Achiral Dihydroxylation of Olefins by Osmate (OsO42−) Stabilised on Nanocrystalline Magnesium Oxide

A recoverable and reusable new heterogeneous AP‐Mg‐OsO₄ catalyst was designed and developed for the first time via a counterionic stabilisation of OsO₄²⁻ with Mg²⁺ present on the corner or edge of nanocrystalline MgO. AP‐Mg‐OsO₄ catalysed the dihydroxylation of olefins to afford diols with excellent yields in the presence of N‐methylmorpholine N‐oxide for the first time. The absence of osmium and no progress of the dihydroxylation reaction with the filtrate samples withdrawn periodically during the reaction rule out the leaching of osmium unambiguously and provide evidence for the heterogeneity of the reaction. Identification of surface intermediate species by XPS and TGA‐DTA‐mass thermography gives an insight into the mechanism of the dihydroxylation reaction.     

A Novel Chemoentrapment Approach for Supportless Recycling of a Catalyst: Catalytic Asymmetric Dihydroxylation

A simple method of recycling a metal catalyst through chemoentrapment in an aqueous layer using ethyl vinyl ether has been developed. Using this new methodology, a highly efficient, filtration‐free recycling of osmium for catalytic asymmetric dihydroxylation was accomplished. By means of the formation of a water‐soluble OsO₄²⁻ using EVE, AD reactions of mono‐ and disubstituted olefins with 1 mol % of OsO₄ proceeded for up to 9 cycles without any loss of yields and enantioselectivities.     

Silica Gel‐Supported Cinchona Alkaloid‐OsO4 Complex for Catalytic Heterogeneous Asymmetric Dihydroxylation of Olefins by H2O2 using a Titanium Silicalite‐Based Coupled Catalytic System

A triple catalytic system designed for asymmetric dihydroxylation of olefins, composed of NMM and two divergent heterogeneous catalysts, titanium silicalite and silica gel‐supported 1,4‐bis(9‐O‐dihydroquinidinyl)phthalazine [SGS‐(DHQD)₂PHAL)]‐OsO₄ complex relays the transport of two electrons from olefin to H₂O₂ used as a terminal oxidant to provide chiral diols with good yields and high enantiomeric excesses in a single pot.     

Nanocrystalline Magnesium Oxide‐Stabilized Palladium(0): An Efficient and Reusable Catalyst for Suzuki and Stille Cross‐Coupling of Aryl Halides

A nanocrystalline magnesium oxide‐stabilized palladium(0) catalyst is prepared by counterion stabilization of PdCl₄²⁻ with nanocrystalline MgO followed by reduction. This ligand‐free heterogeneous nanocrystalline MgO‐stabilized nanopalladium [NAP Mg Pd(0)] catalyst using the basic MgO in place of basic ligands exhibits excellent activity in Suzuki and Stille cross‐coupling of haloarenes (chloro, bromo and iodo) to afford the unsymmetrical biaryls. The catalyst is quantitatively recovered by simple filtration and reused for four cycles with almost consistent activity.     

TiOx/Pd interfacial catalysts with controllable geometrical/electronic effects for industrial H2O2 production

Aiming at controllable modulating metal−support interactions to achieve an optimal trade-off of geometric/electronic effect in supported catalysts, we developed a reliable approach based on the typical 2D material layered double hydroxide (LDHs). A series of TiO_x/Pd/MgTiAl-MMO-X catalysts with adjustable interfacial effect were acquired by loading PdCl₄²⁻ precursor and further preciously adjusting the topological reduction temperature, based on the regulatory effect of Mg–O–Ti–O–Al–O structure in the support on the reducibility and mobility of Ti⁴⁺. The catalysts with semi-continuous and accessible TiO_x/Pd interface, confirmed by AC-HAADF-STEM, CO chemisorption, XPS, exhibit much higher H₂O₂ yield than the catalyst with over-encapsulation structure. The TiO_x/Pd/MgTiAl-MMO-450 catalysts possessed optimal geometric and electronic structure exhibited the highest activity with TOF of 9.75 s⁻¹, excellent H₂O₂ yield of 11.4 g/L, as well as good stability.     

Effects of inorganic salts on the spectral behavior of poly(N‐vinyl‐2‐pyrrolidone) in aqueous solutions

Electronic spectral behavior of poly(N‐vinyl‐2‐pyrrolidone) (PVP) was determined in aqueous solutions including a variety of inorganic salts (phosphates, mono‐ and dihydrogen phosphates, sulfates, chlorides, nitrates, bisulfites, and persulfates) for several concentrations. The n → π* excitations are shifted to longer wavelengths depending on the nature and the concentration of salt. The resulting dependence of λ_max on the molar concentration can be expressed to show the increasing effect of anionic and cationic species in bathochromic shift. The increasing order of effectiveness of anions in shifting the λ_max is S₂O₈ ⁼ > S₂O₅ ⁼ > PO₄ ³⁻ > HPO₄ ²⁻ > SO₄ ²⁻ > H₂PO₄ ²⁻ > Cl⁻. The order for the cation is as Na⁺ ≈ K⁺ ≈ NH₄ ⁺ in the 0.1–0.6M concentration range and Na⁺ ≈ K⁺ > NH₄ ⁺ in > 0.6M aqueous solutions. The changes observed in λ_max by the salt were correlated with the changes occurring in the structure of water and the polymer–solvent interactions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1434–1439, 2000     

Fast swelling behaviors of thermosensitive poly(N‐isopropylacrylamide‐co‐methacryloxyethyltrimethyl ammonium chloride)/Na2WO4 cationic composite hydrogels

A facile method was explored to synthesize thermosensitive poly[N‐isopropylacrylamide (NIPAM)‐co‐methacryloxyethyltrimethyl ammonium chloride (DMC)]/Na₂WO₄ cationic hydrogels via copolymerization of NIPAM and DMC in the presence of Na₂WO₄. Na₂WO₄ acted as both a physical crosslinking agent and a porogen precursor. The hydrogels were characterized by Fourier transform infrared spectroscopy, energy dispersive X‐ray, thermogravimetry, environmental scanning electron microscopy, and transmission electron microscopy. Effects of various salt solutions, pH solutions on swelling were investigated. Thermosensitivity of the hydrogels were also investigated in various polar solvents at different temperatures. The resultant hydrogel showed a fast swelling rate and good salt tolerance. The hydrogels reached the swelling equilibrium within 10 min. Moreover, the swelling ratio of the hydrogels increased with the increase of the polarity of the solvent. In the water, the swelling ratio decreased with the increasing of temperature, but remained at a high level even at 80 °C since the pore structure weaken the lower critical solution temperature effect of PNIPAM. The swelling ratio increased instead in low polar solvent, while it became negligible in nonpolar solvent with the increasing of temperature. The whole swelling kinetics was fit for Schott's pseudo‐second order model. The hydrogels have a great potential as catalysts and smart materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46375.     

Microencapsulated Osmium Tetroxide‐Catalyzed Asymmetric Dihydroxylation of Olefins in Water without Using Organic Cosolvents

The asymmetric dihydroxylation of olefin using phenoxyethoxymethyl‐polystyrene (PEM)‐based microencapsulated osmium tetroxide (PEM‐MC OsO₄) proceeded smoothly in water as the sole solvent. The catalyst was recovered quantitatively by simple filtration and reused several times without loss of activity.     

Manganese‐containing redox catalysts for selective hydrogen combustion under a cyclic redox scheme

Selective hydrogen combustion (SHC) in the presence of light hydrocarbons was demonstrated with a series of Mn‐containing mixed oxide redox catalysts in the context of a chemical looping‐oxidative dehydrogenation scheme. Unpromoted and 20 wt % Na₂WO₄‐promoted Mg₆MnO₈, SrMnO₃, and CaMnO₃ exhibited varying SHC capabilities at temperatures between 550 and 850°C. Reduction temperature of unpromoted redox catalysts increased in the order Mg₆MnO₈ < SrMnO₃ < CaMnO₃. Promotion with 20 wt % Na₂WO₄ resulted in more selective redox catalysts capable of high‐temperature SHC. XPS analysis revealed a correlation between suppression of near‐surface Mn and SHC selectivity. Na₂WO₄/CaMnO₃ showed steady SHC performance (89% H₂ conversion, 88% selectivity) at 850°C over 50 redox cycles. In series with a Cr₂O₃/Al₂O₃ ethane dehydrogenation catalyst, Na₂WO₄/CaMnO₃ combusted 84% of H₂ produced while limiting CO_x yield below 2%. The redox catalysts reported can be suitable for SHC in a cyclic redox scheme for the production of light olefins from alkanes. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3141–3150, 2018     

Heterogeneous Bifunctional Catalysts for the Synthesis of Chiral Vicinal Diols

Heterogeneous bifunctional catalysts consisting of palladate–osmate and osmate–tungstate developed by the ion exchange on quaternary ammonium salts covalently bound to resin, and their homogeneous bimetallic analogs are evaluated for the synthesis of chiral vicinal diols. The heterogeneous bifunctional catalyst (resin-PdOs) and its homogeneous analog are used in the tandem Heck-asymmetric dihydroxylation (AD) to afford diols with excellent yields and enantiomeric excesses (ee's) in the presence of various co-oxidants. The other bifunctional catalyst (resin-OsW) and its homogeneous analog are used in a simultaneous asymmetric dihydroxylation-N-oxidation of a wide range of olefins to obtain chiral vicinal diols with higher yields and ee's using H₂O₂ as terminal oxidant. The bifunctional resin catalysts are recovered quantitatively by a simple filtration and reused for a number of cycles with consistent activity.     

MCM-41 Anchored Cinchona Alkaloid for Catalytic Asymmetric Dihydroxylation of Olefins: A Clean Protocol for Chiral Diols Using Molecular Oxygen

MCM-41 anchored 1,4-bis(9-O-quininyl)phthalazine (MCM-(QN)₂PHAL)-OsO₄, is prepared for the first time and used in the heterogeneous asymmetric dihydroxylation of olefins to afford diols with good to excellent enantiomeric excesses in the presence of N-methylmorpholine N-oxide, K₃Fe(CN)₆ or molecular oxygen as cooxidants.     

Efficient Anchorage of Palladium Nanoparticles on the Multi‐Walled Carbon Nanotubes as Electrocatalyst for the Hydrazine Electrooxidation in Strong Acidic Solutions

A facile homogeneous precipitation–reduction reaction method, which involves PdCl₂ → PdO · H₂O → Pd⁰ reaction path, is used to synthesize the multi‐walled carbon nanotubes (MWCNTs) supported Pd nanoparticles (Pd/MWCNTs) catalysts. The particle size of Pd/MWCNTs catalysts can be easily tuned by controlling the hydrolysis temperature of PdCl₂. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) measurements show the particle size of Pd/MWCNTs catalysts increases with hydrolysis temperature of PdCl₂, which is ascribed to the fact that the particle size of PdO · H₂O nanoparticles increases with hydrolysis temperature of PdCl₂. At the lower hydrolysis temperature, the as‐prepared Pd/MWCNTs catalyst possesses the higher dispersion and the smaller particle size. Consequently, the resultant Pd/MWCNTs catalyst exhibits the big electrochemical active surface area and the excellent electrocatalytic performance for hydrazine electrooxidation in strong acidic solutions. In addition, the electrochemical measurement indicate that particle size effect of Pd‐NPs occurs during the N₂H₄ electrooxidation. In brief, the mass activity and specific activity of the Pd/MWCNTs catalyst increases and decreases with decreasing the particle size of Pd‐NPs for the N₂H₄ electrooxidation, respectively.     

Fe(PyTACN)‐Catalyzed cis‐Dihydroxylation of Olefins with Hydrogen Peroxide

A family of iron complexes with general formula [Fe(II)(^R,Y,XPyTACN)(CF₃SO₃)₂], where ^R,Y,XPyTACN=1‐[2′‐(4‐Y‐6‐X‐pyridyl)methyl]‐4,7‐dialkyl‐1,4,7‐triazacyclononane, X and Y refer to the groups at positions 4 and 6 of the pyridine, respectively, and R refers to the alkyl substitution at N‐4 and N‐7 of the triazacyclononane ring, are shown to be catalysts for efficient and selective alkene oxidation (epoxidation and cis‐dihydroxylation) employing hydrogen peroxide as oxidant. Complex [Fe(II)(^Me,Me,HPyTACN)(CF₃SO₃)₂] ( 7 ), was identified as the most efficient and selective cis‐dihydroxylation catalyst among the family. The high activity of 7 allows the oxidation of alkenes to proceed rapidly (30 min) at room temperature and under conditions where the olefin is not used in large amounts but instead is the limiting reagent. In the presence of 3 mol% of 7 , 2 equiv. of H₂O₂ as oxidant and 15 equiv. of water, in acetonitrile solution, alkenes are cis‐dihydroxylated reaching yields that might be interesting for synthetic purposes. Competition experiments show that 7 exhibits preferential selectivity towards the oxidation of cis olefins over the trans analogues, and also affords better yields and high [syn‐diol]/[epoxide] ratios when cis olefins are oxidized. For aliphatic substrates, reaction yields attained with the present system compare favourably with state of the art Fe‐catalyzed cis‐dihydroxylation systems, and it can be regarded as an attractive complement to the iron and manganese systems described recently and which show optimum activity against electron‐deficient and aromatic olefins.     

Ion-cyclotron resonance study of elementary stages of the catalytic oxidation of CO by N2O in the presence of VIA-group metal ions

Gas phase reactions of Mo⁺ and W⁺ ions with the molecules of various oxidants (NO, O₂, N₂O, CH₂O, C₂H₄O) were studied using ion cyclotron resonance. In oxidation with N₂O the mono-, di- and trioxide metal cations are formed consecutively. The trioxide MO₃ ⁺ ions of both metals react with CO to form CO₂ and MO₂ ⁺ ions. In this way, catalytic reaction N₂O + CO N₂ + CO₂ occurs in the gas phase with MoO₃ ⁺ /MoO₂ ⁺ and WO₃ ⁺/WO₂ ⁺ couples as catalysts. The rate constants have been measured for both stages of the catalytic cycle as well as for the stages of the catalyst preparation. Metal-oxygen bond energies were estimated for MoO_x ⁺ and WO_x ⁺ species with various x. The mechanism of CO oxidation with MoO_x ⁺ and WO_x ⁺ cations as catalysts in the gas phase is discussed in comparison with that for the oxidation over classical solid oxide catalysts.     

Polymerization of N-substituted 2-propynamides with transition metal catalysts

Summary Polymerization of N-substituted 2-propynamides proceeded in the presence of Pd(II) catalysts such as [Pd(CH₃CN)₄](BF₄)₂, PdCl₂(PhCN)₂-n-BuLi, and PdCl₂(nbd)-n-BuLi. The molecular weights of the obtained polymers ranged 8,500 to 14,000, depending on the catalysts. From the ¹H NMR spectra, these polymers were found to have alternating double bonds in the main chain. Received: 25 December 2000/Revised version: 17 January 2001/Accepted: 19 January 2001     

Sharpless Asymmetric Dihydroxylation of Olefins in WaterSurfactant Media with Recycling of the Catalytic System by Membrane Nanofiltration

This paper presents a new and more sustainable alternative approach for the Sharpless catalytic asymmetric dihydroxylation (AD) of olefins using a water/surfactant system as reaction media. The AD reaction was performed using several cationic and anionic surfactants allowing yields and enantiomeric excesses higher or comparable with the conventional systems (using organic mixtures). The use of this water/surfactant medium offers the additional advantage of performing the reactions without the need of a slow addition of olefins. Asymmetric dihydroxylation of 1‐hexene in a 1.5 mM sodium cholate aqueous solution, using N‐methylmorpholine N‐oxide (NMO) as co‐oxidant was selected as model system to evaluate the feasibility of recycling the Sharpless catalytic system by nanofiltration. The reaction media was processed by nanofiltration, the product was isolated in the permeate, whereas the catalytic system and surfactant were retained by the membrane and recycled through six successive reactions, improving the catalyst turn‐over number. The experimental results were compared with the ones calculated on the basis of mass balances, membrane rejections to product and reaction yields.     

Effect of precipitants during the preparation of Cu-ZnO-Al2O3/Zr-ferrierite catalyst on the DME synthesis from syngas

The synthesis of dimethyl ether (DME) from biomass-derived model synthesis gas has been investigated on Cu-ZnO-Al₂O₃/Zr-ferrierite bifunctional catalysts. The catalysts are prepared by co-precipitation–impregnation method using Na₂CO₃, K₂CO₃ and (NH₄)₂CO₃ as the precipitants. The catalytic activity tests reveal that the best yield of DME can be obtained on the catalyst precipitated by using (NH₄)₂CO₃. Detailed characterization studies conducted on the catalysts to measure their properties such as surface area, acidity by temperature-programmed desorption of ammonia (NH₃-TPD), reducibility of Cu oxide by temperature-programmed reduction (TPR), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and copper surface area and particle size measurements by N₂O titration method. Increasing the number of moderate acidic sites and facilitation of easily reducible copper species with small particle size are found to be the prime reasons for the superior functionality of the (NH₄)₂CO₃ precipitated catalyst. The usage of (NH₄)₂CO₃ also leaves no residual ions, whereas the presence of residual K⁺ and Na⁺ ions in the case of K₂CO₃ and Na₂CO₃ precipitated catalysts leads to lower activity and selectivity.     

Synthesis of cubic sodium tungsten bronze NaxWO3 in air

A solid‐state reaction route was used to synthesis cubic sodium tungsten bronze, Na_xWO₃. The Na_xWO₃ crystals were successfully prepared through reducing Na₂WO₄ with boron carbide (B₄C) in air condition, followed by washing with hot‐water. The solid‐state reaction between Na₂WO₄ and B₄C occurred at 600‐700°C, and the insertion amount of sodium ion is as high as 0.82. The obtained Na_xWO₃ crystals present an orange color, and the crystal size can grow to ~40 μm in just 20 minutes. The advantage of the method lies in the potential energy and cost savings over other conventional synthetic routes.     

Polymeric cinchona alkaloids for the catalytic asymmetric dihydroxylation of olefins

Three cinchona alkaloid copolymers (PMMA‐BQTP, PMA‐BQTP, PAN‐BQTP) have been synthesized by copolymerization. Their structure was characterized by FTIR, GPC, and element analysis. The catalytic activity of these copolymers in asymmetric dihydroxylation (AD) of olefins by OsO₄ was studied. The products enantiomeric excesses (ee) and the conversion of the substrate in the dihydroxylation reactions were determined using HPLC. The effect of time, temperature, and recycle times on the reaction was also discussed. The results showed that the copolymers catalyzed the dihydroxylation of the olefins to get diols in high optical yield. However, their catalytic efficiency was largely depended on the nature of olefins. The polymeric cinchona alkaloid can be simply recovered at the end of the reaction by centrifugation and then reused without radical change of activity or enantioselectivity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The Cation Radical Chain Cycloaddition Polymerization of N,3‐Bis(trans‐1‐2)carbazole: The Critical Importance of Intramolecular Hole Transfer in Cation Radical Cycloaddition Polymerization

The synthesis and polymerization of N,3‐[bis(trans‐1‐2)]carbazole ( 1 ) is reported. Using either the stable cation radical salt tris(4‐2)aminium hexachloroantimonate ( 2 ^+. ) or anodic oxidation to initiate the reaction, novel cycloaddition polymers are obtained in which the intermonomer linkages are of the cyclobutane, and to some extent of the Diels−Alder, type. A novel cation radical chain mechanism is proposed for the reaction, and extensive support for this mechanism is presented. The greatly enhanced reactivity of difunctional, as opposed to monofunctional, substrates in cation radical cycloadditions is dramatically highlighted by a comparison of the cycloaddition reactivity (rapid polymerization) of 1 versus N‐propenylcarbazole (inefficient cyclodimerization) under electrochemical oxidation conditions. The sharply enhanced reactivity of 1 is attributed to the availability of intramolecular hole transfer in the bifunctional but not the monofunctional case.