PdCl2 Complexes Research Articles

Erratum to: DNA Binding and Equilibrium Investigation of the Interaction of a Model Pd(II) Complex with Some Selected Biorelevant Ligands

The Pd(DAP)Cl2 complex, where DAP is 2,6-diaminopyridine, was synthesized and characterized. The stoichiometries and stability constants of the complexes formed between various biologically relevant ligands (amino acids, amides, DNA constituents, and dicarboxylic acids) and [Pd(DAP)(H2O)2]2+ were investigated at 25 °C and at constant 0.1 mol·dm−3 ionic strength. The concentration distribution diagrams of the various species formed were evaluated. A further investigation of the binding properties of the diaqua complex [Pd(DAP)(H2O)2]2+ with calf thymus DNA (CT-DNA) was investigated by UV–Vis spectroscopy. The intrinsic binding constants (K b) calculated from UV–Vis absorption studies is 1.04 × 103 mol·dm−3. The calculated (K b) value was found to be of lower magnitude than that of the classical intercalator EB (ethidium bromide) (K b = 1.23 (±0.07) × 105 mol·dm−3), suggesting an electrostatic and/or groove binding mode for the interaction with CT-DNA.

Convenient Transfer Semihydrogenation Methodology for Alkynes Using a PdII-NHC Precatalyst

A convenient and easy-to-use protocol for the Z-selective transfer semihydrogenation of alkynes was developed, using ammonium formate as the hydrogen source and the easily prepared and commercially available, highly stable complex PdCl(η3-C3H5)(IMes) (1) as the (pre)catalyst. Combined with triphenyl posphine as an additional ligand, this system provides a robust catalytic synthetic method that shows little to no over-reduction or isomerization after full substrate conversion. The system allows the direct use of solvents and reagents, as received from the supplier without drying or purification, thus providing a practical method for semihydrogenation of a broad range of alkynes. The mechanism behind these high and enhanced selectivities was determined through a set of kinetic experiments.

Tiara-like Octanuclear Palladium(II) and Platinum(II) Thiolates and Their Inclusion Complexes with Dihalo- or Iodoalkanes

A tiara-like octanuclear palladium thiolate complex, [Pd(μ-SCH2CO2Me)2]8, that has a toroidal structure was synthesized via reactions of either PdCl2 with methyl thioglycolate/N,N-diisopropylethylamine (DIEA) (conventional method) or [PdCl2(MeCN)2] with m-C6H4(CMe2SCH2CO2Me)2 (alternative method). In the latter method, the tiara-like complex formed via the corresponding SCS-pincer complex and/or 1:1 PdCl2 and ligand complexes. With respect to the platinum analogues, the alternative method efficiently produced the tiara-like octanuclear complex [Pt(μ-SCH2CO2Me)2]8 in high purity. Small molecules, such as CH2Cl2, ClCH2CH2Cl, CH2Br2, and CH3I, were accommodated in the inner voids of the tiara rings to form 1:1 inclusion complexes. These complexes are stabilized not only by weak CH···X hydrogen bonds (X = Cl or Br) between the methylene protons of four or eight axially positioned methoxycarbonylmethyl groups on the tiara rings and the halogen atoms of the guest molecules but also by weak coordination of the halogen atoms to the transition-metal atoms.

Aging and Ball-Milling as Low-Energy and Environmentally Friendly Methods for the Synthesis of Pd(II) Photosensitizers

Simple and efficient solid-state synthetic methods, aging and ball milling (liquid-assisted grinding, LAG), have been employed to achieve reactions of triphenylphosphine (tpp) and 1,1′-bis(diphenylphosphino)ferrocene (dppf) with dicyclopalladated azobenzenes (DMF)PdCl(μ-R1C6H3N═NC6H3R2)PdCl(DMF), R1 = H, OCH3, N(CH3)2 and R2 = H, NO2. For the first time the aging processes have been applied in the formation of Pd(II) heteroleptic complexes. Both synthetic procedures lead to four types of tetra- or pentacoordinated complexes (tpp)PdCl{(μ-Cl)(μ-R1C6H3N═NC6H3R2)}Pd(tpp) 1A–3A, (tpp)2PdCl(μ-R1C6H3N═NC6H3R2)PdCl(tpp)2 1B–3B, PdCl{(μ-Cl)(μ-R1C6H3N═NC6H3R2)}Pd(dppf) 1C–3C, and (dppf)PdCl(μ-R1C6H3N═NC6H3R2)PdCl(dppf) 1D–3D, in which azobenzenes simultaneously act as monodentate C- and bidentate C,N-donors (A, B, and C complexes) or, for the first time, only as double C-donors (D complexes). Although their formation requires complex intramolecular transformations, aging and ball milling have been proved to be effi...

A new enantiopure d-camphor-derived palladacycle

d-Camphor O-methyloxime (HL, 1) was prepared as a 92:8 mixture of E and Z isomers in 74% yield from d-camphor, methoxyamine hydrochloride and NaOAc in ethanol. Reaction of oxime 1 with Na2PdCl4 in a 2:1 ratio in MeOH at rt provided the coordination complex PdCl2(HL)2 (2) in 67% yield. Cyclopalladation of oxime 1 using Pd(OAc)2 in acetic acid at 80 °C followed by treatment with LiCl furnished the chloro-bridged dimeric cyclopalladated complex [μ-ClPdL]2, 3, in 66% yield. Compound 3 was converted to the mononuclear PPh3 adduct 4 in 98% yield. The proposed structures of new complexes 2–4 were confirmed by 1H, 13C{1H}, DEPT, and 2D NMR spectra. X-ray crystal study of complex 3 revealed the anti geometry of two cyclopalladated ligands as well as the presence of the (sp3)C–Pd bond.

Palladium(II) Complexes Containing Mixed Nitrogen-Sulphur Donor Ligands: Interaction of [Pd(Methionine Methyl Ester)(H2O)2](2+) with Biorelevant Ligands.

Pd(MME)Cl2 complex (MME = methionine methyl ester) was synthesised and characterized by physicochemical measurements. The reaction of [Pd(MME)(H2O)2]2+ with amino acids, peptides, or dicarboxylic acids was investigated at 25°C and 0.1 M ionic strength. Amino acids and dicarboxylic acids form 1 : 1 complexes. Peptides form both 1 : 1 complexes and the corresponding deprotonated amide species. The stability of the complexes formed was determined and the binding centres of the ligands were assigned. Effect of solvent on the stability constant of Pd(MME)-CBDCA complex, taken as a representative example, shows that the complex is more favoured in a medium of low dielectric constant. The concentration distribution diagrams of the complexes were evaluated.

Palladium(II) complexes containing N,N′-bidentate N-cycloalkyl 2-iminomethylpyridine and 2-iminomethylquinoline: Synthesis, characterisation and methyl methacrylate polymerisation

The reaction of [Pd(CH3CN)2Cl2] with N-cyclopentyl-1-(pyridin-2-yl)methanimine (L1), N-cyclohexyl-1-(pyridin-2-yl)methanimine (L2), N-(piperidin-1-yl)-1-(pyridin-2-yl)methanimine (L3) or N-cyclopentyl-1-(quinolin-2-yl)methanimine (L4) in ethanol yields the bidentate (NN’) PdCl2 complexes [L1PdCl2], [L2PdCl2], [L3PdCl2] and [L4PdCl2], respectively. The X-ray crystal structure of the Pd(II) complexes revealed that the Pd atom in [LnPdCl2] (Ln=L1, L2, L3, L4) shows a distorted square planar geometry involving two nitrogen atoms and two chloro ligands. The complexes [L1PdCl2] and [L4PdCl2] (of which the ligands are N-cyclopentyl substituted) showed the highest catalytic activity for the polymerisation of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) with an activity of 1.45×105g PMMA/mol Pd h at 60°C and a PMMA syndiotacticity (characterized using 13C NMR spectroscopy) of ca. 0.70.

Complexes of PdCl2 with chiral oximes of α-(o-anisidino)caranone and α-(o-anisidino)pinanone: synthesis and crystal structures

3-(2-Methoxyphenylamino)caran-4-one and 2-(2-methoxyphenylamino)pinan-3-one E-oximes obtained from appropriate natural terpenes were transformed into 1: 1 complexes with PdCl2. The structures of the complexes were examined by X-ray diffraction.

Coordination properties of Palladium(II) complex taken as a model of an antitumour agent with some selected amino acids, peptides and DNA constituents

Pd(DHP)Cl2 complex ( DHP = 1,3-diamino-2-hydroxopropane ), was synthesized and characterized by physico-chemical measurements. The coordination of [Pd(DHP) (H2O)2]2+ with some selected bio-relevant ligands as phenylglycine, phenylalanine, lysine, valine, ethanolamine, glycineamide, glycylphenylalanine, glycylleucine, inosine, guanosine and inosine-5’-monophosphate disodium salt was investigated.Stoichiometry and stability constants of the complexes formed are reported at 25 0C and 0.1M ionic strength. The results show the formation of 1:1 complexes with amino acids. DNA constituents form 1:1 and 1:2 complexes. Peptides form both 1:1 complexes and the coresponding deprotonated amide species. The effect of chloride ion concentration on the formation constant of inosine, taken as a representaive ofDNA constituents, complex with Pd(DHP)2+ was reported.

Suzuki-Miyaura cross-coupling reaction catalyzed by a highly stable Pd(P-Phos)Cl2 complex at room temperature under air

A new Pd(P-Phos)Cl 2 complex was synthesized and characterized by 1 H NMR, 13 C NMR, 31 P NMR, and X-ray single crystal structure determination. The complex proved to be a highly stable and efficient catalyst for substrates with a wide range of functional groups in Suzuki-Miyaura cross-coupling reactions under air at room temperature. Low catalyst loadings were employed and turnover number of up to 49000 was obtained. A new Pd(P-Phos)Cl 2 complex has been synthesized and characterized. The complex catalyzed the Suzuki-Miyaura cross-coupling reactions of various aryl halide and arylboronic acids in medium to excellent yields under air at room temperature.

Electrostatic Control of Pd2+ → Ag+ Transmetalation of a Bis-Imidazoliophosphine Ligand

Attempts to prepare a tetracationic Pd2+ complex of the dicationic bis-imidazoliophosphine ligand 1 by AgOTf-mediated chloride abstraction from the corresponding PdCl2 complex led to the observation of a Pd2+ → Ag+ transmetalation giving a tricationic (1)Ag+ complex. The driving force of the process is attributed to the relaxation of electrostatic repulsion between the formal positive charges. VTP 31P NMR experiments in CD2Cl2 afford evidence of a fast equilibrium between the mononuclear (1)Ag+ complex and its dimer. The X-ray crystal structure of the latter reveals that bridging TfO– anions allow maintenance of the overall cohesion of the structure through attractive electrostatic interactions.

Monodentate Chiral N-Heterocyclic Carbene-Palladium-Catalyzed Asymmetric Suzuki-Miyaura and Kumada Coupling

N-Heterocyclic carbene ligands derived from <i>C</i> ₂-symmetric diamine with naphthyl side chains are introduced as chiral monodentate ligands, and their palladium complexes (NHC)Pd(cin)Cl are prepared. These compounds exist as a mixture of diastereomers, and the palladium complexes can be successfully separated. When used in the asymmetric Suzuki–Miyaura and ­Kumada coupling, chiral biaryls can be obtained in high yield and moderate selectivity.

Insight into PdCl2(bipy) complex as an efficient catalyst for heck reaction and kinetic investigations in homogeneous medium

PdCl2(bipy) complex (bipy = 2,2′-bipyrydine) efficiently catalyzes the vinylation of aryl halides. The activity of this catalyst for the Heck reactionwas demonstrated for a variety of aryl halides and olefins in the presence of different organic and inorganic bases. The catalyst is stable under the reaction conditions and no degradation was observed. The kinetics of the Heck coupling of styrene with iodobenzene using the PdCl2(bipy) complex with potassium acetate as a base was studied over a temperature range of 393–413 K in 2-nitro-2-methyl-1-propanol medium. An empirical rate model has been proposed to fit the observed data and is found to be in good agreement with experimental results. The activation energy of the reactionwas found to be 98.70 kJ/mol.

The speciation and transport of palladium in hydrothermal fluids: Experimental modeling and thermodynamic constraints

The solubility of PdO(cr) was measured in NaOH (to 0.1m, mol/kg H2O) solutions at 400°C, 1kbar, and the solubility of Pd(cr) was determined at 400–500°C, 1kbar in acidic chloride solutions (to 1.5m NaCl) buffered with respect to hydrogen. The Pd electrode potential Eo(PdCl42-)/Pd(cr) for the reaction PdCl42- + 2e−=Pd(cr) + 4Cl− was determined at 50 and 70°C in 1m chloride solutions. These data, together with reliable literature values, were used for calculation of the standard thermodynamic properties and the formation constants for Pd–OH, Pd–Cl, and Pd–S–HS complexes within the framework of the revised Helgeson–Kirkham–Flowers model. It was found that PdCl3- and PdCl42- become the most important Pd complexes in high temperature (t>300°C), chloride-rich fluids, and PdCl42- predominates at m(Cl)>0.1. The stability of Pd–Cl complexes increases sharply with increase in temperature. The near-neutral chloride–sulfide solutions (1m NaCl, <0.1m Stot) can transport Pd at ppm concentration levels at t⩾600°C, whereas decrease in temperature and increase in pH can lead to effective deposition of Pd minerals. The stability of Pd–S–HS complexes (Pd(HS)2°, Pd(HS)3- and PdS(HS)2−) decreases with increase in temperature. Therefore, the role of these complexes in hydrothermal transport of palladium is restricted to the low temperature solutions (t<100°C) and sulfur can be considered an efficient depositing agent for Pd. The calculated HKF Equation of State parameters were used to predict thermodynamic properties of Pd2+, Pd–OH, Pd–Cl, and Pd–S–HS complexes to 700°C, 2kbar. These parameters are incorporated into the FreeGs web-enabled database (http://www-b.ga.gov.au/minerals/research/methodology/geofluids/thermo/calculator/search.jsp) that can be used for geochemical application of thermodynamic data obtained in the present study.

Novel Pd(II) coordination compounds involving 2-[(2-hydroxyphenyl)methylene]hydrazine-N-(2-propenyl)-carbothioamide as a ligand or pro-ligand: Synthesis, crystal structures and analytical application

Novel palladium(II) complexes with a thiourea derivative 2-[(2-hydroxyphenyl)methylene]hydrazine-N-(2-propenyl)-carbothioamide have been synthesized and characterized by single crystal X-ray diffraction, IR, UV–Vis, 1H and 13C NMR spectroscopy. Depending on synthesis conditions the ligand could be coordinated to the metal ion as a neutral molecule or mono-/bianion forming complexes Pd(H2L)Cl (I), Pd(HL)H3L (II), Pd(HL′)Cl (III). The different coordination of two ligand molecules realize in the complex (II), where one carbothioamide molecule coordinates in a tridentate manner being in the thiol form and another one binds to the metal by the sulfur of the thioureide group in a monodentate manner being in the thione tautomeric form. The compound (III) is synthesized in the acidic medium that causes the cyclization of the allyl fragment of carbothioamide. The selected ligand also reacts with Pd(II) as a dibasic acid to yield an anionic complex [Pd(HL)Cl]−, which is isolated as a salt of the astraphloxin basic dye, [Pd(HL)Cl][AF]. The last one is used for developing a procedure for selective extraction of Pd2+ from aqueous solutions containing a mixture of platinum metals.

The first “Kuhn verdazyl” ligand and comparative studies of its PdCl2 complex with analogous 6-oxoverdazyl ligands

The synthesis and characterization of two new N,N'-diarylverdazyl radical ligands and their corresponding PdCl2 complexes are described. One of the two radicals is of the "Kuhn verdazyl" structure type and was made by adaptation of standard synthetic procedures for this class of verdazyl. The N,N'-diphenyl-6-oxoverdazyl was prepared by hydrolysis of a related tetrazane; the resulting N,N'-diphenylcarbohydrazide was condensed with pyridinecarboxaldehyde and then oxidized to the verdazyl according to standard protocols. Square planar PdCl2 complexes of both verdazyls were prepared by reactions of the radicals with PdCl2 in acetonitrile solution. The structural, spectroscopic, and electrochemical properties of the new verdazyl ligands and their Pd complexes are reported; generally the distinct ligand-centred properties associated with each verdazyl type carry over into the properties of the complexes. The electrochemical studies reveal ligand-centred oxidation and reduction processes; despite the minimal extent of spin delocalization onto Pd in the metal complexes, large shifts in oxidation and reduction potentials (relative to those of the free verdazyl ligands) are discussed.

Efficient catalytic aryl amination of bromoarenes using 3-iminophosphine palladium(II) chloride

While pursuing the development of new hydroamination catalysts, a 3-iminophosphine palladium(II) chloride complex [(3IP)PdCl2] was synthesized that has subsequently proven to be an effective precatalyst for the aryl amination of bromoarenes. This (3IP)PdCl2 complex has been utilized in the catalytic aryl amination of both bromobenzene and bromopyridine derivatives, specifically yielding excellent activity in coupling reactions involving bromobenzene, 4-bromotoluene, and 2-bromopyridine. Using a standard set of catalytic conditions, many alkyl and aryl amines have been investigated as coupling partners in the aryl amination of bromoarenes. In general, secondary alkyl amines and ortho-substituted anilines proved to be the best substrates for this reaction, commonly giving quantitative conversion to products, while primary amines and other anilines gave only poor to moderate results. Catalytic screening data, product yields, and full characterization of isolated products are included.

Synthesis and structural characterization of Pd(N,N-dimethylaminopropylamine)Cl2 complex – The interaction with bio-relevant ligands with reference to the effect of cysteine on the deactivation of metal-based drug

The synthesis and X-ray structural characterization of Pd(DMPA)Cl2 complex, where DMPA=N,N-dimethylaminopropylamine, is reported. The complex crystallizes in the space group P21/c, a=8.8923(4), b=10.9050(5), c=11.5006(7) Å, β=120.00(18)°, V=948.25(8) Å3, Z=4. The palladium centre has a typical square-planar geometry with a tetrahedral distortion. Stoichiometry and stability constants of the complexes formed between [Pd(DMPA)(H2O)2]2+ and some selected DNA constituents and cytsteine are investigated at 25°C and at constant 0.1M ionic strength. The concentration distribution diagrams of the various species formed are evaluated. The equilibrium constants for the displacement of coordinated ligands as inosine by cysteine are calculated. The results are expected to contribute to the chemistry of tumour therapy.

The interaction of [Pd(N,N-dimethylaminopropylamine)(H2O)]2+ with dicarboxylic acids and inosine: Thermodynamic model for carboplatin drug

Abstract The Pd(DMPA)Cl2 complex, where DMPA = N,N-dimethylaminoproylamine, was synthesized and characterized. The stoichiometry and stability constants of the complexes formed between various dicarboxylic acids and [Pd(DMPA)(H2O)2]2+ were investigated. The effect of solvent dielectric constant, chloride ion concentration of the medium and temperature on the stability constant of the cyclobutanedicaroxylic acid (CBDCA) complex was investigated. The equilibrium constants for the displacement of coordinated CBDCA by inosine, taken as an example of DNA constituents, were calculated. The results are expected to contribute to the chemistry of antitumour agents.

Theoretical study on a new active species for the Pd(II)-catalyzed Mizoroki–Heck reaction

The formation process of an active species for the Pd(II)-catalyzed Mizoroki–Heck reaction between bromobenzene and ethylene was investigated theoretically using the DFT(B3PW91) method. In this mechanism, one need not consider the dissociation of the chloride ion from the PdCl2(dppe) complex. It was confirmed that the ethylene insertion into the Pd–Cl bond (Path A) occurs more easily than the C–Br oxidative addition (Path B) and the Cl− dissociation (Path Z) for the PdCl2(dppe) complex. In the next step, the C6H5Br approaches the Pd center of the complex with ethylene via the C–Br oxidative addition, followed by the ethylene insertion into the Pd–Cl bond (Path D) to form a six-coordinate complex, PdBrCl(C2H4Cl)(C6H5)(dppe). In the final step, a C–Cl elimination proceeds from the complex to give a four-coordinate complex, PdBr(C6H5)(dppe). The rate-determining step of Path D is the C–Cl reductive elimination, and the energy difference between reactant and TS was calculated to be 30.4 kcal/mol. Similar mechanisms releasing Cl–C4H8–Cl (Path E and F) are also acceptable, since those barrier heights were calculated to be 32.3 and 17.6 kcal/mol. Path D, E and F are plausible candidates to form the PdBr(C6H5)(dppe) complex as a starting complex of the catalytic cycle. The rate-determining step of the entire catalytic reaction using the PdBr(C6H5)(dppe) complex is the β–H abstraction about the electronic energy of solute in solution and the free energy in solution, and those barrier heights were calculated to be 26.4 and 24.9 kcal/mol, respectively. As a result, the first step of the catalytic reaction mechanism is not the Cl− dissociation from the PdCl2(dppe) complex. Instead, the ethylene insertion into the Pd–Cl bond first proceeds to produce an active species, and next the PdBr(C6H5)(dppe) complex forms through Path D, E or F. It is concluded that the catalytic cycle of the Mizoroki–Heck reaction starts from PdBr(C6H5)(dppe).