Homogeneous Catalyst System Research Articles

Study on Dynamic Performance of Novel Isoprene Rubber Synthesized with Homogeneous Rare-Earth Catalyst System

The homogeneous rare-earth catalytic system was used to initiate the polymerization of isoprene, and a novel IR was synthesized with high molecular weight and narrow molecular weight distribution. According to the self-developed rare-earth IR properties, a study on IR and IR/NR blend was made. The effect of JiHua rare-earth IR on the vulcanization characteristics and dynamic properties in IR/NR blend was investigated and compared with IR (SKI-3) synthesized with titanium catalyst system and rare-earth isoprene rubber (SKI-5) made in Russia. The results showed that JiHua rare-earth IR to be developed independently was a novel synthetic rubber with excellent comprehensive performance, and it can be used independently and partly substitute natural rubber to make tire. In the IR/NR blend, Not only vulcanization characteristics and the safety in operation for NR was greatly improved, But also dynamic properties of vulcanizates such as dynamic cutting resistance, abrasion resistance, wet-skid resistance and aging resistance were improved to different degrees. These properties reach or surpass the level of the foreign similar products like Russia SKI-3 and Russia SKI-5.

New catalyst systems for the degradation of chlorophenols

The aim of this study is to investigate new catalyst systems for the oxidative degradation of chlorophenol (CP) derivatives that have been classified as first-degree toxic pollutants. Oxidative degradation and degradation products of chlorinated phenols, namely 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol, are discussed in detail. Homogenous catalyst systems Fenton [Fe(II)/H2O2] and Fenton-like [Cu(II)/H2O2 and V(IV)/H2O2] methods were employed at higher CP concentrations (1×10−2mol/L). Heterogeneous catalyst systems titanium dioxide [TiO2/UV] and silver loaded titanium dioxide [Ag-TiO2/UV] processes were also investigated at lower concentrations. Chemical oxygen demand (COD), which is defined as oxygen equivalent of organic matter before and after degradation system was determined.The removal of each CP was determined by GC/MS analysis after derivatization. CPs are generally resistant to degradation and in some cases oxidation byproducts are produced rather than the destruction of molecular structure. High degradation and removal efficiencies for each CP derivative have already been obtained by the Fenton system and this was supported by both GC/MS and COD results. However the Ag-TiO2/UV photocatalytic system achieved the most effective degradation of all CPs studied in this work. In addition, the results indicate that the silver loaded catalyst system achieves the best degradation efficiencies in a short exposure period.

Ti(OC4H9)4/2,5-Dimethoxytetrahydrofuran/ TEA/Ethylene Chlorobromide] as a Novel Homogeneous Catalyst System Effective for the Ethylene Dimerization Reaction

Ti(OC4H9)4/2,5-Dimethoxytetrahydrofuran/ TEA/Ethylene Chlorobromide] as a Novel Homogeneous Catalyst System Effective for the Ethylene Dimerization Reaction

Highly active, thermo-responsive polymeric catalytic system for reuse in aqueous and organic CuAAC reactions

Tris-(benzyltriazolylmethyl)amine (TBTA) has been immobilized onto a styrenic monomer and subsequently copolymerized with N-isopropyl acrylamide (NIPAM) to afford catalytically active thermo-responsive copolymers for copper assisted click chemistry. P(TBTA-co-NIPAM) copolymers were synthesized with incorporation of between 2 and 10 ligand units per chain and tuneable molecular weight (28–148 kDa). A combination of 1H NMR spectroscopy, size exclusion chromatography (SEC) and elemental analysis (EA) confirmed the controlled synthesis of these polymers and allowed for quantification of the degree of TBTA-functionalized monomer incorporation. After loading with copper(I) bromide, this homogeneous catalyst system was added to a water/ethyl acetate two-phase system. Using this biphasic system aqueous click reactions could be performed at room temperature, while organic click chemistry could be performed above the cloud point temperature of the catalyst system. The polymer catalyst system could be regenerated via extraction by making use of its lower critical solution temperature (LCST)-behavior, and then reused for further copper(I) catalyzed azide-alkyne cycloaddition (CuAAC) reactions. While a reduced catalytic activity is observed as a result of copper leaching in aqueous click reactions, the recycling experiments in the organic phase demonstrated that this copolymer supported system allows for efficient recycling and reuse. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

ChemInform Abstract: An Efficient Synthesis of 2‐Arylbenzothiazoles Using Silica Sulfuric Acid, Oxalic Acid and Aluminum Chloride Hydrate as Heterogeneous and Homogeneous Catalyst Systems.

A convenient method for the synthesis of 2-arylbenzothiazoles from condensation of aromatic/heteroaromatic aldehydes with 2-aminothiophenol has been developed using inexpensive, green and reusable solid acids – silica sulfuric acid (SSA), oxalic acid or AlCl 3 ·6H 2 O as efficient catalysts. The reactions occurred under mild conditions to afford the corresponding 2-arylbenzothiazoles in good to excellent yields.

An efficient synthesis of 2-arylbenzothiazoles using silica sulfuric acid, oxalic acid and aluminum chloride hydrate as heterogeneous and homogeneous catalyst systems

A convenient method for the synthesis of 2-arylbenzothiazoles from condensation of aromatic/heteroaromatic aldehydes with 2-aminothiophenol has been developed using inexpensive, green and reusable solid acids – silica sulfuric acid (SSA), oxalic acid or AlCl3·6H2O as efficient catalysts. The reactions occurred under mild conditions to afford the corresponding 2-arylbenzothiazoles in good to excellent yields.

ChemInform Abstract: Orthogonal Enantioselectivity Approaches Using Homogeneous and Heterogeneous Catalyst Systems: Friedel—Crafts Alkylation of Indole.

AbstractEither enantiomeric alkylated indole (III) can be selectively obtained in the presence of a copper catalyst derived from dihydroxylated brucine.

Catalytic Solvolysis of Ammonia Borane

Hydrogen on tap: A homogeneous catalyst system for the rapid and quantitative solvolysis of ammonia borane (AB) has been developed. The iridium catalyst is remarkably stable and can be reused with no observable degradation in activity. In the absence of solvent, the mixture of catalyst and AB efficiently generates hydrogen upon exposure to water vapor, thereby resulting in a system with considerable hydrogen storage capacity (see picture).

A Kinetic Model for Selective Ethene Trimerization to 1‐Hexene by a Novel Chromium Catalyst System

AbstractA numerical model for the kinetics of the selective trimerization of ethene to 1‐hexene has been developed on the basis of mechanistic investigations and extensive experimental parameter studies. The reaction is catalyzed by a homogeneous catalyst system, comprising the chromium source [CrCl3(thf)3], a Ph2PN(iPr)P(Ph)N(iPr)H ligand, and triethylaluminum as activator. The kinetic model is designed as a tool for laboratory data evaluation, design and planning of meaningful experiments in the multidimensional parameter space, and parameter identification, and, moreover, it includes all features needed to eventually facilitate the transfer of the laboratory results into the technical environment. In particular, the model is designed to deliver the intrinsic chemical kinetics of the homogeneous catalytic system and to rule out any undetected influence of phase‐transfer limitations. Key kinetic parameters are determined by fitting the numerical simulations to the experimental results. In general, the model calculations and experimental data are in excellent agreement. In conjunction with mechanistic investigations, the model helps to elucidate the complex reaction network.

Immobilized Chromium Catalyst System for Selective Ethene Trimerization to 1‐Hexene with a PNPNH Ligand

Tie me catalyst down, support: A selective homogeneous chromium-based ethene trimerization catalyst is heterogenized by immobilization on a functionalized polymer support. The immobilized catalyst displays good selectivity towards 1-hexene, and retains high activity for long times on-stream, combining advantages of homogeneous and heterogeneous catalyst systems.

ChemInform Abstract: Synthesis of Large-Ring Keto Lactones by the Homogeneous and Polymer- Supported Palladium-Catalyzed Carbonylative Coupling of Esters Having Vinyl Triflate and Vinylstannane Termini.

Large-ring keto lactones having from 12 to 16 members were synthesized in fair yield by the palladium-catalyzed carbonylative coupling of long-chain esters having vinyl triflate and vinylstannane termini. A polystyrene-supported bis(diphenylphosphino) ferrocene ligand system was synthesized by the copolymerization of styrene, p-divinylbenzene, and bis(diphenylphosphino) vinylferrocene. Palladium catalysts supported on this polymer were more selective in these carbonylative cyclizations than were corresponding homogeneous catalyst systems

ChemInform Abstract: Metathesis of Functionalized Acyclic Olefins

Abstract The metathesis of functionally substituted olefins, i.e olefins containing one or more heteroatoms, affords interesting prospects in the synthesis of valuable organic products. Since the first report on the successful metathesis of certain functional olefins, viz. longchain fatty acid esters, much research has been done into the possibilities of this reaction. It appears that many types of functionalized olefins undergo metathesis in the presence of a suitable catalyst. Despite the fact that many metathesis catalysts are inactive, interesting results have been obtained in the past with two catalyst systems, viz. the homogeneous system WCl6-Sn(CH3)4 and the heterogeneous system Re2O7/Al2O3-Sn(CH3)4. The scope of the reaction of functionalized olefins has been studied for a number of groups. The functional groups suited for metathesis include -COOR, -OCOR, -COR, -OR, -CN, -OSiR3, -Cl etc. Unsaturated carboxylic acids and alcohols can be metathesized by introducing a protecting group, e.g. a trimethylsilyl group. New homogeneous catalyst systems developed in recent years are nearly all based on tungsten compounds. Generally, however, the heterogeneous rhenium-based catalyst system turns out to be more attractive. The catalyst is active even at room temperature and can be recovered easily. In addition it is active towards certain compounds, especially allyl compounds, that are inactive with the tungsten catalysts. An important development was the access to the metathesis of unsaturated nitriles. Here, the system Re2O7/Al2O3-SnR4 in particular gives good results. Higher activities than those observed for the Re2O7/ Al2O3 catalysts can be achieved using modified rhenium catalysts. Thus, noteworthy results were obtained when a third metal oxide was incorporated and when a different support was used, e.g. silica-alumina. These developments are the subject of further study at the present time and will lead to catalysts with activities of practical interest.

Highly stereospecific polymerization of isoprene with homogeneous binary Ziegler-Natta catalysts based on NCN-pincer neodymium precursor

The aryldiimine NCN-pincer stabilized neodymium dichloride combined with aluminum alkyls established a new type of homogeneous binary neutral Ziegler-Natta catalyst system. This system exhibited high activity and high cis-1,4 selectivity for the polymerization of isoprene (T p = 20 °C, 98.2%; T p = −20 °C, > 99%). Such catalytic performances remained under a broad range of polymerization temperatures and monomer-to-neodymium ratios (from 500 to 8000), reaching high number-average molecular weight (M n = 1582 kg/mol) and relatively narrow molecular weight distribution (PDI = 1.68), which was, however, influenced by the amount and bulkiness of aluminum alkyls. Dynamic investigation of the polymerization was performed, which showed the number-average molecular weight of the resultant polyisoprene had an almost linear correlation with the conversion, suggesting, in some degree, the polymerization with this catalytic system was controllable.

Solution Electrospinning of Polyolefins: The Effect of Comonomers in Propylene/α‐Olefin Copolymers

AbstractTwo propylene copolymers with similar comonomer content and molecular weight were electrospun from solution. The 1‐octene and 1‐decene copolymers yielded ribbon‐like fibers. Isotactic poly(propylene) prepared by both heterogeneous and homogeneous catalyst systems could not be electrospun from the same solvent system used for the copolymers. The presence of the higher 1‐alkene comonomers in small amounts (about 1 mol‐%) not only affects the crystallinity of the polymer compared to the homopolymer, but appears to influence the solubility as well. The combined effect of lowering crystallinity and increasing solubility indicates that the use of higher 1‐alkene comonomers in low amounts could be a route to prepare poly(propylene) based electrospun fibers.magnified image

Orthogonal Enantioselectivity Approaches Using Homogeneous and Heterogeneous Catalyst Systems: Friedel–Crafts Alkylation of Indole

Heterogeneous chiral catalysts have attracted considerable attention from a wide range of scientific disciplines because of their fundamental and practical importance. Recent efforts have focused on the development of more efficient and practical immobilization methods for homogeneous chiral catalysts, and notable success has been achieved by using covalent tethering strategies in asymmetric reactions. Although different conformational preferences between homogeneous and heterogeneous systems are possible, successful orthogonal enantioselectivity using heterogeneous systems—that is, orthogonal to that observed with homogeneous systems—has not yet been achieved. Herein we describe the first example of such selectivity. Our rationale was based on the premise that solid supports, such as zeolites and silicates, would immobilize homogeneous chiral metal complexes, which are generated from rigid multifunctional brucine-derived ligands 1, through electrostatic interactions. This mode is believed to provide a facile mechanism for inducing conformational changes with immobilized chiral complexes.

Orthogonal Enantioselectivity Approaches Using Homogeneous and Heterogeneous Catalyst Systems: Friedel–Crafts Alkylation of Indole

Orthogonal Enantioselectivity Approaches Using Homogeneous and Heterogeneous Catalyst Systems: Friedel–Crafts Alkylation of Indole

Development of Molecular and Solid Catalysts for the Direct Low‐Temperature Oxidation of Methane to Methanol

The direct low-temperature oxidation of methane to methanol is demonstrated on a highly active homogeneous molecular catalyst system and on heterogeneous molecular catalysts based on polymeric materials possessing ligand motifs within the material structure. The N-(2-methylpropyl)-4,5-diazacarbazolyl-dichloro-platinum(II) complex reaches significantly higher activity compared to the well-known Periana system and allows first conclusions on electronic and structural requirements for high catalytic activity in this reaction. Interestingly, comparable activities could be achieved utilizing a platinum modified poly(benzimidazole) material, which demonstrates for the first time a solid catalyst with superior activity compared to the Periana system. Although the material shows platinum leaching, improved activity and altered electronic properties, compared to the conventional Periana system, support the proposed conclusions on structure-activity relationships. In comparison, platinum modified triazine-based catalysts show lower catalytic activity, but rather stable platinum coordination even after several catalytic cycles. Based on these systems, further development of improved solid catalysts for the direct low-temperature oxidation of methane to methanol is feasible.

Homogeneous photocatalytic production of hydrogen from water by a bioinspired [Fe2S2] catalyst with high turnover numbers

A three-component homogeneous catalyst system, composed of a cyclometalated iridium(iii) photosensitizer, a bioinspired diiron complex, and TEA in aqueous acetone, proved to be catalytically active for photoinduced H(2) production, with up to 660 turnovers over 8 h of irradiation.

Heterogenized copper catalysts for the amination of arylhalide: Synthesis, characterization and catalytic applications

This research investigated the synthesis, characterization and catalytic activity of heterogenized copper complexes for the selective amination of aryl halides. Amination reactions using homogeneous copper catalyst systems are not generally selective and it is also difficult to recover the catalyst from the homogeneous system for recycling. To overcome these difficulties, our efforts were directed towards the development of cheaper heterogeneous catalyst systems, which can be easily recovered and recycled. Heterogenized analogs of the homogenous Cu complexes were prepared using two methods: (a) encapsulation of copper complexes in zeolite-Y and (b) tethering of copper complexes on various supports like zeolite-Y, silica, charcoal, or clay. The encapsulated and tethered copper catalysts on zeolite-Y were characterized using EPR, Diffused reflectance UV–vis, XRD, IAS, ICPES, SEM, and TEM. The results confirmed that the copper complexes were truly heterogenized in zeolite-Y support. Encapsulated and tethered copper complexes were tested for amination of aryl iodide. The effects of various reaction parameters were examined using tethered Cu(Phen)(PPh 3)Br-PTA-Y catalyst to determine optimum conditions. A recycle study of encapsulated and tethered Cu catalyst was carried out to test their robustness for possible commercial exploitation.

Chiral Mn (III) salen complexes covalently bonded on zirconium oligostyrenylphosphonate-phosphates as catalysts for enantioselective epoxidation of nonfunctionalized alkenes

A class of zirconium oligostyrenyl-phosphonate-phosphates in a number of stoichiometric pendant group ratios has been synthesized (Zr (HPO 4) 2− x [O 3P–(CH(C 6H 5CH 2)CH 2) n ] x · mH 2O). A general method for the covalent attachment of chiral Mn (III) salen complex to those materials has been devised. The heterogeneous catalysts showed higher chiral induction for enantioselective epoxidation of α-methylstyrene (ee, 57–71%) in the presence of pyridine N-oxide as axial base using aqueous NaOCl as oxidant than that observed in homogeneous catalyst system (ee, 54%). Meanwhile, styrene and indene were efficiently epoxidized with these supported catalysts, and the results were comparable to that for the homogeneous system. In addition, the influence of x values of zirconium oligostyrenyl-phosphonate-phosphates on the catalytic performance of the heterogeneous Mn (III) salen catalysts was investigated in detail. Intermediate x values result in intermediate steric constraints, resulting in spacing values between the two organic groups. The heterogeneous catalysts are relatively stable and can be recycled nine times.