Palladium Complexes Research Articles

Synthesis and catalytic properties of palladium(II) complexes with P,π-chelating ferrocene phosphinoallyl ligands and their non-tethered analogues.

Hybrid phosphines usually combine a phosphine moiety with another heteroatom secondary donor group in their structures while compounds equipped with hydrocarbyl π-donor moieties remain uncommon. This contribution reports the synthesis and structural characterization of the first P/π-allyl-chelating complexes that were obtained using the structurally flexible and redox-active ferrocene unit as the scaffold, viz. [PdCl(R2PfcCHCHCH2-η3:κP)] (1R; R = Ph and cyclohexyl (Cy); fc = ferrocene-1,1'-diyl). These compounds were synthesized from the respective phosphinoferrocene carboxaldehydes R2PfcCHO via reaction with vinylmagnesium bromide to generate 1-(phosphinoferrocenyl)allyl alcohols, which were subsequently acetylated. The resulting allyl acetates reacted smoothly with [Pd2(dba)3]/[Et3NH]Cl (dba = dibenzylideneacetone) to produce the target compounds. Complexes 1R and their nontethered analogues [PdCl(η3-C3H5)(FcPR2-κP)] (5R; Fc = ferrocenyl) were evaluated as pre-catalysts for the Pd-catalysed allylic amination of cinnamyl acetate with aliphatic amines and Suzuki-Miyaura-type cross-coupling of 4-tolylboronic acid with benzoyl chloride. In these reactions, better results were achieved with compounds 5R (particularly with 5Ph), presumably because they form more stable LPd(0)-type catalysts.

Synthesis, characterization, cytotoxicity study, interaction with DNA and topoisomerase IIα of square-planar complexes with thiosemicarbazones

In this study, we report the synthesis and characterization of eight new palladium complexes and a nickel complex containing thiosemicarbazone ligands derived from chalcones and benzalketones. The techniques of Infrared and UV–visible spectroscopy, Nuclear Magnetic Resonance, Mass Spectrometry, and Elemental Analysis fully characterized the compounds. Crystallography was successful for five complexes and two ligands, allowing for X-ray Diffraction analysis. Molecular docking studies and assays involving DNA interaction via agarose gel electrophoresis and UV–Vis titration revealed no DNA interaction or inhibition of topoisomerase IIα enzyme activity. However, these compounds demonstrated potent cytotoxic effects (IC50) against breast tumor (MCF-7) and prostate (DU-145) cell lines, as well as non-tumor prostate (PNT2) cell lines. These findings highlight the relevance of structural variations and the metallic center's nature in achieving cytotoxic effects, offering insights into the development of bioactive compounds.

Crystal structure of bis{2-[5-(3,4,5-trimethoxyphenyl)-4H-1,2,4-triazol-3-yl]pyridine}palladium(II) bis(trifluoroacetate) trifluoroacetic acid disolvate

The new palladium(II) complex, [Pd(C16H16N4O3)2](CF3COO)2·2CF3COOH, crystallizes in the triclinic space group P\overline{1} with the asymmetric unit containing half the cation (PdII site symmetry Ci ), one trifluoroactetate anion and one co-crystallized trifluoroacetic acid molecule. Two neutral chelating 2-[5-(3,4,5-trimethoxyphenyl)-4H-1,2,4-triazol-3-yl]pyridine ligands coordinate to the PdII ion through the triazole-N and pyridine-N atoms in a distorted trans-PdN4 square-planar configuration [Pd—N 1.991 (2), 2.037 (2) Å; cis N—Pd—N 79.65 (8), 100.35 (8)°]. The complex cation is quite planar, except for the methoxo groups (δ = 0.117 Å for one of the C atoms). The planar configuration is supported by two intramolecular C—H...N hydrogen bonds. In the crystal, the π–π-stacked cations are arranged in sheets parallel to the ab plane that are flanked on both sides by the trifluoroacetic acid–trifluoroacetate anion pairs. Apart from classical N/O—H...O hydrogen-bonding interactions, weak C—H...F/N/O contacts consolidate the three-dimensional architecture. Both trifluoroacetic moieties were found to be disordered over two resolvable positions with a refined occupancy ratio of 0.587 (1):0.413 (17) and 0.530 (6):0.470 (6) for the protonated and deprotonated forms, respectively.

Mixed N‐heterocyclic carbene and benzyl‐, phenethyl‐, and biphenylamine coordinated Pd complexes: Anticancer activities and stereo‐electronic effects

A series of mixed N‐heterocylic carbene (NHC) palladium complexes bearing C^N bidentate ligands derived from benzylamine, phenethylamine, and biphenylamine were prepared and fully characterized by NMR spectroscopy, ESI‐MS spectrometry, and X‐ray diffraction analyses. The complexes were potent in inhibiting proliferation of HepG2 and Caco2 cancer cells, and a SAR (structure–activity relationship) study revealed C^N ligands with stronger electron donation and moderate steric hindrance are more cytotoxic. DNA binding study through UV–vis absorption titration indicated that such complexes bound stronger to CT‐DNA molecules with higher binding constants. Additional molecular docking of the best performer suggested a groove binding mode through hydrogen bonding and π‐π stacking interactions. The apoptosis induced by the two best performers of α,α‐dimethylbenzylamine and S‐α‐methylbenzylamine ligated complexes was further analyzed by morphology change, cell cycle distribution, ROS production, and mitochondrial membrane potential studies.

Palladium Complexes Derived from Waste as Catalysts for C-H Functionalisation and C-N Bond Formation

Three-way catalysts (TWCs) are widely used in vehicles to convert the exhaust emissions from internal combustion engines into less toxic pollutants. After around 8–10 years of use, the declining catalytic activity of TWCs causes them to need replacing, leading to the generation of substantial amounts of spent TWC material containing precious metals, including palladium. It has previously been reported that [NnBu4]2[Pd2I6] is obtained in high yield and purity from model TWC material using a simple, inexpensive and mild reaction based on tetrabutylammonium iodide in the presence of iodine. In this contribution, it is shown that, through a simple ligand exchange reaction, this dimeric recovery complex can be converted into PdI2(dppf) (dppf = 1,1′-bis(diphenylphosphino)ferrocene), which is a direct analogue of a commonly used catalyst, PdCl2(dppf). [NnBu4]2[Pd2I6] displayed high catalytic activity in the oxidative functionalisation of benzo[h]quinoline to 10-alkoxybenzo[h]quinoline and 8-methylquinoline to 8-(methoxymethyl)quinoline in the presence of an oxidant, PhI(OAc)2. Near-quantitative conversions to the desired product were obtained using a catalyst recovered from waste under milder conditions (50 °C, 1–2 mol% Pd loading) and shorter reaction times (2 h) than those typically used in the literature. The [NnBu4]2[Pd2I6] catalyst could also be recovered and re-used multiple times after the reaction, providing additional sustainability benefits. Both [NnBu4]2[Pd2I6] and PdI2(dppf) were also found to be active in Buchwald–Hartwig amination reactions, and their performance was optimised through a Design of Experiments (DoE) study. The optimised conditions for this waste-derived palladium catalyst (1–2 mol% Pd loading, 3–6 mol% of dppf) in a bioderived solvent, cyclopentyl methyl ether (CPME), offer a more sustainable approach to C-N bond formation than comparable amination protocols.

(SC,RS)-Bromido-(N-{4-methyl-1-[(4-methyl-phenyl)sul-fan-yl]-pentan-2-yl}-N'-(pyridin-2-yl)imidazol-2-yl-idene)palladium(II) bromide.

The mol-ecule of the title NCNHCS pincer N-heterocyclic carbene palladium(II) complex, [PdBr(C21H25N3S)]Br, exhibits a slightly distorted square-planar coordination at the palladium(II) atom, with the five-membered chelate ring nearly planar. The six-membered chelate ring adopts an envelope conformation. Upon chelation, the sulfur atom becomes a stereogenic centre with an RS configuration induced by the chiral carbon of the precursor imidazolium salt. There are intra-molecular C-H⋯Br-Pd hydrogen bonds in the structure. The two inter-stitial Br atoms, as the counter-anion of the structure, are both located on crystallographic twofold axes and are connected to the complex cations via C-H⋯·Br hydrogen bonds.

Synthesis, Spectroscopic Properties, and Metalation of 3-Alkoxybenziporphyrins.

A series of 5-alkoxy-1,3-benzenedicarbaldehydes and related dimers were prepared in three steps from dimethyl 5-hydroxyisophthalate. Acid catalyzed condensation of the dialdehydes with a tripyrrane dicarboxylic acid, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, afforded good yields of 3-alkoxybenziporphyrins, although dimeric tetraaldehydes failed to give isolatable porphyrinoid products. Proton NMR spectroscopy gave no indication of an aromatic ring current, but addition of trifluoroacetic acid resulted in the formation of dications that exhibited weakly diatropic characteristics. Spectroscopic titration with TFA demonstrated that stepwise protonation took place, generating monocationic and dicationic species. 3-Alkoxybenziporphyrins reacted with nickel(II) or palladium(II) acetate to give the related nickel(II) or palladium(II) complexes. These stable organometallic derivatives showed increased diatropic properties that were most pronounced for the palladium(II) complexes. These unique porphyrinoids provide further insights into the properties of benziporphyrins.

Nickel(II) and Palladium(II) complexes with imine-based tridentate ligand: Synthesis, spectral characterization, Antimicrobial, cytotoxicity and DFT studies

The organic compound (Z)-2-bromo-2-(5-bromo-2-hydroxy-3-methoxybenzylidene)-N-metylhydrazine-1-carbothioamide (L1H2) and its nickel(II) complex [Ni(L1)(PPh3)](1) and palladium(II) complex [Pd(L1)(PPh3)](2) were synthesized and characterized using various spectroscopic methods, including NMR,FT-IR, HRMS, and UV–Vis spectroscopy. Single-crystal X-ray diffraction analysis was used to determine the crystal structures of [Ni(L1)(PPh3)](1) and [Pd(L1) (PPh3)](2). The Hirshfeld surface analysis was used to study various interactions in the crystal structure of complexes. In addition, an energy framework computational analysis was also done to gain a further understanding of the structural details of the complexes. DFT-based calculations were done for the ligand and its associated metal complexes to establish the correlations between their structural characteristics and integral properties. Ligand and its complexes were evaluated for their antimicrobial effects. The antimicrobial effects of ligands and their complexes were assessed. It was found that both Ni(II) and Pd(II) complexes showed better antimicrobial activity.The minimum inhibitory concentration for the [Ni(L1)(PPh3)] complex ranges from 1.95–250 µM; for the [Pd(L1)(PPh3)] complex, it ranges from 3.5–250 µM; and for the ligand, it ranges from 62.5–250 µM against both bacterial and fungal strains. The synthesized compounds were tested for anti-proliferative assays against the HELA carcinoma cell line. The IC50 values obtained were 98.83 µM for the ligand, 83.09 µM for the Ni(II) complex, and 86.74 µM for the Pd(II) complex, suggesting Ni(II) complex a stronger anti-cancerous agent compared to the Pd(II) complex.Noteworthy, both complexes and standard drugs (ciprofloxacin and nystatin) showed non-cytotoxic behavior towards the normal HEK-293 cell line. The increased efficacy and selective cytotoxicity of the complexes highlight their potential as a candidate for further investigation and development into a potent therapeutic agent as an antimicrobial and anticancer agent.

Exploring Raloxifene-based Metallodrugs: A Versatile Vector Combined with Pt(II), Palladium(II) and Nickel(II) Dichlorides and Carborates against Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) poses challenges in therapy due to the absence of target expression such as estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Frequently, the treatment of TNBC involves the combination of several therapeutics. However, an enhanced therapeutic effect can be also achieved within a single molecule. The efficacy of raloxifene can be improved by designing a raloxifene-based hybrid drug bearing a 2,2'-bipyridine moiety (2). Integration of platinum(II), palladium(II), and nickel(II) complexes into this structure dramatically changed the cytotoxicity. The platinum(II) dichloride complex 3 did not demonstrate any activity, while palladium(II) and nickel(II) dichloride complexes 4 and 5 exhibited various cytotoxic behavior towards different types of hormone-receptor positive (HR+) cancer and TNBC cell lines. The replacement of the two chlorido ligands in 3‒5 with a dicarbollide (carborate) ion [C2B9H11]2- resulted in reduced activity of compounds 6, 7, and 8. However, the palladacarborane complex 7 demonstrated higher selectivity towards TNBC. Furthermore, the mechanism of action was shifted from cytotoxic to explicitly cytostatic with detectable proliferation arrest and accelerated aging, characterized by senescence-associated phenotype of TNBC cells. This study provides valuable insights into the development of hybrid therapeutics against TNBC.

Catalytically Active SiO2 Aerogels Comprising Chelate Complexes of Palladium.

A series of silica-based aerogels comprising novel bifunctional chelating ligands was prepared. To produce target aerogels, two aminosilanes, namely (3-aminopropyl)trimethoxysilane (APTMS) and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPTMS), were acylated by natural amino acids ((S)-(+)-2-phenylglycine or L-phenylalanine), followed by gelation and supercritical drying (SCD). Lithium tetrachloropalladate was used as the metal ion source to prepare strong complexes of Pd2+ with amino acids covalently bonded to a silica matrix. Aerogels bearing chelate complexes retain the Pd2+ oxidation state after supercritical drying in CO2, but the Pd ion is reduced to Pd metal after SCD in isopropanol. Depending on the structure of amino complexes, Pd-containing aerogels showed catalytic activity and selectivity in the hydrogenation reactions of C=C, C≡C and C=O bonds.

Gold(III), Mercury(II), and Palladium(II) Complexes of a Series of Isomeric Bis(mono- and dialkoxyphenyl)pyridines: Introduction of Gold through Transmetalation and Catalysis.

A series of isomeric bis-2,6-(monoalkoxyphenyl)pyridine and bis-2,6-(dialkoxyphenyl)pyridine ligands were synthesized and characterized. In order to prepare their chlorogold(III) complexes, intermediate chloromercury(II) complexes were first prepared, but unlike observations from previous studies where they were obtained impure and at best in moderate yield, here pure complexes were synthesized, many in rather high yields. Depending on the substitution pattern of the alkoxy chains on the ligands, mono- and/or dimercurated complexes were obtained, characterized by 1H, 13C{1H}, and 199Hg NMR spectroscopy as well as, in several cases, by X-ray crystallography. Factors that may explain this unusual reactivity are discussed. In most cases, transmetalation to the related chlorogold(III) complex proceeded smoothly, although lower yields were obtained when starting from doubly mercurated precursors. Prompted by the propensity of these ligands to mercurate, attempts were made to effect direct auration, but none was successful. However, dimeric, orthometalated complexes of palladium(II) could be prepared and were also amenable to transmetalation to the chlorogold(III) complex, providing for a mercury-free synthesis.

Dithienylethene-Based Photoswitchable Phosphines for the Palladium-Catalyzed Stille Coupling Reaction.

Homogeneous transition metal catalysis is a constantly developing field in chemical sciences. A growing interest in this area is photoswitchable catalysis, which pursues in situ modulation of catalyst activity through noninvasive light irradiation. Phosphorus ligands are excellent targets to accomplish this goal by introducing photoswitchable moieties; however, only a limited number of examples have been reported so far. In this work, we have developed a series of palladium complexes capable of catalyzing the Stille coupling reaction that contain photoisomerizable phosphine ligands based on dithienylethene switches. Incorporation of electron-withdrawing substituents into these dithienylethene moieties allows variation of the electron density on the phosphorus atom of the ligands upon light irradiation, which in turn leads to a modulation of the catalytic properties of the formed complexes and their activity in a model Stille coupling reaction. These results are supported by theoretical computations, which show that the energy barriers for the rate-determining steps of the catalytic cycle decrease when the photoswitchable phosphine ligands are converted to their closed state.

Effective Prevention of Palladium Metal Particles Sintering by Histidine Stabilization on Silica Catalyst Support

AbstractA robust method for enhancing the dispersion and stabilization of small metal nanoparticles in heterogeneous catalysts is developed. It involves in situ complexation of palladium(II) by histidine, in water, prior to impregnation in fumed silica. TEM images show that the histidine facilitates dispersion of the Pd(II) into finer nanoscale particles (≈2 nm) uniformly distributed on the support, rather than the large clusters (≈5 nm) seen in the absence of histidine. After hydrogen reduction, assessments using CO chemisorption and propylene hydrogenation indicate that the coordinated histidine might obscure the active sites on the Pd particles. However, as histidine decomposes between 220 and 300 °C in air, these materials are treated at 225 °C in air for 48 h. Afterwards the Pd(II) particles remain the same size, but after hydrogen reduction, there is a 2.4‐fold increase in CO gas adsorption, indicative of an expanded Pd surface area. Furthermore, superior catalyst stability (activity >200 h) is observed during propylene hydrogenation at 250 °C. This is consistent with histidine use having generated widely spaced, uniformly small, Pd nanoparticles on the silica support which is expected to help prevent agglomeration (sintering) during catalysis. This is a convenient low‐cost strategy for reducing metal content, preventing sintering and optimizing catalyst performance.

Palladium‐Catalyzed/Mn(OAc)3‐Mediated 1,2‐Diazidation and 1,2‐Acetoxy/Hydroxylation of N‐Allyl Sulfonamides

Palladium‐catalyzed conditions for diazidation or acetoxy/hydroxylation of N‐allyl sulfonamides by using Pd(OAc)2 as the catalyst combined with Mn(OAc)3·2H2O have been developed. The 1,2‐diazidation reaction of the carbon‐carbon double bond occurs in mild conditions (i.e. NaN3 as azide source in THF at room temperature), whereas the 1,2‐acetoxy/hydroxylation requires an excess of Mn(OAc)3·2H2O. The well‐known ability of this reagent to act through single‐electron transfer (SET) makes plausible a radical mechanism involving high valent palladium complexes.

Synthesis, theoretical analysis, and biological properties of a novel tridentate Schiff base palladium (II) complex.

Schiff base complexes play a crucial role in bioinorganic chemistry. A novel curcumin/phenylalanine tridentate Schiff base ligand and its palladium (II) complex were synthesized so that they were stable in aqueous buffer. The structure of the complex was investigated using a variety of methods, including DFT, NBO analysis, FMOs, and MESP. The interaction of the complex with a plasmid (pUC19) and CT-DNA was studied. The anticancer, antibacterial, and antioxidant activities of the complex were examined. The statistical analysis of the MTT assay was compared using the 1-way ANOVA and Tukey test. Results showed that the complexes were stable in aqueous buffer, pH 8. The extrinsic fluorescence emission of the plasmid and CT-DNA was quenched while interacting with the complex. The complex had an IC50 of 72.47 µM against MCF-7 cells. The ANOVA and Tukey analysis of MTT data demonstrated a statistically significant difference between groups (P < 0.0001). The minimum inhibitory concentrations (MIC) of the complex for E. coli and S. aureus were 300 and 200µg/mL, with 96.3 and 95.2% biofilm growth inhibition at 250µg/mL, respectively. The sample concentrations contributing to 50% radical inhibition in the 1,1-diphenyl-2-picrylhydrazyl (DPPH) test for curcumin, ligand, and palladium (II) complex were 33.62, 21.27, and 51.26 µM, respectively. The results suggest that the complex interaction with DNA is one of the potential mechanisms for eliminating cancer cells and bacteria in the planktonic and biofilm. On the other hand, while stability in an aqueous buffer at pH 8 increases, the modified curcumin antioxidant effect decreases.

Thiosalicylanilide complexes of nickel(II), palladium(II) and platinum(II)

Reactions of the complexes cis-[PtCl2(PPh3)2], [PtCl2(dppf)] {dppf = Fe(C5H4PPh2)2}, [PdCl2(PPh3)2], [PdCl2(dppe)] (dppe = Ph2PCH2CH2PPh2) and [NiCl2(dppe)] with thiosalicylanilide (HSC6H4CONHPh, H2-1a) and its substituted derivatives H2-1b to H2-1d (where H2-1b = p-Cl-HSC6H4CONHPh, H2-1c = p-CH3-HSC6H4CONHPh, and H2-1d = m-OCH3-HSC6H4CONHPh) gave a series of square-planar MS2P2-type complexes. The complexes were characterised by ESI MS, 1H and 31P{1H} NMR, FTIR, and microelemental analyses, and in some cases by single crystal X-ray crystallography. The predominant coordination mode is through bonding of deprotonated thiol group of two ligands. However, the tendency to form complexes with a single, chelating S,N- and S,O-donor ligand was observed by 31P{1H} NMR in some reactions. In addition, cis/trans isomerisation was observed in some complexes by 31P{1H} NMR and confirmed by X-ray structure determinations on trans-[Pt(H-1b)2(PPh3)2] and trans-[Pd(H-1b)2(PPh3)2]. A comparison of the energetics of the reaction systems involving [Pt(1b)(PPh3)2]/[Pt(H-1b)2(PPh3)2], [Pt(1d)(PPh3)2]/[Pt(H-1d)2(PPh3)2] and [Pd(1b)(dppe)]/[Pd(H-1b)2(dppe)] using Density Functional Theory (DFT) revealed that the MS2P2 systems [Pt(H-1b)2(PPh3)2], [Pt(H-1d)2(PPh3)2] and [Pd(H-1b)2(dppe)] have lower Gibbs free energies than the S,N-chelate systems [Pt(1b)(PPh3)2], [Pt(1d)(PPh3)2] and [Pd(1b)(dppe)], and are thermodynamically favoured. Intermolecular interactions quantified and visualized on Hirshfeld surfaces for trans-[Pt(H-1b)2(PPh3)2], [Pt(H-1d)2(PPh3)2].H2O, and [Pd(H-1a)2(dppe)] revealed the dominant contribution of H···H contacts to crystal packing.

Competing Mechanisms in Palladium-Catalyzed Alkoxycarbonylation of Styrene.

Palladium-catalyzed carbonylation is a versatile method for the synthesis of various aldehydes, esters, lactones, or lactams. Alkoxycarbonylation of alkenes with carbon monoxide and alcohol produces either saturated or unsaturated esters as a result of two distinct catalytic cycles. The existing literature presents an inconsistent account of the procedures favoring oxidative carbonylation products. In this study, we have monitored the intermediates featured in both catalytic cycles of the methoxycarbonylation of styrene PhCH=CH2 as a model substrate, including all short-lived intermediates, using mass spectrometry. Comparing the reaction kinetics of the intermediates in both cycles in the same reaction mixture shows that the reaction proceeding via alkoxy intermediate [PdII]-OR, which gives rise to the unsaturated product PhCH=CHCO2Me, is faster. However, with an advancing reaction time, the gradually changing reaction conditions begin to favor the catalytic cycle dominated by palladium hydride [PdII]-H and alkyl intermediates, affording the saturated products PhCH2CH2CO2Me and PhCH(CO2Me)CH3 preferentially. The role of the oxidant proved to be crucial: using p-benzoquinone results in a gradual decrease of the pH during the reaction, swaying the system from oxidative conditions toward the palladium hydride cycle. By contrast, copper(II) acetate as an oxidant guards the pH within the 5-7 range and facilitates the formation of the alkoxy palladium complex [PdII]-OR, which favors the oxidative reaction producing PhCH=CHCO2Me with high selectivity. Hence, it is the oxidant, rather than the catalyst, that controls the reaction outcome by a mechanistic switch. Unraveling these principles broadens the scope for developing alkoxycarbonylation reactions and their application in organic synthesis.

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.

A Review on the Development of Polymer Supported Heterogeneous Palladium Materials for Organic Synthesis and Electrochemical Applications

Abstract:: This comprehensive review explores the advancements in catalytic transformation, focusing on the use of heterogeneous catalytic systems with a particular emphasis on polymeric-supported palladium (Pd) complexes. This study explores the limitations associated with conventional homogeneous reagents, emphasizes the transition to eco-friendly catalytic systems, and emphasizes the importance of Pd nanoparticles. These nanoparticles are particularly noteworthy for their distinctive properties, including elevated catalytic activity, making them promising for various applications in organic synthesis. The review thoroughly examines the design and synthesis of heterogeneous catalysts, emphasizing the crucial selection of safe and recyclable supports to augment the longevity and reusability of metallic catalysts. Diverse polymer varieties, including polystyrene (PS), polyethylene (PE), polyacrylate derivatives, polyethylene glycol (PEG), and grafted polymers, are investigated as viable supports for Pd complexes. The authors intricately describe the synthesis techniques for these polymer-supported Pd catalysts and furnish illustrative examples showcasing their effectiveness in organic transformation. This comprehensive review additionally highlights the synthesis of polymer-supported palladium (Pd) materials and discusses their applications in electrochemistry. The focus extends to the electrocatalytic properties of Pdbased polymeric nanomaterials, showcasing their effectiveness in glucose sensing, hydrogen peroxide detection, and the sensing of other biological analytes. Furthermore, the catalytic capabilities of Pd nanoparticles in various electrochemical applications, including wastewater treatment and electrochemical capacitors, are explored. Integrating polymer-supported Pd materials into these electrochemical processes underscores their versatility and potential contributions to advancements in catalysis and electrochemical sensing. Catalytic applications featuring polymer-supported palladium complexes with polymeric ligands in organic synthesis processes use the Sonogashira reaction, Suzuki-Miyaura coupling, Heck reaction, Catalytic asymmetric transformations, etc. The subsequent section of the paper focuses on the creation of polymeric palladium complexes, achieved by the complexation of polymeric ligands with palladium precursors. It delves into noteworthy examples of catalytic processes employing polymer-supported palladium complexes featuring polymeric ligands, emphasizing distinct polymers, such as PS, PE, polyacrylate derivatives, PEG, and grafting polymers. The review concludes by exploring catalytic asymmetric transformations using chiral palladium complexes immobilized on polymer supports and discusses various chiral ligands and their immobilization on polymer supports, emphasizing their application in asymmetric allylic alkylation. The review furnishes a comprehensive summary of recent advancements, challenges, and prospective avenues in catalytic oxidation facilitated by polymer- supported palladium catalysts with electrochemical applications.

The cytotoxicity of palladium (II) complexes containing 1,2‐ or 1,4‐diazine bridging ligands on squamous cell carcinoma cells in vitro: Insights in the mechanisms of action

Binuclear [{Pd (dien)}2(μ‐pz)](ClO4)4 (Pd1) and [{Pd (dien)}2(μ‐pydz)](ClO4)4 (Pd2) complexes, where pz is 1,4‐diazine and pydz is 1,2‐diazine bridging ligands and dien (diethylenetriamine) is a tridentately coordinated triamine ligand, were synthesized and characterized using elemental analysis, NMR (1H and 13C) spectroscopy, and UV–Vis spectrophotometry. Electronic absorption spectrophotometry and fluorescence spectroscopy were used to study the interactions of the prepared Pd1 and Pd2 complexes with deoxyribonucleic acid (CT‐DNA) and bovine serum albumin (BSA). According to the UV–Vis spectrophotometric data, the complexes interact with CT‐DNA and bind to the BSA as a possible carrier to the target site. The antitumor properties of the tested palladium compounds were evaluated on three types of human cancer cells, namely, squamous cell carcinoma cells SCC‐4, cervical carcinoma cells HeLa and colorectal carcinoma cells HCT116, and one type of malignantly unchanged cells, MRC‐5 fibroblasts. The highest cytotoxicity was shown by the Pd1 compound against SCC‐4 cell, with an IC50 value of 5.4 ± 1.2 μM. The results showed that the cytotoxic potential against SCC‐4 cells of our new palladium complexes Pd1 and Pd2 was comparable with the cytotoxic potential of cisplatin and oxaliplatin. However, Pd1 and Pd2 displayed significantly lower cytotoxicity in comparison with cisplatin and oxaliplatin against non‐malignant cells, fibroblasts MRC5, so these results may suggest that local and systemic complications of antitumor therapy could be reduced and/or avoided. Both compounds selectively decreased the viability of SCC‐4 cells by induction of apoptosis. Also, Pd1 and Pd2 induced S‐phase cell cycle arrest in human SCC‐4 cells, so that could be another mechanism to halt the uncontrolled growth and division of cancer cells. Moreover, the precise molecular mechanism of Pd1 and Pd2 complexes‐induced apoptosis was the activation of the intrinsic signaling pathway of apoptosis, which also included activation of caspase‐3. Therefore, our new palladium (II) complexes might have a promising role as the potential future cytostatic agents.