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Since the elucidation of the leaching process by Mizoroki in the 1970s, the research focused on this problem has increased. As a result, it has been discovered that the leached metals can not only hinder product yield, but they can also remain as contaminants of the final products. Thus, it can be concluded that metal leaching needs to be diminished or avoided more efficiently. This problem is important for the industry and the environment because of the increases in costs and pollution. In 2014, we reported a brief review related to this important feature; now we would like to report on the latest findings on this important phenomenon, including an update on the mechanisms used to explain leaching and the reactions that support those mechanisms and including patents related to leaching in catalysis that have appeared in recent years.

Palladium(0) nanoparticles have been widely used in cross coupling reactions, including Heck reactions. For this study, we synthesized palladium(0) nanoparticles in colloidal suspension using different combinations of solvents and reducing methods under aerobic conditions. The variation in systems used to synthesize palladium(0) nanoparticles resulted in different nanoparticle sizes. To investigate whether the particle size had an effect on catalysis, we first used common Heck C–C cross-coupling reaction conditions (200 °C and 18 h). In addition, we omitted the use of stabilizing agents, other than the solvent and/or the anions in the initial nanoparticle synthesis, since the use of stabilizing agents adds cost and processing time to catalysis. All of the catalysts investigated worked in the cross coupling C–C Heck reaction, but yields did not show appreciable differences, as high temperature and long reaction times promote a high reduction of palladium(II). Therefore, we decided to work with a temperature and reaction time in which conversion would start to be observed (minimum reaction conditions). The experiments to determine minimum reaction conditions showed that this would be 120 °C and 10 h, therefore we used these conditions in Heck C–C cross-coupling reactions and all the palladium nanoparticle systems. The best C–C catalysis conversion was observed when N,N-dimethylformamide was used as solvent in the absence of reducing agent. This catalyst system resulted in the largest possible nanoparticles, which were kept in dispersion (did not precipitate out), showing that size is important in obtaining good yields in C–C Heck catalysis (where cocktail-type catalysis could explain the conversion). Nanoparticles of this size also act as a reservoir of soluble palladium species that behave as the true catalyst. The second best conversion was observed in N,N-dimethylformamide with sodium citrate, where citrate may have added extra protection, and since the palladium(0) nanoparticles were small, cocktail-type catalysis was not involved in obtaining high yields.

The as-synthesized, europium-doped, yttrium orthovanadate nanostructures exhibited photoluminescence properties that can vary based on the preparation conditions. All the samples exhibit red emissions, and the strongest emission band was observed at 620 nm and assigned to the 5D0 → 7F2 transition of Eu3+. The high intensity of the band is a consequence of the lack of inversion symmetry at the Eu3+ site (D2d symmetry) in the host lattice. The optimal europium doping concentration was 6 mol% for both preparation methods. These samples were annealed to obtain micro and nanoscale crystallite sizes in a range of 7.56 nm to 132.65 nm, and the emission spectra were obtained. The results revealed that the photoluminescence (PL) properties were dependent on crystallite size, the PL quantum yield measurements increased with increasing crystallite size. The introduction of the dopant ions induced changes in the TL glow curve structure and the kinetic properties, modifying the radiative recombination efficiency. The TL results suggest that both europium and europium-dysprosium doped YVO4 nanocrystalline phosphor present good potential for β-irradiation dosimeter applications.

The formation of M@dendrimer composites (M = platinum, iridium) is reported, at room temperature, by mechanical milling of commercially available metallic precursors, sodium borohydride and small g...

The obtaining of Pt(0), Ir(0), and Pt(0)-Ir(0) nanoparticles (NPs) is accomplished using readily available metallic precursors through their reduction with NaBH 4 in solid state. Byproducts are removed by water/acetone washes and the influence of a final heat treatment step whether using air or nitrogen is compared with untreated samples. Characterization by PXRD shows NPs with diameters >10 nm and satisfactory results for unheated samples. Further analysis by XPS, TEM, and catalytic reduction of 4-nitrophenol provides evidence to confirm the presence of zero-valent NPs and the formation of an alloy in the Pt(0)-Ir(0).

An easy pathway to synthesize a variety of cupric oxide (CuO) nanoshapes by a one-step wet chemical method is reported. CuO nanoparticles and nanorods were obtained from CuCl2 in a mixture of water and DMSO in the absence of a base at room temperature. 1-D CuO nanostructures resembling wires inside tubes, or nanopea pods, were shaped when polyamidoamine (PAMAM) dendrimers of generation 2 (16-NH2 end groups) or 2.5 (32-COO− end groups) were added to the CuO colloids. The evolution in time of the different nanostructures was followed by UV–visible spectroscopy. The XRD patterns, Raman spectroscopy and high-resolution transmission electron microscopy show clear evidence that all nanoshapes obtained in this work are composed by CuO. This method is a simple, versatile, and economical alternative for the fabrication of CuO nanostructures and might provide a practical reference for the controlled synthesis of other nanoarchitectures.

POCOP pincers have been used as ligands to obtain robust coordination/organometallic compounds, unfortunately the synthesis of these ligands is not the easiest one thus researchers work with similar but easier ligands. In this paper, we present the synthesis and obtaining of composites and organometallic POCOP- Pd(0)/Pd(0) nanoparticles and the comparison of their catalytic behavior. The organometallic POCOP-Pd(II) compounds were better catalysts than the composite Pd(0) nanoparticle-POCOP pincers with 80% yield compared with a 20% on the better yield of the composites. This might be because the nanoparticles do not have good protection from oxidation before the catalyst reaction. Another good result about this type of materials is that depending on the catalyst employed. Two different catalytic mechanisms can be applied depending on the material used: 1) the Pd(II)/Pd(IV) mechanism with organometallic Pd(II)-POCOP compounds and composites with Pd(II) nanoparticles with sodium citrate used as reducer, as catalysts; and 2) the Pd(0)/Pd(II) mechanism with Pd(0) nanoparticles obtained with sodium borohydride as reducer, as catalyst.

This paper presents a novel solventless method for the synthesis of zero-valent ruthenium nanoparticles Ru(0). The proposed method, although not entirely new in the nanomaterials world, was used for the first time to synthesize zero-valent ruthenium nanoparticles. This new approach has proved to be an environmentally friendly, clean, cheap, fast, and reproducible technique which employs low amounts of solvent. It was optimized through varying amounts of reducing salt on a determined quantity of precursor and measuring the effect of this variation on the average particle size obtained. The resulting products were fully characterized by powder XRD, TEM, HR-TEM, and XPS studies, all of which corroborated the purity of the nanoparticles achieved. In order to verify the advantages of our method over other techniques, we compared our nanoparticles with two common colloidal-synthesized ruthenium nanoparticles.

The expedited synthesis of odd generation triazine dendrimers up to generation 9 can be executed in high yields using microwave irradiation. The efforts commence from commercially-available and inexpensive materials. Execution is facilitated by automated chromatography.

A versatile methodology to develop an inherently fluorescent and thus traceable multifunctional nanodelivery platform based on miktoarm polymers is reported. Miktoarm stars containing covalently linked tetraiodofluorescein dye, polyethylene glycol, and polycaprolactone self-assemble into micelles, and integrate multiple functions including fluorescent tags for imaging, a hydrophobic core for drug incorporation, and a hydrophilic corona for micelle stabilization. Curcumin, a pleiotropic but very poorly water-soluble drug, is loaded into these micelles with an efficiency of 25-60 wt%. It leads to a 25 000-fold increase in its aqueous solubility, and a sustained release over a period of 7 d. These micelles are rapidly internalized into murine J774A.1 macrophages, and accumulated into discrete cellular compartments, whereas the free and physically encapsulated dye is diffused in the cytoplasm. Curcumin-loaded micelles reduce lipopolysaccharide-induced nitric oxide release. The studies establish miktoarm star based nanocarriers as highly efficient in tracking their fate and expanding the scope of pharmacological agents with limited utility in experimental medicine.

In this article, we present the results of a solvent-free synthesis of iridium(0) nanoparticles, both water washed and unwashed. IrCl3 and NaBH4, as starting materials, are mixed using an agate mortar and milled for 15 min until a black powder is obtained, which is heated in a nitrogen-controlled atmosphere oven at 200 °C for 2 h. If the product of the reaction is not washed before heating, NaBH4 and IrO2 impurities are observed. On the other hand, if the reaction product is washed before the heating, the obtained powder is free of impurities. We study the effect of the variation in reducing agent concentration and the annealing temperature used after the reaction. In all cases, the calculated particle size is less than 10 nm.

A simple synthesis method of silver nanoparticles and its application as an active surface-enhanced Raman spectroscopy (SERS) colloid are presented in this work. The photoreduction of AgNO3 in presence of sodium citrate (NaCit) was carried out by irradiation with different light sources (UV, white, blue, cyan, green, and orange) at room temperature. The evaluation of silver nanoparticles obtained as a function of irradiation time (1–24 h) and light source was followed by UV-visible absorption spectroscopy. This light-modification process results in a colloid with distinctive optical properties that can be related to the size and shape of the particles. The Ag colloids, as prepared, were employed as active colloids in SERS. Pyridine and caffeine were used as test molecules. Copyright © 2008 John Wiley & Sons, Ltd.

Several studies on dendrimer synthesis and reactivity have been carried out in order to control the size and functionality of compounds. From such studies, it has been suggested that these molecules may be used as ligands to synthesize potential homogeneous catalysts, firstly, in order to get the benefits of both homo- and heterogeneous catalysis (i.e. high activity and/or selectivity, good reproducibility, accessibility of the metal site, intermediaries detection, etc.); secondly, because, unlike other polymeric species, they can be readily recoverable after reaction. In this paper, following our interest in homogeneous catalysts, we would like to present our findings from studies on the synthesis and characterization of a prime molecule, triazine aminoalcohol, as starting or zero generation dendrimer and its interaction-reaction with palladium nanoparticles as well as our results on the reactivity on Heck type catalysis.

International audience; Ruthenium nanoparticles (NPs) are prepared by milling under air ruthenium chloride (RuCl3), sodium borohydride (NaBH4) and a polyphosphorhydrazone (PPH) dendron (generation 0 to 2) having an alkyl chain at the focal point and triarylphosphines on the surface. The resulting NPs have a diameter in the 2 to 3 nm range and they are stable upon storage in solution or as powders. They can efficiently catalyze hydrogenation of styrene. The interaction between the dendrons and the NPs is studied, and the influence of the alkyl chain length and dendron generation is also discussed.

The organometallic tin(IV) complexes [SnPh 2 (SR F ) 2 ] SR F = − SC 6 F 4 -4-H ( 1 ), − SC 6 F 5 ( 2 ), were synthesized and their reactivity with [MCl 2 (PPh 3 ) 2 ] M = Ni, Pd and Pt explored. Thus, transmetallation products were obtained affording polymeric [Ni(SR F )(μ-SR F )] n , monomeric cis -[Pt(PPh 3 ) 2 (SC 6 F 4 -4-H) 2 ] ( 3 ) and cis -[Pt(PPh 3 ) 2 (SC 6 F 5 ) 2 ] ( 4 ) and dimeric species [Pd(PPh 3 )(SC 6 F 4 -4-H)(μ-SC 6 F 4 -4-H)] 2 ( 5 ) and [Pd(PPh 3 )(SC 6 F 5 )(μ-SC 6 F 5 )] 2 ( 6 ) for Ni, Pt and Pd, respectively. The crystal structures of complexes 1 , 2 , 3 , 4 and 6 were determined.

One-step room-temperature synthesis of nanocrystalline Mn3O4 hausmannite, without heating posttreatment, was carried out from a simple dissolution of manganese(II) acetate in a mixture of N,N'-dimethylformamide (DMF) and water. Homogeneous nanocrystals like rods were obtained, with an average width and length of 6.6+/-1.2 nm and 17.4+/-4.1 nm, respectively, and a preferential growth along the 001 direction. Magnetization measurements on a powdered sample showed ferrimagnetic behavior at low temperatures. Under zero-field cooling (ZFC) measurement at 100 Oe, the observed blocking temperature (T(B)) was 37 K.

Nanocrystalline Mn3O4 hausmannite has been easily prepared from manganese(II) acetate tetrahydrated, dissolved in a mixture of N,N’-dimethylformamide (DMF) and water (10%) at room temperature, without post-treatment of heating. Stability of the Mn3O4 colloidal dispersion was monitored by UV-visible electronic absorption spectroscopy. X-ray powder diffraction (XRD) pattern demonstrates its good phase purity. Analysis by transmission electron microscopy (TEM) image shows homogeneous nanorods with a narrow size distribution, being the average diameter and length of 6.58 nm and 17.44 nm, respectively. Moreover, the facility of the hausmannite nanorods to adhere to glass wall in this solvent mixture has allowed the formation of thin films which were analyzed by atomic force microscopy (AFM).

A series of palladium thiolate complexes of the [Pd(Ph2PC6H4-2-(CH2NMe2))(SRF)2] type have been synthesized in good yields by metathetical reactions of [Pd(Ph2PC6H4-2-(CH2NMe2))Cl2] (1) with [Pb(SRF)2], (SRF = S − C6F5, S − C6F4-4-H, S − C6H4-2-CF3, S − C6H4-4-F, S − C6H4-2-F) and their crystal structures determined. Heck coupling reactions were carried out using [Pd(Ph2PC6H4-2-(CH2NMe2))(SRF)2], SRF = S − C6F5 (2), S − C6F4-4-H (3), S − C6H4-2-CF3 (4), S − C6H4-4-F (5), S − C6H4-2-F (6) complexes as catalysts in order to examine the effect of the thiolates in the reaction of bromobenzene and styrene. The results obtained indicate that the less electron-withdrawing substituents on the thiolate moiety may favor higher yields in the Pd catalyzed Heck reaction using [Pd(Ph2PC6H4-2-(CH2NMe2))(SRF)2] as catalysts.

The reactions of two equivalents of the ligands POT or POZ with one equivalent of the rhodium complex [Rh(μ-Cl)(CO)2]2 afford the complexes [(POT)Rh(CO)Cl] (1) and [(POZ)Rh(CO)Cl] (2), respectively. The crystal structures of both complexes have been determined showing the rhodium centers to be into slightly distorted square planar environments. Preliminary screening of the catalytic systems POT/Rh and POZ/Rh in the asymmetric hydroformylation of styrene has been carried out.

A series of palladium thiolate complexes of the type [Pd(dppf)(SRF)2] have been synthesized in good yields by metathetical reactions of [Pd(dppf)Cl2] with [Pb(SRF)2], (SRF=−SC6F5, −SC6F4-4-H, −SC6H4-2-CF3, −SC6H4-4-F, −SC6H4-3-F) and their crystal structures determined. The effect of the different thiolates in the structural properties of the complexes both in the solid state and in solution have been analyzed. Heck coupling reactions were carried out using the complexes [Pd(dppf)(SRF)2], SRF=−SC6F5 (1), −SC6F4-4-H (2), −SC6H4-2-CF3 (3), −SC6H4-4-F (4), −SC6H4-3-F (5) as catalysts in order to examine both the effect of the thiolates and the P–Pd–P bite angles in the reaction of bromobenzene and styrene. The results obtained indicate that electron-withdrawing substituents may favor higher yields in the Pd catalyzed Heck reaction using [Pd(dppf)(SRF)2] as catalysts.

The novel phosphinito iridium PCP pincer complex, IrH4{C6H3-2,6-(OPPri2)2} can be conveniently synthesized and isolated in 74% overall yield. The complex catalyzes the dehydrogenation of linear alkanes to alkenes at the rate of 13 turnovers min−1 at 200 °C. This catalytic activity is slightly higher than that exhibited by iridium complexes of analogous bis(phosphino) PCP ligands. The bis(phosphinito) complex is resistant to decomposition for periods up to 7 days at temperatures as high as 200 °C thus matching the thermal stability of the bis(phosphino) pincer complexes.

In solution, allyl palladium homobimetallic complexes bridged by fluorinated benzenethiolates, [{Pd(μ-SR)(η3-C3H5)}2] where R=C6F5, 1; C6HF4-4, 2; C6H4F-2, 3; C6H4F-3, 4 and C6H4F-4, 5, are found as a mixture of syn/anti and cis/trans isomers. The variable temperature 1H and 19F NMR study of these compounds show that the four isomers undergo interconversion through two probable mechanisms, allyl rotation assisted by the solvent and inversion of the configuration at the sulphur atoms. The X-ray crystal structure determination of [{Pd(μ-SC6F5)(η3-C3H5)}2] and [{Pd(μ-S C6HF4-4)(η3-C3H5)}2] shown both complexes to be bimetallic with the metal centres found in a slightly distorted square planar environments.

The bimetallic complexes [(η 3 -C 3 H 5 )Pd(μ-SR f )] 2 [R f =C 6 F 5 , ( 1 ); C 6 F 4 H-4, ( 2 ); C 6 H 4 F-2, ( 3 ); C 6 H 4 F-3, ( 4 ) and C 6 H 4 F-4, ( 5 )] in the presence of para -substituted phosphines P(C 6 H 4 X-4) 3 [X=OCH 3 , CH 3 , H, F, Cl, and CF 3 ] are efficient catalytic systems in the allylic alkylation couplings of ( E )-3-acetoxy-1,3-diphenyl-1-propene and dimethyl malonate. Results concerning the electronic effects of both sulfur and phosphorus substituents in this reaction are discussed.

The novel palladium phosphino-thioether P–S chelate complex, [PdCl2{MeSC6H4-2-(CH2PPh2)}] (3) is a highly efficient catalyst for the olefinic coupling of aryl bromo and iodo compounds to olefins under aerobic conditions, leading to more than 10 6 turnovers for the reactions with bromo and iodo benzenes. © 2002 Elsevier Science B.V. All rights reserved.

Since the discovery of catalysis, the identification of the different species in the mechanism involved in the reaction has been a challenge. When nanocatalysis entered the scene, the detection of material that came out from solutions attracted the attention and raised several questions: was this solid part of the nanocatalyst? was it the precursor of the nanocatalysts (the so-called precatalyst)? or was it the nanocatalyst itself? The discussion focuses on whether the catalysis is determined by the species that exist in solution or if it is generated from the support and hence the catalytic reaction is carried out with these soluble species. Furthermore, it appears that leaching is a phenomenon which occurs mainly in palladium- catalyzed reactions and that involves palladium nanoparticles (NPs). The research, findings and patents in the leaching process in catalytic reactions are reviewed in the present paper.

Treatment of the di-μ-chloride allyl–palladium complex [(η3-C3H5)Pd(μ-Cl)2Pd(η3-C3H5)] with Pb(SR)2 in acetone affords dinuclear fluorothiolate bridged complexes of the type [(η3-C3H5)Pd(μ-SR)2Pd(η3-C3H5)] (R=C6F5, 1; C6HF4-4, 2; C6H4F-2, 3; C6H4F-3, 4 and C6H4F-4, 5). Complex 1 reacts with para-substituted phosphines P(C6H4X-4)3 to give the mononuclear perfluorobenzenethiolate complexes [Pd(SC6F5)(η3-C3H5)(P(C6H4X-4)3)] (X=F, 6; CF3, 7; OCH3, 8 and CH3, 9). The single crystal X-ray diffraction structure of [(η3-C3H5)Pd(μ-SC6H4F-4)2Pd(η3-C3H5)] (5) has been resolved.

The extremely reactive and air-sensitive nitrosyl-ruthenium(0) species trans-[RuCl(NO)(PPh3)2] (2) oxidatively adds HCl to give the octahedral ruthenium(II) complex [RuHCl2(NO)(PPh3)2] (3). On treatment of 2 with O2, the five-coordinate 1:1 adduct [RuCl(NO)(η2-O2)(PPh3)2] (4) is formed. The dioxygen complex has been characterised by X-ray structural analysis.

The PCP pincer complex, IrH2{C6H3-2,6-(CH2P-t-Bu2)2} (1) catalyzes the transfer dehydrogenation of primary and secondary alcohols. Dehydrogenation occurs across the C—O bond rather than the C—C bonds and the corresponding aldehydes or ketones are obtained as the sole products arising from the dehydrogenation reactions. Methanol is an exception to this pattern of reactivity and undergoes only stoichiometric dehydrogenation with 1 to give the carbonyl complex, Ir(CO){C6H3-2,6-(CH2P-t-Bu2)2} (2). The products are obtained in nearly quantitative yields when the reactions are carried out in toluene solutions. Under the same conditions, 2,5-hexanediol is converted to the annulated product, 3-methyl-2-cyclopenten-1-one which has been isolated in 91% yield in a preparative scale reaction.Key words: alcohol, dehydrogenation, ketones, iridium pincer complex, annulation.

The PCP ligand precursor 1,3-bis(diisopropylphosphinito)benzene is conveniently prepared from the reaction of chlorodiisopropylphosphine and resorcinol in the presence of 4-dimethylaminopyridine. Refluxing the bis(phosphinito)benzene with Pd(COD)Cl2 in toluene for 5 h yields the palladium complex PdCl{C6H3-2,6-(OPPri 2)2} (1). The molecular structure of the complex was determined through a single-crystal X-ray diffraction study. The complex is a highly efficient catalyst for the olefinic coupling of aryl bromo and iodo compounds under aerobic conditions. Disubstituted alkenes were obtained in good yields from the catalytic coupling of styrene and aryl iodides, whereas styrene reactions with aryl bromides yield exclusively trisubstituted alkenes. Trisubstituted alkenes were also obtained from the reactions of 1,1 disubstituted alkenes (α-methylstyrene, n-butylacrylate) and bromobenzene. Conditions have been found which result in the regioselective product ion of one isomer of the trisubstituted alkene products in≥90% yield.

The behavior of palladium C-bound enolates [Pd(CH2C(O)CR3)Cl(PPh3)2] (R = H, 1; R = Me, 2) and [Pd(CH2C(O)CR3)(PPh3)2(NCMe)](BF4) (R = H, 5; R = Me, 6) has been studied. Dimeric species with bridging enolate moieties are formed in solution when a coordination site on the metal is made available, either with Pd2{μ-κ2-C,O-CH2C(O)CR3}2 or with mixed Pd2{μ-κ2-C,O-CH2C(O)CR3}(μ-X) (X = Cl, OH) bridges. It is proposed that π back-donation is important to stabilize oxygen bonding. Complexes 1 and 2 undergo exchange between free and coordinated phosphine in solution. Kinetic experiments support an intramolecular associative mechanism which could involve an oxoallyl-like transition state. The reactivity of the complexes has been explored. Some reactions typical of Pd-alkyls have been observed such as insertion of CO to give CR3C(O)CH2COOH. Electrophilic attack on oxygen is very important: the hydrolysis of the enolate complexes has been studied and also the reaction with ClSiMe3 to give silyl enol ethers.

Since the discovery of catalysis, the identification of the different species in the mechanism involved in the reaction has been a challenge. When nanocatalysis entered the scene, the detection of material that came out from solutions attracted the attention and raised several questions: was this solid part of the nanocatalyst? was it the precursor of the nanocatalysts (the so-called precatalyst)? or was it the nanocatalyst itself? The discussion focuses on whether the catalysis is determined by the species that exist in solution or if it is generated from the support and hence the catalytic reaction is carried out with these soluble species. Furthermore, it appears that leaching is a phenomenon which occurs mainly in palladium- catalyzed reactions and that involves palladium nanoparticles (NPs). The research, findings and patents in the leaching process in catalytic reactions are reviewed in the present paper.

Amphiphiles with a dendritic structure are attractive materials as they combine the features of dendrimers with the self-assembling properties and interfacial behavior of water-air affinities. We have synthesized three generations of polyester dendrimers and studied their interfacial properties on the Langmuir films. The behavior obtained was, as a rule, the lowest generation dendrimers behaving like traditional amphiphiles and the larger molecules presenting complicated isotherms. The Langmuir films of these compounds have been characterized by their surface pressure versus molecular area (π/A) and Brewster angle microscopy (BAM) observations.

The PCP pincer complex, IrH2{C6H3-2,6-(CH2P-t-Bu2)2} (1) catalyzes the transfer dehydrogenation of primary and secondary alcohols. Dehydrogenation occurs across the C—O bond rather than the C—C bon...

In the present work, an optical study of silver nanoparticles obtained by different methods is informed. These nanoparticles shown a strong plasmonic bands which depend on size and morphology. The Ag colloids were proved as enhancers of Raman spectroscopy. In all cases they were effective in SERS, due to the optical frequency for the electromagnetic contribution to it.

The reactions of IrH2{C6H3-2,6-(CH2PBut 2)2} with ethylene and 1-octene have been carried out, products containing the olefin compounds coordinated in a #951;2 fashion have been obtained. Both complexes have been characterized by multinuclear NMR probing unequivocally the proposed formulations. Examination of the thermal stability of both complexes under catalytic conditions shows the 1-octene adduct to be more stable.