Olefins oxidation with molecular O2 in the presence of chiral Mn (III) salen complex supported on magnetic CoFe2O4@SiO2@CPTMS

In the present study, CoFe₂O₄@SiO₂@CPTMS nanocomposite was synthesized and the homogeneous chiral Mn‐salen complex was anchored covalently onto the surface of CoFe₂O₄@SiO₂@CPTMS nanocomposite. The heterogeneous Mn‐salen magnetic nanocatalyst (CoFe₂O₄@SiO₂@CPTMS@ chiral Mn (III) Complex) was characterized by different techniques including transmission electron microscopy (TEM), Fourier transform infrared (FT‐IR), vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), powder X‐ray diffraction (XRD) and thermogravimetric analysis (TGA). Then, the aerobic enantioselective oxidation of olefins to the corresponding epoxide was investigated in the presence of magnetic chiral CoFe₂O₄@SiO₂@Mn (III) complex at ambient conditions within 90 min. The results showed the corresponding products were synthesized with excellent yields and selectivity. In addition, the heterogeneous CoFe₂O₄@SiO₂@ CPTMS@ chiral Mn (III) complex has benefits such as high selectivity and comparable catalytic reactivity with its homogeneous analog as well as mild reaction condition, facile recovery, and recycling of the heterogeneous catalyst.     

Mn(III)-based reaction of alkenes with quinolinones. Formation of peroxyquinolinones and quinoline-related derivatives

The reactions of 1,1-disubstituted alkenes with 4-hydroxyquinolin-2(1H)-ones under both Mn(III)-catalyzed aerobic oxidation conditions at room temperature and Mn(III)-mediated oxidation conditions at reflux temperature are described. The Mn(III)-catalyzed aerobic oxidation afforded bis(hydroperoxyethyl)quinolinones and azatrioxa[4.4.3]propellanes, while the oxidation with Mn(OAc)₃·2H₂O produced furo[3,2-c]quinolin-4-one analogues. The existence of a substituent at the 3-position of the 4-hydroxyquinolin-2(1H)-ones prevented a double reaction with the alkenes, and (endoperoxy)quinolinones and/or (hydroperoxyethyl)quinolinones were obtained under the Mn(III)-catalyzed aerobic conditions, while furo[3,2-c]quinolinone hemiacetals and vinylquinolinones were selectively produced under the Mn(III)-mediated oxidation conditions depending on the reaction temperature and times. Cyclic assembly of quinolinone-related 1,3-dicarbonyl compounds such as dihydropyridinones, pyranones, and dimedone derivatives was also examined under elevated temperature conditions.     

Highly enantioselective homogeneous catalysis of chiral rare earth phosphates in the hetero-Diels-Alder reaction

Two types of novel rare earth (RE) complexes were synthesized and used as a chiral Lewis acid catalyst for the hetero-Diels-Alder reaction of carbonyl compounds with the Danishefsky's diene under homogeneous conditions. The Y[(R)-H₈-BNP]₃ (3-Y)-catalyzed reaction of aromatic aldehydes and the Yb[(R)-BNP]₃ (1-Yb)-catalyzed reaction of phenylglyoxylates afforded the corresponding cycloadducts with excellent optical purities (up to 99% ee) in high yields at room temperature. The successful recycling uses of the scandium catalyst (3-Sc) are also described.     

Substitution Patterns of Cellulose Ethers - Influence of the Synthetic Pathway

Commercial cellulose ethers are usually prepared under heterogeneous reaction conditions. In contrast, this contribution also describes the derivatization under homogeneous conditions in N-methylmorpholine-N-oxide monohydrate (NMMNO*H₂O) and under heterogeneous conditions after converting native cellulose to amorphous cellulose. Amorphous cellulose is prepared by dissolving cellulose in NMMNO*H₂O followed by precipitation in different media. The degree of order and the porosity of the regenerated cellulose is significantly influenced by the content of water in the precipitating agent. The differences are described by measurements using wide angle X-ray scattering, solid-state ¹³C-NMR, mercury porosimetry, and water/liquid retention values. Three synthetic pathways (heterogeneous, heterogeneous with amorphous cellulose and homogeneous) are compared regarding the structure-property relationship of the cellulose ethers formed. Carboxymethylation, hydroxyethylation, hydroxypropylation and sulfoethylation are considered in detail. The choice of synthetic pathway has a significant influence on the degree of substitution (DS), the distribution of substituents on the level of the anhydroglucose unit (AGU), solubility behavior, and the viscosity of aqueous solutions. In general an increasing solubility and an increasing viscosity are observed from heterogeneous to heterogeneous with amorphous cellulose to homogeneous reaction conditions. There is a remarkable difference between the heterogeneously produced cellulose ethers with a DS distribution C2 ≥ C6 > C3 and the strictly homogeneous etherification in NMMNO*H₂O/organic solvent systems with a DS distribution of C3 > C2 ≫ C6. This high regioselectivity at the secondary OH-groups of the AGU may be caused by the strong solvation behavior of NMMNO*H₂O and thereby a protecting function at the C6-OH-group.     

Highly efficient C-H insertion reactions of hydrogen peroxide catalyzed by homogeneous and heterogeneous methyltrioxorhenium systems in ionic liquids

A convenient and efficient C-H insertion reaction of environment friendly H₂O₂ into representative hydrocarbon derivatives by homogeneous methyltrioxorhenium (MTO), heterogeneous poly(4-vinylpyridine)/methyltrioxorhenium (PVP/MTO) and microencapsulated polystyrene/methyltrioxorhenium (PS/MTO) systems in ionic liquids, is described. In some cases a higher activity was observed if compared with the same reaction in molecular solvents. The heterogeneous catalysts are stable systems under the reaction conditions and can be recycled for more transformations.     

Catalytic decomposition of organic peroxides by 4,4′-diamino-trans-stilbene (DTS)/montmorillonite complex: II.p-nitro andp-methyl dibenzoyl peroxide

The kinetics of the induced decomposition ofp-NO₂- andp-CH₃-dibenzoyl peroxide in the presence of 4,4-diamino-trans-stilbene (DTS) were studied in ethanol under both homogenous and heterogeneous conditions. The heterogeneous reaction was carried out in the presence of the DTS/montmorillonite complex. The decomposition reaction was found to be second order and three-halves order for the peroxide concentration in homogeneous and heterogeneous systems, respectively. The reaction was first order for the amine concentration in the homogeneous system. The activation energies for the decomposition reaction were obtained as 54.7±2 and 59.5±3 kJ mol^–1 forp-NO₂- andp-CH₃-dibenzoyl peroxides, respectively, in the homogeneous systems and are higher than the corresponding values of 41±1.5 and 47.6±1 kJ mol^–1 for thep-NO₂ andp-CH₃ derivatives in heterogeneous media.     

Enhanced Catalytic Activity of Cobalt Porphyrin in CO2 Electroreduction upon Immobilization on Carbon Materials

In a comparative study of the electrocatalytic CO₂ reduction, cobalt meso-tetraphenylporphyrin (CoTPP) is used as a model molecular catalyst under both homogeneous and heterogeneous conditions. In the former case, employing N,N-dimethylformamide as solvent, CoTPP performs poorly as an electrocatalyst giving low product selectivity in a slow reaction at a high overpotential. However, upon straightforward immobilization of CoTPP onto carbon nanotubes, a remarkable enhancement of the electrocatalytic abilities is seen with CO₂ becoming selectively reduced to CO (>90 %) at a low overpotential in aqueous medium. This effect is ascribed to the particular environment created by the aqueous medium at the catalytic site of the immobilized catalyst that facilitates the adsorption and further reaction of CO₂. This work highlights the significance of assessing an immobilized molecular catalyst from more than homogeneous measurements alone.     

Reactivity and regioselectivity in Stille couplings of 3-substituted 2,4-dichloropyridines

The influence of substituents at C-3 of 2,4-dichloropyridines on their reactivity and regioselectivity in Pd-catalyzed cross-couplings is studied. As a model reaction, the (Ph₃P)₂PdCl₂-catalyzed Stille coupling between 2-furyl(tributyl)tin and pyridines is chosen. Increased electron-withdrawing ability of a substituent at the pyridine 3-position improves the overall reactivity. Absolute selectivity for coupling at C-2 is achieved with an amino group at C-3, and the selectivity is totally reversed when the amino group is exchanged for a nitro substituent.     

Kinetic Study of the Catalyzed Substitution Reaction of Benzal Chloride and Sodium Iodide in Acetone

The substitution reaction of benzal chloride (PhCHCl₂) and sodium iodide in acetone needs a metal-ion catalyst. Without considering the effects of solubility and the dissociation of salt, salts of Cr(III), Mn(II), Fe(II, III), Co(II), Ni(II), Cu(II)m Zn(II), Cd(II), Hg(I, II), and Sb(III) ions are used to study their catalytic reactivities. It is found that the Fe(II) ion exhibits acceptable catalytic effect. The overall Fe(II)-catalyzed PhCHCl₂-NaI reaction can be described by the following competitive consecutive scheme: PhCHCl₂ → PhCHCII → PhCHI₂. Under suitable conditions, coupling products such as PhCH=CHPh and PhCHClCHClPh are also found. The rate of the first-stage substitution of the PhCHCl₂-NaI reaction increases linearly with the PhCHCl₂ concentration. It increases asymptotically with the FeCl₂ concentration. However, there is an optimum concentration for Nal. The apparent activation energies are 104 ± 4 kJ/mol and 133 ± 4 kJ/mol for the Fe(II)-catalyzed PhCHCl₂-NaI and PhCHCH-NaI reactions, respectively.     

Encapsulation of a binuclear manganese(II) complex with an amino acid-based ligand in zeolite Y and its catalytic epoxidation of cyclohexene

A Schiff base ligand was synthesized by the condensation of salicylaldehyde with l-tyrosine. Interaction of this ligand with Mn(II)-exchanged zeolite Y leads to encapsulation of the ligand within the zeolite and complexation of the metal. The encapsulated complex has been characterized by spectroscopic studies and chemical analyses. This material serves as a catalyst for the oxidation of cyclohexene to cyclohexene epoxide and 2-cyclohexene-1-ol using H₂O₂ as oxidant. The reaction conditions have been optimized for solvent, temperature and amount of oxidant and catalyst. The catalyst shows high activity and selectivity toward production of cyclohexene epoxide in acetonitrile at 60 °C with [H₂O₂]/[C₆H₁₀] = 2.5 molar ratio. Comparison of the encapsulated catalyst with the corresponding homogeneous catalyst showed that the heterogeneous catalyst had higher activity and selectivity than the homogeneous catalyst.     

The activity of solutions of Ru3(CO)12 as catalysts for the fischer-tropsch reaction

Solutions of dodecacarbonyl-triangulo-triruthenium [Ru₃(CO)₁₂] have been shown to be catalyst precursors for the Fischer-Tropsch reaction; the catalyst formed under the reaction conditions is heterogeneous; no indication of homogeneous activity was found.     

Towards a Practical Development of Light‐Driven Acceptorless Alkane Dehydrogenation

The efficient catalytic dehydrogenation of alkanes to olefins is one of the most investigated reactions in organic synthesis. In the coming years, an increased supply of shorter‐chain alkanes from natural and shale gas will offer new opportunities for inexpensive carbon feedstock through such dehydrogenation processes. Existing methods for alkane dehydrogenation using heterogeneous catalysts require harsh reaction conditions and have a lack of selectivity, whereas homogeneous catalysis methods result in significant waste generation. A strong need exists for atom‐efficient alkane dehydrogenations on a useful scale. Herein, we have developed improved acceptorless catalytic systems under optimal light transmittance conditions using trans‐[Rh(PMe₃)₂(CO)Cl] as the catalyst with different additives. Unprecedented catalyst turnover numbers are obtained for the dehydrogenation of cyclic and linear (from C₄) alkanes and liquid organic hydrogen carriers. These reactions proceed with unique conversion, thereby providing a basis for practical alkane dehydrogenations.     

Rhodium-Catalyzed Pauson–Khand-Type Cyclization of 1,5-Allene-Alkynes: A Chirality Transfer Strategy for Optically Active Bicyclic Ketones

An efficient chirality transfer in the [RhCl(CO)₂]₂-catalyzed [2+2+1] cyclization of optically active axially chiral 1,3-disubstituted allenynes with CO to access optically active bicyclopentenone compounds has been developed. The distal C=C bond of allenes reacted with the alknye unit and CO to afford [4.3.0]-bicyclic products with high ee values under mild reaction conditions with an excellent selectivity.     

Ruthenium(III)-catalyzed and uncatalyzed kinetic studies on the oxidation of sulfanilic acid by chloramine-T in perchloric acid medium: a mechanistic approach

The kinetics of the oxidation of sulfanilic acid (SAA) by sodium N-chloro-p-toluenesulfonamide (CAT) in the presence and absence of ruthenium(III) chloride have been investigated at 303 K in perchloric acid medium. The reaction shows a first-order dependence on [CAT]_o and a non-linear dependence on both [SAA]_o and [HClO₄] for both the ruthenium(III)-catalyzed and uncatalyzed reactions. The order with respect to [Ru^III] is unity. The effects of added p-toluenesulfonamide, halide, ionic strength, and dielectric constant have been studied. Activation parameters have been evaluated. The rate of the reaction increases in the D₂O medium. The stoichiometry of the reaction was found to be 1:1 and the oxidation product of SAA was identified as N-hydroxyaminobenzene-4-sulfonic acid. The ruthenium(III)-catalyzed reactions are about four-fold faster than the uncatalyzed reactions. The protonated conjugate acid (CH₃C₆H₄SO₂NH₂Cl⁺) is postulated as the reactive oxidizing species in both the cases.     

Mn(III) complex supported on Fe3O4 nanoparticles: magnetically separable nanocatalyst for selective oxidation of thiols to disulfides

A manganese(III) complex, [Mn(phox)₂(CH₃OH)₂]ClO₄ (phox?=?2-(2′-hydroxyphenyl)oxazoline), was immobilized on silica-coated magnetic Fe₃O₄ nanoparticles through the amino propyl linkage using a grafting process in dichloromethane. The resulting Fe₃O₄@SiO₂–NH₂@Mn(III) nanoparticles are used as efficient and recyclable catalysts for selective oxidation of thiols to disulfides using urea-hydrogen peroxide as the oxidant. The nanocatalyst was recycled several times. Leaching and recycling experiments revealed that the nanocatalyst can be recovered, recycled, and reused more than five times, without the loss of catalytic activity and magnetic properties. The recycling of the nanocatalyst in six consecutive runs afforded a total turnover number of more than 10,000. The heterogeneous Fe₃O₄@SiO₂–NH₂@Mn(III) nanoparticle shows more selectivity for the formation of disulfides in comparison with the homogeneous manganese complex.     

Synthesis,characterization and catalytic application of a new organometallic oligomer based on polyhedral oligomeric silsesquioxane

Although homogeneous catalysts provide high performance and selectivity, the difficulty of separation and recycling of these catalysts has bothered the scientific community worldwide. Therefore, the demand for heterogeneous catalysts that possess the advantages of homogeneous ones, with ease of separation and recyclability remains a topic of major impact. The oligomeric catalyst synthesized in this work was characterized using elemental analysis, Fourier transform infrared, ¹³C NMR, ²⁹Si NMR and energy‐dispersive X‐ray spectroscopies, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy and Brunauer–Emmett–Teller analysis and compared to its homogeneous counterpart [W(CO)₃Br₂(ATC)] in the epoxidation of 1‐octene, cyclooctene, (S )‐limonene, cis ‐3‐hexen‐1‐ol, trans ‐3‐hexen‐1‐ol and styrene. The results showed that the percentage conversion for the homogeneous species [W(CO)₃Br₂(ATC)] was slightly higher than for the oligomeric catalyst (POSS‐ATC‐[W(CO)₃Br₂]). Furthermore, the selectivity for epoxide of the oligomeric catalyst was greater than that of the homogeneous catalyst by about 25% when (S )‐limonene was used. Great conversions (yields) of products were obtained with a wide range of substrates and the catalyst was recycled many times without any substantial loss of its catalytic activity.     

Oxidation of alkenes catalysed by molybdenum(VI)–oxodiperoxo complex anchored on the surface of magnetic nanoparticles under solvent‐free conditions

A new epoxidation catalyst has been prepared by grafting a molybdenum(VI)–oxodiperoxo complex containing an oxazine ligand, [MoO(O₂)₂(phox)], on chloro‐functionalized Fe₃O₄ nanoparticles. The synthesized heterogeneous catalyst (MoO(O₂)₂(phox)/Fe₃O₄ was characterized using powder X‐ray diffraction, scanning and transmission electron microscopies, vibrating sample magnetometry, energy‐dispersive X‐ray analysis, Fourier transform infrared spectroscopy and inductively coupled plasma atomic emission spectroscopy. The immobilized complex gave high product yields and high selectivity for epoxide compared to the corresponding homogeneous one in the epoxidation of various olefins in the presence of tert ‐butyl hydroperoxide at 95°C without any co‐solvent. Also, the heterogeneous catalyst can be recycled without a noticeable change in activity and selectivity.     

Silica Chloride (SiO2-Cl) and Trimethylsilyl Chloride (TMSCl) Promote Facile and Efficient Dehydration of Tertiary Alcohols

Abstract

Silica chloride (SiO₂-Cl), as a heterogeneous reagent, has been used for the efficient dehydration of tertiary alcohols under mild reaction conditions. For comparison, we have also used trimethylsilyl chloride (TMSCl) as a homogeneous reagent for this purpose. We have found that silica chloride is a more efficient reagnet than trimethylsilyl chloride for this purpose. Handling of SiO₂-Cl is much safer and easier than TMSCl, especially for large-scale operation. The selectivity of the method is also demonstrated by several competitive reactions. Ether formation, rearranged products, and polymerization have not been observed in the reactions.     

12-Tungstophosphoric acid supported on inorganic oxides as heterogeneous and reusable catalysts for the selective preparation of alkoxymethyl ethers and their deprotections under different reaction conditions

A wide variety of primary and secondary alcohols were efficiently converted to their corresponding methoxymethyl (MOM) and ethoxymethyl (EOM) ethers in the presence of catalytic amounts of supported H₃PW₁₂O₄₀ on silica gel and zirconia at room temperature and under microwave irradiation at solvent-free conditions, whereas, phenols and tertiary alcohols remained intact under the same reaction conditions. Deprotection of these ethers to their parent alcohols was also achieved using these heterogeneous catalysts in ethanol, as a green solvent, under reflux conditions and microwave irradiation. Selective deprotection of primary and secondary MOM- and EOM-ethers in the presence of phenolic and tertiary ones, methyl and benzyl ethers, esters and trimethylsilyl ethers was achieved by these reagent systems. The present methodology offers several advantages such as short reaction times, high yields, simple procedure, heterogeneous reaction conditions, selectivity, non-toxicity and reusability of the catalysts.     

Stereoselective Aldol Reaction of α-Phenylseleno Esters

Abstract

The TiCl₄-catalyzed reaction of a-phenylseleno esters with aldehydes in the presence of Ph₃P or Ph₃P=O gives aldol products with high syn selectivity.