Palladium Source Research Articles

Study of Electron Beam Irradiated Palladium on Carbon Catalysts for Transfer Hydrogenation Reactions of Nitroarenes Compounds

Palladium-catalyzed hydrogenation is considered a crucial stage in the entire synthesis of difficult natural products as well as a crucial step in the manufacturing of fine compounds used in pharmaceuticals. When it comes to the reaction rate and simplicity of work-up, using Pd/C as heterogeneous catalyst is one of the best choice for process efficiency. In this study, nitroarenes compounds viz. 3-bromo nitrobenzene, 4-fluoro nitrobenzene, 3-methyl nitrobenzene, 4-hydroxy nitrobenzene reduced by using macro 10% Pd/C and micro 10% Pd/C to 3-bromo aniline, 4-fluoro aniline, 3-methyl aniline, 4-hydroxy aniline respectively and verified from 1H NMR studies. The reduction reactions were similar conditions using electron beam irradiated 250 kGy macro and micro 10% Pd/C catalyst. The effectiveness of commercial sources of palladium on carbon (Pd/C) varies widely, leading to the appreciable variations in the reaction times. The decrease in reaction time has been attributed to the higher dispersion of Pd particles upon irradiation. The physico-chemical characteristics of effective hydrogenation catalysts were determined to be: (i) small Pd particle size and (ii) homogeneous distribution of Pd on the carbon support. With no significant loss of catalytic activity, the electron beam-irradiated catalyst can be used again for five runs. These days, chemists can determine as well as forecast the effectiveness of catalysts before investing time and money in expensive synthetic materials.

A Thermally Stable, Alkene-Free Palladium Source for Oxidative Addition Complex Formation and High-Turnover Catalysis

A Thermally Stable, Alkene-Free Palladium Source for Oxidative Addition Complex Formation and High-Turnover Catalysis

Implementing a sustainable process for the recovery of palladium from spent catalysts at industrial scale: A LCA approach

Due to its unique physicochemical properties, palladium is widely used in several industry applications (e.g., vehicle emission control). In view of the circular economy, it is essential to explore secondary sources of palladium, such as urban mines. Current technologies for effective palladium recovery involve high energy consumption and severe environmental impact. More recently, a novel green method for recovering palladium from spent catalysts through a combination of mild acidic leaching and photodeposition on ZnO nanoparticles was proposed on a laboratory scale. In the present study, the environmental impacts of this recovery method, properly upscaled and modelled, was assessed by employing the LCA approach. Specifically, a comparative LCA was carried out for the process with as well as without recycling key components, such as Cu (II) and NaCl for the leaching solution and ZnO. The outcomes identified critical areas and drove the investigation of alternative process configurations to reduce its environmental footprint, such as the use of carbon dioxide in the photodeposition process with the aim of decreasing the resulting terrestrial ecotoxicity. This study marks a significant step forward in advancing research toward industrial−scale implementation of palladium recovery. It provides valuable insights for researchers in the field of green physicochemical processes for metal recovery, thus offering guidance for future decision−making towards more sustainable practices.

The Multifaceted Chemistry of [2.2]Paracyclophane‐Based Thioethers with Palladium(II) Complexes

AbstractThe reactions of planar chiral ([2.2]paracyclophan‐4‐yl)methyl thioethers ([2.2]PCP‐CH2‐SR) with various palladium(II) sources (PdL2) were studied. Unexpectedly, with most of the sulfur substrates investigated (SR=Ph, 2‐pyridyl, Me, n‐dodecyl), and independently of the PdL2 salt employed (L=TFA, OAc, OPiv, Cl, Br), loss of the SR sulfanyl unit, along with incorporation of one palladium L ligand to the lateral benzylic position of the [2.2]PCP core, has been observed. In contrast, the precursor featuring a t‐butylsulfanyl group (R=t‐Bu) exhibited a distinct reactivity. An ortho C(sp2)−H activation took place, and allowed the formation of a [2.2]paracyclophane‐based SC‐palladacycle, in an efficient and highly diastereoselective manner (83 % yield, single diastereoisomer).

Green synthesis of palladium nanoparticles mediated by Acer L. leaves as reducing agent, stabilizer, and carrier for Suzuki reaction

Plant fiber‐supported palladium nanocatalysts (Pdx/FAL) with high catalytic activity and good stability were synthesized by one‐pot method using Na2PdCl4 as palladium source, Acer L. leaves as reducing agent, stabilizer, and carrier without adding chemical reducing agents or stabilizers. The as‐prepared catalysts were characterized by XRD, FT‐IR, SEM, TEM, and so forth. During the preparation process, the extraction of organic matter from Acer L. leaves, the reduction and stabilization of Pd2+, and the loading of palladium nanoparticles (PdNPs) were carried out simultaneously, which greatly simplified the preparation steps and reduced the cost. Oxygen‐ and nitrogen‐containing groups in the Acer L. leaf extract preferentially formed complexes with Pd2+, and then, the polyphenols reduced Pd2+ to Pd0, which ensured that PdNPs with small particle sizes were formed and embedded in porous plant fibers (extraction residue of Acer L. leaves) with oxygen‐containing groups, thereby improving the catalytic activity and stability of the catalyst. The characterization results showed that the prepared PdNPs with a face‐centered cubic structure were uniformly distributed on the support, and the average particle size was 3.08 nm. The Suzuki coupling reaction of 4‐bromonitrobenzene and phenylboronic acid by the prepared catalysts at 40°C showed that the reaction yield could reach 97.72%, and the TOF could reach 3,240.6 h−1, exhibiting high catalytic performance. The reaction of 4‐bromotoluene with phenylboronic acid gave a yield of 98.58%, which remained above 90% after seven repetitions. This article provided a simple, high‐performance, and eco‐friendly synthesis idea for nanopalladium catalysts.

Kumada-Tamao-Corriu Type Reaction of Aromatic Bromo- and Iodoamines with Grignard Reagents.

The first example of the Kumada-Tamao-Corriu type reaction of unprotected bromoanilines with Grignard reagents is described. The method uses a palladium source and a newly designed Buchwald-type ligand as the catalytic system. Secondary and tertiary bromo- and iodoamines were also successfully coupled to alkyl Grignard reagents. The products of the competitive β-hydride elimination reaction were successfully reduced using a highly efficient electron-deficient phosphine ligand (BPhos). Mechanistic considerations allowed us to establish that the less electron-rich phosphine ligands stabilize the transition state much better than the electron-rich ones; hence, they increase the reaction yield and reduce the amount of β-hydride elimination products. The developed method proved to be tolerant of many functional groups and can be applied to many different aromatic bromo- and iodoamines. Multigram synthesis of p-toluidine from 4-bromoaniline was achieved with a palladium catalyst loading of only 0.03 mol%.

A Hierarchy of Ligands Controls Formation and Reaction of Aryl Radicals in Pd-Catalyzed Ground-State Base-Promoted Coupling Reactions.

Palladium salts and complexes were tested separately and in the presence of added ligands as potential sources of aryl radicals in ground-state coupling reactions of aryl halide with arenes under basic conditions (KOtBu). Our recently developed assay for aryl radicals was employed to test for aryl radicals. In this assay, aryl radicals derived from the test substrate, 1-iodo-2,6-dimethylbenzene 7, undergo base-promoted homolytic aromatic substitution (BHAS) with benzene to produce 2,6-dimethylbiphenyl 8 and biphenyl 9 in an approximately 1:4 ratio as well as m-xylene 10. The biphenyl arises from a diagnostic radical transfer reaction with the solvent benzene. Using substrate 7 with a range of Pd sources as potential initiators led to formation of 8, 9, and 10 in varying amounts. However, when any one of a range of diphosphinoferrocenes (e.g., dppf or dippf) or BINAP or the monophosphine, diphenylphosphinoferrocene, was added as a ligand to Pd(OAc)2, the ratio of [2,6-dimethylbiphenyl 8: biphenyl 9] moved decisively to that expected from the BHAS (radical) pathway. Further studies were conducted with dppf. When dppf was added to each of the other Pd sources, the ratio of coupled products was also diverted to that expected for radical BHAS chemistry. Deuterium isotope studies and radical trap experiments provide strong additional support for the involvement of aryl radicals. Accordingly, under these ground-state conditions, palladium sources, in the presence of defined ligands, convert aryl iodides to aryl radicals. A rationale is proposed for these observations.

Synthesis of a Water‐Soluble Pd‐Based Catalyst with a Thymine‐Modified β‐Cyclodextrin Ligand for Suzuki Coupling Reactions

AbstractHerein, the synthesis and crystal structure identification of thymine‐modified β‐cyclodextrin (mono‐(6‐Thymine‐6‐deoxy)‐β‐CD, Thy‐CD) are reported. The catalyst system (Pd@Thy‐CD) was prepared by using the thymine‐modified β‐cyclodextrin as ligand and palladium acetate (Pd(OAc)2) as palladium source. The as‐obtained Pd@Thy‐CD catalyst was characterized by NMR, IR, SEM, and XPS analysis. The catalyst can efficiently catalyze the aqueous phase Suzuki coupling reaction in situ. Under mild reaction conditions, the catalyst system provides excellent yields for the Suzuki coupling reaction of aryl halides, including with aryl chlorides and aryl boronic acids in water. The major advantages of this technique are the ease of preparation of the palladium catalyst, the aqueous phase coupling reaction, the broad functional group tolerance, and the easy recyclability.

Direct Valorization of Recycled Palladium as Heterogeneous Catalysts for Total Oxidation of Methane

Electronic waste as an alternative source of palladium is used for the preparation of heterogeneous catalysts for methane oxidation. The strategy developed in this paper involves two steps: optimization of the leaching protocol to recover the Pd from the waste, and development of a suitable impregnation protocol directly from the leachate, which is a strongly acidic solution. The precipitation-deposition technique is particularly suitable for the preparation of catalysts from acidic media. The impact of Ba, Bi, and Ag impurities on the catalytic performance is studied on model catalysts. The presence of these elements and their impact on the catalytic properties are analyzed and discussed using X-ray diffraction, nitrogen physisorption, scanning and transmission electron microscopy. Through variation of the pH, the impurities co-deposited with Pd can be limited and the catalytic performance of catalysts derived from real waste can be greatly enhanced.

Synthesis, crystal structure, and photophysical properties of mononuclear and dinuclear palladium BODIPY chromophores

AbstractMononuclear and dinuclear palladium‐centered boron dipyrromethene (BODIPY) complexes, HBDPPdI and BDPPd2I2, respectively, were synthesized by the direct insertion of a palladium source into iodine‐substituted BODIPY chromophores. The molecular structures of both metal complexes were characterized using several analytical techniques, including single crystal x‐ray diffraction, to find that Pd(0) is coordinated directly to the ligand through a PdC bond facilitated by the insertion reaction. The photophysical properties of these complexes were also detailed.

Fabrication and catalytic performance of a new diaminopyridine Pd(II) monolayer supported on graphene oxide for catalyzing Suzuki coupling reaction

A new “Chanel like” diaminopyridine Pd(II) catalytic monolayer supported on Graphene Oxide (called GO@DAP-Pd) was prepared by self-assembly (SA) and characterized by XRD, Raman, FT-IR, SEM, TEM and XPS. Catalytic property of GO@DAP-Pd prepared use different Pd source in Suzuki coupling reaction was explored, in which the catalytic activity can be influenced with different palladium sources due to the different size of Pd nanoparticles formed. GO@DAP-Pd1 fabricated with (C6H5CN)2PdCl2 as Pd source, exhibited a higher catalytic activity and could be reused at least 7 times. The deactivation of catalyst was mainly due to the aggregation of active Pd and the loss of a small amount of active Pd, resulting in the deactivation of the catalyst. The catalytic mechanism was detail explored by hot filtration, poisoning experiments, XRD, Raman, XPS and React IR, and the results showed that catalytic process occurred at the interface, including substrates adsorption, intermediate formation and product desorption. The structure and synergy in active sites containing PdO(110), Pd(200, 111) and Pd(111)/PdO(002) are crucial to enhance the catalytic activity. The method to form the multi-active sites in situ on the surface of organometallic monolayer can supply an efficient way to design and prepare the high active catalytic monolayer.

One Pot Access to 2′‐Aryl‐2,3′‐Bithiophenes via Twofold Palladium‐Catalyzed C−X/C−H Coupling Associated to a Pd‐1,4‐Migration

AbstractThe reactivity of 1,2‐dihalobenzenes in palladium catalyzed polyheteroarylation via C−H bond functionalization was investigated. The first catalytic cycle using thiophene as the heteroarene gives the expected 2‐(2‐bromophenyl)thiophenes. In the course of the second catalytic cycle, in the presence of heteroarenes having a free C3‐position, a partial Pd‐1,4‐migration occurred giving rise to aryl‐substituted biheteroarenes such as 2′‐aryl‐2,3′‐bithiophenes as well as the expected 1,2‐di(thiophen‐2‐yl)benzenes. The best selectivities in favor of the formation of 2′‐aryl‐2,3′‐bithiophenes were obtained with electron‐rich 1,2‐dihalobenzenes. A wide variety of thiophene derivatives bearing useful functions such as formyl, acetyl, cyclopropylmethanone, 2‐methyl‐1,3‐dioxolane, ester, nitrile or chloro was tolerated allowing to prepare poly‐functionalized 2′‐aryl‐2,3′‐bithiophenes. Moreover, this one pot preparation of 2′‐aryl‐2,3′‐bithiophenes employs a low loading of an air stable commercially available palladium source associated to an inexpensive base.magnified image

Asymmetric Suzuki Cross‐Coupling Reactions Catalyzed by Chiral Surfactant‐Stabilized Palladium Nanoparticles

AbstractWe report the synthesis of cinchonine and hydrocinchonine derived surfactants by reacting with various mono alkylating agents (hexyl, octyl, octadecyl, dodecyl bromides) and di‐alkylating agent such as α,α’‐p‐xylene‐di‐bromide. A series of chiral surfactants have been used to stabilize palladium nanoparticles (NPs) which are water soluble. These Pd NPs were utilized in asymmetric Suzuki cross coupling reaction of naphthalene boronic acids with substituted naphthalene bromides to get binaphthalenes and terephenylenes. It was observed that, the surfactant's alkyl‐chain length and the palladium source played a major role in this catalytic reaction. The high solubility and positive zeta potential of gemini‐surfactant (GS) stabilized Pd NPs make them attractive as a potential candidate for the synthesis of binaphthalenes and terephenylenes with high yields.

Solvent-Free Synthesis of Core-Functionalised Naphthalene Diimides by Using a Vibratory Ball Mill: Suzuki, Sonogashira and Buchwald-Hartwig Reactions.

Solvent‐free synthesis by using a vibratory ball mill (VBM) offers the chance to access new chemical reactivity, whilst reducing solvent waste and minimising reaction times. Herein, we report the core functionalisation of N,N’‐bis(2‐ethylhexyl)‐2,6‐dibromo‐1,4,5,8‐naphthalenetetracarboxylic acid (Br2‐NDI) by using Suzuki, Sonogashira and Buchwald–Hartwig coupling reactions. The products of these reactions are important building blocks in many areas of organic electronics including organic light‐emitting diodes (OLEDs), organic field‐effect transistors (OFETs) and organic photovoltaic cells (OPVCs). The reactions proceed in as little as 1 h, use commercially available palladium sources (frequently Pd(OAc)2) and are tolerant to air and atmospheric moisture. Furthermore, the real‐world potential of this green VBM protocol is demonstrated by the double Suzuki coupling of a monobromo(NDI) residue to a bis(thiophene) pinacol ester. The resulting dimeric NDI species has been demonstrated to behave as an electron acceptor in functioning OPVCs.

Deracemization of Binaphthyl by Suzuki Diarylation: The Role of Electronic and Steric Effects.

We report a Suzuki 2,2'-diarylation of the racemic 2,2'-diiodo-1,1'-binaphthyl which proceeds with deracemization via a pallada(IV)cyclic intermediate, induced by a simple chiral ligand─BINAP [2,2'-bis(diphenylphosphino)-1,1',-binaphthyl]. A systematic study of the reaction scope, using 45 arylboronic acids, reveals that the diarylated product is formed when meta- and/or para-substituted phenylboronic acids are functionalized with a substituent with the Hammett constant from -0.5 to +0.4. Multiparametric analysis accounting for the effect of geometry on the reactivity using Boltzmann-weighted Sterimol parameters and electronic effects described by Hammett descriptors shows that the enantioselectivity depends on steric effects only, with enhanced enantioselectivity observed for substituents with a larger length, wL, and reduced for substituents with a larger maximum width, wB5. We show that careful tuning of these parameters, with the aid of the presented mathematical model, can lead to excellent enantioselectivity. Additional factors that are investigated and found to affect the stereoselective course of the reaction include the reaction temperature, palladium source, palladium to ligand ratio, and the type of boronic acid derivative. During the chromatographic separation of diarylated products on an achiral silica gel, we observed a rare phenomenon: the diarylated products undergo self-disproportionation of enantiomers, with the major enantiomer being eluted first.

Palladium-Catalyzed One-Step Synthesis of Stereodefined Difunctionalized Glycals

Palladium-Catalyzed One-Step Synthesis of Stereodefined Difunctionalized Glycals

A Review of Recovery of Palladium from the Spent Automobile Catalysts

The spent automobile catalysts (SAC) is the major secondary source of palladium and the production of SAC is increasing rapidly over years. The price of palladium keeps rising over the years, which demonstrates its preciousness and urgent industrial demand. Recovering palladium from the spent automobile catalysts benefits a lot from economic and environmental protection aspects. This review aims to provide some new considerations of recovering palladium from the spent automotive catalysts by summarizing and discussing both hydrometallurgical and pyrometallurgical methods. The processes of pretreatment, leaching/extraction, and separation/recovery of palladium from the spent catalysts are introduced, and related reaction mechanisms and process flows are given, especially detailed for hydrometallurgical methods. Hydrometallurgical methods such as chloride leaching with oxidants possess a high selectivity of palladium and low consumption of energy, and are cost-effective and flexible for different volume feeds compared with pyrometallurgical methods. The recovery ratios of palladium and other platinum-group metals should be the focus of competition since their prices have been rapidly increased over the years, and hence more efficient extractants with high selectivity of palladium even in the complexed leachate should be proposed in the future.

Sustainable Pd-Catalyzed Direct Arylation of Thienyl Derivatives with (Hetero)aromatic Bromides under Air in Deep Eutectic Solvents

An optimized protocol for the Pd-catalyzed direct arylation of 3,4-ethylenedioxythiophene (EDOT) and other substituted thiophenes with (hetero)aromatic bromides in a deep eutectic solvent made of a mixture of choline chloride/glycerol (1:2) is presented. The coupling reactions have been successfully run under air, in nonanhydrous conditions, using PdCl2 as a palladium source, with a catalyst loading as low as 1 mol %. The adjustment of each reaction component allowed finding robust conditions for the introduction of both electron-poor and electron-rich (hetero)aryl bromides with moderate-to-high yields. The sustainability of the protocol was established through calculations of green metrics, such as Eco-scale and E-factor, and compared with the literature, when possible. Remarkably, such procedure can be successfully applied for the simple preparation of conjugated organic compounds with potential applications in optoelectronics, as we have shown, by obtaining two molecules previously reported as a hole transport material for perovskite solar cells and the final intermediate of a photosensitizer for dye-sensitized solar cells.

Recent developments in C–C bond formation catalyzed by solid supported palladium: a greener perspective

Abstract The world today is struggling to achieve sustainable means for synthetic processes. Standing at this juncture, we need to develop and implement greener and reusable approaches towards organic synthesis. Transition metals especially palladium is a wonder element which has the ability to catalyze a range of useful organic syntheses. However, the expensive nature of palladium has urged synthetic chemists to search for protocols where a single palladium source may be used repeatedly in successive reactions, thus making the overall process cost effective. Palladium when anchored to solid supports leads to catalytic systems which can be easily separated from the organic phase post reaction and can be reused in successive cycles. Not only does this make the process economically viable but also ensures that no metal contaminates the purity of the final organic product. In this review we will highlight the recent developments in C–C bond formation (which is by far the most fundamental mode of bond making in organic synthesis) via the use of solid supported palladium catalytic systems. We will use this opportunity to illustrate the synthetic processes from a greener sustainable point of view which we feel is of utmost relevance in the current scientific scenario.

The Mizoroki‐Heck Reaction in Tunable Aryl Alkyl Ionic Liquids

AbstractWe report the use of imidazolium based tunable aryl alkyl ionic liquids (TAAILs) as solvents in the Mizoroki–Heck reaction. Different commercially available palladium sources, inorganic bases, TAAILs and reaction conditions were tested for the synthesis of trans‐stilbene using bromobenzene and styrene. A variety of different stilbene derivatives were synthesized with exclusive formation of the (E)‐isomers and isolated yields up to 97 %. We were able to optimize the reaction conditions using only 0.25 mol% of Pd(OAc)2 as the catalyst and a reaction time of 4 hours. No additional ligands or additives are used in the reaction. The catalytic system using TAAILs achieved higher yields than commercially available imidazolium and phosphonium ionic liquids, demonstrating the potential of tailored ionic liquids as a reaction medium for the Mizoroki–Heck reaction.