Non-activated Aryl Research Articles

Imidazolin-2-ylidenaminophosphines as Highly Electron-Rich Ligands for Transition-Metal Catalysts.

A variety of chemical transformations benefit from the use of strong electron-donating ancillary ligands, such as alkylphosphines or N-heterocyclic carbenes when electron-rich metal centers are required. Herein, we describe a facile and highly modular access to monodentate and bidentate imidazolin-2-ylidenamino-substituted phosphines. Evaluation of the phosphine's electronic properties substantiate that the formal replacement of alkyl or aryl groups by imidazolin-2-ylidenamino groups dramatically enhance their donor ability beyond that of alkylphosphines and even N-heterocyclic carbenes. The new phosphines have been coordinated onto palladium(II) centers, and the beneficial effect of the novel substitution patterns has been explored by using the corresponding complexes in the palladium-catalyzed Suzuki-Miyaura cross-coupling reaction of non-activated aryl chloride substrates.

Pd/graphene nanocomposite as highly active catalyst for the Heck reactions

The graphene-supported Pd (Pd/graphene) catalyst was synthesized using the graphene oxide and Pd salt as precursor; then both Pd nanoparticles and graphene oxide were chemical reduced by hydrazine hydrate. Transmission electron microscope and powder X-ray diffraction analysis indicated the Pd nanoparticles, which supported on the surface of the graphene sheets with the size of 2–6nm. The catalytic activity of Pd/graphene was investigated in Heck coupling reactions with activated and non-activated aryl substrates. The Pd/graphene composites exhibit an excellent catalytic activity, low Pd leaching, and reuse ability of at least five recycles in air for the Heck carbon-carbon coupling reaction. The experimental results showed the graphene sheets were great support for ligand-free Pd catalyst.

Arylation of non-activated C–Cl bond with Grignard reagents catalyzed by pincer [PCP]-nickel complexes

A series of pincer Ni(II) complexes were prepared and utilized in the cross-coupling reaction of non-activated aryl chlorides with Grignard reagents (The Kumada reaction). Catalytic studies revealed that complex 5 ([Ph-PNCNP-Ph]-Ni-Cl) showed the highest catalytic activity for the cross-coupling reaction in the presence of 2mol% catalyst under mild reaction condition.

ChemInform Abstract: Copper(I)‐Catalyzed Intramolecular Direct C‐Arylation of Azoles with Aryl Bromides.

A concise route to access 5H-imidazo[2,1-a]isoindole heterofused compounds by copper(I)-catalyzed intramolecular coupling of non-activated aryl bromides with azoles is reported. With CuI as catalyst, 1,10-phenanthroline as ligand, and K3PO4 as base, the reactions of 1-(2-bromobenzyl)-1H-imidazoles in DMF/o-xylene (1:1, V:V) at 145°C afford the corresponding substituted 5H-imidazo[2,1-a]isoindoles in high yields via intramolecular C-arylation.

Syntheses, characterization, and structural studies of copper(I) complexes containing 1,1'-bis(di-tert-butylphosphino)ferrocene (dtbpf) and their application in palladium-catalyzed Sonogashira coupling of aryl halides.

Four copper(I) complexes [Cu4(μ3-Cl)4(μ-dtbpf)2] (1), [Cu6(μ3-Br)4(μ2-Br)2(μ-dtbpf)3] (2), [Cu4(μ2-I)2(μ3-I)2(μ-dtbpf)2] (2) and [Cu2(μ1-CN)2(κ(2)-dtbpf)2] (4) were prepared using CuX (X = Cl, Br, I, CN) and 1,1'-bis(di-tert-butylphosphino)ferrocene (dtbpf) in 2 : 1 molar ratio in DCM-MeOH (50 : 50 V/V) at room temperature. These complexes were characterized by elemental analyses, IR, (1)H and (31)P NMR, ESI(+)-MS and electronic absorption spectroscopy. Molecular structures of the complexes 1,2 and 3 were determined crystallographically. Complexes 1 and 3 are tetrameric Cu(I) pseudo-cubane like structures with a Cu4Cl4 core, and a stepped cubane-like structure with a Cu4I4 core, respectively, whereas complex 2 shows a trimeric copper(I) framework containing two [Cu3(μ3-Br)2(μ2-Br)] units that are bridged by three bidentate μ-dtbpf ligands. Each [Cu3(μ3-Br)2(μ2-Br)] unit forms a pyramid with one copper atom at the apex and one of the triangular faces capped by one bromine atom. All the complexes were found to be efficient catalysts for the Sonogashira reaction. The coupling products were obtained in moderate to good yields (58-99%) using Pd loadings of 0.2 mol% as well as complex loading of 0.1 mol%. The (31)P NMR studies show that all the complexes are unstable during the course of tandem catalytic reaction and the dtbpf ligand migrates from copper(I) to palladium(II), which promotes palladium Sonogashira cross-coupling of activated and non-activated aryl halides.

C,N‐Palladacycles Containing N‐Heterocyclic Carbene and Azido Ligands – Effective Catalysts for Suzuki–Miyaura Cross‐Coupling Reactions

AbstractAzido‐palladacycles containing C,N‐donor and N‐heterocyclic carbene ligands, [(C,N‐L)Pd(N3)(NHC)] [NHC = IPr; 1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene], were prepared from (i) IPr and dinuclear PdII azides, [Pd(μ‐N3)(C,N‐Ln)]2 [C,N‐L1H = N,N′‐dimethylbenzylamine; C,N‐L2H = 2‐(2′‐thienyl)pyridine; C,N‐L3H = azobenzene; C,N‐L4H = 2‐(p‐tolyl)pyridine], or from (ii) NaN3 and mononuclear PdII chloride, [Pd(Cl)(IPr)(C,N‐Ln)], in aqueous solution. The structures of two of these products were determined by X‐ray crystallography. The palladacycles showed high catalytic efficiency toward activated and nonactivated aryl bromides (at room temperature) as well as aryl chlorides (at 80 °C) in Suzuki–Miyaura cross‐coupling reactions. In addition, coupling reactions of aryl chlorides using potassium aryl trifluoroborates instead of phenyl boronic acid gave good‐to‐excellent product yields.

An unprecedented iron-catalyzed cross-coupling of primary and secondary alkyl Grignard reagents with non-activated aryl chlorides

The use of N-heterocyclic carbene ligands in the iron-catalyzed cross-coupling of alkyl Grignards has allowed, for the first time, coupling of non-activated, electron rich aryl chlorides. Surprisingly, the tetrahydrate of FeCl2 was found to be a better pre-catalyst than anhydrous FeCl2. Primary Grignard reagents coupled in excellent yields while secondary Grignard reagents coupled in modest yields. The use of acyclic secondary Grignard reagents resulted in the formation of isomers in addition to the desired product. These isomeric products were formed via reversible β-hydrogen elimination, indicating that the cross-coupling proceeds through an ionic pathway.

General and highly efficient fluorinated-N-heterocyclic carbene–based catalysts for the palladium-catalyzed Suzuki–Miyaura reaction

A general and highly efficient trifluoromethylated-N-heterocyclic carbene (NHC)-based catalyst for the palladium-catalyzed Suzuki–Miyaura reaction was reported. In the presence of the catalyst, reactions of non-activated aryl chlorides and triflates with aryl boronic acids occurred at room temperature with good to excellent yields (63–98%). In addition, catalysts generated from a combination of Pd(OAc)2/imidazolium salt 6a is not only effective for the coupling of heteroaryl boronic acid with aryl halides and heteroaryl halides, but also efficient for coupling of other heteroaryl halides and heteroaryl boronic acids. Finally, the catalyst is highly effective for Suzuki–Miyaura reaction of aryl bromides and chlorides with 0.01–0.1mol% loading if the temperature was raised at refluxed THF/H2O.

Intermolecular direct arylation of five-membered ring heterocycles by non-activated aryl chlorides

The use of non-activated aryl chloride electrophiles in the direct arylation of carbon–hydrogen bonds in five-membered ring heterocycles is described. Specifically, palladium-, ruthenium-, and nickel-catalyzed transformations, as well as reactions proceeding via benzyne intermediates, are discussed.

Structure and catalytic properties of Pd encapsulated in mesoporous silica SBA-15 fabricated by two-solvent strategy

The two-solvent method was employed to prepare Pd encapsulated in mesoporous silica (Pd/SBA-15). A 3.01 wt% Pd loading was achieved without the loss of pore ordering. Highly dispersed and uniform palladium nanoparticles could be detected using transmission electron microscopy confirming also the absence of large particles outside the mesopore silica. The catalytic activities of the Pd/SBA-15 nanocomposites were investigated in Heck coupling reactions with activated and non-activated aryl substrates. The Pd/SBA-15 nanocomposite exhibits excellent catalytic activities and reuse ability in air for the Heck carbon–carbon coupling reactions.

Heterogeneously catalyzed Suzuki–Miyaura conversion of broad scope

The reaction tolerates a broad range of functional groups in the coupling partners and is usually performed in solution under homogeneous conditions at T ¢ 60 uC using 2–3 mol% catalytic amounts. The catalyst is often a Pd(0) complex with triarylphosphane ligands. 2 The catalytic cycle (Scheme 2) begins with the oxidative addition of an aryl halide to a Pd(0) species formed in situ to form an arylpalladium(II) halide intermediate. 3 Chloroarenes, especially nonactivated aryl chlorides, are notoriously less reactive due to the stability of the C–Cl bond (the relative reactivity of Ar–X is correlated to the respective bond dissociation energy: Ph–Cl: 96 kcal mol 21 ,P h–Br: 81 kcal mol 21 ,P h–I: 65 kcal mol 21 ). This, from a practical viewpoint adds cost to the products of traditional Suzuki–Miyaura reactions, because aryl chlorides are considerably less costly than iodo and bromoarenes. Another significant problem preventing widespread utilization of palladium homogeneous catalysis lies in the Pd impurities left in the reaction product since the upper limit for residual Pd levels in active pharmaceutical ingredients is typically very low (less than 5 ppb). 4 Removing residual palladium in a pharmaceutical substance to reduce its content to the maximum acceptable concentration limit requires rigorous product–catalyst separation processing (a purification process that often makes use of silica-based Pd scavengers). Intense research activities have therefore being devoted in the last decade to finding heterogeneous Pd catalysts of broad scope, capable of affording the recovery and reuse of the valued palladium while avoiding time-consuming catalyst separation and product purification steps which impact cost and worsen the environmental footprint of the reaction. 5

Fast Suzuki–Miyaura cross-coupling reaction catalyzed by the Na2Pd2Cl6 complex with ethyl calix[4]aryl acetate at room temperature in aqueous medium under ligand-free and ambient atmosphere

The new Na2Pd2Cl6 complex with ethyl calix[4]aryl acetate 2 was prepared simply and efficiently by the extraction of sodium ion from Na2PdCl4 aqueous solution with ethyl calix[4]aryl acetate. The structure of complex 2 could be verified by X-ray single crystal structure determination. The complex 2 was tested as catalyst in Suzuki–Miyaura cross-coupling reaction at room temperature in CH3OH/H2O medium under ambient conditions. Using 0.2 mol% of the complex 2 in the presence of K2CO3 as base offered excellent yields in the reaction of activated and non-activated aryl bromides with aryl boronic acids within 10 min. The key for achieving a very rapid and almost quantitative coupling is probably the use of ethyl calix[4]aryl acetate possessing extended hydrophobic host cavities and surface active properties. In addition, it was found that both solvent and base had a fundamental influence on the reaction.

Palladium-Catalyzed Heck Reaction of Aryl Chlorides under Mild Conditions Promoted by Organic Ionic Bases

An efficient Pd-catalyzed Heck reaction of aryl chlorides with olefins under mild conditions is described. High yields of products were achieved with n-Bu(4)N(+)OAc(-) as base. Significantly, the temperature of the Heck reaction of diverse nonactivated aryl chlorides can be lowered to 80 °C. The new reaction system can also tolerate a wider range of olefins.

Palladium‐Catalyzed Synthesis of Arylpropargyl Ethers

Adamant about this: A variety of aryl and heteroaryl propargyl ethers are obtained in good to excellent yields from activated and non-activated aryl bromides and chlorides in the presence of a sterically hindered, air-stable ligand by using a general palladium-catalyzed synthesis. Our protocol complements the known syntheses for alkynyl aryl ethers and 2H-1-benzopyrans and should find further applications in organic synthesis.

Copper‐Catalyzed Cross‐Coupling Reaction of Organoboron Compounds with Primary Alkyl Halides and Pseudohalides

With the crucial use of LiOtBu as the base, the copper-catalyzed cross-coupling of non-activated aryl electrophiles with organoboron compounds tolerates iodide, bromide, tosylate, mesylate, and even chloride as the leaving group.

P,O-Ferrocenes in Suzuki−Miyaura C,C Couplings

It is generally accepted that efficient Suzuki−Miyaura catalysts contain sterically demanding and strongly Lewis-basic phosphines. Herein we report on the use of chiral P,O-ferrocenes in the synthesis of sterically hindered biaryls by the palladium-catalyzed Suzuki−Miyaura coupling. It is apparent that a decrease of the phosphine Tolman cone angle results in a higher catalytic productivity, which is contradictory to what is known as a good Suzuki−Miyaura catalyst. In addition, the P,O-ferrocenes were successfully applied for couplings of nonactivated aryl bromides with aromatic boronic acids at catalyst loadings as low as 1 ppm achieving quite high turnover numbers (TONs) of up to 750,000.

Synthesis, characterization and application of pincer-type nickel iminophosphinite complexes

Two pincer-type nickel iminophosphinite complexes, [(2-(CH NR)-6-(OPR′ 2)C 6H 3)NiCl] (R = 2,6- iPr 2C 6H 3, R′ = Ph ( 2a) or iPr ( 2b)), were synthesized from the reactions of bis(1,5-cyclooctadiene)nickel(0) and corresponding iminophosphinite ligands. The solid state structures of the nickel pincer complexes were determined by X-ray single crystal diffraction studies. They were successfully employed in the Kumada reaction of non-activated aryl chlorides and phenylmagnesium bromide at room temperature.

Cu-Catalyzed Carbon-Heteroatom Coupling Reactions under Mild Conditions Promoted by Resin-Bound Organic Ionic Bases

Resin-bound organic ionic bases (RBOIBs) were developed in which tetraalkyl-ammonium or phosphonium cations are covalently attached to solid resins. The application tests showed that the performance of the tetraalkyl-ammonium-type RBOIBs is slightly better than that of the corresponding Cs salts in Cu-catalyzed C-N cross-couplings, while the tetraalkylphosphonium-type RBOIBs are significantly better than all the inorganic bases. With these newly developed RBOIBs, room-temperature Cu-catalyzed C-N coupling with various nonactivated aryl iodides and even aryl bromides can be readily accomplished. Moreover, RBOIBs can be easily recycled and reused for a number of times without much drop of activity. The good performances of RBOIBs are proposed to arise from the relatively weak binding forces between the cationic polymer backbone and basic anions, as opposed to the strong metal-anion interactions in the inorganic bases. Further applications of RBOIBs in Ni-catalyzed Suzuki-type couplings at room temperature, Cu-catalyzed C-N couplings at -30 °C, a Pd-catalyzed Heck reaction at 60 °C, and Cu-catalyzed C-S couplings at room temperature demonstrate that RBOIBs are generally applicable bases with improved performance for many other types of organic transformations.

ChemInform Abstract: The First Successful Copper(I)-Catalysed Alkoxydehalogenation of Non- Activated Aryl Chlorides.

A study of the stability of the copper catalyst has led to the first successful copper(I) catalysed alkoxydehalogenation of non-activated aryl chlorides.

Carboranyl phosphites: the electronic effect in the Suzuki- Miyaura reaction

Isomeric carborane-containing phosphite ligands possessing different electronic properties have been synthesized. Their use in the Pd-catalyzed Suzuki-Miyaura reaction involving activated aryl bromides showed that phosphite with 9-o-carborane substituent has proved more efficient, with carboranyl phosphite having 1-m- carborane fragment being more efficient in the reactions with nonactivated aryl bromides.