Oxo‐vanadium(IV) Schiff base complex supported on modified MCM‐41: a reusable and efficient catalyst for the oxidation of sulfides and oxidative S–S coupling of thiols

Oxo‐vanadium(IV) Schiff base complex supported on MCM‐41 as an organic–inorganic hybrid heterogeneous catalyst was synthesized with post‐grafting of MCM‐41 with 3‐aminoropropyltrimethoxysilane and subsequent reaction with 3,4‐dihydroxybenzaldehyde and then complexation with oxo‐vanadium acetylacetonate salt. The catalyst was analysed using a series of characterization techniques such as Fourier transform infrared spectroscopy, small‐angle X‐ray diffraction, nitrogen absorption isotherm, transmission electron microscopy and thermogravimetric analysis. The data collected provided evidence that the vanadium complex was anchored onto MCM‐41. High catalytic activity of this catalyst was observed in the oxidation of various sulfides and thiols (into sulfoxides and disulfides, respectively) with urea hydrogen peroxide as oxidant in high to excellent yields and selectivity under mild conditions. The heterogeneous catalyst could be recovered easily and reused several times without significant loss in catalytic activity and selectivity. Copyright © 2015 John Wiley & Sons, Ltd.     

Catalytic asymmetric oxidation of sulfide and styrene derivatives using macroporous resins containing chiral metalloporphyrins (Fe, Ru)

Chiral metalloporphyrin (Fe, Ru) complexes, functionalized with four vinyl groups, have been polymerized with styrene and divinylbenzene (or ethylene glycol) to obtain supported iron and ruthenium complexes. The heterogeneous asymmetric oxidation of sulfides and styrene derivatives was carried out by using these polymers as catalysts. The reaction proceeded under mild conditions and gave sulfoxides and epoxides with good enantiomeric excesses (up to 75–76%). The catalysts keep constant ee values for the recycle tests of up to six times for asymmetric oxidation of styrene derivatives and of up to 14 times for asymmetric oxidation of sulfides with only traces of sulfones.     

中孔MCM-41锚合Zr（IV）-salen催化剂制备及用于硫化物氧化制亚砜和Knoevenagel缩合反应

通过NH2-MCM-41与水杨醛反应得到席夫碱配体,然后加入八水氧氯化锆形成络合物,制得Zr(IV)-salen-MCM-41催化剂。采用X射线衍射、N2吸附-脱附、热重、红外光谱、电感耦合等离子体发射光谱和能量散射谱等分析手段对催化剂结构进行了表征。在含有该催化剂的体系中进行了硫化物选择氧化为亚砜以及醛与丙二腈和氰乙酸乙酯的Knoveonagel缩合反应,并考察了催化剂的循环使用性能。     

Synthesis and characterization of VO–vanillin complex immobilized on MCM-41 and its facile catalytic application in the sulfoxidation reaction,and synthesis of 2,3-dihydroquinazolin-4(1H)-ones and disulfides in green media

In this work, a vanillin complex is immobilized onto MCM-41 and characterized by FT-IR, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetric analysis, and BET techniques. This supported Schiff base complex was found to be an efficient and recoverable catalyst for the chemoselective oxidation of sulfides into sulfoxides and thiols into their corresponding disulfides (using hydrogen peroxide as a green oxidant) and also a suitable catalyst for the preparation of 2,3-dihydroquinazolin-4(1H)-one derivatives in water at 90°C. Using this protocol, we show that a variety of disulfides, sulfoxides, and 2,3-dihydroquinazolin-4(1H)-one derivatives can be synthesized in green conditions. The catalyst can be recovered and recycled for further reactions without appreciable loss of catalytic performance.     

Selective and solventless oxidation of organic sulfides and alcohols using new supported molybdenum (VI) complex in microwave and conventional methods

A new dioxo-molybdenum (VI) complex supported on functionalized Merrifield resin ( MR-Mo ) has been synthesized and characterized by elemental, scanning electron mcroscopy, energy-dispersive X-ray analysis, TGA, Brunauer–Emmett–Teller method, powder-X-ray diffraction, Fourier transform infrared, X-ray photoelectron spectroscopy and DRS–UV–vis analysis. The virgin Merrifield resin ( MR ) was functionalized by carbonylation followed by Schiff base formation with ethanolamine ( MR-SB ). Experimental data showed that the Schiff base coordinated with the MoO₂²⁺ moiety via O- and N-atoms. The catalytic activity of MR-Mo was explored under solventless conditions toward the oxidation of organic sulfides and alcohols using 30% aqueous H₂O₂ as oxidant. The oxidation reactions were conducted under microwave and conventional methods. The microwave-assisted oxidation reactions were found to be many times faster than the conventional methods. The oxidation reactions were selective and formed sulfoxides or aldehydes as the sole product with superior TOF values among the molybdenum (VI)-based complexes. Besides these, the MR-Mo was purely heterogeneous in nature and can be recycled for at least five reaction cycles without the loss of catalytic efficiency and product selectivity.     

Economical Oxygenation of Olefins and Sulfides Catalyzed by New Molybdenum(VI) Tridentate Schiff Base Complexes: Synthesis and Crystal Structure

Abstract. New cis‐dioxomolybdenum(VI) complexes (MoO₂Y^xCH₃OH) were synthesized using MoO₂(acac)₂ and 2[(1‐hydroxy‐2‐methylpropane‐2‐ylimino)methyl]phenol derivatives as tridentate ONO donor Schiff base ligands (H₂Y^x). MoY¹ was crystallized in orthorhombic space group Pbca. The epoxidation of olefins using tert‐butyl hydroperoxide and oxidation of sulfides to the sulfoxides by hydrogen peroxide were efficiently enhanced by the catalytic activity of title Mo^VI complexes with excellent selectivity. The high efficiency and relative stability of the catalysts was observed by turnover number and UV/Vis investigations. The electron‐rich and bulky ligands promoted the effectiveness of the catalysts.     

Electronic and steric effects on the oxygenation of organic sulfides and sulfoxides with oxo(salen)chromium(V) complexes

The kinetics of oxygenation of several para-substituted phenyl methyl sulfides and sulfoxides with a series of 5-substituted and sterically hindered oxo(salen)chromium(V) complexes have been studied by a spectrophotometric technique. Though the reaction of sulfides follows simple second-order kinetics, sulfoxides bind strongly with the metal center of the oxidant and the oxygen atom is transferred from the oxidant-sulfoxide adduct to the substrate. The reduction potentials, E(red), of eight Cr(V) complexes correlate well with the Hammett sigma constants, and the reactivity of the metal complexes is in accordance with the E(red) values. The metal complexes carrying bulky tert-butyl groups entail steric effects. Organic sulfides follow a simple electrophilic oxidation mechanism, and the nonligated sulfoxides undergo electrophilic oxidation to sulfones using the oxidant-sulfoxide adduct as the oxidant. Sulfoxides catalyze the Cr(V)-salen complexes' oxygenation of organic sulfides, and the catalytic activity of sulfoxides is comparable to pyridine N-oxide and triphenylphosphine oxide. The rate constants obtained for the oxidation of sulfides and sulfoxides clearly indicate the operation of a pronounced electronic and steric effect in the oxygenation reaction with oxo(salen)chromium(V) complexes.     

Highly efficient and excellent reusable catalysts of molybdenum(VI) complexes grafted on ZPS‐PVPA for epoxidation of olefins with tert‐BuOOH

Four new kinds of heterogeneous catalysts for olefins epoxidation were obtained by grafting diamines on organic polymer–inorganic hybrid material, zirconium poly (styrene‐phenylvinylphosphonate)‐phosphate (ZPS‐PVPA), and subsequently coordinating with Schiff base Mo(VI) complexes. The catalysts were characterized by IR, XPS, SEM and TEM. All catalysts were evaluated through the epoxidation of olefins using tert‐BuOOH as oxidant. The heterogeneous catalysts possess the advantages of high conversion, selectivity and excellent reusability. The catalysts were easily separated from the reaction systems and could be reused 13 times without significant loss of catalytic activity. Copyright © 2010 John Wiley & Sons, Ltd.     

Catalytic activity of an iron(III) Schiff base complex bound in a polymer resin

An iron(III)–ferrocene complex and its heterogeneous analogue bound in a polymer resin have been prepared and employed as catalysts for the oxidation of various organic substrates. Characterization of the heterogeneous and homogeneous complexes was done by SEM, EDAX, TGA, FT-IR, DRS-UV, and spectroscopy. The catalyst’s activity, stability, and reusability were investigated through industrially relevant oxidation reactions. The solid iron(III)–ferrocene Schiff base complex gave more effective results than the solid-supported ferrocene Schiff base ligand. The antimicrobial activities of the molecular complex and free ligand were studied for Gram-positive and Gram-negative bacteria.     

Synthesis of Fe3O4@SiO2@DOPisatin‐Ni(II) and Cu(II) nanoparticles: Highly efficient catalyst for the synthesis of sulfoxides and disulfides

The catalytic activity of two magnetic catalysts Fe₃O₄@SiO₂@DOPisatin‐M(II) (M = Ni, Cu) was investigated in the environmentally green H₂O₂ oxidant‐based oxidation of sulfides to sulfoxides and oxidative coupling of thiols to disulfides. By using these catalysts, various substrates were successfully converted into their corresponding product. These catalysts could also be reused multiple time without significant loss of activity. The physical and chemical properties of the catalysts were determined using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), energy dispersive X‐ray spectroscopy (EDX) and atomic absorption spectroscopy (AAS).     

Preparation and characterization of Cu (II) Schiff base complex functionalized boehmite nanoparticles and its application as an effective catalyst for oxidation of sulfides and thiols

The synthesis, characterization, and evaluation of a Schiff base Cu (II) complex functionalized boehmite nanoparticles (Cu-complex-boehmite) as a new catalyst for oxidation of sulfides and thiols in the presence of hydrogen peroxide with complete selectivity and high conversion under solvent-free and mild reaction conditions were reported. Characterization of the catalyst was performed with various physicochemical methods. This effective catalyst was evaluated in terms of activity and reusability. It indicated high catalytic activity, good recoverability and reusability, and supplied the corresponding products in high yields and short reaction times. In addition, it shows notable advantages such as simplicity of operation, heterogeneous nature, easy work up, and it could be used at least eight times with no significant loss of its activity.     

Graphite oxide: a selective and highly efficient oxidant of thiols and sulfides

The selective oxidation of thiols to disulfides and sulfides to sulfoxides using graphite oxide (GO), a heterogeneous carbocatalyst obtained from low cost, commercial starting materials is described. The aforementioned oxidation reactions were found to proceed rapidly (as short as 10 min in some cases) and in good yield (51-100%) (19 examples). No over-oxidation of the substrates was observed, and GO's heterogeneous nature facilitated isolation and purification of the target products.     

金属催化硫醚的不对称氧化研究进展

手性金属络合物催化硫醚的不对称氧化是合成手性亚砜最有效的方法. 理性设计各种手性金属络合物催化剂应用于催化对映选择性氧化潜手性硫醚反应中, 近年来引起了化学家们较大的关注. 综述了各类手性金属络合物催化剂在硫醚不对称氧化中的应用.     

Stereoselective sulfoxidation catalyzed by achiral Schiff base complexes in the presence of serum albumin in aqueous media

Four coordination complexes ML derived from an achiral Schiff base ligand (H₂L?=?2,2′-[(1,2-ethanediyl)bis(nitrilopropylidyne)]bisphenol) have been synthesized and characterized. A method is described for the enantioselective oxidation of a series of aryl alkyl sulfides using the coordination complexes in the presence of serum albumins (SAs) in an aqueous medium at ambient temperature. The mixture of metal complexes with serum albumins is useful for inducing asymmetric catalysis. The complex, albumin source and substrate influence stereoselective sulfoxidation. At optimal pH with the appropriate oxidant, some of ML/SA systems are identified as very efficient catalysts, giving the corresponding sulfoxides in excellent chemical yield (up to 100%) and good enantioselectivity (up to 94% ee) in certain cases. UV–visible spectroscopic data provide evidence that stronger binding between the complex and serum albumin lead to higher enantioselectivity.     

Oxidation of sulfide with ArIO catalyzed with TPPM(III)Cl

Various sulfides were easily converted to the corresponding sulfoxides in high yields in TPPM(III)Cl-catalyzed oxidation with ArIO, to which the influence of structures of sulfides and iodosylaromatics, and kinds of metals centered on the catalysts were investigated.     

2,6-Dicarboxypyridinium chlorochromate: an efficient and selective reagent for the oxidation of thiols to disulfides and sulfides to sulfoxides

2,6-Dicarboxypyridinium chlorochromate (2,6-DCPCC) was found to be an efficient reagent for the conversion of thiols to disulfides and sulfides to sulfoxides under neutral and anhydrous conditions in good to excellent yields. Selective oxidation of thiols in the presence of sulfides at room temperature is also observed with this reagent.     

An efficient solvent free catalytic oxidation of sulfides to sulfoxides with hydrogen peroxide catalyzed by a binaphthyl-bridged Schiff base titanium complex

A titanium binaphthyl-bridged Schiff base complex proved to be an efficient catalyst for the hydrogen peroxide oxidation of aromatic and aliphatic sulfides to the corresponding sulfoxides in satisfactory yields under solvent-free conditions.     

Homogeneous and heterogeneous styrene epoxidation catalyzed by copper(II) and nickel(II) Schiff base complexes

Both monomeric Schiff base complexes and 1D helical polymeric complexes of Cu(II) and Ni(II) were synthesized and characterized by physicochemical and spectroscopic methods. X-ray single-crystal studies were made on [K₂(CuL)₂Ni(CN)₄]_n·0.5nEt₂O and [K₂(NiL)₂Ni(CN)₄]_n·0.5nEt₂O. The polymers were screened as heterogeneous catalysts for styrene epoxidation. For comparison, the catalytic properties of the homogeneous and heterogeneous catalysts were also examined under identical reaction conditions, and the influence of various solvents and oxidants was studied. The polymeric catalysts showed better activities in chloroform when using tert-butyl hydroperoxide as oxidant, suggesting that heterogenization increased the activity of the catalyst under this condition.     

Co(II), Fe(III) or VO(II) Schiff base metal complexes immobilized on graphene oxide for styrene epoxidation

Cobalt(II), iron(III) or oxovanadium(II) Schiff base metal complexes have been covalently grafted onto graphene oxide ( GO ) previously functionalized with 3‐aminopropyltriethoxysilane. Potential catalytic behaviors were tested in the epoxidation of styrene, using air as the oxidant. The catalysts were characterized using infrared (IR) and Raman spectroscopies, thermogravimetric analyses, inductively coupled plasma atomic emission spectrometry (ICP‐AES), X‐ray diffraction, nitrogen adsorption–desorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). IR spectroscopy, thermogravimetric analyses and ICP‐AES confirmed the successful incorporation of the metal Schiff base complexes onto GO . X‐ray diffraction, nitrogen adsorption–desorption, Raman spectroscopy, SEM and TEM showed the intact structure of the GO . Co-GO and Fe-GO showed high styrene conversion (90.8 versus 86.7%) and epoxide selectivity (63.7 versus 51.4%). Nevertheless, VO-GO showed poorer catalytic performance compared with Co-GO and Fe-GO . The recycling results of these heterogeneous catalysts showed good recoverability without significant loss of activity and selectivity within four successive runs. Copyright © 2015 John Wiley & Sons, Ltd.     

Catalytic efficacy of an oxido-peroxido tungsten(VI) complex: synthesis,X-ray structure and oxidation of sulfides and olefins

An oxido-peroxido tungsten(VI) complex [WO(O₂)L(CH₃OH)] using salicylidene benzoyl hydrazine as a tridentate ONO donor Schiff base (H₂L) has been synthesized and characterized by elemental analysis, IR, ¹H NMR, molar conductance data, and single-crystal X-ray analysis. The complex was used as a catalyst for epoxidation of olefins and oxidation of sulfides. The results show that epoxides and sulfoxides were produced in high yield, turnover number, and selectivity.