Water-soluble Palladium Research Articles

Synthesis of water-soluble palladium(ii) complexes with N-heterocyclic carbene chelate ligands and their use in the aerobic oxidation of 1-phenylethanol.

The synthesis of palladium(ii) complexes containing N-heterocyclic carbene chelate ligands is reported. These chelate ligands have methylene or ethylene ring bridges and sulfonate, carbonate or ammonium functionalities to render the complexes soluble in water. Bis- [(bis-NHC)PdX2] (X = Cl, Br or I) and tetra-carbene [(bis-NHC)2Pd] complexes have been prepared and the crystal structures of two of them have been determined. The NHC ligand is coordinated to the metal center in normal (C2-bound) or abnormal (C4-bound) mode. Processes involving the formation of NHC-Pd bonds or the transfer of NHC ligands have been explored in water. The behavior of the bis-carbene complexes as catalysts for the aerobic oxidation of 1-phenylethanol is also discussed.

Novel water soluble palladium(II) complexes featuring tetrazolylacetic acids and their esters

2-R-2H-Tetrazol-5-ylacetic acids (R=iso-Pr, tert-Bu, CH2COOH) (1a–c) react with PdCl2 in 5% (w/w) MeOH in 1M HCl furnishing the palladium(II) water soluble complexes trans-[PdCl2L2] (2a–c). In the presence of EtOH in the reaction mixture, esterification of the tetrazolylacetoxy groups occurs leading to trans-[PdCl2(ethyl 2-R-2H-tetrazol-5-ylacetate)2] (3a–c). In the case of reaction of 2-tert-butyl-tetrazol-5-ylacetic acid 1b with PdCl2 increasing of the proportion of methanol up to 50% (w/w) led to the esterification to give trans-[PdCl2(methyl 2-tert-butyl-tetrazol-5-ylacetate)2] 4b. Complexation of isomeric 5-methyl-1H-tetrazol-1-ylacetic acid 5 with PdCl2 at the same conditions leads to trans-[PdCl2(5-methyl-1H-tetrazol-1-ylacetic acid)2] 6 and trans-[PdCl2(ethyl 2-(5-methyl-1H-tetrazol-1-yl)acetate)2] 7. The complexes obtained were characterized by HRESI+-MS, 1H, 13C{1H} NMR, and IR spectroscopies as well as by X-ray diffraction (for 2a, 3a, 3b, 4b and 6·H2O). According DSC/TG analysis the thermal decomposition of the complexes occurs by the same mechanism similar to that of the free ligands. In all cases it starts with evolution of molecular nitrogen from the tetrazole ligand which is accompanied by an exothermic effect.

Unsupported micellar palladium nanoparticles for biphasic hydrogenation and isomerization of hydrophobic allylic alcohols in water

This article presents the evaluation of water-soluble palladium nanoparticles with hydrophobic active sites that are ideal for the biphasic colloidal catalysis of water-insoluble organic substrates in aqueous solution. Palladium nanoparticles stabilized with ω-carboxylate-functionalized alkanethiolate are first synthesized using ω-carboxylate-S-alkylthiosulfate as their ligand precursor. The biphasic catalysis is carried out for the reaction of hydrophobic allylic alcohols without using any additional mixing solvent or surfactant, which results in the complete consumption of substrates under the atmospheric pressure of H2 gas and at room temperature in less than 24h. Systematic investigations on the influence of pH and substrate size are also performed to examine the utility of these thiolate-capped palladium nanoparticles as structurally stable and water-soluble micellar catalysts for the biphasic reaction.

New water-soluble palladium(II) complexes of lidocaine and phenylcyanamide derivative ligands: cytotoxicity and cellular response mechanisms.

Three new palladium(II) complexes of lidocaine and phenylcyanamide derivative ligands of formula K[Pd(2,6-Me2pcyd)2(LC)], 1, K[Pd(2,6-Et2pcyd)2(LC)], 2, K[Pd(2,6-Cl2pcyd)2(LC)], 3 (LC: lidocaine, 2,6-Me2pcyd: 2,6-dimethyl phenylcyanamide, 2,6-Et2pcyd: 2,6-diethyl phenylcyanamide, 2,6-Cl2pcyd: 2,6-dichloro phenylcyanamide) have been synthesized and fully characterized. The complexes 1-3 revealed a significant in vitro antiproliferative activity against human ovarian carcinoma (A2780), colorectal adenocarcinoma (HT29), breast (MCF-7), liver hepatocellular carcinoma (HepG-2) and lung adenocarcinoma (A549) cancer cell lines. All the complexes are more active than cisplatin and follow the trend 2>1>3. Mechanistic studies showed that the trend in cytotoxicity of the Pd(II) complexes is mainly consistent with their ability to accumulate into cancer cells and to increase intracellular basal reactive oxygen species levels, which consequently results in the loss of mitochondrial membrane potential and apoptosis induction.

Insight into the binding evaluation of two antitumor Pd(II) complexes with human serum albumin

The interaction between two novel water-soluble palladium(II) complexes (Pd(bpy)(pyr-dtc)]NO3, complex I and ([Pd(phen)(pyr-dtc)]NO3, complex II, where bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline and pyr-dtc = pyrrolidinedithiocarbame) and human serum albumin (HSA) was investigated by fluorescence quenching spectroscopy, synchronous, fluorescence resonance energy transfer (FRET) and three-dimensional fluorescence combined with UV–Vis absorption spectroscopy and circular dichroism technique under simulative physiological conditions. Fluorescence analysis demonstrated that the quenching mechanism of HSA by Pd(II) complexes was static fluorescence quenching and hydrogen bonds and van der Waals interactions were the main intermolecular force based on thermodynamic data. The HSA–Pd(II) complex interaction had a high affinity of 105 M−1, and the number of binding sites n is almost 1. The results of synchronous fluorescence, three-dimensional fluorescence spectra, UV–Vis absorption and CD spectroscopy indicated that these two complexes may induce the microenvironment around the tryptophan residues and the conformation of human serum albumin. The binding distance (r) in the interaction between Pd(II) complex and HSA was estimated by the efficiency of fluorescence resonance energy transfer (FRET). Furthermore, results from multiple spectroscopic studies are consistent and indicate that the antitumor Pd(II) complexes can efficiently bind with human serum albumin molecules, providing a reasonable model that can help in understanding the design, transportation and toxic effects of anticancer agents.

Activation of aryl chlorides in water for Suzuki coupling with a hydrophilic salen-Pd(II) catalyst

For exploiting aqueous condition, we have designed a simple water-soluble palladium Schiff-base catalyst for Suzuki-Miyaura reactions of aryl halides with arylboronic acids. The reactions could be performed in neat water with aryl bromides and iodides at room temperature and with aryl chlorides at 100°C. Good-to-excellent yields of cross-coupling products were obtained with a diverse range of aryl halides including heteroaryl halides. Interestingly, the homogeneous catalyst could be conveniently recycled with aryl bromides or chlorides for at least four times, although a progressive decrease in the product yields were noticed.

Functionalized β-cyclodextrin as supramolecular ligand and their Pd(OAc)2 complex: highly efficient and reusable catalyst for Mizoroki–Heck cross-coupling reactions in aqueous medium

A novel class of water soluble palladium complexes with recognition abilities based on functionalized β-cyclodextrin has been synthesized. The complex demonstrated high catalytic activity and a supramolecular platform for phosphine-free Mizoroki–Heck cross-coupling reactions in water. The efficient arylation of alkenes was carried out using different iodo- and bromo-arenes with good to excellent yields (up to 96%). The advantages, like recyclability of catalysts, operational simplicity and accessibility in aqueous medium, make this protocol eco-friendly.

Size-Controlled Formation of Noble-Metal Nanoparticles in Aqueous Solution with a Thiol-Free Tripeptide.

A combinatorial screening revealed the peptide H-His-d-Leu-d-Asp-NH2 (1) as an additive for the generation of monodisperse, water-soluble palladium nanoparticles with average diameters of 3 nm and stabilities of over 9 months. The tripeptide proved to be also applicable for the size-controlled formation of other noble-metal nanoparticles (Pt and Au). Studies with close analogues of peptide 1 revealed a specific role of each of the three amino acids for the formation and stabilization of the nanoparticles. These data combined with microscopic and spectroscopic analyses provided insight into the structure of the self-assembled peptidic monolayer around the metal core. The results open interesting prospects for the development of functionalized metal nanoparticles.

Palladium Mediated Rapid Deprotection of N-Terminal Cysteine under Native Chemical Ligation Conditions for the Efficient Preparation of Synthetically Challenging Proteins.

Facilitating the process of chemical protein synthesis is an important goal in order to enable the efficient preparation of large and novel protein analogues. Native chemical ligation, which is widely used in the synthesis and semisynthesis of proteins, has been going through several developments to expedite the synthetic process and to obtain the target protein in high yield. A key aspect of this approach is the utilization of protecting groups for the N-terminal Cys in the middle fragments, which bear simultaneously the two reactive groups, i.e., N-terminal Cys and C-terminal thioester. Despite important progress in this area, as has been demonstrated in the use of thiazolidine protecting group in the synthesis of over 100 proteins, finding optimal protecting group(s) remains a challenge. For example, the thiazolidine removal step is very slow (>8 h), and in some cases the applied conditions lead to undesired side reactions. Here we show that water-soluble palladium(II) complexes are excellent reagents for the effective unmasking of thiazolidine, enabling its complete removal within 15 min under native chemical ligation conditions. Moreover, palladium is also able to rapidly remove propargyloxycarbonyl-protecting group from the N-terminal Cys in a similar efficiency. The utility of the new removal conditions for both protecting groups is exemplified in the rapid and efficient synthesis of Lys34-ubiquitinated H2B and for the first time neddlyated peptides derived from cullin1. The current approach expands the use of palladium in protein chemistry and should significantly facilitate the chemical and semisynthesis of synthetically challenging proteins from multiple fragments.

New water-soluble palladium(II) iodide complexes derived from N-protonated or N-alkyl-1,3,5-triaza-7-phosphaadamantanes: Synthesis, crystal structure and catalytic properties in aqua media

Reactions of [NH4]2[PdCl4] with N-protonated or N-alkyl-1,3,5-triaza-7-phosphaadamantane iodide salts [PTA-R]I (R=H, Me, Et, nPr, nBu) give the water-soluble palladium(II) complexes of type [PdI3(PTA-R)] in isolated yields of 62–81%. All these compounds have been fully characterized by IR and NMR spectroscopies and elemental analyses. Their molecular structures were confirmed by single crystal X-ray diffraction analysis. The complexes belong to the relatively unusual zwitterionic, coordination compounds. Moreover, they constitute, as far as we are aware, the first reported examples of palladium compounds bearing N-alkyl-1,3,5-triaza-7-phosphaadamantane ligands. The complexes catalyze efficiently Heck reaction of iodobenzene and n-butyl acrylate as well as iodobenzene and substituted styrenes, under mild conditions in water as a solvent.

Design, synthesis, characterization, cytotoxicity, molecular docking and analysis of binding interactions of novel acetylacetonatopalladium(ii) alanine and valine complexes with CT-DNA and BSA

The neutral, water soluble palladium(ii) amino acid complexes, interact with CT-DNA (groove binding) and BSA (H-binding in main pocket). Molecular docking supports the interactions.

Water-Soluble Palladium(II) Complexes with Sulfonated N-Heterocyclic Carbenes in Suzuki Cross-Coupling and Hydrodehalogenation Reactions

Water-soluble Pd(II) complexes of general formula Nax[(NHC)PdCl2L] (L = Cl– (1), PPh3 (2), PPh2(C6H4-m-SO3Na) (3), and 4-Mepy (4)), where NHC is a dianionic sulfonated and sterically hindered N-heterocyclic carbene, have been prepared. The new complexes are active catalysts for the Suzuki–Miyaura cross-coupling of aryl chlorides and boronic acids in mixtures of isopropyl alcohol/water or, in the case of water-soluble aryl chlorides, in pure water. The trichloride complex 1, the crystal structure of which is reported, catalyzes the coupling of inactivated and sterically hindered substrates under mild conditions (60 °C, 0.1 mol % Pd). The corresponding biphenyls are obtained in almost quantitative yields, except in the case of some of the most hindered aryl chlorides, for which small amounts of arene are also formed by a competitive hydrodehalogenation process.

ChemInform Abstract: Recent Advances in Green Catalytic Oxidations of Alcohols in Aqueous Media

AbstractReview: 147 refs.

Production of hydrogen in a ternary photocatalytic system based on water-soluble palladium(II) porphyrin

A new photocatalyst, water-soluble palladium(II) complex with meso-tetrakis(4-N,N,N-trimethylammoniophenyl) porphyrin, was suggested as a component of a photocatalytic system for water reduction to hydrogen. In the ternary system palladium(II) porphyrin-methyl viologen-triethanolamine, the metalloporphyrin phosphorescence is quenched only by methyl viologen by the mechanism of oxidative electron transfer. The reduced form of methyl viologen is accumulated in the solution, and hydrogen is evolved in the presence of colloidal platinum. The highest quantum yield of the formation of the reduced methyl viologen form and hydrogen in the system reaches 0.4. After 1-h irradiation of the system, 125 mol of hydrogen is evolved per mole of metalloporphyrin.

Recent advances in green catalytic oxidations of alcohols in aqueous media

Catalytic oxidations of alcohols, with dioxygen or hydrogen peroxide as the primary oxidant, in aqueous reaction media are reviewed. Selective alcohol oxidations with hydrogen peroxide generally involve early transition elements, mostly tungsten, molybdenum and vanadium, in high oxidation states and peroxometal complexes as the active oxidants. Aerobic oxidations, in contrast, involve oxidative dehydrogenation, usually catalyzed by late transition elements, e.g. water soluble palladium(II)-diamine complexes, or supported nanoparticles of Pd or Au as hybrid species at the interface of homogeneous and heterogeneous catalysis. Alternatively, water soluble organocatalysts, exemplified by stable N-oxy radicals such as TEMPO and derivatives thereof, in conjunction with copper catalysts, are efficient catalysts for the aerobic oxidation of alcohols. Metal-free variants of these systems, e.g. employing nitrite or nitric acid as a cocatalyst, are also effective catalysts for aerobic alcohol oxidations. Finally, enzymatic aerobic oxidations of alcohols employing oxidases as catalysts are described. In particular, the laccase/TEMPO system is receiving much attention because of possible applications in the selective oxidations of diols and carbohydrates derived from renewable resources.

The Effects of Extending of Co-planarity in a Series of Structurally Relative Polypyridyl Palladium(II) Complexes on DNA-binding and Cytotoxicity Properties.

In depth interaction studies between calf thymus deoxyribonucleic acid (CT-DNA) and a series of four structurally relative palladium(II) complexes [Pd(en)(HB)](NO3)2 (a-d), where en is ethylenediamine and heterocyclic base (HB) is 2,2'-bipyridine (bpy, a); 1,10-phenanthroline (phen, b); dipyridoquinoxaline (dpq, c) and dipyridophenazine (dppz, d) (Figure 1), were performed. These studies have been investigated by utilizing the electronic absorption spectroscopy, fluorescence spectra and ethidium bromide (EBr) displacement and gel filtration techniques. a-d complexes cooperatively bind and denature the DNA at low concentrations. Their concentration at midpoint of transition, L1/2, follows the order a >> b > c > d. Also the g, the number of binding sites per 1000 nucleotides, follows the order a >> b ~ c > d. EBr and Scatchard experiments for a-d complexes suggest efficient intercalative binding affinity to CT-DNA giving the order: d > c > b > a. Several binding and thermodynamic parameters are also described. The biological activity of these cationic and water soluble palladium complexes were tested against chronic myelogenous leukemia cell line, K562. b, c and d complexes show cytotoxic concentration (Cc50) values much lower than cisplatin.

Pd-tetrahydrosalan-type complexes as catalysts for sonogashira couplings in water: efficient greening of the procedure.

New sulfonated tetrahydrosalen-type ligands and their water-soluble palladium(II) complexes have been synthesized. The palladium(II) complexes catalyze the Sonogashira coupling (23 examples) of various aryl halides (including chloroarenes) with terminal alkynes, with good to excellent conversions under mild conditions (80°C, air, no Cu(I) cocatalyst) in aqueous-organic mixtures and turnover frequencies of up to 2790 h(-1) . Under optimized reaction conditions to minimize environmental contamination, diphenylacetylenes can be isolated in 76-98% yield. The aqueous catalyst solution can be recycled four times with decreasing activity; however, yields between 93 and 98% can still be achieved with extended reaction times. Several water-insoluble products can be isolated in excellent yield by simple filtration and purification by washing with water; this method is used, for the first time, for this type of C-C coupling procedure.

One‐Pot Synthesis of Functionalized Noble Metal Nanoparticles Using a Rationally Designed Phosphopeptide

The rational design of a capping peptide for the synthesis of various noble metal nanoparticles is presented. The peptide contains nonnatural, phosphonated amino acids introduced via the Huisgen cycloaddition reaction for improved binding to mineralized tissue. As proof of the design concept, water-soluble palladium, platinum, silver, gold, and rhodium nanocrystals are synthesized in one step from simple precursors.

Water-Soluble Ionic Palladium Complexes: Effect of Pendant Ionic Groups on Palladium Nanoparticles and Suzuki-Miyaura Reaction in Neat Water.

Three ionic nitrogen-containing chelating ligands (L1-L3) are synthesized readily through alkylation and quaternization of 2,2'-dipyridylamine. The charge distributions and natural bond orbital analyses of their cations are implemented by using density functional theory calculations. The catalytic performances of their water-soluble palladium complexes are evaluated preliminarily by using the Suzuki-Miyaura cross-coupling reaction, and high catalytic activities of aryl bromides and chlorides are achieved in neat water. The mercury drop test, poison experiments, and TEM analysis are used to demonstrate the formation of palladium nanoparticles (NPs) after the catalytic reaction. The effects of pendant ionic groups in L1-L3 on the catalytic activities and structures of the palladium NPs are disclosed. These NPs are stable in water for several weeks; they are stabilized by synergetic interactions between the chelating coordination of the 2,2'-dipyridylamino group to the surface of the palladium NPs and the electrostatic repulsion of the ionic groups in L1-L3.

ChemInform Abstract: A Palladium Complex with Functionalized β‐Cyclodextrin: A Promising Catalyst Featuring Recognition Abilities for Suzuki—Miyaura Coupling Reactions in Water.

A water-soluble palladium complex (PdLn@β-CD) was designed and prepared based on functionalized β-cyclodextrin. It showed high turnover numbers (TONs) and turnover frequencies (TOFs) of up to 9.9 × 108 and 4.9 × 108 h−1, respectively, in aqueous Suzuki–Miyaura coupling reactions. The detailed reason for the excellent catalytic activity was studied.