Hydroxyapatite-supported palladium nanoclusters: a highly active heterogeneous catalyst for selective oxidation of alcohols by use of molecular oxygen

Treatment of a stoichiometric hydroxyapatite (HAP), Ca10(PO4)6(OH)2, with PdCl2(PhCN)2 gives a new type of palladium-grafted hydroxyapatite. Analysis by means of powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray (EDX), IR, and Pd K-edge X-ray absorption fine structure (XAFS) proves that a monomeric PdCl2 species is chemisorbed on the HAP surface, which is readily transformed into Pd nanoclusters with a narrow size distribution in the presence of alcohol. Nanoclustered Pd0 species can effectively promote the alcohol oxidation under an atmospheric O2 pressure, giving a remarkably high turnover number (TON) of up to 236,000 with an excellent turnover frequency (TOF) of approximately 9800 h(-1) for a 250-mmol-scale oxidation of 1-phenylethanol under solvent-free conditions. In addition to advantages such as a simple workup procedure and the ability to recycle the catalyst, the present Pd catalyst does not require additives to complete the catalytic cycle. The diameters of the generated Pd nanoclusters can be controlled upon acting on the alcohol substrates used. Oxidation of alcohols is proposed to occur primarily on low-coordination sites within a regular arrangement of the Pd nanocluster by performing calculations on the palladium crystallites.     

Unusual selective allylation of norbornadiene in the presence of palladium nanoclusters

The reaction of norbornadiene (NBD) with allyl acetate in the presence of the nanocluster Pd₁₄₇phen₃₂O₆₀(OCOBu^t)₃₀ (Pd-147; phen is 1,10-phenanthroline) and PPh₃ in acetonitrile is nonselective and is accompanied by the decomposition of the cluster, affording the same allylation products of NBD as the reaction with Pd₃(OAc)₆ or Pd(dba)₂ (dba is dibenzylideneacetone) combined with PPh₃. In contrast, in the ionic liquid [bmim][BF₄] (bmim is 1-butyl-3-methylimidazolinium), the Pd-147 is not decomposed and the reaction occurs selectively to give methylidene(vinyl)norbornene as the sole product. The data obtained suggest that in an ionic liquid, the reaction under study is catalyzed by the nanocluster Pd-147 rather than by the products of its decomposition.     

Surfactant-free synthesis of palladium nanoclusters for their use in catalytic cross-coupling reactions

Surfactant-free Pd nanoclusters (Pd NCs) (size: 1-1.5 nm) showed high catalytic activity in the Suzuki-Miyaura cross-coupling and Mizoroki-Heck reactions. The Pd NCs had a high turnover number, up to 6.0 × 10(8), which can be recycled at least five times without loss of catalytic activity.     

Facile synthesis of palladium nanoclusters and their catalytic activity in Sonogashira coupling reactions

This work reports a facile synthesis of palladium nanoclusters (PdNCs) in MeCN/MeOH mixture without any stabilizer. The PdNCs were found to be effective catalysts for copper-free, amine-free and ligand-free Songashira coupling reactions under ambient conditions.     

Formation of bimetallic Ag-Pd nanoclusters via the reaction between Ag nanoclusters and Pd2+ ions

We have investigated systematically the mechanistic aspects of the Ag-Pd bimetallic cluster formation within sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles by using in-situ X-ray absorption spectroscopy (XAS). A two-step sequential reduction method is employed for the synthesis of Ag-Pd bimetallic clusters. The first step involves preparation of Ag nanoclusters, by mixing the Ag+ ions containing the AOT microemulsion system with a reducing agent hydrazine (N2H4) containing the AOT microemulsion system. In the second step, the addition of Pd2+ ions to Ag nanoclusters led to the formation of Ag-Pd bimetallic clusters via the reaction between Ag nanoclusters and Pd2+ ions in AOT reverse micelles. The reduction of silver ions and the formation of corresponding Ag nanoclusters are monitored as a function of the dosage of the reducing agent, hydrazine. In-situ XAS allowed probing of the reaction between Ag nanoclusters and Pd2+ ions during the formation of Ag-Pd bimetallic clusters. Analysis of Ag and Pd K-edge XAS spectra reveals that in the final stage Ag-Pd clusters, in which "Ag" atoms prefer to be surrounded by "Pd" and "Pd" atoms prefer to be surrounded by "Pd", were formed. On the basis of XAS results presented here, we are able to propose a structural model for each step so that this work provides a detailed insight into the mechanism of nucleation and growth of Ag-Pd bimetallic clusters. We also discussed the atomic distribution of Ag and Pd atoms in Ag-Pd bimetallic clusters based on the calculated XAS structural parameters.     

Synthesis and characterization of NiO nanoclusters via thermal decomposition

Thermal decomposition process has been developed to synthesize nickel oxide (NiO) nanoclusters via the reaction between a new precursor, nickel oxalate [Ni(O₄C₂)(H₂O)₄] and oleylamine (C₁₈H₃₇N). The combination of triphenylphosphine (C₁₈H₁₅P) and C₁₈H₃₇N were added as surfactants to control the particle size. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and ultraviolet–visible (UV–Vis) spectroscopy. The synthesized NiO nanoclusters have a cubic structure with average size 2–10 nm.     

Edge plane sites on highly ordered pyrolytic graphite as templates for making palladium nanowires via electrochemical decoration

An approach for the fabrication of metal nanowires is presented. Palladium wires with diameters less than 50 nm were produced by electrochemical decoration of step edge sites on the surface of highly ordered pyrolytic graphite via the following three steps. First an electrochemical activation step was used to oxidize the edge plane sites on highly ordered pyrolytic graphite surfaces in 0.5 M Na(2)SO(4). Second, a potential cycling step in a 1 mM PdCl(2) solution in 0.1 M H(2)SO(4) was used to form palladium oxide (s) and/or complexes of Pd on the step edges. Third, Pd nanowires were formed by electroreduction after transfer of the graphite to 0.1 M H(2)SO(4). The resulting wires showed a high degree of uniformity. A merit of this approach is that it allowed metal nanowires to be fabricated without the simultaneous formation of nanoparticles on the basal plane terraces, in contrast to other studies of this type. The mesoscopic palladium wires are shown to be useful for the electrochemical sensing of hydrazine.     

Modified cotton fabric with durable anti-fouling performance for separation of surfactant-stabilized oil-in-water emulsions

Membrane applications for the separation of surfactant-stabilized emulsions are often constrained by a deficiency in permeability and anti-fouling properties. Herein, special wetted cotton fabric with a protective layer (P-MH@CF) for durable anti-fouling performance was synthesized by a two-step method, which was related to interfacial ion migration technology and unilateral spraying treatment. Permeability of water and separation performance of P-MH@CF membrane were investigated systematically. Emulsions stabilized by anionic, cationic, or non-ionic surfactant were successfully separated with high efficiency. In the process of separation, the oil droplets surrounded by surfactants were difficult to demulsify and gathered physically on the membrane surface to form a “cream layer”. The stearic acid acted as a protective layer, like a quilt, protecting the membrane from contamination. The membrane retained robust reusability for separation even after the “cream layer” had been washed off, which was promising for the remediation of oily wastewater containing surfactants.

Graphical abstract

     

Growth of palladium nanoparticles on nanostructured highly ordered pyrolytic graphite

We report on the growth of palladium nanoparticles on the basal plane of as‐cleaved highly oriented pyrolytic graphite (HOPG) samples, and on CO₂ ion sputtered nanostructured HOPG surfaces. The morphology of Pd nanostructures grown at room temperature is investigated by scanning tunneling microscopy (STM). The STM observations indicate that the morphology of the Pd films is strongly dependent on the HOPG surface. Stabilized Pd particles only form on the sputtered surface, while ramified Pd particles decorate the clean HOPG terraces. The prestructuring of HOPG surface leads to a selective location of particles at the rim of the nanopits generated by the CO₂ ion sputtering and annealing of the surface. The correlation between size, form, density, spatial distribution of the Pd nanoparticles and the quantity of metal added on surface is discussed. We also describe trench channeling of graphite or graphene basal planes by means of Pd nanoparticles in an ambient environment. Copyright © 2014 John Wiley & Sons, Ltd.     

Catalytic properties of palladium nanoclusters synthesized within diblock copolymer films: hydrogenation of ethylene and propylene

Palladium nanoclusters were synthesized within microphase-separated diblock copolymer films of [MTD]₁₁₃[Pd(Cp^N)PA]₅₀ (MTD=methyltetracyclododecene, Cp^N=endo-2-(cyclopentadienylmethyl)norborn-5-ene, PA=η³-1-phenylallyl). The organometallic repeat units were reduced by exposing the films to hydrogen at 100°C, leading to the formation of nearly monodisperse palladium nanoclusters. TEM, SAXS, and WAXS were used to characterized the polymer morphology and cluster size. The nanocomposites were active catalysts for hydrogenation of ethylene and propylene. The cluster size and voids within the polymer matrix were important factors in determining the catalyst activity, expressed as the moles of alkene hydrogenated per mole palladium per second. In contrast to permeation results that showed that the permeability of propylene in polyMTD is greater than that of ethylene, the catalyst activity for hydrogenation of ethylene was greater than that for propylene.     

Formation of bi-aryls via a domino palladium catalysis

Synthesis of bi-aryls via a domino Pd-catalyzed reaction of 1-(2-bromophenyl)-2-methylpropan-1-ones/(2-bromophenyl)(cyclohexyl)methanones is presented. The mechanism of the reaction is believed to proceed through a five membered palladacycle that combines with a second molecule of halo-arene to yield the bi-aryls. This method is quite successful to deliver highly sterically crowded bi-aryls with dense functionalities on the aromatic rings.     

N-arylation of carbamate-protected glycine derivatives via palladium catalysis

A synthesis of N-aryl and N-heteroaryl amino acid derivatives using palladium catalysis is described. Several carbamate-protected glycine derivatives react with aryl and heteroaryl halides using a palladium/Xantphos catalyst system to access the desired synthons.     

寡聚核苷酸稳定银纳米簇荧光探针的合成及含巯基药物的高选择性分析测定

金属纳米团簇具有很好的光电特性,但因其化学活性高而不易稳定存在于水介质中.根据核苷酸的所有碱基中胞嘧啶与Ag+的结合能力最强,寡聚鸟苷酸易折叠和序列中同时存在腺嘌呤和胸腺嘧啶易发生杂交导致自身团聚等因素,本文设计了胞嘧啶和腺嘌呤各占50%的寡聚核苷酸序列模板分子用于合成稳定性好、荧光性能优异的银纳米簇,并进一步应用于含巯基药物的分析测定.研究表明,含巯基药物通过巯基能高选择性地与银纳米簇发生相互作用形成Ag?S键,使得银纳米簇的荧光发生静态猝灭.据此,本文建立了以抗高血压药物卡托普利为代表的含巯基物质的分析方法.该方法快速、准确、选择性好、灵敏度高,可成功应用于卡托普利片剂的分析.     

Carbonized cotton fibers via a facile method for highly sensitive solid‐phase microextraction of polycyclic aromatic hydrocarbons

Cotton fiber is an environmentally friendly and natural material with a certain extraction capacity, while its enrichment ability is poor. In order to improve the extraction efficiency of cotton fibers, it was carbonized to form a layer of amorphous carbon as the sorbent by a simple carbonization method. Carbonized cotton fibers were filled into a polyetheretherketone tube for in‐tube solid‐phase microextraction. The carbonization time was investigated to obtain high extraction efficiency. Coupled to high‐performance liquid chromatography, the extraction tube was evaluated with polycyclic aromatic hydrocarbons, estrogens and phthalates, and it exhibited best extraction efficiency for polycyclic aromatic hydrocarbons. Under the optimum conditions, an online analysis method for several polycyclic aromatic hydrocarbons was established with large linear ranges (0.016–0.20 μg/L), low limits of detection (0.005–0.020 μg/L), and high enrichment factors (948–2874). Analysis method was successfully applied to the detection of targets in the real samples and shown satisfactory durability and chemical stability. Moreover, the relative recoveries ranged from 82 to 119.2%, which demonstrated the applicability of carbonized cotton fibers in sample preparation. Compared with other reported methods, the proposed method provided shorter extraction time, higher enrichment factors, comparable limits of detection, and recoveries.     

Stereospecific synthesis of highly substituted skipped dienes through multifunctional palladium catalysis

[reaction: see text] Multifunctional palladium catalysis is utilized in the one-pot stereocontrolled synthesis of tetrasubstituted alkenes. The homogeneous palladium dihalide catalyst utilized for bromo-/chloroallylation of alkynes is then reused in situ for a subsequent Suzuki cross-coupling reaction.     

The use of palladium complexes in highly selective multistep organic synthesis

Palladium complexes are versatile catalysts for the selective construction of organic molecules. The use of a model system containing a norbornyl-palladium bond stable toward -hydrogen elimination allows the formation of a variety of molecules. Carbon monoxide is a particularly advantageous building block in these multistep reactions, because it helps to induce the formation of various types of carbon-carbon bonds. Some palladium-catalyzed multistep reactions, which proceed in sequence and have a common initial step,i.e., oxidative addition, are described.This review is based on material from a report delivered at the conference INEOS-94: The Modern Problems of Organometallic Chemistry (May 21–27, 1994, Moscow).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 412–420, March, 1995.