Reusable Palladium Research Articles

ChemInform Abstract: An Efficient, Stable and Reusable Palladium Nanocatalyst: Chemoselective Reduction of Aldehydes with Molecular Hydrogen in Water.

AbstractPd‐nanoparticles stabilized by a binaphthyl‐backbone are used for the chemoselective reduction of aldehydes to give the corresponding benzylic alcohols.

Development of reusable palladium catalysts supported on hydrogen titanate nanotubes for the Heck reaction

Palladium catalysts supported on hydrogen titanate nanotubes were prepared by adsorption of palladium(II) acetate from dichloromethane solutions. At low Pd(OAc)2 loadings (up to 5wt.%), the catalysts contained only highly dispersed chemisorbed Pd0 and Pd2+O species (XPS). Characteristic signals of Pd(OAc)2 were not detected in these catalysts by FT-IR, FT-Raman, of XPS, indicating decomposition of the precursor salt due to the strong metal–support interaction. An increase in the palladium loading resulted in an increase in the proportion of Pd0 species and the appearance of some supported Pd(AcO)2 (XPS). In the sample with the highest palladium loading (8.84wt.% of Pd(OAc)2), formation of small (∼1.2–2.4nm) palladium-containing clusters was detected on the support surface by HRTEM. Catalytic activity was tested in the Heck reaction between 4-bromobenzaldehyde or 4-bromostyrene and styrene. Only the E-isomers of the corresponding cross-coupled products were obtained. The activity and TON numbers of the supported Pd catalysts were higher than those of the palladium(II) acetate under homogeneous catalysis conditions. Strong palladium–support interaction resulted in the generation of catalytically active Pd(0) species without additional reduction pretreatment of the catalyst. The possibility of reuse of the same catalysts in several catalytic cycles was tested. It was found that both the Pd loading in the catalysts and the amount of water in the support have a strong influence on the catalyst’s deactivation. A catalyst with stable activity, able to be recycled at least five times, was prepared with Pd loading of 5wt.% of Pd(AcO)2 using titanate nanotubes calcined at 350°C for 2h prior to the preparation of the catalyst.

An Efficient, Stable and Reusable Palladium Nanocatalyst: Chemoselective Reduction of Aldehydes with Molecular Hydrogen in Water

AbstractPalladium nanoparticles (Pd‐BNP) stabilized by a binaphthyl‐backbone can be efficiently used for the chemoselective reduction of aldehydes in the presence of hydrogen at room temperature in water. The Pd‐BNP catalyst is easily recovered and reused for five catalytic cycles.magnified image

ChemInform Abstract: Mizoroki—Heck Reaction of Aryl Halides and Dialkyl Allylphosphonates in Water Catalyzed by Reusable Palladium Nanoparticles.

AbstractVarious aryl‐substituted allylphosphonates are synthesized using commercial PdCl2(NH3)2 as catalyst under aerobic conditions.

Reusable palladium nanoparticles in one-pot domino Sonogashira-cyclization: regio- and stereo-selective syntheses of (Z)-3-methyleneisoindoline-1-ones and furo[3,2-h]quinolines in water

Nanodomain Pd(0) mediated regio- and stereo-selective synthesis of (Z)-3-methyleneisoindoline-1-ones and furo[3,2-h]quinolines in water was achieved in high yield. The novel one-pot domino-Sonogashira-cyclization protocol is environment friendly as it eliminates the use of ligands, copper, organic solvents or ionic liquids and homogeneous catalysts. More importantly, the nanocatalyst can be recovered in high yield and recycled for five consecutive reactions without any significant loss of reactivity.

Mizoroki–Heck Reaction of Aryl Halides and Dialkyl Allylphosphonates in Water Catalyzed by Reusable Palladium Nanoparticles

AbstractCommercial [PdCl2(NH3)2] was applied to catalyze the Mizoroki–Heck coupling of aryl halides with dialkyl allylphosphonates using iPr2NH as the base in water under aerobic conditions. The reaction was conducted at 80 °C (for aryl iodides) or 120 °C (for aryl bromides) for 36 h, giving the corresponding aryl‐substituted allylphosphonates in good to excellent yields, and both water‐soluble and insoluble aryl halides could be utilized in this reaction. After extracting the reaction solution with ethyl acetate, the residual aqueous solution was reused for the same reaction several times, and the true catalyst was found to be palladium nanoparticles. In addition, a one‐pot synthesis of 1,4‐diarylbuta‐1,3‐dienes, which combined this catalytic reaction with the Horner–Wadsworth–Emmons–Wittig reaction, was also performed.

ChemInform Abstract: Palladium‐Catalyzed Dehydrogenative Generation of Imines from Amines. A Nature‐Inspired Route to Indoles via Cross‐Couplings of Amines with Arylhydrazines.

AbstractSeveral different linear and branched aliphatic primary amines are oxidized with reusable palladium on charcoal to the corresponding primary imines entrapped as arylhydrazones that can be isolated as such.

Palladium‐Catalysed Dehydrogenative Generation of Imines from Amines. A Nature‐Inspired Route to Indoles via Cross‐Couplings of Amines with Arylhydrazines

AbstractH‐substituted imines are elusive compounds formed when aldehydes or ketones are mixed with ammonia. However, this class of molecules can be prepared through selective removal of a hydrogen molecule from a primary amine using a transition metal catalyst. This biomimetic transformation, previously employed for the N‐alkylation of anilines, is applied here to a domino preparation of differently substituted indoles from aliphatic primary amines and arylhydrazines. Several different linear and branched aliphatic primary amines are oxidized with reusable palladium on charcoal to the corresponding primary imines entrapped as arylhydrazones that can be isolated as such. Arylhydrazones can be further converted into N‐alkylindole derivatives via an acid‐mediated indolisation reaction. The one‐pot domino hydrogen transfer Fischer indole synthesis under heterogeneous catalysis is also possible, giving access to diverse substituted indoles, including NH indoles obtained after deprotection of the corresponding benzyl compounds. The truly heterogeneous nature of the catalyst was demonstrated by recycling the catalyst in the same reaction, and in other palladium‐catalysed transformations.magnified image

Heterogeneous Cyanation Reaction of Aryl Halides Catalyzed by a Reusable Palladium Schiff Base Complex in Water

Heterogeneous cyanation reaction of aryl halides with K4[Fe(CN)6] was studied over a polymer supported macrocyclic palladium complex. The reaction proceeded smoothly by adding TX100 (2 wt%) in water without organic solvents. The catalyst exhibited effective catalytic activities to afford the corresponding products in good to excellent yields. Furthermore, the catalyst could be easily recovered and reused for several times without a significant loss of its activity. Heterogeneous cyanation reaction of aryl halides with K4[Fe(CN)6] was studied over a polymer supported macrocyclic palladium complex. The reaction proceeded smoothly by adding TX100 (2 wt%) in water without organic solvents.

ChemInform Abstract: An Efficient and Reusable Palladium Catalyst Supported on a Rasta Resin for Suzuki—Miyaura Cross‐Couplings.

AbstractThe catalyst can be reused up to five times without loss of efficiency.

Silica-supported palladium complex: An efficient, highly selective and reusable organic–inorganic hybrid catalyst for the synthesis of E-stilbenes

A novel, highly efficient and reusable palladium based catalyst has been synthesized by covalent grafting of diphenyldiketone–monothiosemicarbazone on silica gel followed by metallation with palladium chloride, and the resulting organic–inorganic hybrid material was found to be highly effective catalyst for Suzuki-Miyaura cross-coupling reaction of various aryl halides with alkenyl boronic acid to give stilbenes. The catalyst was characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, energy dispersive X-ray fluorescence (ED-XRF), BET surface area analysis, solid-state 13C CPMAS NMR spectroscopy, atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM) and elemental analysis. High turnover frequency, mild reaction conditions, high selectivity for E-stilbenes, and easy recovery and reusability of the catalyst renders the present protocol highly indispensable to address the industrial prerequisites and environmental concerns.

An Efficient and Reusable Palladium Catalyst Supported on a Rasta Resin for Suzuki–Miyaura Cross‐Couplings

AbstractA short and efficient synthesis of a heterogeneous palladium catalyst supported on a rasta resin bearing diphenylphosphanyl ligands is reported. This catalyst was used successfully for Suzuki–Miyaura reactions of aryl bromides in the presence of only 0.25 milli‐equiv. of supported palladium. The catalyst was reused several times with no loss of efficiency, and the amount of palladium leached in the reaction medium is extremely low (< 1 % of the initial amount).

Highly active and reusable palladium nanoparticle catalyst stabilized by polydimethylsiloxane for hydrogenation of aromatic compounds in supercritical carbon dioxide

This study describes a hydrogenation method for degrading polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in supercritical carbon dioxide catalyzed by palladium nanoparticles stabilized in polydimethylsiloxane (Pd/PDMS). The process of synthesizing metal nanoparticles embedded in PDMS polymers involves the preparation of a homogenous mixture of metal salt, silicone elastomer, and a curing agent, followed by hydrogen reduction. PCBs and PAHs can be effectively hydrogenated to saturated hydrocarbons with greater than 99% efficiency in an hour under 200atm of CO2 containing 10atm of H2 at 313K using Pd/PDMS catalysts. The proposed Pd/PDMS catalysts can be reused without losing their activity and are significantly more active than commercial catalysts and a previously reported Pd nanoparticle catalyst stabilized in high-density polyethylene.

ChemInform Abstract: Heterogeneous Copper‐Free Sonogashira Reaction Catalyzed by a Reusable Palladium Schiff Base Complex in Water.

AbstractThe reaction of various aryl iodides tolerates electron‐donating and ‐withdrawing substituents at para‐, meta‐ and ortho positions.

Heterogeneous copper-free Sonogashira coupling reaction catalyzed by a reusable palladium Schiff base complex in water

Heterogeneous Sonogashira coupling of terminal alkynes with aryl halides was studied over a polymer-supported macrocyclic Schiff base palladium complex. The cross-coupling reaction proceeded smoothly by adding a piperidine in water medium. The catalyst exhibited effective catalytic activities to afford the corresponding products in good to excellent yields under copper-free conditions. Furthermore, the catalyst could be easily recovered and reused for several times without a significant loss of its activity.

Heterogeneously catalyzed phosphine-free heck cross-coupling reaction of aryl halides with reusable palladium(II) schiff base complex

The coupling between aryl halides with terminal alkenes (Heck reaction) has been investigated in the presence of a polystyrene-supported Schiff base palladium(II) catalyst. The present catalyst is air and moisture-stable and has significant catalytic activity in Heck cross-coupling reactions under operating conditions. Various aryl halides and terminal alkenes were coupled smoothly under air, to afford the corresponding cross-coupled products in excellent yields. Furthermore, the catalyst can be easily recovered quantitatively by simple filtration and reused up to seven cycles without losing its activity.

ChemInform Abstract: pH‐Dependent Conjugate Addition of Arylboronic Acids to α,β‐Unsaturated Enones Catalyzed by a Reusable Palladium(II)/Cationic 2,2′‐Bipyridyl System in Water under Air.

AbstractPalladium‐catalyzed conjugate addition reaction of cyclic and acyclic enones with arylboronic acids in water gives coupling products in high yields when an aqueous solution of HBF4 is used to adjust the pH value to 1.0.

ChemInform Abstract: Heterogeneous Suzuki and Copper‐Free Sonogashira Cross‐Coupling Reactions Catalyzed by a Reusable Palladium(II) Complex in Water Medium.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

PH‐Dependent conjugate addition of arylboronic acids to α,β‐unsaturated enones catalyzed by a reusable palladium(II)/cationic 2,2′‐bipyridyl system in water under air

AbstractA reusable Pd(NH3)2Cl2/cationic 2,2′‐bipyridyl system for the catalysis of the conjugate addition of arylboronic acids to α,β‐unsaturated enones in water under air was developed. Addition of arylboronic acids to both cyclic and acyclic enones progressed smoothly, providing the products in good to high yields, the best result being obtained when HBF4 was used to adjust the pH value to 1.0. After the reaction, the residual aqueous solution could be reused several times, making the reaction greener and reducing wastage of precious metals. Copyright © 2010 John Wiley & Sons, Ltd.

Heterogeneous Suzuki and copper-free Sonogashira cross-coupling reactions catalyzed by a reusable palladium(II) complex in water medium

An efficient heterogeneous Pd(II) azo complex catalyst for Suzuki and Sonogashira cross-coupling reaction has been developed. The catalyst showed an excellent activity for these reactions in water medium under aerial conditions. A new polystyrene anchored Pd(II) azo complex has been synthesized and characterized. The present Pd(II) azo complex behaves as a very efficient heterogeneous catalyst in the Suzuki coupling and Sonogashira coupling reaction in water medium. Aryl halides, coupled with phenylboronic acids (Suzuki–Miyaura reaction) or terminal alkyne (Sonogashira reaction), smoothly afford the corresponding cross-coupling products in excellent yields (83–100% yield for Suzuki reaction and 68–96% yield for Sonogashira reaction of aryl halides) under phosphine-free reaction conditions in the presence of polystyrene anchored Pd(II) azo complex catalyst in water medium. Furthermore, the catalyst has shown good thermal stability and recyclability. This polymer-supported Pd(II) catalyst could be easily recovered by simple filtration of the reaction mixture and reused for more than six consecutive trials without a significant loss of its catalytic activity.