Palladium catalyzed Heck-Mizoroki and Suzuki-Miyaura coupling reactions (Review)

This article is about the progress of palladium compounds as a catalyst for Heck-Mizoroki and Suzuki-Miyaura coupling reactions. Industrial catalysts with broad applicability need continuous catalyst development process through modification of ligand design, geometry and functionality. Recently catalysts have been synthesized through attachment of the activated palladium complexes on the surface of polymer support, particularly, insoluble in reaction medium. An appropriate mixture of palladium salt and ligand is also used as an important modification in some cases to get better results. We surveyed the important palladium compounds synthesized up to early 2014 for Heck-Mizoroki and Suzuki-Miyaura coupling reactions and summarize their progress in terms of ligand modification and other associated parameters.     

Palladium catalyzed coupling reactions of cationic porphyrins with organoboranes (Suzuki) and alkenes (Heck)

The carbon-carbon coupling reaction in aqueous medium between 5,10,15-tri-(4-N-methylpyridyl)-20-(4-bromophenyl)-porphyrin and a variety of organoboranes, fluoroorganoboranes and alkenes using palladium catalyst (Suzuki and Heck) is explored.     

Palladium catalyzed Suzuki coupling reactions using cobalt-containing bulky phosphine ligands

Three bulky mono-dentate alkyne-bridged dicobalt-phosphine complexes [(μ-PPh₂CH₂PPh₂)Co₂(CO)₄](μ,η-PhCCPPh₂) 4a, [(μ-PPh₂CH₂PPh₂)Co₂(CO)₄](μ,η-Me₃CCCPPh₂) 5a and [(μ-PPh₂CH₂PPh₂)Co₂(CO)₄](μ,η-Me₃SiCCPPh₂) 6a were prepared from the reactions of the bis(diphenylphosphino)methylene (dppm) bridged dicobalt complex Co₂(CO)₆(μ-Ph₂PCH₂PPh₂) with PhCCPPh₂1, Me₃CCCPPh₂2, and Me₃SiCCPPh₂3, respectively. These three metal-containing compounds 4a, 5a and 6a were employed as ligands, replacing conventional organic phosphines, in the Suzuki cross-coupling reactions and have been proved to be effective, authentic mono-dentate phosphine ligands.     

Palladium catalyzed C-C coupling reactions of 3,5-dichloro-4H-1,2,6-thiadiazin-4-one

Palladium catalyzed Suzuki-Miyaura, Stille, and Sonogashira coupling reactions are reported for the electron-deficient heterocyclic scaffold 3,5-dichloro-4H-1,2,6-thiadiazin-4-one (1). Furthermore, 3,5-di(thien-2-yl)-4H-1,2,6-thiadiazin-4-one (7m) is further elaborated to afford the tetrathienyl 3,5-bis[(2,2'-bithien)-5-yl]-4H-1,2,6-thiadiazin-4-one (9). All compounds are fully characterized.     

Palladium(II) thiocarboxamide complexes: synthesis, characterisation and application to catalytic Suzuki coupling reactions

A simple route to synthesise palladium(II) complexes from the reaction of N-substituted pyridine-2-thiocarboxamide ligands and PdCl(2)(PPh(3))(2) has been developed. The new complexes are very soluble in common solvents and have been fully characterised (elemental analysis, FT-IR, (1)H, (31)P, (13)C-NMR), including an X-ray diffraction analysis. The molecular structures of all the complexes were determined and reveal the presence of square planar geometry around Pd with little distortion. The complexes were tested in the Suzuki coupling of electronically deactivated aryl and heteroaryl bromides and were found to have much greater activity, without using any promoting additives or phase transfer agent under aerobic conditions. Higher reaction rates are obtained by varying R substituents on the aromatic ring of pyridine-2-thiocarboxamide. The effect of other variables on the cross-coupling reaction, such as temperature, solvent and base, is also reported.     

Palladium catalyzed arylation reactions of meta photocycloadducts

We describe the first application of a Heck arylation reaction being performed on a meta photocycloadduct. The resulting arylation/fragmentation process leads to the formation of a bridged bicyclic ketone and constitutes a dramatic increase in molecular complexity after just two synthetic operations.     

Palladium (II/IV) catalyzed cyclopropanation reactions: scope and mechanism

This report describes detailed studies of the scope and mechanism of a new Pd-catalyzed oxidation reaction for the stereospecific conversion of enynes into cyclopropyl ketones. Unlike related Pd^II/0, Au, and Pt-catalyzed cyclopropane-forming reactions, these transformations proceed with net inversion of geometry with respect to the starting alkene. This result, along with other mechanistic data, is consistent with a Pd^II/IV mechanism in which the key cyclopropane-forming step involves nucleophilic attack of a tethered olefin onto a Pd^IV-C bond.     

Palladium catalyzed C-P cross-coupling reactions in ionic liquids

C-P cross-coupling reactions between phosphine-borane complexes and aryl iodides are successfully performed in imidazolium based ionic liquids (ILs). To improve the recycling of the catalyst, a monophosphine covalently attached to a pyridinium salt was prepared. Associated to palladium, this catalyst shows a high catalytic activity and stays immobilized in the IL. It was reused at least in six cycles.     

Palladium catalyzed reductive homocoupling reactions of aromatic halides in dimethyl sulfoxide (DMSO) solution

Biaryls were obtained in good to excellent yields from the palladium catalyzed reductive homocoupling reactions of various aryl iodides and bromides in dimethyl sulfoxide (DMSO) solution without the need for any additional reducing reagents. Pd(dppf)Cl₂ is the most effective among the screened palladium catalysts for the homocoupling reactions. Fluorides, carbonates, acetates and hydroxides can be used as bases at promoting the palladium catalyzed reductive homocoupling of aryl halides in DMSO solution. X-ray photoelectron spectroscopic (XPS) analysis shows that the oxidative Pd²⁺(dppf) species can be reduced into the Pd⁰(dppf) active species by solvent DMSO molecules to furnish the catalytic cycle, indicating that DMSO plays a dual role as both solvent and reducing reagent. A plausible reaction mechanism has been discussed. Elimination of additional reducing reagents will not only reduce the reaction operation cost, but will also simplify the product separation and purification.     

Palladium catalyzed arylation for the synthesis of polyarenes

We present the current understanding on the mechanism of palladium-catalyzed arylation, which involves a proton abstraction by the base. In addition, we present selected examples of the application of this reaction for the synthesis of large polyarenes to highlight the variety of catalysts and reaction conditions that are currently used.     

1,2,3-Triazol-5-ylidene-palladium complex catalyzed Mizoroki-Heck and Sonogashira coupling reactions

The bis-1,4-dimesityl-1,2,3-triazol-5-ylidene-palladium complex (1a) successfully catalyzes the Mizoroki-Heck and Sonogashira coupling reactions with aryl bromides to give the corresponding alkenes and alkynes, respectively, in good to excellent yields. In the Mizoroki-Heck reaction, electron-rich, electron-poor, and functionalized aryl bromides and alkenes are tolerated, while the substrates are limited to electron-poor aryl halides in the Sonogashira coupling reaction. The palladium complex also catalyzes cross-coupling reactions with aryl chlorides to give higher yields of products than does the bis-IMes-Pd complex analogue (2), under specific conditions.     

Cu_2O/丁二酮肟催化芳基碘与芳胺偶联反应研究

钯催化的Ullmann反应合成C-N键获得成功~([1-3]),在各种配体参与下廉价的铜催化Ullmann反应形成C-N键,引起了人们的关注~([4-5]).配体在活化铜催化的偶联反应中非常关键,就此类催化体系所选的配体而言,目前报道的主要有N,N配体(如1,10-邻菲咯啉~([6])和二胺~([7])等)、N,-COOH配体(如氨基酸~([4]))、O,O配体(如联萘二酚~([8])和1,3-二酮~([9]))、N,P配体~([10-11])等,作者也曾用空气稳定的三价膦配体促进了此类反应~([12]).     

Palladium catalyzed synthesis of a chromenes and chromenols

Palladium catalyzed coupling of tertiary allylic alcohols (having five, ten or fifteen carbon atoms) with 2-iodophenols or hydroquinones furnishes the corresponding 2,2-disubstituted chromenes (2H-1-benzopyrans) and chromen-6-ols.     

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.     

Palladium(II) catalyzed carbonylative dimerization of allenyl ketones: efficient synthesis of difuranylketones

Palladium(II) catalyzed carbonylation of 1,2-allenyl ketones 1 in the presence of p-benzoquinone (1 equiv) under a CO atmosphere (balloon) afforded difuranylketones 4 in moderate to good yields. Mechanistically, the electron-withdrawing nature of the acyl group should enhance the electrophilicity of the acylpalladium species B, and thus promote the oxypalladation of an additional molecule of 1, leading to the difuranyl ketone 4.     

Palladium(II) catalyzed cyclization of alkynoic acids

Under the catalytic action of palladium(II) in the presence of triethylamine, 3-, 4-, and 5-alkynoic acids afford 3-buten-4-olides, 4-penten-4-olides, and 5-hexen-5-olide, respectively, in good to excellent yields.     

Highly efficient Suzuki-Miyaura coupling reactions catalyzed by bis(oxazolinyl)phenyl-Pd(II) complex

Bis(oxazolinyl)phenyl-palladium(II)(Phebox-Pd) complexes were found to be efficient catalysts for Suzuki-Miyaura coupling reactions of aryl boronic acids and their derivatives with aryl halides to give the corresponding biaryl products in high yield along with moderate enantioslectivities in the case of axially chiral induction. The catalytic activity was attained more than 900,000 of TON and 45,000 of TOF. The catalyst can be recovered quantitatively and could be reused for Suzuki-Miyaura reactions.     

Palladium complexes with ethylene-bridged bis(N-heterocyclic carbene) for C-C coupling reactions

A series of new ethylene-bridged bis(imidazolium) halides with various N-substitutions were synthesized. Complexation of these imidazolium halides with Pd(OAc)₂ produced new Pd(II) ethylene-bridged bis(carbene) complexes. Crystallographic analyses of some of the new imidazolium salts and Pd(II) complexes were determined. Applications of these seven-member palladacycles in Suzuki and Heck coupling reactions produced comparable catalytic activities to those of six-member analogs.