羧甲基纤维素负载钯催化剂的制备及对Heck反应的催化性能

通过较简单的方法合成了羧甲基纤维素钠负载钯(0)配合物,用XPS、TG、DTA等手段对其进行了表征。该配合物在空气氛围中、较低温度下能很好地催化丙烯酸、苯乙烯与芳基碘的Heck反应,立体选择性地生成取代的反式肉桂酸、1,2-二苯乙烯。羧甲基纤维素钠负载钯(0)配合物能够较方便地从反应体系中分离出来,具有较好的重复使用性能。     

Catalytic Activity of a Thermoregulated, Phase-Separable Pd(II)-perfluoroalkylphthalocyanine Complex in an Organic/Fluorous Biphasic System: Hydrogenation of Olefins

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.     

Selective Pd(II) and Pt(IV) sorption using novel polymers containing azamacrocycle functional groups

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).     

Studies on the hydrogenation of olefins using polymer-bound palladium (II) species

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.     

聚苯乙烯负载二环己胺钯催化Heck反应的研究

以聚苯乙烯树脂为载体、二环己胺为配体制备聚苯乙烯负载胺钯催化剂。采用XPS、XRD、TG、DTA和SEM等方法对其进行表征,针对不同催化体系探讨丙烯酸、苯乙烯与芳基碘的Heck反应的催化性能。结果表明,高分子胺配体与钯之间形成配位作用,制备的催化剂在室温～200 ℃有较好的热稳定性。该负载型催化剂在N₂氛围只需少量的催化剂就能较好地催化丙烯酸、苯乙烯与芳基碘的Heck反应,较高收率地生成取代的反式肉桂酸和1,2-二苯基乙烯。     

A highly efficient polymer‐anchored palladium(II) complex catalyst for hydrogenation,Heck cross‐coupling and cyanation reactions

BACKGROUND: Precise architectures of steric and electronic properties of palladium species play a crucial role in designing highly functionalized catalyst systems responsible for target organic transformations. Pd catalysts supported on polymer materials have been employed extensively as catalysts not only for hydrogenation but also for coupling reactions in the production of fine chemicals. RESULTS: A new polymer‐anchored Pd(II) complex has been synthesized and characterized. The catalyst shows high catalytic activity in the hydrogenation of styrene oxide, Heck cross‐coupling and cyanation reactions of aryl halides. The effect of various reaction parameters were investigated to optimize reaction conditions. The catalytic system shows good activity in the hydrogenation of styrene oxide (conversion 98%) with a selectivity to 2‐phenylethanol (93%) which is higher than its homogeneous analogues. The catalyst also exhibits excellent catalytic activity for the Heck cross‐coupling and cyanation reactions of various substituted and non‐substituted aryl halides. CONCLUSIONS: Results demonstrate that the catalyst is robust and stable and can be recovered quantitatively by simple filtration and reused several times without loss of activity. Copyright © 2010 Society of Chemical Industry     

Highly Efficient Catalytic Dimerization of Styrenes via Cationic Palladium(II) Complexes

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.

     

Polymer–metal composite particles: Metal particles on poly(St‐co‐MAA) microspheres

Poly(styrene‐co‐methacrylic acid) P(St‐co‐MAA) microspheres with a monodisperse size distribution were prepared by emulsifier‐free emulsion copolymerization of St and MAA. The effects of MAA content on the polymerization rate and the content of MAA in the copolymer were investigated by gravimetrical and IR methods, respectively. The results of XPS measurement indicated the presence of a carboxyl functional group. By chemical metal deposition, nickel or palladium particles were formed and deposited on the surface of P(St‐co‐MAA) microspheres to form P(St‐co‐MAA)Ni or P(St‐co‐MAA)Pd composite particles. XRD measurement and TEM observation confirmed that nickel and palladium metal particles in a small size (20–40 nm) were distributed on surface of the copolymer microspheres. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1693–1698, 2000     

“Click” Polymer‐Supported Palladium Nanoparticles as Highly Efficient Catalysts for Olefin Hydrogenation and Suzuki Coupling Reactions under Ambient Conditions

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.     

Methods for correction of selectivity of N-(2-sulfoethyl)chitosan-based materials towards platinum(IV) and palladium(II) ions

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.     

Asymmetric Glyoxylate-Ene Reactions Catalyzed by Chiral Pd(II) Complexes in the Ionic Liquid [bmim][PF6]

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.     

Well-defined N-heterocyclic carbenes-palladium(II) precatalysts for cross-coupling reactions

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.     

Polymerization of Methylthiirane initiated by platinum(II)- and palladium(II)-complexes

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.     

Economic feasibility of silica and palladium composite membranes for industrial dehydrogenation reactions

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.     

Nonlinear stress relaxation in palladium(II) complexes with triblock copolymers of styrene and butadiene

Above 200% strain, the mechanical response of triblock copolymers which contain styrene and butadiene is modified significantly by complexation with dichlorobis(acetonitrile)palladium(II). This pseudosquare‐planar transition metal salt forms π‐complexes with, and catalyzes the dimerization of, alkene groups in the main chain and the side group of Kraton's butadiene midblock. Between 10 and 100% strain, the plastic flow regime is similar for undiluted Kraton? and its Pd²⁺ complexes, but the level of engineering stress is approximately twofold larger for the complex that contains 4 mol % palladium(II) [Pd(II)]. Nonlinear stress relaxation measurements in the plastic flow regime (i.e., beyond the yield point but before the large upturn in stress) are analyzed at several different levels of strain. Transient relaxation moduli were modeled by a three‐parameter biexponential decay with two viscoelastic time constants. The longer relaxation time for Kraton? increases at higher strain, and in the presence of 4 mol % palladium chloride. A phenomenological model is proposed to describe the effect of strain on relaxation times. This model is consistent with the fact that greater length scales are required for cooperative segmental reorganization at larger strain. The resistance Ω to conformational reorganization during stress relaxation is estimated via integration of the normalized relaxation modulus versus time data. This resistance increases at higher initial jump strain because conformational rearrangements are influenced strongly by knots and entanglements at larger strain. The effect of strain on Ω is analyzed in terms of time‐strain separability of the relaxation modulus. Linear behavior is observed for Ω versus inverse strain (i.e., 1/ε), and the magnitude of the slope [i.e., ?dΩ/d(1/ε)] is threefold larger in the absence of PdCl₂(CH₃CN)₂. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1329–1336, 2004     

SOLVENT EXTRACTION OF PALLADIUM(II) WITH A SCHIFF BASE AND SEPARATION OF PALLADIUM FROM Pd(II)-Pt(VI) MIXTURE

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.     

Carbenes Made Easy: Formation of Unsymmetrically Substituted N‐Heterocyclic Carbene Complexes of Palladium(II), Platinum(II) and Gold(I) from Coordinated Isonitriles and their Catalytic Activity

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.     

Poly(N‐isopropylacrylamide) gel‐based macroporous monolith for continuous‐flow recovery of palladium(II) ions

Macroporous monoliths, composed of thermoresponsive, tertiary‐aminated, and crosslinking monomers, were prepared for continuous‐flow separation of palladium(II) ions. N ‐Isopropylacrylamide was required to form the porous structure in the monoliths, indicating that the mechanism of porous structure formation involved polymerization‐induced phase separation of the poly(N ‐isopropylacrylamide) gel. Tertiary‐aminated monoliths showed adsorption selectivity for palladium(II) ions in hydrochloric media, compared with copper(II) ions. The maximum capacities of the monoliths with tertiary amine contents of 10, 20, 30, and 70 mol % for palladium(II) ions were 0.6, 1.1, 1.3, and 2.3 mmol/g, respectively. Darcy's permeabilities of water through the macroporous monolith were 10^?14 to 10^?13 m², and those were comparable to that through a commercially available membrane filter with a pore size of several micrometers. In the continuous‐flow process, the macroporous monolith with tertiary amine selectively adsorbed palladium(II) ions in the coexistence of copper(II) ions with 10 times higher concentration than the palladium(II) ions. The palladium(II) ions were eluted from the macroporous monolith, and the concentration of palladium(II) ions in the eluate was up to 45 times of that in the feed solution. The average enrichment factor and total recovery percentage of palladium(II) ions were 8.7 times and 95%, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44385.     

Formic acid oxidation on Pd-modified Pt(100) and Pt(111) electrodes: A DEMS study

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.     

Insoluble Perfluoroalkylated Polymers: New Solid Supports for Supported Fluorous Phase Catalysis

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.