Hydrothermal Synthesis of Platinum‐Group‐Metal Nanoparticles by Using HEPES as a Reductant and Stabilizer

Platinum‐group‐metal (Ru, Os, Rh, Ir, Pd and Pt) nanoparticles are synthesized in an aqueous buffer solution of 4‐(2‐hydroxyethyl)‐1‐piperazineethanesulfonic acid (HEPES) (200 mM , pH 7.4) under hydrothermal conditions (180 °C). Monodispersed (monodispersity: 11–15 %) metal nanoparticles were obtained with an average particle size of less than 5 nm (Ru: 1.8±0.2, Os: 1.6±0.2, Rh: 4.5±0.5, Ir: 2.0±0.3, Pd: 3.8±0.4, Pt: 1.9±0.2 nm). The size, monodispersity, and stability of the as‐obtained metal nanoparticles were affected by the HEPES concentration, pH of the HEPES buffer solution, and reaction temperature. HEPES with two tertiary amines (piperazine groups) and terminal hydroxyl groups can act as a reductant and stabilizer. The HEPES molecules can bind to the surface of metal nanoparticles to prevent metal nanoparticles from aggregation. These platinum‐group‐metal nanoparticles could be deposited onto the surface of graphite, which catalyzed the aerobic oxidation of alcohols to aldehydes.     

Mechanistic Insight into the Intramolecular Benzylic C−H Nitrene Insertion Catalyzed by Bimetallic Paddlewheel Complexes: Influence of the Metal Centers

The intramolecular benzylic C?H amination catalyzed by bimetallic paddlewheel complexes was investigated by using density functional theory calculations. The metal–metal bonding characters were investigated and the structures featuring either a small HOMO–LUMO gap or a compact SOMO energy scope were estimated to facilitate an easier one‐electron oxidation of the bimetallic center. The hydrogen‐abstraction step was found to occur through three manners, that is, hydride transfer, hydrogen migration, and proton transfer. The imido N species are more preferred in the Ru–Ru and Pd–Mn cases whereas coexisting N species, namely, singlet/triplet nitrene and imido, were observed in the Rh–Rh and Pd–Co cases. On the other hand, the triplet nitrene N species were found to be predominant in the Pd–Ni and Pd–Zn systems. A concerted asynchronous mechanism was found to be modestly favorable in the Rh–Rh‐catalyzed reactions whereas the Pd–Co‐catalyzed reactions demonstrated a slight preference for a stepwise pathway. Favored stepwise pathways were seen in each Ru–Ru‐ and Pd–Mn‐catalyzed reactions and in the triplet nitrene involved Pd–Ni and Pd–Zn reactions. The calculations suggest the feasibility of the Pd–Mn, Pd–Co, and Pd–Ni paddlewheel complexes as being economical alternatives for the expensive dirhodium/diruthenium complexes in C?H amination catalysis.     

Practical and efficient Suzuki-Miyaura cross-coupling of 2-iodocycloenones with arylboronic acids catalyzed by recyclable Pd(0)/C

The first Suzuki-Miyaura cross-coupling of 2-iodocycloenones with arylboronic acids catalyzed by 10% Pd(0)/C is described as an interesting alternative to classical homogeneous conditions. Most of the substrate reacted under mild condition at 25 degrees C under air in aqueous DME. The conditions described tolerate a wide range of iodoenones and boronic acids. Notably, the procedure features inexpensive reagents and solvents with low toxicity rendering the method environmentally benign. Additionally 10% Pd(0)/C could be recovered and efficiently reused at least five times without significant alteration of the yields of the cross-coupled product.     

Catalytic effects of peroxidase-like metalloporphyrins on the fluorescence reaction of homovanillic acid with hydrogen peroxide

Summary The catalytic effects of peroxidase-like metalloporphyrins (Me-P) on the fluorescence reaction of homovanillic acid with hydrogen peroxide have been studied. These metalloporphyrins are the complexes of Mn with tetrakis(carboxyphenyl)porphyrin (TPPC) and trikis(sulfophenyl)porphyrin(TPPS₃), Fe, Co, Ni, Cu, Zn, Ag and Sn with tetrakis(sulfophenyl)porphyrin(TPPS₄), and Rh, Pt and Pd with tetrakis(N-methylpyridiniumyl)porphyrin-(TMPyP) and hemin. The complexes of Mn, Fe, Co, Rh and Pt with porphyrins catalyzed the formation of the fluorescence product, while the complexes of Ni, Cu, Zn, Ag, Sn and Pd did not. Traces of hydrogen peroxide and glucose can be determined using the metalloporphyrins. The characteristics of peroxidase-like metalloporphyrins have been compared with those of horseradish peroxidase (HRP).     

Palladium catalyzed Heck reaction of 2-iodoanilines under ligand-free conditions in air

Palladium catalyzed Heck reaction of 2-iodoanilines and acrylate has been developed. The palladium catalyzed Heck reaction of 2-iodoanilines can readily occur in CH₃CN using Pd(OAc)₂ (5.0?mol%) as catalyst, NEt₃ as base under ligand-free conditions. And 2-alkenylanilines were obtained as the cross-coupling products with medium to high yield.     

Decomposition of NH3 on Pd and Ir Comparison with Pt and Rh

The unimolecular decompositions of NH₃ on polycrystalline wires and foils of Pd and Ir are examined and compared with the corresponding ones on Pt and Rh. The reactions were carried out in a differential flow reactor, at pressures from 0.01 to 1 Torr and temperatures from 500 to 1900 K. It was found that the rates of product formation could be fit by Langmuir-Hinshelwood unimolecular rate expressions, with an accuracy of ±20% under all conditions. Ammonia decomposes to N₂ and the rate of decomposition is fastest on Ir by several orders of magnitude when compared with that on the other metals, becoming flux limited above about 750 K. Ir appears to be the choice catalyst for dehydrogenating ammonia. The heats of adsorption of NH₃ on Pt, Rh and Pd are similar and equal to 16.7, 16.8 and 17.4 kcal/mol, respectively. The apparent activation energy for this reaction is similar on Pt and Rh and equal to 21 kcal/mol, while for Pd and Ir it is 26.2 and 31.2 kcal/mol, respectively.     

Efficient aziridination of olefins catalyzed by mixed-valent dirhodium(II,III) caprolactamate

[reaction: see text] A mild, efficient, and selective aziridination of olefins catalyzed by dirhodium(II) caprolactamate [Rh(2)(cap)(4).2CH(3)CN] is described. Use of p-toluenesulfonamide (TsNH(2)), N-bromosuccinimide (NBS), and potassium carbonate readily affords aziridines in isolated yields of up to 95% under extremely mild conditions with as little as 0.01 mol % Rh(2)(cap)(4). Aziridine formation occurs through Rh(2)(5+)-catalyzed aminobromination and subsequent base-induced ring closure. An X-ray crystal structure of a Rh(2)(5+) halide complex, formed from the reaction between Rh(2)(cap)(4) and N-chlorosuccinimide, has been obtained.     

Reactivity of 2-formylphenylboronic acid toward secondary aromatic amines in amination-reduction reactions

The synthesis of 2-(arylaminomethyl)phenylboronic acid via an amination-reduction reaction has been investigated within a model system comprising 2-formylphenylboronic acid and N-ethylaniline. Adoption of the appropriate reaction conditions influences the reactivity of 2-formylphenylboronic acid, enabling efficient synthesis of so-far unobtainable 2-(arylaminomethyl)phenylboronic compounds. The first crystal structure of the aromatic amine derivative has been determined and described.     

Studies on the Formation of Catalytically Active PGM Nanoparticles from Model Solutions as a Basis for the Recycling of Spent Catalysts

The paper presents basic studies on the precipitation of platinum, palladium, rhodium, and ruthenium nanoparticles from model acidic solutions using sodium borohydride, ascorbic acid, and sodium formate as reducing agents and polyvinylpyrrolidone as a stabilizing agent. The size of the obtained PGM particles after precipitation with NaBH₄ solution does not exceed 55 nm. NaBH₄ is an efficient reducer; the precipitation yields for Pt, Pd, Ru, Rh are 75, 90, 65 and 85%, respectively. By precipitation with ascorbic acid, it is possible to efficiently separate Pt, Rh, and Ru from Pd from the two-component mixtures. The obtained Pt, Pd, and Rh precipitates have the catalytic ability of the catalytic reaction of p-nitrophenol to p-aminophenol. The morphological characteristic of the PGM precipitates was analyzed by AFM, SEM-EDS, and TEM.     

Heterogeneous Versus Homogeneous Palladium Catalysts for Ligandless Mizoroki–Heck Reactions: A Comparison of Batch/Microwave and Continuous‐Flow Processing

Mizoroki–Heck couplings of aryl iodides and bromides with butyl acrylate were investigated as model systems to perform transition‐metal‐catalyzed transformations in continuous‐flow mode. As a suitable ligandless catalyst system for the Mizoroki–Heck couplings both heterogeneous and homogeneous Pd catalysts (Pd/C and Pd acetate) were considered. In batch mode, full conversion with excellent selectivity for coupling was achieved applying high‐temperature microwave conditions with Pd levels as low as 10^?3 mol %. In continuous‐flow mode with Pd/C as a catalyst, significant Pd leaching from the heterogeneous catalyst was observed as these Mizoroki–Heck couplings proceed by a homogeneous mechanism involving soluble Pd colloids/nanoparticles. By applying low levels of Pd acetate as homogeneous Pd precatalyst, successful continuous‐flow Mizoroki–Heck transformations were performed in a high‐temperature/pressure flow reactor. For both aryl iodides and bromides, high isolated product yields of the cinnamic esters were obtained. Mechanistic issues involving the Pd‐catalyzed Mizoroki–Heck reactions are discussed.     

贵金属催化p-叔丁基-α-甲基肉桂醛加氢

采用傅里叶变换红外光谱仪(FT-IR)、N₂吸脱附、X射线衍射(XRD)、透射电子显微镜(TEM)揭示了微波辅助-KOH处理对活性炭的物理化学性能的影响规律。 结果表明,活性炭表面的含氧基团的种类增加,微孔明显减少,中大孔的比例增大。 通过浸渍-原位还原方法制备了Pt、Pd、Ru、Rh负载微波辅助-KOH处理活性炭催化剂,并对其催化p-叔丁基-α-甲基肉桂醛选择性加氢性能进行了研究。 发现Pt具有优异的C=O加氢选择性,而Pd具有优良的C=C加氢选择性。 进一步研究了Pd-Pt双组分催化剂催化p-叔丁基-α-甲基肉桂醛加氢产物分布,随着Pt含量的增加, C=O选择性逐步提高, C=C选择性逐渐下降,且当m(Pd)∶m(Pt)=4∶1时,其催化剂的催化性能最佳。     

Facile synthesis of indene and fluorene derivatives through AlCl3‐catalyzed cyclization of in situ formed iminium ions

A simple AlCl₃‐catalyzed condensation/cyclization cascade process between aldehydes and sulfonamide is reported, in which two new bonds and one five‐membered ring are simultaneously formed with water as the byproduct. This method provides a rapid access to indenamine and 9‐aminofluorene derivatives. Additionally, these products can be transformed into corresponding indanones and fluorenones under the developed conditions.     

Rhodium catalyzed reaction of internal alkynes with organoborons under CO atmosphere: a product tunable reaction

Alkynes react with organoborons under a CO atmosphere in the presence of a rhodium(I) catalyst to afford mainly 5-aryl-2(5H)-furanones, α,β-unsaturated ketones, and indanones. The product selectivity can be tuned by modifying the reaction conditions.     

Specificity of noble metals dynamic sorption preconcentration on reversed-phase sorbents

The reversible sorption preconcentration of noble metals (NMs) using different schemes “sorbent–reagent–eluent” was investigated. The extraction of Au, Pd, Pt, Ir, Rh and Ru chlorocomplexes from hydrochloric acid solutions on hyper-crosslinked polysterene MN-200 in the form of ion associates with tributylamine (TBA) and 4-(n-octyl)diethylenetriamine (ODETA) was investigated. It was found that Pd, Pt and Au were quantitatively and reversibly extracted using TBA on hyper-crosslinked polysterene; the appropriate eluent for desorption was 1 M solution of HCl in ethanol. Ir, Rh and Ru under these conditions were not sorbed quantitatively. It was found that sorbent hydrophobicity is not the main characteristic that defines the efficiency of sorption of a particular NM ion associate. Different efficiencies of hyper-crosslinked polysterene MN-200 for sorption of square-planar chlorcomplexes of Pt, Pd and Au and octahedral complexes of Ir, Rh and Ru were found. For the first time, the sorbents with their own N-atoms – StrataX and StrataX-AW – were used for the sorption of Ir, Rh and Ru. Using these sorbents, the sorption of Ir was increased up to 95%, and the sorption of Ru and Rh was increased to about 40%. We can explain these results by nonspecific interaction of chlorcomplexes of Ir, Rh and Ru with ethylenediamine groups of the sorbent. Weak bases with large anions may be applied for desorption of Ir, Rh and Ru. Two schemes of dynamic sorption preconcentration of NMs from hydrochloric acid solutions were proposed – hyper-crosslinked polysterene MN-200 for the determination of Au, Pd, Pt, and StrataX-AW for Ir, Rh and Ru.     

Cooperative Effect of Two Metals: CoPd(OAc)4‐Catalyzed CH Amination and Aziridination

The first Co/Pd‐cocatalyzed intramolecular C?H amination and aziridination reactions were developed. Sulfamate esters were converted to oxathiazinanes by using CoPd(OAc)₄ as catalyst and PhI(OAc)₂ as oxidant. The mutual presence of both Co and Pd is crucial for the catalytic activity. This combination of two metals with simple acetate ligands provides an economical alternative to the Rh‐catalyzed insertion of nitrenoids into C?H bonds.     

PVC-二亚乙基三胺(DETA)-Pd对Heck反应的催化性能研究

以聚氯乙烯为原料,用较简单的方法得到了聚氯乙烯二亚乙基三胺负载钯配合物(PVC-DETA-Pd).PVC-DETA-Pd具有较高的热稳定性,可以满足Heck反应所需要的高温条件.在110℃、氮气氛围,四丁基溴化铵(TBAB)做溶剂的条件下,PVC-DETA-Pd催化溴苯与苯乙烯的反应产率可以达到99%.PVC-DETA-Pd在多种缚酸剂的存在下均可有效地催化芳基溴的Heck反应,但在三丁胺中具有最好的效果.在适当的反应条件下,以PVC-DETA-Pd为催化剂,各种带取代基芳基溴、芳基氯均可以有效地与乙烯基化合物反应,反应产率>70%.PVC-DETA-Pd还具有较好的重复使用性能.     

Recyclable Palladium Catalysts for the Heck/Sonogashira Reaction under Microwave‐assisted Thermomorphic Conditions

The reaction of allyl palladium(II) chloride dimer and 4,4′‐bis(R_fCH₂OCH₂)‐2,2′‐bpy, 1a–b , in the presence of AgOT_f resulted in the synthesis of cationic palladium complex, [Pd(η³‐allyl)(4,4′‐bis‐(R_fCH₂OCH₂)‐2,2′‐bpy)](OT_f), 2a–b where R_f = C₉F₁₉ ( a ), C₁₀F₂₁ ( b ), respectively. The reaction of [PdCl₂(CH₃CN)] or K₂PdCl₄ with 1b , gave rise to the synthesis of [PdCl₂(4,4′‐bis‐(C₁₀F₂₁CH₂OCH₂)‐2,2′‐bpy)], 3b . The quantitatively determined solubility curves of 2a–b and 3b in DMF indicated dramatic increase of solubility for 2a – b and 3b from ?40 to 90 °C. The catalyst‐recoverable Pd‐catalyzed Heck/Sonogashira reactions were successfully achieved in DMF with microwave‐assistance. The cationic Pd‐catalyzed Heck arylation of methyl acrylate was selected to demonstrate the feasibility of recycling 2a–b using DMF as a solvent under microwave‐assisted thermomorphic conditions. At the end of each cycle, the product mixtures were cooled, and then the catalysts were recovered by decantation. The Heck arylation catalyzed by 2b under microwave‐assisted mode exhibited good recycling results favoring the trans product. To our knowledge, this is the first example of cationic Pd‐catalyzed Heck arylation under microwave‐assisted thermomorphic conditions. Additionally, recoverable 3b ‐catalyzed Sonogashira reactions were also achieved successfully in DMF. The reactions under microwave‐assistance gave much better results in yield and in efficiency than that under conventional thermal heating.     

Influence of the reaction parameters on the Pd—HCl catalysed synthesis of phenylacetic acid derivatives via reduction of mandelic acid derivatives with carbon monoxide

The catalytic system Pd/C—HCl is highly active in the reduction of mandelic acid derivatives to phenylacetic acid derivatives with carbon monoxide when the aromatic ring is para-substituted with a hydroxy group. Typical reaction conditions are: 70–110 °C, 20–100 atm of carbon monoxide, benzene—ethanol as reaction medium, substrate/Pd=10²–10⁴/1, HCl/substrate=0.3–0.8/1. [Pd] = 10⁻² −10⁻⁴ M. When the catalytic system is used in combination with PPh₃ a slightly higher activity is observed. Comparable results are observed when using a Pd(II) catalyst precursor such as PdX₂, in combination with PPh₃, or PdX₂(PPh₃)₂ (XCl, AcO). When operating at 110 °C, decomposition to metallic palladium occurs. Pd(II) complexes with diphosphine ligands, such as diphenylphosphinemethane, -ethane, -propane or -butane, do not show any catalytic activity and are recovered unchanged. These observations suggest that Pd(0) complexes play a key role in the catalytic cycle. The proposed catalytic cycle proceeds as follows: the chloride ArCHClCOOR, formed in situ upon reaction of ArCHOHCOOR with hydrochloric acid, oxidatively adds to a Pd(0) species with formation of a catalytic intermediate having a Pd—[CH(Ar)COOR] moiety, which inserts a CO molecule, yielding an acyl intermediate of the type Pd—[COCH(Ar)COOR]. The nucleophilic attack of H₂O on the carbon atom of the carbonyl ligand gives back the Pd(0) complex to the catalytic cycle and yields a phenylmalonic acid derivative, which produces the final product, ArCH₂COOR, upon CO₂ evolution. Alternatively, protonolysis of the intermediate having a Pd—[CH(Ar)COOR] moiety yields directly the final product and a Pd(II) species, which is then reduced by CO to Pd(0). Moreover, no catalytic activity is observed when the Pd/C—HCl system is used in combination with any one of the above diphosphine ligands, probably because these ligands block the sites on the catalyst able to promote the catalytic cycle or because they prevent the reduction of Pd(II) to Pd(0). The influence of the following reaction parameters has been studied: concentration of HCl, PPh₃, palladium and substrate, pressure of carbon monoxide, the temperature, reaction time and solvent. The results are compared with those obtained in the carbonylation of aromatic aldehydes to phenylacetic acid derivatives catalyzed by the same system, for which it has been proposed that the catalysis occurs via carbonylation of the aldehyde to a mandelic acid derivative as an intermediate, which is further reduced with CO to yield the final product.     

乙酸中碘催化氧化苄醇为相应醛或酮(英文)

本文报道了用I2/NaNO2/4-OH-TEMPO为催化剂,空气为氧化剂,在冰乙酸中催化氧化苄醇的方法.文中考察了催化剂各组分和温度对催化氧化反应的影响,在催化过程中碘替代过渡金属作为4-OH-TEMPO的共催化剂,在选择条件下苄醇氧反应的产物产率达到90%,在反应过程中生成醛或酮.     

石墨炉原子吸收光谱法测定矿石中铂、钯、铑、铱

矿石样品铂、钯、铑和铱经铅试金富集,所得金属合粒用硝酸-盐酸溶解,用石墨炉原子吸收光谱法测定矿石样品中铂、钯、铑和铱的含量。在优化的石墨炉工作条件下测得:铂的质量浓度在20～150μg.L-1、钯在15～120μg.L-1、铑和铱在6～100μg.L-1范围内与其吸光度呈线性关系,检出限(3s/k)依次为4.6,4.0,1.5,1.5μg.L-1。方法用于分析了2种矿石国家标准物质(GBW 07341、GBW 07342),测定结果与认定值相符。方法的回收率在87.6%～105.5%之间。测定值的日内和日间相对标准偏差(n=7)分别在2.8%～3.6%和3.5%～4.7%之间。