Palladium Catalyst Research Articles

Exploring the energetics of Suzuki cross-coupling reaction: A computational study of palladium and nickel catalysts

The present study employed density-functional theory (DFT) calculations to investigate the Suzuki-Miyaura Cross-Coupling reaction using single atom catalysis (SAC) via palladium or nickel. The reaction barriers for chloride bond cleavage in phenyl chloride were found to be 34.68 kJ/mol and 24.24 kJ/mol for palladium and nickel catalysts, respectively. During the transmetalation process, the energy barrier for boronic acid release from phenyl trihydroxyboronate using SAC via palladium and SAC via nickel was calculated to be 74.17 kJ/mol and 65.22 kJ/mol, respectively. The results indicated that in the oxidative addition and transmetalation reactions, the SAC via nickel outperforms the SAC via palladium, while the SAC via palladium excels in the reductive elimination reaction. These findings suggest the effectiveness of a SAC via nickel as a substitute for SAC via palladium in the synthesis of biphenyls in the Suzuki-Miyaura cross-coupling reaction.

Palladium catalyst immobilized on functionalized hyper–cross-linked polymers with 8-hydroxyquinoline as monomer for Suzuki–Miyaura coupling reactions

Palladium catalyst immobilized on functionalized hyper–cross-linked polymers with 8-hydroxyquinoline as monomer for Suzuki–Miyaura coupling reactions

Hydrogen generation based on a gel-like formate system with a palladium catalyst

Catalytic formate decomposition under mild conditions is a promising strategy for hydrogen production as an efficient hydrogen carrier. Most of previous studies performed formate decomposition for hydrogen generation in liquid phase or using formate as a promoter for formic acid decomposition, which exhibits relatively low hydrogen energy density by mass. Here, we reported a gel-like formate system for catalytic hydrogen generation under mild conditions. A H2 yield of 100% with hydrogen energy density by weight of 2.38 wt% was achieved, and the palladium catalyst shows high stability and recyclability for KCOOH gel decomposition. Moreover, the constructed gel-like formate filled in an aluminum cylinder could continuously and steadily supply hydrogen to a 12V/35W fuel cell to drive a LED display. This work may provide a new thought for safe hydrogen storage and production system for hydrogen energy usage in the future.

The synthesis of asymmetrical anilinotropone nickel and palladium complexes for olefin polymerization

For the Coordination-insertion olefin polymerization, the development of high-performance transition-metal catalysts is always the key issue and extensive efforts have been made in this field. In this contribution, we designed several asymmetrical anilinotropone nickel and palladium catalysts. Compared to palladium complex, the nickel catalysts exhibited high activity in ethylene polymerization. The topology microstructure of polyethylene could be modulated by different polymerization temperature. The anilinotropone nickel catalysts Ni2 and Ni3 in this work demonstrated higher thermolability, generating polyethylene with higher molecular weight (up to 285.9 kg mol−1). Moreover, these nickel systems also promoted the copolymerization of ethylene with norbornene-type polar monomers (NB–COOMe, NB-OAc), which demonstrated great polar group tolerance in this system. The generated copolymer exhibited high molecular weight (up to 93.1 kg mol−1) and high polar monomer incorporation ratio (up to 6.9 mol%). The design of asymmetrical anilinotropone catalysts in this work presented a unique form in olefin polymerization and may attract wide application interests in metal catalysis areas.

Effect of Iron Content in Alumina-Supported Palladium Catalysts and Their Reduction Conditions on Diclofenac Hydrodechlorination in an Aqueous Medium

Effect of Iron Content in Alumina-Supported Palladium Catalysts and Their Reduction Conditions on Diclofenac Hydrodechlorination in an Aqueous Medium

Palladium-Catalyzed Regioselective Insertion of Carbenes into γ-C(sp3)-H Bonds of Aliphatic Amines.

A migratory insertion of carbenes into distal γ-C(sp3)-H bonds of aliphatic amines has been successfully developed. The synergistic interplay among a palladium catalyst, picolinamide directing group, a carefully selected base additive, and an essential ligand proved crucial in achieving high yields. These findings hold significant value for advancing the exploration of regioselective carbene insertions into nonactivated C(sp3)-H bonds.

Controllable Chemoselectivity Cascade Reactions for the Synthesis of Phenanthrenols via Palladium-Catalyzed-Suzuki/Heck Reaction and Michael Addition.

Palladium serves as a multi-functional catalyst which is controllable by tuning reaction conditions. This work demonstrated the utilization of a palladium catalyst for the synthesis of phenanthrenols by cascade palladium-catalyzed Suzuki/Heck reaction between chalcone and 2-bromophenylboronic acid, followed by Michael addition. The sequential reaction could be controlled by reactivity of the palladium catalyst in different solvents and concentrations of reagents. This protocol could be applied to a broad range of substrates to give products in low to good yields.

Regioselective chain‐straightening polymerization of α‐olefins through 2,ω‐enchainment using amine–imine nickel catalysts

AbstractThe control of the regioselectivity of metal‐catalyzed α‐olefins polymerization is of everlasting interest. Most nickel and palladium catalysts show high regioselectivity involving 2,1‐insertion of α‐olefins and 1,ω‐enchainment chain‐straightening, especially α‐diimine nickel catalysts. In this contribution, we report extremely rare regioselective chain‐straightening polymerization of α‐olefins through 2,ω‐enchainment using unsymmetrical amine–imine nickel catalysts. The polymerizations of α‐olefins (1‐hexene, 1‐octene, and 1‐decene) were studied in detail, and the effects of catalyst structure, reaction temperature, and monomer concentration on the polymerization activity and the regioselectivity were examined. The unsymmetrical N‐substituents of the amine–imine nickel catalysts play a crucial role in the regioselectivity. High regioselectivity involving 80.4% 1,2‐insertion and 84.5% 2,ω‐enchainment is realized to produce amorphous polyolefins without melting temperatures.

A Palladium Catalyst Supported on Boron-Doped Porous Carbon for Efficient Dehydrogenation of Formic Acid.

Formic acid has emerged as a highly promising hydrogen storage material, and the development of efficient catalysts to facilitate its dehydrogenation remains imperative. In this study, a novel catalyst consisting of palladium nanoparticles supported on boron-doped porous carbon (Pd/BPC) was successfully synthesized to enable efficient hydrogen production through the dehydrogenation of formic acid. The impacts of the boron doping ratio, doping temperature, and palladium reduction temperature on the catalyst's performance were systemically investigated. The results demonstrated the Pd/BPC catalyst synthesized with a carbon-to-boron ratio of 1:5 by calcination at 900 °C and subsequent reduction at 60 °C exhibited superior formic acid dehydrogenation performance, being 2.9 and 3.8 times greater than that of the Pd/PC catalysts without boron doping and commercial Pd/C, respectively. Additionally, the catalyst showed excellent cycle stability with no significant activity reduction after five consecutive cycles. Experimental and theoretical results reveal that boron doping not only facilitates the homogenous distribution of Pd nanoparticles but also induces a stronger support-metal interaction, thereby reinforcing the catalytic performance. This research is expected to provide valuable insights into the economically viable and efficient production of environmentally friendly hydrogen energy.

Acid-resisting covalent organic framework enabling high-efficiency palladium recovery from used palladium catalyst under strong acid

Pd recovery from used sources is now receiving growing attentions, due to its scarcity and important application in many fields, however, which is still seriously restricted by the lack available adsorbent that can effectively capture palladium (Pd) from strong acid (>3 M). To this end, we report herein an acid-resisting covalent organic framework (COF), namely ECUT-COF-20, for such use. This new adsorbent is found to perform a benchmark Pd recovery performance from 6 M acidity such as the fast adsorption kinetics (1 min) and high uptake capacity (181 mg/g). The breakthrough test from a Pd/C-digested solution is used to confirm its practical application, giving an exceptionally one-round 95 % Pd recovery efficiency. The mechanism, as unveiled by characterization and DFT calculation, is due to a spatial and functional separation in this adsorbent, which could consequently not only overcome the influence of strong acid, but also provide abundant hydrogen bonds for fixing Pd ions.

Additively Manufactured Silicone Polymer Composite with High Hydrogen Getter Content and Hydrogen Absorption Capacity.

Hydrogen getters consisting of 1,4-bis[phenylethynyl] benzene (DEB) and a carbon-supported palladium catalyst (Pd/C) have been used to mitigate the accumulation of unwanted hydrogen gas in a sealed system. Here, we report the formulation of a composite resin consisting of silicone polymer plus DEB-Pd/C as an active getter material and the additive manufacturing of silicone getter composites with a high getter content (up to 50 wt %). NMR and DSC studies suggest no reaction between the silicone polymer resin and DEB even at elevated curing temperatures (75 °C). Getter composites with varying amounts of getter and filler were formulated, and their rheological properties were studied. The two composite resins with good printability parameters and different getter contents were chosen to make 3D-printed samples. The hydrogen absorption capacity of these samples was studied at a low hydrogen pressure of 750 mTorr of pure hydrogen. The getter composite with 50 wt% of getter showed normalized DEB conversion of 83%, with the hydrogen adsorption capacity of 100.2 mL of H2 per gram of polymer getter composite.

A Comparison of β–Phenyl Elimination in Nickel and Palladium Alkyl Complexes: A Potentially Relevant Process in the Mizoroki–Heck Reaction

There is currently much interest in avoiding precious metals in catalysis. The development of nickel catalysts to replace palladium in the Mizoroki–Heck reaction is a relevant case in this line of research, since both elements share many chemical features. This contribution focuses on β–phenyl (β–Ph) elimination in alkyl—nickel complexes. This is the microscopic reverse of olefin insertion (or carbometallation), a fundamental step in the Heck cycle that is usually considered irreversible and selectivity-determining. However, the potential reversibility of carbometallation is generally concealed by the facile β–hydrogen (β–H) elimination that follows. Where β–hydrogen elimination is hindered, β–aryl elimination may ensue. We have previously shown that cationic 2–methyl–2–phenylpropyl (neophyl) palladium complexes supported by bidentate ligands experience β–Ph elimination, which can be seen as an example of olefin de-insertion. In this contribution, we report that β–Ph elimination can also occur in their nickel analogs, in which case fast hydrolyses of the resulting phenyl product can follow the reaction. We investigated the mechanism of these processes and compared their feasibility for nickel and palladium catalysts using DFT calculations. These results are relevant information for the design of nickel-based catalysts for the Heck reaction.

Quinoline-8-carboxamides Synthesis via Aldehyde C–H Bond Activation Using Palladium Catalyst

Quinoline-8-carboxamides Synthesis via Aldehyde C–H Bond Activation Using Palladium Catalyst

Chitosan-functionalized poly(3-hydroxybutyrate) bead as a novel biosupport for palladium in the Suzuki cross-coupling reaction

The utilization of environmentally friendly biopolymer poly(3-hydroxybutyrate) (PHB) as a support for metal catalysts is an unexplored area. Herein, exploring a stable and recyclable heterogeneous palladium (Pd) catalyst based on PHB for the Suzuki cross-coupling reaction is an attractive topic. In this study, a novel hydrophobic and hydrophilic core-shell bead supported Pd catalyst was developed by using PHB particle as a hydrophobic rigid framework and hydrophilic chitosan (CS) as the surface of the supporting matrix to fix Pd nanoparticles (NPs). The results of structural characterization showed that the Pd NPs with a small average size of 2.3±0.82 nm were uniformly distributed on the surface of the PHB-CS bead with a Pd content of 0.12 wt%. This demonstrated that the PHB-CS bead created a stable coordinated environment for Pd fixation, preventing Pd leaching. Furthermore, the Pd@PHB-CS catalyst exhibited high catalytic efficiency with 99% conversion in the Suzuki reaction under mild conditions, using a solvent mixture of EtOH and H2O (1:1) for 0.5 h. It is worth noting that the catalyst exhibits excellent stability, and reusability. It can be reused five times without a significant reduction in activity while maintaining its structural integrity. The successful construction of Pd@PHB-CS will further expand the application of PHB in the field of metal catalysts and may help establish a green and environmentally friendly multifunctional platform for the development of highly recyclable heterogeneous catalysts containing metal nanoparticles.

Fundamental Structural and Electronic Understanding of Palladium Catalysts on Nitride and Oxide Supports.

The nature of the support can fundamentally affect the function of a heterogeneous catalyst. For the novel type of isolated metal atom catalysts, sometimes referred to as single-atom catalysts, systematic correlations are still rare. Here, we report a general finding that Pd on nitride supports (non-metal and metal nitride) features a higher oxidation state compared to that on oxide supports (non-metal and metal oxide). Through thorough oxidation state investigations by X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), CO-DRIFTS, and density functional theory (DFT) coupled with Bader charge analysis, it is found that Pd atoms prefer to interact with surface hydroxyl group to form a Pd(OH)x species on oxide supports, while on nitride supports, Pd atoms incorporate into the surface structure in the form of Pd-N bonds. Moreover, a correlation was built between the formal oxidation state and computational Bader charge, based on the periodic trend in electronegativity.

Selective hydrogenation of acetylene over Pd/In2O3@SiO2: The effect of the catalyst reduction temperature

Tuning the hydrogenation activity of Pd is an effective method to achieve selective hydrogenation of acetylene. The previous study shows that Pd has a strong interaction with In2O3, causing a significant change in the electronic structure of the palladium catalyst. Herein, Pd/In2O3@SiO2 was prepared by a deposition-precipitation method for selective hydrogenation of acetylene. After the reduction by flowing hydrogen, Pd-In intermetallic compounds can be formed. The concentration of the formed intermetallic compounds is closely associated with the reduction temperature. The Pd-In intermetallic compounds suppress the hydrogen activation ability of Pd and significantly weaken the adsorption of ethylene. Especially, a weak adsorption of di-σ-bonded ethylene is observed, which facilitates the desorption of ethylene and promotes the ethylene selectivity in the semi-hydrogenation of acetylene. The experimental study confirms that there exists an optimum reduction temperature (250 °C) for the formation of the Pd-In intermetallic compounds, with which ∼ 80 % ethylene selectivity and 100 % acetylene conversion have been achieved at 140 °C.

Fundamental structural and electronic understanding of palladium catalysts on nitride and oxide supports

The nature of the support can fundamentally affect the function of a heterogeneous catalyst. For the novel type of isolated metal atom catalysts, sometimes referred to as single‐atom catalysts, systematic correlations are still rare. Here, we report a general finding that Pd on nitride supports (non‐metal and metal nitride) always features a higher oxidation state compared to that on oxide supports (non‐metal and metal oxide). Through thorough oxidation state investigations by X‐ray absorption spectroscopy (XAS), X‐ray photoelectron spectroscopy (XPS), CO‐DRIFTS, and density functional theory (DFT) coupled with Bader charge analysis, it is found that Pd atoms prefer to interact with surface hydroxyl group to form a Pd(OH)x species on oxide supports, while on nitride supports, Pd atoms incorporate into the surface structure in the form of Pd−N bonds. Moreover, a correlation was built between the formal oxidation state and the computational Bader charge, based on the periodic trend in electronegativity.

Effect of I- ligand and surface oxygen-containing groups on catalytic activity and stability of activated carbon-supported Pd catalysts in acetylene dicarbonylation

The support and ligand play a crucial role in regulating the catalytic performance, selectivity, and stability of heterogeneous catalysis. Herein, activated carbon (AC) supported palladium (Pd) catalysts (2.0 wt%) were prepared by impregnation for acetylene dicarbonylation. The oxygen-containing groups on the surface of the AC support were modulated by nitric acid (HNO3) to investigate metal–support interactions on the catalytic performance and stability of the Pd/AC. The characterization of the chemical composition and structure of the supports and catalysts demonstrates that high concentrations of oxygen-containing groups on the surface of the carbon support lead to the fine dispersion of Pd nanoparticles. Notably, the finely dispersed Pd/AC70 catalyst exhibited good activity and stability for acetylene dicarbonylation under high-pressure CO conditions after several rounds of regeneration. Furthermore, operational parameters including the type of support, co-catalyst (KI), and reaction time and temperature were identified for their impact on the reaction. It was found that I- anions serve as a co-catalyst and can ligate with Pd species, thereby preventing the leaching of Pd and improving reaction selectivity. This study presents a straightforward and sustainable modulation strategy to improve the dispersion of active metals, as well as to prevent the leaching and sintering of these metals during high-pressure CO reactions.

Nickel‐Catalyzed Sonogashira Couplings: Extending the Reaction Scope to Aryl Bromides and Chlorides

AbstractThe alkyne motif is present in several naturally occurring molecules and specialty chemicals. The Sonogashira reaction is recognized as one of the most exploited methods for the synthesis of substituted alkynes. While palladium catalysts have been traditionally employed, recent efforts have been directed towards developing alternatives based on Earth‐abundant metals such as nickel. However, nickel‐catalyzed Sonogashira couplings still present important substrate limitations. While more reactive aryl iodides have been well documented, the coupling of more challenging yet cost‐effective aryl bromides and chlorides lags significantly behind. Herein, we present a method for the nickel‐catalyzed Sonogashira coupling of aryl bromides and chlorides, whose discovery was accelerated thanks to high‐throughput experimentation. Fine‐tuning of the bipyridine ligand was essential to activate chemoselectively C(sp2)−Br or C(sp2)−Cl bonds. A wide range of functionally diverse alkynes, including examples of active ingredients and their intermediates, were accessed in a single step and with yields up to 98%. The developed methodology is expected to be widely adopted by academia and industry, marking a step forward in the field of base metal catalysis.

Tandem catalysis enables chlorine-containing waste as chlorination reagents

Chlorinated compounds are ubiquitous. However, accumulation of chlorine-containing waste has a negative impact on human health and the environment due to the inapplicability of common disposal methods, such as landfill and incineration. Here we report a sustainable approach to valorize chlorine-containing hydrocarbon waste, including solids (chlorinated polymers) and liquids (chlorinated solvents), based on copper and palladium catalysts with a NaNO3 promoter. In the process, waste is oxidized to release the chlorine in the presence of N-directing arenes to afford valuable aryl chlorides, such as the FDA-approved drug vismodegib. The remaining hydrocarbon component is mineralized to afford CO, CO2 and H2O. Moreover, the CO and CO2 generated could be further utilized directly. Thus, chlorine-containing hydrocarbon waste, including mixed waste, can serve as chlorination reagents that neither generate hazardous by-products nor involve specialty chlorination reagents. This tandem catalytic approach represents a promising method for the viable management of a wide and diverse range of chlorine-containing hydrocarbon wastes.