Hartwig-Buchwald amination on solid supports: a novel access to a diverse set of 1H-benzotriazoles

Hartwig-Buchwald amination reactions of bromo- and chloroarenes were performed on solid supports with triazene-linked arenes. Immobilized 2-haloarenes were treated with diverse primary amines and anilines at 100 degrees C under palladium catalysis to yield N-substituted 2-aminoarenes. The latter were alternatively formed through reaction of bromo- and chloroarenes with immobilized primary 2-aminobenzenes. Subsequent acidic cleavage furnished 1H-benzotriazoles in high purities. The two described routes allow a broad range of the substitution pattern of N-substituted 1H-benzotriazoles.     

Layered double hydroxide supported nanopalladium catalyst for Heck-, Suzuki-, Sonogashira-, and Stille-type coupling reactions of chloroarenes

Layered double hydroxide and Merrifield resin supported nanopalladium(0) catalysts are prepared by an exchange of PdCl(4)(2-) followed by reduction and well characterized for the first time. The ligand-free heterogeneous layered double hydroxide supported nanopalladium (LDH-Pd(0)) catalyst using the basic LDH in place of basic ligands indeed exhibits higher activity and selectivity in the Heck olefination of electron-poor and electron-rich chloroarenes in nonaqueous ionic liquids (NAIL) over the homogeneous PdCl(2) system. Using microwave irradiation, the rate of the Heck olefination reaction is accelerated, manifold with the highest turnover frequency ever recorded in the case of both electron-poor and electron-rich chloroarenes. The basic LDH-Pd(0) shows a superior activity over a range of supported catalysts, from acidic to weakly basic Pd/C, Pd/SiO(2,) Pd/Al(2)O(3), and resin-PdCl(4)(2-) in the Heck olefination of deactivated electron-rich 4-chloroanisole. The use of LDH-Pd(0) is extended to the Suzuki-, Sonogashira-, and Stille-type coupling reactions of chloroarenes in an effort to understand the scope and utility of the reaction. The catalyst is quantitatively recovered from the reaction by a simple filtration and reused for a number of cycles with almost consistent activity in all the coupling reactions. The heterogeneity studies provide an insight into mechanistic aspects of the Heck olefination reaction and evidence that the reaction proceeds on the surface of the nanopalladium particles of the heterogeneous catalyst. TEM images of the fresh and used catalyst indeed show that the nanostructured palladium supported on LDH remains unchanged at the end of the reaction, while the XPS and evolved gas detection by TGA-MS of the used catalyst identify ArPdX species on the heterogeneous surface. Thus, the ligand-free nanopalladium supported on LDH, synthesized by the simple protocol, displays superior activity over the other heterogeneous catalysts inclusive of nanopalladium in the C-C coupling reactions of chloroarenes.     

Introduction of (2‐CF3)Phenyl Group via Nickel‐catalyzed C–Cl Bond Activation and Arylation

A simple and mild catalytic arylation via C–Cl bond activation is described. The phenyl group containing a 2‐trifluoromethyl group was introduced into the aromatic imine molecules through C,C‐coupling reaction between chloroarenes and the organozinc reagent, bis(2‐(trifluoromethyl)phenyl)zinc, with tetrakis(trimethylphosphine)nickel(0) complex as an effective catalyst. Under catalytic conditions chlorinated benzalimines were quantitatively converted into the expected benzalimines with trifluoromethyl group(s).     

Palladium-catalyzed alpha-arylation of esters with chloroarenes

Palladium-catalyzed alpha-arylations of esters with chloroarenes are reported. The reactions of chloroarenes with the sodium enolates of tert-butyl propionate and methyl isobutyrate occur in high yields with 0.2-1 mol % of {[P(t-Bu)3]PdBr}2 or the combination of Pd(dba)2 and P(t-Bu)3 as catalyst. The reactions of chloroarenes with the Reformatsky reagent of tert-butyl acetate were most challenging but occurred in high yields for chlorobenzene and electron-poor chloroarenes catalyzed by 1 mol % of Pd(dba)2 and pentaphenylferrocenyl di-tert-butylphosphine (Q-phos).     

Take the Right Catalyst: Palladium-Catalyzed C-C, C-N, and C-O Bond Formation on Chloroarenes

Unreactive chloroarenes have been outwitted: The key to successful C-C, C-N, and C-O bond formation on chloroarenes is the development and optimization of suitable catalysts. Electron-rich alkylphosphanes are mandatory as ligands in these palladium-catalyzed reactions.     

Efficient dendritic diphosphino Pd(II) catalysts for the Suzuki reaction of chloroarenes

reaction: see text]. The monomeric diphosphino Pd(II) complex 1 and the first three generations of dendritic analogues G1, G2, and G3 are efficient catalysts for the Suzuki coupling reaction of halogenoarenes, including chloroarenes with phenylboronic acid. The recovery and reuse of the dendritic catalysts G1, G2, and G3 are discussed.     

Atom-efficient Pd-catalyzed cross-couplings of chloroarenes with triarylbismuth reagents

Various Pd-catalyzed protocols have been developed for the atom-efficient cross-coupling of chloroarenes with triarylbismuth reagents. Using the developed protocols, an efficient synthesis of unsymmetrical biaryls in good to excellent yields was achieved by employing electron-deficient chloroarenes and a range of triarylbismuth reagents.     

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.     

Palladium nanoparticles stabilized by sterically hindered phosphonium salts as Suzuki cross-coupling catalysts

Palladium nanoparticles with an average size of 2.5±0.5 nm formed from palladium acetate in the presence of tri-tert-butyl(decyl)phosphonium tetrafluoroborate without an additional reducing agent exhibit high activity as a catalyst for the Suzuki cross-coupling reaction involving bromo- and chloroarenes under mild conditions.     

Copper-catalyzed Suzuki cross-coupling using mixed nanocluster catalysts

A small library of copper and noble metal nanoclusters is designed and synthesized. These clusters are tested as catalysts in the Suzuki cross-coupling of various aryl halides with phenylboronic acid. It is found that copper and copper/noble metal combination nanoclusters are active catalysts for this reaction, the most active being the combined copper/palladium clusters. Iodo-, bromo-, and chloroarenes can be used. In the case of p-nitrobromobenzene, a one-pot cross-coupling and selective hydrogenation is achieved.     

Progress in the palladium-catalyzed cyanation of aryl chlorides

The development of new palladium catalysts for the cyanation of various aryl and heteroaryl chlorides is described. The combination of amine co-catalysts with chelating phosphine ligands, for example, 1,4-bis(diphenylphosphino)butane (dppb) or 1,5-bis(diphenylphosphino)pentane (dpppe), allows an efficient cyanation of chloroarenes with simple potassium cyanide. General palladium-catalyzed cyanation of nonactivated and deactivated chloroarenes is possible for the first time. Studies of the oxidative addition of aryl halides to palladium triphenylphosphine complexes in the presence and absence of amines suggest that the co-catalyst is capable of preventing catalyst deactivation caused by the presence of excess cyanide ions in solution.     

Sequential photostimulated reactions of trimethylstannyl anions with aromatic compounds followed by palladium-catalyzed cross-coupling processes

The photostimulated reactions of several mono-, di-, and trichloroarenes and aryltrimethylammonium salts with Me(3)Sn(-) ions in liquid ammonia gave good yields of stannanes by the S(RN)1 mechanism. If the chloroarenes are not soluble in liquid ammonia, diglyme is another solvent to perform these reactions. The stannanes thus obtained can be arylated by further reaction with haloarenes through palladium-catalyzed reactions. If the palladium-catalyzed reaction is performed with a chloroiodoarene as substrate, the stannane reacts faster by the C-I bond via chemoselective cross-coupling reaction to give a chloroarene as product, which can be further arylated by a consecutive S(RN)1-Stille reaction or react with other substrates by another palladium-catalyzed reaction. These sequential reactions can also be performed with substrates with two leaving groups to give products in high yields.     

Hydrogenation and dehalogenation under aqueous conditions with an amphiphilic-polymer-supported nanopalladium catalyst

An amphiphilic polystyrene-poly(ethylene glycol) resin supported nanopalladium particle catalyzed hydrogenation of olefins and hydrodechlorination of chloroarenes under aqueous conditions is presented.     

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.     

Chloropalladated propargyl amine: a highly efficient phosphine-free catalyst precursor for the Heck reaction

[reaction: see text] The palladacycle (Pd[k(1)-C, k(1)-N-C=(C(6)H(5))C(Cl)CH(2)NMe(2)](mu-Cl))(2) 1 derived from the chloropalladation of 3-(dimethylamino)-1-phenyl-1-propyne promotes the arylation of olefins under relatively mild reaction conditions. The coupling of iodoarenes and activated bromoarenes with n-butylacrylate and styrene occurs at room temperature. Turnover numbers of up to 85 000 have been achieved with deactivated bromoarenes and up to 1000 for activated chloroarenes at higher temperatures (80-150 degrees C).     

Thermal Reactions of Chloroarenes with Hydrogen Sulfide in the Presence of Methanol

Gas-phase reactions of chloroarenes (ClC₆H₄X, X = H, 4-CH₃, 4-OH, 4-Cl, 4-CF₃) with hydrogen sulfide or its precursors were investigated in the presence of methanol, which was a stronger H-donor than hydrogen sulfide. Introducing methanol increased the selectivity of arenethiols formation at X = H and 4-CH₃ and did not affect the reaction selectivity at acceptor X. The efficiency of methanol influence was considered from the viewpoint of free-radical reaction mechanism and the stability of the arenethiyl radicals.     

Productive chloroarene C-cl bond activation: palladium/phosphine-catalyzed methods for oxidation of alcohols and hydrodechlorination of chloroarenes

The palladium/phosphine-catalyzed productive chloroarene C-Cl bond activation provides general, efficient, and functional group friendly methods for the selective oxidation of alcohols and the hydrodechlorination of chloroarenes.     

Synthesis of aromatic acids via catalysed methyl formate-chloroarene reactions

Chlorobenzene and more generally, chloroarenes, can be converted into aromatic acids via catalytic reaction with aqueous methyl formate under biphasic conditions. The only efficient catalyst is [PdCl₂(PCy₃)₂] (Cy = cyclohexyl). [RU₃(CO)₁₂] and ammonium formate improve yield and selectivity. The mechanism should involve oxidative addition of the C---Cl bond to a zero-valent Pd species followed by CO insertion. The palladium catalyst may also directly activate methyl formate. The procedure is convenient (no solvent, no initial pressurization) and at least as efficient as previously described methods.     

Synthesis and physical properties of liquid crystals having a chlorine atom in the lateral position of a benzene ring

Novel liquid crystalline 3,6-disubstituted cyclohex-2-en-1-ones and 1,4-disubstituted 2-chlorobenzenes are presented. The method of transformation of cyclohex-2-en-1-ones into chloroarenes in a one-pot procedure, together with the nature of the mesomorphic phases and some physical properties of single compounds and nematic mixtures comprising them are reported.     

Nonaqueous ionic liquids: superior reaction media for the catalytic Heck-vinylation of chloroarenes

Nonaqueous ionic liquids, that is molten salts, constitute an activating and stabilizing noninnocent solvent for the palladium-catalyzed Heck-vinylation of all types of aryl halides. Especially with chloroarenes an improved activity and stability of almost any known catalyst system is observed as compared to conventional, molecular solvents (e.g. dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP), or dioxane). Thus, even catalytic amounts of ligand-free PdCl2 yield stilbene from technically interesting chlorobenzene and styrene in high yield (turnover number (TON) = 18) without the need for further promoting salt additives such as tetraphenylphosphonium chloride. The scope of the new reaction medium is outlined for the first time for the vinylation of various aryl halides using different mono- and disubstituted olefins as well as a variety of known palladium(0) and palladium(II) catalyst systems. Furthermore, a novel means of catalyst recycling is presented and its scope is evaluated.