Kinetics and Mechanism of Electroreduction of Palladium(II) Bisethylenediamine Complexes on a Dropping Mercury Electrode

Kinetics of electroreduction of complexes Pd(en)²⁺ ₂(2 × 10^–5M) on a dropping mercury electrode is studied in solutions with various concentrations of ethylenediamine and supporting electrolytes (NaF, NaClO₄) at pH 4.5–11 and different instantaneous current recording times. Diffusion coefficients for reducing complexes and kinetic parameters of the slow electrochemical stage are determined. The concentration of supporting electrolytes is found to affect the half-wave potential, which points to an inner-sphere mechanism of electrochemical stage at supporting electrolyte concentrations of 0.005 to 0.03 M and to a predominantly outer-sphere mechanism at higher concentrations.     

Kinetics and Mechanism of Reduction of Palladium(II) Complexes with Ethanolamine on a Dropping Mercury Electrode

The kinetics of electroreduction of palladium(II) complexes with ethanolamine (mea) is studied by ac and dc polarography at pH 6.2–11.5 and different ethanolamine concentrations. At c _mea 0.3–1 M and pH 6.2, commensurate quantities of Pd(mea)²⁺ ₄ and Pd(mea)²⁺ ₃ complexes are present in solutions. The latter, as opposed to the former, contains one bidentate-coordinated ligand. The equilibrium constant for the reaction of mutual conversion of these two complexes at pH 6.2 is determined, along with the equilibrium constant for a similar reaction at pH 7.2. A diffusion nature of observed limiting currents is established. Kinetic parameters of the slow electrochemical stage are determined. The E _1/2 shift in the negative direction with pH adjusted from 9.5 to 11.5 is due to the preceding reversible chemical stage of protonation of the Pd(mea)₃(H_–1mea)⁺ complexes predominant in solution in the pH interval mentioned.     

Anionic Palladium(0) and Palladium(II) Ate Complexes

Palladium ate complexes are frequently invoked as important intermediates in Heck and cross‐coupling reactions, but so far have largely eluded characterization at the molecular level. Here, we use electrospray‐ionization mass spectrometry, electrical conductivity measurements, and NMR spectroscopy to show that the electron‐poor catalyst [L₃Pd] (L=tris[3,5‐bis(trifluoromethyl)phenyl]phosphine) readily reacts with Br⁻ ions to afford the anionic, zero‐valent ate complex [L₃PdBr]⁻. In contrast, more‐electron‐rich Pd catalysts display lower tendencies toward the formation of ate complexes. Combining [L₃Pd] with LiI and an aryl iodide substrate (ArI) results in the observation of the Pd^II ate complex [L₂Pd(Ar)I₂]⁻.     

Palladium(II) Pyridinecarboxaldimine Complexes Derived from Unsaturated Amines

Pyridinecarboxaldimines (N–N′) derived from pyridin-2-ylcarboxaldehydes and unsaturated amines add to [PdCl₂(coe)]₂ (coe = cis-cyclooctene) to give complexes of the type PdCl₂(N–N′) in moderate yields. The palladium complexes have been investigated as substrates for hydroboration reactions and as antifungal agents against Aspergillus niger, A. flavus, Candida albicans, and Saccharomyces cerevisiae.     

Kinetics and Mechanism of the Decarbonylation of Benzoylformyl Palladium(II) Complex

The benzoylformyl Pd(II) complex, Pd(PPh₃)₂(Cl)(COCOPh), thermally decomposes to the corresponding benzoyl complex by the loss of CO. The predominant route of decarbonylation is led by a reversible dissociation of a phosphine ligand. The disappearance of the benzoylformyl complex in solutions follows first order kinetics not only in the existence of excess PPh₃ but also in the absence of added PPh₃. Through the treatments of both preequilibrium and the steady state approximations to the kinetic data, the rate constants of the intramolecular acyl migration, k₁ and k₂; as well as the equilibrium constant and the individual rate constants of the reversible phosphine dissociation step, K, k_d and k_d, were determined in CHCl₃. The activation parameters for k_d, being ^ΔH^? = 25.4 Kcal Mol^?1, ^ΔS^? = 15.9 eu, ^ΔG^? = 20.7 Kcal Mol^?1;and for k_?d, being ^ΔH^? = 13.0 Kcal Mol^?1, ^ΔS^? = ?7.9 eu, ^ΔG^? = 15.4 Kcal Mol^?1, were evaluated.     

Palladium(II) Complexes of 1-vinylimidazole

Two new co-ordination compounds of Pd^II with 1-vinylimidazole of the formulae [PdL₄]Cl₂·3H₂O and trans-[PdL₂Cl₂], where L is a 1-vinylimidazole molecule, have been obtained. The compounds were characterised by spectroscopic, molar conductivity, thermogravimetric and magnetochemical measurements. Single crystal X-ray structure analyses of the complexes were also carried out. The compounds are diamagnetic with square-planar coordinatination around the palladium(II) ions. Other physico-chemical properties of the both complexes are compatible with their structures.     

Sulfobridged Polynuclear Complexes of Platinum(II) and Palladium(II)

When the platinum(II) and palladium(II) salts interact with ligands such as cystamine-(mercamine) HSCH₂CH₂NH₂ and 2-mercaptoethanol HSCH₂CH₂OH under certain conditions, polynuclear complexes of the compositions are obtained: [Pt₆(SCH₂CH₂NH₂)₈]Cl₄. 5H₂O and [Pd₆(SCH₂CH₂OH)₈]Cl₄. In a comparative study of the IR and X-ray spectra of synthesized complexes and ligands, as well as the results of X-ray diffraction studies, it was established that sulfur atoms of 2-mercaptoethanol occupy a bridge position with a mixed coordination of ligands in the palladium complex. In the platinum(II) complex bidentate coordination of ligands is realized through sulfur and nitrogen atoms.     

Kinetics and Mechanism of Reactions Occurring in Electrodeposition of Silver from Thiosulfate Solutions

The kinetics and mechanism of processes occurring in reduction of silver thiosulfate complexes on stationary and rotating disc electrodes and on fluidized glass-bead electrode were studied voltammetrically.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 1, 2005, pp. 86–89.Original Russian Text Copyright © 2005 by Shvab, Gur’yanova, Omel’chuk.     

Quantum-Chemical Calculations of Palladium(II) Complexes and Clusters

The structural parameters of stable palladium(II) compounds, namely, [Pd(-OAc)₂]₃, Pd(OAc)₂ · 2NHEt₂, [Pd(OAc)(-OAc)(CH₃)₂SO]₂, [Pd(-OAc)(-SEt)]₄, and [Pd(-SEt)₂]₆, were determined by relativistic and nonrelativistic calculations using the density functional method with account taken of all electrons or with the use of pseudopotentials. The gradient functional (PBE) and local density functional (LSDA) ensure good agreement between the calculated structural parameters of the Pd(II) complexes and clusters under study and data of X-ray diffraction analysis.     

Kinetics of Sn(II) Contact Reduction in Alkaline Solutions with Compact and Dispersed Aluminum

The kinetics of contact reduction of tin on aluminum from alkaline stannite solutions was studied by atomic absorption analysis, iodometry, gravimetry, X-ray phase analysis, and method of polarization diagrams.     

Influence of the Degree of Chitosan Sulfoethylation on the Sorption of Palladium(II) Chloride Complexes from Multicomponent Solutions

The influence exerted by the degree of substitution of sulfoethylated chitosan cross-linked with glutaraldehyde on the sorption of Pd(II) chloride complexes from multicomponent solutions containing Pt(IV), Cu(II), Ni(II), Co(II), Cd(II), and Zn(II) was studied. The sorption of transition metal ions under the conditions of the experiment at pH 0.5–5.0 is virtually fully suppressed. The strongest interfering effect on the Pd(II) sorption is exerted by Pt(IV). Calculation of the selectivity coefficients K_Pd/Pt shows that the selectivity of the Pd(II) sorption relative to Pt(IV) increases with an increase in the degree of substitution of chitosan from 0.3 to 0.5. Integral kinetic curves of the Pd(II) sorption were obtained, and the dependences were subjected to mathematical processing using the models of diffusion and chemical kinetics. The equilibrium in the palladium(II) chloride solution–sorbent system is attained within 40 min. Pd and Pt are quantitatively desorbed from the sorbent surface under dynamic conditions with 3.5 M HCl solution.     

Oscillopolarography of Palladium(II)–Tropeolin 0 Complexes

The electrochemical behavior of palladium(II) complexes of Tropeolin 0 (Tr0) was studied by linear-potential-sweep voltammetry in acetate–ammonia buffer solutions. The optimum conditions for determining palladium(II) with Tr0 were found. The composition of the complex was found to be Pd : Tr0 = 1 : 2. A procedure was proposed for determining palladium(II) with a detection limit of 2.54 × 10^–7M. The procedure was used for determining palladium(II) in capacitors.     

Interaction of Palladium(II) Acido Complexes with DNA

Interaction of K₂[PdCl₄] (I) and (C₅H₁₂NO)₂[PdCl₄] (II) with DNA in vitro is studied. No fragmentation of DNA occurs under the action of II. The interstrand cross-links are formed due to the formation of complexes with purine and pyrimidine bases; no interaction with DNA phosphates is observed. The cation does not play an essential role in the formation of cross-links.     

Thermal Behaviour and Decomposition Kinetics for Two Palladium(II) Complexes with 1-aminopyrene and its Derivative

The thermal decomposition studies for two palladium(II) complexes Pd(apyr)₂Cl₂ and Pd(pmpa)Cl₂ (apyr=1–aminopyrene and pmpa=N–(2–pyridylmethylene)–1–pyrenylamine) were carried out in pure nitrogen using TG-DTG techniques. The non-isothermal kinetic parameters for the two complexes were evaluated employing the method suggested by Málek, esták, Koga et al. Based on the above results, thermal behaviour of the complexes were carefully discussed, which showed that not only the parameters value, but also the decomposition pattern and mechanism for complex 1 are different from complex 2.This revised version was published online in November 2005 with corrections to the Cover Date.     

Chemistry of N,N-Dimethylaminoalkylchalcogenolate Complexes of Palladium(II) and Platinum(II)

Abstract

Four different series of N,N-dimethylaminoalkylchalcogenolates, viz. Me₂NCH₂ CH₂E^?, Me₂NCH(Me)CH₂E^?, Me₂NCH₂CH(Me)E^?, and Me₂NCH₂CH₂CH₂E^? (E = S, Se, Te), (referred as E^∩N) have been synthesized and characterized. Their reactions with palladium(II) and platinum(II) precursors have been explored. Complexes of the general formula, [MCl(E^∩N)]_n, [MCl(E^∩N)₂]_n, [MCl(E^∩N)(PR₃)], [M₂Cl₂(μ-E^∩N)₂(PR₃)₂], [M₂(μ-E^∩N)₂(P^∩P)₂]²⁺, etc. have been isolated. All the complexes have been characterized by elemental analysis, IR, NMR (¹H, ¹³C, ³¹P, ⁷⁷Se, ¹²⁵Te, ¹⁹⁵Pt), UV-vis, and FAB mass spectral data. A weak absorption in the electronic spectra of [MCl(E^∩N)(PR₃)] has been attributed to metal mediated ligand-to-ligand charge transfer and showed pronounced chalcogen dependence being red shifted on moving from S → Se → Te. Structures of several complexes have been established by X-ray diffraction analyses. Thermal behavior of some of these complexes has been investigated by TGA.     

Carbonyl Complexes of Platinum (II) and Palladium(II) with Heterocyclic Cyclometalating Ligands

Russian Journal of General Chemistry -     

Kinetics and Mechanism of the Reaction of Chloroplatinum(II) Complexes with Alkyl Radicals

The reaction between certain platinum(II) complexes and alky radicals produces an unstable organoplatinum(III) intermediate, {Pt^III -R}. The kinetics of this step were evaluated by laser flash photolysis with ABTS² (2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) ion) and TMPD (tetramethylphenylenediamine) as kinetic probes. The rate constants for PtCl₄^2? are: k_Pt/10⁸ L mol^?1 s^?1 = 5.2, 2.8 and 0.27 for CH_3, C₂H₅, and CH₂Cl in aqueous solution at pH 1. Those with cis-Pt(NH₃)₂Cl₂ are somewhat smaller, and those for Pt(NH₃)₄²⁺ too small to measure will) this technique. The product analysis indicates that the decomposition of organoplatinum takes place by hydrolysis and (for R = C₂H₅ only) by β-elimination, The kinetic isotope effect on die β-elimination of DCH₂CH₂PtC₄,^2? is k_H/k_D = 1.2. The β-elimination step produces a Pt^III-hydride that releases hydrogen gas and forms {Pt_III-OH}. The short-lived Pt(III) intermediate may disproportionate or oxidize the Co^II complex that is produced in the radical-generating step.     

Kinetics and Mechanism of the Demetallation of Macrocyclic Nickel(II) Complexes by Cyanide

The kinetics and the mechanism of the cyanide‐induced demetallation of a series of Ni²⁺ complexes with macrocyclic ligands of different ring size (12‐ to 14‐membered; see 1 – 4 ) and steric constraints was studied. Although the rates differ by almost five orders of magnitude when compared to each other under fixed experimental conditions (pH 10.5, [CN^?]=10^?2 M ), all reactions proceed through the relatively rapid formation of cyano adducts [Ni(CN)_nL] (n=1, 2), which then react with additional CN^? or HCN to give the final products. Of paramount importance for the reaction rate is the geometry and configuration of the cyano adducts [Ni(CN)_nL] (n=1,2). cis‐Dicyano derivatives with a folded macrocycle react faster than trans‐compounds. In the case of (1,4,8,11‐tetraazacyclotetradecane)nickel(2+) ([Ni ( 4 )]²⁺), which gives a trans‐ dicyano adduct, the base‐catalyzed N‐inversion necessary to obtain the cis‐dicyano derivative becomes rate determining at high CN^? concentrations.