Preparation and electrochemical properties of palladium(0) complexes coordinated by quinones and 1,5-cyclooctadiene

The complexes Pd(quinone)(COD) (COD = 1,5-cyclooctadiene) are prepared by a ligand substitution reaction of Pd₂(DBA)₃ (DBA = dibenzylideneacetone) in the presence of both quinone and COD. Palladium(0) complexes coordinated by quinones only are formed in the reaction in the absence of COD. The cyclic voltammetric behavior of Pd(quinone)(COD) has been studied. The reduction potentials for quinones shifted toward negative values on coordination to palladium(0). The oxidation potentials for the central palladium(0) in Pd(quinone)(COD) depend on the electron-withdrawing ability of the free quinones, and are in the following series: quinone = p-benzoquinone < 5,8-dihydro-1,4-naphthoquinone ～ 1,4-naphthoquinone < duroquinone. The shift of oxidation potentials for Pd(quinone)(COD) on changing the quinones as ligands is in contrast to that of Pd(quinone)(triphenylphosphine)₂.     

Dichloro-bis(pentafluorophenyl)(chelate) complexes of palladium(IV)

Four organometallic palladium(IV) complexes: Cl₂(C₆F₅)₂Pd(LL) (LL being a bidentate nitrogen-donor ligand) have been prepared by the oxidative addition of chlorine to the corresponding bis(pentafluorophenyl)palladium(II) complexes, (C₆F₅)₂Pd(LL). Some of their properties are described.     

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.     

Formation of palladium phosphides in the reaction of bis(dibenzylideneacetone)palladium(0) with white phosphorus

The reaction of bis(dibenzylideneacetone)palladium(0) with white phosphorus was studied using the methods of NMR, UV spectroscopy, and X-ray powder diffraction. The products of the reaction are shown to be palladium phosphides, their composition depending on the ratio of the reagents. The mechanism of the formation of the palladium-enriched phosphides is suggested, which includes the formation of palladium diphosphide PdP₂ that subsequently reacts with the excess of bis(dibenzylideneacetone)palladium(0) leading to palladium phosphides Pd₅P₂, Pd₃P_0.8, Pd_4.8P, and free dibenzylideneacetone.     

Metal π-allyl chemistry III. The preparation of π-allylpalladium complexes from palladium(II) salts

A number of routes for the preparation of π-allylpalladium complexes from palladium(II) salts were investigated with a view to obtaining a quantitative yield. Quantitative yields were obtained rapidly when a stream of ethylene was passed through an aqueous solution of Na₂PdCl₄ and the allylic chloride, and more slowly on vigorously shaking an aqueous solution of Na₂PdCl₄ with a 3-fold excess of allyl chloride.Spectroscopic evidence is presented to confirm that the first stage of the reaction of allylic compounds with palladium(II) salts involves the formation of an olefinic complex. It is found that such palladium(II)olefin complexes of CH₂CHCH₂X are very much less susceptible to nucleophilic attack when X = Cl than when X = C₅H₁₁, OH or OAc, which are all attacked rapidly by nucleophilic solvents, such as methanol, with deposition of palladium metal.     

Thermal properties of mercury(II) and palladium(II) purine and pyrimidine complexes

Six solid Pd(II) and Hg(II) complexes of some purines and pyrimidines have been prepared and characterized by elemental analyses, IR, UV–Vis spectra, magnetic measurements, and thermal analyses. The data suggest tetrahedral and square planar geometries for mercury and palladium complexes, respectively. The thermal behavior of the complexes has been studied applying TG, DTA, and DSC techniques, and the thermodynamic parameters and mechanisms of the decompositions were evaluated. The ?S* values of the decomposition steps of the metal complexes indicated that the activated fragments have more ordered structure than the undecomposed complexes, and/or the decomposition reactions are slow. The thermal processes proceeded in complicated mechanisms where the bond between the central metal ion and the ligands dissociates after losing small molecules such as H₂O, HCl or C=O. The palladium adenine complex is ended with the metal as a final product. However, the thermal reactions of the other five palladium and mercury pyrimidines complexes are ended with metal bonded to O, N, or S of the pyrimidine ring.     

Acyl-platinum(II) and -palladium(II) complexes derived from 2-hydroxybenzaldehyde derivatives. X-ray structure of [Pt(OC6H4CO) (P(p-CH3C6H4)3)2]

Platinum(II) and palladium(II) complexes containing chelating acyl ligands have been synthesized from salicylaldehyde, 2-hydroxynaphthaldehyde and 2-hydroxy-3-methoxybenzaldehyde. The platinum(II) complexes [Pt(acyl)L₂], acyl  OC₆H₄CO, OC₁₀H₆CO, O(m-CH₃OC₆H₃CO), L  tertiary phosphine, 1/2 diphenylphosphinoethane, can be isolated with both monodentate and chelating diphosphines, whereas for palladium only the compounds with chelating phosphines are readily obtainable. The reactions of [Pt(OC₆H₄CO)L₂] with HCl afford trans-[PtCl(OHC₆H₄CO)L₂], L  monodentate tertiary phosphine and cis-[PtCl(OHC₆H₄CO)L₂], L2  1,2-bis-diphenylphosphinoethane, in which the metal—carbon bond remains intact. The structure of [Pt(OC₆H₄CO)-(P(p-CH₃C₆H₄)₃)₂] has been determined by X-ray diffraction methods and found to have the expected square planar structure. Some relevant bond lengths and angles are: PtP; 2.271(4) and 2.348(5) Å; PtC; 1.96(2) Å and PtO; 2.07(1) Å; PPtP  101°, CPtO  82°.     

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.     

Synthesis,structures, electrochemistry and catalytic activities of copper(II) and palladium(II) complexes with asymmetric tetraazacycloannulenes

Copper(II) and palladium(II) complexes with 15-membered asymmetric 5,9-dihydro-2,4,10,12-tetramethyl-1,5,9,13-monobenzotetraazacyclo[15]tetradecine have been synthesized and characterized. The electrochemical behaviors of the complexes showed a reduction and two one-electron irreversible oxidation waves in given potential ranges due to the metal ion and macrocycle ring, respectively. The electrocatalytic reduction of dioxygen on glassy carbon electrodes electropolymerized by such 15-membered and 14-membered tetraazaannulene complexes occurred at 160–280 mV (versus SCE), less negative than on the bared one at pH 7.0. The catalytic activities of the copper(II) complexes in the oxidation of p-Xstyrene (X = OCH₃, CH₃, H, F, Cl) were higher than those of the palladium(II) ones. The structures of the 15-membered copper(II) and palladium(II) complexes were determined using the X-ray diffraction method.     

Anti-Markovnikov hydroaminations of styrene catalyzed by palladium(II) N-heterocyclic carbene complexes under conventional and microwave heating

Six palladium(II) complexes with benzimidazole-based N-heterocyclic carbene ligands were synthesized by transmetallation reactions between silver(I) N-heterocyclic carbene complexes and PdCl₂(PhCN)₂. The complexes were characterized by physicochemical and spectroscopic methods. The palladium complexes were tested as catalysts for intermolecular hydroamination reactions of styrene with various anilines in ionic liquids under both conventional and microwave heating. All of these complexes proved to be catalytically active in these reactions. The anti-Markovnikov addition products were selectively obtained by using 1 mol% of the palladium complex.     

Organic azo complexes of molybdenum and their reactions with electrophiles

Organic azo(1) and N,N-disubstituted hydrazido-N'(2) complexes of molybdenum have been prepared by the reactions of certain molybdenum-oxo complexes with hydrazines.     

Synthesis of silver(I) and palladium(II) <Emphasis Type="Italic">N</Emphasis>-heterocyclic carbene complexes and their use as catalysts for the direct C5 arylation of heteroaromatic compounds

Silver(I) N-heterocyclic carbene complexes were synthesized in good yields by the reactions of 1,3-dialkylperhydrobenzimidazolium salts with silver(I) oxide in dichloromethane. The silver complexes were used as carbene-transfer agents to synthesize palladium(II) N-heterocyclic carbene complexes. All of the complexes were characterized by physicochemical and spectroscopic methods. The new palladium complexes were tested as catalysts in the direct C5 arylation of 2-n-butylfuran, 2-n-butylthiophene and 2-n-propylthiazole with aryl bromides at 130 °C in N,N-dimethylacetamide. The arylation reactions proceeded selectively at the C5 position of the heteroaromatic compounds, and the corresponding coupling products were obtained in moderate to good yields by using 0.5 mol% of the palladium complex.     

Fluorooxoperoxo complexes of vanadium(V)

Substances crystallizing under various conditions from the MVO₃(MF, HF)H₂O₂H₂O (M = NH₄, K) systems have been characterized by elemental analysis, infrared and Raman spectra and X-ray powder patterns. Besides the known M₂[VO(O₂)₂F] complexes, complexes of two new types have been obtained: M₃[HV₂O₂(O₂)₃F₄·2H₂O and (NH₄)₃[V₂O₂(O₂)₄F]·nH₂O (n≈2). Vibrational spectra of new complexes are consistent with the presence of dimeric anions containing V(μ₂O₂)V and VFV bridges, respectively.     

Studies on novel unsymmetrical azomethines—III : Copper(II) complexes of unsymmetrical tetradentate azomethines

Copper(II) complexes of unsymmetrical bifunctional tetradentate azomethines having the general formulae, (OC₁₀H₆CH:NXN:C(R)C₆H₄O)Cu, (OC₁₀H₆CH:NXN:C(CH₃)CHC(CH₃)OCu, (OC₆H₄CH:NXN:C(CH₃)C₆H₄O)Cu, (OC₆H₄C(R);NXN:C(CH₃)CHC(CH₃)O)Cu (where R = H or CH₃, X = (CH₂)₃, (CH₂)₄, (CH₂)₆ or -oC₆H₄) have been synthesized by the reactions of preformed mixed imine complexes of the type, CuLL′ (where L and L′ are two different imines such as 2-hydroxy-1-naphthaldimine, salicylaldimine, o-hydroxyacetophenonimine or acetylacetonimine) with diamines such as 1,3-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane or o-phenylenediamine. These complexes have been characterized by elemental analyses, TLC, conductance, magnetic measurements, IR and electronic spectra.     

Intramolecular metallation of o-carboranylphosphine-palladium(II) and -platinum(II) complexes

Preparation of trans-[P^cb₂MCl₂]-type complexes (P^cb= o-HCB₁₀H₁₀CCH₂PPh₂ M = Pd, Pt), which readily undergo intramolecular metallation through the BH bonds of the carborane cage to form exocyclic compounds involving a $\text{PCCBM}$ bond system, is described. Both monomeric compounds, trans-[MCl(B-P)P^cb], and bridged complexes, such as [Pd₂Cl₂(BP)₂], are formed, where (BP) is intramolecular-metallated carborane phosphine. The bridging bond is readily cleaved under the action of various ligands (pyridine, PEt₃, etc.) to form monomeric compounds.     

The reaction of bis(phenyldimethylphosphine)bis(diphenylsilyl)platinum(II) with acetylenes

The synthesis and the reactions of cationic complexes of rhodium(I) and iridium(I) of the type [M(NN′)(COD)]⁺ and [M(NN′)(CO)₂]⁺ (NN′  Schiff bases of pyridine-2-aldehyde; COD  cis,cis-1,5-cyclooctadiene) are reported.     

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.     

The reactions of alkyltrimethylphosphinenickel complexes with isocyanides and alkynes

t-Butylisocyanide reacts with NiRCl(PMe₃)₂ (R  CH₃, Ia; R  CH₂SiMe₃, Ib) to give, successively, the products of mono- and di-insertion into the nickelcarbon bonds; with more than two equivalents of isocyanide, trimethylphosphine ligands are displaced. In contrast to related palladium reactions, cyclohexyl isocyanide gives mono-insertion products only, while benzyl isocyanide is polymerised. The reactions of diphenylacetylene with Ia and Ib in methanol give (Z) vinylnickel complexes, trans-Ni{C(Ph)C(Ph)R}Cl(PMe₃)₂, while from reaction in diethyl ether a precursor complex [NiMeCl(PMe₃)₂ · (PhCCPh)_0.5] can be isolated. On heating the (Z)-vinyl complexes come into thermodynamic equilibrium with their (E)-isomers. The vinyl complexes are stereochemically rigid and resistant to further insertion.     

Cationic organocarbonyl palladium(II) complexes

The carbonylation under normal pressure, at 0°C, of organometallic perchlorato palladium(II) complexes in solution leads to the displacement of the perchlorato group and the formation of a series of cationic organocarbonyl palladium(II) compounds of the general formula [CO(C₆F₅)PdL₂]ClO₄, where L₂ are either two tertiary phosphine groups or a nitrogen chelate, such as 2,2′-bipyridine, 1,10-phenanthroline or N,N,N′,N′-tetramethylethylenediamine.     

Palladium assisted organic reactions: VI. A new method for the preparation of cyclopalladated benzalimines

A new, improved method is described for the preparation of cyclopalladated benzalimines; it consists of reacting the ortho-bromobenzalimine with bis(dibenzylideneacetone) palladium(0). A number of substituted o-bromobenzalimines has been studied; the bridged bromide dimers and the corresponding bromo (N-substituted benzalimine-6,C,N)triphenylphosphinepalladium(II) complexes have been fully characterised and ¹H and ¹³C NMR spectral data recorded. In the cases of the N-phenylbenzalimines studied, bis(triphenylphosphine) complexes were also isolated and characterised.