Carbonylative Stille coupling reactions of benzyl chlorides with allyltributylstannane catalyzed by palladium nanoparticles

The carbonylative Stille coupling reaction of benzyl chlorides with allyltributylstannane was successfully conducted by using palladium nanoparticles as the catalyst under phosphine ligand-free conditions. The corresponding α,β-unsaturated ketone products were obtained in good to excellent yields.     

纳米钯催化苄基氯代物与烯丙基硼酸频哪醇酯的羧化Suzuki偶联反应

CO2是廉价的C1源,同时具有无毒、储量丰富的优点, 符合绿色化学发展要求. 利用 CO2构筑新的 C–C 键是化学固定CO2的重要方法. Β,γ-不饱和酯类结构单元是许多生物活性分子的重要组成部分, 经由双π-烯丙基钯中间体与 CO2反应, 合成新的β,γ-不饱和酯类化合物, 具有重要意义. CO2与有机硼化合物的羧化反应已有报道, 有机硼化合物具有低毒、对水不敏感等优点. 但是已报道的羧化 Suzuki 偶联反应存在诸多缺点: (1) 需要使用含膦或者氮杂环卡宾配体的催化剂, 而这些催化剂的制备过程使前期实验步骤变得冗长, 同时反应液的酸化后处理过程也会造成环境污染; (2) 有机硼试剂的官能团兼容范围窄, 限制了底物范围的拓展. 本课题组以原位生成的纳米钯粒子为催化剂, 在 CO2存在的温和条件下, 高效实现了苄氯与烯丙基硼酸频哪醇酯的羧化 Suzuki 偶联反应. 反应过程中无其它配体加入, 反应结束后不需要酸化或酯化的后处理过程. 该反应将具有广泛的官能团兼容性.本文以 TBAB 稳定的纳米钯粒子为催化剂, 在温和条件下, 实现了氯甲基芳香化合物、烯丙基硼酸频哪醇酯和 CO2的三组分羧化 Suzuki 偶联反应. 最佳反应条件为: Pd(acac)2(5 mol%)、TBAB (0.7 mmol, 1.4 equiv.)、KF (1 mmol, 2.0 equiv.)、苄基卤代物 (0.5 mmol)、烯丙基硼酸频哪醇酯 (0.6 mmol, 1.2 equiv.)、CO2(2.0 Mpa)、溶剂 THF (5 mL), 50 oC 反应 24 h. 在最佳反应条件下, 苯环、萘环以及杂芳环的氯甲基化合物均可发生该羧化反应. 苯环上取代基的位置对产物的收率有影响. 当使用 1-溴甲基萘作为底物时反应也能够发生, 收率与 1-氯甲基萘作为底物时的收率相当. 与已报道有机硼试剂的羧化反应相比, 该反应体系无需加入配体, 原位生成了纳米钯粒子, 避免了催化剂或者配体的复杂制备过程. 该反应中, 氟离子的存在是必要的, 对烯丙基硼酸频哪醇酯具有活化作用.     

Suzuki cross-coupling reactions catalyzed by palladium nanoparticles in aqueous solution

Palladium nanoparticles stabilized by poly(N-vinyl-2-pyrrolidone) (PVP) are efficient catalysts for the Suzuki reactions in aqueous medium. The time dependence of the fluorescence intensity of the biphenyl product in the reaction between iodobenzene and phenylboronic acid is used to determine the initial rate of the catalytic reaction. The initial rate depends linearly on the concentration of Pd catalyst, suggesting that the catalytic reaction occurs on the surface of the Pd nanoparticles.     

Cross-coupling reactions of aryl and vinyl chlorides catalyzed by a palladium complex derived from an air-stable H-phosphonate

A palladium complex derived from air-stable TADDOLP(O)H catalyzes efficiently Hiyama, Stille, Kumada and Suzuki cross-coupling reactions of aryl and vinyl chlorides.     

Continuous biphasic catalysis: palladium catalyzed cross coupling reactions

The immobilisation of polymer tagged catalysts in a stationary solvent in a reactor and the flow of reactants dissolved in another immiscible solvent through it, allows the conversion of a continuous feed of reactants into a product stream, as exemplified by the Sonogashira coupling of aryl halides and acetylenes.     

Aerobic ligand-free Suzuki coupling catalyzed by in situ-generated palladium nanoparticles in water

A simple and efficient procedure for Suzuki coupling of aryl bromides/iodides with aryl- and alkylboronic acids catalyzed by in situ-generated palladium(0) nanoparticles in water without any ligand in open air to produce a variety of functionalized biaryls and alkyl-aryls has been developed. The boronic acids act here as the reducing agent for the formation of Pd nanoparticles. The reactions are remarkably fast (5 min) and high yielding. The catalyst is recyclable up to three runs without loss of efficiency.     

Microwave-assisted aqueous Suzuki coupling reactions catalyzed by ionic palladium(II) complexes

Suzuki coupling is one of the most powerful methods for the synthesis of biaryls. We have prepared and characterized a series of unsymmetrical sulfonated water-soluble Pd(II)-pyridyl imine complexes and investigated them as catalysts for the Suzuki cross-coupling reaction in water under microwave irradiation. The compounds proved to be effective catalysts.     

Titanium catalyzed one-pot multicomponent coupling reactions for direct access to substituted pyrimidines

A titanium-catalyzed 3-component coupling reaction can be used to generate tautomers of 1,3-diimines. These diimines produced in situ undergo condensation with amidines in a one-pot procedure to provide substituted pyrimidines. Seventeen examples of pyrimidines are provided using this one-pot, 4-component procedure from simple starting materials. In some cases, catalyst architecture can be tuned to control the regioselectivity of the alkyne addition. Finally, the regioselectivity of amidine addition to unsymmetrical 1,3-diimines is discussed.     

Stille coupling reactions catalysed by a polymer supported palladium complex

The coupling between aryl iodides and bromides with organostannanes (Stille reaction) has been investigated in the presence of a polymer supported palladium catalyst. The reaction could be performed in air without any activating ligand and with non-dried solvents. The catalyst, which acts by releasing controlled amounts of soluble active species, could be recycled several times in the coupling between Sn(CH₃)₄ or ⁿBu₃SnPh with iodoarenes or activated bromoarenes.     

Synthesis of pyrazine-bridged diimidazolium salts and their application in palladium catalyzed Heck-type coupling reactions

Reaction of imidazole derivatives with 2,3-di(bromomethyl)pyrazine results in the formation of the new pyrazine-bridged diimidazolium salts 1-8. These salts proved to be valuable precursors for dinuclear complexes with mixed NHC/pyrazine ligands. Two of the pyrazine-bridged diimidazolium salts 3·H₂O and 8·2H₂O have been characterized by X-ray diffraction. Furthermore, the first catalytic studies with mixtures of palladium acetate and the imidazolium salts have been carried out. The in situ prepared palladium complexes derived from the diimidazolium salts 1-8 exhibit a modest catalytic activity in Heck-type coupling reactions between 4-bromo benzaldehyde and styrene or n-butyl acrylate.     

Ligand control in palladium—catalyzed coupling reactions between organozirconium compounds and allylic species

A (π-allylic)Pd(II) complex can serve as a catalyst precursor for selective coupling between allylic halides or acetates and alkenylsirconium complexes.     

Suzuki–Miyaura coupling catalyzed by palladium nanoparticles biosynthesized using Glycyrrhiza glabra as reducing and stabilyzing agent

An unprecedented environmentally friendly method has been developed for the synthesis of palladium nanoparticles supported on Glycyrrhiza glabra. The synthesized nanoparticles were utilized in Suzuki–Miyaura reaction between different aryl halides and aryl bronic acid in aqueous media. This heterogeneous catalyst can be reused and recycled repeatedly more than five times with only slight loss of its initial catalytic efficiency. This reaction carrid out under atmospheric pressure with high efficiency, unique and simple work‐up procedure and excellent yields.     

钯配合物催化的芳基-芳基不对称偶联反应

本文以三种匀性膦作配体制成了零价钯配合物, 并分虽试验了由它们催化苯酚得到的α-溴-β-苄氧基萘和进一步衍生而得的格氏试剂的偶联反应, 制成了β'β'-二苄氧基-α', α'-联萘.     

Sonogashira coupling of aryl halides catalyzed by palladium on charcoal

With the proper choice of solvent, palladium on charcoal acts as an efficient catalyst in the Sonogashira cross-coupling reaction of aryl bromides. The catalytically active species in the process is probably palladium, which leaches into the solution but returns onto the surface of the charcoal at the end of the reaction.     

A case for enantioselective allylic alkylation catalyzed by palladium nanoparticles

Palladium nanoparticles (4 nm, fcc) were prepared through decomposition of [Pd2(dba)3] by H2 in the presence of a chiral xylofuranoside diphosphite. These particles catalyze the allylic alkylation of rac-3-acetoxy-1,3-diphenyl-1-propene with dimethyl malonate leading to an almost total conversion of the (R) enantiomer and almost no reaction with the (S). This gives rise to 97% ee for the alkylation product and a kinetic resolution of the substrate recovered with ca. 90% ee. This behavior was compared to that of a molecular catalyst at various dilutions, and the differences between the two systems are discussed. This is the first colloidal system shown to display such a high enantioselectivity besides the well-known Pt/cinchonidine system.     

Ion- and atom-leaching mechanisms from palladium nanoparticles in cross-coupling reactions

Leaching of palladium species from Pd nanoparticles under C--C coupling conditions was observed for both Heck and Suzuki reactions by using a special membrane reactor. The membrane allows the passage of palladium atoms and ions, but not of species larger than 5 nm. Three possible mechanistic scenarios for palladium leaching were investigated with the aim of identifying the true catalytic species. Firstly, we examined whether or not palladium(0) atoms could leach from clusters under non-oxidising conditions. By using our membrane reactor, we proved that this indeed happens. We then investigated whether or not small palladium(0) clusters could in fact be the active catalytic species by analysing the reaction composition and the palladium species that diffused through the membrane. Neither TEM nor ICP analysis supported this scenario. Finally, we tested whether or not palladium(II) ions could be leached in the presence of PhI by oxidative addition and the formation of [Pd(II)ArI] complexes. Using mass spectrometry, UV-visible spectroscopy and 13C NMR spectroscopy, we observed and monitored the formation and diffusion of these complexes, which showed that the first and the third mechanistic scenarios were both possible, and were likely to occur simultaneously. Based on these findings, we maintain that palladium nanoparticles are not the true catalysts in C--C coupling reactions. Instead, catalysis is carried out by either palladium(0) atoms or palladium(II) ions that leach into solution.     

Highly selective and efficient oxidation of sulfides with hydrogen peroxide catalyzed by a chromium substituted Keggin type polyoxometalate

The catalytic oxidation of sulfides into the corresponding sulfones by a chromium substituted Keggin type polyoxometalate, (TBA)₄[PW₁₁CrO₃₉]·3H₂O, was achieved using mild reaction conditions. Excellent yields were obtained using four equivalents of 30% H₂O₂. Under these reaction conditions, the sulfide group was highly reactive and other functional groups such as hydroxyl or a double bond were unaffected. Using a commercially available, eco-friendly, and cheap oxidant, mild reaction conditions, operational simplicity, practicality, short reaction times, high to excellent yields, and excellent chemoselectivity are some of the advantages of this catalytic system.     

Stereoselective synthesis of 1,3-dienylstannanes by palladium catalyzed cross-coupling reactions

(Z)-α-Bromovinylstannanes are new difunctional group reagents, which undergo palladium catalyzed cross-coupling reactions with (E)-alkenylzirconium complexes to give stereoselectively 1,3-dienylstannanes in good yields.     

Synthesis of small palladium nanoparticles stabilized by bisphosphine BINAP bearing an alkyl chain and their palladium nanoparticle-catalyzed carbon-carbon coupling reactions under room-temperature

A new bisphosphine ligand, C8-BINAP, and C8-BINAP-stabilized palladium nanoparticles have been prepared; C8-BINAP was found to be an effective protecting ligand for preparing and stabilizing palladium nanoparticles with very small core size and narrow size distribution and the C8-BINAP-Pd nanoparticles behave as an efficient catalyst for carbon-carbon coupling reactions at room temperature.     

Biosynthesis of palladium nanoparticles as a heterogeneous and reusable nanocatalyst for reduction of nitroarenes and Suzuki coupling reactions

A facile and green route for the synthesis of palladium nanoparticles (Pd‐NPs) was developed utilizing non‐toxic and renewable natural green tea extract as the reducing, stabilizing and capping agent. The as‐prepared Pd‐NPs@Oak Gum catalyst was characterized using UV–visible spectroscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and energy dispersive X‐ray spectroscopy. The Pd‐NPs@Oak Gum catalyst could be used as an efficient and heterogeneous catalyst for Suzuki coupling reactions between phenylboronic acid and a range of aryl halides containing iodo, bromo and chloro moieties and also for the reduction of nitroarenes using sodium borohydride in an environmental friendly medium. Excellent yields of products were obtained with a wide range of substrates and the catalyst was recycled multiple times without any significant loss of its catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.