The Actual Active Species of Sulfur‐Modified Gold‐Supported Palladium as a Highly Effective Palladium Reservoir in the Suzuki–Miyaura Coupling

The actual active species of the recently developed sulfur‐modified, gold‐supported palladium material, S ‐modified A u‐supported Pd (SAPd), with one of the lowest Pd‐releasing levels and high recyclability in the Suzuki–Miyaura coupling, was investigated. Also, SAPd was found to work repeatedly as an excellent Pd reservoir for liquid‐phase combinatorial synthesis.     

Palladium‐Iminodiacetic Acid Immobilized on pH‐Responsive Polymeric Microspheres: Efficient Quasi‐Homogeneous Catalyst for Suzuki and Heck Reactions in Aqueous Solution

The pH‐responsive core‐shell microspheres of poly(styrene‐co‐methylacrylic acid) (PS‐co‐PMAA) containing a polystyrene (PS) core and a poly(methylacrylic acid) (PMAA) shell are synthesized by one‐stage soap‐free copolymerization and the catalyst system palladium‐iminodiacetic acid (IDA‐Pd) is immobilized on the outer shell‐layer of the core‐shell microspheres to form the quasi‐homogeneous and easily accessible catalyst PS‐co‐PMAA‐IDA‐Pd. This quasi‐homogeneous PS‐co‐PMAA‐IDA‐Pd catalyst is highly dispersed in the reaction medium just like a homogeneous one and can be separated like a heterogeneous catalyst by adjusting the pH of the reaction medium. Suzuki reactions employing the quasi‐homogeneous PS‐co‐PMAA‐IDA‐Pd catalyst are efficiently performed in water as the sole solvent under mild conditions such as room temperature. The PS‐co‐PMAA‐IDA‐Pd catalyst is also used in Heck reactions of a wide range of aryl halides with styrene and proves to be efficient in aqueous solution. The PS‐co‐PMAA‐IDA‐Pd catalyst has a low leaching loss and can be reused at least 4 times without loss of activity.     

Development of a Method for Preparing a Highly Reactive and Stable,Recyclable and Environmentally Benign Organopalladium Catalyst Supported on Sulfur‐Terminated Gallium Arsenide(001): A Three‐Component Catalyst, {Pd}‐S‐GaAs(001), and its Properties

We have developed a method for preparing a recyclable and environmentally benign organopalladium catalyst for the Heck reaction supported on sulfur‐terminated gallium arsenide(001). This three‐component catalyst, {Pd}‐S‐GaAs(001), exhibited high stability and activity, furthermore, it tolerated reuse in 10 runs of the Heck reaction (average yield, 97 %) under aerobic conditions. The sulfur layer was very important to stabilize this catalyst. Only trace amounts of Pd were leached from this catalyst to the reaction mixture, as measured by ICP‐mass. The valence of immobilized Pd was zero by XPS spectrometry.     

Palladium on Carbon‐Catalyzed Cross‐Coupling using Triarylbismuths

Simple and efficient protocols for the 10% palladium on carbon (Pd/C)‐catalyzed cross‐coupling reactions between triarylbismuths and aryl halides have been developed. A variety of iodo‐ and bromobenzenes possessing an electron‐withdrawing group on the aromatic nucleus were smoothly cross‐coupled in the presence of 10% Pd/C, sodium phosphate dodecahydrate (Na₃PO₄⋅12 H₂O) and 1,4‐diazabicyclo[2.2.2]octane (DABCO) in heated N‐methyl‐2‐pyrrolidone (NMP) as the solvent. For the arylations of iodobenzenes, the reactions effectively proceeded under the combined use of caesium fluoride (CsF) and 2,2′‐biquinoline. Furthermore, a ligand‐free 10% Pd/C‐catalyzed cross‐coupling reaction between the aryl iodides and triarylbismuths was also established by the addition of tetra‐n‐buthylammonium fluoride trihydrate (TBAF⋅3 H₂O) in which the palladium metals were hardly leached from the catalyst into the reaction media.     

Air‐Stable and Highly Active Dendritic Phosphine Oxide‐ Stabilized Palladium Nanoparticles: Preparation,Characterization and Applications in the Carbon‐Carbon Bond Formation and Hydrogenation Reactions

Dendrimer‐stabilized palladium nanoparticles were formed in the reduction of palldium bis(acetylacetonate) [Pd(acac)₂] in the presence of phosphine dendrimer ligands using hydrogen in tetrahydrofuran. The resulting Pd nanoparticles were characterized by TEM, ³¹P NMR and ³¹P MAS NMR. The results indicated that the dendritic phosphine ligands were oxidized to phosphine oxides. These dendrimer‐stabilized Pd nanoparticles were demonstrated to be efficient catalysts for Suzuki and Stille coupling reactions and hydrogenations. The dendritic wedges served as a stabilizer for keeping the nanoparticles from aggregating, and as a vehicle for facilitating the separation and/or the recycling of the Pd catalyst. In the case of the Suzuki coupling reaction, these Pd nanoparticles exhibited high catalytic efficiency (TON up to 65,000) and air stability as compared with the commonly used homogeneous catalyst tetrakis(triphenylphosphine)palladium [Pd(PPh₃)₄]. In addition, the results obtained from the bulky dendritic substrate suggest that the Pd nanoparticles might act as reservoir of catalytically active species, and that the reaction is actually catalyzed by the soluble Pd(0) and/or Pd(II) species leached from the nanoparticle surface.     

Safe Removal of the Allyl Protecting Groups of Allyl Esters using a Recyclable,Low‐Leaching and Ligand‐Free Palladium Nanoparticle Catalyst

A safe, facile and low‐leaching (up to 0.04 ppm) method has been developed for the removal of allyl, prenyl and benzyl protecting groups from the corresponding esters, using a sulfur‐modified gold‐supported palladium (SAPd) nanoparticle catalyst, which is known to be non‐flammable. The catalyst itself was found to be recyclable and the reaction appeared to proceed on the surface of the SAPd.

     

Ligand‐Free and Heterogeneous Palladium on Carbon‐Catalyzed Hetero‐Suzuki–Miyaura Cross‐Coupling

A ligand‐free and heterogeneous palladium on carbon (Pd/C)‐catalyzed hetero‐Suzuki–Miyaura coupling reaction has been developed. The protocol enables the construction of both heterocyclic‐alicyclic and heterocyclic‐heterocyclic biaryl derivatives in good to excellent yields. Furthermore, Pd/C could be reused. The time‐course study clarified that palladium was leached into the reaction media as the reaction proceeded and then completely deposited on the carbon support.     

Synthesis of 3,4‐Disubstituted Quinolin‐2‐(1H)‐ones via Palladium‐Catalyzed Decarboxylative Arylation Reactions

The Pd‐catalyzed decarboxylative cross‐coupling reaction of 4‐substituted quinolin‐2(1H)‐one‐3‐carboxylic acids with (hetero)aryl halides is described. With palladium(II) bromide and triphenylarsine ligand as the catalyst system, a variety of 4‐substituted 3‐(hetero)aryl quinolin‐2(1 H)‐ones and related heterocycles, such as 4‐substituted 3‐arylcoumarins can be prepared in good to excellent yields.     

Kinetics of glycerol conversion to hydrocarbon fuels over Pd/H‐ZSM‐5 catalyst

The utilization of glycerol, primary byproduct of biodiesel production, is important to enhance process economics. In our recent prior work, it was shown that glycerol can be converted to hydrocarbon fuels over bifunctional catalysts, containing a noble metal supported on H‐ZSM‐5. Over Pd/H‐ZSM‐5 catalyst, an optimal ～60% yield of hydrocarbon fuels was obtained. In the present work, based on experimental data over Pd/H‐ZSM‐5 catalyst, a lumped reaction network and kinetic model are developed. Using differential kinetic experiments over the temperature range 300–450°C, the rate constants, reaction orders, and activation energies are obtained for each reaction step. The predicted values match well with experimental data for glycerol conversion up to ～90%. © 2017 American Institute of Chemical Engineers AIChE J, 63: 5445–5451, 2017     

Efficient Allylation of Nucleophiles Catalyzed by a Bifunctional Heterogeneous Palladium Complex‐Tertiary Amine System

We demonstrate the synergistic catalysis of a silica‐supported diaminopalladium complex and a tertiary amine (SiO₂/diamine/Pd/NEt₂) as well as synthetic scope of the Tsuji–Trost reaction of 1,3‐dicarbonyls, phenols, and carboxylic acids with allyl carbonate and acetates. The synergistic catalysis of SiO₂/diamine/Pd/NEt₂ exhibited wide applicability and high activity for the Tsuji–Trost reaction. For example, the reaction of ethyl 3‐oxobutanate with allyl methyl carbonate afforded the allylated product in >99% yield at 70 °C for 5 h. The yield of allylated products was 26% for SiO₂/diamine/Pd, without immobilization of the tertiary amine group. In the reaction of 1.0 mmol of ethyl 3‐oxobutanate using 0.60 μmol of Pd in SiO₂/diamine/Pd/NEt₂, the turnover number (TON) of Pd reached up to 1070 within 24 h. Phenols with electron‐withdrawing groups, such as nitro and chloro groups, on the para position resulted in high product yields. The SiO₂/diamine/Pd/NEt₂ catalyst was reusable at least 4 times without appreciable loss of its activity and selectivity in the reaction of p‐chlorophenol.     

Palladium(II) Complexes of C2‐Bridged Chiral Diphosphines: Application to Enantioselective Carbonyl‐Ene Reactions

(11bR,11′bR)‐4,4′‐(1,2‐Phenylene)bis[4,5‐dihydro‐3H‐dinaphtho[2,1‐c:1′,2′‐e]phosphepin] [abbreviated as (R)‐BINAPHANE], (3R,3′R,4S,4′S,11bS,11′bS)‐4,4′‐bis(1,1‐dimethylethyl)‐4,4′,5,5′‐tetrahydro‐3,3′‐bi‐3H‐dinaphtho[2,1‐c:1′,2′‐e]phosphepin [(S)‐BINAPINE], (1S,1′S,2R,2′R)‐1,1′‐bis(1,1‐dimethylethyl)‐2,2′‐biphospholane [(S,S,R,R)‐TANGPHOS] and (2R,2′R,5R,5′R)‐1,1′‐(1,2‐phenylene)bis[2,5‐bis(1‐methylethyl)phospholane] [(R,R)‐i‐Pr‐DUPHOS] are C₂‐bridged chiral diphosphines that form stable complexes with palladium(II) and platinum(II) containing a five‐membered chelate ring. The Pd(II)‐BINAPHANE catalyst displayed good to excellent enantioselectivities with ee values as high as 99.0% albeit in low yields for the carbonyl‐ene reaction between phenylglyoxal and alkenes. Its Pt(II) counterpart afforded improved yields while retaining satisfactory enantioselectivity. For the carbonyl‐ene reaction between ethyl trifluoropyruvate and alkenes, the Pd(II)‐BINAPHANE catalyst afforded both good yields and extremely high enantioselectivities with ees as high as 99.6%. A comparative study on the Pd(II) catalysts of the four C₂‐bridged chiral diphosphines revealed that Pd(II)‐BINAPHANE afforded the best enantioselectivity. The ee values derived from Pd(II)‐BINAPHANE are much higher than those derived from the other three Pd(II) catalysts. A comparison of the catalyst structures shows that the Pd(II)‐BINAPHANE catalyst is the only one that has two bulky (R)‐binaphthyl groups close to the reaction site. Hence it creates a deep chiral space that can efficiently control the reaction behavior in the carbonyl‐ene reactions resulting in excellent enantioselectivity.     

Bifunctional Metal Organic Framework Catalysts for Multistep Reactions: MOF‐Cu(BTC)‐[Pd] Catalyst for One‐Pot Heteroannulation of Acetylenic Compounds

A bifunctional metal organic framework catalyst containing palladium and copper(II) benzene‐1,3,5‐tricarboxylate – MOF‐Cu(BTC)‐[Pd] – has been prepared. This catalyst enables the performance of the tandem Sonogashira/click reaction starting from 2‐iodobenzylbromide, sodium azide and alkynes to produce 8H‐[1,2,3]triazolo[5,1‐a]isoindoles with good yields under mild reaction conditions.     

Kinetics of hydrogenation of 4‐chloro‐2‐nitrophenol catalyzed by Pt/carbon catalyst

Hydrogenation of 4‐chloro‐2‐nitrophenol (CNP) was carried out at moderate hydrogen pressures, 7–28 atm, and temperatures in the range 298–313 K using Pt/carbon and Pd/γ‐Al₂O₃ as catalysts in a stirred pressure reactor. Hydrogenation of CNP under the above conditions gave 4‐chloro‐2‐aminophenol (CAP). Dechlorination to form 2‐aminophenol and 2‐nitrophenol is observed when hydrogenation of CNP is carried out above 338 K, particularly with Pd/γ‐Al₂O₃ catalyst. Among the catalysts tested, 1%Pt/C was found to be an effective catalyst for the hydrogenation of CNP to form CAP, exclusively. To confirm the absence of gas–liquid mass transfer effects on the reaction, the effect of stirring speed (200–1000 rpm) and catalyst loading (0.02–0.16 g) on the initial reaction rate at maximum temperature 310 K and substrate concentration (0.25 mole) were thoroughly studied. The kinetics of hydrogenation of CNP carried out using 1%Pt/C indicated that the initial rates of hydrogenation had first order dependence with respect to substrate, catalyst and hydrogen pressure in the range of concentrations varied. From the Arrhenius plot of ln rate vs 1000/T, an apparent activation energy of 22 kJ mol^?1 was estimated. © 2001 Society of Chemical Industry     

Liquid‐Phase Catalytic Hydrogenation of p‐Chlorobenzophenone to p‐Chlorobenzhydrol over a 5 % Pd/C Catalyst

The kinetics of the liquid‐phase catalytic hydrogenation of p‐chlorobenzophenone have been investigated over a 5 % Pd/C catalyst. The effects of hydrogen partial pressure (800–2200 kPa), catalyst loading (0.4–1.6 gm dm^–3), p‐chlorobenzophenone concentration (0.37–1.5 mol dm^–3), and temperature (303–313 K) were studied. A stirring speed > 20 rps has no effect on the initial rate of reaction. Effects of various catalysts (Pd/C, Pd/BaSO₄, Pd/CaCO₃, Pt/C, Raney nickel) and solvents (2‐propanol, methanol, dimethylformamide, toluene, xylene, hexane) on the hydrogenation of p‐chlorobenzophenone were also investigated. The reaction was found to be first order with respect to hydrogen partial pressure and catalyst loading, and zero order with respect to p‐chlorobenzophenone concentration. Several Langmuir‐Hinshelwood type models were considered and the experimental data fitted to a model involving reaction between adsorbed p‐chlorobenzophenone and hydrogen in the liquid phase.     

Cyclopropyl Building Blocks for Organic Synthesis, 131. Palladium‐Catalyzed Bicyclization with Carbonyl Insertion of Alkenyl‐Tethered Propargyl Carbonates Towards a Scalable Synthesis of Various 2‐(Bicyclo[3.1.0]hex‐1‐yl)acrylates

The Pd‐catalyzed 5‐exo‐trig‐3‐exo‐trig cascade cyclization of 1,6‐enynes with a propargyl carbonate terminus offers the shortest synthetic route to variously substituted 2‐(bicyclo[3.1.0]hex‐1‐yl)acrylates, a novel class of prospective monomers for low‐shrinkage polymers. To apply this reaction to large‐scale preparations of the said bicyclic acrylates, a flexible Pd catalyst system with tunable reactivity has been developed. The dependence of the product and diastereomer distribution on both the reaction conditions, including the type of palladium catalyst used, and on the nature of the substrate has been investigated. A variety of methyl 2‐(bicyclo[3.1.0]hex‐1‐yl)acrylates and parent carboxylic acids as well as some of their derivatives of potential interest towards a technical application were prepared on a multigram scale. A general large‐scale synthesis of the cyclization precursors bearing one or two carbonyl groups in the tether is also disclosed.     

Performance of silicon‐carbide foams as supports for Pd‐based methane combustion catalysts

BACKGROUND: Cellular foam materials are a new type of catalyst support that provides improved mass and heat transport characteristics and similar pressure drops to other well‐established structured supports such as monoliths. RESULTS: A Pd‐based catalyst has been prepared using a moderate surface area (25 m² g^?1) β‐SiC foam support without further washcoating. The stability of this catalyst has been tested for methane combustion at lean conditions, showing a small decrease of activity during the first 10 h followed by stable performance. Characterization of fresh and aged catalyst shows no significant changes. The influence of the most important reaction conditions, such as reactor loading (0.25–1 g), temperature (300–550 °C) and inlet methane concentration (833 and 1724 ppm), was studied in a fixed‐bed reactor. The results were fitted to three kinetic models: Mars‐van Krevelen; Langmuir‐Hinselwood; power‐law kinetics. CONCLUSIONS: The Pd/β‐SiC foam catalyst, prepared without the previous addition of a washcoating has been demonstrated to be stable for the combustion of methane‐air lean mixtures. A Mars‐van Krevelen kinetic model provides the best fit to the results obtained. Copyright © 2011 Society of Chemical Industry     

Thiosemicarbazone Salicylaldiminato‐Palladium(II)‐Catalyzed Mizoroki–Heck Reactions

Four tridentate thiosemicarbazone salicylaldiminato‐palladium(II) complexes of the general formula [Pd(saltsc‐R)PPh₃] [saltsc=salicylaldehyde thiosemicarbazone; R=H ( 1 ), 3‐tert‐butyl ( 2 ), 3‐methoxy ( 3 ), 5‐chloro ( 4 )], have been evaluated as catalyst precursors for the Mizoroki–Heck coupling reaction between a variety of electron‐rich and electron‐poor aryl halides and olefins. The palladium complexes (0.1–1 mol% loading) were found to effectively catalyze these reactions with high yields being obtained when aryl iodides and aryl bromides were utilized. The effects of base, catalyst loading, reaction temperature and reaction time on the catalytic activity of the most active complex were also investigated.     

Pd‐Ag/α‐Al2O3 Catalyst Deactivation in Acetylene Selective Hydrogenation Process

The selective hydrogenation of acetylene to ethylene over Pd‐Ag/α‐Al₂O₃ catalysts prepared by different impregnation/reduction methods was studied. The best catalytic performance was achieved with the sample prepared by sequential impregnation. A kinetic model based on first order in acetylene and 0.5th order in hydrogen for the main reaction and second‐order independent decay law for catalyst deactivation was used to fit the conversion time data and to obtain quantitative assessment of catalyst performances. Fair fits were observed from which the reaction and deactivation rate constants were evaluated. Coke deposition amounts showed a good correlation with catalyst deactivation rate constants, indicating that coke formation should be the main cause of catalyst deactivation.     

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.     

Novel Palladium‐on‐Carbon/Diphenyl Sulfide Complex for Chemoselective Hydrogenation: Preparation,Characterization, and Application

A diphenyl sulfide immobilized on palladium‐on‐carbon system, Pd/C[Ph₂S], was developed to achieve the highly chemoselective hydrogenation of alkenes, acetylenes, azides, and nitro groups in the presence of aromatic ketones, halides, benzyl esters, and N‐Cbz protective groups. Instrumental analyses of the heterogeneous catalyst demonstrated that diphenyl sulfide was embedded on Pd/C via coordination of its sulfur atom to palladium metal or physical interaction with graphite layers of the activated carbon. The catalyst could be recovered and reused at least five times without any significant loss of the reactivity.