Pd Catalyst System Research Articles

Palladium-catalyzed radical arylation of N-hydroxyphthalimides with triphenyl phosphites as an unusual arylating agent via C(sp2)–O bond cleavage

An approach has been developed for producing aryl radical intermediates by utilizing readily accessible triphenyl phosphite as the radical precursor in a Pd-catalyst system under air conditions. Moreover, the possible mechanism was proposed.

Palladium-Catalyzed Cross-Coupling of gem-Difluorocyclopropanes with gem-Diborylalkanes for the Synthesis of Boryl-Substituted Fluorinated Alkenes.

This study presents a novel method for the regioselective coupling of gem-difluorinated cyclopropanes with gem-diborylmethane, utilizing a Pd-catalyst system. This innovative approach enables the synthesis of 2-fluoroalkenyl monoboronate scaffolds with high Z-selectivity. The resulting products undergo further transformations, including oxidation, Suzuki cross-coupling, and trifluoroborylation, all of which are achieved with good yields. This work introduces a valuable synthetic pathway to access important fluorinated compounds for various applications in organic chemistry.

Cooperative Chiral Lewis Base/Palladium-Catalyzed Asymmetric Syntheses of Methylene-Containing δ-Lactams.

We herein report a two-step approach for the enantioselective synthesis of novel chiral δ-lactams. By using a cooperative chiral ITU/achiral Pd-catalyst system, this protocol proceeds via an asymmetric α-allylation of activated aryl esters first, followed by an acid-mediated lactam formation. A variety of differently substituted products could be obtained with usually high levels of enantioselectivities and in reasonable yields (16 examples, up to 98 : 2 er and 73 % yield over two steps). In addition, further utilizations of the products via transformations of the exocyclic double bond were successfully carried out as well.

Synergic Palladium Catalysis for Aerobic Oxidative Coupling

AbstractAerobic oxidative coupling is a dehydrogenative organic transformation in which molecular oxygen acts as a re‐oxidant for the catalyst system. Pd has emerged as one of the most popular transition metal catalysts for such reactions. Combinations of Pd with other transition metal catalysts can also provide effective catalytic cycles together with highly atom‐ and step‐economical organic transformations. A synergic Pd catalyst system can promote such reactions with a high degree of efficiency based on a re‐oxidation step exhibiting improved kinetics in which two electrons are transferred from another transition metal. This occurs in conjunction with a lower energy barrier than that associated with direct re‐oxidation by molecular oxygen. This review highlights recent developments in aerobic oxidative coupling reactions catalyzed by synergic combinations of Pd with other transition metals. Highlighted reactions include dehydrogenative C−C bond formation such as arylation of arenes, heteroarenes, alkenes and dehydrogenative C−N and C−O bond formations with unsaturated hydrocarbons such as alkenes, 1,3‐dienes and allenes. Moreover, mechanistic insights into these aerobic reactions based on experimental, computational and optical studies are detailed.

Catalytic Asymmetric Benzylation of Azomethine Ylides Enabled by Synergistic Lewis Acid/Palladium Catalysis.

The synergistic chiral Lewis acid/achiral Pd catalyst system was successfully applied in the enantioselective benzylation of various imine esters, giving a range of α-benzyl-substituted α-amino acid derivatives in satisfactory yield with excellent enantioselectivity. It is worth noting that this strategy exhibits good tolerance for bicyclic and monocyclic benzylic electrophiles. Furthermore, the utility of this synthetic protocol was demonstrated by the expedient preparation of enantioenriched antihypertensive drug α-methyl-l-dopa.

Immobilized Pd on a NHC-functionalized metal-organic FrameworkMIL-101(Cr): An efficient heterogeneous catalyst in the heck and copper-free Sonogashira coupling reactions

A heterogeneous palladium catalyst system based on immobilization of palladium moieties on a N-heterocyclic carbene (NHC) modified metal organic framework (MOF) was developed for the Heck and copper-free Sonogashira coupling reactions. In order to prepare this catalyst system, first, MIL-101(Cr) was functionalized with NHC moieties through a post synthetic modification (PSM) approach, and then Pd metal was stabilized on the prepered MIL-101(Cr)-NHC substrate. This material was characterized using various microscopic and spectroscopic techniques and then was used as an efficient heterogeneous Pd catalyst system in the Heck and copper-free Sonogashira reactions. Results of the heterogeneity tests showed that the Pd-NHC-MIL-101(Cr) catalyst can efficiently catalyzed these coupling reactions heterogeneously and no remarkable changes observed in the morphology and structure of MIL-101(Cr) template during the reaction progress. Also, existence of palladium nanoparticles immobilized on the MOF structure affirmed by the TEM and XPS analysis confirmed the oxidation state of Pd. A variety of alkene and alkyne derivatives were synthesized in good to excellent yields using this heterogeneous Pd catalyst system under normal conditions. More importantly Pd-NHC-MIL-101(Cr) catalyst was simply recovered from the reaction medium without remarkable decreasing in its catalytic activities after five times of reusability. The ICP analysis showed the very low Pd and Cr metals leaching, representing high stability and applicability of this catalyst in Pd coupling reactions.

Palladium-Catalyzed Monoarylation of Arylhydrazines with Aryl Tosylates.

A palladium-catalyzed C-N bond coupling reaction between arylhydrazines and aryl tosylates for facile synthesis of unsymmetrical N,N-diarylhydrazines has been developed. Employing the catalyst system of Pd(TFA)2 associated with newly developed phosphine ligand L1, the monoarylation of arylhydrazine proceeds smoothly to afford desired products in good-to-excellent yields (up to 95%) with good functional group compatibility. This method provides an alternative synthetic pathway for accessing structurally diversified N,N-diarylhydrazines from simple and easily accessible coupling components.

Palladium-catalyzed aryloxy- and alkoxycarbonylation of aromatic iodides in γ-valerolactone as bio-based solvent

Fossil-based solvents and triethylamine as a toxic and volatile base were successfully replaced with γ-valerolactone as a non-volatile solvent and K2CO3 as inorganic base in the alkoxy- and aryloxycarbonylation of aryl iodides using phosphine-free Pd catalyst systems. By this, the traditional systems were not simply replaced but also significantly improved. In the study, the effects of different reaction parameters, i.e. the use of several other solvents, the temperature, the carbon monoxide pressure, the base and the catalyst concentrations, were evaluated in details on the efficiency of the carbonylations. To gather some information on the mechanism of these reactions, the effects of the electronic parameters (σ) of various aromatic substituents of the aryl iodides as well as the influence of para-substitution of phenol were investigated on the activity. For a comparison, the aryl-substituted aryl iodides were also reacted with methanol and aryl iodide was also alkoxycarbonylated using several different lower alcohols. From the observed correlations between the electronic parameters of the aromatic substituents and the rates, it appears that the rate determining step is the oxidative addition of Ar–I to Pd0, provided that sufficient amounts of nucleophiles are present for the ester formation. If this is not the case, the rate of nucleophile attack might determine the overall rate.

Immobilized Pd on a NHC functionalized metal–organic framework MIL‐101(Cr): an efficient heterogeneous catalyst in Suzuki−Miyaura coupling reaction in water

A novel Pd−NHC functionalized metal–organic framework (MOF) based on MIL‐101(Cr) was synthesized and used as an efficient heterogeneous catalyst in the C‐C bond formation reactions. Using this heterogeneous Pd catalyst system, the Suzuki−Miyaura coupling reaction was accomplished well in water, and coupling products were obtained in good to excellent yields in short reaction time. The Pd−NHC−MIL‐101(Cr) was characterized using some different techniques, including Fourier transform‐infrared, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy, inductively coupled plasma and elemental analysis. The microscopic techniques showed the discrete octahedron structure of MIL‐101(Cr), which is also stable after chemical modification process to prepare the catalyst system. The TEM images of the catalyst showed the existence of palladium nanoparticles immobilized in the structure of the catalyst, while no reducing agent was used. It seems that the NHC groups and imidazolium moieties in the structure of the MOF can reduce Pd (II) to Pd (0) species. This modified MOF substrate can also prevent aggregation of Pd nanoparticles, resulting in high stability of them in organic transformation. The Pd−NHC−MIL‐101(Cr) catalyst system could be simply extracted from the reaction mixture, providing an efficient synthetic method for the synthesis of biaryls derivatives using the aforementioned coupling reaction. The Pd−NHC−MIL‐101(Cr) catalyst could be recycled in this organic reaction with almost consistent catalytic efficiency.

Mussel‐Inspired Flexible, Durable, and Conductive Fibers Manufacturing for Finger‐Monitoring Sensors

AbstractHere a bioinspired facile and versatile method is reported for fabricating highly durable, washable, and electrically conductive fibers and yarns. Self‐polymerized dopamine plays as adherent layers for substrates and then captures Pd2+ catalyst for subsequent metal deposition on substrates. The Pd2+ ions are chelated and partially reduced to nanoparticles by polydopamine (PDA)‐modified substrates and the catalytic performance is investigated in surface electroless deposition. Importantly, this is the first report about PDA as both ligand and enhancement in Pd catalyst system, and the mechanism of their excellent catalytic performance is studied by X‐ray photoelectron spectroscopy. This approach can be extended as a general method for fabricating conductors from all kinds of substrates and precursory research about PDA/Pd catalyst application in surface catalysis.

Convergent Synthesis of the NS5B Inhibitor GSK8175 Enabled by Transition Metal Catalysis.

A convergent eight-stage synthesis of the boron-containing NS5B inhibitor GSK8175 is described. The previous route involves 13 steps in a completely linear sequence, with an overall 10% yield. Key issues include a multiday SNAr arylation of a secondary sulfonamide using HMPA as solvent, multiple functional group interconversions after all of the carbon atoms are installed (including a Sandmeyer halogenation), use of carcinogenic chloromethyl methyl ether to install a protecting group late in the synthesis, and an unreliable Pd-catalyzed Miyaura borylation as the penultimate step. We have devised an orthogonal approach using a Chan-Lam coupling between a halogenated aryl pinacol boronate ester and an aryl methanesulfonamide. This reaction is performed using a cationic Cu(I) precatalyst, which can be easily generated in situ using KPF6 as a halide abstractor. High-throughput screening revealed a new Pd catalyst system to effect the penultimate borylation chemistry using simple monodentate phosphine ligands, with PCyPh2 identified as optimal. Reaction progress analysis of this borylation indicated likely mass-transfer rate limitations under standard conditions using KOAc as the base. We have devised a K2CO3/pivalic acid system as an alternative, which dramatically outperforms the standard conditions. This new synthesis proceeds in eight stages with a 20% overall yield.

The Stability of Cu Electroless Deposition Solution Employing Copper Nanoparticle As the Catalyst

Cu electroless deposition (ELD) technology has been widely used in the metallization of non-conductive materials, such as a printed circuit board (PCB) and polyimide film (PI). In the ELD process, industries use traditional Sn/Pd colloid as the catalyst to initiate the Cu ELD. However, palladium is an expensive noble metal. In addition, the residual palladium adsorbed on the resin surface has to be removed after copper patterning to prevent a possible short between two copper lines in the semi-additive process (SAP). This would increase the overall process cost. As a result, we use copper nanoparticle (CuNP) as the catalyst to initiate the Cu ELD on the resin surface and the sidewall of through holes of a PCB. In this work, the stability of the Cu ELD solution is important for industrial production. We select different chelators and reducers to study their effect on the stability of Cu ELD solution under the condition of using CuNP as the catalyst. The stability of the Cu ELD solution was characterized by UV-Vis spectroscopy and electrochemical analysis. The morphology of the ELD Cu layer was imaged by scanning electron microscope (SEM) and optical microscope (OM). Results show that the Cu ELD solution (i.e., formula) is different from that is formulated for Pd catalyst system. Keywords: Electroless copper deposition, Copper nanoparticle, Stability, Semi-additive process Reference: Kyung Ju Park, Hyo-Chol Koo, Taeho Lim,a Myung Jun Kim, Oh Joong Kwon, and Jae Jeong Kim, “Evaluation of Stability and Reactivity of Cu Electroless Deposition Solution by In-Situ Transmittance Measurement”, Journal of The Electrochemical Society, vol. 158, pp. D541-D545, 2011.Fumihiro Inoue, Harold Philipsen, Alex Radisic, Silvia Armini, Yann Civale, Shoso Shingubara, and Peter Leunissena, “Electroless Copper Bath Stability Monitoring with UV-VIS Spectroscopy, pH, and Mixed Potential Measurements”, Journal of The Electrochemical Society, vol. 159, pp. D437-D441, 2012.

Synthesis of pentafluorosulfanyl (SF5) containing aromatic amino acids

Herein, a series of aromatic pentafluorosulfanyl (SF5) containing amino acids are reported. A Negishi cross-coupling strategy utilising a catalyst system of Pd(dba)2 and SPhos afforded the aforementioned SF5 amino acids in yields between 32% and 42%. Two dipeptides utilising both the amine and carboxylic functionalities of the synthesised SF5 containing amino acids were prepared, demonstrating their compatibility with common amide/peptide coupling reagents and strategies.

Supported Palladium on Magnetic Nanoparticles–Starch Substrate (Pd-MNPSS): Highly Efficient Magnetic Reusable Catalyst for C–C Coupling Reactions in Water

A novel heterogeneous Pd–catalyst system (Pd-MNPSS) was developed using immobilization of Pd species (PdII and Pd0) on starch-functionalized magnetic nanoparticles. For the synthesis of Pd-MNPSS catalyst, first, magnetic nanoparticles (MNPs) were prepared and coated with a silica layer (Fe3O4@SiO2) to increase their stability and functionalization capability. The Fe3O4@SiO2 particles were reacted with thionyl chloride (SOCl2) to generate chlorosilyl groups on the surface of MNPs. Reaction of starch with chloro-functionalized MNPs leads to a magnetic reusable poly-hydroxy-functionalized substrate (MNPSS), which is highly suitable for immobilization of Pd metal on its surface. This catalyst system was designed to be applied in Pd-catalyzed organic coupling reactions in water. Finally, the Pd-MNPSS catalyst was prepared via reaction of MNPSS and Pd(OAc)2. After characterization of the Pd-MNPSS catalyst it was applied in the Heck and Sonogashira coupling reactions in water solvent, and excellent results were ...

Palladium-catalysed enantioselective hydroaryloxycarbonylation of styrenes by 4-substituted phenols

Palladium-catalysed hydroaryloxycarbonylation of a set of styrenes was performed under carbon monoxide atmosphere towards the corresponding propanoic acid aryl esters. The reaction conditions were optimized and several phosphine ligands (achiral mono- and bidentate, chiral (enantiopure) bidentate) were investigated in Pd-catalyst systems generated in situ. In general, the application of mono- and diphosphines favours the formation of branched and linear regioisomers, respectively. Carrying out the reaction in enantioselective fashion, the DIOP modified catalyst proved to be the most efficient one among the chiral ligands studied. The substituent effect on the regio- and enantioselectivity was also investigated regarding both the substrate (styrene) and the O-nucleophile (phenol) with Pd-DIOP system. Simultaneous modifications of substituents of the ‘reactants’ were also carried out. The preference of the linear ester regioisomer and low enantiomeric excesses were obtained.

Enantioselective Palladium-Catalyzed Oxidative Cascade Cyclization of Aliphatic Alkenyl Amides.

The catalyst system of Pd(TFA)2/(S,S)-diPh-pyrox is reported to promote the highly efficient enantioselective oxidative cascade cyclization of alkene-tethered aliphatic acrylamides under mild aerobic conditions. A series of pyrrolizidine derivatives have been synthesized in good yield and excellent enantioselectivity. Deuterium-labeling experiments have revealed that the reaction proceeded through an anti-aminopalladation (anti-AP) pathway with high selectivity. The transition states for the anti-AP step have been calculated to account for the observed enantioselectivity.

Highly Selective Upgrading of Biomass-Derived Alcohol Mixtures for Jet/Diesel-Fuel Components.

In light of the increasing concern about the energy and environmental problems caused by the combustion of petroleum-based fuels (e.g., jet and diesel fuels), the development of new procedures for their sustainable production from renewable biomass-derived platform compounds has attracted tremendous attention recently. Long-chain ketones/alcohols are promising fuel components owing to the fuel properties that closely resemble those of traditional fuels. The focus of this report is the production of long-chain ketones/alcohols by direct upgrading of biomass-derived short-chain alcohol mixtures (e.g., isopropanol-butanol-ethanol mixtures) in pure water. An efficient Pd catalyst system was developed for these highly selective transformations. Long-chain ketones/alcohols (C8 -C19 ), which can be used as precursors for renewable jet/diesel fuel, were obtained in good-to-high selectivity (>90 %) by using the developed Pd catalyst.

Novel Catalyst System for Suzuki-Miyaura Coupling of Challenging DNA-Linked Aryl Chlorides.

A novel Pd catalyst system, [(t-Bu)2P(OH)]2PdCl2 (POPd) with the ligand sodium 2'-(dicyclohexylphosphino)-2,6-dimethoxy-[1,1'-biphenyl]-3-sulfonate, is reported. It effectively catalyzes the Suzuki-Miyaura coupling of challenging phenyl chlorides and pyrimidinyl chlorides that are covalently linked to a double-stranded DNA-template with various boronic acids/esters.

Nanostructured palladium catalyst poisoning depressed by cobalt phosphide in the electro-oxidation of formic acid for fuel cells

Abstract Nanostructured palladium is considered as the best catalyst materials for direct formic acid fuel cells but catalyst poisoning suffering from the intermediates seriously reduces catalytic activity and stability, thus further hinders the commercial application of fuel cells technology. Herein, we report the tricky Pd catalyst poisoning problem could be greatly depressed by cobalt phosphide (CoP) material during formic acid oxidation, so an extremely active and stable Pd catalyst with very low Pd loading (5 wt%) is realized. The high anti-poisoning ability was evidenced by a significantly faster kinetics study and less poisoning intermediates adsorbed on its surface compared with Pd/C catalyst. When integrated into a real fuel cells model, a power density of 150 mW cm −2 catalyzed by this Pd-CoP/C catalyst (5 wt%, Pd) was comparable to that of the commercial Pd/C catalyst (20 wt%, Pd) indicating a very promising application in the electrochemical energy devices. This work opens an avenue to overcome the universal catalyst poisoning issue and pushes Pd catalyst system much stronger for commercial application in fuel cells technology.

Palladium Nanoparticles Supported on Nitrogen‐Doped Carbon Nanotubes as a Release‐and‐Catch Catalytic System in Aerobic Liquid‐Phase Ethanol Oxidation

AbstractPd nanoparticles supported on carbon nanotubes were applied in the selective oxidation of ethanol in the liquid phase. The characterization of the surface and bulk properties combined with the catalytic tests indicated the dissolution and redeposition of Pd under the reaction conditions. A dynamic interplay within the Pd life cycle was identified to be responsible for the overall reactivity. Nitrogen‐doped carbon nanotubes were found to act as an excellent support for the Pd catalyst system by efficiently stabilizing and recapturing the Pd species, which resulted in high activity and selectivity to acetic acid.