Pd nanoparticles as efficient catalysts for Suzuki and Stille coupling reactions of aryl halides in ionic liquids

Pd-catalyzed Suzuki and Stille cross-couplings of aryl bromides and chlorides were carried out in quaternary ammonium salts as solvents under mild conditions and with the recycling of the catalyst.     

Highly efficient and functional-group-tolerant catalysts for the palladium-catalyzed coupling of aryl chlorides with thiols

The cross-coupling reaction of aryl chlorides with aliphatic and aromatic thiols catalyzed by palladium complexes of the strongly binding bisphosphine CyPF-tBu ligand (1) is reported. Most of the reactions catalyzed by complexes of ligand 1 occur with turnover numbers that exceed those of previous catalysts by two orders of magnitude. The reactions occur with excellent yields, broad scope and high tolerance of functional groups. Coupling of aryl halides with thiols in the presence of low loadings of catalysts derived from other Josiphos type ligands, as well as ligands of other structural types, are also described.     

Highly active catalysts for the Suzuki coupling of aryl chlorides

Simple tricyclohexylphosphine adducts of palladium complexes with orthometallated N-donor ligands show by far the highest activity yet reported in the Suzuki coupling of aryl chlorides, even under aerobic conditions.     

Nickel(II) complexes of bidentate N-heterocyclic carbene/phosphine ligands: efficient catalysts for Suzuki coupling of aryl chlorides

Nickel(II) complexes of bidentate N-heterocyclic carbene (NHC)/phosphane ligand L were prepared and structurally characterized. Unlike palladium, which forms [PdCl(2)(L)], the stable nickel product isolated is the ionic [Ni(L)(2)]Cl(2). These Ni(II) complexes are highly robust in air. Among different N-substituents on the ligand framework, the nickel complex of ligand L bearing N-1-naphthylmethyl groups (2 a) is a highly effective catalyst for Suzuki cross-coupling between phenylboronic acid and a range of aryl halides, including unreactive aryl chlorides. The activities of 2 a are largely superior to those of other reported nickel NHC complexes and their palladium counterparts. Unlike the previously reported [NiCl(2)(dppe)] (dppe=1,2-bis(diphenylphosphino)ethane), 2 a can effectively catalyze the cross-coupling reaction without the need for a catalytic amount of PPh(3), and this suggests that the PPh(2) functionality of hybrid NHC ligand L can partially take on the role of free PPh(3). However, for unreactive aryl chlorides at low catalyst loading, the presence of PPh(3) accelerates the reaction.     

Rapid and efficient Pd-catalyzed Sonogashira coupling of aryl chlorides

An efficient and effective microwave-assisted cross-coupling of terminal alkynes with various aryl chlorides including sterically hindered, electron-rich, electron-neutral, and electron-deficient aryl chloride is developed. It proceeds faster and generally gives good to excellent yields and also can be extended successfully to the Suzuki coupling and Buchwald-Hartwig amination, as well as the Heck coupling with inert aryl chlorides. The short reaction times and simple reaction conditions coupling with a broad substrate scope render this method particularly attractive for the efficient preparation of biologically and medicinally interesting molecules.     

An efficient palladium-catalyzed Heck coupling of aryl chlorides with alkenes

Catalyst system PdCl₂(PCy₃)₂/Cs₂CO₃ in dioxane was found to be the efficient catalyst system for Heck cross-coupling reactions of deactivated, neutral, and activated aryl chlorides with a variety of alkenes under mild conditions to afford selectively E-arylated alkenes in good to excellent yields.     

Di- and tri-alkylphosphine adducts of S-donor palladacycles as catalysts in the Suzuki coupling of aryl chlorides

The reaction of tricyclohexylphosphine with the S-based palladacycle [(Pd(mu-OAc)(kappa2-S,C-C(6)H(4)CH(2)SMe))(2)] gives several products, regardless of stoichiometry, one of which, [Pd(kappa1-OAc)(eta1-C(6)H(4)CH(2)SMe)(PCy3)2], has been characterised crystallographically. Despite this, catalysts formed in situ from di- and tri-alkylphosphines and [(Pd(mu-OAc)(kappa2-S,C-C(6)H(4)CH(2)SMe))2] show excellent activity in the Suzuki coupling of a range of deactivated, non-activated and activated aryl chloride substrates.     

Highly active palladium catalysts supported by bulky proazaphosphatrane ligands for Stille cross-coupling: coupling of aryl and vinyl chlorides, room temperature coupling of aryl bromides, coupling of aryl triflates, and synthesis of sterically hindered biaryls

A family of proazaphosphatrane ligands [P(RNCH2CH2)2N(R'NCH2CH2): R = R' = i-Bu, 1; R = Bz, R' = i-Bu, 3; R = R' = Bz, 4] for palladium-catalyzed Stille reactions of aryl chlorides is described. Catalysts derived from ligands 1 and 4 efficiently catalyze the coupling of electronically diverse aryl chlorides with an array of organotin reagents. The catalyst system based on the ligand 3 is active for the synthesis of sterically hindered biaryls (di-, tri-, and tetra-ortho substituted). The use of ligand 4 allows room-temperature coupling of aryl bromides and it also permits aryl triflates and vinyl chlorides to participate in Stille coupling.     

Highly efficient and reusable supported pd catalysts for Suzuki-Miyaura reactions of aryl chlorides

Syntheses of air- and moisture-stable heterogeneous (tert-butylarylphosphino)polystyrene-supported Pd catalysts and their use for versatile Suzuki-Miyaura reactions of aryl chlorides and arylboronic acids under non-anhydrous conditions are reported. The catalysts are easily recovered by filtration. They can be used many times (more than seven) without showing any loss of activity, and the amount of Pd leached is extremely low (<0.1%).     

Eumelanin as a support for efficient palladium nanoparticle catalyst for Suzuki coupling reaction of aryl chlorides in water

Eumelanin-supported palladium (Pd) nanoparticle (NP) catalysts was found to exhibit excellent catalytic activities with high turnover number (TON, 2000) and turnover frequency (TOF, 1000 h^?1) for Suzuki cross coupling reaction of aryl chlorides in water. We propose that the amphiphilic property of the eumelanin support helps Pd NPs to catalyse the C–C coupling reaction in water through hydrophobic effect.     

An efficient and general method for the Heck and Buchwald-Hartwig coupling reactions of aryl chlorides

The β-diketiminatophosphane Pd complex acted as a powerful catalyst for the Heck coupling of aryl chlorides with alkenes. Various aryl and heteroaryl chlorides were coupled efficiently under relatively mild conditions. Furthermore, this catalytic system also proved to be highly active in the Buchwald-Hartwig coupling of deactivated and sterically hindered aryl chlorides at room temperature.     

The development of efficient catalysts for palladium-catalyzed coupling reactions of aryl halides

In the mid 1990s, we started a program on the development of more efficient palladium catalysts for the C-C and C-N coupling reactions of aryl halides, especially aryl chlorides. In this contribution, our investigations on new catalyst systems and their application in organic synthesis are summarized.     

Palladium-catalyzed coupling reactions of aryl chlorides

Collectively, palladium-catalyzed coupling reactions represent some of the most powerful and versatile tools available to synthetic organic chemists. Their widespread popularity stems in part from the fact that they are generally tolerant to a large number of functional groups, which allows them to be employed in a wide range of applications. However, for many years a major limitation of palladium-catalyzed coupling processes has been the poor reactivity of aryl chlorides, which from the standpoints of cost and availability are more attractive substrates than the corresponding bromides, iodides, and triflates. Traditional palladium/triarylphosphane catalysts are only effective for the coupling of certain activated aryl chlorides (for example, heteroaryl chlorides and substrates that bear electron-withdrawing groups), but not for aryl chlorides in general. Since 1998, major advances have been described by a number of research groups addressing this challenge; catalysts based on bulky, electron-rich phosphanes and carbenes have proved to be particularly mild and versatile. This review summarizes both the seminal early work and the exciting recent developments in the area of palladium-catalyzed couplings of aryl chlorides.     

Biphenylene-substituted ruthenocenylphosphine for Suzuki-Miyaura coupling of aryl chlorides

High activity in the palladium-catalyzed Suzuki-Miyaura reactions of aryl chlorides with arylboronic acids was furnished using biphenylene-substituted di- tert-butylruthenocenylphosphine (R-Phos) as a supporting ligand. Substrate combinations even for the construction of highly hindered tetra- ortho-substituted biaryls can be achieved in good to excellent yields with low catalyst loadings in short reaction times.     

Extremely high activity catalysts for the Suzuki coupling of aryl chlorides: the importance of catalyst longevity

The incorporation of a new pi-acidic, orthometallated phosphite ligand into a palladium pre-catalyst gives considerably enhanced catalyst longevity and thus extremely high activity in the Suzuki coupling of deactivated, activated and sterically hindered aryl chloride substrates.     

Efficient Stille cross-coupling reaction using aryl chlorides or bromides in water

An efficient Stille cross-coupling reaction using a variety of aryl halides in neat water has been developed. Employing palladium-phosphinous acid catalyst [(t-Bu)(2)P(OH)](2)PdCl(2) allows formation of biaryls from aryl chlorides and bromides in good to high yields. Functional groups such as ketones and nitriles are tolerated, and organic cosolvents are not required. The air stability and solubility in water of the palladium complexes used in this study facilitate operation of the coupling reaction and product isolation. The feasibility of catalyst recycling has also been demonstrated.     

Design and synthesis of thioether-imidazolium chlorides as efficient ligands for palladium-catalyzed Suzuki-Miyaura coupling of aryl bromides with arylboronic acids

The catalyst composed of 0.25-0.025 mol % of [Pd(allyl)Cl]₂ and 0.5-0.05 mol % of the thioether-imidazolium chloride 3c was proven to be efficient in the Suzuki-Miyaura cross-coupling reactions of aryl bromides with arylboronic acids.