Suzuki cross-coupling reaction was successfully carried out in ethanol utilizing a palladium colloidal solution stabilized by polyvinylpyrrolidone (PVP). High isolated yields (75-97%) to biaryls were obtained using different bases, aryl halides, and aryl boronic acids with a small loading of the palladium catalyst. Pd(0)-PVP nanoparticles with 3-6 nm of medium diameter were prepared from Pd(OAc)2 in the presence of the stabilizer PVP using methanol as the reducing agent. 相似文献
The three-component aminoallylation reaction of the activated olefins 2 with the phthalimide 1a and allyl chloride proceeded very smoothly in the presence of Pd(2)dba(3).CHCl(3) (5 mol %)/P(4-FC(6)H(4))(3) (40 mol %) and Cs(2)CO(3) (3 equiv against 2) in dichloromethane at room temperature to give the corresponding aminoallylated products, N-pent-4-enylphthalimides 3, in 58-99% yields. The reaction of oxazolidinone 1b also proceeded very smoothly to give N-(2,2-dicyano-1-phenylpent-4-enyl)oxazolidinone in a quantitative yield; however, the Tsuji-Trost-type allylation products 4 were obtained in the case of dibenzylamine, N-tosylaniline, and pyrrolidin-2-one. Further, 2 underwent cycloaddition with N-tosylvinylaziridine 9a in the presence of Pd(2)dba(3).CHCl(3) (5 mol %)/P(4-FC(6)H(4))(3) (40 mol %) in THF at room temperature, giving the corresponding pyrrolidines 11 in 69-99% yields. 相似文献
Adsorption of ethanol onto silica surfaces from ethanol-cyclohexane binary liquids was investigated by a combination of colloidal probe atomic force microscopy, adsorption excess isotherm measurement, and FTIR spectroscopy using the attenuated total reflection (ATR) mode. An unusually long-range attraction was found between the silica (glass) surfaces in the presence of ethanol in the concentration range of 0.1-1.4 mol % at room temperature. At 0.1 mol % ethanol, the attraction appeared at a distance of 35 +/- 3 nm and turned into a repulsion below 3.5 +/- 1.5 nm upon compression. Half of the attraction range agreed with the adsorption layer thickness estimated from the adsorption excess amount by assuming that the adsorption layer was composed only of ethanol. This indicated that the observed long-range attraction was caused by the contact of opposed adsorption layers of ethanol on the silica surfaces and that the sharp increase of repulsion at shorter distance was caused by the overlap of structured ethanol clusters adjacent to the surface. ATR-FTIR spectra demonstrated that ethanol adsorbed on the silica (silicon oxide) surfaces formed hydrogen-bonded clusters (polymers). Practically no ethanol clusters were formed on the hydrogen-terminated silicon surface. These results indicated that the cluster formation involved hydrogen-bonding interactions between surface silanol groups and ethanol hydroxyl groups in addition to those between ethanol hydroxyl groups. At higher temperatures (30-50 degrees C), the range and the strength of attraction decreased owing to the decrease in the hydrogen-bonded clusters monitored by FTIR spectroscopy, reflecting the nature of hydrogen bonding. The range and the strength of the attraction also changed when the ethanol concentration increased: The long-range attraction started to decrease at 0.6 mol % ethanol at room temperature and disappeared at 1.4 mol % while the adsorption excess amount remained almost constant as did the FTIR peak intensity of the hydrogen-bonded OH group of adsorbed ethanol. In the bulk solution, ethanol clusters appeared at 0.5 mol % ethanol; thus, this change in the attraction could be accounted for in terms of the exchange of ethanol molecules between the surface clusters and bulk clusters. The novel self-assembled structure of alcohol on the surface, found in this study may be called a "surface molecular macrocluster" because the hydrogen-bonded clusters extend to distances of ca. 20 nm longer than the typical sizes of common clusters, 2-4 nm, of alcohol (e.g., ethanol). 相似文献
Palladium loaded calcium-hydroxyapatite, Pd(z)/CaHAp, and calcium-fluoroapatite, Pd(z)/CaFAp, were synthesised and characterised by TEM, XRD, IR and UV–vis–NIR spectroscopies. Introduction of palladium does not change the structure of CaHAp and CaFAp. The average size of PdO particles was found to be around 4–5 nm on Pd(1)/CaHAp but larger (6–7 nm) on Pd(1)/CaFap. The acid–base properties of the supports and of the catalysts were studied using butan-2-ol conversion. On CaHAp and CaFAp, the butenes yield (dehydration reaction) is very low either in the absence or in the presence of oxygen. The methyl ethyl ketone yield (dehydrogenation reaction) is significant only in the presence of oxygen and higher over CaFAp. Conversely, the performances of Pd(z)/CaHAp are better than those of Pd(z)/CaFAp below 180 °C. Above 180 °C, buta-2-ol combustion is favoured on Pd/CaHAp but not on Pd/CaFAp.
In methane oxidation, Pd(z)/CaHAp showed also a much larger activity than Pd(z)/CaFAp. On 2 wt% Pd loaded CaHAp, the methane oxidation reaches a conversion of almost 100% at 350 °C, which is comparable with the performance of conventional Pd/Al2O3 catalysts. The reducibility of PdO under methane–oxygen mixtures is lower on Pd(z)/CaHAp. For both reactions, the lower activity of Pd(z)/CaFAp is related to its higher acidity, resulting from the substitution of OH− by F−, and to the larger PdO particle size. 相似文献
Formation of a quaternary carbon center through the allylation of beta-keto esters and 1,3-diketones with alkynes is accomplished by the use of Pd(0)/benzoic acid catalyst. Reactions of various cyclic beta-keto esters and 1,3-diketones with alkynes in the presence of Pd(2)dba(3).CHCl(3) (5 mol %), PPh(3) (40 mol %), and PhCOOH (10 mol %) proceeded at 100 degrees C in toluene (5 M) to give the corresponding allylation products in high yields in a regio- and stereoselective manner. The possibility of asymmetric allylation is also discussed. 相似文献
We report on the use of mesoporous silica microparticles (μPs) functionalized with quarternary amino groups for the isolation of platinum and palladium tetrachloro complexes from aqueous road dust digests. The μPs have a size ranging from 450 to 850 nm and are suspended directly in the aqueous digests, upon which the anionic Pt and Pd complexes are retained on the cationic surface. Subsequently, the μPs are separated by centrifugation. Elements that cause spectral interferences in ICP-MS determination of Pt and Pd can be quantitatively removed by adding fresh 0.240 mol L−1 HCl to the μPs and by repeating the centrifugation step. The analyte-loaded μPs are then dissolved in 0.1 mL of 2 mol L−1 HF, diluted to 2 mL, and the solutions thus obtained are analyzed by quadrupole ICP-MS. This method avoids analyte elution from the sorbent. This “dispersed particle extraction” approach yielded a run-to-run relative standard deviation ≤ 5 % for Pt and ≤ 4 % for Pd (at 0.1 ng mL−1, n = 4 road dust digests). Method detection limits (expressed as concentrations in the dust samples) are 2 and 1 ng g−1 for Pt and Pd, respectively. The method was validated by analysis of a reference material (BCR CRM 723) and applied to the analysis of road dust samples collected in downtown Vienna. Pt and Pd concentrations in samples collected in summer and in winter were compared, with concentrations ranging from 205 to 1445 ng g−1 for Pt and from 201 to 1230 ng g−1 for Pd.
Mesoporous silica microparticles (μPs) functionalized with quarternary amino groups were used for isolating platinum and palladium from aqueous road dust digests. The μPs were suspended directly in the aqueous digests, and the analyte-loaded μPs were analyzed using “dispersed particle extraction”.
The heat of adsorption and sticking probability of CO on well-defined Pd nanoparticles were measured as a function of particle size using single crystal adsorption microcalorimetry. Pd particles of different average sizes ranging from 120 to 4900 atoms per particle (or from 1.8 to 8 nm) and Pd(111) were used that were supported on a model in situ grown Fe(3)O(4)/Pt(111) oxide film. To precisely quantify the adsorption energies, the reflectivities of the investigated model surfaces were measured as a function of the thickness of the Fe(3)O(4) oxide layer and the amount of deposited Pd. A substantial decrease of the binding energy of CO was found with decreasing particle size. Initial heat of adsorption obtained on the virtually adsorbate-free surface was observed to be reduced by about 20-40 kJ mol(-1) on the smallest 1.8 nm sized Pd particles as compared to the larger Pd clusters and the extended Pd(111) single crystal surface. This effect is discussed in terms of the size-dependent properties of the Pd nanoparticles. The CO adsorption kinetics indicates a strong enhancement of the adsorbate flux onto the metal particles due to a capture zone effect, which involves trapping of adsorbates on the support and diffusion to metal clusters. The CO adsorption rate was found to be enhanced by a factor of ~8 for the smallest 1.8 nm sized particles and by ~1.4 for the particles of 7-8 nm size. 相似文献
The palladium-catalyzed cross-coupling of aryl halides or vinylic halides or triflates and 1-(1-alkynyl)cyclobutanols affords good yields of stereoisomerically pure 2-arylidene- or 2-(2-alkenylidene)cyclopentanones, respectively. The process involves (1) oxidative addition of the organic halide or triflate to Pd(0), (2) regioselective, intermolecular carbopalladation of the carbon-carbon triple bond of the 1-(1-alkynyl)cyclobutanol to produce a vinylic palladium intermediate, (3) regioselective ring expansion to a palladacycle, and (4) reductive elimination of the 2-alkylidenecyclopentanone with simultaneous regeneration of the Pd(0) catalyst. Generally, the best results are obtained by employing 10 mol % of Pd(OAc)(2), 20 mol % of PPh(3), 2 equiv of the aryl or vinylic iodide or vinylic triflate, 2 equiv of diisopropylethylamine, and n-Bu(4)NCl in DMF as the solvent. 相似文献
The heteropolynuclear complexes [Pd(2)M'(2)(mu-pz)(6)] (M'=Ag (1), Au (2); pzH=pyrazole), HT-[Pd(2)M'(2)(mu-3-tBupz)(6)] (M'=Ag (3 a), Au (4 a); 3-tBupzH=3-tert-butylpyrazole), and HH-[Pd(2)Au(2)(mu-3-tBupz)(6)] (4 b) have been prepared and some of them were structurally characterized. When 3-tert-butylpyrazolate was employed as a bridging ligand, two linkage isomers (head-to-tail (HT) and head-to-head (HH)) arise from the difference in orientation of the substituent groups on the pyrazolate bridges between the two Pd atoms. (1)H NMR spectroscopy has been used to identify and to follow the reversible stereochemical rearrangement of the HH isomer of [Pd(2)Ag(2)(mu-3-tBupz)(6)] (3 b) to form the HT isomer 3 a in CDCl(3) and the HT isomer of [Pd(2)Au(2)(mu-3-tBupz)(6)] (4 a) to form the HH isomer 4 b in C(6)D(6). Kinetic studies of the reaction have established the rate law to be -d(HH)/dt=d(HT)/dt=k(2)[HH]-k(1)[HT] for 3 b and -d(HT)/dt=d(HH)/dt=k(1)[HT]-k(2)[HH] for 4 a, where k(1) and k(2) denote the rate of isomerization from the HT to the HH isomer and that from the HH to the HT isomer, respectively. For typical runs at 50 degrees C in C(6)D(6), k(1)=13.8x10(-5) s(-1), k(2)=18.6x10(-5) s(-1), and K(eq)=k(2)/k(1)=1.24 for 3 b, and k(1)=1.26x10(-5) s(-1), k(2)=3.52x10(-5) s(-1), and K(eq)=k(1)/k(2)=0.36 for 4 a. Temperature-dependent rate measurements reveal DeltaH(not equal) and DeltaS(not equal) to be 100(1) kJ mol(-1) and 0(3) J mol(-1) K(-1) for 3 b and 112(5) kJ mol(-1) and 20(17) J mol(-1) K(-1) for 4 a, respectively. The rate of isomerization is essentially unaffected by the concentration of the complex or by the presence of neutral bridging ligands. These data and observations imply that the isomerization involves an intramolecular exchange process. 相似文献
Two phosphorescent complexes Ir(FFBI)2(pmp) and Ir(FFBI)2(pti) based on cyclometalated ligand 1-(4-fluorobenzyl)-2-(4-fluorophenyl)-1H-benzo[d]imidazole (FFBI) and ancillary ligands 2-(phenyliminomethyl)phenol (pmp) or 3-(pyridin-2-yl)-4,5,6,7-tetrahydro-2H-indazole (pti) were synthesized. The single crystal of Ir(FFBI)2(pmp) was obtained. The light emitting and electrochemical properties of these complexes were studied. The electroluminescent devices based on these two complexes with the structure of ITO/NPB (40 nm)/Ir complex: CBP (30 nm)/BCP (15 nm)/Alq (30 nm)/LiF (1 nm)/Al (100 nm) emitted cyan color, with high brightness and efficiencies. The maximum external quantum efficiencies reached to 6.8% and 11.6%, respectively. 相似文献
2-Benzoylpyridine N-methyl-N-phenylhydrazone, HL, is a versatile ligand which reacts with [Pd(PhCN)2Cl2] forming the coordination compound [HLPdCl2], 1, characterized by the presence of the N(py)/N(im) chelate ring. When HL reacts with [Pd3(OAc)6] this gives rise to the orthometallated complex [LPd(OAc)],. In this case the Pd(II) environment consists of a N(py)/N(im) ring fused to the N(im)/C palladacycle and a monodentate acetate anion. Complex undergoes methatetical reactions with alkaline halides and complexes of general formula [LPdX](3: X = Cl; 4: X = Br; 5: X = I) are obtained. The molecular structures 3-5 of determined by single-crystal X-ray analysis proved the formation in all cases of mononuclear Pd(II) complexes containing a N(py)/N(im)/C terdentate ligand. As solid samples only compounds 3-5 exhibited luminescence at room temperature (lambdamax approximately 610 nm). This property, quite unusual in Pd(II) complexes, is discussed in terms of pi-pi] interactions, which are mainly responsible for the existence in the crystalline solid state of dimeric units. 相似文献
Decomposition of H2O2 over Pd (5%)/carbon in an aqueous sulfuric acid solution at different acid concentrations (0-10 mol/L) and temperatures (281-313
K) in a magnetically stirred glass reactor has been investigated. The catalytic activity, activation energy and frequency
factor for the decomposition decrease with increasing acid concentration; the decrease in the activation energy is, however,
very small.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
1-Alkynyl- and 1-alkenyl-3-arylimidazo[1,5-a]pyridines were synthesized. The Sonogashira coupling of 3-aryl-1-iodoimidazo[1,5-a]pyridines and various terminal alkynes with Pd(PPh(3))(2)Cl(2) (10 mol %) and CuI (10 mol %) in triethylamine at 80 °C for 12 h afforded the corresponding 1-alkenyl-3-arylimidazo[1,5-a]pyridines in good to excellent yields. The Mizoroki-Heck reaction of 3-aryl-1-iodoimidazo[1,5-a]pyridines and various styrene derivatives proceeded smoothly with Pd(OAc)(2) (5 mol %), IMes·HCl (10 mol %), and Cs(2)CO(3) (2 equiv) in DMA at 130 °C for 20 h to give the alkenylated imidazo[1,5-a]pyridines in moderate to high yields. The fluorescence maxima and fluorescence quantum yields of the alkynylated products were 458-560 nm and Φ(F) = 0.08-0.26 in chloroform solution, and those of the alkenylated imidazopyridines were 479-537 nm and Φ(F) = 0.03-0.13. The absorption behaviors of the obtained alkynylated and alkenylated imidazo[1,5-a]pyridines showed a good fit to the values predicted by TDDFT calculations at the B3LYP/6-311++G(d,p) level. In addition, the alkynylated imidazo[1,5-a]pyridines obtained showed linear correlations between the Hammett substituent constants of the substituents on the arylalkynyl group and their fluorescence wavelengths. 相似文献
The in situ combination of oxidative coupling of benzene to biphenyl and reductive coupling of chlorobenzene (also to biphenyl) using palladium catalysts (Pd(2+)/Pd(0)) is described. In each cycle, the reductive process regenerates the catalyst for the oxidative process and vice versa. Kinetic investigations show that the reaction rate depends on [C(6)H(6)], [C(6)H(6)Cl], and catalyst loading, with E(a)() = 13 kcal mol(-)(1). The reduced palladium catalyst undergoes deactivation through aggregation and precipitation, but it is observed that during this deactivation process the Pd(0) becomes an active catalyst for the reductive coupling of chlorobenzene. Accordingly, while Pd(0)/C particles are inactive, Pd(0) colloids do catalyze the tandem reaction. Conversion is increased in the presence of a phase-transfer catalyst, presumably due to stabilization of the active Pd(0) clusters. The two halves of the catalytic cycle are examined in the light of previous research, regarding analogous oxidative and reductive coupling reactions, using stoichiometric amounts of PdCl(2) and Pd(0), respectively. The roles of homogeneous PdCl(2) and Pd(0) clusters are discussed. 相似文献
Reaction of 1-trimethylsilylalkyne with copper(I) chloride in a polar solvent, DMF, at 60 degrees C under an aerobic conditions smoothly undergoes homo-coupling to give the corresponding symmetrical 1,3-butadiynes in 70-99% yields. In addition, (arylethynyl)trimethylsilanes are found to couple with aryl triflates and chlorides in the presence of Cu(I)/Pd(0) (10 mol %/5 or 10 mol %) cocatalyst system to give the corresponding diarylethynes in 49-99% yields. The cross-coupling reaction is applied to a one-pot synthesis of the corresponding unsymmetrical diarylethynes from (trimethylsilyl)ethyne via sequential Sonogashira-Hagihara and the present cross-coupling reactions using two different aryl triflates. The reactions of (arylethynyl)trimethylsilanes with aryl(chloro)ethynes in the presence of 10 mol % of CuCl also yield the corresponding unsymmetrical 1,3-butadiynes in 43-97% yields. 相似文献