Palladium‐Catalyzed Decarboxylative sp‐sp2 Cross‐Coupling Reactions of Aryl and Vinyl Halides and Triflates with α,β‐Ynoic Acids using Silver Oxide

Palladium‐catalyzed decarboxylative sp‐sp² cross‐coupling reactions of aryl and vinyl halides and triflates with α,β‐ynoic acids using silver oxide have been developed. A variety of α,β‐ynoic acids were readily decarboxylated in the presence of silver oxide and then, generated in situ, silver acetylides were coupled with electrophiles in the presence of a palladium(0) catalyst under neutral conditions, producing either symmetrical or unsymmetrical diarylacetylenes, arylalkylacetylenes and arylvinylacetylenes in good to excellent yields.     

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     

Fluorapatite‐Supported Palladium Catalyst for Suzuki and Heck Coupling Reactions of Haloarenes

A fluorapatite‐supported palladium catalyst (PdFAP) was synthesized by treatment of fluorapatite (prepared by incorporating the basic species fluoride ion into apatite in situ by co‐precipitation) with bis(benzonitrile)palladium(II ) chloride in acetone. The catalyst displayed high catalytic activity for Suzuki coupling of aryl iodides and bromides with boronic acids at room temperature and chloroarenes at 130 °C in the presence of tetrabutylammonium bromide to give biaryls in excellent yields. Heck olefination of chloroarenes was also successfully carried out by this catalyst. PdFAP was recovered quantitatively by simple filtration and reused with consistent activity. PdFAP was well characterized by XRD, FTIR, XPS, ICP‐AES, CO₂ TPD and CHN elemental analysis.     

Preparation of Arylphosphonates by Palladium(0)‐Catalyzed Cross‐Coupling in the Presence of Acetate Additives: Synthetic and Mechanistic Studies

An efficient protocol for the synthesis of arylphosphonate diesters via a palladium‐catalyzed cross‐coupling of H‐phosphonate diesters with aryl electrophiles, promoted by acetate ions, was developed. A significant shortening of the cross‐coupling time in the presence of the added acetate ions was achieved for bidentate and monodentate supporting ligands, and for different aryl electrophiles (iodo, bromo and triflate derivatives). The reaction conditions were optimized in terms of amount of the catalyst, supporting ligands, and source of the acetate ion used. Various arylphosphonates, including those of potential biological significance, were synthesized using this newly developed protocol. Some mechanistic aspects of the investigated reactions are also discussed.     

Diethanol amine‐functionalized polymer‐supported palladium (0) complex as catalyst for Suzuki cross‐coupling reaction in water

Diethanol amine‐functionalized polymer‐supported palladium (0) complex as catalyst for Suzuki cross‐coupling reaction in water was synthesized and characterized. The catalyst exhibits excellent catalytic activity and stability in the Suzuki cross‐coupling reaction. Various aryl bromides were coupled with aryl boronic acids in water, under air, and in the presence of 0.5 mol % of the catalyst to afford corresponding cross‐coupled products in high yields at 100°C. Furthermore, the heterogeneous catalyst can be readily recovered by simple filtration and reused for several times only with a slight decrease in its activity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Photo‐Induced Sonogashira C?C Coupling Reaction Catalyzed by Simple Copper(I) Chloride Salt at Room Temperature

The conventional thermal Sonogashira C C coupling reaction requires the use of a palladium catalyst and a large amount of ligands. Although there were a few reports describing the use of inexpensive metal catalysts, such as, copper (Cu), iron (Fe), and nickel (Ni), for replacement of palladium (Pd) in the Sonogashira reactions, it was later questioned that the observed effects were due to ppb levels contamination of Pd present in the reagents used in the reactions. Herein, we report that simple copper(I) chloride (CuCl) salt, in the absence of Pd and ligands, can catalyze the Sonogashira reaction with high yields (80–99%) under blue LED light irradiation at room temperature. Control experiments show that no cross‐coupling product was formed, when palladium(II) chloride (PdCl₂) was used to replace CuCl as a catalyst. A series of electron‐rich and electron‐poor substituted aryl halides (bromides and iodides) as well as aryl‐ and alkylacetylenes are examined and the reaction mechanism is discussed.     

取代溴苯的钯催化偶联反应

以 4 氟溴苯、3,4 二氟溴苯、3,4,5 三氟溴苯、4 碘溴苯、4 甲氧基溴苯、4 丙基溴苯为原料 ,分别与 2 甲基 3 丁炔 2 醇发生钯催化偶联反应 ,合成了 6个苯基炔醇液晶用中间体。分别在 40℃、70℃、89℃ ,用两种不同活性催化剂条件下 ,测定了 6种反应原料发生钯催化偶联反应所需时间及相应产率。分析了温度、催化剂、不同取代基团对取代溴苯发生钯催化偶联反应活性的影响。     

Macrocyclic Palladium(II) Complexes in C?C Coupling Reactions: Efficient Catalysis by Controlled Temporary Release of Active Species

Stabilization of palladium species against agglomeration is essential for reasonable catalytic activity in C C coupling reactions. In contrast to common methods of palladium(0) complex or particle stabilization, a new concept is introduced here: it is demonstrated that a controlled release of palladium from an inactive precatalyst provides stability, too, and leads to high catalytic activity. This paper presents surprising catalytic results for Heck and Suzuki reactions with aryl chlorides and bromides, using three highly stable macrocyclic palladium complexes as catalyst precursors. Three different behaviour patterns for the macrocyclic complexes can be deduced from the evaluation of catalytic activities, UV‐Vis spectroscopy, recycling studies of immobilized complexes, and ligand addition experiments. (i) Palladium tetraphenylporphyrin reversibly releases only extremely low amounts of palladium during the reactions, and low coupling activities are observed. (ii) Release of palladium from its phthalocyanine complex is irreversible; cumulative release of palladium into the reaction mixtures leads to high catalytic activity. (iii) Extraordinary results were obtained with a Robson‐type complex of palladium, which reversibly releases effectual amounts of palladium into solution under reaction conditions. This controlled release prevents the formation of inactive palladium agglomerates under harsh conditions and leads to high catalytic performances. Even strongly deactivated electron‐rich aryl chlorides (4‐chloroanisole) can be completely and selectively converted by the in situ formed anionic palladium halide complexes; the addition of typical stabilizing additives (TBAB) was found to be unnecessary. The bimetallic palladium complex is regenerated at the end of the reaction. These results contribute to the current understanding of the active species in C C coupling reactions of Heck and Suzuki types.     

Palladium/Copper‐Catalyzed Di‐α‐arylation of Acetic Acid Esters

A bimetallic palladium/copper catalyst system was found to effectively promote the diarylation of alkyl acetates with aryl halides under unprecedentedly mild conditions. The phenanthroline‐copper‐phosphine catalyst stabilizes the enolate intermediate to the extent that the deprotonation of esters can be achieved even with the mild base potassium phosphate. The palladium tri‐tert‐butylphosphine co‐catalyst mediates the coupling of the resulting copper enolate with a wide variety of aryl halides with selective formation of the corresponding diarylacetic acid esters.     

An Amine‐, Copper‐ and Phosphine‐Free Sonogashira Coupling Reaction Catalyzed by Immobilization of Palladium in Organic–Inorganic Hybrid Materials

An immobilization of palladium in organic‐inorganic hybrid materials‐catalyzed Sonogashira coupling reaction has been described. Terminal alkynes reacted with aryl iodides and aryl bromides only in the presence of a 3‐(2‐aminoethylamino)propyl‐functionalized, silica gel‐immobilized palladium catalyst under amine‐, copper‐ and phosphine‐free reaction conditions. The reaction generates the corresponding cross‐coupling products in excellent yields. Furthermore, the silica‐supported palladium can be recovered and recycled by a simple filtration of the reaction solution and used for 30 consecutive trials without any decreases in activity.     

Palladium on Carbon‐Catalyzed Cross‐Coupling using Triarylbismuths

Simple and efficient protocols for the 10% palladium on carbon (Pd/C)‐catalyzed cross‐coupling reactions between triarylbismuths and aryl halides have been developed. A variety of iodo‐ and bromobenzenes possessing an electron‐withdrawing group on the aromatic nucleus were smoothly cross‐coupled in the presence of 10% Pd/C, sodium phosphate dodecahydrate (Na₃PO₄⋅12 H₂O) and 1,4‐diazabicyclo[2.2.2]octane (DABCO) in heated N‐methyl‐2‐pyrrolidone (NMP) as the solvent. For the arylations of iodobenzenes, the reactions effectively proceeded under the combined use of caesium fluoride (CsF) and 2,2′‐biquinoline. Furthermore, a ligand‐free 10% Pd/C‐catalyzed cross‐coupling reaction between the aryl iodides and triarylbismuths was also established by the addition of tetra‐n‐buthylammonium fluoride trihydrate (TBAF⋅3 H₂O) in which the palladium metals were hardly leached from the catalyst into the reaction media.     

Sulfonated N‐Heterocyclic Carbenes for Pd‐Catalyzed Sonogashira and Suzuki–Miyaura Coupling in Aqueous Solvents

The reactions of the N,N′‐diarylimidazolium and N,N′‐diarylimidazolinium salts with chlorosulfonic acid result in the formation of the respective disulfonated N‐heterocyclic carbene (NHC) precursors in reasonable yields (46–77%). Water‐soluble palladium catalyst complexes, in situ obtained from the respective sulfonated imidazolinium salt, sodium tetrachloropalladate (Na₂PdCl₄) and potassium hydroxide (KOH) in water, were successfully applied in the copper‐free Sonogashira coupling reaction in isopropyl alcohol/water mixtures using 0.2 mol% catalyst loading. The preformed (disulfonatedNHC)PdCl(cinnamyl) complex was used in aqueous Suzuki–Miyaura reactions at 0.1 mol% catalyst loading. The coupling protocol reported here is very useful for Sonogashira reactions of N‐ and S‐heterocyclic aryl bromides and chlorides with aryl‐ and alkylacetylenes.     

Expanded Heterogeneous Suzuki–Miyaura Coupling Reactions of Aryl and Heteroaryl Chlorides under Mild Conditions

A mesoporous LTA zeolite (MP‐LTA)‐supported palladium catalyst was developed for the highly efficient Suzuki–Miyaura reaction of aryl and heteroaryl chlorides. The couplings of various aryl chlorides with arylboronic acids in aqueous ethanol were efficiently achieved in the presence of 1.0 mol% of the catalyst. Furthermore, the scope of this catalyst was extended to the coupling of heteroaryl chlorides. Regardless of the substituents, all of the coupling reactions were very clean and highly efficient under mild heating. It shows that our catalyst is one of the most powerful heterogeneous catalysts for the coupling of a wide range of aryl and heteroaryl chlorides. The catalyst could be repetitively used at least 10 times without a significant loss of its catalytic activity. Compared to mesoporous SBA‐15 and MCM‐41 materials, the MP‐LTA support proved to be very stable and robust to prevent degradation upon reuse.     

Ullmann偶联反应催化剂研究进展

Ullmann偶联反应是典型的碳碳键偶联反应,反应合成的联苯类化合物是重要有机化工原料,应用前景广阔。初期采用均相Pd催化剂,不能重复利用,工业化生产受到限制。改用多相Pd催化剂催化反应,需要添加剂导致产物分离困难。多相Au催化剂适用性受到限制,反应底物局限于碘代芳烃,双金属催化剂在催化活性与选择性方面均有较好的优势。综述Ullmann-type偶联反应中均相Pd催化体系、多相Pd催化体系、多相Au催化体系以及多相双金属催化体系催化剂的研究进展,阐述反应机理,并对Ullmann偶联反应研究进行展望。     

Palladium Nanoparticles Immobilized on Nano‐Silica Triazine Dendritic Polymer (Pdnp‐nSTDP): An Efficient and Reusable Catalyst for Suzuki–Miyaura Cross‐Coupling and Heck Reactions

A new catalyst based on palladium nanoparticles immobilized on nano‐silica triazine dendritic polymer (Pd_np‐nSTDP) was synthesized and characterized by FT‐IR spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, energy dispersive X‐ray, transmission electron microscopy and elemental analysis. The size of the palladium nanoparticles was determined to be 3.1±0.5 nm. This catalytic system showed high activity in the Suzuki–Miyaura cross‐coupling of aryl iodides, bromides and chlorides with arylboronic acids and also in the Heck reaction of these aryl halides with styrenes. These reactions were best performed in a dimethylformamide (DMF)/water mixture (1:3) in the presence of only 0.006 mol% and 0.01 mol% of the catalyst, respectively, under conventional conditions and microwave irradiation to afford the desired coupling products in high yields. The Pd_np‐nSTDP was also used as an efficient catalyst for the preparation of a series of star‐ and banana‐shaped compounds with a benzene, pyridine, pyrimidine or 1,3,5‐triazine unit as the central core. Moreover, the catalyst could be recovered easily and reused several times without any considerable loss of its catalytic activity.     

Heck Cross‐Coupling of Aryldiazonium Tetrafluoroborate with Acrylates Catalyzed by Palladium on Charcoal

A property‐activity relationship study of various palladium supported on charcoal (Pd/C) catalysts has been undertaken for the Heck reaction of aryldiazonium tetrafluoroborate with acrylates. The optimized protocol enables the cross‐coupling with a low loading of palladium at room temperature in technical grade methanol. Although the catalyst could not be recycled at this time, measurement of the palladium content by inductively coupled plasma mass spectrometry (ICP‐MS) shows low palladium contamination of the solvent and product, rendering this method safer for the environment compared to homogeneous conditions.     

氯代芳烃偶联反应中钯催化剂的研究进展

在合适的钯催化作用下,可将廉价易得、低活性的氯代芳烃应用于C—C键和C杂键形成的偶联反应。对偶联反应用钯催化剂的研究进行了综述。通过选择合适的配体,钯催化剂可有效地催化带有多种体取代基的氯代芳烃或氯代杂芳烃,发生Suzuki、Negishi、Stille和Heck等多种偶联反应,获得较高的收率和很高的选择性。     

Palladium‐Catalyzed Efficient and One‐Pot Synthesis of Diarylacetylenes from the Reaction of Aryl Chlorides with 2‐Methyl‐3‐butyn‐2‐ol

An efficient and practical synthetic method has been developed for the preparation of symmetrical diarylacetylenes from the direct reaction of aryl chlorides with 2‐methyl‐3‐butyn‐2‐ol catalyzed by palladium(II) chloride‐bis(tricyclohexylphosphine) [PdCl₂(PCy₃)₂] under mild reaction conditions. Unsymmetrical diarylated acetylenes could be also obtained by using two different aryl chlorides simultaneously. The catalytic procedure includes a novel one‐pot palladium‐catalyzed, double Sonogashira coupling of inactivated aryl chlorides without use of copper(I) as co‐catalyst.     

Thiosemicarbazone Salicylaldiminato‐Palladium(II)‐Catalyzed Mizoroki–Heck Reactions

Four tridentate thiosemicarbazone salicylaldiminato‐palladium(II) complexes of the general formula [Pd(saltsc‐R)PPh₃] [saltsc=salicylaldehyde thiosemicarbazone; R=H ( 1 ), 3‐tert‐butyl ( 2 ), 3‐methoxy ( 3 ), 5‐chloro ( 4 )], have been evaluated as catalyst precursors for the Mizoroki–Heck coupling reaction between a variety of electron‐rich and electron‐poor aryl halides and olefins. The palladium complexes (0.1–1 mol% loading) were found to effectively catalyze these reactions with high yields being obtained when aryl iodides and aryl bromides were utilized. The effects of base, catalyst loading, reaction temperature and reaction time on the catalytic activity of the most active complex were also investigated.     

The First Fluoride‐Free Hiyama Reaction of Vinylsiloxanes Promoted by Sodium Hydroxide in Water

The first cross‐coupling reaction between vinylalkoxysilanes and aryl bromides or chlorides promoted by aqueous sodium hydroxide under fluoride‐free conditions to provide styrenes is reported. The reaction is catalyzed by palladium(II) acetate or a 4‐hydroxyacetophenone oxime‐derived palladacycle either under thermal or microwave heating at 120 °C with low catalyst loading (0.01–1 mol % of palladium) in the presence of tetra‐n‐butylammonium bromide (TBAB) as additive in air. In the case of styryltriethoxysilane, the coupling with aryl or vinyl bromides takes place stereospecifically to give the corresponding stilbenes or dienes, respectively. These mild and simple reaction conditions prevent undesirable polymerization of the products.