Activation of molecular hydrogen by transition-metal complexes. 2. Formation of complexes,of palladium (O) and (+1) with a metal-metal bond during hydrogenolysis of [Ph3PPd(OAc)2]2

Conclusions The reaction of dipalladium -diacetatediacetatoditriphenylphosphine [Ph₃PPd(OAc)₂]₂ with hydrogen leads to formation of complexes of Pd(0), (Ph₃P)₂Pd₂, and of Pd(+l), (Ph₃PPd(OAc)₂, with a metal-metal bond.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1687–1690, August, 1979.     

Reaction of coordinated phosphines: VI. Divalent palladium promoted cleavage of carbon—phosphorus bonds in tertiary phosphines

The important role of divalent palladium in the cleavage of carbon—phosphorus bond of tertiary phosphines is revealed by the study of the phenylation in the Pd(OAc)₂Ph₃P-styrene system under various conditions; reaction atmosphere, ratio of Ph₃P/Pd(OAc)₂, and addition of ethanol or Cu^II(OAc)₂ · H₂O.     

Reaction of cationic palladium(II) and rhodium(I) complexes with the t-butylperoxy anion: Preparation of t-butylperoxo-palladium(II) and -rhodium(I) complexes

Treatment of the coordinatively unsaturated cationic complexes, [(η-C₃H₅)(Ph₃P)₂Pd^II]PF₆ and [(1,5-COD)₂Rh^I]BF₄, with potassium t-butylperoxide in dichloromethane gives the t-butylperoxometal complexes; (η-C₃H₅)(Ph₃P)(t-BuOO)Pd^II and [(1,5-COD)(t-BuOO)Rh^I](KBF₄), via nucleophilic attack by t-BuOO⁻ on the cationic metal center.     

Mechanism of the formation of palladium complexes serving as catalysts in hydrogenation reactions : II. Reactivity of palladium phosphine halides towards molecular hydrogen

[(PPh₃)₃(PPh₂)₂Pd₃Cl] Cl, benzene and aniline hydrochloride were isolated as products of the reactions of (PPh₃)₂PdCl₂]₂ or [(PPh₃)PdCl₂]₂ with H₂ in organic amines (Am). Similar products were obtained when (Ph₃P)₂Pd(Ph)Br was treated with H2₃ Both in amines and aromatic solvents. The reaction between H₂ and [(PBu₃)PdCl₂]₂ resulted in the formation of [(PBu₃(PBu_2)PdCl2 ·. 2 Am The kinetic data for H₂ absorption by solutions of palladium(II) complexes are consistent with the heterolytic mechanism of cleavage fo hte HH bond in the coordination sphere of palladium(II); the function of the H⁺ acceptor being performed by the bases (e.g. Am or Ph). The reaction between the palladium complexes and H₂ is autocatalytic. Reduction of the initial Pd^II complexes leads to lower oxidation state palladium complexes, which catalyse the reduction of Pd^II complexes. In the coordination sphere of the lower oxidation state palladium complexes, the oxidative addition of PR₃ to Pd takes place with formation of compounds containing a Pd-R bond. It is the reaction between these complexes and H₂ that yields palladium compounds with PR₂ ligands.     

Square planar complexes of nickel(II), palladium(II) and platinum(II) with 1-(2-hydroxyphenyl)-3,5-diphenylformazan

Summary A novel series of formazan complexes of general formula FoML [H₂Fo = 1-(2-hydroxyphenyl)-3,5-diphenylformazan; M = Ni^II, Pd^II or Pt^II; L = NH₃, py and Ph₃P] are described. The formazan nickel(II) system shows linkage isomerism; one isomer, A, contains an unusual five-membered formazan chelate ring, whereas the other, isomer B, has the usual six-membered ring.¹³C n.m.r., u.v. and i.r. spectra are presented and interpreted. From these the palladium and platinum complexes appear to contain the six-membered ring of the B type isomer.     

Formation of XPhos-Ligated Palladium(0) Complexes and Reactivity in Oxidative Additions

Understanding the nature of the intermediate species operating within a palladium catalytic cycle is crucial for developing efficient cross-coupling reactions. Even though the XPhos/Pd(OAc)₂ catalytic system has found numerous applications, the nature of the active catalytic species remains elusive. A Pd⁰ complex ligated to XPhos has been detected and characterized in situ for the first time using cyclic voltammetry and NMR techniques. In the presence of XPhos, Pd(OAc)₂ initially associates with the ligand to form a complex in solution, which has been characterized as Pd^II(OAc)₂(XPhos). This Pd^II center is then reduced to the Pd⁰(XPhos)₂ species by an intramolecular process. This study also sheds light on the formation of Pd^I–Pd^I dimers. Finally, a kinetic study probes a dissociative mechanism for the oxidative addition with aryl halides involving Pd⁰(XPhos) as the reactive species in equilibrium with the unreactive Pd⁰(XPhos)₂. Remarkably, the reportedly poorly reactive PhCl reacts at room temperature in the oxidative addition, which confirms the crucial role of the XPhos ligand in the activation of aryl chlorides.     

Catalytic and antibacterial properties of 3-dentate carboxamide Pd/Pt complexes obtained via a benign route

The complexes Pd^II(qcq)(OAc) and Pt^II(qcq)Cl have been synthesized using environmentally benign synthesized ligands and characterized by elemental analyses: Fourier transform infrared spectroscopy, UV–visible spectroscopy, ¹H NMR spectroscopy, and X-ray diffraction. The catalytic activity of the complex was assessed, in different media, for the Mizoroki–Heck coupling reaction for typical aryl halides and terminal olefins under aerobic conditions. Since the base and the solvent were found to influence the efficiency of the reaction, reaction conditions, temperature, time, and the amount of K₃PO₄ and a mixture of H₂O/PEG, were optimized. We found, for the Mizoroki–Heck reaction coupling less reactive aryl chloride derivatives with olefins, promising activity for palladium catalysts. The electrochemical behavior of Hqcq and the Pd(II) complex was investigated by cyclic voltammetry and irreversible Pd^II/I reductions were observed. Hqcq and the Pd(II) and Pt(II) complexes were also screened for their in vitro antibacterial activity. They showed promising antibacterial activity comparable to that of the antibiotic penicillin.     

Preparation of novel palladium(II) complexes with dithiocarbimates from sulfonamides

Potassium N-R-sulfonyldithiocarbimates, K₂(RSO₂N=CS₂) (R = Me, Ph, 2-MeC₆H₄), react with Pd(OAc)₂ to yield complex anions bis(N-R-sulfonyldithiocarbimato)palladate(II), [Pd(RSO₂N=CS₂)₂]^2–, which were isolated as their n-Bu₄N⁺ salts. When the reaction was performed in the presence of Ph₃P in a 2:1 ratio with respect to Pd(OAc)₂, the N-R-sulfonyldithiocarbimatobis(triphenylphosphine)palladium(II) complexes were obtained. Elemental analyses, i.r. spectra and electronic spectra data were consistent with the formation of palladium–sulfur diamagnetic square planar complexes in the first case and mixed square planar complexes of palladium with Ph₃P and dithiocarbimates in the second case. The ¹H-n.m.r., ¹³C-n.m.r. and ³¹P-n.m.r. spectra showed the expected signals for the Bu₄N⁺ cation, Ph₃P and the dithiocarbimate moieties.     

Synthesis and analytical characterization of novel pyridyl‐substituted 1,1′‐ethenedithiolato complexes

Some 1,1′‐ethenedithiolato complexes of nickel(II), palladium(II), and platinum(II) with different phosphine ligands, such as PPh₃, PEt₃, and dppe were prepared. Starting from 2‐, 3‐ as well as 4‐pyridyl methyl ketone, the complexes 1–15 were obtained in an one‐pot synthesis through reaction with carbon disulfide, using potassium‐tert‐butylate as a base. They were characterized by ¹H, ¹³C, and ³¹P NMR, mass spectra, infrared spectra, and UV–VIS spectra. The molecular structures of the (Ph₃P)₂Pd^II complex 9 containing the 3‐pyridyl‐ethenedithiolato ligand and of the (Et₃P)₂Pt^II complex 12 containing the 4‐pyridyl‐ethenedithiolato ligand were determined. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:369–378, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20103     

Studies of the oxidation of palladium complexes by the advanced oxidation process Pretreatment of model catalysts for precious metal analysis

The advanced oxidation process (AOP) for the pretreatment of model palladium catalysts has been studied. Most standard metal analysis techniques are for metal ions free of organic ligands. Spent palladium catalysts contain organic ligands that need to be removed prior to analysis. AOP uses a combination of hydrogen peroxide and UV light to generate radicals that decompose such ligands, freeing up metals for further analysis. Palladium acetate Pd(OAc)₂, palladium acetylacetonate Pd(acac)₂, and tris(dibenzylideneacetone)dipalladium (Pd₂(dba)₃) were chosen as model precious metal catalysts for investigation. AOP was found to decompose ligands in Pd(OAc)₂, Pd(acac)₂ and give accurate Pd(II) quantification, while ligand decomposition and oxidation of Pd(0) to Pd(II) were demonstrated in treatments involving Pd₂(dba)₃. The effects of solubility of the palladium complexes, continuous addition of H₂O₂ during AOP treatments, sample pH, concentration of H₂O₂, and length of UV irradiation are reported.     

Synthesis and characterization of silver(I) complexes with N‐thiophosphorylated thiobenzamide or thiourea and phosphines

A reaction of the potassium salts of RC(S)NHP(S)(OiPr)₂ (R = PhNH, HL ^I; Ph, HL ^II) with a mixture of AgNO₃ and Ph₂P(CH₂)_{1 − 3}PPh₂ or Ph₂P(C₅H₄FeC₅H₄)PPh₂ in aqueous EtOH/CH₂Cl₂ leads to [Ag₂(Ph₂PCH₂PPh₂)₂L^INO₃] ( 1 ), [Ag{Ph₂P (CH₂)₂PPh₂}L^I,II] ( 2, 6 ), [Ag{Ph₂P(CH₂)₃PPh₂}L^I,II] ( 3, 7 ), [Ag{Ph₂P(C₅H₄FeC₅H₄)PPh₂}L^I,II] ( 4, 8 ), and [Ag₂(Ph₂PCH₂PPh₂)L^II₂] ( 5 ) complexes. The structures of these compounds were investigated by ¹H and ³¹P{¹H} NMR spectroscopy and elemental analyses. It was established that the binuclear complexes 1 and 5 are luminescent in the solid state at ambient conditions. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:386–391, 2010; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20627     

Selective and efficient oxidation of ethylene to ethylene glycol acetates with H2O2 catalyzed by Pd(OAc)2-di(2-pyridyl)ketone-di(2-pyridyl)methanesulfonate system

Novel systems for palladium-catalyzed selective oxidation of ethylene to a mixture of ethylene glycol mono- and di-acetates as the major reaction products (90-95% selectivity) with H₂O₂ in acetic acid solution at ambient pressure and 20 °C were developed. The catalytic reaction is very efficient with up to 90% combined yield of glycol acetates with H₂O₂ as a limiting reagent and 1 mol% catalyst loading. The catalytic systems developed are comprised of a mixture of Pd(OAc)₂, and 6-methyl substituted (2-pyridyl)methanesulfonate and/or di(6-pyridyl)ketone ligands. Compositions of the binary, Pd(OAc)₂-dpk, Pd(OAc)₂-Me-dpms, and ternary, Pd(OAc)₂-dpk-Me-dpms, systems have been studied by means of ¹H NMR spectroscopy and ESI mass spectrometry. Kinetics studies were performed as well and plausible reaction mechanism was suggested, which features facially chelating ligand-enabled facile oxidation of Pd^IIC₂H₄OAc intermediates with H₂O₂ to form Pd^IVC₂H₄OAc transients.     

Optical spectra of Pd-561 nanoclusters in aqueous solutions

Optical absorption spectra of aqueous solutions of the giant cluster Pd₅₆₁Phen₆₀(OAc)₁₈₀ (1) were studied in air and after treatment with H₂. The results obtained were compared with the corresponding data for 2—4-nm nanoparticles of colloidal palladium prepared by the radiochemical and chemical reduction of the Pd^II complexes in aqueous solutions. The optical spectra of cluster 1 and nanoparticles of colloidal palladium are of the same nature and are caused by the light absorption by free electrons in the metal.     

Catalytic C-phenylation of methyl acrylate with tetraphenylantimony(v) halides and carboxylates

Catalytic C-phenylation of methyl acrylate to methyl cinnamate with the Ph₄SbX complexes (X = F, Cl, Br, OH, OAc, O₂CEt) in the presence of the palladium compounds PdCl₂, Pd(OAc)₂, Pd₂(dba)₃, Pd(Ph₃P)₂Cl₂, and Pd(dppf)Cl₂ (dba is dibenzylideneacetone and dppf is bis(diphenylphosphinoferrocene)) was studied in organic solvents (MeCN, THF, DMF, MeOH, and AcOH). The highest yield of methyl cinnamate (73% based on the starting organometallic compound) was obtained for the Ph₄SbCl—PdCl₂ (1 : 0.04) system in acetonitrile.     

Unexpected participation of nucleophiles in the reaction of palladium(II) acetate with divalent 3<Emphasis Type="Italic">d</Emphasis> metals

The kinetics of reactions of palladium(II) acetate with cobalt(II), nickel(II), and copper(II) acetates were studied by spectrophotometry. These reactions produce heterobimetallic complexes Pd^II(μ-OOCMe)₄M^II(OH₂)(HOOCMe)₂, where M = Co, Ni, or Cu. These reactions are very slow in carefully dehydrated (<0.01% H₂O) acetic acid, but are considerably enhanced by water or acetonitrile. Our data indicate that the activation of the kinetically inert ring structure of the initial palladium complex Pd₃(μ-OOCMe)₆ by means of the nucleophilic attack of an H₂O or acetonitrile molecule is the key step of the reaction mechanism.     

Reduction of nitrosoarene ligands in binuclear palladium(ii) complexes

Reduction of the binuclear Pd^II complexes Pd₂(OCOR)₂(o-CH₂C₆H₄—NO)₂ (1) and Pd₂(OCOR)₂(o-PhN—C₆H₄—NO)₂ (2) (where R = Me, CF₃, Bu^t, or Ph) by sodium borohydride, an ethanolic solution of KOH, or molecular hydrogen was examined. The first stage of reduction was demonstrated to afford metallic palladium and aromatic amines, viz., o-toluidine o-Me—C₆H₄—NH₂ from complex 1 and aniline Ph—NH₂ from complex 2. The reactions with molecular hydrogen involve deeper stages to yield cyclic ketones (o-methylcyclohexanone and cyclohexanone) and then cycloalkanes (methylcyclohexane and cyclohexane, respectively). The latter reactions are accompanied by elimination of N₂. The mechanism of reduction of complexes 1 and 2 with molecular hydrogen was proposed.     

Complex Formation Equilibria of Amine-Bridged Dinuclearpalladium(II) Complexes with DNA Constituents

The complex formation equilibria involving trans-diamminepalladium(II) chloride (Pd^II), 1,6-hexanediamine (HDA), and DNA constituents were investigated. The formation constant of all possible mononuclear and binuclear complexes were determined at 25 °C and 0.1 mol⋅L⁻¹ NaNO₃. The speciation diagrams of the binuclear complex of Pd^II–HDA–DNA reveal that these complexes predominate in the physiological pH range and the reaction of the binuclear complex Pd^II–HDA–Pd^II with DNA constituents is quite feasible.     

Preparation and x-ray crystal structure of [Pd2(μ-O2CMe)2(C6H5)2(PPh3)2], a binuclear acetate-bridged palladium(II) phenyl complex formed by PC bond cleavage of triphenylphosphine

The new binuclear complex [Pd₂(μ-O₂CMe)₂(C₆H₅)₂(PPh₃)₂] is formed when [Pd₃(O₂CMe)₆] reacts with PPh₃ in methanol. An X-ray crystal structure analysis shows the complex to comprise two square planar palladium(II) atoms bridged by two acetate ligands in a cis fashion. The phosphine and phenyl ligands on each metal atom adopt positions which are mutually trans to the equivalent ligand on the other metal atom, so that the complex has an approximate two-fold axis perpendicular to the plane of the four acetate oxygens. The NMR (¹H, ¹³C and ³¹P) spectra are reported.     

New mono- and binuclear Pd(II) complexes containing 1,2,4-triazole moieties

The reaction of AMTT (AMTT = 4-amino-3-methyl-1,2,4-triazol-5-thione, HL1) with palladium(II) chloride and triphenylphosphane as a co-ligand in acetonitrile afforded the mononuclear Pd^II-complex [(PPh₃)Pd(HL1)Cl]Cl·2CH₃CN (1). The complex [(PPh₃)Pd(HL1)I]Cl·1/2H₂O (2) was prepared via halogen exchange between 1 and sodium iodide in methanol/acetonitrile. The first binuclear palladium(II) complex containing singly deprotonated HL1, [(PPh₃)₂ClPd(L1)Pd(PPh₃)Cl]Cl·1/3H₂O·CH₃OH (3), was prepared by the reaction of HL1 with palladium(II) chloride and triphenylphosphane in the presence of sodium acetate in methanol.     

Preparation and properties of palladium(II) and rhodium(I) complexes containing bidentate phosphine sulphide and selenide ligands

Summary The synthesis and properties of cationic complexes of general formula [ML₂{CH₂(Ph₂PE)₂}]BF₄, where M = Pd^II and Rh^II, L₂ = ³-MeC₃H₄, {P(O)(OR)₂}₂H (R = Me, Et), COD, (CO)₂, (CO)PPh₃ and E = S, Se are described. The methylene proton of the coordinated phosphine sulphide or selenide ligands react with strong bases as BuLi in n-hexane or NaH in THF, to give neutral complexes of the type [ML₂{CH(Ph₂PE)₂}], where M = Pd^II, Rh^I; L₂ = ³-MeC₃H₄, COD and E = S, Se. The complexes have been characterized by elemental analyses, molar conductivities, i.r., ¹H n.m.r. and ³¹P{¹H} n.m.r. spectroscopy.