Disperse Amphiphilic Submicron Particles as Non‐Covalent Supports for Cationic Homogeneous Catalysts

A simple method for the effective immobilization of homogeneous catalysts on polystyrene colloids via non‐covalent binding is demonstrated. Stable latices with sufficiently high loading of accessible borate anions are prepared via emulsion polymerization. Incorporation of cationic rhodium complexes, supported via their borate counter‐anion is efficient, and these supported homogeneous catalysts maintain constant catalytic activity for CC hydrogenation during several recycles, with very low metal leaching.     

Synthesis of Rhodium Colloidal Nano‐Coating Grafted Mesoporous Silica Composite and its Application as Efficient Environmentally Benign Catalyst for Heck‐Type Reaction of Arylboronic Acids

The synthesis and characterization of rhodium colloidal layer grafted mesoporous SBA‐15 material, designated as SBA‐Rh, are presented. In the preparation of this new catalyst, SBA‐15 mesoporous material was used as support without any pretreatment. The Si H functional groups were introduced onto the surface which resulted in highly dispersed metal colloid layer both on the outer and inner surface of the supporting material. The material was investigated for Heck‐type coupling reactions of alkenes with ayboronic in organic/water solvent. The ultrahigh specific area, large pore opening, and highly dispersed catalyst species in SBA‐Rh material created one of the most active heterogeneous catalysts for such reactions. Rhodium element was not detected in the final mixture by ICP after reaction. The catalyst species showed very high stability against leaching from the matrix and can be recycled for repeated use.     

Highly Modular P‐O‐P Ligands for Asymmetric Hydrogenation

The preparation of a library of new P‐O‐P ligands (phosphine‐phosphites and phosphine‐phosphinites), easily available in two synthetic steps from enantiopure Sharpless epoxy ethers, is reported. The “lead” catalyst of the series has proven to have outstanding catalytic properties in the rhodium‐catalysed asymmetric hydrogenation of a wide variety of functionalised alkenes (16 examples). The excellent performance and modular design of the catalysts makes them attractive for future applications.     

Suzuki–Miyaura Reactions of Aryl Chloride Derivatives with Arylboronic Acids using Mesoporous Silica‐Supported Aryldicyclohexylphosphine

The Suzuki–Miyaura reactions using mesoporous‐supported aryldicyclohexylphosphine as ligand have been investigated. The catalysts were based on SBA‐15 type mesoporous silica which was transformed in a four‐step synthesis leading to a phosphine‐containing hybrid material The most productive catalytic system studied was generated in situ from this material and the homogeneous palladium complex, Pd(OAc)₂. Other catalytic systems were studied for comparison [homogeneous cataysts, a “preformed” catalyst obtained by reaction of PdCl₂(PhCN)₂ and the phosphine‐containing material]. Variations involving the solvent system, the substrate aryl chloride and the arylboronic acid reactant were also studied. For both in situ and preformed catalyst systems, high conversions and yields are obtained for activated aryl chlorides. Success of the reaction for unactivated aryl chlorides was limited to the catalyst formed in situ. The catalyst formed in situ was also shown to be reactive under aqueous reaction conditions in the cross‐coupling of 1‐(4‐chlorophenyl)ethanone with phenylboronic acid.     

Selectivity of Rhodium‐Catalyzed Hydroformylation of 1‐Octene during Batch and Semi‐Batch Reaction using Trifluoromethyl‐Substituted Ligands

The regioselectivity of catalysts generated in situ from dicarbonyl rhodium(I)(2,4‐pentanedione) and trifluoromethyl‐substituted triphenylphosphine ligands has been evaluated during the hydroformylation of 1‐octene. The influence of batch or semi‐batch operation, the solvent, and the number of trifluoromethyl substituents has been investigated. During batch operation in a supercritical carbon dioxide (CO₂)‐rich system the differential n:iso ratio increases from approximately 4 to a value of 12–16 at about 90–95 % conversion for the catalyst based on bis[3,5‐bis(trifluoromethyl)phenyl]phenylphosphine. For semi‐batch conditions using hexane a constant n:iso ratio is obtained over a broad conversion range. Batch hydroformylation in neat 1‐octene is faster than in a supercritical CO₂‐rich, one‐phase system, with a similar overall selectivity as observed in the supercritical case. The results provide further directions for the development of ligands that are especially designed for the separation of homogeneous catalysts in continuously operated hydroformylation in scCO₂.     

Preparation,characterization, and polymerization of chromium complexes‐grafted Al/SBA‐15 and Ti/SBA‐15 nanosupports

Ethylene polymerization catalysts have been prepared by grafting chromium (III) nitrate onto Al/SBA‐15 and Ti/SBA‐15 mesoporous materials. A combination of XRD, nitrogen adsorption, TEM, and inductively coupled plasma‐atomic emission spectroscopy (ICP‐AES), were used to characterize the catalysts. Polymerization activity of Cr/SBA‐15 catalyst is significantly improved by Al or Ti insertion to the supports. Particularly, the chromium catalyst prepared with Ti/SBA‐15 support is more active than Al/SBA‐15 catalyst. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Heterogeneous Palladium Catalysts Applied to the Synthesis of 2‐ and 2,3‐Functionalised Indoles

Heterogeneous palladium catalysts ([Pd(NH₃)₄]²⁺/NaY and [Pd]/SBA‐15) were applied to the synthesis of 2‐functionalised indoles, giving generally high conversions and selectivities (>89% yield) using only 1 mol % [Pd]‐catalyst under standard reaction conditions (polar solvent, 80 °C). For the synthesis of 2,3‐functionalised indoles by cross‐coupling arylation, the [Pd]/SBA‐15 catalyst was found to be particularly interesting, producing the expected compound with =35% yield after 12 days of reaction, which is comparable to the homogeneous catalyst, Pd(OAc)₂ (=48% yield). In the course of the study, the dual reactivity of the indole nucleus was demonstrated: aryl bromides gave clean C C coupling while aryl iodides led to a clean C N coupling.     

Cationic Carboxylato Complexes of Dirhodium(II) with Oxo Thioethers: Catalysts for Silane Alcoholysis under Homogeneous and Liquid‐Liquid Biphasic Conditions

A set of cationic dirhodium(II) complexes with oxo thioethers was prepared and employed as catalysts for the silane alcoholysis reaction. The complexes were found to be highly active under homogeneous conditions, both in the absence and in the presence of a solvent, including coordinating solvents such as N,N‐dimethylformamide; the catalysts could be conveniently employed in concentrations as low as 0.01 mol %, and a maximum TON of 30000 was recorded after 24 h. The same catalysts were also employed under liquid‐liquid biphasic conditions with an ionic liquid as the catalyst‐containing phase: comparable catalytic activity was observed under these conditions, and the catalyst‐containing phase could be recovered and recycled. A chiral cationic dirhodium(II) complex was also prepared in the frame of this work; kinetic resolution of a racemic alcohol was attempted with this catalyst, unfortunately without success.     

High catalytic efficiency in liquid‐phase oxidation of 1,4‐dioxane using a Pt/CeO2‐ZrO2‐SnO2/SBA‐16 catalyst

A Pt/CeO₂–ZrO₂–SnO₂/SBA‐16 (SBA‐16: Santa Barbara Amorphous No. 16) catalyst was developed for the efficient removal of 1,4‐dioxane. Because the catalyst showed synergistic action between the high catalytic activity of Pt and the high oxygen release and storage abilities of CeO₂–ZrO₂–SnO₂, high catalytic efficiency in the liquid phase was obtained in an air atmosphere without the supply of any strongly oxidizing additives or photoirradiation. After reaction at 80°C for 4 h, the residual percentage of 1,4‐dioxane reached 31%. Furthermore, the Pt/CeO₂–ZrO₂–SnO₂/SBA‐16 catalyst exhibited high reusability and durability and the rate of net decrease in 1,4‐dioxane reached 44% at 80°C.     

Continuous Gas‐Phase Hydroformylation of 1‐Butene using Supported Ionic Liquid Phase (SILP) Catalysts

The concept of supported ionic liquid phase (SILP) catalysis has been extended to 1‐butene hydroformylation. A rhodium‐sulfoxantphos complex was dissolved in [BMIM][n‐C₈H₁₇OSO₃] and this solution was highly dispersed on silica. Continuous gas‐phase experiments in a fixed‐bed reactor revealed these SILP catalysts to be highly active, selective and long‐term stable. Kinetic data have been acquired by variation of temperature, pressure, syngas composition, substrate and catalyst concentration. A linear dependency in rhodium concentration could be established over a large concentration range giving another excellent hint for truly homogeneous catalysis in the SILP system. Compared to former studies using propene, the SILP system showed significantly higher activity and selectivity with 1‐butene as feedstock. These findings could be elucidated by solubility measurements using a magnetic microbalance.     

Asymmetric Homogeneous Hydrogenation in Flow using a Tube‐in‐Tube Reactor

In this update, the asymmetric homogeneous hydrogenation of a number of trisubstituted olefins utilizing the recently developed tube‐in‐tube gas‐liquid flow reactor is described. A number of chiral iridium‐ and rhodium‐based catalysts and other parameters such as pressure, solvent, temperature and catalyst loading were screened. The advantage of the flow set‐up for rapid screening and optimization of reaction parameters is illustrated. Furthermore, a comparative study using batch conditions aided in the optimization of the flow reaction set‐up. The set‐up was further modified to recycle the catalyst which prolonged catalytic activity.     

Rhodium‐Catalyzed Tandem Isomerization/Hydroformylation of the Bio‐Sourced 10‐Undecenenitrile: Selective and Productive Catalysts for Production of Polyamide‐12 Precursor

The hydroformylation of 10‐undecenenitrile ( 1 ) – a substrate readily prepared from renewable castor oil – in the presence of rhodium‐phosphane catalysts systems is reported. The corresponding linear aldehyde ( 2 ) can be prepared in high yields and regioselectivities with a (dicarbonyl)rhodium acetoacetonate‐biphephos [Rh(acac)(CO)₂‐biphephos] catalyst. The hydroformylation process is accompanied by isomerization of 1 into internal isomers of undecenenitrile ( 1‐int ); yet, it is shown that the Rh‐biphephos catalyst effectively isomerizes back 1‐int into 1 , eventually allowing high conversions of 1 / 1‐int into 2 . Recycling of the catalyst by vacuum distillation under a controlled atmosphere was demonstrated over 4–5 runs, leading to high productivities up to 230,000 mol ( 2 )⋅mol (Rh)⁻¹ and 5,750 mol ( 2 )⋅mol (biphephos)⁻¹. Attempted recycling of the catalyst using a thermomorphic multicomponent solvent (TMS) phase‐separation procedure proved ineffective because the final product 2 and the Rh‐biphephos catalyst were always found in the same polar phase. Auto‐oxidation of the linear aldehyde 2 into the fatty 10‐cyano‐2‐methyldecanoic acid ( 5 ) proceeds readily upon exposure to air at room temperature, opening a new effective entry toward polyamide‐12.

     

Preparation of shish‐kebab and nanofiber polyethylene with chromium/Santa Barbara amorphous silica‐15 catalysts

Cr/SBA‐15 catalysts were prepared by the grafting of chromium nitrate nonahydrate [Cr(NO₃)₃·9H₂O] complexes onto SBA‐15 mesoporous materials. Shish‐kebab and nanofiber polyethylenes (PEs) were prepared under different temperatures via ethylene extrusion polymerization with the Cr(NO₃)₃·9H₂O catalytic system. The diameter of a single nanofiber was 100–250 nm. Scanning electron microscopy images showed that the polymer obtained from the SBA‐15‐supported catalyst under different polymerization temperatures produced nanofiber and/or shish‐kebab morphologies. X‐ray diffraction and differential scanning calorimetry were used to characterize microstructures of the materials. Polymers obtained with all of the catalysts showed a melting temperature, bulk density, and high load melt index; this indicated the formation of linear high‐density PE. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of ethoxy‐terminated ladder‐like polymethylsilsesquioxane oligomer

A fully ethoxy‐terminated ladder‐like polymethylsilsesquioxane oligomer (EtO‐Me‐T) has been synthesized and characterized for the first time using an effective transient catalyst (tetramethylammonium hydroxide, TMAH) via the dehydration alcoholysis reaction of hydroxy‐terminated ladder‐like polymethylsilsesquioxane (HO‐Me‐T) prepared by a modified stepwise coupling polymerization approach. Compared with the common acidic or basic catalysts, use of the transient catalyst TMAH can not only make the HO‐Me‐T molecules fully ethoxy‐terminated but also enables the catalyst to be readily and thoroughly removed after completion of the alcoholysis reaction. It is noteworthy that the common acidic or basic catalysts widely used in the dehydration alcoholysis reaction are clearly unsuitable for the preparation of EtO‐Me‐T oligomer because the latter would be hydrolyzed unavoidably back to the parent HO‐Me‐T during the washing process. In addition, preliminary exploration indicates that, when compared with the tetraethyl orthosilicate (Si(OEt)₄) generally used as a crosslinking agent for the room‐temperature vulcanization of silicone rubber (RTV‐SR), the oligomer EtO‐Me‐T is a promising replacement which can greatly improve the mechanical properties of RTV‐SR Copyright © 2003 Society of Chemical Industry     

Gold‐Catalyzed Cyclizations: A Comparative Study of ortho,ortho′‐Substituted KITPHOS Monophosphines with their Biaryl Monophosphine Counterpart SPHOS

Electrophilic gold(I) triflimide (trifluoromethanesulfonimide) complexes of electron‐rich ortho,ortho′‐disubstituted KITPHOS (11‐dicyclohexylphosphino‐12‐phenyl‐9,10‐ethenoanthracene) monophosphines are efficient catalysts for intramolecular cycloisomerizations that afford phenols, 3‐acylindenes and methylene‐oxazolines; comparative catalyst testing showed that these catalysts either competed with or outperformed that based on SPHOS [2‐(2′,6′‐dimethoxybiphenyl)dicyclohexylphosphine]. An electron‐rich biarylmonophosphine containing a single ortho‐methoxy substituent, prepared by rhodium‐catalyzed [2+2+2] cycloaddition between a 1‐alkynyl(dicyclohexylphosphine) oxide and 1,7‐octadiyne, also formed a highly efficient catalyst for the same transformations. Monitoring of comparative catalyst testing between a KITPHOS‐based gold(I) triflimide complex containing a coordinated tetrahydrothiophene and its counterpart coordinated solely by the triflimide anion revealed that the former is an order of magnitude less efficient than the latter, confirming that tetrahydrothiophene can be an effective catalyst inhibitor.     

Copolymerization of ethylene and in situ‐generated α‐olefins to high‐performance linear low‐density polyethylene with a two‐catalyst system supported on mesoporous molecular sieves

The manufacture of linear low‐density polyethylene (LLDPE) is of great significance in academia and industry. The employment of a single monomer, i.e. ethylene, to produce LLDPE by introducing two catalysts into one reactor to conduct ethylene copolymerization with in situ‐generated α‐olefins has proved to be an effective way in this case. Moreover, immobilization of catalysts affords LLDPE with better morphology and improved physical properties. An iron‐based diimine complex immobilized on methylaluminoxane (MAO)‐treated mesoporous molecular sieves was used to oligomerize ethylene to α‐olefins with improved selectivity to lower molar mass fractions. Based on this, zirconocene compound was also supported on mesoporous molecular sieves to comprise a two‐catalyst system to produce LLDPE from a single ethylene monomer. Copolymerization performed at both atmospheric and high pressure produced LLDPE of high molecular weight and broad molecular weight distribution without using MAO during the polymerization processes. Physical and mechanical measurements evidenced significant increases in tensile strength, tensile modulus and Izod impact strength. A marked shear‐thinning phenomenon and improved storage modulus of LLDPE produced using catalysts supported on MCM‐41 and SBA‐15 mesoporous molecular sieves indicated a stronger interfacial interaction between the molecular sieve support and the polymeric matrix. Copyright © 2010 Society of Chemical Industry     

Highly Active and Enantioselective Rhodium‐Catalyzed Asymmetric 1,4‐Addition of Arylboronic Acid to α,β‐ Unsaturated Ketone by using Electron‐Poor MeO‐F12‐BIPHEP

The asymmetric 1,4‐addition of phenylboronic acid to cyclohexenone were performed by using a low amount of rhodium/(R)‐(6,6′‐dimethoxybiphenyl‐2,2′‐diyl)bis[bis(3,4,5‐trifluorophenyl)phosphine] (MeO‐F₁₂‐BIPHEP) catalyst. Because the catalyst shows thermal resistance at 100 °C, up to 0.00025 mol% Rh catalyst showed good catalytic activity. The highest turnover frequency (TOF) and turnover number (TON) observed were 53,000 h⁻¹ and 320,000, respectively. The enantioselectivities of the products were maintained at a high level of 98% ee in these reactions. The Eyring plots gave the following kinetic parameters (ΔΔH^≠=−4.0±0.1 kcal mol⁻¹ and ΔΔS^≠=−1.3±0.3 cal mol⁻¹ K⁻¹), indicating that the entropy contribution is relatively small. Both the result and consideration of the transition state in the insertion step at the B3LYP/6‐31G(d) [LANL2DZ for rhodium] levels indicated that the less σ‐donating electron‐poor (R)‐MeO‐F₁₂‐BIPHEP could be creating a rigid chiral environment around the rhodium catalyst even at high temperature.     

Catalytic Activity of Cu/SBA‐15 for Peroxidation of Pyridine Bearing Wastewater at Atmospheric Condition

In this study, Cu‐loaded Santa Barbara amorphous (SBA)‐15 catalysts were synthesized by impregnation method and further used for catalytic wet peroxidation (CWPO) of pyridine from aqueous solution using hydrogen peroxide as oxidant. The synthesized catalysts have been characterized by Brunauer–Emmett–Teller surface area: temperature‐programmed reduction, H₂‐chemisorption, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy. Characterization results indicate good dispersion of Cu species inside the porous structure of SBA‐15. The effect of various parameters such as Cu loading on SBA‐15, pH, catalyst dose, H₂O₂ concentration, and temperature have been studied for their effect on CWPO of pyridine. More than 97% pyridine removal and 92% total organic carbon removal was achieved at optimum condition. Cu/SBA‐15 showed stable performance during reuse for six cycles with negligible copper leaching. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2577–2586, 2013     

Selective Hydrogenation of 5‐Ethoxymethylfurfural over Alumina‐Supported Heterogeneous Catalysts

We report here the synthesis and testing of a set of 48 alumina‐supported catalysts for hydrogenation of 5‐ethoxymethylfurfural. This catalytic reaction is very important in the context of converting biomass to biofuels. The catalysts are composed of one main metal (gold, copper, iridium, nickel, palladium, platinum, rhodium, ruthenium) and one promoter metal (bismuth, chromium, iron, sodium, tin, tungsten). Using a 16‐parallel trickle‐flow reactor, we tested all 48 catalyst combinations under a variety of conditions. The results show that both substrate conversion and product selectivity are sensitive towards temperature changes and solvent effects. The best results of >99% yield to the desired product, 5‐ethoxymethylfurfuryl alcohol, are obtained using an iridium/chromium (Ir/Cr) catalyst. The mechanistic implications of different possible reaction pathways in this complex hydrogenation system are discussed.     

Interesterification of Soybean Oil and Methyl Stearate Catalyzed by Guanidine‐Functionalized SBA‐15 Silica

The main purpose of this study was to develop a heterogeneous interesterification catalyst for the modification of edible oils to enhance their physicochemical and functional performances. To achieve this, 1,3‐dicyclohexyl‐2‐octylguanidine was covalently immobilized on the SBA‐15 (Santa Barbara Amorphous 15) material and then used as solid catalysts for the interesterification between soybean oil and methyl stearate. The characterization of the guanidine‐functionalized SBA‐15 material included Fourier transform infrared spectra, scanning electron microscopy, elemental analysis, and nitrogen adsorption–desorption techniques. It was shown that the solid base catalyst could efficiently catalyze the interesterification reaction. After the interesterification, the fatty acid profiles and triacylglycerol compositions of interesterified products were substantially varied. The influence of interesterification parameters, such as the substrate ratio, reaction time, reaction temperature and catalyst loading, on the interesterification reaction was investigated regarding the percentage of stearic acid in interesterified triacylglycerols. The stearic acid percentage of 27.9 % was achieved at 100 °C within 4 h when the methyl stearate/soybean oil molar ratio of 6:1 was employed. The catalyst could be recovered easily by filtration and reused without significant loss of activity.