyramids. These compounds show interesting catalytic properties in the oxidation of alcohols using H2O2 as the terminal oxidant. In the case of aromatics, including benzylic and cinnamylic alcohols, the oxidation occurs selectively, affording aldehydes or ketones with reasonably high turnover numbers. Taking benzyl alcohol as a representative case, a probable mechanism of the alcohol-to-aldehyde conversion mediated by the prepared catalysts is suggested. The oxidation of aliphatic primary alcohols, under the same conditions, does not show the above selectivity: the reaction yields the corresponding aldehydes as well as carboxylic acids. The work was also extended to study the catalytic activity towards the oxidation of phenol and various sulfides and amines using the same oxidants.

Novel oxo-peroxo molybdenum(VI) complexes incorporating 8-quinolinol: synthesis, structure and catalytic uses in the environmentally benign and cost-effective oxidation method of methyl benzenes: Ar(CH3)n (n = 1, 2)

A hitherto unknown distorted pentagonal bipyramidal complex, [MoO(O2)(QO)2], very efficiently catalyses homogeneous liquid phase oxidation of methylbenzenes, viz. toluene and o- and p-xylenes to benzoic acid, phthalic acid and p-toluic acid respectively, using H2O2 and O2 as oxidants.