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.     

Orthopalladated and -platinated bulky triarylphosphite complexes: synthesis,reactivity and application as high-activity catalysts for Suzuki and Stille coupling reactions

Bulky triarylphosphite ligands undergo facile orthometallation reactions with palladium and platinum precursors. The crystal structure of an example of the resultant palladacycles has been determined. The reactivity of some of the metallacycles with HCl, monodentate and bidentate phosphines and sodium diethyldithiocarbamate has been investigated, and the crystal structure of a diethyldithiocarbamate adduct of a palladacycle is presented. The palladacyclic complexes prove to be extremely active catalysts for the Suzuki coupling of aryl bromides with aryl boronic acids. They can also be used as catalysts for the coupling of alkylboronic acids. Meanwhile di- and trialkyl phosphine adducts of one of the palladacycles shows very high activity in the Suzuki coupling of aryl chlorides and can also be used to good effect for the Stille coupling of these substrates. The role of the phosphite ligand in the Suzuki coupling of aryl chlorides seems to be one of increasing catalyst longevity by stabilisation of the Pd(0) resting state.     

The air-stable and highly efficient P, N-chelated palladium(II) complexes as catalysts for the Suzuki cross-coupling reaction at room temperature

Two air-stable P, N-chelated palladium(II) complexes have been evaluated as highly efficient and simple catalysts for Suzuki cross-coupling reaction between aryl bromides and arylboronic acids. They exhibit high activity and selectivity at room temperature.     

果胶负载钯催化剂的制备及Suzuki反应催化性能

以柑橘皮果胶为载体,采用吸附法制备了果胶负载钯催化剂,并将其应用于四苯硼钠与溴代芳烃的交叉偶联反应中.该反应体系以聚乙二醇400(PEG 400)/H2O为反应溶剂,三乙胺为碱,在空气中于110℃反应15~60 min,四苯硼钠中4个苯基均可顺利参与反应,高产率地获得相应的目标化合物.该方法具有条件温和、反应时间短、收率高且催化剂可循环利用等优点.     

环钯化二茂铁亚胺-三苯基膦配合物的合成、表征及催化Suzuki反应研究

为筛选高效催化Suzuki反应的催化剂, 合成了3种新的环钯化二茂铁亚胺-三苯基膦配合物2~4, 经元素分析(或HRMS)、 红外光谱和核磁共振谱对其结构进行了表征, 并通过X射线单晶衍射测定了化合物3的晶体结构. 这些化合物容易合成, 在空气和溶液中稳定, 可用作芳基溴及杂芳基溴与苯基硼酸偶联的Suzuki反应催化剂. 使用摩尔分数为0.01%的催化剂3, 以2倍量的K3PO4为碱, 于110 ℃下, 在甲苯中反应5~15 h, 使具有不同电子和位阻效应的取代芳基溴及杂芳基溴能以较高的产率与苯基硼酸反应生成偶联产物; 与溴苯相比, 带吸电子基的溴苯反应活性较高, 催化剂的摩尔分数降低至0.001%时, 仍能得到较高产率, 而带强给电子基的溴苯如4-溴苯甲醚及带邻位取代基的溴苯在其它条件相同时, 需要延长反应时间才能得到较高的产率.     

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%.     

The synthesis and characterisation of immobilised palladium carbene complexes and their application to heterogeneous catalysis

Silica supported palladium NHC complexes have been prepared by two different routes: one involving the reaction of silica-supported imidazolium salts with palladium acetate and a direct immobilisation of a pre-formed complex by reacting a (trimethoxysilylpropyl)-N-aryl-imidazolylidene palladium complex with surface hydroxyl groups. A small range of catalysts of varying steric bulk were prepared in order to evaluate the effect on catalytic conversion. The activity of the palladium catalysts in Suzuki cross-coupling reactions has been established. The catalysts prepared by immobilising pre-formed palladium complexes gave superior results for the conversion of aryl bromides and aryl chlorides. In addition, use of sterically bulky NHCs (such as the N-2,6-(diisopropyl)phenyl-substituted ligand) resulted in increased catalytic activity, which is analogous to the trends noted in homogeneous catalysis.     

Air stable,sterically hindered ferrocenyl dialkylphosphines for palladium-catalyzed C[bond]C,C[bond]N,and C[bond]O bond-forming cross-couplings

Pentaphenylferrocenyl di-tert-butylphosphine has been prepared in high yield from a two-step synthetic procedure, and the scope of various cross-coupling processes catalyzed by complexes bearing this ligand has been investigated. This ligand creates a remarkably general palladium catalyst for aryl halide amination and for Suzuki coupling. Turnovers of roughly 1000 were observed for aminations with unactivated aryl bromides or chlorides. In addition, complexes of this ligand catalyzed the formation of selected aryl ethers under mild conditions. The reactions encompassed electron-rich and electron-poor aryl bromides and chlorides. In the presence of catalysts containing this ligand, these aryl halides coupled with acyclic or cyclic secondary alkyl- and arylamines, with primary alkyl- and arylamines, and with aryl- and primary alkylboronic acids. These last couplings provide the first general procedure for reaction of terminal alkylboronic acids with aryl halides without toxic or expensive bases. The ligand not only generates highly active palladium catalysts, but it is air stable in solution and in the solid state. Palladium(0) complexes of this ligand are also air stable as a solid and react only slowly with oxygen in solution.     

Alcoholic solvent‐assisted ligand‐free room temperature Suzuki–Miyaura cross‐coupling reaction

We have observed the enhancing effect of alcoholic solvents in palladium‐catalysed ligand‐free Suzuki–Miyaura reactions. No extra additives or ligands are required for the Suzuki–Miyaura reaction of aryl bromides with arylboronic acids when we carried out the reaction in alcoholic or aqueous alcoholic solvents. Moreover, ethanol or aqueous ethanol is found to be a very good solvent for the Suzuki–Miyaura reaction involving electronically diverse aryl bromides and arylboronic acids under mild and ligand‐free conditions with low catalyst loading. It is observed from Hg(0) poisoning tests that the in situ generated palladium(0) species is the actual catalytic species for the reaction. Copyright © 2015 John Wiley & Sons, Ltd.     

Use of polymer-supported dialkylphosphinobiphenyl ligands for palladium-catalyzed amination and Suzuki reactions

The preparations of polymer-supported dialkylphosphinobiphenyl ligands (3) are reported. A palladium catalyst based on ligand 3a is active for amination and Suzuki reactions using unactivated aryl iodides, bromides, or chlorides. Filtration of the catalyst from the reaction mixture allows for simplified product isolation via an aqueous workup. The resin-bound catalyst can be recycled without additional palladium in both the amination and Suzuki reactions.     

Ligand-free palladium catalysis of the Suzuki reaction in water using microwave heating

[reaction: see text] We report the ligand-free palladium catalysis of the Suzuki reaction in water using microwave heating. Our methodology uses low palladium loadings (0.4 mol %), is fast (5-10 min reaction time), and is useful for couplings involving boronic acids and aryl iodides, bromides, and chlorides.     

Active palladium catalyst supported by bulky diimine ligand catalyzed Suzuki–Miyaura coupling reaction in water under phosphane‐free and low catalyst loading conditions

A new catalytic system based on palladium and bulky diimine ligand for Suzuki–Miyaura coupling reaction of aryl iodides, bromides and chlorides in neat water is described. The desired biphenyl products were obtained in high to excellent yields for aryl iodides and bromides in the presence of low catalyst loading. Air‐stable catalyst has been recycled for the reaction of iodobenzene with phenylboronic acid for five consecutive runs. Copyright © 2014 John Wiley & Sons, Ltd.     

2‐Pyridylquinoxaline derivatives as N,N‐ligands for palladium‐catalyzed Suzuki–Miyaura reaction

The Suzuki–Miyaura reaction of aryl bromides with benzeneboronic acid catalyzed by bis(chloro)(2‐pyridylquinoxaline)palladium(II) was investigated. The scope of the bis(chloro)(2‐pyridylquinoxaline)palladium(II) was determined in toluene at 80 °C using KOH as base. Using a 0.1% molar ratio of bis(chloro)(2‐pyridylquinoxaline)palladium(II) C1 as a catalyst, aryl bromides reacted with benzeneboronic acid to afford diaryl derivatives in excellent yield. Copyright © 2009 John Wiley & Sons, Ltd.     

Phosphine-free polystyrene-supported palladium(II) complex as an efficient catalyst for the Heck and Suzuki coupling reactions in water

A palladium complex, 1-phenyl-1,2-propanedione-2-oxime thiosemi-carbazone-functionalized polystyrene resin supported Pd(II), is found to be a highly active catalyst for the Heck reaction of methyl acrylate with aryl halides and Suzuki reaction of phenylboronic acid with aryl iodides and bromides, giving excellent yields. The reactions were performed under phosphine-free conditions in an air atmosphere. The palladium catalyst is easily separated, and can be reused for several times without a significant loss in its catalytic activity.     

Nickel-promoted ligand-free palladium-catalyzed Suzuki coupling reaction

Summary A Ni-promoted ligand free palladium catalyst system for Suzuki coupling of aryl bromides has been developed in high efficiency under mild reaction conditions. It was obtained in situ by introducing NiCl₂ to PdCl₂/PVP using a parallel high-throughput screening technique. A wide range of aryl bromides bearing a variety of functional groups was evaluated.     

Effective palladium(II)-bis(oxazoline) catalysts: synthesis,crystal structure,and catalytic coupling reactions

New bis(oxazoline) ligands and their palladium complexes were synthesized and characterized. X-ray crystal structures of the two new complexes showed distorted square planar geometry with the palladium ion bonded to nitrogens of two bidentate heterocycles in addition to two bromides and two acetate ions for Pd-BOX-1 and Pd-BOX-2, respectively. The complexes adopt a chair structure with a rigid curvature inducing an inherent chirality. The complexes were effective catalysts for Suzuki–Miyaura, Mizoroki–Heck, and copper-free Sonogashira coupling reactions in aqueous dimethylformamide and under aerobic conditions. The reaction conditions were optimized for best solvent, base, and temperature. The substrate scope of the new catalytic system was evaluated for coupling reactions of a variety of aryl halides with aryl boronic acids, alkenes, and alkynes.     

Palladium charcoal-catalyzed, ligandless Suzuki reaction by using tetraarylborates in water

In water and without using any ligand, palladium charcoal-catalyzed Suzuki coupling reaction of tetraarylborates with aryl bromides could be achieved in excellent yield. A concise mechanism consisting of four catalytic cycles is depicted in this paper.     

Phosphine-free Pd-salen complexes as efficient and inexpensive catalysts for Heck and Suzuki reactions under aerobic conditions

Phosphine-free palladium-salen complexes, N,N′-bis(salicylidene)-ethylenediamino-palladium and N,N′-bis(salicylidene)-1,2-phenylenediamino palladium, are found to be highly active catalysts for the Heck olefination of aryl iodides and Suzuki reaction of aryl iodides and bromides giving excellent yields (70-90%) of products under aerobic conditions, in short reaction times (10-60 min).     

Ruphos-mediated Suzuki cross-coupling of secondary alkyl trifluoroborates

A Ruphos-mediated Suzuki cross-coupling between (hetero)aryl bromides and secondary alkyltrifluoroborates is described using palladium catalysis. The Ruphos ligand showed superior properties as compared to S-Phos in this type of reaction. This method constitutes a valuable extension to current methods for the straightforward production of secondary-alkylated (hetero)aryl derivatives.     

Macroporous polystyrene-supported palladium catalyst containing a bulky N-heterocyclic carbene ligand for Suzuki reaction of aryl chlorides

Macroporous polystyrene (MPS)-supported 1-mesitylimidazolium chloride resin was prepared by reacting macroporous chloromethyl polystyrene with 1-mesitylimidazole as a supported N-heterocyclic carbene (NHC) precursor for the immobilization of a palladium catalyst. This MPS-supported NHC precursor readily formed a stable complex with Pd(OAc)2, which effectively catalyzed the Suzuki reaction of aryl iodide and bromides at room temperature and even aryl chlorides at elevated temperatures (100 degrees C). This catalyst showed reusability in the Suzuki reaction of aryl bromide.