A fluoroalkene-soluble tetrakis[heptadecafluorononyl]-substituted Pd(II)-phthalocyanine complex has been studied for olefin (styrene, 1-octene, trans-2-octene and cyclohexene) hydrogenation with molecular hydrogen in an organic/fluorous biphasic system [n-hexane/perfluoromethylcyclohexane (PFMCH)]. The palladium complex was found to be an active catalyst for styrene (100% conversion, TON = 634) and 1-octene (92%, TON = 596) at 80 °C and 15 bar of H2 after 6 h of reaction time. The catalyst was recycled in nine consecutive reactions for the hydrogenation of styrene without the loss of activity or metal contamination. 相似文献
The synthesis of a new coordinating polymer containing nitrogen atoms by the copolymerization of a 15-membered triolefinic azamacrocycle, 9, named (E,E,E)-1-[(4-methylphenyl)sulfonyl]-6-[(2-trimethylsilylethyl)sulfonyl]-11-[(4-vinylphenyl)sulfonyl)]-1,6,11-triazacyclopentadeca-3,8,13-triene, with styrene is achieved. The novel polymeric material is characterized by means of elemental analysis, IR, 13C-CP MAS, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques. We also report the study of palladium and platinum sorption from acidic solutions. A capacity of 0.36 mmol g−1 of polymer for Pd(II) and 0.28 mmol g−1 of polymer for Pt(IV) is determined by the batch-mode. The functionalised polymer presents a high selectivity towards precious metals over base metals such us Cu(II) and Ni(II). 相似文献
bis-Benzonitriledichloropalladium(II) [(PhCN)2PdCl2] has been supported on two copolymers containing carboxyl and pyridyl groups and has been employed as a catalyst for the hydrogenation of olefins under mild conditions. The coordination environment and the nature of the metal species on the polymer have been studied by IR, ESCA, X-ray and a chemical test based on KCN treatment. Based on experimental evidence it is proposed that the polymer-palladium complexes initially contain palladium atoms with chlorine atom bridges which are cleaved in the activation. The catalysts were found to be active towards the hydrogenation of olefins under ambient conditions (room temperature and 1 atmosphere total pressure). The kinetic and mechanistic aspects of the hydrogenation of styrene and acrylonitrile and recycling capacity data using one catalyst (Cat-I) are reported. 相似文献
A highly efficient head‐to‐tail dimerization of a styrene was developed using a cationic palladium(II)‐catalyzed selective C C bond forming reaction. The complex [AllylPd(PPh3)]+OTf−, which is believed to generate ‘palladium hydride’ (Pd H), catalyzed the dimerization of various styrenes in excellent yields as single isomers. This Pd(II)‐catalyzed reaction provides a new economical C C bond forming method.
Complexation of palladium(II) acetate [Pd(OAc)2] or dipotassium tetrachloropalladate [K2PdCl4] to “click” polymers functionalized with phenyl, ferrocenyl and sodium sulfonate groups gave polymeric palladium(II)‐triazolyl complexes that were reduced to “click” polymer‐stabilized palladium nanoparticles (PdNPs). Transmission electron microscopy (TEM) showed that reduction using sodium borohydride (NaBH4) produced PdNPs in the 1–3 nm range of diameters depending on the nature of the functional group, whereas slow reduction using methanol yielded PdNPs in the 22–25 nm range. The most active of these PdNPs (0.01% mol Pd), stabilized by poly(ferrocenyltriazolylmethyl)styrene, catalyzed the hydrogenation of styrene at 25 °C and 1 atm hydrogen, with turnover numbers (TONs) of 200,000. When stabilized by the water‐soluble poly(sodium sulfonate‐triazolylmethyl)styrene, the PdNPs (0.01% mol Pd) catalyze the Suzuki–Miyaura coupling between iodobenzene (PhI) and phenylboronic acid [PhB(OH)2] in water/ethanol (H2O/EtOH) at 25 °C with TONs of 8,200. This high catalytic activity is comparable to that obtained with “click” dendrimer‐stabilized PdNPs under ambient conditions. 相似文献
In this paper, we report methods for correction of selectivity of sorbents based on N-(2-sulfoethyl)chitosan towards platinum(IV) and palladium(II) in HCl solutions. The common method for correction of selectivity of the sorbents is variation of their modification degree with complexing groups. An increase in the degree of sulfoethylation of the chitosan leads to the significant increase in selectivity of sorption of palladium(II) over platinum(IV). Application of the N-(2-sulfoethyl)chitosan with the highest degree of sulfoethylation allows for selective separation palladium(II) from platinum(IV) (рН = 5.0). Palladium is quantitatively desorbed from the surface of the N-(2-sulfoethyl)chitosans by 3.5 mol/dm3 solution of HCl. 相似文献
The room temperature ionic liquid [bmim][PF6] was employed as the reaction medium in the asymmetric glyoxylate-ene reaction of α-methyl styrene (4a) with ethyl glyoxylate using chiral palladium(II) complexes as the catalysts. [Pd(S-BINAP)(3,5-CF3-PhCN)2](SbF6)2 (1b) showed the highest catalytic activity. Under the reaction conditions of 40 °C, 0.5 h, and 1b/4a molar ratio of 0.05, ethyl α-hydroxy-4-phenyl-4-pentenoate was obtained in excellent chemical yield (94 %) with high enantioselectivity (70 %). Other α-hydroxy esters can also be obtained in high chemical yields and enantioselectities through the glyoxylate-ene reactions of alkenes with glyoxylates catalyzed by 1b in [bmim][PF6]. Moreover, the ionic liquid [bmim][PF6] which contained the palladium(II) complex could be recycled and reused several times without significant loss of the catalytic activity. 相似文献
Metal-catalyzed cross-coupling reactions, notably those permitting C-C bond formation, have witnessed a meteoritic development and are now routinely employed as a powerful synthetic tool both in academia and in industry. In this context, palladium is arguably the most studied transition metal, and tertiary phosphines occupy a preponderant place as ancillary ligands. Seriously challenging this situation, the use of N-heterocyclic carbenes (NHCs) as alternative ligands in palladium-catalyzed cross-coupling reactions is rapidly gaining in popularity. These two-electron donor ligands combine strong sigma-donating properties with a shielding steric pattern that allows for both stabilization of the metal center and enhancement of its catalytic activity. As a result, the number of well-defined NHC-containing palladium(II) complexes is growing, and their use in coupling reactions is witnessing increasing interest. In this Account, we highlight the advantages of this family of palladium complexes and review their synthesis and applications in cross-coupling chemistry. They generally exhibit high stability, allowing for indefinite storage and easy handling. The use of well-defined complexes permits a strict control of the Pd/ligand ratio (optimally 1/1), avoiding the use of excess costly ligand that usually requires end-game removal. Furthermore, it partly removes the "black box" character often associated with cross-coupling chemistry and catalyst formation. In the present Account, four main classes of NHC-containing palladium(II) complexes will be presented: palladium dimers with bridging halogens, palladacycles, palladium acetates and acetylacetonates, and finally pi-allyl complexes. These additional ligands are best described as a protecting shell that will be discarded going from the palladium(II) precatalyst to the palladium(0) true catalyst. The synthesis of all these precatalysts generally requires simple and short synthetic procedures. Their catalytic activity in different cross-coupling reactions is discussed and put into context. Remarkably, some NHC-containing catalytic systems can achieve extremely challenging coupling reactions such as the formation of tetra-ortho-biphenyl compounds and perform reactions at very low loadings of palladium (ppm levels). The chemistry described here, combining fundamental organometallic, catalysis, and pure organic methodology, remains rich in opportunities considering that only a handful of palladium(II) architectures have been studied. Hence, en route to an "ideal catalyst", [(NHC)Pd(II)] compounds exhibit remarkable stability and allow for fine-tuning of the NHC and of surrounding ligands in order to control the activation and the catalytic activity. Finally, unlike [Pd(PPh(3))(4)], [(NHC)Pd(II)] compounds have so far been examined only in palladium-mediated reactions (most often cross-coupling such as the Suzuki-Miyaura and Heck reactions), leaving a treasure trove of exciting discoveries to come. 相似文献
Summary Some complexes derived from platinum(II) and palladium(II) initiate stereospecific polymerization of methylthiirane in homogeneous phase.When the metal environment is chiral no stereoelective polymerization occurs. The mechanism of polymerization initiated by platinum complexes seems to be similar to those proposed for zinc or cadmium derivatives whereas analogies are apparent between palladium and some aluminum derivatives, especially in the formation of great amounts of disulfide bonds during the polymerization. 相似文献
This article addresses the economic feasibility of silica and palladium composite membranes for gaseous dehydrogenation reaction schemes. Unlike other methodologies addressed so far, this work presents the economic assessment of dehydrogenation reaction schemes using a conceptual design based simulation methodology for the comparative economic assessment of membrane reactors with conventional reactors. The suggested methodology is applied to two industrially prominent reaction schemes namely styrene (from ethylbenzene) and propylene (from propane) production using silica and palladium composite membrane reactors. Various sub-cases studied in this work include the influence of membrane area per reaction zone volume, reaction zone temperature, reaction and permeation zone pressure, membrane thickness and sweep gas flow rate on process economics. Based on this work, the propylene production scheme is evaluated to provide 60–70% excess profits using membrane reactors when compared with the conventional reactor based technology. However, the gross profit profiles for both conventional reactor and membrane reactor configurations have been found to be similar for styrene production case. For all cases, the cost contribution of membranes and other auxiliary equipment is estimated not to exceed 20% of the total costs. In addition, similar economic performance has been observed for both silica and palladium membranes. Based on these studies, it has been concluded that the industrial applicability of membrane reactors is economically suitable for those dehydrogenation reactions that enable significant conversion enhancement with respect to the conventional reactor technologies. 相似文献
ABSTRACT A new Schiff base extractant, N,N'-bis[l-phenyl-3-methyl-5-hydroxy-pyrazole-4-benzylidenyl]-l,3-propylene diamine (H2A) was synthesized and characterized. The extraction mechanism of palladium(II) from HNO3 or HClO4 medium with H2A in chloroform or toluene was investigated. The influences of the Schiff base concentration in the organic phase, the concentration of palladium, the pH and anions (Cl?, S04?, NO3?, ClO4?) in the aqueous phase and the temperature on the distribution ratio for palladium (II) have been examined. The extracted complex has been confirmed by chemical analysis, thermoanalyses and IR spectroscopy. It was found that palladium is extracted according to the following extraction reaction: The extraction equilibrium constants of palladium(II) were 8·4 and 21·3 in chloroform and toluene diluents, respectively. The values for the enthalpy and standard free energy of extraction were also obtained. The separation of Pd(II) from the mixed solution of Pd(II)-Pt(IV) was achieved by adjusting the pH. 相似文献
From palladium(II) or platinum(II) bis(isonitrile) complexes and from gold(I) isonitrile complexes, both easily available from simple precursors, the corresponding mono‐N‐heterocyclic carbene (NHC) complexes could be obtained selectively in good yields under very mild conditions. The reagents are simple β‐chloroammonium salts in the presence of a weak base. Unsymmetric NHC complexes are accessible. Thus over only two steps from simple metal precursors a broad variety of NHC complexes is available, the method is ideal to quickly assemble catalyst libraries. The palladium complexes are active pre‐catalysts in Suzuki cross‐coupling even with the additional isonitrile ligand on palladium. 相似文献
Formic acid oxidation on palladium submonolayers on well-defined Pt(100) and Pt(111) electrodes has been studied using voltammetry and Differential Electrochemical Mass Spectrometry (DEMS). A combination of the two techniques allows a better understanding of the reaction taking place on the electrode surface. Thus, an exact correlation between the CO2 mass signal and the current density in the voltammogram corresponding to the formic acid oxidation has been obtained. On palladium modified Pt(100) electrodes and in the potential region below 0.3 V, the currents in the positive scan are higher than those recorded in the negative scan. This diminution on the signal in the negative scan has been associated with CO2 reduction to CO on the palladium adlayer. In addition, the CO2 reduction reaction seems to take place on the border of the palladium islands. Finally, the adsorption of (bi)sulfate anions has an inhibiting behavior on the formic acid oxidation reaction. 相似文献
New perfluoroalkylated polystyrene resins have been prepared by the suspension polymerisation of 4‐(perfluoro‐n‐octyl)styrene. The evaluation of these highly fluorinated insoluble materials as catalyst supports for rhodium‐catalysed hydrogenation of styrene and palladium‐mediated Suzuki–Miyaura carbon‐carbon bond forming reactions with 4‐bromoacetophenone and 4‐bromoanisole revealed improvements in the recycling of the perfluoroalkylated catalysts as compared to that achieved using fluorous reverse‐phase silica gel. 相似文献