Alkoxide Catalyst Research Articles

Polystyrenic porphyrins as catalysts for alkane oxidation

We report herein the catalytic effect of metalloporphyrins (MnP–PS, CoP–PS, ZnP–PS) covalently bonded with one or four arms of polystyrene. These metalloporphyrins were employed as active catalysts for oxidation of ethylbenzene in the presence of freshly prepared O2. Our results show that one-arm polystyrenic porphyrins demonstrate enhanced catalytic efficiency, with better yield as compared with four-arm polystyrenic porphyrins. In addition, the catalytic efficiencies of the studied metalloporphyrins, calculated from gas chromatography–mass spectrometry (GC–MS) analysis, were found to be dependent on the central metal in the order Mn > Co > Zn. We also found that these catalysts have advantages of higher stability, facile separation, and good recyclability with comparable efficiencies.

Gold on thiol-functionalized magnetic mesoporous silica sphere catalyst for the aerobic oxidation of olefins

We have synthesized a new catalyst based on thiol-functionalized silica-coated magnetic mesoporous nanocrystals as support and Au nanoparticles as active sites through a facile and environment-friendly approach and characterized by transmission electron microscopy (TEM), N2 adsorption–desorption, elemental analysis and inductive coupled plasma atomic emission spectrometer (ICP-AES), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometry (VSM). The synthesized catalyst exhibited high catalytic activity in the oxidations of cyclohexene and styrene by molecular oxygen at atmospheric pressure. Furthermore, this catalyst had an excellent recyclability, evidenced by being extensively reused for five times without any substantial loss of activity, which was mainly attributed to the enough strong combination between the Au nanoparticles and thiol groups onto the surface of support. Meanwhile, the catalyst could be easily separated from the reaction solution by applying an external magnetic field.

Cobalt salophen complex supported on imidazole functionalized magnetic nanoparticles as a recoverable catalyst for oxidation of alkenes

A new magnetically separable catalyst consisting of Co(II) salophen complex covalently supported on imidazole functionalized silica coated cobalt ferrite was prepared. The synthesized catalyst was characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), thermogravimetric analysis (TGA), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and Fourier transform infrared (FT-IR). The immobilized catalyst was shown to be an efficient heterogeneous catalyst for the oxidation of some alkenes using hydrogen peroxide (H2O2) as oxidant. The catalyst could be easily and efficiently isolated from the final product solution by magnetic decantation and be reused for 5 consecutive reactions without showing any significant activity degradation.

Preparation of macrodiols and polyols by chopping high‐molecular‐weight aliphatic polycarbonates

ABSTRACTHigh‐molecular‐weight poly(1,4‐butylene carbonate) (PBC) (Mn: 40,000−90,000) was prepared through the condensation polymerization of dimethyl carbonate (DMC) and 1,4‐butanediol (BD) in the presence of 0.05 mol % sodium alkoxide catalyst. The subsequent feeding of 15 mol % HOAOH, such as 1,6‐hexanediol, 1,5‐pentanediol, 1,4‐cyclohexanedimethanol, or 1,4‐benzenedimethanol and stirring at 190–150 °C converted the extremely thick high‐molecular‐weight polymer to low‐molecular‐weight macrodiols with GPC‐measured Mn ∼2000. The analysis of the 1H NMR spectra indicated that the –A– units and 1,4‐butylene units were randomly distributed in the resulting oligomers. The chopping of the high‐molecular‐weight PBC using either triols or tetraols such as glycerol propoxylate, 1,1,1‐tris(hydroxymethyl)ethane, or pentaerythritol also afforded macropolyols containing branched chains with GPC‐measured Mn ∼2000. When the chopped polymers were genuine PBCs, the resulting macrodiols or polyols were in a waxy state at room temperature. However, permanently oily compounds were obtained when the chopped polymers were prepared using 0.90 mole fraction of BD admixed with various other diols. The macrodiols and polyols synthesized in this study may have potential applications in the polyurethane industry. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1570–1580

Characteristics of silica-supported tin(II) methoxide catalysts for ring-opening polymerization (ROP) of L-lactide

Supported Sn(OMe)2 catalysts were prepared on pretreated silica with various tin contents. A series of bulk polymerizations of l-lactide were conducted with homogeneous methoxide catalyst and silica-supported tin alkoxide catalyst to compare with their characteristics of the polylactide (PLA) produced. The conversion of l-lactide with the silica-supported methoxide catalysts was higher than that with the homogeneous catalyst at each monomer/catalyst molar ratio. The highest catalytic conversion and propagation constant (kp) was achieved at 180°C. The spent catalyst was successfully recovered up to 85% by simple filtration of the polymer product. The heterogeneous catalyst system is advantageous for recycling the catalyst and the production of highly purified, metal-free grade PLA.

Chromium(vi) grafted mesoporous polyaniline as a reusable heterogeneous catalyst for oxidation reactions in aqueous medium

A new Cr(VI)-grafted mesoporous polyaniline material (Cr-MPANI) has been prepared via simple and facile in situ radical polymerization of aniline followed by reaction with potassium dichromate. This material has been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), UV-vis diffuse reflectance spectroscopy (DRS) and Thermogravimetric analysis (TGA). Powder XRD and TEM studies suggested the presence of mesophase and disordered wormhole-like mesopores in this sample. Cr-MPANI acts as a very efficient catalyst for the liquid phase oxidation of alkenes, alkanes and aromatic alcohols using 30% H2O2 as oxidant in water. Oxidation reactions were carried out under very mild conditions, and the desired products were obtained with very high selectivity and relatively high yields. Cr-MPANI can be recycled more than five times without an appreciable loss in activity for its respective catalytic reactions.

Synthesis, structural characterization and application of a 2D coordination polymer of Mn-terephthalate as a heterogeneous catalyst for olefin oxidation

A metal–organic coordination polymer of [Mn3(1,4-benzenedicarboxylate)3(DMF)4] ([Mn3(BDC)3(DMF)4]n) was synthesized and characterized by IR spectra, elemental analysis (CHN), thermal gravimetric analysis (TGA) and single crystal X-ray diffraction analysis. The structure of [Mn3(BDC)3(DMF)4]n is a 2D-periodic framework based on Mn(II)-terephthalate secondary building units (SBUs). The catalytic oxidation of various olefins was effectively carried out with [Mn3(BDC)3(DMF)4]n. Moreover, the influence of key reaction parameters, including the solvents, reaction temperatures and nature of oxidant were studied. The optimized conditions were achieved by TBHP as the efficient oxidant in 1,2-dichloroethane solvent at 75°C. Finally, this catalyst was used for four cycles efficiently without a significant loss of yield.

Using Reduced Catalysts for Oxidation Reactions: Mechanistic Studies of the “Periana-Catalytica” System for CH4 Oxidation

Designing oxidation catalysts based on CH activation with reduced, low oxidation state species is a seeming dilemma given the proclivity for catalyst deactivation by overoxidation. This dilemma has been recognized in the Shilov system where reduced Pt(II) is used to catalyze methane functionalization. Thus, it is generally accepted that key to replacing Pt(IV) in that system with more practical oxidants is ensuring that the oxidant does not over-oxidize the reduced Pt(II) species. The "Periana-Catalytica" system, which utilizes (bpym)Pt(II)Cl2 in concentrated sulfuric acid solvent at 200 °C, is a highly stable catalyst for the selective, high yield oxy-functionalization of methane. In lieu of the over-oxidation dilemma, the high stability and observed rapid oxidation of (bpym)Pt(II)Cl2 to Pt(IV) in the absence of methane would seem to contradict the originally proposed mechanism involving CH activation by a reduced Pt(II) species. Mechanistic studies show that the originally proposed mechanism is incomplete and that while CH activation does proceed with Pt(II) there is a solution to the over-oxidation dilemma. Importantly, contrary to the accepted view to minimize Pt(II) overoxidation, these studies also show that increasing that rate could increase the rate of catalysis and catalyst stability. The mechanistic basis for this counterintuitive prediction could help to guide the design of new catalysts for alkane oxidation that operate by CH activation.

Syntheses, crystal structures, and catalysis by polymeric dioxomolybdenum(VI) complexes with similar (iso)nicotinohydrazones

Polymeric dioxomolybdenum(VI) complexes, [MoO2L]n (L = L1 = N′-(2-hydroxybenzylidene)nicotinohydrazide for 1, L = L2 = N′-(2-hydroxy-5-methoxybenzylidene)isonicotinohydrazide for 2), were prepared and characterized by physico-chemical, spectroscopic methods, and single-crystal X-ray determination. Complex 1 crystallizes in the orthorhombic space group P212121 with a = 7.6568(4), b = 11.6315(7), c = 15.2211(9) Å, V = 1355.59(13) Å3, Z = 4, R 1 = 0.0181, wR 2 = 0.0464, and S = 1.097. Complex 2 crystallizes in the monoclinic space group P2 1 /n with a = 11.2516(6), b = 11.8134(7), c = 12.4371(6) Å, β = 116.2210(10)°, V = 1483.02(14) Å3, Z = 4, R 1 = 0.0399, wR 2 = 0.0874, and S = 1.096. X-ray analysis indicates that Mo in each complex is octahedral with two oxo groups and N2O2 donor set of the nicotinohydrazone or isonicotinohydrazone. The complexes are efficient catalysts for oxidation of olefins.

Electrochemical and Catalytic Studies of a Manganese(III)Complex with a Tetradentate Schiff‐Base Ligand Encapsulated in NaY Zeolite

The manganese(III) complex with a Schiff-base salen-type ligand (1,5-bis{[(1E)-(2-hydroxyphenyl)methylene]amino}-1H-imidazole-4-carbonitrile) has been encapsulated in the nanopores of a Y zeolite by using two different methodologies, the flexible ligand and in situ complex preparation methods. Cyclic voltammetry studies revealed that the neat complex undergoes reversible oxidation in dmf, which has been attributed to the MnII/III redox couple, whereas the two heterogeneous catalysts show different electrochemical behaviour in aqueous medium. The encapsulated and non-encapsulated homogeneous MnIIIsalen complexes were screened as catalysts for olefin oxidation by using tBuOOH as the oxygen source in different solvents. Under the optimized conditions, the catalysts exhibited moderate activity. Both heterogeneous catalysts catalysed the oxidation of cyclohexene with tBuOOH, primarily to give the allylic oxidation products. These catalysts were found to be reusable after the catalytic cycle, but with some loss of activity. A DFT study confirmed the distortion of the complex in the zeolite cage, the main difference being observed for the bonded chloride.

Synthesis and characterisation of cobalt, nickel and copper complexes with tripodal 4N ligands as novel catalysts for the homogeneous partial oxidation of alkanes

Four new compounds of the general formula [M(L)(CH3COO)][PF6], where L is a tetradentate tripodal ligand such as tris[2-(dimethylamino)ethyl]amine (L1) or (2-aminoethyl)bis(2-pyridylmethyl)amine (L2) and M is Co(II), Ni(II) or Cu(II), have been prepared employing a simple two-step synthesis. The compounds have been characterised by elemental analysis, mass spectroscopy, IR spectroscopy and X-ray diffraction. The catalytic properties of the derivatives containing the aliphatic ligand L1 have been investigated in particular toward the oxidation of cyclohexane and adamantane in the presence of the sacrificial oxidant m-CPBA (meta-chloroperbenzoic acid). Good TONs and selectivity have been determined for the cobalt and nickel compounds.

ChemInform Abstract: Catalytic, Mild, and Selective Oxyfunctionalization of Linear Alkanes: Current Challenges.

AbstractReview: 166 refs.

A sandwich N-doped graphene/Co3O4 hybrid: an efficient catalyst for selective oxidation of olefins and alcohols

A sandwich-like N-doped graphene/Co3O4 hybrid was prepared via a simple one-pot hydrothermal reaction in a solution of NH3. Characterizations disclosed that highly dispersed Co3O4 nanoparticles with dominant exposed {112} and {110} planes were fabricated on both sides of well-exfoliated N-doped graphene; N-dopants in the graphene matrix can prevent re-graphitization of graphene, strengthen the interaction between Co3O4 and the graphene matrix, and improve the dispersion of Co3O4. This hybrid (Co3O4/RGO-N) exhibited superior activity and stability for the epoxidation of styrene compared to bulk Co3O4 and N-free graphene supported Co3O4. At the same time, the resulting catalyst also showed high compatibility with various olefins and alcohols with good conversion and high selectivity. This synergistic strategy can provide simple, efficient and versatile blue-prints for low-cost fabrication of graphene-based nanocomposites for extending applications where graphene has rarely been exploited and beyond.

Single-site bismuth alkoxide catalysts for the ring-opening polymerization of lactide

Salen bismuth alkoxides, where the salen ligand contains 2,4-di-tert-butylphenoxy groups and one of ethylene, cyclohexane or ortho-phenyl as a backbone have been prepared from reactions involving Bi[N(SiMe₃)₂]₃ and the free salen ligand followed by alcoholysis (ButOH, PriOH and 2,6-But₂C₆H₃OH). The molecular structures of the salen ligand with the cyclohexyl back-bone have been determined for the complexes salenBiCl and salenBiOC₆H₃-2,6-But₂. The chloro compound is a dimer with chloride bridges while the phenoxide is monomeric with an unusually distorted five-coordinate geometry. The phenoxide and tert-butoxide complexes have been employed in the ring-opening polymerization of lactides (L- and rac-) to give polylactides, PLAs. With rac-LA heterotactic PLA is formed preferentially, Pr = ~0.9, in dichloromethane or toluene at room temperature. The reaction is first order in [Bi] and is notably faster than most aluminum and zinc initiators as well as tin(II) octanoate. These results are discussed in terms of a recent report on the polymerization of LA by Peptobismol® and bismuth subsalicylate.

Yttrium catalysts for syndioselective β-butyrolactone polymerization: on the origin of ligand-induced stereoselectivity

Synthesis of aliphatic polyesters has been studied intensively due to their biocompatible and biodegradable properties and their applications in medical and agricultural fields. Among them, polyhydroxybutyrate (PHB), which is a naturally occurring polymer, is synthesized by a variety of bacteria and algae. However, this polymer has poor mechanical properties due to its brittleness. Herein is presented a practical route to a highly syndiotactic PHB by way of a one-pot reaction. We report the results of a comprehensive investigation of the newly discovered stereoselective and controlled polymerization of racemic β-butyrolactone (rac-BBL) using an initiator prepared in situ from yttrium(III) isopropoxide Y(OiPr)3, and a bisphenoxide ligand. DFT studies on the alkoxide catalyst reveal that the R and S monomers are almost equivalent for the first ring-opening reaction. The selectivity of the next insertion was scrutinized, demonstrating that the polymerization process is predicted to be stationary (back-side insertion).

Synthesis and characterization of NaY zeolite-encapsulated Mn-hydrazone Schiff base: an efficient and reusable catalyst for oxidation of olefins

The Mn-hydrazone Schiff base has been prepared, characterized, and encapsulated into NaY to prepare a new heterogeneous catalyst. Elemental analysis, UV-Vis, infrared spectroscopic analysis, diffuse reflectance spectroscopy, thermal analysis, small angle X-ray diffraction, and N2 sorption indicate the presence of Mn-hydrazone Schiff base within the nanocavity pores of zeolite-Y. The catalysts showed excellent catalytic efficiency in epoxidation with various olefinic compounds including cyclooctene, using tert-BuOOH as oxidant. Cyclooctene showed high conversion (97%) as well as epoxide selectivity (89%) with tert-BuOOH. Moreover, the encapsulated complex showed good recoverability without significant loss of activity and selectivity within successive runs.

Polyol‐Derived Alkoxide/Hydroxide Base Catalysts II: Transesterification Reactions

AbstractBiodiesel, fatty acid methyl ester (FAME), was produced by transesterification of canola oil with methanol in the presence of a series of alkoxide/hydroxide base catalysts produced from glycerol, 1,2‐propanediol, 1,3‐propanediol, xylitol, or sorbitol produced by dehydration reaction of sodium hydroxide in the presence of polyols. Transesterification reactions proceeded efficiently in the presence of sodium alkoxide catalysts prepared at three different mole ratios of sodium hydroxide to glycerol (1:1, 2:1, and 3:1). The production of methyl ester during the course of the reaction was determined repeatedly and the reaction progress was compared with that achieved in a reaction catalyzed by freshly prepared anhydrous sodium methoxide as a standard catalyst. Sodium alkoxide/hydroxide catalysts activity during the first 2 min of the reaction was in the order of: sorbitol < xylitol < sodium methoxide < 1,2‐propanediol < 1,3‐propanediol < glycerol regardless of the mole ratio of sodium hydroxide to glycerol. All catalysts showed a higher methyl ester accumulation at higher ratios of sodium hydroxide to polyol and had the following order 1:1 < 2:1 < 3:1 (sodium hydroxide:glycerol). Several of these catalysts were as powerful as sodium methoxide in catalyzing the transesterification reaction at the same mole concentration. All alkoxide/hydroxide catalysts resulted in a high FAME accumulation (>95 wt%) in a single transesterification batch reaction.

Polyol‐Derived Alkoxide/Hydroxide Base Catalysts I. Production

AbstractA metal methoxide is more expensive than a metal hydroxide and dissolves in methanol releasing a methoxide ion without producing water. The methoxide ion has a higher reaction rate making it more preferred for industrial biodiesel production. This study describes the preparation of alkoxide catalysts from metal hydroxides and non‐volatile, non‐toxic polyols. Heating aqueous solutions of metal hydroxides and different polyols (1,2‐propanediol, 1,3‐propanediol, glycerol, xylitol and sorbitol) under vacuum yielded polyol‐derived alkoxide base catalysts (PDABC). Comparison of the drying process for respective sodium hydroxide‐polyol combinations at two mole ratios of sodium hydroxide to polyol showed that drying at 2:1 mole ratio (metal hydroxide to polyol) was more efficient than that of 3:1. Dehydration of alkaline solutions containing three or more hydroxyl groups (glycerol, sorbitol and xylitol) was faster than drying similar solutions of diols. The empirical formula determined confirmed that the resulting powders contained mono‐sodium substituted alkoxides at 1:1, 2:1 and 3:1 (sodium hydroxide: polyol) mole ratio. Fatty acid methyl esters were prepared from canola oil and methanol using glycerol sodium alkylate as a catalyst. The conversion yield of oil to methyl ester was greater than 99 %.

Catalytic, Mild, and Selective Oxyfunctionalization of Linear Alkanes: Current Challenges

Selective catalysts for sustainable oxidation of alkanes are highly demanded because of the abundance of these molecules in the environment, the possibility to transform them into higher-value compounds, such as chemicals or synthetic fuels, and the fact that, kinetically speaking, this is a difficult reaction. Numerous chemical and biological catalysts have been developed in the lasts decades for this purpose, rendering the overview over this field of chemistry difficult. After giving a definition of the ideal catalyst for alkane oxyfunctionalization, this review aims to present the catalysts available today that are closest to ideal.

Magnetic cobalt ferrite nanoparticles as an efficient catalyst for oxidation of alkenes

Cobalt ferrite magnetic nanoparticles with mean sizes of 25 nm were used as a catalyst for the oxidation of various alkenes in the presence of tert- butylhydroperoxide (t-BuOOH). This study has demonstrated that CoFe2O4 nanoparticles can act as an efficient catalyst for the conversion of alkenes to the related aldehydes or epoxides, with almost quantitative yields. The catalyst can be readily isolated by using an external magnet and no obvious loss of activity was observed when the catalyst was reused in five consecutive runs. The effects of some parameters, such as temperature, types of oxidant and solvents, on the oxidation reactions were also investigated. The results showed that when CoFe2O4 is used with t-BuOOH as oxidant for the oxidation of some alkenes, better results are obtained compared to most of the studied similar ferrites.