Catalysts For Epoxidation Of Cyclooctene Research Articles

Impact of POM's coordination mode and Mo-hybrid constituents on the binding, stability, and catalytic properties of hybrid (pre)catalysts.

The assembly of MoVIO2 2+ and methoxy-substituted salicylaldehyde nicotinoyl hydrazone ligands afforded two classes of hybrid polyoxometalates (POMs). In the Class I architectures, [MoO2(HL1-3)(D)]2[Mo6O19]·xCH3COCH3 (D = CH3COCH3 or H2O, x = 0 or 2, and L1-3 = ligands bearing the OMe group at position 3, 4 and 5, respectively), the main driving force for self-assembly is the electrostatic interaction between the components. Class II architectures are composed of a POM anion covalently linked to two Mo-complex units through the terminal Ot or bridging μ2-OPOM oxygen atoms, as found in Lindqvist-based hybrids [{MoO2(HL1-3)}2Mo6O19]·xCH3CN (x = 0 or 2) and the asymmetrical β-octamolybdate-based hybrid [{Mo2O4(HL2)(H2L)}{MoO2(HL2)}2Mo8O26]·CH3CN·H2O. Quantum chemical calculations were applied to evaluate the impact of the POM hybrid constituents on the hybrid-type stability, showing that it strongly depends on the ligand substituent position and ancillary ligand nature. Hybrids were tested as catalysts for cyclooctene epoxidation using tert-butyl hydroperoxide (TBHP in water or decane) and with or without the addition of acetonitrile (CH3CN) as an organic solvent. The catalytic results provided by the use of TBHP in decane are the best ones and classify all the prepared catalysts as very active, with the conversion of cyclooctene >90%, and high selectivity towards epoxide, >80%. We also examined the influence of the ligand structure, POM's hybrid type, and coordination mode on the Mo-hybrid activity and selectivity.

Preparative and Catalytic Properties of MoVI Mononuclear and Metallosupramolecular Coordination Assemblies Bearing Hydrazonato Ligands.

A series of polynuclear, dinuclear, and mononuclear Mo(VI) complexes were synthesized with the hydrazonato ligands derived from 5-methoxysalicylaldehyde and the corresponding hydrazides (isonicotinic hydrazide (H2L1), nicotinic hydrazide (H2L2), 2-aminobenzhydrazide (H2L3), or 4-aminobenzhydrazide (H2L4)). The metallosupramolecular compounds obtained from non-coordinating solvents, [MoO2(L1,2)]n (1 and 2) and [MoO2(L3,4)]2 (3 and 4), formed infinite structures and metallacycles, respectively. By blocking two coordination sites with cis-dioxo ligands, the molybdenum centers have three coordination sites occupied by the ONO donor atoms from the rigid hydrazone ligands and one by the N atom of pyridyl or amine-functionalized ligand subcomponents from the neighboring Mo building units. The reaction in methanol afforded the mononuclear analogs [MoO2(L1-4)(MeOH)] (1a-4a) with additional monodentate MeOH ligands. All isolated complexes were tested as catalysts for cyclooctene epoxidation using tert-butyl hydroperoxide (TBHP) as an oxidant in water. The impact of the structure and ligand lability on the catalytic efficiency in homogeneous cyclooctene epoxidation was elucidated based on theoretical considerations. Thus, dinuclear assemblies exhibited better catalytic activity than mononuclear or polynuclear complexes.

Heterostructured V2O5/FeVO4 for enhanced liquid-phase epoxidation of cyclooctene.

Efficient cyclooctene epoxidation process under mild reaction conditions highly relies on the rational design and synthesis of high-performance heterogeneous catalysts. Herein, we report the facile one-pot synthesis of V2O5/FeVO4 heterostructures featured with heterointerfaces for the boosted epoxidation of cyclooctene. The intensive interfacial electronic interaction between the V2O5 and FeVO4 phases is versatile in the modulation of coordination microenvironment and formation of abundant oxygen vacancies, contributing to the performance enhancement. Under the optimal reaction conditions, a high yield of 87.0% can be achieved with the cyclooctene conversion of 96.5% (initial reaction rate of 55.1mmolgcat-1h-1) and cyclooctene oxide selectivity of 90.2%. Additionally, the V2O5/FeVO4 catalyst is stable and recyclable, endowing it a promising prospect for practical applications. This study demonstrates that the application of interface engineering strategy can be an appealing avenue towards the development of high-performance catalysts for epoxidation of cyclooctene and beyond.

Catalytic performance of a wide range of rare-earth titanate pyrochlore (RE2Ti2O7, RE = Sm, Gd, Dy, and Yb) microstructures in the epoxidation of cyclooctene: An electro-structural investigation

A series of rare-earth titanate oxides RE2Ti2O7 (RE =Sm, Gd, Dy and Yb) were synthesized using a solid state method. The pyrochlore structures of these compounds were confirmed by the Rietveld method from X-ray diffraction data (XRD). XRD results showed that RE2Ti2O7 structures had cubic crystal system with the Fd3m space group. Morphology and mean particle sizes of the samples were obtained by the scanning electron microscope (SEM). Chemical characterizations of the samples were confirmed by energy dispersive x-ray spectroscopy (EDX). The specific surface areas were calculated using BET analyses. Fourier transform infrared spectra of the obtained compounds in (400–4000 cm−1) range were also studied. The obtained RE2Ti2O7 pyrochlore materials were used as catalysts for epoxidation of cyclooctene as a model alkene with tert-butyl hydroperoxide. Various parameters including catalyst type and amount, solvent type and amount, oxidant/substrate ratio, and time have been optimized and high catalytic activity and epoxide selectivity have been found. Gd2Ti2O7 showed the best activity and epoxide selectivity.

Synthesis and characterization of a series of acylpyrazolone transition metal complexes: Crystal structures and catalytic performance in the epoxidation of cyclooctene

A series of transition metal complexes of 4-acetyl-3-methyl-1-phenyl-2-pyrazoline-5-one with Ni(II), Cu(II), Fe(III) and Mn (II) central metal ions have been synthesized and characterized by X-ray crystallography, UV–Vis and FTIR spectroscopy, and elemental analysis. The complexes were used as a catalyst for epoxidation of cyclooctene with tert-butylhydroperoxide. Various parameters, including catalyst type and amount, solvent type and amount, oxidant/substrate ratio and time, have been optimized. The highest catalytic activity was found for Cu(II) complex at the optimized conditions. Very high selectivity for the epoxide product (cyclooctene oxide) was also obtained.

Discrete mononuclear and dinuclear compounds containing a MoO22+core and 4-aminobenzhydrazone ligands: synthesis, structure and organic-solvent-free epoxidation activity

New aroylhydrazone molybdenum(vi) complexes have been synthesized, characterized and used as (pre)catalysts for epoxidation of cyclooctene using aqueous TBHP as the oxidant.

Six‐coordinated vanadium(IV) complexes with tridentate task‐specific ionic liquid Schiff base ligands: Synthesis, characterization and effect of ionic nature on catalytic activity

By reaction of 5‐(chloromethyl)salicylaldehyde with triphenylphosphine and N‐methylimidazole in two separate reactions, salicylaldehydetriphenylphosphonium chloride (S2) and salicylaldehydemethylimidazolinium chloride (S3) were prepared. Reaction of 2‐(aminomethyl)pyridine with these aldehydes resulted in the task‐specific ionic liquid Schiff base ligands L1 and L2, respectively. Then six‐coordinated vanadium(IV) Schiff base complexes of VO(acac)L1–4 were synthesized by reactions of these tridentate Schiff base ligands and VO(acac)2 in 1:1 stoichiometry. The aldehydes, ligands and VO(acac)L1–4 complexes were characterized using infrared, 1H NMR, 13C NMR, 31P NMR, UV–visible and mass spectroscopies, as well as elemental analysis. Paramagnetic property of the complexes was also studied using magnetic susceptibility measurements. The complexes were used as catalysts in epoxidation of cyclooctene and oxidation of methylphenyl sulfide and the reaction parameters were optimized. The effect of the ionic nature of the complexes was investigated in these oxidation reactions. The catalytic activity of the complexes could be varied by changing the ionic (cationic or anionic) character of VO(acac)L1–4 catalysts in which counter anion variation showed a greater effect than cationic moiety variation.

A novel inorganic–organic hybrid compound based on heteropolyoxomolybdate nanocluster as selective catalyst for epoxidation of cyclooctene

A new Co2+-centered heteropolyoxomolybdate nanocluster containing the bipy ligand (4,4′-bipy=4,4′-bipyridine), with formula [4,4′-H2bipy][Co0.23Mo6O20]·2H2O (1), has been hydrothermally synthesized and structurally characterized by means of FT-IR, atomic absorption spectroscopy, single-crystal and powder X-ray diffraction (XRD). The catalytic investigations disclosed that 1 displayed both good activity and stability in the epoxidation of cyclooctene. It can also be recovered easily and reused in the reaction without significant loss of activity or selectivity. Furthermore, the effect of the type of oxidant and solvent on the conversion of the reaction was investigated.

Schiff base complexes of methyltrioxorhenium (VII): Synthesis and catalytic application

Schiff bases coordinate smoothly with methyltrioxorhenium (MTO) to yield the corresponding MTO–Schiff base adducts, which were characterized by IR, NMR and elemental analysis. The X-ray structure of one of the complexes was exemplary determined. The compounds were used as catalysts for cyclooctene epoxidation in ionic liquids with UHP (urea hydrogen peroxide adduct) as oxidant at room temperature. The results show that (N-salicylidene)aniline derived Schiff base complexes of MTO displayed higher catalytic activity and selectivity than di-nitrogen Schiff base complexes of MTO. No diol byproduct formation is observed.

Effect of pore sizes on catalytic activities of arenetricarbonyl metal complexes constructed within Zr-based MOFs

Arenetricarbonyl metal complexes ([-phM(CO)3-] and [-biphM(CO)3-]; ph = phenylene, biph = biphenylene, M = Mo, Cr) constructed within Zr-based MOFs act as highly active and selective catalysts for epoxidation of cyclooctene. Catalytic activities of these complexes are enhanced with increasing the pore sizes of Zr-based MOFs.

Crystal structure, electrochemistry, and catalytic studies of a series of new oxidovanadium(IV) Schiff-base complexes derived from 1,2-diphenyl-1,2-ethylenediamine

New derivatives of N2O2 tetradentate Schiff bases, from condensation of meso-1,2-diphenyl-1,2-ethylenediamine and salicylaldehyde derivatives (X-salicylaldehyde; X = 3-OMe, 4-OMe, 5-OMe, 6-OMe, 5-Cl, 5-Me), and oxidovanadium(IV) complexes were synthesized and characterized by 1H NMR, UV-Vis, IR spectroscopy, and elemental analysis. Crystal structure of 5-OMe; H2L3 and two of the complexes (VOL2 and VOL3) were also obtained. In the crystals, the molecule of H2L3 is Ci symmetrical, as it occupies the special position on the center of symmetry; its conformation is partially determined by classical intramolecular O–H···N hydrogen bonds. The complexes have monomeric structures with a distorted square pyramid of vanadium, with the oxo ligand in the apical position. Cyclic voltammetry studies show quasi-reversible VIV/VV redox for which the presence of electron-withdrawing groups on salicylaldehyde derivatives shifts the E° to more positive values. The complexes were used as catalysts for selective epoxidation of cyclooctene with tert-butylhydroperoxide as oxidant, in various solvents and reaction conditions. High catalytic activities and excellent selectivity was found. The catalytic activity of the complexes increased increasing E°, a consequence of the presence of electronegative substituents. This epoxidation process with the new catalysts was also studied under solvent-free condition and excellent reactivity was observed.

Two hydrogen-bond-cross-linked molybdenum (VI) network polymers: synthesis, crystal structures and cyclooctene epoxidation with H2O2

Two molybdenum (VI) hydrogen-bonded network polymers [MoO2F4]·(4,4′-H2bpd)(H2O)2 (1) and [MoO2Cl3(H2O)]·(4,4′-H2bpd)Cl (2) (bpd = bipiperidine) have been synthesized and examined as catalysts for epoxidation of cyclooctene. Complexes of the Mo compounds containing the bpd ligand are prepared and characterized by infrared spectroscopy, thermogravimetric and elemental analyses. They have been structurally characterized by single crystal X-ray diffraction analysis. The structures of both the complexes are shown to be comprised of molybdenum and two protonated N-ligand cations that have resulted in a cross-linked hydrogen-bonded network structure. These complexes are applicable as catalysts for the cis-cyclooctene epoxidation reactions with hydrogen peroxide as a source of oxygen and NaHCO3 as a cocatalyst. It has been observed that the formation of the oxidant peroxymonocarbonate ion, HCO4 − by hydrogen peroxide and bicarbonate enhances the epoxidation reaction. Both the complexes have exhibited a good activity and a very high selectivity for the formation of cyclooctene oxide.

Gel derived niobium–silicon mixed oxides: Characterization and catalytic activity for cyclooctene epoxidation

Abstract Niobium–silicon mixed oxide nanocomposites, containing 7–37 wt.% Nb, were synthesized by a new sol–gel route and characterized for textural and acid properties by N 2 adsorption, NH 3 TPD and FTIR of adsorbed acetonitrile. The materials were tested as catalysts for epoxidation of cyclooctene with H 2 O 2 . High surface areas (>150 m 2 g −1 ), decreasing with Nb content, were found for materials containing up to 23.0 wt.% Nb. FTIR and TPD measurements evidenced the presence of both Bronsted and Lewis acid sites with different strength. The amount of strong acid sites, relative to those of low or moderate strength, increased with Nb content. The materials containing up to 23.0 wt.% Nb were active and stable catalysts for the epoxidation of cyclooctene. The highest activity and H 2 O 2 selectivity was found for the catalyst with the lowest Nb content, that showed also high stability in reuse. Catalytic properties were related to acid sites and to the presence of NbO x species with different coordination.

Homogeneous green catalyst for epoxidation of cyclooctene by mono oxovanadium(IV) complexes of N 2O 2 donate ligand system

A significant effort has been done towards the development of new catalysts for the synthesis of epoxides in a more environmental friendly way. We have found that the mono oxovanadium(IV) complexes of the N 2O 2 donor set ligands are able to catalyze selective epoxidation of cyclooctene with high yield using O 2 in polar solvents. In general, catalytic activity increases by decreases of the number of electron – donating groups and the catalytic selectivity varies according to the types of substituents in the ligands. The vanadium complexes with strongly donor ligands, are more stable during the oxidation process. The conversion of cyclooctene increases with the E redox 0 ′ /Δ E p ratio of V 5+/V 4+ couples.

Grafting of a tetrahydro-salen copper(II) complex on surface modified mesoporous materials and its catalytic behaviour

A tetrahydro-salen copper(II) complex ( 1) is grafted on the iodosilane modified surfaces of MCM-41 and MCM-48. The presence of complex 1 on the surfaces is evidenced by 1H MAS–NMR, elemental analysis and TG-MS. The strucutre of the supports after modification remains intact, which is evident from powder XRD, N 2 adsorption/desorption (BET), and TEM analysis. The grafted materials are applicable as catalysts for cyclooctene epoxidation and they are found to maintain activity for several runs.

Organotin-oxomolybdate coordination polymers as catalysts for the epoxidation of cyclooctene

The organotin-oxomolybdate coordination polymers [(R 3Sn) 2MoO 4]· nH 2O (R = methyl, n-butyl, cyclohexyl, phenyl, benzyl) were tested as catalysts for the liquid-phase epoxidation of cyclooctene with 30% aqueous hydrogen peroxide at 35 °C and atmospheric pressure. Water, acetonitrile and dichloromethane were examined as additional co-solvents for the reaction. The catalytic results vary considerably with the nature of the tin-bound R group and the co-solvent. For all systems, cyclooctene oxide was the only observed reaction product. Apart from the trimethyltin derivative, the best results were obtained without additional co-solvent or with CH 2Cl 2, while addition of water or CH 3CN had a detrimental effect on catalytic performance. The highest turnover frequency ( 46 mol mo l Mo − 1 h − 1 ) was obtained for the system containing the tri- n-butyltin derivative as catalyst and CH 2Cl 2 as solvent. Complete conversion of the substrate was achieved for this system within 4 h. Using water instead of CH 2Cl 2 with the n-butyl catalyst reduced the catalytic activity considerably at the beginning of the reaction, although 91% conversion was achieved after 24 h. The behavior of the trimethyltin derivative was atypical in that conversion of cyclooctene was only possible when CH 3CN was used as the co-solvent. Experiments were also carried out using a urea/hydrogen peroxide adduct as a water-free source of H 2O 2. However, the catalytic activities observed were significantly lower than those obtained using aqueous H 2O 2.

Mesoporous MCM-41 Materials Modified with Oxodiperoxo Molybdenum Complexes: Efficient Catalysts for the Epoxidation of Cyclooctene

An organic−inorganic hybrid heterogeneous catalyst system was synthesized by covalently anchoring oxodiperoxo molybdenum complexes [(L−L)MoO(O2)2] (L−L = (3-triethoxysilylpropyl)[3-(2-pyridyl)-1-pyrazolyl]acetamide) onto the mesoporous silica MCM-41 (Si−MCM-41) and aluminosilicate MCM-41 (Al−MCM-41) materials. Characterization of the functionalized materials by powder X-ray diffraction (XRD), N2 adsorption, and solid-state CP-MAS NMR spectroscopy (13C and 29Si) demonstrates that the oxodiperoxo molybdenum complexes are grafted successfully into the mesoporous MCM-41 materials. The structures of both the mesoporous materials and the molybdenum complex are preserved during the grafting process. All the hybrid materials are active and truly heterogeneous catalysts for the liquid-phase epoxidation of cyclooctene with tBuOOH as the oxygen source. The catalytic properties (activity and recyclability) of the supported materials can be improved by their further silylation using Me3SiCl, which can be explained by ...

Iron polynitroporphyrins bearing up to eight beta-nitro groups as interesting new catalysts for H2O2-dependent hydrocarbon oxidation: unusual regioselectivity in hydroxylation of alkoxybenzenes.

A series of iron porphyrins bearing one to eight beta-nitro substituents were synthesized and evalauted as catalysts for hydrocarbon oxidation with H2O2; iron porphyrins bearing five or six beta-nitro groups were the best catalysts for cyclooctene epoxidation and adamantane or anisole hydroxylation without need of a cocatalyst, and led to very different regioselectivities with either H2O2 or PhIO as oxidants, as shown by an unusual ortho-hydroxylation of alkoxybenzenes highly favored in the H2O2-dependent oxidations.

Synthesis of fluorinated metalloporphyrinosilica imprinted with templates through sol–gel process

We present the synthesis of a hybrid material containing fluorinated iron porphyrins through hydrolysis and polycondensation of iron porphyrin bearing a trifluorosilyl function with tetraethoxysilane in the presence of nitrogen bases acting as template molecules. The presence of metalloporphyrin Soret band is detected in the ultraviolet–visible absorption spectra of all metalloporphyrinosilica-templates. Thermogravimetric analysis and electron paramagnetic resonance of the materials also confirm the presence of metalloporphyrin in a silica network. Electron spectroscopy imaging was that of a non-crystalline microstructure. The iron and silicon distribution are homogeneous for the elements in all particle sites. The iron porphyrinosilicas-template were active as catalysts for cyclooctene epoxidation using iodozylbenzene as oxygen donor. In general, the epoxidation yield is larger for iron porphyrinosilicas-template than for manganese porphyrinosilicas-template. The manganese porphyrinosilicas-template had a smaller activity due to their manganese oxidation state. The largest catalytic yield were obtained with the iron porphyrinosilica-pyridine (85%).