Highly effective activation of aryl chlorides for Suzuki coupling in aqueous media using a ferrocene-based Pd(II)–diimine catalyst

The Suzuki coupling of aryl chlorides with boronic acids using a ferrocene-containing Pd(II)–diimine complex as catalyst, in aqueous media, under microwave heating is reported. A small amount of the catalyst (0.1%) was found to be highly effective for coupling unactivated aryl chlorides with boronic acids to form sterically hindered ortho-substituted biaryls. The same catalyst also enabled the coupling of aryl bromides and iodides with various boronic acids in very high yields. The catalyst is air stable and the catalytic reaction can be completed in 15 min.     

Sterically demanding, bioxazoline-derived N-heterocyclic carbene ligands with restricted flexibility for catalysis

A unique family of N-heterocyclic carbenes derived from bioxazolines (IBiox) suitable for application in transition-metal catalysis is described. The ligands are electron rich, sterically demanding, and have restricted flexibility. Their usefulness has been demonstrated in the Suzuki-Miyaura cross-coupling of sterically hindered aryl chlorides and boronic acids. For the first time, tetraortho-substituted biaryls with methyl and larger ortho-substituents have been synthesized from aryl chlorides using the Suzuki-Miyaura method.     

General and efficient methodology for the Suzuki-Miyaura reaction in technical grade 2-propanol

The reaction profile of a series of palladium-based catalysts was examined in the Suzuki-Miyaura reaction using technical grade 2-propanol as solvent and potassium t-butoxide as base. The results generally show high activity. The method allows for the coupling of electron-rich aryl chlorides with sterically hindered aryl boronic acids to produce tri-ortho-substituted biaryls in high yields using very mild conditions and short reaction times.     

A highly active and stable imidazolidine-bridged N,O-donor ligand for efficient palladium catalyzed Suzuki–Miyaura reactions in water

Abstract  

We have used the sterically hindered N,O-donor ligand 1,4-bis(2-hydroxy-3,5-di-tert-butyl-benzyl)-imidazolidine with various Pd salts as a catalyst for the Suzuki reaction. This system exhibited excellent catalytic activity in Suzuki reactions of arylboronic acids with aryl halides, including aryl iodides, aryl bromides and activated aryl chlorides, using aqueous methanol as solvent under mild conditions. The catalytic system can be reused once without significant loss of activity.     

Highly efficient monophosphine-based catalyst for the palladium-catalyzed suzuki-miyaura reaction of heteroaryl halides and heteroaryl boronic acids and esters

A highly active and efficient catalyst system derived from a palladium precatalyst and monophosphine ligands 1 or 2 for the Suzuki-Miyaura cross-coupling reaction of heteroaryl boronic acids and esters has been developed. This method allows for the preparation of a wide variety of heterobiaryls in good to excellent yields and displays a high level of activity for the coupling of heteroaryl chlorides as well as hindered aryl and heteroaryl halides. Specific factors that govern the efficacy of the transformation for certain heterocyclic motifs were also investigated.     

Microwave-promoted Suzuki reactions of aryl chlorides in aqueous media

[reaction: see text] The microwave-promoted Suzuki coupling reaction of aryl chlorides with boronic acids performed in an aqueous media was studied using the air- and moisture-stable catalyst POPd2 (dihydrogen di-mu-chlorodichlorobis(di-tert-butylphosphinito-kappaP)dipalladate (2-)). This catalyst system under microwave conditions (150 degrees C, 15 min) provided coupled products with yields ranging from 64% to 99%. This method tolerated a variety of substituents and sterically hindered substrates.     

Ligand-supported palladium-catalyzed cross-coupling reactions of (hetero) aryl chlorides

The introduction of electron rich and sterically hindered ligands has made otherwise inert aryl chlorides and hetero aryl chlorides viable coupling partners in palladium-catalyzed Suzuki-Miyaura, Sonogashira, Stille and other types of cross-coupling reactions. This review gives highlights of cross-coupling of aryl chlorides employing in situ generated palladium catalytic systems.     

Modified (NHC)Pd(allyl)Cl (NHC = N-heterocyclic carbene) complexes for room-temperature Suzuki-Miyaura and Buchwald-Hartwig reactions

A series of (NHC)Pd(R-allyl)Cl complexes [NHC: IPr = N,N'-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, SIPr = N,N'-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene; R = H, Me, gem-Me2, Ph] have been synthesized and fully characterized. When compared to (NHC)Pd(allyl)Cl, substitution at the terminal position of the allyl scaffold favors a more facile activation step. This translates into higher catalytic activity in the Suzuki-Miyaura and Buchwald-Hartwig reactions, allowing for the coupling of unactivated aryl chlorides at room temperature in minutes. In the Suzuki-Miyaura reaction, aryl triflates, bromides, and chlorides react with boronic acids using very low catalyst loading. In the N-aryl amination reaction, a wide range of substrates has been coupled efficiently; primary-, secondary-, alkyl-, or aryl-amines react in high yields with unactivated, neutral, and activated aryl chlorides and bromides. In both reactions, extremely hindered substrates such as tri-ortho-substituted biaryls and tetra-ortho-substituted diarylamines can be produced without loss of activity. Finally, the present catalytic system has proven to be efficient with as low as 10 parts-per-million (ppm) of precatalyst in the Buchwald-Hartwig reaction and 50 ppm in the Suzuki-Miyaura reaction.     

Carbene adduct of cyclopalladated ferrocenylimine: Efficient catalyst for the Suzuki coupling of sterically hindered aryl chlorides with a weaker base and low catalyst loading

One-pot synthesis of the N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) adduct of cyclopalladated ferrocenylimine complex 1 has been described. This complex has been successfully applied to Suzuki coupling reaction. Various aryl chlorides and boronic acids can be coupled efficiently with a mild base K₃PO₄·7H₂O and low catalyst loadings. This system has been proven to be compatible with the sterically hindered aryl chlorides and some boronic acids leading to form di- and tri-ortho-substituted biaryls in high yields.     

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.     

Novel class of tertiary phosphine ligands based on a phospha-adamantane framework and use in the Suzuki cross-coupling reactions of aryl halides under mild conditions

[reaction: see text] A new class of sterically hindered phosphines based on a phospha-adamantane framework is described. Arylation or alkylation of the 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phospha-adamantane system allows for the preparation of tertiary phosphines suitable for use in palladium-catalyzed cross-coupling reactions. For example, use of a catalytic system incorporating Pd(2)(dba)(3) and 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phenyl-6-phospha-adamantane is shown to promote the Suzuki cross-coupling of aryl iodides, bromides, and activated chlorides with a variety of aryl boronic acids at room temperature in a few hours with high yields.     

Generation of an aromatic amide-derived phosphane (Aphos) library by self-assisted molecular editing and applications of Aphos in room-temperature Suzuki-Miyaura reactions

Aromatic amide-derived phosphanes (Aphos) are hemilabile P,O-coordinating ligands, which, when combined with a Pd precursor, yield a promising precatalyst system for Suzuki-Miyaura cross-coupling reactions. A focused library of Aphos ligands has been constructed for structural optimization, with the target of improving catalytic efficacy. By using microwave irradiation at accurately regulated temperature, an expeditious and reproducible one-pot synthesis and screening protocol was designed and experimentally validated. The success is based on a unique self-assisted molecular editing (SAME) process in which both the substrate and the product molecules catalyze formation of the product. Thus, starting from a 4-chlorobenzamide-derived Aphos as the substrate, parallel reactions with a selected set of arylboronic acids, in the absence of an added external phosphane ligand to Pd, produced a family of structurally edited Aphos ligands. The resultant reaction mixture containing the new Aphos, the Pd species, and the base could be used for in situ screening of the Aphos efficacy in a reference Suzuki-Miyaura coupling reaction. The structures of all Aphos ligands were characterized by 31P NMR spectroscopy and their catalytic profiles in the reference reaction were evaluated by HPLC analysis. These data allowed the identification of an efficient Aphos ligand, capable of promoting room-temperature Suzuki-Miyaura coupling of unactivated and sterically hindered aryl chlorides with arylboronic acids under mildly basic conditions.     

An extremely active and general catalyst for Suzuki coupling reaction of unreactive aryl chlorides

β-Diketiminatophosphane Pd complex 2a acted as a powerful catalyst which allows easy access to the Suzuki coupling reaction of less reactive aryl chlorides under mild conditions. A wide range of sterically hindered and deactivated aryl chlorides could be efficiently coupled at a low catalyst loading of 0.1 mol %. Furthermore, this catalytic system also proved to be highly effective in one-pot multiple couplings.     

Rapid room temperature Buchwald-Hartwig and Suzuki-Miyaura couplings of heteroaromatic compounds employing low catalyst loadings

The use of second-generation [(NHC)Pd(R-allyl)Cl] complexes for Suzuki-Miyaura and Buchwald-Hartwig cross-coupling reactions involving heteroaromatic halides at room temperature is reported. The first examples of room temperature Suzuki-Miyaura cross-coupling of deactivated aryl chlorides with alkenyl boronic acids are also disclosed. Terminal substitution at the allyl moiety of the palladium complex facilitates its activation at room temperature leading to very active catalytic species enabling the present catalytic transformations to be performed rapidly using very mild reaction conditions. Catalyst loadings can be as low as 10 ppm for the Buchwald-Hartwig aryl amination and 50 ppm for the Suzuki-Miyaura reaction.     

Carbonylative cross-coupling of ortho-disubstituted aryl iodides. convenient synthesis of sterically hindered aryl ketones

A mild and general protocol for the carbonylative cross-coupling of sterically hindered ortho-disubstituted aryl iodides is reported. Carbonylative Suzuki-Miyaura couplings of a variety of aryl boronic acids provide an array of substituted biaryl ketones in modest to excellent yield. A carbonylative Negishi coupling that utilizes alkynyl nucleophiles is also described.     

Suzuki-Miyaura cross-coupling of aryl and alkyl halides using palladium/imidazolium salt protocols

A simple new protocol for the high yielding Suzuki-Miyaura cross-couplings of aryl chlorides with aryl boronic acids using a palladium/imidazolium salt catalytic system is presented. The first examples of a palladium/imidazolium salt protocol for sp³-sp³ Suzuki-Miyaura couplings of alkyl halides are also disclosed.     

Palladium-catalyzed cross-coupling of B-benzyl-9-borabicyclo[3.3.1]nonane to furnish methylene-linked biaryls

[reaction: see text] Benzylboranes are noticeably uncommon partners within Suzuki-Miyaura coupling reactions. B-Benzyl-9-BBN was successfully coupled to a range of aryl/heteroaryl bromides, chlorides, and triflates to give pharmacologically important methylene-linked biaryl structures. Activated, deactivated, and sterically hindered substrates were successfully coupled in high yield using Pd(PPh(3))(4) or Pd(OAc)(2) with SPhos as the catalyst system.     

A novel ditopic ring-expanded N-heterocyclic carbene ligand-assisted Suzuki-Miyaura coupling reaction in aqueous media

A series of seven-membered ditopic ring-expanded N-heterocyclic carbene (dre-NHC) precursors, bearing sterically demanding and electron-rich aryl groups, were synthesised in moderate yields via the reaction of 1,2,4,5-tetrakis(bromomethyl)benzene with the corresponding N,N′-diarylformamidines in the presence of K₂CO₃ in acetonitrile under an air atmosphere. All new compounds were characterised by HRMS, NMR spectroscopy, and microanalysis, as well as X-ray crystallography for compound 1c. The development of an efficient catalytic system for the Suzuki-Miyaura coupling reaction of aryl chlorides with various boronic acids was also investigated using the in situ generated dre-NHC ligands.     

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.     

Synthesis,Crystal Structure and Catalytic Activity Palladium (Ⅱ) Complexes Containing Bulky Azole Ligands

Bulky azole ligands in combination with PdCl_2 provide three new palladium(II) complexes. All these complexes, as pre-catalysts, have high catalytic efficiency for the Suzuki-Miyaura cross-coupling reactions of sterically hindered aryl chlorides and good to high yields are obtained with low catalysts loadings(0.1 mol%) under mild conditions in air.