Design and Synthesis of Bis-thioureas Ligands for Pd-Catalyzed Heck Reaction

The palladium-catalyzed arylation of olefins (the Heck reaction) is one of the most versatile tools for C-C bond formation in organic synthesis. Phosphine ligands are generally used to stabilize the reactive palladium intermediates, the air-sensitivity of phosphine ligands, however, places significant limits on their synthetic applications. Recently, Yang1 and we2 have reported Heck and Suzuki reactions of highly active arenediazonium salts and halides catalyzed by air-stable monothiourea-Pd…     

Aqueous-phase, palladium-catalyzed cross-coupling of aryl bromides under mild conditions, using water-soluble, sterically demanding alkylphosphines

Sterically demanding, water-soluble alkylphosphines have been used in combination with various palladium salts in Suzuki, Sonogashira, and Heck couplings of aryl bromides under mild conditions in aqueous solvents. The tert-butyl-substituted ligands 2-(di-tert-butylphosphino)ethyltrimethylammonium chloride (t-Bu-Amphos) and 4-(di-tert-butylphosphino)-N,N-dimethylpiperidinium chloride (t-Bu-Pip-phos) in combination with palladium(II) salts were found to give catalysts that were significantly more active than catalysts derived from tri(3-sulfonatophenyl)phosphine trisodium (TPPTS). Suzuki couplings of unactivated aryl bromides occurred efficiently at room temperature in water/acetonitrile and water/toluene biphasic mixtures or in neat water. Notably, Suzuki couplings of hydrophilic aryl bromides gave high yields without using organic solvents for the reaction or purification. This methodology has been applied to a highly efficient synthesis of diflunisal. The catalyst derived from t-Bu-Amphos was recycled three times in Suzuki couplings in water/toluene before catalyst activity began to significantly drop. The average yield of four cycles was >80% per cycle. Heck and Sonogashira couplings were carried out under mild conditions (50 and 80 degrees C, respectively) with unactivated aryl bromides to give coupled products in high yield.     

Effective binuclear Pd(II) complexes for Suzuki reactions in water

A series of new ionic binuclear Pd(II) complexes supported by water‐soluble bis(α‐diimine) ligands were prepared and employed as catalysts for the palladium‐catalyzed Suzuki reaction in aqueous media. The binuclear nature of the complexes increased the reaction rate, while electronic and steric modification of the ligand frameworks had a remarkable influence upon the catalytic activity of the palladium complexes. The catalysts were shown to be homogeneous through mercury poisoning experiments and complexes could be recycled more than 10 times without loss of catalytic activity. Copyright © 2013 John Wiley & Sons, Ltd.     

Pd(quinoline-8-carboxylate)(2) as a low-priced, phosphine-free catalyst for Heck and Suzuki reactions

N,O-Bidentate compounds were systematically evaluated as phosphine-free ligands for Pd-catalyzed C-C bond-formation reactions through kinetic measurements. Pd(quinoline-8-carboxylate)2 was identified as one of the most efficient, yet still low-priced, phosphine-free catalysts for Heck as well as Suzuki reactions of unactivated aryl bromides with high turnover numbers up to ca. 10,000.     

High-intensity ultrasound and microwave, alone or combined, promote Pd/C-catalyzed aryl-aryl couplings

Pd-catalyzed homo- and cross-couplings of boronic acids and aryl halides were successfully carried out both in aqueous media under high-intensity ultrasound (US) and in DME under microwave (MW). Heterogeneous catalysis with Pd/C was employed, avoiding phosphine ligands and phase-transfer catalysts. In a trial series involving 15 different iodo- and bromoaryls and 7 boronic acids, both energy sources drastically reduced reaction times affording biaryls in acceptable to good yields. With palladium(II) acetate as catalyst, electron-deficient aryl chlorides also reacted, affording a few biaryls in acceptable yields. Ullmann-type zinc-mediated homocoupling of iodo- and bromoaryls in the presence of Pd/C under CO₂ atmosphere was achieved in aqueous media under US, though not under MW. Suzuki homo- and cross-couplings were also carried out in a new reactor developed in our laboratory, featuring combined US and MW irradiation, further improving a green synthetic method.     

无配体Pd/LDH-F催化剂在Heck和Suzuki反应中的应用

 以氟离子插层的水滑石LDH-F为载体,用逐滴浸渍法制备了新型Pd/LDH-F催化剂,并用其催化溴代芳烃的Heck和Suzuki偶联反应. 用X射线衍射表征了催化剂的晶相,以等离子体发射光谱测定了溶剂中钯的流失量. 结果表明,对于Heck反应,在无配体存在和低钯用量(Pd/溴代芳烃摩尔比为0.001)的情况下, Pd/LDH-F的催化性能优于其它载体负载的Pd催化剂,显示出很高的催化活性和选择性. 在140 ℃和12 h的条件下, Pd/LDH-F催化溴苯与苯乙烯Heck反应产物的收率可达86％, 反应后催化剂经过分离,可循环使用四次其催化活性基本不变. 在DMF/水摩尔比为0.5的混合溶剂中,在室温和3 h 的条件下, Pd/LDH-F (Pd/溴代芳烃摩尔比为0.005)催化溴苯与苯基硼酸盐的Suzuki反应中,目标产物收率为99%.     

Catalytic activity of palladium supported on single wall carbon nanotubes compared to palladium supported on activated carbon Study of the Heck and Suzuki couplings, aerobic alcohol oxidation and selective hydrogenation

Nanoparticles (2–10 nm) of palladium have been deposited on single wall carbon nanotubes (SWNT) by spontaneous reduction from Pd(OAc)₂ or from oxime carbapalladacycle. These catalysts exhibit higher catalytic activity than palladium over activated carbon (Pd/C) for the Heck reaction of styrene and iodobenzene and for the Suzuki coupling of phenylboronic and iodobenzene. This fact has been attributed as reflecting the dramatic influence of the size particle on the activity of the palladium catalyst for CC bond forming reactions as compared to other reaction types less demanding from the point of view of the particle size. Thus, in contrast to the Heck and Suzuki reactions, Pd/C is more active than palladium nanoparticles deposited on SWNT for the catalytic oxidation by molecular oxygen of cinnamyl alcohol to cinnamaldehyde and for the hydrogenation of cinnamaldehyde to 3-phenylpropionaldehyde.     

Cyclopalladated complexes of 2-phenylaniline and their catalytic activity in Suzuki and Heck reactions under mild conditions

A series of palladium complexes bearing monodentate and bidentate ligands were applied in the Suzuki reaction of aryl halides and the Heck reaction of styrene with phenylboronic acid. The complexes were found to be effective catalysts for these reactions affording the cross-coupled products in moderate to excellent yields.     

A COMPARATIVE STUDY OF SOME Pd-CATALYSED HECK REACTIONS IN POLAR- AND AQUEOUS BIPHASIC MEDIA

A comparative study of some Pd-catalysed reactions was carried out making use of various ligands and catalyst precursors in polar polar/aqueous biphasic media, the results of which assist in the judicious selection of the appropriate reaction conditions for such Heck reactions.     

Palladium nanoparticles supported on agarose‐catalyzed Heck–Matsuda and Suzuki–Miyaura coupling reactions using aryl diazonium salts

In this article, palladium nanoparticles supported on agarose were used as an efficient catalyst for Heck–Matsuda and Suzuki–Miyaura coupling reactions of structurally different aryldiazonium tetrafluoroborate substrates in aqueous media. Heck–Matsuda reactions proceeded at 40°C whereas Suzuki‐Miyaura reactions were carried out at room temperature. Both reactions required low catalyst loading. The catalyst was also recycled for the model reaction for three runs. Copyright © 2012 John Wiley & Sons, Ltd.     

Recyclable and eco-friendly Pd-complexed graphene oxide/N-heterocyclic carbene catalyst for various coupling reactions in aqueous phase

In this study, we report recyclable Pd-complexed graphene oxide (GO) catalysts with a bulky N-heterocyclic carbene (NHC) ligand (GO/NHC-Pd) for various cross-coupling reactions in the aqueous phase. To prepare GO/NHC-Pd, the NHC precursor and a trimethoxy-silane linker were combined on the GO surface via condensation, followed by the Pd chelation over GO/NHC. The GO-based catalysts were applied to three types of CC cross-coupling reactions including Suzuki, Heck and Sonogashira reactions in the aqueous phase, to evaluate their catalytic performance. The reusability of the catalysts was tested by performing five consequent cross-coupling reactions.     

Pd nanoparticle catalysed one-pot sequential Heck and Suzuki couplings of bromo-chloroarenes in ionic liquids and water

Pd nanoparticles generated in green reaction media (viz. ionic liquids and water) catalyze the one-pot sequential Heck and Suzuki coupling reactions of bromo-chloroarenes to afford unsymmetrically substituted arenes in good yields.     

Reusable,magnetic Raney nickel based palladium catalysts for the Heck coupling in aqueous media

Russian Chemical Bulletin - Hybrid materials based on Pd- and Cu-doped Raney nickel appeared to be highly efficient catalysts for the Heck reaction in aqueous media in the absence of organic...     

Phosphorylated PEG (PPEG) as a new support for generation of nano‐Pd(0): application to the Heck–Mizoroki and Suzuki–Miyaura coupling reactions

Polyethylene glycols (PEGs) with different molecular weights (M_w = 200, 400, 1000) were phosphorylated to their bis‐diphenyl phosphinite derivatives as stable solids which are melted in the range 140–160°C. These phosphorylated PEGs were used as ligands and reducing agents to generate nano‐Pd(0) catalysts in 2.5–8.3 nm. The nano‐Pd(0) particles supported on phosphorylated PEG₂₀₀ were applied for the efficient Heck–Mizoroki carbon–carbon coupling reactions of ArX (X = Cl, Br, I) at 80–100°C under solvent‐free conditions and for the Suzuki–Miyaura coupling reaction in ethanol at 70°C. The catalyst was recycled easily and reused for several runs. Copyright © 2013 John Wiley & Sons, Ltd.     

含有酯基二茂铁亚胺环钯化合物催化Suzuki和Heck反应

合成并表征了系列含有酯基二茂铁亚胺环钯化合物.结果表明,该系列环钯催化剂在纯水或有机溶剂中均能高效催化Heck和Suzuki偶联反应.     

Efficient aqueous-phase Heck and Suzuki couplings of aryl bromides using tri(4,6-dimethyl-3- sulfonatophenyl)phosphine trisodium salt (TXPTS)

[reaction: see text] Sterically demanding, sulfonated arylphosphines TXPTS and TMAPTS have been applied to the aqueous-phase Heck and Suzuki coupling of aryl bromides. TXPTS provides good yields of Heck coupling products from aryl bromides at 80 degrees C, while both TMAPTS and TPPTS gave significantly less active catalysts. TXPTS is the first ligand to promote the aqueous-phase Heck coupling under such mild conditions. Both TXPTS and TMAPTS provide active catalysts for Suzuki couplings of aryl bromides at 50 degrees C.     

Organometall‐Reaktionen in Wasser

Water has attracted significant attention as an alternative solvent for organometallic reactions because it is nontoxic, nonflammable, and inexpensive, and is easily separated from organic products. Organometallic reactions, like the palladium‐catalyzed couplings of organic halides with organoboron compounds (Suzuki) and organotin reagents (Stille), are among the most widely used reactions for the formation of carbon‐carbon bonds. Owing to the discovery of water‐soluble, sulfonated phosphane derivatives and particularly the design of water‐soluble palladium‐catalysts it was possible to import these reactions into aqueous media. Another efficient, metal‐catalyzed, carbon‐carbon bond‐forming process that is nowadays possible in aqueous media is the olefin metathesis. The approaches so far include the use of water‐soluble ruthenium‐catalysts, surfactants and additives, ultrasonication, the introduction of polar quaternary ammonium groups or the incorporation of PEG as a water solubilizing moiety. The last point bears also a great potential for further developments in the removal of ruthenium‐containing byproducts. Additionally, water is the ideal reaction environment for polar, water soluble substrates such as natural product or pharmaceuticals.     

Heck reactions of iodobenzene and methyl acrylate with conventional supported palladium catalysts in the presence of organic and/or inorganic bases without ligands

The vinylation of iodobenzene with methyl acrylate has been studied with several supported palladium catalysts in N-methylpyrrolidone in the presence of triethylamine and/or sodium carbonate. The reaction can be performed in air without any solubilizing or activating ligands. It was found that significant amounts of palladium leach out into the solvent and these dissolved Pd species essentially catalyze the reaction. It is interesting, however, that almost all the palladium species in the solution can redeposit onto the surface of the supports after the reaction has been completed (at 100% conversion of iodobenzene). Thus, the catalysts were recyclable without loss of activity. The use of both inorganic and organic bases is very effective in the promotion of the palladium redeposition as well as in the enhancement of the reaction rate. For Heck reactions with bromobenzene and chlorobenzene it was found that the use of triethylamine and sodium carbonate increases the selectivity of the Heck coupling product (benzene is also produced for these two substrates), but the mixed bases do not affect the overall rate of reaction as much.     

Selenium-ligated palladium(II) complexes as highly active catalysts for carbon-carbon coupling reactions: the Heck reaction

Three selenium-ligated Pd(II) complexes were readily synthesized and shown to be extremely active catalysts for the Heck reaction of various aryl bromides, including deactivated and heterocyclic ones. The catalytic activity of the selenide-based Pd(II) complexes not only rivals but vastly outperforms that of the corresponding phosphorus and sulfur analogues. Practical advantages of the selenium-based catalysts include their straightforward synthesis and high activity in the absence of any additives as well as the enhanced stability of the selenide ligands toward air oxidation.     

Controlled synthesis of hydroxyapatite-supported palladium complexes as highly efficient heterogeneous catalysts

Achieving precise control of active species on solid surfaces is one of the most important goals in the development of highly functionalized heterogeneous catalysts. The treatment of hydroxyapatites with PdCl(2)(PhCN)(2) gives two new types of hydroxyapatite-bound Pd complexes. Using the stoichiometric hydroxyapatite, Ca(10)(PO(4))(6)(OH)(2), we found that monomeric PdCl(2) species can be grafted on its surface, which are easily transformed into Pd(0) particles with narrow size distribution in the presence of alcohols. Such metallic Pd species can effectively promote alcohol oxidation using molecular oxygen and are shown to give a remarkably high TON of up to 236 000. Another monomeric Pd(II) phosphate complex can be generated at a Ca-deficient site of the nonstoichiometric hydroxyapatite, Ca(9)(HPO(4))(PO(4))(5)(OH), affording a catalyst with Pd(II) structure and high activity for the Heck and Suzuki reactions. To the best of our knowledge, the PdHAP are one of the most active heterogeneous catalysts for both alcohol oxidation under an atmospheric O(2)() pressure and the Heck reaction reported to date. These Pd catalysts are recyclable in the above organic reactions. Our approach to catalyst preparation based on the control of Ca/P ratios of hydroxyapatites represents a particularly attractive method for the nanoscale design of catalysts.