Single‐Electron‐Transfer‐Induced Coupling of Arylzinc Reagents with Aryl and Alkenyl Halides

Arylzinc reagents, prepared from aryl halides/zinc powder or aryl Grignard reagents/zinc chloride, were found to undergo coupling with aryl and alkenyl halides without the aid of transition‐metal catalysis to give biaryls and styrene derivatives, respectively. In this context, we have already reported the corresponding reaction using aryl Grignard reagents instead of arylzinc reagents. Compared with the Grignard cross‐coupling, the present reaction features high functional‐group tolerance, whereby electrophilic groups such as alkoxycarbonyl and cyano groups are compatible as substituents on both the arylzinc reagents and the aryl halides. Aryl halides receive a single electron and thereby become activated as the corresponding anion radicals, which react with arylzinc reagents, thus leading to the cross‐coupling products.     

A Robust and Broadly Applicable Cobalt‐Catalyzed Cross‐Coupling of Functionalized Bench‐Stable Organozinc Pivalates with Unsaturated Halides

We report a robust and broadly applicable CoCl₂‐catalyzed cross‐coupling between functionalized aryl and heteroaryl zinc pivalates and various electron‐poor aryl and heteroaryl halides (X=Cl, Br, I). Couplings with (E)‐ or (Z)‐bromo‐ or iodo‐alkenes proceed with retention of configuration. Also, alkynyl bromides react with arylzinc pivalates providing arylated alkynes.     

Room‐temperature Suzuki–Miyaura cross‐coupling reaction with α‐diimine Pd(II) catalysts

An α‐diimine Pd(II) complex containing chiral sec‐phenethyl groups, {bis[N,N′‐(4‐methyl‐2‐sec‐phenethylphenyl)imino]‐2,3‐butadiene}dichloropalladium (rac‐ C1 ), was synthesized and characterized. rac‐ C1 was applied as an efficient catalyst for the Suzuki–Miyaura cross‐coupling reaction between various aniline halides and arylboronic acid in PEG‐400–H₂O at room temperature. Among a series of aniline halides, rac‐ C1 did not catalyze the cross‐coupling of aniline chlorides and fluorides but efficiently catalyzed the cross‐coupling of aniline bromides and iodides with phenylboronic acid. The catalytic activity reduced slightly with increasing steric hindrance of the aniline bromides. The complexes {bis[N,N′‐(4‐fluoro‐2,6‐diphenylphenyl)imino]‐2,3‐butadiene}dichloropalladium and {bis[N,N′‐(4‐fluoro‐2,6‐diphenylphenyl)imino]acenaphthene}dichloropalladium were also found to be efficient catalysts for the reaction. Copyright © 2015 John Wiley & Sons, Ltd.     

CuO Nanoparticles as Effective Reusable Heterogeneous Catalyst for S‐Arylation Reactions

Copper(II) oxide nanoparticles have been synthesized from Cu(OAc)₂ via a simple hydrolysis route and were found to be an efficient and inexpensive catalyst for ligand free C? S cross‐coupling reactions of malononitrile? CS₂ adduct with various aryl halides. Aryl iodides and bromides, with electron‐withdrawing as well as electron‐releasing groups on the aromatic ring, undergo coupling reactions in good yields.     

Stereospecific synthesis of a family of novel (E)‐2‐aryl‐1‐silylalka‐1,4‐dienes or (E)‐4‐aryl‐5‐silylpenta‐1,2,4‐trienes via a cross‐coupling of (Z)‐silyl(stannyl)ethenes with allyl halides or propargyl bromide

Stereospecific synthesis of a family of novel (E)‐2‐aryl‐1‐silylalka‐1,4‐dienes or (E)‐4‐aryl‐5‐silylpenta‐1,2,4‐trienes via a cross‐coupling of (Z)‐silyl(stannyl)ethenes with allyl halides or propargyl bromide is described. In the reaction with allyl bromide, either a Pd(dba)₂? CuI combination (dba, dibenzylideneacetone) in DMF or copper(I) iodide in DMSO–THF readily catalyzes or mediates the coupling reaction of (Z)‐silyl(stannyl)ethenes at room temperature, producing novel vinylsilanes bearing an allyl group β to silicon with cis ‐disposition in good yields. Allyl chlorides as halides can be used in the CuI‐mediated reaction. CuI alone much more effectively mediates the cross‐coupling reaction with propargyl bromide in DMSO–THF at room temperature compared with a Pd(dba)₂? CuI combination catalysis in DMF, providing novel stereodefined vinylsilanes bearing an allenyl group β to silicon with cis ‐disposition in good yields. Copyright © 2008 John Wiley & Sons, Ltd.     

Palladium supported on silica–chitosan hybrid material (Pd‐CS@SiO2) for Suzuki–Miyaura and Mizoroki–Heck cross‐coupling reactions

Palladium supported on silica–chitosan hybrid material was prepared and characterized using thermogravimetric and differential thermogravimetric analyses, scanning electron microscopy, and Fourier transform infrared, energy‐dispersive X‐ray and X‐ray photoelectron spectroscopies. The prepared Pd‐CS@SiO₂ catalyst (1 mol%) was used for the Suzuki–Miyaura cross‐coupling reaction of various aryl halides and arylboronic acids in 95% ethanol at 80 °C and the Mizoroki–Heck reaction in dimethylformamide at 110 °C using K₂CO₃ as a base. The developed catalyst is well suitable for the 3R approach (recoverable, robust, recyclable) for cross‐coupling reactions without appreciable loss of its activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Palladium‐catalysed Suzuki cross‐coupling of primary alkylboronic acids with alkenyl halides

The Suzuki reaction of primary alkylboronic acids with alkenyl halides proceeds nicely using the air‐stable catalyst PdCl(C₃H₅)(dppb), Cs₂CO₃ as base and toluene or xylene as solvent. A minor effect of the substituent position of the alkenyl bromide was observed. Quite similar yields were observed in the presence of α‐ or β‐substituted alkenyl bromides such as 2‐bromobut‐1‐ene or 1‐bromo‐2‐methylprop‐1‐ene with this catalyst. This reaction proceeded with a variety of alkylboronic acids such as 2‐phenylethylboronic acid or n‐octylboronic acid. Lower yields of coupling products were obtained in the presence of an alkenyl chloride. Copyright © 2008 John Wiley & Sons, Ltd.     

Highly Efficient Palladacycle/Dihydroimidazolium Chloride System for the Suzuki‐Miyaura Cross‐Coupling of Aryl Halides (I,Br, Cl) with Arylboronic Acids

A combination of a tertiary amine‐based palladacycle and an N‐heterocyclic carbene ligand precursor ( 1 , N,N‐bis‐mesityl‐4,5‐dihydroimidazolium chloride) has been applied to catalyze the Suzuki‐Miyaura cross‐coupling of aryl halides with arylboronic acids. The substrate scope is general: a variety of electron rich and deficient aryl halides (I, Br, Cl) and arylboronic acids were found to undergo the cross‐coupling reaction in good to excellent yields at low catalyst loading of 0.01–1 mol%.     

Pd(0)‐Catalyzed Tandem One‐Pot Reaction of Biphenyl Ketones/Aldehydes to the Corresponding Di‐substituted Aryl Olefins

Synthesis of di‐substituted aryl olefins via a Pd(0)‐catalyzed cross‐coupling reaction of biphenyl ketones/aldehydes, tosylhydrazide, and aryl bromides (or benzyl halides) was developed. This methodology was achieved by one‐pot two‐step reactions involving the preparation of N ‐tosylhydrazones by reacting tosylhydrazide with biphenyl ketones/aldehydes, followed by coupling with aryl bromides (or benzyl halides) in the presence of Pd(PPh₃ )₄ and lithium t ‐butoxide to produce various di‐substituted aryl olefins in moderate to good yields.     

Pd‐SBT@MCM‐41: As an efficient,stable and recyclable organometallic catalyst for C‐C coupling reactions and synthesis of 5‐substituted tetrazoles

A palladium S‐benzylisothiourea complex was anchored on functionalized MCM‐41 (Pd‐SBT@MCM‐41) and applied as efficient and reusable catalyst for the synthesis of 5‐substituted 1H –tetrazoles using [2 + 3] cycloaddition reaction of various organic nitriles with sodium azide (NaN₃) in poly(ethylene glycol) (PEG) as green solvent. Also this catalyst was applied as an versatile organometallic catalyst for Suzuki cross‐coupling reaction of aryl halides and phenylboronic acid (PhB(OH)₂) or sodium tetraphenyl borate (NaB(Ph)₄). This nanocatalyst was characterized by thermal gravimetric analysis (TGA), X‐ray Diffraction (XRD), scanning electron microscopy (SEM), inductively Coupled Plasma (ICP) and N₂ adsorption–desorption isotherms techniques. Recovery of the catalyst is easily achieved by centrifugation for several consecutive runs.     

Mild Cobalt‐Catalyzed Negishi Cross‐Couplings of (Hetero)arylzinc Reagents with (Hetero)aryl Halides

A catalytic system consisting of CoCl₂ ? 2 LiCl (5 mol %) and HCO₂Na (50 mol %) enables the cross‐coupling of various N‐heterocyclic chlorides and bromides as well as aromatic halogenated ketones with various electron‐rich and ‐poor arylzinc reagents. The reactions reached full conversion within a few hours at 25 °C.     

The first stereospecific arylation of (Z)‐germyl(stannyl)ethenes with an aryl halide or heteroaryl halide under palladium‐catalysis

A combination catalyst of Pd(dba)₂‐PPh₃‐CuI‐LiCl or Pd(dba)₂‐P(2‐furyl)₃‐CuI‐LiCl effectively catalyzed the cross‐coupling of (Z)‐germyl(stannyl)ethenes with aryl halides, providing novel triethyl(2,2‐diarylethenyl)germanes in good to high yields. The reaction proceeds with retention of configuration. Cross‐coupling results in the formation of phenylene or phenyleneethynylene derivatives with terminal stereochemically defined vinylgermane unit(s). Copyright © 2008 John Wiley & Sons, Ltd.     

Mechanism of (Salen)manganese(III)‐Catalyzed Oxidation of Aryl Phenyl Sulfides with Sodium Hypochlorite

The oxidation of 4‐substituted phenyl phenyl sulfides was carried out with several oxo(salen)manganese(V) complexes in MeCN/H₂O 9 : 1. The kinetic data show that the reaction is first‐order each in the oxidant and sulfide. Electron‐attracting substituents in the sulfides and electron‐releasing substituents in salen of the oxo(salen)manganese(V) complexes reduce the rate of oxidation. A Hammett analysis of the rate constants for the oxidation of 4‐substituted phenyl phenyl sulfides gives a negative ρ value (ρ=?2.16) indicating an electron‐deficient transition state. The log k₂ values observed in the oxidation of each 4‐substituted phenyl phenyl sulfide by substituted oxo(salen)manganese(V) complexes also correlate with Hammett σ constants, giving a positive ρ value. The substituent‐, acid‐, and solvent‐effect studies indicate direct O‐atom transfer from the oxidant to the substrate in the rate‐determining step.     

Carbon–carbon coupling reactions catalyzed by supported Pd porphyrins

The tetrakis(4‐N‐methylpyridinium)porphyrinatopalladium(II) iodide, [Pd(TMPyP)]I₄, supported on Dowex 50WX8 and Amberlite IR‐120 ion‐exchange resins, was used as heterogeneous, recyclable and active catalyst for the Suzuki–Miyaura and Heck cross‐coupling reactions. These catalysts were applied to coupling of various aryl halides with phenylboronic acid and styrene in Suzuki and Heck reactions, respectively, and the corresponding products were obtained in excellent yields and short reaction times. The catalysts could be recovered easily by simple filtration and reused several times without significant loss of their catalytic activity. The catalysts were characterized by diffuse‐reflectance UV–visible spectroscopy and scanning electron microscopy, and their stability was confirmed by TGA. Copyright © 2014 John Wiley & Sons, Ltd.     

Palladium‐Catalyzed Cross‐Coupling of Unactivated Aryl Sulfides with Arylzinc Reagents under Mild Conditions

Cross‐coupling of general aryl alkyl sulfides with arylzinc reagents proceeds smoothly, even at room temperature or below, with a palladium–N‐heterocyclic carbene (NHC) catalyst. When combined with reactions that are unique to organosulfurs, that is, the S_NAr sulfanylation or Pummerer reaction, the cross‐coupling offers interesting transformations that are otherwise difficult to achieve. An alkylsulfanyl group is preferentially converted whilst leaving the tosyloxy and chloro intact, which expands the variety of orthogonal cross‐coupling.     

N‐heterocyclic carbene–palladium(II) complex supported on magnetic mesoporous silica for Heck cross‐coupling reaction

Magnetic mesoporous silica was prepared via embedding magnetite nanoparticles between channels of mesoporous silica (SBA‐15). The prepared composite (Fe₃O₄@SiO₂‐SBA) was then reacted with 3‐chloropropyltriethoxysilane, sodium imidazolide and 2‐bromopyridine to give 3‐(pyridin‐2‐yl)‐1H‐imidazol‐3‐iumpropyl‐functionalized Fe₃O₄@SiO₂‐SBA as a supported pincer ligand for Pd(II). The functionalized magnetic mesoporous silica was further reacted with [PdCl₂(SMe₂)₂] to produce a supported N‐heterocyclic carbene–Pd(II) complex. The obtained catalyst was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, energy‐dispersive X‐ray analysis, vibrating sample magnetometry, Brunauer–Emmett–Teller surface area measurement and X‐ray diffraction. The amount of the loaded complex was 80.3 mg g^?1, as calculated through thermogravimetric analysis. The formation of the ordered mesoporous structure of SBA‐15 was confirmed using low‐angle X‐ray diffraction and transmission electron microscopy. Also, X‐ray photoelectron spectroscopy confirmed the presence of the Pd(II) complex on the magnetic support. The prepared magnetic catalyst was then effectively used in the coupling reaction of olefins with aryl halides, i.e. the Heck reaction, in the presence of a base. The reaction parameters, such as solvent, base, temperature, amount of catalyst and reactant ratio, were optimized by choosing the coupling reaction of 1‐bromonaphthalene and styrene as a model Heck reaction. N‐Methylpyrrolidone as solvent, 0.25 mol% catalyst, K₂CO₃ as base, reaction temperature of 120°C and ultrasonication of the catalyst for 10 min before use provided the best conditions for the Heck cross‐coupling reaction. The best results were observed for aryl bromides and iodides while aryl chlorides were found to be less reactive. The catalyst exhibited noticeable stability and reusability.     

Kinetics and mechanism of the reaction of substituted benzyl bromides with copper in dimethylformamide

The reaction of copper metal with various substituted benzyl bromides in dimethylformamide has been studied and the kinetic and thermodynamic parameters of the reaction have been obtained. Hammett plots of log(k/k°) vs the substituent constant σ gave good correlations (ρ = 0.24, S_ρ = 0.03, r = 0.951). The structure of the organic group has little effect on the rate of reaction of substituted benzyl bromides with copper. In the absence of atmospheric oxygen, oxidative dissolution of copper occurred by the mechanism of single‐electron transfer with the formation of 1,2‐diphenylethanes and copper(I) complexes. The stereochemistry and intermediate compound were also studied and the reaction mechanism is discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

Application of ortho‐palladated homoveratrylamine complex containing mixed phosphorus–nitrogen donors in the Suzuki reaction

The catalytic activity of [Pd{C₆H₂(CH₂CH₂NH₂)‐(OMe)₂,3,4}Br(PPh₃)] monomeric ortho‐palladated complex of homoveratrylamine and triphenylphosphine was investigated in the Suzuki cross‐coupling reaction of various aryl halides with aryl boronic acids. The substituted biaryls were produced in excellent yields using a catalytic amount of this complex in ethanol at 60°C. Copyright © 2012 John Wiley & Sons, Ltd.     

Kinetic Studies on the Palladium(II)‐Catalyzed Oxidative Cross‐Coupling of Thiophenes with Arylboron Compounds and Their Mechanistic Implications

Reaction orders for the key components in the palladium(II)‐catalyzed oxidative cross‐coupling between phenylboronic acid and ethyl thiophen‐3‐yl acetate were obtained by the method of initial rates. It turned out that the reaction rate not only depended on the concentration of palladium trifluoroacetate (reaction order: 0.97) and phenylboronic acid (reaction order: 1.26), but also on the concentration of the thiophene (reaction order: 0.55) and silver oxide (reaction order: ?1.27). NMR spectroscopy titration studies established the existence of 1:1 complexes between the silver salt and both phenylboronic acid and ethyl thiophen‐3‐yl acetate. A low inverse kinetic isotope effect (k_H/k_D=0.93) was determined upon employing the 4‐deuterated isotopomer of ethyl thiophen‐3‐yl acetate and monitoring its reaction to the 4‐phenyl‐substituted product. A Hammett analysis performed with para‐substituted 2‐phenylthiophenes gave a negative ρ value for oxidative cross‐coupling with phenylboronic acid. Based on the kinetic data and additional evidence, a mechanism is suggested that invokes transfer of the phenyl group from phenylboronic acid to a 1:1 complex of palladium trifluoroacetate and thiophene as the rate‐determining step. Proposals for the structure of relevant intermediates are made and discussed.     

Hiyama cross‐coupling reaction catalyzed by a palladium salt of 1‐benzyl‐4‐aza‐1‐azoniabicyclo[2.2.2]octane chloride under microwave irradiation

An efficient catalytic system using 1‐benzyl‐4‐aza‐1‐azoniabicyclo[2.2.2]octane chloride ((BeDABCO)₂Pd₂Cl₆) was developed for the Hiyama cross‐coupling reaction of various aryl halides with triethoxy(phenyl)silane. The substituted biaryls were produced in excellent yields in short reaction times using a catalytic amount of this catalyst in NMP at 100 °C. Copyright © 2014 John Wiley & Sons, Ltd.