Electrochemical properties of palladium(0) complexes coordinated by quinone derivatives

The polagrophic and cyclic voltammetric behavior of quinone derivatives (Q) and their palladium(0) complexes, (Q)₁ or ²Pd(PPh₃)₂, has been studied. All free quinone derivatives except 5,8,9,10-tetrahydro-1,4-naphthoquinone (THNQ) showed two reversible waves, and all palladium(0) complexes showed irreversible waves. The reduction half-wave potentials for free quinone derivatives lie in the following order:7,7,8,8-tetracyanoquinodimethane (TCNQ) ? p-benzoquinone (BQ) ? 5,8-dihydro-1,4-naphthoquinone (DHNQ) ? 1,4-naphthoquinone (NQ) ? THNQ. The reduction potentials for quinone derivatives shifted toward the negative or coordination to palladium(0). The extents of the shifts depended on the electron-withdrawing ability of the free quinone derivatives. On the other hand, the oxidation potentials for the central palladium(0) in their complexes showed more positive values in comparison with the potential for Pd(PPh₃)₄. However, the oxidation potentials were almost constant for all complexes of the quinone derivatives. On the basis of these facts, the phenomena of charge transfer in the complexes are discussed.     

A new type of palladium(0) complex having both electron-withdrawing and -donating sites in a ligand: 5,8-dihydro- and 5,8,9,10-tetrahydro-1,4-naphthoquinone complexes

A new type of palladium(0) complex, (5,8-dihydro-1,4-naphthoquinone)Pd(PPh₃)₂ and (5,8,9,10-tetrahydro-1,4-naphthoquinone)Pd(PPh₃)₂, having both olefin and quinone or dihydro-quinone sites in a ligand molecule was prepared. IR and ¹H NMR spectroscopic studies of these complexes suggested that it is the quinone or dihydro-quinone CC bond which is complexed to Pd. Ligand exchange reactions showed that the stability order of the olefinic quinone complexes was as follows: (1,4-naphthoquinone)Pd(PPh₃)₂ > (5,8-dihydro-1,4-naphthoquinone) Pd(PPh₃)₂>(5,8,9,10-tetrahydro-1,4-naphthoquinone)Pd(PPh₃)₂.     

单核零价过渡金属配合物的研究——Ⅱ.含有π-键合醌及双齿氮配体的混配零价钯配合物的合成与表征

本工作合成了一系列十个新的零价钯混配配合物,并对这些配合物进行了表征.研究了配体的立体效应和电子效应的差别,讨论了配体间的相互作用.一.配合物的合成与组成据文献合成dba(PhCH=CHCOCH=CHPh)和Pd_2(dba)_3(CHCl_3).其余试剂及溶剂均为市售商品,用前经无水无氧处理.     

Preparation and spectroscopic and electrochemical properties of complexes of dibenzo-and dipyrido-substituted 1,4-diazines

The spectroscopic and electrochemical properties of palladium ethylenediamine complexes [Pd(N^N)En]Cl₂ with 1,4-diazine derivatives of o-phenanthroline [(N^N) = dipyrido[a,c]phenazine (dppz), dipyrido[f,h]quinoxaline (dpq)] were studied in comparison with those of the free diimine (N^N) ligands, dibenzo-substituted 1,4-diazines [dibenzo[f,h]quinoxaline (dbq), dibenzo[a,c]phenazine (dbpz)], and cyclometallated dichloride [Pd(C^N)(μ-Cl)]₂ and ethylenediamine [Pd(C^N)En]Cl complexes derived from dibenzo-substituted 1,4-diazines.     

单核零价过渡金属配合物的研究——Ⅱ.含有π-键合醌及双齿氮配体的混配零价钯配合物的合成与表征

本工作合成了一系列十个新的零价钯混配配合物,并对这些配合物进行了表征.研究了配体的立体效应和电子效应的差别,讨论了配体间的相互作用.     

Synthesis,characterization, and cytotoxicity of complexes of palladium(II) with 1,4-diaminobutane/1,3-diaminopropane and 4-toluenesulfonyl-L-amino acid dianion

Eight new palladium(II) complexes with 4-toluenesulfonyl-L-amino acid dianion and 1,4-dab/1,3-dap, [Pd(1,4-dab)(TsglyNO)]?·?H₂O (1), [Pd(1,4-dab)(TsvalNO)] (2), [Pd(1,4-dab)(TsleuNO)] (3), [Pd(1,4-dab)(TsileNO)] (4), [Pd(1,4-dab)(TsserNO)]?·?0.5H₂O (5), [Pd(1,4-dab)(TspheNO)]?·?0.5H₂O (6), [Pd(1,4-dab)(TsthrNO)]?·?H₂O (7), and [Pd(1,3-dap)(TsserNO)] (8), have been synthesized and characterized by elemental analysis, IR, UV, ¹H NMR, and mass spectrometry. Crystal structure of 8 has been determined by X-ray diffraction. The cytotoxicities were tested by MTT assay. The results indicate the complexes exert cytotoxic effects against HL-60 and Bel-7402. The structure–activity relationship suggests that both amino acids and N-containing ligands have important effects on cytotoxicity, but the IC₅₀ values do not show definite correlation with variation of these ligands.     

Neutral and cationic complexes with P-bonded 2-pyridylphosphines as N-donor ligands toward rhodium. Electrical charge vs steric hindrance on the conformational control

Bimetallic palladium(II)-rhodium(I) and gold(I)-rhodium(I) complexes of the type [(4,4'-Me2-bipy)(C6F5)Pd(mu-PPh(3-n)Pyn)Rh(diene)](BF4)2 and [(C6F5)Au(mu-PPh(3-n)Pyn)Rh(diene)](BF4) (n = 2, 3; Py = 2-pyridyl) have been synthesized. The P donor atom of the bridging ligands (mu-PPh(3-n)Pyn) is coordinated to the Pd or to the Au center. The resulting complexes react with [Rh(diolefin)(solv)2]+ (solv = acetone) in a way similar to pyrazolylborates, affording square-planar or pentacoordinated rhodium complexes with two or the three N-donor ends chelating the Rh atom. The metallacycles formed upon chelation can adopt one of two conformations in the square-planar Rh(I) complexes, either bringing the other metal close to the Rh center or bringing it to a remote position. The first conformation is preferred for the gold P-coordinated complexes and the second for the palladium complexes. The X-ray structures of [(4,4'-Me2-bipy)](C6F5)Pd(mu-PPhPy2)Rh(COD)](BF4)2 (COD = 1,5 cyclooctadiene) and [Au(C6F5)(mu-PPhPy2)Rh(TFB)](BF4) (TFB = 5,6,7,8-tetrafuoro-1,4-dihydro-1,4-etenonaphthalene) are reported.     

New biimidazole and bibenzimidazole derivatives: mono and binuclear palladium(II) or platinum(II) complexes and heterobinuclear palladium(II)-rhodium(I) or platinum(II)-rhodium(I) complexes

Novel neutral biimidazolate or bibenzimidazolate palladium(II) and platinum(II) complexes of the type M(NN)₂(dpe) [M = Pd, Pt; (NN)₂^2? = BiIm^2?, BiBzIm^2?. dpe = 1,2-bis(diphenylphosphino) ethane] have been obtained by reacting MCl₂(dpe) with TI₂(NN)₂. Complexes M(NN)₂(dpe) which are Lewis bases react with HClO₄ or [M(dpe)(Me₂CO)₂](ClO₄)₂ to yield, respectively, mononuclear cationic complexes of general formula [M{H₂(NN)₂](dpe) (M = Pd, Pt; H₂(NN)₂ = H₂BiIm, H₂BiBzIm) and homobinuclear palladium(II) or platinum(II) cationic complexes of the type [M₂{μ - (NN)₂}(dpe)₂](ClO₄)₂. Reactions of M(BiBzIm)(dpe) with [Rh(COD) (Me₂CO)_X](ClO₄) render similar heterobinuclear palladium(II)-rhodium(I) and platinum(II)-rhodium(I) cationic complexes, of general formula [(dpe)M(μ-BiBzIm)Rh(COD)](ClO₄) (M = Pd, Pt; COD = 1,5-cyclooctadiene). Di- and mono-carbonyl derivatives [(dpe)M(μ-BiBzIm)Rh(CO)L](ClO₄) (M = Pd, Pt; L = CO, PPh₃) have also been prepared. The structures of the resulting complexes have been elucidated by conductance studies and IR spectroscopy.     

Reduction of palladium(II) monoglycinate complexes at rotating disc palladium electrode in acid media

Reduction of palladium(II) glycinate complexes in strongly acid 0.5 M NaClO₄ solutions (pH 0.6 and 1.0) with variable palladium(II) complex and free glycine concentration was studied by the taking of cyclic voltammograms at palladium rotating disc electrode. It is shown that it was a chelate monoglycinate palladium(II) complex that was present in all studied solutions and underwent the reduction. The diffusion coefficient of the chelate monoglycinate palladium(II) complex D = (6.5 ± 0.5) × 10⁻⁶ cm²/s was determined from the limiting diffusion current of the complex reduction. The monoglycinate palladium(II) complex reduction occurred in the double-layer segment of the palladium charging curve; it was not complicated by hydrogen adsorption at electrodes. The palladium(II) complex reduction half-wave potential was determined (E _1/2 = ∼0.300 to 0.330 V (SCE)). It is shown that the decreasing of the number of ligands coordinated by palladium via nitrogen atom facilitates the complex reduction process. In particular, the reduction potentials of palladium(II) complexes with different ligand number at palladium electrode shifted markedly toward negative potentials in the series: Pdgly⁺ < Pd(gly)2 < Pd(gly)₄²⁻.     

The Mechanism and Kinetic Models of the Catalytic Oxidation of Ethylene by <Emphasis Type="Italic">p</Emphasis>-Benzoquinone in Aqueous–Acetonitrile Solutions of Pd(II) Cationic Complexes

A kinetic study of ethylene oxidation to acetaldehyde by p-benzoquinone in the Pd(OAc)₂–HClO₄?LiClO₄–CH₃CN–H₂O system has been carried out under conditions when palladium(II) cationic complexes exist at a molar fraction of water of 0.67 and 30°С. For a reaction that mostly lead to the formation ofPd(CH₃CN)(H₂O) ₃ ²⁺ two-route mechanism and a kinetic model have been proposed that describe adequately the experimental dependence of the reaction initial rate on the concentration of p-benzoquinone, HClO₄, and palladium. The model takes into account previous findings on the H₂O/D₂O and C₂H₄/C₂D₄ kinetic isotope effects and the important role of Pd(0) quinone complexes.     

Palladium- and Ruthenium-Catalyzed Intramolecular Carbene CAr−H Functionalization of γ-Amino-α-diazoesters for the Synthesis of Tetrahydroquinolines

A synthetic method to prepare tetrahydroquinoline-4-carboxylic acid esters has been developed through the transition-metal-catalyzed intramolecular aromatic C−H functionalization of α-diazoesters. Both [{Pd(IMes)(NQ)}₂] (IMes=1,3-dimesitylimidazol-2-ylidene, NQ=1,4-naphthoquinone) and the first-generation Grubbs catalyst proved effective for this purpose. The ruthenium catalyst was found to be the most versatile, although in a few cases the palladium complex afforded better yields or selectivities. According to DFT calculations, Pd⁰- and Ru^II-catalyzed sp²-C_Ar−H functionalization proceeds through different reaction mechanisms. Thus, the Pd⁰-catalyzed reaction involves a Pd-mediated 1,6-H migration from the sp²-C_Ar−H bond to the carbene carbon atom, followed by a reductive elimination process. In contrast, electrophilic addition of the ruthenacarbene intermediate to the aromatic ring and subsequent 1,2-proton migration are operative in the Grubbs catalyst promoted reaction.     

Aminodefluorination of 2-X-pentafluoro-1,4-naphthoquinones (X = NHBu, NEt2, and OMe)

Aminodefluorination of 2-n-butylamino- and 2-diethylaminopentafluoro-1,4-naphthoquinone by alkylamines HNR¹R² (NR¹R² = NHEt, NHⁿBu and NEt₂) occurs at the 6- or 8-position and further, accordingly, at the 8- or at one of the 5- and 6-sites. The isomer ratio changes significantly in favor of a β-replacement product with solvent variation in the sequence: toluene < 1,4-dioxane < DMSO. n-Butylaminodefluorination of 2-methoxypentafluoro-1,4-naphthoquinone gives mixtures of fluorine substitution products both on the benzene and quinone rings.     

Mixed ligand complexes with 2-piperidine-carboxylic acid as primary ligand and ethylene diamine, 2,2′-bipyridyl, 1,10-phenanthroline and 2(2′-pyridyl)quinoxaline as secondary ligands: preparation,characterization and biological activity

Synthesis procedures are described for the new stable mixed ligand complexes, [Pd(Hpa)(pa)]Cl, [Pd(pa)(H₂O)₂]Cl, [Pd(pa)(en)]Cl, [Pd(pa)(bpy)]Cl, [Pd(pa)(phen)Cl], [Pd(pa)(pyq)Cl], cis-[MoO₂(pa)₂], [Ag(pa)(bpy)], [Ag(pa)(pyq)], trans-[UO₂(pa)(pyq)](BPh₄) and [ReO(PPh₃)(pa)₂]Cl (Hpa = 2-piperidine-carboxylic acid, en = ethylene diamine, bpy = 2,2′-bipyridyl, phen = 1,10-phenanthroline, pyq = 2(2′-pyridyl)quinoxaline). Their elemental analyses, conductance, thermal measurements, Raman, IR, electronic, ¹H-n.m.r. and mass spectra have been measured and discussed. 2-Piperidine-carboxylic acid and its palladium complexes have been tested as growth inhibitors against Ehrlich ascites tumour cells (EAC) in Swiss albino mice.     

Thermal stability of Pd(1,4-bis(2-hydroxyethyl)piperazine)Cl2 and its role in the catalysis of base hydrolysis of α-amino acid esters

Pd(BHEP)Cl₂ was synthesized and characterized (BHEP = 1,4-bis(2-hydroxyethyl)piperazine). The complex decomposes in two steps, leaving a residue of palladium metal. Amino acid ester (L) reacts with [Pd(BHEP)(H₂O)₂]²⁺ (BHEP = 1,4-bis(2-hydroxyethyl)piperazine), giving mixed-ligand complexes, [Pd(BHEP)L]²⁺. The kinetics of hydrolysis of [Pd(BHEP)L]²⁺ have been studied by pH-stat technique, and rate constants were obtained. Rate acceleration observed for glycine methyl ester is high. The effect with methionine methyl ester is much less marked, as the mixed-ligand complexes with these ligands do not involve alkoxycarbonyl donors. Possible mechanisms for these reactions are considered.     

Photoreactions of p-quinones with dimethyl sulfide and dimethyl sulfoxide in aqueous acetonitrile. goerner@mpi-muelheim.mpg.de

The effects of dimethyl sulfide (DMS) and dimethyl sulfoxide (DMSO) on the photoreactions of 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), 9,10-anthraquinone (AQ) and several derivatives in acetonitrile/water were studied. The observed triplet state of the quinones is quenched and the rate constant is close to the diffusion-controlled limit for reactions of most quinones with DMS and lower with DMSO. Semiquinone radical anions (Q*-) produced by electron transfer from sulfur to the triplet quinone were detected. For both DMS and DMSO the yield of Q*- is similar, being generally low for BQ and NQ, substantial for AQ and largest for chloranil. The specific quencher concentrations and the effects of quinone structure and redox potentials on the time-resolved photochemical properties are discussed.     

Kinetics of cyclohexene oxidation by <Emphasis Type="Italic">p</Emphasis>-quinones in aqueous-organic solutions of cationic palladium(II) complexes

A kinetic study of cyclohexene oxidation by p-quinones in water-acetonitrile solutions of cationic Pd(II) complexes has been carried out for the first time. The observed kinetic regularities (dependence of the initial rate on the HClO₄ and p-benzoquinone concentrations) and the shape of the kinetic curves differ radically from those for the chloride systems. The unsteady-state process can be described only under the assumption that complexes of reduced palladium species with quinones are catalytically active forms. The role of solvated palladiumcarbenium ions in particular steps of the mechanism is discussed.     

Reactions of cyclopalladated azobenzenes with xanthates and dithiocarbamates. Spectral characterisation and electrochemical studies of the products

Binuclear chloro-bridged cyclopalladated azobenzenes [Pd(A)Cl]₂ (A = ortho-metallated azobenzene or its derivatives) have been reacted with aqueous AgNO₃ to yield aquo-derivatives followed by the addition of xanthates, or dithiocarbamates (RCS₂ ^–) to synthesise ternary complexes, [Pd(A)(RCS₂)]. These complexes occur as configurational isomers and their compositions have been established by ¹H-n.m.r. spectroscopy. Cyclic voltammetric studies show azo reduction at negative and thiol oxidation at positive potentials relative to s.c.e., respectively. Dissociation of RCS₂ ^– under the electrode field is chemically supported by using a sulfide extractor, HgCl₂, Hg(OAc)₂, or AgOAc, to precipitate out the binuclear [Pd(A)Cl]₂/[Pd(A)(OAc)]₂ complexes.     

Palladium(0) complexes coordinated with substituted olefins and tertiary phosphine ligands

New palladium(0) complexes with a variety of coordinated olefins [Pd(olefin)(PMePh₂)₂] (II) (olefin = styrene, ethyl methacrylate, methyl methacrylate, methyl acrylate, methacrylonitrile, and dimethyl maleate), were prepared by the reactions of [PdEt₂(PMePh₂)₂] (I) with corresponding olefins in toluene. These complexes were characterized by means of elemental analysis, IR and ¹H NMR spectroscopy and the chemical reactions. The dissociation of the coordinated olefin from complex II in solution was confirmed by spectroscopic studies of [Pd(mma)(PMePh₂)₂] (mma = methyl methacrylate). From the variable temperature NMR study, kinetic parameters for the dissociation process were determined as E_a = 7 kcal/mol, and ΔS³ (293 K) = -30 cal/deg · mol. Some new hydrido complexes, [Pd(H)ClL₂] (IV) (L = PMePh₂, PEtPh₂ and PEt₂Ph), were prepared by the reactions of [Pd(olefin)L₂] with dry HCl.     

Hydrogen‐transfer reduction of α,β‐unsaturated carbonyl compounds catalyzed by naphthyridine‐functionalized N‐heterocyclic carbene complexes

Substitution of silver complex of 2‐chloro‐7‐(mesitylimidazolylidenylmethyl)naphthyridine (NpNHC) with palladium(II), rhodium(I) and iridium(I) metal precursors provided [Pd(C ,N ‐NpNHC)(η³‐allyl)](BF₄) ( 5 ), RhCl(COD)(C ‐NpNHC) ( 6a ) and IrCl(COD)(C ‐NpNHC) ( 6b ), respectively. Abstraction of chloride from 6a and 6b with AgBF₄ provided the chelation complexes [Rh(COD)(C ,N ‐NpNHC)](BF₄) ( 7a ) and Ir(COD)(C ,N ‐NpNHC)(BF₄) ( 7b ), respectively. All complexes were characterized using NMR and elemental analyses and the structural details of 5 and 6a were further confirmed using X‐ray crystallography. In catalytic activity studies, complex 5 was found to be an effective catalyst in the hydrogen‐transfer reduction of α,β‐unsaturated carbonyl compounds into the corresponding saturated carbonyl compounds.     

Reactions of 1,4-diaza-3-methylbutadien-2-ylpalladium(II) derivatives with chloro-bridged rhodium(I) complexes

The reactions of the organometallic 1,4-diazabutadienes, RN=C(R′)C(Me)=NR″ [R = R″ = p-C₆H₄OMe, R′ = trans-PdCl(PPh₃)₂ (DAB); R = p-C₆H₄OMe, R″ = Me, R′ = trans-PdCl(PPh₃)₂ (DAB^I; R = R″ = p-C₆H₄OMe, R′ = Pd(dmtc)-(PPh₃), dmtc = dimethyldithiocarbamate (DAB^II); R = R″ = p-C₆H₄OMe, R′ = PdCl(diphos), diphos = 1,2-bis(diphenylphosphino)ethane (DAB^III)] with [RhCl(COD)]₂ (COD = 1,5-cyclooctadiene, Pd/Rh ratio = $\text{1}\text{2}$) depend on the nature of the ancillary ligands at the Pd atom in group R′. In the reactions with DAB and DAB^I transfer of one PPh₃ ligand from Pd to Rh occurs yielding [RhCl(COD)(PPh₃)] and the new binuclear complexes [Rh(COD) {RN=C(R?)-C(Me)=NR″}], in which the diazabutadiene moiety acts as a chelating bidentate ligand. Exchange of ligands between the two different metallic centers also occurs in the reaction with DAB^II. In this case, the migration of the bidentate dmtc anion yields [Rh(COD)Pdmtc] and [Rh(COD) {RN=C(R?)C(Me)=NR″}]. In contrast, the reaction with DAB^III leads to the ionic product [Rh(COD)- (DAB^III)][RhCl₂(COD)], with no transfer of ligands. The cationic complex [Rh(COD)(DAB^III)]⁺ can be isolated as the perchlorate salt from the same reaction (Pd/Rh ratio = 1/1) in the presence of an excess of NaClO₄. In all the binuclear complexes the coordinated 1,5-cyclooctadiene can be readily displaced by carbon monoxide to give the corresponding dicarbonyl derivatives. The reaction of [RhCl(CO)₂]₂ with DAB and/or DAB^I yields trinuclear complexes of the type [RhCl(CO)₂]₂(DAB), in which the diazabutadiene group acts as a bridging bidentate ligand. Some reactions of the organic diazabutadiene RN=C(Me)C(Me)=NR (R = p-C₆H₄OMe) are also reported for comparison.