Catalytic activity of palladium(II) diaminocarbene complexes in the Sonogashira and Suzuki reactions

Palladium(II) complexes with chelating and non-chelating diaminocarbene ligands were assessed as catalysts in the cross-coupling reactions of haloarenes with oct-1-yne (Sonogashira reaction) and phenylboronic acid (Suzuki reaction). Both complexes exhibited a higher catalytic activity than traditional phosphine ligandbased systems in the Sonogashira reaction, and they ensured cross-coupling not only with iodoarenes but also with bromoarenes activated by electron-withdrawing substituents. The catalytic activities of the examined complexes in the Suzuki reaction were appreciably different: the palladium(II) complex with the chelating ligand turned out to be considerably less active than the complex with the non-chelating ligand.     

Sonogashira coupling reaction with diminished homocoupling

[reaction: see text] The side product from homocoupling reaction of two terminal acetylenes in the Sonogashira reaction can be reduced to about 2% using an atmosphere of hydrogen gas diluted with nitrogen or argon. Terminal arylethynes, diarylethynes, and a few new arylpyridylethynes with donor substituents have been synthesized in very good yields. Comparative control experiments suggest that the homocoupling yield is determined by concentration of both catalyst and oxygen.     

Pd-catalyzed decarboxylative coupling of propiolic acids: one-pot synthesis of 1,4-disubstituted 1,3-diynes via Sonogashira-homocoupling sequence

One-pot synthesis of symmetric 1,4-disubstituted 1,3-diynes from iodoarenes and propiolic acid via Sonogashira reaction followed by Pd-catalyzed decarboxylative homocoupling is developed in high yields. Also, this system allows the one-pot synthesis of unsymmetric 1,4-disubstituted 1,3-diynes by cross-coupling of two different 3-substituted propiolic acids.     

Convenient palladium-catalyzed homocoupling of iodoarenes in an ionic liquid

Symmetrical functionalized biaryls are obtained in good yields via TDAE/Pd-promoted homocoupling reaction of iodoarenes using the ionic liquid, [bmim]PF₆, as the solvent. The catalyst could be recycled and reused four times in this reaction.     

Heterogeneous Suzuki and copper-free Sonogashira cross-coupling reactions catalyzed by a reusable palladium(II) complex in water medium

A new polystyrene anchored Pd(II) azo complex has been synthesized and characterized. The present Pd(II) azo complex behaves as a very efficient heterogeneous catalyst in the Suzuki coupling and Sonogashira coupling reaction in water medium. Aryl halides, coupled with phenylboronic acids (Suzuki-Miyaura reaction) or terminal alkyne (Sonogashira reaction), smoothly afford the corresponding cross-coupling products in excellent yields (83-100% yield for Suzuki reaction and 68-96% yield for Sonogashira reaction of aryl halides) under phosphine-free reaction conditions in the presence of polystyrene anchored Pd(II) azo complex catalyst in water medium. Furthermore, the catalyst has shown good thermal stability and recyclability. This polymer-supported Pd(II) catalyst could be easily recovered by simple filtration of the reaction mixture and reused for more than six consecutive trials without a significant loss of its catalytic activity.     

Copper fluorapatite catalyzed N-arylation of heterocycles with bromo and iodoarenes

Copper exchanged fluorapatite (CuFAP) is an effective heterogeneous catalyst for N-arylation of heterocycles with bromo- or iodoarenes using K₂CO₃ as base. N-Arylated products were isolated in good to excellent yields, demonstrating the versatility of the reaction.     

Steric effect of substituents in haloarenes on the rate of cross-coupling reactions

The relative reactivity of ortho- and para-methyl-substituted iodoarenes in the Sonogashira reaction and palladium-catalyzed methoxycarbonylation, as well as of similarly substituted bromoarenes in the Suzuki reactions and cobalt-catalyzed methoxycarbonylation, was studied. Introduction of a methyl group into the para position of aryl halide slows down the cross-coupling. o-Methylhaloarenes are less reactive in palladiumcatalyzed reactions as compared to both unsubstituted haloarene and para-substituted analog. The presence of a methyl group in the ortho position with respect to the reaction center accelerates cobalt-catalyzed methoxycarbonylation.     

Mesoporous Silica MCM‐41 Supported N‐Heterocyclic Carbene‐Pd Complex for Heck and Sonogashira Coupling Reactions

Heterocyclic carbene‐Pd complex was anchored onto the mesoporous silica MCM‐41 which exhibits high catalytic activity in Heck reaction under phosphine free reaction conditions for the reaction of iodo/bromoarenes with olefinic compounds such as butyl acrylate, isopropyl acrylate and styrene. This catalytic system also showed high activity for Sonogashira coupling reaction of various aryl halides under copper, phosphine and solvent‐free reaction conditions. The air and thermally stable catalyst were reused several times without significant loss of its activity. High efficiency of the catalyst along with its recycling ability and the rather low Pd‐loading demonstrated in both Heck and Sonogashira coupling reactions are the merits of the presented catalyst system.     

Sonogashira cross-couplings of ynamides. Syntheses of urethane- and sulfonamide-terminated conjugated phenylacetylenic systems

[reaction: see text] The first successful Sonogashira coupling of ynamides with aryl and vinyl iodides is described here. This study resolves the problem of the competing pathway involving homocoupling of ynamides and provides a practical entry to novel urethane- or sulfonamide-terminated conjugated acetylenic systems. An interesting tandem hydrohalogenation and Sonogashira coupling was also observed to give an en-ynamide.     

金属有机配合物对格氏试剂与酰氯交叉偶联反应的催化活性

本文采用镍-膦配合物、有机钛化合物、氯化钕、乙酰丙酮希土配合物、含二茂铁基羰基三氟丙酮希土配合物(HL)_3Ln·xH_2O共十余种,作为苯甲酰氯与正丁基格氏试剂的交叉偶联反应的催化剂,发现各种有机钛化合物都具有和经典镍膦配合物类同或略好些的催化活性,而(HL)_3Ln,当Ln为Ce、Pr、Nd、Sm、Ho、Er时,均表现良好催化活性,反应产率高,反应选择性很好(～100％),本文同时讨论了反应的催化作用过程。     

Copper-free Sonogashira cross-coupling reaction catalyzed by polymer-supported N-heterocyclic carbene palladium complex

A core-shell type of polymer-supported N-heterocyclic carbene (NHC) palladium catalyst was applied to Sonogashira cross-coupling reactions without copper cocatalyst under ambient atmosphere. This supported NHC-palladium complex efficiently catalyzed the copper-free Sonogashira reaction of various aryl iodides and bromides with terminal alkynes; the reaction exhibited high dependency on the temperature and the amount of base as well as its nature. In addition, this heterogeneous catalyst exhibited good reusability for the copper-free Sonogashira reaction.     

Cyclopalladated ferrocenylimines: efficient catalysts for homocoupling and Sonogashira reaction of terminal alkynes

A novel pathway for homocoupling of terminal alkynes has been described using cyclopalladated ferrocenylimine 1 or 2/CuI as catalyst in the air. This catalytic system could tolerate several functional groups. The palladacycle 2 in the presence of n-Bu₄NBr as an additive could be applied to Sonogashira cross-coupling reaction of aryl iodides, aryl bromides, and some activated aryl chlorides with terminal alkynes under amine- and copper-free conditions, mostly to give moderate to excellent yields.     

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.     

Gold nanoparticles supported on cellulose aerogel as a new efficient catalyst for epoxidation of styrene

A new efficient heterogeneous catalyst was introduced for the epoxidation of styrene. The catalyst was obtained from deposition of gold nanoparticles on the cellulose aerogel. The catalyst was characterized with XRD, TGA, EDX, BET, FAAS and SEM. High yield and excellent selectivity were achieved for the epoxidation of styrene in solvent-free conditions at room temperature using H₂O₂ as a green oxidant during 1 h. The reaction has some advantages such as solvent-free and mild reaction conditions, low catalyst loading, high yield, excellent selectivity, green oxidant and short reaction duration. In addition, the catalyst is recyclable and applicable for six times without decrease in yield.     

Efficient palladium-catalyzed homocoupling reaction and Sonogashira cross-coupling reaction of terminal alkynes under aerobic conditions

An efficient method for palladium-catalyzed homocoupling reaction of terminal alkynes in the synthesis of symmetric diynes is presented. The results showed that both Pd(OAc)(2) and CuI played crucial roles in the reaction. In the presence of 2 mol % Pd(OAc)(2), 2 mol % CuI, 3 equiv of Dabco, and air, homocoupling of various terminal alkynes afforded the corresponding symmetrical diynes in moderate to excellent yields, whereas low yields were obtained without either Pd(OAc)(2) or CuI. Moreover, high TONs (turnover numbers; up to 940 000 for the reaction of phenylacetylene) for the homocoupling reaction were observed. Under similar reaction conditions, cross-coupling of 1-iodo-4-nitrobenzene with phenylacetylene was also carried out smoothly in quantitative yield. However, the presence of CuI disfavored the palladium-catalyzed Sonogashira cross-coupling reactions of the less active aryl iodides and bromides. In the presence of 0.01-2 mol % Pd(OAc)(2), a number of aryl iodides and bromides were coupled with terminal alkynes in good to excellent yields. It is noteworthy that this protocol employs mild, efficient, aerobic, copper-free, and ligand-free conditions.     

Task-specific ionic liquid as base, ligand and reaction medium for the palladium-catalyzed Heck reaction

A novel ionic liquid, which was based on ethanolamine-functionalized quaternary ammonium salt was designed and synthesized. 4-Di(hydroxyethyl)aminobutyl tributylammonium bromide (DHEABTBAB) 1, a task-specific ionic liquid, which acts as a base, ligand and reaction medium, exhibits a very high activity and recyclability to palladium-catalyzed Heck reaction. The olefinations of iodoarenes, bromoarenes and chloroarenes with olefins generated the corresponding cross-coupling products in good to excellent yields only in the presence of DHEABTBAB and palladium acetate under phosphine-free reaction conditions. It is noteworthy that palladium and DHEABTBAB could be repeatedly recycled and reused for six consecutive trials without significant loss of their activities.     

Synergistic Activities in the Ullmann Coupling of Chloroarenes at Ambient Temperature by Pd‐Supported Calcined Ferrocenated La2O3

Novel palladium‐doped nanoparticles have been explored to serve as the first metal oxide‐derived heterogeneous catalyst for Ullmann reaction of chloroarenes under mild condition (34 °C). This heterogeneous catalyst exhibited high catalytic activity towards the Ullmann homocoupling of chloroarenes into a series of useful symmetrically biaryl products with good to excellent yields in the presence of ethanol and NaOH, thereby leading to green and economical Ullmann reaction. The produced nanoparticles were successfully characterized by various techniques including PXRD, XPS, HRTEM, SEM‐EDS, BET, TGA techniques, elemental mapping analysis and ICP‐OES. Interestingly, based on characterization and experimental data, a reasonable mechanism has been proposed. Also, the formation of aryl methyl ketone as a by‐product has been further confirmed by isotopic labelling experiments that the acetyl moiety is derived from ethanol. Moreover, the catalyst was stable and could be easily reused up to 5 times under atmospheric air without suffering significant loss in catalytic activity.     

Carbonylative Sonogashira annulation sequence: One-pot synthesis of 4-quinolone and 4H-chromen-4-one derivatives

Carbonylative Sonogashira annulation sequence for one pot synthesis of 4-quinolone and 4H-chromen-4-one has been developed in presence of Pd-NHC catalyst. Substituted 2-iodoaniline and 2-iodophenol independently underwent in the carbonylative Sonogashira annulation reaction with a variety of acetylenes to result in 4-quinolone and flavone derivatives respectively in good to excellent yield. Moreover, this protocol does not require toxic CO gas, high catalyst loading and any expensive salt/additive. Herein we, for the first time, are using Mo(CO)₆, as solid CO source for the one pot synthesis of flavone derivatives via carbonylative Sonogashira annulation reaction.     

Synthesis of a diverse set of phosphorus ligands on solid support and their screening in the Heck reaction

Representative members from five different families of supported phosphine and phosphinite ligands have been prepared from common templates—polymer-bound aminoalcohols. These include β-aminophosphines, N,β-diphosphinoamines, α,β-diphosphinoamines, β-aminophosphinites and N-phosphino-β-aminophosphinites. Representatives of each family of ligands were complexed with Pd(OAc)₂ and screened in the Heck reaction of iodo- and bromobenzene. While the reaction of iodoarenes is ligand-independent, the reaction of bromoarenes is ligand-sensitive. The rationale for this behavior is suggested. Lead ligands for the reaction of bromoarenes were determined.     

Cu(I)-amido complexes in the Ullmann reaction: reactions of Cu(I)-amido complexes with iodoarenes with and without autocatalysis by CuI

A series of Cu(I)-amido complexes both lacking ancillary ligands and containing 1,10-phenanthroline (phen) as ancillary ligand have been prepared. These complexes react with iodoarenes to form arylamine products, and this reactivity is consistent with the intermediacy of such complexes in catalytic Ullmann amination reactions. The stoichiometric reactions of the Cu(I)-amido complexes with iodoarenes are autocatalytic, with the free CuI generated during the reaction serving as the catalyst. Such autocatalytic behavior was not observed for reactions of iodoarenes with copper(I) amidates, imidates, or phenoxides. The selectivity of these complexes for two sterically distinct aryl halides under various conditions imply that the autocatalytic reaction proceeds by forming highly reactive [CuNPh(2)](n) lacking phen. Reactions with radical probes imply that the reactions of phen-ligated Cu(I)-amido complexes with iodoarenes occur without the intermediacy of aryl radicals. Density functional theory calculations on the oxidative addition of iodoarenes to Cu(I) species are consistent with faster reactions of iodoarenes with CuNPh(2) species lacking phen in DMSO than reactions of iodoarenes with LCuNPh(2) in which L = phen. The free-energy barrier computed for the reaction of PhI with (DMSO)CuNPh(2) was 21.8 kcal/mol, while that for the reaction of PhI with (phen)CuNPh(2) was 33.4 kcal/mol.