Bis-diimidazolylidine complexes of nickel: investigations into nickel catalyzed coupling reactions

Air and moisture stable homoleptic bis(diimidazolylidine)nickel(II) complexes, ([(diNHC)(2)Ni](2+)) 3a,b and their corresponding silver(I) 4a,b and palladium(II) 5a,b complexes were synthesized and characterized by NMR and single crystal X-ray analysis. The catalytic potential of complex 3a was assessed in Mizoroki-Heck and Suzuki-Miyaura coupling reactions. In the Suzuki-Miyaura coupling reaction, nickel precatalyst 3a was active for the coupling of aryl chlorides as well as aryl fluorides. The analogously synthesized Pd(II) complexes resulted in formation of (diNHC)PdCl(2) species which were not active for the coupling of aryl fluorides. For the Mizoroki-Heck reaction, it was found that aryl iodides could be activated in the absence of nickel or palladium precatalysts when using Na(2)CO(3) or NEt(3) as base while aryl iodides and aryl bromides could be activated in the Suzuki-Miyaura reaction sans precatalyst when K(3)PO(4) was used as base.     

Transition-metal-free Suzuki-type coupling reactions: scope and limitations of the methodology

The scope and limitations of the transition-metal-free Suzuki-type coupling of aryl halides and arylboronic acids to form biaryls are presented. Confirmation that the reaction is indeed metal-free is presented. The effects of changing base, solvent, reaction temperature, phase-transfer catalyst, and substrate are shown and the implications of these results discussed in terms of their impact on the synthetic versatility of the methodology. The main findings are that the reaction works well for aryl bromides, water is necessary as a solvent for the reaction, the optimum temperature for the reaction is 150 degrees C, the reaction is best performed by using microwave promotion with the exception of an electron-poor aryl bromide example where conventional heating may be used, only limited boronic acids can be used as coupling partners, sodium carbonate is the best base for the reaction, tetrabutylammonium bromide proves to be the best phase-transfer catalyst for the reaction, the reaction is limited to couplings between aryl halides and aryl boronic acids with sp(2)-sp(3) couplings proving ineffective, and NaBPh(4) can be used in the place of phenylboronic acid as a phenylating agent.     

Silica‐supported terpyridine palladium(II) complex as an efficient and reusable catalyst for Heck and Suzuki cross‐coupling reactions

Silica‐supported terpyridine palladium(II) was prepared and used as an effective and recyclable catalyst in Mizoroki–Heck and Suzuki–Miyaura coupling reactions. The catalyst was very effective for the Mizoroki–Heck reaction of aryl halides with olefins and conversion was in most cases excellent. The catalyst showed good thermal stability (up to 230 °C) and could be recovered and reused for four reaction cycles. The Suzuki coupling of aryl iodides with aryl boronic acids in the presence of the catalyst was also investigated and the reaction proceeded with a short reaction time and excellent conversion. Copyright © 2013 John Wiley & Sons, Ltd.     

Amino acid promoted CuI-catalyzed C-N bond formation between aryl halides and amines or N-containing heterocycles

CuI-catalyzed coupling reaction of electron-deficient aryl iodides with aliphatic primary amines occurs at 40 degrees C under the promotion of N-methylglycine. Using l-proline as the promoter, coupling reaction of aryl iodides or aryl bromides with aliphatic primary amines, aliphatic cyclic secondary amines, or electron-rich primary arylamines proceeds at 60-90 degrees C; an intramolecular coupling reaction between aryl chloride and primary amine moieties gives indoline at 70 degrees C; coupling reaction of aryl iodides with indole, pyrrole, carbazole, imidazole, or pyrazole can be carried out at 75-90 degrees C; and coupling reaction of electron-deficient aryl bromides with imidazole or pyrazole occurs at 60-90 degrees C to provide the corresponding N-aryl products in good to excellent yields. In addition, N,N-dimethylglycine promotes the coupling reaction of electron-rich aryl bromides with imidazole or pyrazole to afford the corresponding N-aryl imidazoles or pyrazoles at 110 degrees C. The possible action of amino acids in these coupling reactions is discussed.     

钯催化偶联-消去法合成芳基末端炔的研究进展

钯催化偶联-消去法合成芳基末端炔的研究进展;芳炔;偶联反应;钯催化剂;合成;综述     

Selected Copper‐Based Reactions for C−N,C−O,C−S,and C−C Bond Formation

Metal‐catalyzed cross‐coupling reactions belong to the most important transformations in organic synthesis. Copper catalysis has received great attention owing to the low toxicity and low cost of copper. However, traditional Ullmann‐type couplings suffer from limited substrate scopes and harsh reaction conditions. The introduction of several bidentate ligands, such as amino acids, diamines, 1,3‐diketones, and oxalic diamides, over the past two decades has totally changed this situation as these ligands enable the copper‐catalyzed coupling of aryl halides and nucleophiles at both low reaction temperatures and catalyst loadings. The reaction scope has also been greatly expanded, rendering this copper‐based cross‐coupling attractive for both academia and industry. In this Review, we have summarized the latest progress in the development of useful reaction conditions for the coupling of (hetero)aryl halides with different nucleophiles. Additionally, recent advances in copper‐catalyzed coupling reactions with aryl boronates and the copper‐based trifluoromethylation of aromatic electrophiles will be discussed.     

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.     

Palladium-catalyzed cross-coupling of aryl triethylammonium bis(catechol) silicates with aryl bromides using microwave irradiation

The scope of the palladium-catalyzed cross-coupling reaction of aryl bis(catechol) silicates has been extended to include the coupling of aryl bromides by employing microwave irradiation. This new set of coupling conditions is tolerant of electron-rich and -deficient aryl bromides. In addition, a variety of substituted aryl bis(catechol) silicates have been successfully cross-coupled.     

Biaryl synthesis from two different aryl halides with tri(2-furyl)germane

[reaction: see text] The coupling reaction of germanium compounds with aryl halides has been developed. The Pd(0)-catalyzed reaction of aryl halides with tri(2-furyl)germane provides aryltri(2-furyl)germanes in good yield. The cross-coupling reaction of aryltri(2-furyl)germanes with aryl halides is achieved. This allows facile synthesis of unsymmetrical biaryls from two different aryl halides.     

Cross-coupling reactions of (1-fluorovinyl)methydiphenylsilane(1) with aryl halides and aryl triflates

The cesium fluoride (CsF)-assisted cross-coupling reaction of (1-fluorovinyl)methyldiphenylsilane (1) with aryl halides and aryl triflates was examined. The reaction with aryl iodides smoothly proceeded to afford the corresponding (1-fluorovinyl)arenes in the presence of a catalytic amount of CuI and Pd(PPh(3))(4) in aprotic polar solvents such as DMF, DMI, DMA, and NMP in good yields. A variety of functional groups (nitro, ester, ketone, and ether) on the aromatic rings can be tolerated under these mild conditions. Aryl iodides are superior to aryl bromides as the coupling reaction partner. The cross-coupling reaction of 1 with aryl triflates instead of aryl halides was also accomplished in the presence of tetrabutylammonium iodide (n-Bu(4)NI) as the additive under similar conditions.     

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.     

A general method for palladium-catalyzed reactions of primary sulfonamides with aryl nonaflates

A general method for Pd-catalyzed sulfonamidation of aryl nonafluorobutanesulfonates (aryl nonaflates) is described. A biaryl phosphine ligand, t-BuXPhos, formed the most active catalyst, and K(3)PO(4) in tert-amyl alcohol was found to be the optimal base-solvent combination for the reaction. The reaction conditions were tolerant of various functional groups such as cyano, nitro, ester, aldehyde, ketone, chloride, carbamate, and phenol. Heterocyclic aryl nonaflates were found to be suitable coupling partners. High yields of the coupled products were obtained from the reactions between inherently disfavored substrates such as electron-rich nonaflates and electron-poor sulfonamides. Kinetic data suggest reductive elimination to be the rate-limiting step for the reaction. The only limitation of this methodology that we have identified is the inability of 2,6-disubstituted aryl nonaflates to efficiently participate in the reaction.     

Cobalt-catalyzed aryl-sulfur bond formation

A new cobalt-catalyzed coupling of aryl halides with thiophenols and alkanethiols is reported. A variety of aryl sulfides can be prepared in excellent yields under mild reaction conditions using 1-2 mol % of CoI2(dppe) and Zn. This new cobalt-catalyzed coupling represents an interesting addition to previously known methods to synthesize thioethers. [reaction: see text].     

Heterogeneous Suzuki and Stille coupling reactions using highly efficient palladium(0) immobilized MCM-41 catalyst

An efficient palladium(0) immobilized MCM-41 catalytic system for C-C cross-coupling reaction has been developed. Ligand-free Pd(0)-MCM-41 catalyst can be successfully used in coupling reaction between various aryl halides including deactivated chlorobenzene with aryl borane and organotin to give biaryls in excellent yields with high turnover frequency (TOF) (the maximal TOFs are up to 6990 for the reaction of bromobenzene with phenylboronic acid). The catalyst can be recycled and reused without any loss of catalytic activity.     

Room-temperature Ni0-catalyzed cross-coupling reactions of aryl arenesulfonates with arylboronic acids

Room-temperature Ni(0)-catalyzed cross-coupling reactions of aryl arenesulfonates with arylboronic acids are described. The Ni(0) catalyst, derived from Ni(COD)2 and PCy3, proved to be a general one for the Suzuki-Miyaura cross-coupling of a variety of aryl arenesulfonates. The mild reaction condition, the readily availability of the catalyst, and excellent coupling yields make aryl arenesulfonates potentially useful substrates in organic synthesis.     

Mechanistic Origin of Cross‐Coupling Selectivity in Ni‐Catalysed Tishchenko Reactions

Mechanistic studies have been performed for the recently developed, Ni‐catalysed selective cross‐coupling reaction between aryl and alkyl aldehydes. A mono‐carbonyl activation (MCA) mechanism (in which one of the carbonyl groups is activated by oxidative addition) was found to be the most favourable pathway, and the rate‐determining step is oxidative addition. Analysing the origin of the observed cross‐coupling selectivity, we found the most favourable carbonyl activation step requires both coordination of the aryl aldehyde and oxidative addition of the alkyl aldehyde. Therefore, the stronger π‐accepting ability of the aryl aldehyde (relative to alkyl aldehyde) and the ease of oxidative addition of the alkyl aldehyde (relative to aryl aldehyde) are responsible for the cross‐coupling selectivity.     

Efforts directed toward the synthesis of colchicine: application of palladium-catalyzed siloxane cross-coupling methodology

[reaction: see text] Colchicine is an important and synthetically challenging natural product. The key synthetic step in this approach to the synthesis of colchicine involved a palladium-catalyzed cross-coupling reaction between 5-bromotropolone (4) and an aryl siloxane to form the aryl-tropolone bond. The coupling of a variety of highly functionalized aryl siloxane derivatives was investigated and optimized coupling conditions were developed. It was discovered that a palladium catalyst with a high degree of phosphine ligand coordination (5 equiv of phosphine/mol Pd) was necessary to efficiently couple aryl siloxanes with 5-bromotropolone (4). In addition, the coupling approach has provided a direct comparison between siloxane and boronic acid coupling technologies that demonstrated that aryl siloxanes and boronic acids produce similar yields of highly functionalized biaryl products.     

Fluorogenic derivatization of aryl halides based on the formation of biphenyl by Suzuki coupling reaction with phenylboronic acid

The fluorogenic derivatization method for aryl halide was developed for the first time. This method was based on the formation of fluorescent biphenyl structure by Suzuki coupling reaction between aryl halides and non-fluorescent phenylboronic acid (PBA). We measured the fluorescence spectra of the products obtained by the reaction of p-substituted aryl bromides (i.e., 4-bromobenzonitrile, 4-bromoanisole, 4-bromobenzoic acid ethyl ester and 4-bromotoluene) with PBA in the presence of palladium (II) acetate as a catalyst. The significant fluorescence at excitation maximum wavelength of 275–290 nm and emission maximum wavelength of 315–350 nm was detected in all the tested aryl bromides. This result demonstrated that non-fluorescent aryl bromides could be converted to the fluorescent biphenyl derivatives by the coupling reaction with non-fluorescent PBA. We tried to determine these aryl bromides by HPLC-fluorescence detection with pre-column derivatization. The aryl bromide derivatives were detected on the chromatogram within 30 min without any interfering peak derived from the reagent blank. The detection limits (S/N = 3) for aryl bromides were 13–157 fmol/injection.     

Palladium-catalyzed aminosulfonylation of aryl halides

The palladium-catalyzed three-component coupling of aryl iodides, sulfur dioxide, and hydrazines to deliver aryl N-aminosulfonamides is described. The colorless crystalline solid DABCO·(SO(2))(2) was used as a convenient source of sulfur dioxide. The reaction tolerates significant variation of both the aryl iodide and hydrazine coupling partners.     

[PdCl2{8-(di-tert-butylphosphinooxy)quinoline)}]: a highly efficient catalyst for Suzuki-Miyaura reaction

The complex [PdCl₂(P-N)] containing the basic and sterically demanding 8-(di-tert-butylphosphinooxy)quinoline ligand (P-N) is a highly efficient catalyst for the coupling of phenylboronic acid with aryl bromides or aryl chlorides. The influence of solvent and base has been investigated, the highest rates being observed at 110 °C in toluene with K₂CO₃ as the base. With aryl bromides the reaction rates are almost independent on the electronic properties of the para aryl substituents, on the contrary, reduced reaction rates are observed when bulky substituents are present on the substrate. Nevertheless the coupling of 2-bromo-1,3,5-trimethylbenzene with phenylboronic acid can be carried out to completion in 2 h using a catalyst loading of 0.02 mol %. Under optimized reaction conditions, turnover frequencies as high as 1900 h⁻¹ can be obtained in the coupling of 4-chloroacetophenone with phenylboronic acid; lower reaction rates are obtained with substrates bearing EDG substituents on the aryl group.