Dinuclear Palladium Complexes Research Articles

Neutral dinuclear palladium(II) complex containing chiral P,S-bridging diamidophosphite-thioether ligands

An unusual neutral dinuclear palladium(II) complex with two head-to-head orientated μ-P,S-bridging ligands was obtained by the reaction of Pd(MeCN)2 Cl2 with (1R,5R)-3-(4-phenylthiobutoxy)-2,4-diphenyl-2,4-diaza-3-phospha-bicyclo[3.4.0]nonane. The dimeric structure of the complex in the solid state and in solution was thoroughly confirmed using appropriate analytical techniques: single crystal X-ray diffraction analysis, HRMS, FTIR and NMR spectroscopy.

Synthesis, characterization, DNA/BSA-binding affinity and biological activity of dinuclear palladium(II) complexes with aromatic N-heterocyclic bridging ligand

Dinuclear palladium(II) complexes, [{Pd(en)Cl}2(μ-L)](NO3)2 (L is bridging ligand pirazine (Pd1), pyrimidine (Pd2), pyridazine (Pd3), phenazine (Pd4) and en is ethylenediamine), were synthesized and characterized. The interactions of the synthesized palladium(II) complexes with biomolecules such as DNA and BSA were studied using UV–Vis spectroscopy and fluorescence spectroscopy. Analysis of tumoricidal activity of investigated complexes, tested on several tumor cell lines of human and mouse origin, revealed that Pd1 and Pd2 exhibited weak cytotoxic potential at lower concentrations. However, Pd3 showed higher cytotoxicity effects on the human MDA-MB 468 breast carcinoma and A375 melanoma cell lines, while Pd4 exhibited tumoricidal potential against MDA-MB 468 cells and A549 human lung adenocarcinoma cells. Interestingly, A375 human melanoma cells were highly sensitive to Pd4 treatment similarly to the effect of cisplatin. Further, the antimicrobial effects of tested compounds were evaluated using different species of Gram-positive and Gram-negative bacteria, as well as yeasts. Pd1–Pd4 showed variable antimicrobial activity depending on the microorganism species. Among tested complexes, Pd4 exhibited the highest antimicrobial activity. The obtained data suggest that palladium(II) complexes might be further investigated as potential antitumor and antimicrobial agents.

Mononuclear nickel(II) and dinuclear palladium(II) complexes of a redox-active iminophenolate-based O,O,N,N,S,S ligand – experimental and theoretical vision

“A new potentially hexadentate redox-active schiff base ligand, H2L = 2-((Z)-(2-(2-(2-((Z)-3,5-di‑tert‑butyl‑2-hydroxybenzylideneamino)phenylthio)ethylthio)phenylimino)methyl)-4,6-di‑tert-butylphenol, reacts with NiII(O2CCH3)2·4H2O and PdCl2 in CH3OH in the presence of air and Et3N affording isolation of yellow and red crystalline solids of composition [Ni(L)] (1) and [Pd2(L)Cl2].2CH2Cl2 (2), respectively. When examined by cyclic voltammetry (CV), 1 exhibits three quasireversible responses at E1/2 = 0.60 V (peak-to peak separation, ΔEp = 80 mV), 0.96 V (ΔEp = 80 mV) and 1.16 V (ΔEp = 160 mV) vs SCE (saturated calomel electrode); while 2 exhibits one quasireversible response at E1/2 = 1.185 V (peak-to peak separation, ΔEp = 130 mV). One electron oxidized species showed EPR spectrum correspond to ferromagnetically coupled system, S = 3/2 (S = 1 for NiII and S = ½ for phenoxyl radical). Structural analysis revealed that 1 is discrete mononuclear and 2 is discrete dinuclear coordination complex. In complex 1, each NiII is in distorted octahedral NiN2O2S2 environment where coordination is satisfied by two nitrogen atoms, two oxygen atoms and two sulfur atoms of the ligand. In complex 2, each Pd is in distorted square planner PdNOSCl environment where coordination is satisfied by one each nitrogen, oxygen and sulfur atoms of the ligand, and a chloride ion. DFT calculations at B3LYP-level of theory adequately describe the electronic structures of 1 and 2, containing a spin-unpaired d8 NiII ion and spin-paired d8 PdII ion. Time-dependent-DFT calculations on 1 and 2 shed light on the origin of UV−vis−NIR spectral absorptions.

Direct Arylation of Benzothiophene and Benzofuran Catalyzed by a Dinuclear Palladium Complex

Direct Arylation of Benzothiophene and Benzofuran Catalyzed by a Dinuclear Palladium Complex

Clamshell Palladium(II) Complexes: Suitable Precursors for Photocatalytic Hydrogen Production from Water

AbstractA series of carboxylato‐bridged dinuclear palladium(II) complexes with cyclopalladated 2‐phenylbenzothiazole ligands were prepared and characterized by elemental analyses, NMR, IR, and UV‐vis spectroscopies, cyclic voltammetry, and X‐ray crystallography. All the complexes have clamshell structures in which two cyclopalladated 2‐phenylbenzothiazole ligands bound to palladium atoms are in the anti‐configuration arranging the ligands in opposite orientations from each other. The Pd−Pd distances of these complexes are shorter than the sum of the van der Waals radii, indicative of the presence of metal‐metal bonding interactions. These dinuclear complexes were used as water reduction catalysts in the photocatalytic system for hydrogen evolution and regarded as precatalysts that are converted into highly catalytically active species.

Dinuclear Palladium(II) and Platinum(II) Complexes of a Readily Accessible Bicyclic Diphosphane

AbstractThe one‐step synthesis (33 % isolated yield) of a novel bicyclic diphosphane, [P(CH2)2NC6H4(4‐NMe2)]2, P−P(NMe2), from the reaction of [P(CH2OH)4]Cl and H2NC6H4(4‐NMe2) in methanol is described. Surprisingly, P−P(NMe2) displays excellent air/solution stability (towards H2O, CH3OH) and can also function efficiently as a bridging ligand. Hence reaction of P−P(NMe2) with [Pd(μ−Cl)(η3‐allyl)]2 (η3‐allyl=C3H5, C4H7) or [Pd(μ−Cl)(κ2−C9H12N)]2 affords the singly‐bridged complexes {Pd(Cl)(η3‐allyl)}2{μ‐P−P(NMe2)} 1 a/1 b and {Pd(Cl)(κ2−C9H12N)}2{μ‐P−P(NMe2)} 1 c whereas treatment with [MX2(η4‐cod)] (M=Pd, Pt; X=Cl, Br, I, Me; η4‐cod=cycloocta‐1,5‐diene) gave (MX2)2{μ‐P−P(NMe2)}2 2 a–e in high yields. Protonation of 2 a–d with HBF4 ⋅ OEt2 gave the corresponding dimethylammonium salts 3 a–d. Single crystal X‐ray studies have been undertaken on P−P(NMe2), 1 b, 2 a, 2 b ⋅ 2CDCl3, 2 d, 2 e, 3 a ⋅ 12CD3CN and 3 b ⋅ 12CD3CN. The P−P bond lengths in free/coordinated P−P(NMe2) remain similar across all compounds studied here and no M ⋅⋅⋅ M contacts were observed within the planar M2P4 ring. In 3 a/3 b the BF4− anion displays a unique secondary interaction with the inorganic six‐membered M2P4 core.

Cyclic Palladium Formamidinate: Synthesis, Structure, Reactivity, and Application to Suzuki-Miyaura Cross-Coupling.

The deprotonation of acyclic palladium amidine chloride (1) with potassium tert-butoxide in tetrahydrofuran results in palladium bis(formamidinate) (2). 2 undergoes a nucleophilic addition reaction with acetonitrile in the presence of PdCl2 or Pd(OAc)2 (OAc = acetate) to give dinuclear cyclic six-membered (triazapentadiene)palladium complexes (4a and 4b). These compounds are also prepared from cyclic six-membered (tap)PdCl2 (5; tap = triazapentadiene) or formamidinium salts (6a-6c) with Pd(OAc)2/NaOAc in acetonitrile, whereas the direct reaction of 2 with acetonitrile or acrylonitrile resulted in palladium black or an acyclic C-N-coupled product (3). A comparison of structure 4 from 2 suggests a possible intermediate dinuclear palladium complex whose structure was identified through theoretical calculations. Further, Suzuki-Miyaura cross-coupling reactions were carried out under different solvents notably in an ethanol/water medium at room temperature.

Direct β-Alkenylation of Thiophenes with Alkenyl Halides Catalyzed by a Dinuclear Palladium Complex

Direct β-Alkenylation of Thiophenes with Alkenyl Halides Catalyzed by a Dinuclear Palladium Complex

Selective Formation of Mononuclear Palladium and Acetonitrile-Bridged Dinuclear Palladium Complexes Containing a Chiral Tridentate Ligand.

From the chiral Schiff base tridentate ligand LPh, unusual acetonitrile-bridged dinuclear palladium complex 1 and organopalladium complex 1' were synthesized selectively by using acetonitrile and ethanol, respectively. The chiral tridentate Schiff base ligand was bound to the palladium metal center with different chelation modes ([ONO] for 1 and [CNO] for 1'). Complex 1 constitutes the first example of dinuclear metal complexes connected only by a bridging acetonitrile, in which an exceptionally short C≡N bond distance [0.945(12) Å] of bridged acetonitrile was observed. To study the influence of a phenyl group attached to an imine, the phenyl-free ligand LH was prepared and used. In that case, an acetonitrile bridge was not observed. Theoretical calculation studies supporting the formation of 1 and 1' are favored.

Isomerization of Functionalized Olefins by Using the Dinuclear Catalyst [PdI (μ-Br)(Pt Bu3 )]2 : A Mechanistic Study.

In a combined experimental and computational study, the isomerization activity of the dinuclear palladium(I) complex [PdI(μ‐Br)(P t Bu3)]2 towards allyl arenes, esters, amides, ethers, and alcohols has been investigated. The calculated energy profiles for catalyst activation for two alternative dinuclear and mononuclear catalytic cycles, and for catalyst deactivation are in good agreement with the experimental results. Comparison of experimentally observed E/Z ratios at incomplete conversion with calculated kinetic selectivities revealed that a substantial amount of product must form via the dinuclear pathway, in which the isomerization is promoted cooperatively by two palladium centers. The dissociation barrier towards mononuclear Pd species is relatively high, and once the catalyst enters the energetically more favorable mononuclear pathway, only a low barrier has to be overcome towards irreversible deactivation.

Synthesis of mononuclear and dinuclear palladium (II) complexes containing oxadithioether ligands and their catalytic activities in norbornene polymerization

AbstractThe Pd (II) complexes trans‐[PdCl2(μ‐L)]2 and [Pd(acac)(L)][BF4] (L = RS(CH2)2O(CH2)2SR, R = Me, Et, nPr, iPr, nBu, iBu, n‐hexyl, benzyl) were obtained through the reaction of Pd(cod)Cl2 or [Pd(acac)(MeCN)2][BF4] with one equivalent of oxadithioether (L). The structural features of these complexes were analyzed by nuclear magnetic resonance (NMR) and Fourier‐transform infrared spectroscopy (FTIR), as well as electrospray ionisation mass spectrometry and density functional theory calculations. The complexes di‐μ‐(2,10‐dimethyl‐6‐oxa‐3,9‐dithiaundecane‐κ2S,S′)‐bis[trans‐dichloropalladium (II)] and (acetylacetonate‐κ2O,O′)(2,10‐dimethyl‐6‐oxa‐3,9‐dithiaundecane‐κ2S,S′)palladium (II) tetrafluoroborate were characterized by X‐ray diffractometry. The X‐ray structures of each complex indicate an axial M–O interaction formed by the endodentate conformation of the oxadithioether ligand. Palladium (II) dichloride complexes with oxadithioethers were demonstrated to have a 16‐membered dinuclear structure with a trans‐configured S2PdCl2 fragment. In the case of cationic palladium acetylacetonate complexes, only mononuclear complexes with a cis configuration of the oxadithioether fragment were observed. Variable temperature 1H and 13C NMR studies of the complexes demonstrate dynamic bonding of the oxadithioether ligands consistent with the presence of diastereoisomers that differ in the orientation of the S‐R groups along with both endodentate and exodentate bonding modes in solution. FTIR studies of the complexes indicate the presence of isomers in the solid state. The palladium catalyst precursors trans‐[PdCl2(μ‐L)]2 and [Pd (acac)(L)][BF4] were found to be active in the addition polymerization of norbornene. In the presence of cocatalysts, such as diisobutylaluminum chloride and boron trifluoride etherate, Pd (II) complexes exhibited activities in the range of 105 to 107 g of polymer (mol of Pd)−1 h−1. The catalyst systems showed good thermostability with a high activity of 1.43 × 107 g of polymer (mol of Pd)−1 h−1 at 75°C. These complexes are examples of Pd (II) complexes bearing thioether ligands, which are rarely observed in the field of olefin polymerization.

Tetra- and Dinuclear Palladium Complexes Based on a Ligand of 2,8-Di-2-pyridinylanthyridine: Preparation, Characterization, and Catalytic Activity

Complexation of L [L = 5-phenyl-2,8-di-2-pyridinyl-anthyridine] with [Pd(CH3CN)4](BF4)2 and [Pd(CH3CN)3Cl](BF4) in a molar ratio of 1:2 rendered the corresponding dinuclear complexes [Pd2L (CH3CN)4](BF4)4 (1) and [Pd2L (CH3CN)2Cl2](BF4)2 (2), respectively. However, treatment of L with (COD)PdCl2 followed by anion exchange yielded a tetranuclear complex [Pd4L3Cl4](PF6)4(4a). Structures of these complexes are characterized by both spectroscopy and X-ray crystallography. Interconversion of these three complexes was studied via the manipulation of stoichiometric ratio of ligand to metal precursor. The catalytic activity of these complexes for carbonylative Suzuki–Miyaura cross-coupling was investigated. Complex 2 shows an excellent catalytic activity on the reaction of aryl iodide with arylboronic acid in the presence of atmospheric pressure of CO to give the corresponding benzophenones.

Coordinative cross-linking of acrylonitrile–butadiene rubber with a macrocyclic dinuclear palladium complex

A dinuclear Pd(II) complex possessing a cyclic ligand was applied as a coordinative cross-linker of acrylonitrile–butadiene rubber (NBR). Tensile tests revealed that the mechanical properties of the coordinatively cross-linked NBRs were improved compared with those of the original NBR. The effects of the loading amount of the complexes and their reusability were also investigated. A dinuclear Pd(II) complex possessing a cyclic ligand was applied as a coordinative cross-linker of acrylonitrile–butadiene rubber (NBR). Tensile tests revealed that the mechanical properties of the coordinatively cross-linked NBRs were improved compared with those of the original NBR. Increasing the loading amount of the complex enhanced Young’s modulus, tensile strength, tensile strain, and toughness. The cross-linked NBR could be reused with a simple dissolution and drying process, which featured coordinative cross-linking.

Potential Antitumor Effect of Newly Synthesized Dinuclear1,5‐Naphthyridine‐Bridging Palladium(II) Complexes

AbstractFive new dinuclear palladium(II) complexes with general formula, [{Pt(L)Cl}2(μ‐1,5‐nphe)](NO3)2 (L is ethylenediamine (en), (±)‐1,2‐propylenediamine (1,2‐pn), trans‐(±)‐1,2‐diaminocyclohexane (dach), 1,3‐propylenediamine (1,3‐pd), (±)‐1,3‐pentanediamine (1,3‐pnd) and 1,5‐nphe is bridging 1,5‐naphthyridine ligand) were synthesised and spectroscopically characterized. In vitro cytotoxic activity of these complexes was evaluated against mouse mammary carcinoma (4T1), colon (CT26), lung cancer cells (LLC1) and melanoma (B16‐F10) as well as human lung adenocarcinoma (A549), mammary carcinoma (MDA‐MB‐468), and colon cancer (HCT 116). The investigated complexes reduced viability of tumor cells in dose dependent manner. Dinuclear Pd(II) complexes act less cytotoxic toward tumor cells, compare to cisplatin, but also have greater selectivity toward mesenchymal stem cells. The potential mechanism of cell death of tumor cells treated with palladium(II) 1,5‐naphthyridine dinuclear complexes is enhanced apoptosis, facilitated by down‐regulation of anti‐apoptotic Bcl‐2 and up‐regulation of pro‐apoptotic Caspase‐3.

Macrocyclic Dinuclear Palladium Complex as a Novel Doubly Threaded [3]Rotaxane Scaffold and Its Application as a Rotaxane Cross-Linker.

A dinuclear PdII complex possessing a cyclic ligand was developed as a novel doubly threaded [3]rotaxane scaffold and applied as a rotaxane cross-linker reagent. The dinuclear complex (PdMC)2 was prepared by one-step macrocyclization followed by the double palladation reaction. 1 H NMR analysis and UV/Vis measurements revealed the formation of a doubly threaded pseudo[3]rotaxane by the complexation of (PdMC)2 with 2 equivalents of 2,6-disubstituted pyridine 3 through double metal coordination. The treatment of (PdMC)2 with 2 equivalents of 4-vinylpyridine (VP) afforded a doubly threaded [3]rotaxane cross-linker (PdMC-VP)2 . Radical co-polymerization of VP and t-butylstyrene in the presence of (PdMC-VP)2 afforded a stable rotaxane cross-linked polymer (RCP). An elastic RCP was also prepared by using n-butyl acrylate as a monomer. The obtained RCPs exhibited higher swelling ability and higher mechanical toughness compared with the corresponding covalent cross-linked polymers.

Macrocyclic Dinuclear Palladium Complex as a Novel Doubly Threaded [3]Rotaxane Scaffold and Its Application as a Rotaxane Cross‐Linker

AbstractA dinuclear PdII complex possessing a cyclic ligand was developed as a novel doubly threaded [3]rotaxane scaffold and applied as a rotaxane cross‐linker reagent. The dinuclear complex (PdMC)2 was prepared by one‐step macrocyclization followed by the double palladation reaction. 1H NMR analysis and UV/Vis measurements revealed the formation of a doubly threaded pseudo[3]rotaxane by the complexation of (PdMC)2 with 2 equivalents of 2,6‐disubstituted pyridine 3 through double metal coordination. The treatment of (PdMC)2 with 2 equivalents of 4‐vinylpyridine (VP) afforded a doubly threaded [3]rotaxane cross‐linker (PdMC‐VP)2. Radical co‐polymerization of VP and t‐butylstyrene in the presence of (PdMC‐VP)2 afforded a stable rotaxane cross‐linked polymer (RCP). An elastic RCP was also prepared by using n‐butyl acrylate as a monomer. The obtained RCPs exhibited higher swelling ability and higher mechanical toughness compared with the corresponding covalent cross‐linked polymers.

Hydrolysis of the Amide Bond in L-Methionine- and L-Histidine-Containing Dipeptides in the Presence of Dinuclear Palladium(II) Complexes with Benzodiazines Bridging Ligands

1H NMR spectroscopy was applied to study the catalytic activity of dinuclear Pd(II)-aqua complexes with different benzodiazine bridging ligands, [{Pd(en)(H2O)}2(μ-qx)]4+ (Pd1), [{Pd(en)(H2O)}2(μ-qz)]4+ (Pd2) and [{Pd(en)(H2O)}2(μ-phtz)]4+ (Pd3) (qx, qz and phtz denote quinoxaline, quinazoline and phthalazine, respectively), in the hydrolytic cleavage of the amide bond in N-acetylated L-methionylglycine (Ac–L–Met–Gly) and L-histidylglycine (Ac–L–His–Gly) dipeptides. All reactions were investigated with an equimolar amount of the reactants at pH = 2.0–2.5 in D2O and at 37 °C. The obtained data for the catalytic activity of Pd1–Pd3 complexes are compared with those previously reported for [{Pt(en)(H2O)}2(μ-L)]4+ (L denotes benzodiazine: qx, qz and phtz), [{Pd(en)(H2O)}2(μ-L)]4+ and [{Pt(en)(H2O)}2(μ-L)]4+ (L denotes diazine: pyrazine and pyridazine) complexes. It was found that catalytic activity of these complexes in peptide cleavage is strongly related to the position of the nitrogen atoms in the benzodiazine or diazine bridging ligand. The investigated dinuclear Pd(II) and Pt(II) complexes show catalytic activity in the selective hydrolysis of the Met–Gly amide bond of Ac–L–Met–Gly dipeptide. Moreover, all the above mentioned Pd(II) complexes were also able to catalyze the regioselective hydrolysis of the His–Gly amide bond of Ac–L–His–Gly dipeptide. However, in the reaction with Ac–L–His–Gly, only Pt(II) aqua complexes containing bridging ligands with two nitrogen atoms in the para-position (quinoxaline and pyrazine) were able to cleave this dipeptide.

In vitro cytotoxic activities, DNA- and BSA-binding studies of dinuclear palladium(II) complexes with different pyridine-based bridging ligands

Three new dinuclear palladium(II) complexes with general formula [{Pd(en)Cl}2(μ-L)]2+ (L is pyridine-based bridging ligand 4,4′-bipyridine (4,4′-bipy, 1), 1,2-bis(4-pyridyl)ethane (bpa, 2), 1,2-bis(4-pyridyl)ethylene (bpe, 3) and en is bidentate coordinated ethylenediamine) were synthesized and characterized by elemental microanalyses, NMR (1H and 13C), IR and UV–Vis spectroscopy. In vitro cytotoxic activity of these complexes against human A549 and murine LLC1 lung cancer cells, as well as two human HCT116 and SW480 and one murine CT26 colon cancer cells was investigated using MTT assay (MTT is 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide). The potential of complexes 1–3 to induce apoptosis was tested by flow cytometric analysis of Annexin V and propidium iodide stained treated cells, while their antiproliferative activity was analyzed by detection of Ki67 expression in treated cancer cells. The DNA binding affinity of complexes 1–3 was evaluated by UV–Vis, fluorescence emission spectroscopy and by viscosity measurements in aqueous phosphate buffer solution at pH 7.40. Furthermore, interaction of these complexes with bovine serum albumin was investigated by fluorescence spectrometry. The present study showed that the nature of pyridine-based bridging ligand (L) in dinuclear [{Pd(en)Cl}2(μ-L)]2+ complex has an influence on the complex preference for the cytotoxic activity and CT-DNA/BSA (CT-DNA is calf thymus DNA and BSA is bovine serum albumin) binding affinity.

Synthesis and catalytic activity of cationic dinuclear palladium (II) complexes supported by thioether ligands containing two di-(2-picolyl) amine arms

The design, synthesis and characterization of a series of dithioether ligands featuring two di-(2-picolyl)amine arms (2a–2d) and their corresponding cationic dinuclear palladium (II) complexes (3a–d) are reported. Crystal structures of ligand 2b and complexes 3b and 3d were determined by X-ray diffraction studies. The molecular structures of 3b and 3d display each of the two di-(2-picolyl)amine fragments coordinated to one palladium(II) atom in a (κ3-N,N,N) tridentate fashion and with the cationic metal centers displaying square-planar geometries. Weak interactions between the metal centers and the thioether fragments are observed. All bimetallic complexes 3a–d were tested as catalytic precursors in the Suzuki couplings of different o- or p-substituted iodo- or bromoaryls with boronic acids. The overall catalytic results indicate that complex 3b is the best precursor of the series demonstrating even more efficient performance compared to commercial palladium sources such as Pd(OAc)2 and the Nájera Catalysts.

Open clamshell dinuclear palladium(ii) complexes possessing out-of-plane anisotropy.

Double cyclometalation of planar, oligomeric phenylpyridines yielded dinuclear palladium(ii) complexes with novel out-of-plane anisotropy. An X-ray crystal structure analysis revealed that the complexes exhibit concave-convex geometry, and 1H NMR measurement evidenced the occurrence of stable out-of-plane anisotropy. The dipole moment and Pd-Pd interaction were investigated by theoretical calculations.