Palladium Complexes Research Articles

Special Issue Foreword from Guest Editors

Dear Colleagues, We are pleased to present this Special Issue «Nano- and Photo- Catalysis in Current Chemistry: Possibilities and Challenges» focused on current trends and innovation in catalysis. Catalysis plays a crucial role in current chemistry and about 90% of the volume of modern chemical production is based on catalytic processes. Catalysts speed up chemical reactions by reducing activation energy, while the catalysts themselves remain unchanged throughout the reaction. This is especially important in industry, where catalysts increase process efficiency, reduce production costs, and enable chemical transformations that would not normally occur. Additionally, catalysis promotes the development of environmentally friendly technologies by minimizing harmful emissions. As a result, the chemical industry becomes more sustainable and environmentally friendly. In this Special Issue, authors from countries such as China, Russia, Czech Republic, Azerbaijan, Uzbekistan and Kazakhstan share their 14 papers in the field of catalysis with readers of the Eurasian Journal of Chemistry. The Guest Editors of this Special Issue have invited new authors with interesting topics and hope that the collected articles will attract reader interest and expand the audience of the Eurasian Journal of Chemistry!

Evaluation of Cobalt, Nickel, and Palladium Complexes as Catalysts for the Hydrogenation and Improvement of Oxidative Stability of Biodiesel

Developing effective catalysts that can selectively hydrogenate C=C bonds in biodiesel samples is vital as it tackles the major problem of oxidative stability, which greatly limits the utilization of biodiesel as an alternative fuel. In this work, Co, Ni, and Pd catalysts stabilized with the bidentate nitrogen ligands N-(3-(triethoxysilyl)propyl)pyridin-2-ylmethylimine and N-(3-(triethoxysilyl)propyl)picolinamide were synthesized, characterized, and used as pre-catalysts in the transfer hydrogenation of C=C bonds in fatty acid methyl esters. The active catalysts from the Co, Ni, and Pd complexes sequentially hydrogenate the C18:2 chains to C18:1, which is further converted to C18:0 in the FAMEs of both methyl linoleate and jatropha biodiesel. The hydrogenation process was kinetically controlled, and after 3 h it yielded a biodiesel sample that contained 25.83% C16:0, 12.52% C18:2, 41.54% C18:1, 14.47% C18:0 and 3.0% C18:2 isomers. The un-hydrogenated jatropha diesel, hydrogenated jatropha diesel, and a B20 blend of jatropha were tested for susceptibility to oxidation reactions using the Rancimat method and FTIR spectroscopy, and the partial hydrogenation had improved the induction period by 3 h.

Palladium(0) and Brønsted Acid Co‐Catalyzed Enantioselective Hydro‐Cyclization of 2,4‐Dienyl Hydrazones and Oximes

AbstractThe transition metal‐catalyzed asymmetric hydro‐functionalization of 1,3‐dienes has been well explored, but most reactions focus on electron‐neutral substrates in an intermolecular manner. Here we first demonstrate that readily available 2,4‐dienyl hydrazones and oximes can be efficiently utilized in the hydro‐cyclization reaction under co‐catalysis of a Brønsted acid and a chiral palladium complex, furnishing multifunctional dihydropyrazones and dihydroisoxazoles, respectively. Diverse substitution patterns for both types of electron‐deficient diene compounds are tolerated, and corresponding heterocycles were generally constructed with moderate to excellent enantioselectivity, which can be elaborated to access products with higher molecular complexity and diversity. Control experiments and density functional theory calculations support that α‐regioselective protonation of dienyl substrates by acid and concurrent π‐Lewis base activation of Pd0 complex is energetically favoured in the formation of active π‐allylpalladium intermediates, and an outer‐sphere allylic amination or etherification mode is adopted to deliver the observed cyclized products enantioselectively.

Synthesis of Palladium Nanomaterials Using Plant Leaf Extract and their Enhanced Photocatalytic Activities against Organic Dyes

Aims and Objectives: This study aimed to carry out the green synthesis of palladium nanoparticles (Pd NPs) using the aqueous leaves extract of Eclipta alba. The appearance of a characteristic surface plasmon resonance peak at 410 nm confirmed the synthesis of Pd NPs. Method: The average particle sizes of 13 nm were observed by using the leaf concentrations of 10 mL with a certain amount of PdCl2 (0.001 M) at 25 ̊ C. The Pd NPs, as synthesized under the optimized conditions (10 mL extract + 60 ̊ C + 0.001 M PdCl2), were spherical in shape, small in size, and uniformly distributed, as depicted by HR-TEM images. Results: FTIR, XRD, DLS, and zeta potential further confirmed the formation of Pd NPs. The Pd NPs synthesized at optimized conditions exhibited strong catalytic activity in dye Eosin yellow, Rose Bengal, Tartrazine, and Ponceau S degradation by discoloration of dyes in 3 hrs. The removal of all dyes by the Pd NPs was optimized by varying specific operating parameters, such as initial dye concentration, solution pH, irradiation time, and temperature. Conclusion: This high activity of Pd NPs may be due to their small size, high dispersion, and surface- capping phytochemicals. result: Bio-fabrication of metallic Pd NPs using different plant extracts compared to other reducing agents is more scalable, rapid, and cost-effective for generating bulk nanoparticles. The phytochemical principles, such as phytoconstituents, reduce the PdCl2 to Pd NPs and are implicated in the capping and stability of the nanoparticles. Hence, the leaves of Eclipta alba have different polyols and are well known. Apart from this, hydroxyl groups in phenolic compounds may participate in the bio-reduction of PdCl2. Such compounds can chelate metal ions to form their quinones form, which is an intermediate palladium complex. Then, stabilization of the intermediate form and reduction of Pd2+ to Pd0 occurred due to free electrons or nascent hydrogen produced during the bio-reduction reaction. Finally, Pd-NPs were prepared due to the collision of neighboring Pd0 atoms. These significant conjugations exist in the keto-enol system within the quinone form of the compound.

Synthesis, Characterization, and Catalysis of Planar Chiral Ferrocene‐based N‐Heterocyclic Carbene Ligands and Its Metal Complexes

This study presents the development of a novel planar chiral ferrocene‐based NHC ligand and its corresponding metal complexes. The key unit of the imidazolium backbone, planar chiral ortho‐isopropyl ferrocenyl amine, was synthesized starting from (R)‐Ugi's amine. Imidazolium was obtained through the sequential condensation of glyoxal with ferrocenyl amine, followed by the ring‐closure of 1,3‐diferrocenyldiimine with chloromethylethyl ether. Chiral imidazolylidene NHC (IFcPr) metal complexes were prepared by treating imidazolium with silver oxide or base followed by transmetalation with appropriate metal salts. The steric and electronic properties of the IFcPr ligand were assessed using %Vbur and TEP, respectively. These assessments indicated that the ligand was as bulky as the adamantyl NHC ligand and exhibited strong donor ability similar to that of a triazolylidene NHC ligand. The catalytic performance of the copper and palladium complexes was evaluated in the asymmetric borylation of ethyl cinnamate and Suzuki–Miyaura coupling reactions, respectively. The IFcPr‐Cu complex catalyzed the borylation of ethyl cinnamate with bis(pinacolato) diboron, followed by oxidation to yield the hydroxy ester with 58% yield and 30% ee. In contrast, the IFcPr‐Pd‐PEPPSI complex provided the axial chiral binaphthyl compound with 59% yield and 51% ee at a low catalyst loading (0.1 mol%, TON = 590).

Synthesis of some metal ion complexes of new imidazole derivative, characterization, and biological activity

Imidazole complexes with high biological activity for some metal complexes prepared by a new imidazole ligand from the reaction of a 1,3-oxazole derivative with hydroxylamine and utilizing this ligand in the preparation of some metal ion complexes. Many of the techniques available for all prepared compounds, such as elemental analysis (CHNS), (FT-IR), (UV-Vis) spectra, and 1H-NMR spectra, will be used in the diagnosis of these complexes, and the forms of the complexes will be deduced from the results obtained. The outcomes demonstrated that the octahedral geometries of all the produced complexes, except for the copper and palladium complexes, which were square planer shapes. The antimicrobial activity of both the ligand and its metal ionic complexes against various microbes was evaluated. KEY WORDS: Imidazole, Oxazole, Spectral data, Bioactivity Bull. Chem. Soc. Ethiop. 2024, 38(6), 1681-1690. DOI: https://dx.doi.org/10.4314/bcse.v38i6.14

Optical Enantiodifferentiation of Chiral Nitriles.

Chiroptical sensing of nitriles is achieved with excellent functional group tolerance by hydrozirconation and subsequent transmetalation of the corresponding iminate to a chromophoric palladium complex. A one-pot workflow that uses the Schwartz reagent and [(η3-1-tert-butylindenyl)(μ-Cl)Pd]2 as sensor generates a palladium complex displaying red-shifted CD inductions and characteristic UV changes. These chiroptical responses are accurately correlated to the enantiomeric ratio and total concentration of the original nitrile.

Structure and Peculiarities of 1H NMR‐Spectra of Palladium(II) Complexes with 3‐(2‐pyridyl)‐5‐Alkyl‐1,2,4‐triazoles

AbstractA series of chelating N N proligands, 3‐(2‐pyridyl)‐5‐alkyl‐1,2,4‐triazoles (HLAlk), where alkyl=methyl, ethyl, isopropyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl was used as building blocks for designing of coordination compounds. Their reaction with an equimolar amount of [PdCl2(CH3CN)2] led to formation of series of six novel palladium complexes [Pd(HLAlk)Cl2], in which ligands are coordinated in the acid form. New proligands and Pd(II) complexes were characterized by IR, 1H and 13C NMR spectroscopy and elemental analysis. The Pd(II) complexes showed an unusual downfield shift in 1H NMR of the aliphatic proton that is the closest to triazole ring, which suggests the C−H…Cl hydrogen bonding, supported by X‐ray data for Pd(HLc−Pr)Cl2 and Pd(HLc−Bu)Cl2.

Mononuclear palladacycles versus acyclic analogues: a structure and reactivity comparison

The metallocyclic ring in mononuclear iminoisoindoline-based palladacycle [(κ2-iminoisoidoline)PdCl(PCy3)] (3) can be ring opened by coordination of phosphine to form the trans bis(phosphine) iminoisoindoline-based palladium(II) complex [(η1-iminoisoidoline)PdCl(PCy3)2] (4) where the η1-iminoisoindoline is coordinated only by an Ar-Pd bond. The ring-opened analogue showed significantly higher coupling activity in Suzuki-Miyaura reactions with aryl chlorides than any iminoisoindoline-based palladacycle studied to date. These results are compared to existing mononuclear palladacycles and reported acyclic analogues.

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.

Photoinduced Palladium-Catalyzed Radical Germylative Arylation of Alkenes with Chlorogermanes.

We describe a visible light-induced palladium-catalyzed radical germylative arylation of alkenes with easily accessible chlorogermanes. This protocol provides expedient access to germanium-substituted indolin-2-ones in good to excellent yields under mild reaction conditions. The key step for this strategy lies in the reductive activation of germanium-chloride bonds with an excited palladium complex under visible light irradiation. The involvement of germanium radicals was evidenced by electron paramagnetic resonance spectroscopy experiments.

Synthesis of tetranuclear cyclopalladated complex using thiosemicarbazone derivative ligand: Spectral, biological and molecular docking studies

New tetranuclear Palladium(II) complex, (Pd-(OMe)-TSC)4, has been successfully synthesized from the reaction of potassium tetrachloridopalladate (II) salt (K2[PdCl4]) with methoxy‑functionalized thiosemicarbazone ligand, OMe-TSC, and characterized using various spectroscopic techniques such as FT-IR, UV–Vis, 1H NMR, 13C NMR, 1H-1H COSY, 13C-APT, 1H-13C HMQC, elemental analyses and high-resolution mass spectroscopy. The in-vitro anticancer activity was investigated by using MTT test in breast cancer cells (MCF-7 cell line). Anticancer activity of the complex was higher than ligand and the results inferred that the complex showed comparable activitiy with cis-platin. Furthermore, fluorescence and UV–Vis spectroscopies had been used to investigate the binding interaction of the synthesized samples with Bovine Serum Albumin (BSA). Three different drugs namely, Warfarin, Ibuprofen, and Digoxin, were employed to study the competitive bindings to different sites on BSA. The obtained results demonstrated that the binding sites were mainly located within site I and II of BSA for the (Pd-(OMe)-TSC)4 complex and (OMe)-TSC ligand, respectively. In addition, the suggested structures of ligand and complex have been optimized by semi-emprical method and the aforementioned results of BSA interaction were supported by molecular docking and molecular dynamics calculations. Also, The free binding energies of -4.16 kcal/mol and -5.80 kcal/mol were calculated for the interaction of the ligand and complex with SARS-CoV-2, respectively, which indicated the interaction is a spontaneous process and is a evidence for antiviral potential of (Pd-(OMe)-TSC)4 complex.

Breaking New Ground towards Innovative Synthesis of Palladacycles: The Electrochemical Synthesis of a Tetranuclear Thiosemicarbazone-[C,N,S] Palladium(II) Complex.

The electrochemical oxidation of anodic metals (M = nickel and palladium) in an acetonitrile solution of the thiosemicarbazone ligands (E)-2-(1-(4-methoxyphenyl)ethylidene)-N-methylhydrazine-1-carbothioamide (a), (E)-2-(1-(p-tolyl)ethylidene)hydrazine-1-carbothioamide (b), and (E)-N-phenyl-2-(1-(p-tolyl)ethylidene)hydrazine-1-carbothioamide (c) yielded the homoleptic complexes [ML2], 1a, 1b, 1c, and 2c and [M4L4], 2a as air-stable solids. The crystal structures for 1a, 1b, 1c, and 2c show the ligands in a transoid disposition with the [S,S] and [N,N] donor atom pairs occupying cis positions on the nearly square planar coordination plane of the metal. The structure for 2a of S4 symmetry comprises a tetranuclear palladacycle where the metalated ligands are arranged around a central Pd4S4 environment: a crown ring with alternating palladium and sulfur atoms. The latter complex is the first example of an electrochemical preparation of a cyclometalated palladium compound, marking a milestone in the chemistry of such species. The compounds have been fully characterized by elemental microanalysis, mass spectrometry, infrared (IR), and 1H nuclear magnetic resonance (NMR) spectra.

Stable Cyclometallated Palladium Complexes of Arylamides: Synthesis, Redox and Anticancer Activities

AbstractAir‐stable cyclometalated palladium(II) complexes with benzamide ligands were synthesized in high yields and characterized by X‐ray diffraction analysis, CVA, 1H NMR, 13C NMR spectroscopy, MALDI‐MS, and ESI‐MS. The electrochemical oxidation of the complexes is reversible in the presence of a quinoline substituent in the ligand and gives Pd (III) species that do not undergo reductive elimination and are detectable by ESR spectroscopy. The complexes showed high cytotoxicity against cervical cancer (M‐HeLa) and duodenal adenocarcinoma (HuTu 80), a human mammary ductal adenocarcinoma line (MCF‐7) and a human lung carcinoma cell line (A549). The possibility of generating reactive oxygen species in solution (such as OH−radicals), which can be responsible for the antitumor activity of the studied complexes, using the ESR method was shown.

Synthesis, spectral, DFT and anticancer studies on bis(N-(3-methoxybenzyl)-N-(pyridin-3-ylmethyl)dithiocarbamato-S,S’)M(II) (M= Pd, Pt)

We reported synthesis of bis(N-(3-methoxybenzyl)-N-(pyridin-3-ylmethyl)dithiocarbamato-S,S’)M(II) (where M(II) = palladium(II) (1), platinum(II) (2)). Both the complexes were characterized by elemental analysis, FTIR, UV–visible, 1H and 13C NMR spectroscopy. Based on FTIR spectral studies, bidentate coordination of dithiocarbamate ligand was proposed for both complexes. UV–visible spectral data confirm the formation of square planar complexes. The structure properties, frontier molecular orbital (FMO), molecular electrostatic potential (MEP), chemical reactivities and Mulliken charges were investigated using density functional theory (DFT)/B3LYP methods with 6-31+G (d, p) basis sets and LanL2DZ for light atoms and heavy atoms, respectively. FMO and Mulliken charges recognize the chemical active sites of 1 and 2 responsible for its chemical activity. In vitro anticancer activity of complexes 1 and 2 were analyzed on MCF-7 by MTT assay method. Results show that platinum complex 2 has higher activity compared to these of palladium complex 1.

Ligand and Metal Effects in the Gas‐Phase Fragmentation of Thiomethoxymethyl Complexes

While the collision‐induced dissociation (CID) of the mass‐selected cation [(Ph3P)2Pt(CH2SCH3)]+ selectively liberates PPh3, the diphosphine complex [(dppe)Pt(CH2SCH3)]+ (dppe = 1,2‐bis(diphenylphosphino)ethane) ejects C2H4, CH2S, and (CH3)2S instead. The analogous palladium complexes [(Ph3P)2Pd(CH2SCH3)]+ and [(dppe)Pd(CH2SCH3)]+ show similar reactivity, except that C–H‐bond activation is completely lacking. For other bidentate diphosphine ligands such as dppm, dppv, dppp, dppb, dppbz, dppf, and xantphos, a correlation of the dominant reaction channels with the bite angle is observed. For bite angles > 90°, hydrogen‐atom transfer is favored, as evidenced by an increase in dimethyl‐sulfide loss. For smaller bite angles (< 90°), intramolecular activation of the thiomethoxymethyl ligand predominates, thus resulting in increased losses of thioformaldehyde and ethene. The results of the CID experiments are compared with those for [(bipy)Pt(CH2SCH3)]+, for which the loss of C2H4 is observed as the main process. DFT calculations for the complexes [(dppe)Pt(CH2SCH3)]+ and [(bipy)Pt(CH2SCH3)]+ together with the experimental findings uncover subtle differences in the underlying reaction mechanisms.

Synthesis, Characterizations and Multivariate Data Analysis of Non- and Nitrile-Functionalized N-Heterocyclic Carbene Complexes of Silver(I) and Palladium(II)

Synthesis, Characterizations and Multivariate Data Analysis of Non- and Nitrile-Functionalized N-Heterocyclic Carbene Complexes of Silver(I) and Palladium(II)

Comparison of In Vitro and In Vivo Biological Screening of Nano‐Palladium (II) and Platinum (II)‐Based Compounds With DFT and Molecular Docking Study

ABSTRACTWithin the current challenges in medicinal chemistry, the creation of novel and improved therapeutic agents stands out. 2‐Cyano‐3‐(thiophen‐2‐yl)prop‐2‐enethioamide (CTPTA) ligand was complexed with palladium (II) and platinum (II) ions within the nanoscale with the molecular formula [M (CTPTA)Cl2]. H2O. The CTPTA ligand and its complexes were characterized by elemental analysis, UV–Vis spectra, FTIR, mass spectra, TGA, magnetic measurement, and the molar conductance technique. Analysis with a scanning electron microscope (SEM) revealed that the nanostructure dimension of both complexes is predominantly between 10 and 30 nm. The CTPTA ligand functions as a bidentate ligand, utilizing thione sulfur, and cyanide nitrogen atoms. Density functional theory was employed to analyze the geometric structure properties of the CTPTA ligand and its complexes. Natural population (NPA) and Mulliken population (MPA) methods were used to calculate the charge distribution. The cytotoxic impact results of all compounds on human liver cancer (HepG2) cell line were satisfactory. The ligand and its complexes were also tested against gram‐negative and gram‐positive bacteria in vitro. The findings of the molecular docking study supported the cytotoxicity and antibacterial effects. The antioxidant and anti‐inflammation activities of synthesized palladium (II) and platinum (II) complexes had a great spectrum of activity. The preclinical pharmacokinetic studies on albino rats revealed that the newly studied complexes achieved excellent antitumor results. This was clear in the investigated parameters, especially the amelioration of AFP levels, liver weight, oxidative stress, and lobular hepatic architecture injury.

Metal-based compounds: Synthesis and characterization of new thiazole-based iridium and palladium complexes with potential anticancer and other biological activities

Thiazoles and their derivatives are one of the most active classes of compounds known for their wide spectrum of bioactivity. Metal complexes, based on them, show antitumor potential that is attractive for investigations. Herein, we report 6 new biologically active thiazole-based complexes have been synthesized. The iridium- and palladium-based coordination compounds obtained by the precipitation method were characterized using elemental analysis (EA), Fourier-transform infrared spectroscopy (FTIR), magnetic measurements, thermogravimetric analysis coupled with mass spectrometry (TGA-MS), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). Spectroscopic data helped to propose the formulas of the complexes and indicated that all ligands acted in a monodentate manner. Water molecules were identified by thermal analysis and FTIR spectroscopy. Mathematical analysis and evaluation of thermodynamic parameters including entropy (ΔS), Gibbs free energy (ΔG), and activation energy (E) were performed using the Coats–Redfern method for all complexes. The biological potential (anticancer, antibacterial, and antifungal properties) of compounds was analyzed by biological evaluation studies. Investigated CT-DNA studies revealed that the prepared compounds were intercalatively bound to the DNA. Cytotoxicity analyses showed that complexation with Ir(III) increased the toxicity of L2 towards both tested cell lines (LN-229 and MDA-MB-231), while complexation of L3 with Pd(II) significantly increased cytotoxic activity against LN-229. Due to this, the further biological studies, such as apoptosis/necrosis detection, cell cycle analysis and JC-1 fluorescence measurements were performed on this pair of compounds.

Multifunctional Palladium Complex Synthesis and Catalytic Properties

Multifunctional Palladium Complex Synthesis and Catalytic Properties