Oxoperoxo Complexes Research Articles

Vanadium Catalyst for C‐ and S‐Alkylation of Benzhydrols in Water: An Experimental Study and Green Metrics Evaluation

AbstractA strategy for the vanadium‐catalyzed dehydrative C‐ and S‐alkylation by nucleophilic substitution of benzhydrols with arenes and thiols is reported. The alkylation was achieved with the divanadium oxoperoxo complex [K3(V+5)2(O22−)4(O2−)2(μ‐OH)] in water under air. The newly developed transformation could accommodate a broad substrate scope, including (hetero)arenes and thiols (34 examples). Both the symmetrical and unsymmetrical benzhydrols furnished excellent yields of the alkylated product under mild reaction conditions. The scope of this strategy was further extended to synthesize bis‐benzylated arenes (poly‐arylated products) in high yields and regioselectivities. The green metrics determination of all the alkylated products suggests the technical and environmental benefits of the present protocol. The longevity experiment reveals the catalytic activity was maintained over seven cycles. To understand the mechanism of the present reaction, spectroscopic and kinetic studies were undertaken. This simple protocol, which affords the desired products with water as the by‐product, can be achieved under mild conditions without needing a base or other additives.

Vanadium (V) and Tungsten (VI) Oxoperoxo-Complexes Anchored on Fe3O4 Magnetic Nanoparticles: Versatile and Efficient Catalysts for the Oxidation of Alcohols and Sulfides

Vanadium (V) and tungsten (VI) oxoperoxo complexes supported on Fe3O4 magnetic nanoparticles were synthesized and characterized. These compounds are assigned as catalyst 1 (C1: Fe3O4@Gly@r-Py@VO3) and catalyst 2 (C2: Fe3O4@Gly@r-Py@WO3), respectively, and were found to be efficient and reusable heterogeneous catalysts for the oxidation of alcohols and sulfides using H2O2.

Nonwoven materials obtained by electrospinning on the basis of epoxydated derivatives syndiotactic 1,2-PB

The production of chemical fibers is an urgent task. Non-woven ultra-thin materials based on thermoplastic elastomers have high physicomechanical and filtering properties. Of particular interest is the production of non-woven materials based on epoxidized derivatives of syndiotactic 1.2-polybutadiene. In this connection, the possibilities of obtaining nonwoven materials based on epoxy derivatives of syndiotactic 1.2-polybutadiene by the method of electrospinning and determining the main factors influencing the formation of fibers and the degree of orientation of fibers of syndiotactic 1.2-polybutadiene in non-woven materials were studied. Epoxidation of syndiotactic 1.2-PB was carried out by the action of tungsten oxo-peroxo complexes. The electro spinning method was used to orient oriented nonwoven materials based on syndiotactic 1.2-polybutadiene. Optimization of the process for obtaining fibers of syndiotactic 1.2-polybutadiene was carried out using the mathematical method of planning the Plaquette-Burman experiment. Investigation of the structure of nonwoven fibrous materials was carried out on a scanning electron microscope. The degree of orientation of the fibers of syndiotactic 1.2-polybutadiene was determined using the MBF program. With the use of the method of electrospinning, nonwoven materials with different degrees and variants of fiber orientation in the composition of nonwovens can be produced. The use of epoxidized derivatives of syndiotactic-1.2- polybutadiene with different content of oxirane groups allows to regulate the diameter of fibers in non-woven materials

Efficient oxidation of ethyl benzene using in situ generated molybdenum acetylide oxo-peroxo complex as recyclable catalyst

Selective oxidation of various alkanes/alkyl aromatics to corresponding carbonyl compounds has been carried out with very high conversion (∼98%) and selectivity (up to 100%) for carbonyl compounds using cyclopentadienyl molybdenum acetylide complex, CpMo(CO)3(CCPh) (1) as catalyst and tert-butyl hydrogen peroxide (TBHP) as an oxidant and turnover number (TON) of 88 was obtained with turnover frequency (TOF) of 2.45h−1. Mo acetylide oxo-peroxo species is formed in situ by reaction of 1 with TBHP during the course of reaction as catalytically active species. Interestingly even though the catalytically active species is homogeneous in nature it could be recycled very easily by recovering the catalytically active species as solid after addition of diethyl ether, and separating the products into organic phase. In the case of ethyl benzene oxidation, even after three recycles no appreciable loss in ethyl benzene conversion and acetophenone selectivity was observed. This complex showed high catalytic activity for the oxo functionalization of other alkyl aromatics and alkanes such as substituted ethyl benzenes, toluene as well as cyclohexane. TBHP was found to be more efficient oxidant than hydrogen peroxide for this oxidation.

51V NMR, 17O NMR, and UV–Vis computational studies of new VBPO functional models: Bromide oxidation reaction

Vanadium oxo-peroxo complexes are known as the best functional models of vanadium haloperoxidases (VHPOs) enzymes. Their quantity and quality structure activity and property relationship can be followed up by NMR calculations. The DFT/B3LYP/6-311+G (d,p)/LANL2DZ method has been used to calculate the geometry and electronic structures and 51V and 17O NMR chemical shifts of a series of 7 oxo-peroxo vanadium (V) complexes mimicking the active site of vanadium bromoperoxidase (VBPO) in the gas and solvent (acetonitrile) phases. They contain tetradentate tripodal amine ligands (TPALs). Compilation of NMR, electronic, and vibrational spectroscopic data and metric parameters for the studied complexes permits us to draw correlations among 51V and 17O peroxo chemical shift, the electronic charge transfer band, the O–O vibrational frequency, and the O–O bond length. A direct dependence of the magnetic shielding of the vanadium center and peroxide group on the electronic character of the ligand was observed in all cases. Studied complexes exhibit 51V and 17O NMR chemical shifts of −590 to −430ppm and 650–740ppm, respectively. A Ramsey-type correlation between the chemical shifts and the energy of the ligand-to-metal charge transfer (LMCT) was found that suggests the electron donating ability of the ligands and the energy gap HOMO–LUMO of the peroxo complexes are linearly correlated. Vibrational frequency and length of the O–O bond also correlate with the inverse LMCT energy. The calculated values of νO–O place above 900cm−1 and O–O distances in the range of 1.40–1.42Å. In general, the more reactive complexes within bromide oxidation contain weakly electron donating TPALs and represent higher energy LMCT, longer O–O length, and lesser 51V and 17O chemical shifts.

Activation of molecular oxygen by a molybdenum complex for catalytic oxidation.

A sterically demanding molybdenum(VI) dioxo complex was found to catalytically activate molecular oxygen and to transfer its oxygen atoms to phosphines. Intermediate peroxo as well as reduced mono-oxo complexes were isolated and fully characterized. Monomeric Mo(IV) monooxo species proved to be of an unusual nature with the coordinated phosphine trans to the oxo group. The reduced molybdenum centers can activate O2 to form a stable Mo(VI) oxo-peroxo complex unambiguously characterized by single crystal X-ray diffraction analysis. NMR experiments demonstrate that both oxygen atoms of the peroxo unit are transferred to an accepting substrate, generating the Mo(IV) intermediate and restarting the catalytic cycle.

DFT studies on the reaction pathway of the catalytic olefin epoxidation with CpMoCF3 dioxo and oxo–peroxo complexes

A comparative gas-phase density functional theory (DFT) study of the catalytic epoxidation of olefins with the possible intermediates [CpMoVI(CF3)(O)2] and CpMoVI(CF3)(OO)(O) is presented. The main focus is the identification of the catalytic active species and relevant transition states. Apparently the peroxo–oxo compound is catalytically more active. The influence of the oxidant, tert-butyl hydroperoxide (TBHP), is also considered. The most likely intermediates (postulated by an experimental study) are compared with respect to their occurrence at the potential energy surface and thus the most feasible pathways for the epoxidation of ethene with an excess of TBHP under Mo–O catalysis are examined.

Decarbonylative Halogenation by a Vanadium Complex

Metal-catalyzed halogenation of the C-H bond and decarbonylation of aldehyde are conventionally done in nature. However, metal-mediated decarbonylative halogenation is unknown. We have developed the first metal-mediated decarbonylative halogenation reaction starting from the divanadium oxoperoxo complex K3V(5+)2(O2(2-))4(O(2-))2(μ-OH) (1). A concerted decarbonylative halogenation reaction was proposed based on experimental observations.

Molybdenum oxo–peroxo complex: A very fast catalyst for oxidation and reduction of sulfur-based compounds

Abstract We have evaluated the catalytic activity of a molybdenum(VI) oxo–peroxo complex through the oxidation and reduction of sulfur-based compounds. Arylalkyl, diaryl and dialkyl sulfides are selectively oxidized to corresponding sulfoxides, with tert -butyl hydroperoxide (TBHP), in the presence of MoO(O 2 )(phox) 2 complex as catalyst. This molybdenum complex was also found to be an efficient catalyst for the deoxygenation of sulfoxides to sulfides with PPh 3 in excellent yields and chemoselectivity.

A Unique Dinuclear Mixed V(V) Oxo-peroxo Complex in the Structural Speciation of the Ternary V(V)-Peroxo-citrate System. Potential Mechanistic and Structural Insight into the Aqueous Synthetic Chemistry of Dinuclear V(V)-Citrate Species with H2O2

Diverse vanadium biological activities entail complex interactions with physiological target ligands in aqueous media and constitute the crux of the undertaken investigation at the synthetic level. Facile aqueous redox reactions, as well as nonredox reactions, of V(III) and V(V) with physiological citric acid and hydrogen peroxide, under pH-specific conditions, led to the synthesis and isolation of a well-formed crystalline material upon the addition of ethanol as the precipitating solvent. Elemental analysis pointed to the molecular formulation (NH4)4[(VO2){VO(O2)}(C6H5O7)2]·1.5H2O (1). Complex 1 was further characterized by Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR), Raman spectroscopy, cyclic voltammetry, and X-ray crystallography. The crystallographic structure of 1 reveals the presence of the first dinuclear V(V)-citrate complex with non-peroxo- and peroxo-containing V(V) ions, concurrently present within the basic VV2O2 core. The nonperoxo unit VO2+ and the peroxo unit VO(O2)+ are each coordinated to a triply deprotonated citrate ligand in a distinct coordination mode and coordination geometry around the V(V) ions. These units are similar to those in homodinuclear complexes bearing oxo or peroxo groups. The unique assembly of both units in the anion of 1 renders the latter as a potential intermediate in the peroxidation process, from [V2O4(C6H5O7)2]4– to [V2O2(O2)2(C6H6O7)2]2–. The transformation reactions of 1 establish its connection with several V(V) and V(IV) dinuclear species present in the aqueous distribution of the V(IV,V)-citrate systems. The shown position of 1 as an intermediate in the mechanism of H2O2 addition to dinuclear V(V)-citrate species portends its role in the complex aqueous distribution of species in the ternary V(V)-peroxo-citrate system and its potential reactivity in (bio)chemically relevant media.

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.

Chemoselective Sulfide and Sulfoxide Oxidations by CpMo(CO)3Cl/HOOR: a DFT Mechanistic Study

The mechanism of sulfide and sulfoxide oxidation with peroxides (ROOH, R = H, Me), catalyzed by Mo(VI) complexes, was investigated by means of DFT/PBE1PBE calculations. Two different catalytic systems were considered: the first is based on the dioxocyclopentadienyl (Cp) complex CpMoO2Cl (Cp = η5-C5H5), also active as a catalyst for olefin epoxidation, and the second based on MoO2Cl2. The most favorable mechanism in the Cp system is initiated by the O−H activation of the HOOR oxidant, which in the presence of CpMoO2Cl leads to formation of CpMoO(OH)(OOR)Cl. Although this is the active species for olefin epoxidation, an alternative pathway with lower energy is available. With the crucial H-bond assistance of another oxidant molecule, the oxoperoxo complex CpMoO(O2)Cl forms, with release of alcohol ROH as byproduct and a calculated energy barrier below 25 kcal mol−1. The mechanisms unveiled for sulfide to sulfoxide oxidation and for sulfoxide to sulfone oxidation are equivalent in their general features and ...

A density functional theory investigation of the bromide oxidation mechanism by a vanadium bromoperoxidase model complex

Density functional theory has been used to study the mechanism of bromide oxidation by the oxo-peroxo complex K[VO(O2)Hheida] (heida = N-(2-hydroxyethyl)iminodiacetic acid), which has the highest reported rate constant for bromide oxidation of any vanadium complex. Two possible mechanisms were explored, involving bromide attack on a protonated or unprotonated peroxo atom. The direct nucleophilic attack of bromide on a protonated peroxo begins the reaction, i.e. the protonated peroxo ligand is the active site of reaction. We examined five different transition states in the mechanism. Two transition states were found to have lower activation barriers. A reduction in the potential energy barriers, when calculated using the polarisable continuum model, indicates that with the involvement of acetonitrile as a solvent the transition states become more stable.

Toward Alkane Functionalization Effected with Cp*W(NO)(alkyl)(η3-allyl) Complexes

Cp*W(NO)(n-alkyl)(η3-allyl) complexes result from the selective activations of the terminal C−H bonds of alkanes. Consequently, the reactions of prototypical members of this family of complexes with a range of electrophiles and nucleophiles have been explored with a view to developing methods for functionalizing the newly formed alkyl ligands. The two principal complexes investigated in this regard have been Cp*W(NO)(CH2SiMe3)(η3-CH2CHCHMe) (1) and Cp*W(NO)(CH2C6H5)(η3-CH2CHCHMe) (2). It has been found that treatment of 1 and 2 with the oxidant I2 at −60 °C produces Cp*W(NO)I2 and terminally functionalized ICH2SiMe3 and ICH2C6H5, respectively. Oxidation of 1 by H2O2 also results in the loss of the allyl ligand and production of the known oxo peroxo complex Cp*W(O)(η2-O2)(CH2SiMe3). Treatment of 1 and 2 with electrophiles affords the products resulting from addition of the electrophile to the electron-rich terminus of the σ−π distorted allyl ligands in the reactants. Thus, reagents of the type E-X (E = tri...

Selective oxidation of aromatic primary alcohols to aldehydes using molybdenum acetylide oxo-peroxo complex as catalyst

Selective oxidation of various aromatic alcohols to aldehydes has been carried out with very high conversion (90%) and selectivity (90%) for aldehydes using cyclopentadienyl molybdenum acetylide complex, CpMo(CO) 3(C CPh) ( 1) as catalyst and hydrogen peroxide as environmentally benign oxidant. Water-soluble Mo acetylide oxo-peroxo species is formed in situ after reaction of 1 with aqueous hydrogen peroxide during the course of reaction as catalytically active species. Interestingly even though the catalyst is homogeneous it could be recycled very easily by separating the products in organic phase and catalyst in aqueous phase using separating funnel. Even after five recycles no appreciable loss in alcohol conversion and aldehyde selectivity was observed.

Oxoperoxo Vanadium(V) Complexes of l-Lactic Acid: Density Functional Theory Study of Structure and NMR Chemical Shifts

Various combinations of density functionals and pseudopotentials with associated valence basis-sets are compared for reproducing the known solid-state structure of [V 2O 2(OO) 2 l-lact 2] (2-) cis . Gas-phase optimizations at the B3LYP/SBKJC level have been found to provide a structure that is close to that seen in the solid state by X-ray diffraction. Although this may result in part from error compensation, this optimized structure allowed satisfactory reproduction of solution multinuclear NMR chemical shifts of the complex in all-electron DFT-IGLO calculations (UDFT-IGLO-PW91 level), suggesting that it is probably close to that found in solution. This combination of approaches has subsequently been used to optimize the structures of the vanadium oxoperoxo complexes [V 2O 3(OO) l-lact 2] (2-) cis , [V 2O 3(OO) l-lact 2] (2-) trans , and [VO(OO)( l-lact)(H 2O)] (-) cis . The (1)H, (13)C, (51)V, and (17)O NMR chemical shifts for these complexes have been calculated and compared with the experimental solution chemical shifts. Excellent agreement is seen with the (13)C chemical shifts, while somewhat inferior agreement is found for (1)H shifts. The (51)V and (17)O chemical shifts of the dioxo vanadium centers are well reproduced, with differences between theoretical and experimental shifts ranging from 22.9 to 35.6 ppm and from 25.1 to 43.7 ppm, respectively. Inferior agreement is found for oxoperoxo vanadium centers, with differences varying from 137.3 to 175.0 ppm for (51)V shifts and from 148.7 to 167.0 ppm for (17)O(oxo) shifts. The larger errors are likely to be due to overestimated peroxo O-O distances. The chosen methodology is able to predict and analyze a number of interesting structural features for vanadium(V) oxoperoxocomplexes of alpha-hydroxycarboxylic acids.

Selective N-oxidation of aromatic amines to nitroso derivatives using a molybdenum acetylide oxo-peroxo complex as catalyst

The molybdenum acetylide oxo-peroxo complex obtained in situ by the treatment of the corresponding molybdenum acetylide carbonyl complex, CpMo(CO) 3(C CPh); Cp = η 5-C 5H 5 with H 2O 2, has been used as an efficient catalyst for selective N-oxidation of primary amines to nitroso derivatives. Excellent amine conversion (up to 100%) and very high selectivity for nitroso compounds (99%) have been obtained using 30% hydrogen peroxide as an oxidant. The oxo peroxo Mo(VI) complex has also been found to be very active for the oxidation of various substituted primary aromatic amines with electron donating as well as electron withdrawing substituents on the aromatic ring.

Selective cis-dihydroxylation of olefins using recyclable homogeneous molybdenum acetylide catalyst

Selective cis-dihydroxylation of various olefins has been carried out using molybdenum acetylide complex CpMo(CO) 3(C CPh) ( 1) as catalyst and hydrogen peroxide as an efficient and environmentally benign oxidant. In case of cyclohexene, very high conversion (95%) and selectivity (86%) for cis-dihydroxylated product has been achieved using H 2O 2 as an oxidant and t-butanol as a solvent. cis-Dihydroxylation of other substrates like styrene, α-methyl styrene, limonene and cyclopentene has also been carried out with very high selectivity for diol. The catalyst and intermediate species have been characterized using FT-IR, UV–vis spectral analysis and XPS studies as well as cyclic voltametric studies. These studies suggest that molybdenum oxo–peroxo complex is the catalytically active species. The intermediate blue complex when characterized by ESI MS suggested the formation of dimeric molybdenum complex and XPS and cyclic voltametric studies confirm the presence of mixed valence Mo(V) and Mo(VI) in the reaction intermediate. Based on the characterization results possible mechanism for dihydroxylation is proposed. Interestingly, even though the catalyst is homogeneous; it could be recovered quantitatively by extraction in aqueous phase and recycled five times without any appreciable loss in cyclohexene conversion and selectivity for cis-1,2-cyclohexanediol.

Comparison of the conventional impregnation method using ammonium heptamolybdate with a simple route to silica-supported molybdenum(VI) materials

Abstract Silica-supported molybdenum oxide materials have been prepared by using the ability of molybdenum oxoperoxo complexes to interact with the surface hydroxyl groups of the support, which after calcination, have a highly dispersed MoO x /SiO 2 structure, and lead to leach-resistant catalysts; with a polyoxo precursor, (NH 4 ) 6 [Mo 7 O 24 ] · 4H 2 O, there is a formation of MoO 3 clusters and a weaker MoO 3 /SiO 2 interaction.

Polymer-anchored oxoperoxo complexes of vanadium(V), molybdenum(VI) and tungsten(VI) as catalyst for the oxidation of phenol and styrene using hydrogen peroxide as oxidant

2-(2-pyridyl)benzimidazole (2-pybmz) and 2-(3-pyridyl)benzimidazole (3-pybmz) have been covalently anchored to chloromethylated polystyrene crossed-linked with 5% divinylbenzene in DMF in presence of triethylamine in ethylacetate. These chelating resins readily react with non-isolable metal peroxo species, prepared in situ by stirring V 2O 5 (in presence of aqueous KOH), MoO 3 or WO 3 · H 2O with an excess of 30% H 2O 2, to give the corresponding oxodiperoxo complexes, PS-K[VO(O 2) 2(L)] (L = 2-pybmz: 1, L = 3-pybmz: 4), PS-[MoO(O 2) 2(L)] (L = 2-pybmz: 2, L = 3-pybmz: 5) and PS-[WO(O 2) 2(L)] (L = 2-pybmz: 3, L = 3-pybmz: 6). PS-2-pybmz and PS-3-pybmz represent polymer-anchored ligands. Structures of these complexes have been established on the basis of spectroscopic (IR and electronic), thermogravimetric studies and elemental analyses. Oxidation of phenol or styrene with selected catalysts was tested using H 2O 2 as an oxidant. Oxidation of phenol with ca. 35% conversion gave a mixture of catechol and p-hydroquinone where selectivity towards catechol is ca. 62%. Oxidation of styrene gave five products, styrene epoxide, benzaldehyde, benzoic acid, phenylacetaldehyde and 1-phenylethane-1,2-diol. Various parameters such as amount of oxidant and catalyst, and temperature of the reaction mixture have been taken into consideration for the maximum conversion of substrates. These catalysts are recyclable without considerable loss in their catalytic activities. IR spectral data of both freshly prepared and recovered catalysts are also identical, which indicate that the metal complex moiety is intact during the catalytic reaction.