Palladium Hydroxide Research Articles

Thermodynamic and kinetic study of palladium(II) complexation with 1-methyl-2-mercaptoimidazole (methimazole) and their importance for structural design of metallodrugs

The acidobasic and complexing properties of 1-methyl-2-mercaptoimidazole (Methimazole, an anti-thyroid drug) were investigated. The pKa 11.49 ± 0.03 was estimated by molecular absorption spectroscopy (I = 0.10 M NaCl, t = 25.0 ± 0.1 °C). This value is in good agreement with the value 11.58 ± 0.05, obtained using the solvent-extraction technique. Theoretical (LFER and quantum chemical calculations) and experimental (1H/13C NMR spectroscopy) methods confirmed that the ligand prefers to be in the thion form, and the proton dissociation takes place on the nitrogen atom. Using glass electrode potentiometry, the complexation of the Pd(II) ion by the methimazole ligand occurs without the participation of protons. The best chemical model considers the [Pd(HL)]2+, [Pd(HL)2]2+ and [Pd(HL)3]2+ complex species, whose stability constants were also determined using spectroscopy and capillary zone electrophoretic (CZE) measurements. The metal complexes dissociate at –log [H+] > 7, where an uncharged palladium(II) hydroxide is formed. The formation kinetics of the palladium(II) complex with methimazole were studied in perchloric and hydrochloric acids (I = 1.00 M, t = 15–40 °C) and the determined rate constants and activation parameters are consistent with literature values determined for the reactions of the Pd(II) ion with thiourea derivatives. The rate constants decrease by two orders of magnitude in both media, which can be assigned to a lower tendency of the chloride ion to dissociate from the [PdCl4]2− complex species than the water molecule from the [Pd(H2O)4]2+ ion. The presented results can be utilized for the design of new Pd and Pt metallodrugs.

Effects of Ring Size and Steric Encumbrance on Boron-to-Palladium Transmetalation from Arylboronic Esters.

The structure of the diol from which an arylboronic ester is derived dramatically influences the rate of transmetalation in the Suzuki-Miyaura cross-coupling reaction. Some esters undergo transmetalation more than 20 times faster than the parent arylboronic acid. Herein, investigations into the influence of arylboronic ester ring size and steric properties on the mechanism of transmetalation in the Suzuki-Miyaura reaction are described. Both factors impact the propensity of an arylboronic ester to bind to a dimeric palladium hydroxide complex. The reaction of hindered arylboronic esters derived from 1,2-diols (1,3,2-dioxaborolanes) with palladium hydroxide dimers to form a complex incorporating a Pd-O-B linkage is thermodynamically favorable, but the barrier to coordination is often higher than the barrier to arene transfer. In contrast, the analogous reaction between arylboronic esters derived from 1,3-diols (1,3,2-dioxaborinanes) and palladium hydroxide dimers is thermodynamically unfavorable, as 1,3,2-dioxaborinanes exhibit decreased electrophilicity compared to esters derived from 1,2- or 1,4-diols. These factors also influence the barrier of the arene transfer step, and in many cases, arylboronic esters that do not easily form Pd-O-B linked complexes undergo transmetalation faster than those that do because of hyperconjugative stabilization of the arene transfer transition state.

Synthesis of Thiazolidinedione Compound Library

Thiazolidinediones (TZDs), also known as Glitazones, have anti-diabetic, anti-inflammatory and anti-cancer properties. A simple, efficient and cost-effective synthesis of a thiazolidinedione compound library was developed. The synthesis is facilitated by microwave irradiation in three of the four steps followed by reduction under pressurized hydrogen gas using palladium hydroxide. All reactions, except one, were completed within an hour and provided desired products in moderate to good yields after a simple work-up.

Palladium Mediated Selective Cleavage of Benzyl and Allyl Phosphates: A Convenient Non‐Hydrogenolytic Method for the Synthesis of Phosphates and Phospholipids.

Allyl and benzyl phosphates can be cleaved selectively using catalytic amounts of Pd/C, Pd(OH)2 and Pd(OH)2 alone, in the absence of hydrogen, respectively.This is of of immense utility during the synthesis of phospholipids and other organophosphates.

Electrocatalytic oxidation of formic acid by palladium nanoparticles electrochemically synthesized from a deep eutectic solvent

Palladium nanoparticles (PdNPs) were formed and supported onto the surface of a glassy carbon electrode (GCE) from a single potentiostatic step using palladium chloride (PdCl2) as the precursor salt, dissolved in a deep eutectic mixture formed by 2-Hydroxy-N,N,N-trimethylethanaminium chloride (choline chloride) and diaminomethanal (urea). Analysis of the potentiostatic current density transients allows to accurately establish the amount of Pd deposited on the GCE surface required to determine the so-called mass activity, as defined by the ratio between methanoic acid (formic acid) oxidation current and palladium mass electrodeposited on the electrode. From SEM analysis of the GCE surface modified with PdNPs, it was found that PdNPs were distributed uniformly over the electrode surface, having an average size of (60 ± 9) nm. EDX and XPS analysis confirm a core-shell morphology constituted by a Pd core surrounded by a palladium (II) Hydroxide- palladium (II) oxide (Pd(OH)2-PdO) shell. The GCE modified with PdNPs (GCE/PdNPs) were used to oxidize formic acid from aqueous electrolytic baths added with perchloric acid (HClO4) or sulfuric acid (H2SO4). It was shown that the maximum mass activity depended on both, the nature of the electrolytic bath and the applied potential for the PdNPs electrodeposition. However, the best mass activity ((5085 ± 129) mA mgPd−1) was achieved with the GCE/PdNPs, formed at −700 mV vs. the silver quasi reference electrode (Ag QRE), immersed in the HClO4 electrolytic bath, even when the formic acid concentration was half that used in the H2SO4 electrolytic bath. Furthermore, the mass activities of the PdNPs reported in this work rank high among other values reported in the literature for nanoparticles based on palladium but synthesized with more complex and expensive processes, having the advantage of being obtained by a simple, rapid, and cost-effective electrochemical method.

Near ambient pressure XPS investigation of hydrous palladium oxide under water and oxygen gas environments

Pd takes various chemical forms according to the types of catalysts and even its pristine chemical state is often subject to change in operation. To understand the mechanism how Pd-based catalysts activate reactions, it is important to have a capability to identify the surface chemical state of Pd-based catalysts in contact with reactants. In this study, we conducted in situ near ambient pressure-x-ray photoelectron spectroscopy (NAP-XPS) in gas conditions with water and oxygen for hydrous Pd oxide, which is also known as palladium hydroxide (Pd(OH)2) and it is the key component of the Pearlman’s catalyst widely used for organic reactions. We found that hydrous Pd oxide showed different spectral features to that of anhydrous Pd oxide under gaseous water environments. We believe that this NAP-XPS study provides new information for a better identification of hydrous Pd oxide under reaction conditions, which is not available from conventional XPS in ultrahigh vacuum.

An investigation on electroless nickel coating on yttria stabilized zirconia nanoparticles via single step surface activation methods

Metal coated ceramic nanopowders have a considerable potential for many fields of applications. Here, electroless coating of pure nickel onto yttria-stabilized zirconia nanoparticles is studied. We introduce a single step method to activate ceramic nanoparticles surface to reduce complexities of electroless coating on ceramic nanoparticles by conventional double step pre-treatments. X-ray diffraction and electron diffraction patterns beside transmission electron microscopy images are used to analyze the coated nanoparticles. We observe that palladium hydroxide acts as a catalyst for electroless nickel reaction like palladium and the ceramic nanopowders surface is effectively activated for electroless reaction by simpler single step activation methods. Atomic absorption spectroscopy results show that the performance of electroless reaction is not enhanced by increase in catalyst amount. Also, relative changes in amount of deposited nickel are investigated via magnetization curves of the coated particles. The vibrating sample magnetometery results demonstrate the magnetic behavior of the processed particles can be modified by deposited nickel amount.

An efficient Pd/C catalyst design based on sequential ligand exchange method for the direct synthesis of H2O2

A new catalyst preparation method involving the sequential ligand exchange of anionic palladium complexes to cationic complexes via the formation of palladium hydroxide intermediates is proposed. The novel method enables the electrostatic adsorption of an anionic palladium complex on the negatively charged carbon surface, and therefore makes it possible to obtain small and highly dispersed Pd nanoparticles. The H2O2 productivity and H2 selectivity of the ligand-exchanged catalyst were 16 and 3.6 times higher than those of the Pd/C catalyst prepared by using the same anionic palladium precursor. The strikingly different activities mainly attributed to the difference in the nanoparticle size and the oxidation state of Pd, which clearly indicates that the activity of Pd/C catalyst for the direct synthesis of H2O2 can be greatly improved by the sequential ligand exchange method.

Direct synthesis of hydrogen peroxide over Pd/C catalyst prepared by selective adsorption deposition method

A new catalyst design based on selective adsorption deposition method was developed to achieve high reaction performance in the direct synthesis of hydrogen peroxide. The activity of the unprecedented Pd/C catalyst was superior to that of the conventionally prepared Pd/C catalysts, and the initial H2O2 productivity and H2 selectivity reached as high as 8606 mmol H2O2/g Pd.h and 95.1%, respectively. This excellent activity may result from the intrinsic structural and electronic features of the active sites, i.e., the extremely small and monodispersed Pd nanoparticles with a high Pd2+/Pd0 ratio, which were realized by combining the selective adsorption of metal precursor cations on a negatively charged activated carbon surface and the subsequent homogeneous surface deposition of palladium hydroxide by the hydroxide ions that are slowly generated upon urea decomposition. The catalytic activity was significantly affected by the oxygen groups of the activated carbon support. The carboxyl groups do not efficiently suppress the unfavorable H-OOH dissociation but rather accelerate the H2O2 hydrolysis by forming hydrogen bonds with H2O2. Moreover, a sharp decrease in the reaction rates of H2O2 hydrogenation and direct synthesis of H2O2 was observed with the increase in the number of carboxyl groups on the activated carbon surface. This loss of activity, as confirmed by acid treatment and olefin hydrogenation experiments, implies that the carboxyl groups in close proximity to the active sites have a detrimental effect by hindering or poisoning the active sites.

Tight-Binding Approximation-Enhanced Global Optimization

Solving and predicting atomic structures from first-principles methodologies is limited by the computational cost of exploring the search space, even when relatively inexpensive density functionals are used. Here, we present an efficient approach where the search is performed using density functional tight-binding, with an automatic adaptive parametrization scheme for the repulsive pair potentials. We successfully apply the method to the genetic algorithm optimization of bulk carbon, titanium dioxide, palladium oxide, and calcium hydroxide, and we assess the stability of the unknown crystal structure of palladium hydroxide.

One pot oxidative dehydration - oxidation of polyhydroxyhexanal oxime to polyhydroxy oxohexanenitrile: A versatile methodology for the facile access of azasugar alkaloids

A unique oxidative dehydration-oxidation of polyhydroxy-oxime (7) to the corresponding ketonitrile (8) in one pot is reported for the first time in carbohydrate literature. Key ketonitrile intermediate (8) upon palladium hydroxide mediated cascade reaction afforded 1-deoxynojirimycin (DNJ) 1b in moderate diastereoselectivity. The cascade reaction involves the conversion of nitrile to amine, heteroannulation, reduction of the imine and subsequent debenzylation to furnish the azasugars. This oxidative dehydration-oxidation and reductive heteroannulation methodology is successfully utilized for the total synthesis of 1-deoxynojirimycin (1b), miglitol (2) and miglustat (3).

Supported palladium hydroxide-catalyzed intramolecular double C[sbnd]H bond functionalization for synthesis of carbazoles and dibenzofurans

Metal oxide-supported palladium hydroxide (Pd(OH)2/MOx) catalysts enabled the oxidative intramolecular couplings of diarylamines to carbazoles and diarylethers to dibenzofurans via double aryl CH bond functionalizations with molecular oxygen as the sole oxidant. While supported PdO, Pd, and palladium acetate catalysts showed poor catalytic activities, supported Pd(OH)2 exhibited remarkably high catalytic activity. Among supported Pd(OH)2 catalysts, Pd(OH)2/ZrO2 was found to be an efficient catalyst in terms of catalytic activities and selectivities for the synthesis of carbazoles and dibenzofurans.

Thermodynamic properties of compounds in the PdO-H2O system at 25°C

Literature thermodynamic data on species and particles existing in the heterogeneous PdO-H2O system were checked for consistency, and the equilibrium constants for dissolution of palladium oxide and hydroxide in water and for Pd2+ (aq) hydrolysis were recommended. Δ f G 298.15 ° obtained in this work for Pd2+(aq) sharply differs (no less than by 6 kJ/mol) from values that are reported in fundamental thermodynamic reference books and based on experimentally measured palladium electrode potential at 25°C. Detailed examination of literature data on the thermodynamic properties of compounds in the Cl-Pd(aq) system is required to account for revealed inconsistency.

Effect of support on activity of palladium catalysts in nitrobenzene hydrogenation

AbstractThe effect of two types of catalysts on the activity of the catalytic hydrogenation of nitrobenzene was studied. Catalysts were prepared by the surface deposition of palladium hydroxide with a simultaneous reduction with formaldehyde in a basic environment and were characterised by X-ray powder diffraction, transmission electron microscopy, adsorption-desorption, and catalytic tests — hydrogenation of nitrobenzene in methanol. The influence of the supports’ (activated carbon and a mixture of activated carbon and multi-walled carbon nanotubes) surface area is discussed. Despite having a size comparable (4–5 nm) to crystallites of metallic palladium, the catalyst prepared on a mixture of activated carbon and nanotubes (Pd/C/CNT) was significantly less active than the catalyst prepared on pure activated carbon (Pd/C); the rate of this reaction was approximately 30 % lower than the initial reaction rate. This feature could be attributed to the lower specific surface area of the Pd/C/CNT (531 m2 g−1) in comparison with the Pd/C (692 m2 g−1).

Optimization of Reductive Debenzylation of Hexabenzylhexaazaisowurtzitane (the Key Step for Synthesis of HNIW) Using Response Surface Methodology

Reductive debenzylation of hexabenzylhexaazaisowurtzitane (HBIW) was carried out using palladium hydroxide deposited on activated carbon catalyst. The catalyst has been characterized using a nitrog...

ChemInform Abstract: Palladium Hydroxide Catalyzed Transformation of Primary Propargylic Alcohols into Aldehydes: Application to the Synthesis of the Tetrahydrofuran Core.

AbstractA Pd‐catalyzed sequential isomerization and reduction of primary propargylic alcohols affords the corresponding saturated aldehydes.

Synthesis and Characterization of Poly(L-glutamic acid) with High Molecular Weight

A high molecular weight poly(L-glutamic acid) (PLGA) was synthesized by the polymerization of γ-benzyl-L-glutama-N-carboxy (BLG-NCA) and by subsequent removal of the benzyl groups. The influence of initiator, monomer/initiator molar ratio, monomer concentration, and reaction temperature of BLG-NCA polymerization upon the molecular weight was investigated. High molecular weight PBLG of 389,000 were achieved at an appropriate combination of all variables. The protecting benzyl groups in the PBLG were removed by hydrogenation with palladium hydroxide on activated charcoal as a catalyst to give a high molecular weight PLGA (molecular weight = 378 000), containing pendant primary carboxyl groups.

Palladium Hydroxide Catalyzed Transformation of Primary Propargylic Alcohols into Aldehydes: Application to the Synthesis of the Tetrahydrofuran Core

A palladium-catalyzed one-pot, two-step sequence involving redox isomerization/reduction of primary propargylic alcohols into the corresponding aldehydes has been achieved at room temperature for the first time in good to excellent yields under mild conditions. The functional group compatibility in this reaction is studied and this new methodology has been successfully applied in the synthesis of the 2,5-<i>trans</i>-tetrahydrofuran ring system of amphidinolides. It is noteworthy that aromatic substituted propargylic alcohols gave a mixture of unsaturated and saturated aldehydes, whereas aliphatic propargylic alcohols gave only saturated aldehydes.

Synthesis of nanostructured polymetallic composites based on palladium and quantum-chemical simulation of initial stages of the process

A simple method, which was laid by the thermally initiated redox reaction of decomposition of a coagulate of colloidal palladium(II) hydroxide stabilized by citrate ion, was suggested for the synthesis of nanostructured polymetallic composites based on palladium, which include one or more transition metals. Metal ions, which are required to enter into the composite were used as coagulants. Selection of the synthesis conditions allows formation of a chemisorption complex between palladium(II) hydroxide and citrate anions. The structure of this complex was suggested and quantum-chemical modeling of its vibrational and electronic absorption spectra was carried out.

Hydrogenolysis of Palladium(II) Hydroxide, Phenoxide, and Alkoxide Complexes

A series of pincer ((tBu)PCP)Pd(II)-OR complexes ((tBu)PCP = 2,6-bis(CH(2)P(t)Bu(2))C(6)H(3), R = H, CH(3), C(6)H(5), CH(2)C(CH(3))(3), CH(2)CH(2)F, CH(2)CHF(2), CH(2)CF(3)) were synthesized to explore the generality of hydrogenolysis reactions of palladium-oxygen bonds. Hydrogenolysis of the Pd hydroxide complex to generate the Pd hydride complex and water was shown to be inhibited by formation of a water-bridged, hydrogen-bonded Pd(II) hydroxide dimer. The Pd alkoxide and aryloxide complexes exhibited more diverse reactivity. Depending on the characteristics of the -OR ligand (steric bulk, electron-donating ability, and/or the presence of β-hydrogen atoms), hydrogenolysis was complicated by hydrolysis by adventitious water, a lack of reactivity with hydrogen, or a competing dissociative β-hydride abstraction reaction pathway. Full selectivity for hydrogenolysis was observed with the partially fluorinated Pd(II) 2-fluoroethoxide complex. The wide range of Pd-OR substrates examined helps to clarify the variety of reaction pathways available to late-transition-metal alkoxides as well as the conditions necessary to tune the reactivity to hydrogenolysis, hydrolysis, or dissociative β-hydride abstraction.