Catalyst For Cross-coupling Reactions Research Articles

Nickel(II) Thiocyanate Complex as a Catalyst for Cross-Coupling Reactions

AbstractA nickel thiocyanate complex was prepared by the reaction of Ni(NCS)2 with (2S,3S)-2,3-bis(diphenylphosphino)butane (Chiraphos) by following a method reported in the literature. The resulting nickel complex was found to be active in the polymerization reactions of 1,4-dihalobenzenes and 2-halo-3-hexylthiophenes, leading to poly-1,4-phenylenes and poly(3-hexylthiophene-2,5-diyl), respectively. The polymerization in the presence of similar catalysts containing other ligands, such as 1,2-bis(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)propane, or N-heterocyclic carbenes, also proceeded in a similar manner. Ni(NCS)2 complexes also successfully catalyzed Suzuki–Miyaura couplings and Buchwald–Hartwig aminations to afford the corresponding biaryls and arylamines, respectively.

Deep eutectic solvents as reusable catalysts and promoter for the greener syntheses of small molecules: Recent advances

Deep eutectic solvents (DESs) are significant environmentally benign media in the field of green chemistry. They are known not only for their inexpensive nature, biodegradability, non-toxicity, and bioavailability, but also for recyclability and their ease of preparation and purification. DESs are made up of hydrogen bond donor substituents (such as urea, carboxylic acid, glycerol, metals, etc.) and hydrogen bond acceptor substituents such as halide salts; they have a lower melting point than each substituent comprising the mixture. DESs find applications in biotransformation, gas separation, biomass valorization, electrochemistry, extraction, and dissolution process as well as in material chemistry and other assorted fields of chemistry. Interestingly, DESs fulfil a unique dual role as green solvents, promoters and catalysts in organic syntheses. Thus, it is noteworthy that chemical progresses and transformation with external catalysts in cross-coupling reactions, oxidations and reductions are not covered in this overview. This review mostly focuses on leading-edge applications of DES as a reusable catalyst in the expeditious synthesis of assorted small molecules central in the assembly of broad-spectrum pharmaceuticals, and total synthesis of common natural products.

Palladium Supported on Porous Organic Polymer as Heterogeneous and Recyclable Catalyst for Cross Coupling Reaction

Palladium immobilized on an amide and ether functionalized porous organic polymer (Pd@AEPOP) is reported to be an effective heterogeneous catalyst for the Heck cross-coupling reaction of aryl iodides with styrene for the synthesis of diphenylethene derivatives. Excellent yields can be obtained using a 0.8 mol% Pd catalyst loading under the optimized reaction condition. The heterogeneous Pd@AEPOP catalyst can also be applied on the Suzuki reaction and the reduction of nitroarene.

Synthesis and Characterization of Two Isostructural POCOP Ni(II) Pincer Complexes Containing Fluorothiophenolate Ligands: [Ni(SC6F4-4-H){C6H2-3-(C2H3O)-2,6-(OPiPr2)2}] and [Ni(SC6F5){C6H2-3-(C2H3O)-2,6-(OPiPr2)2}]

Among their many applications, metal pincer complexes are of interest for their properties as catalysts in cross-coupling reactions. Pincer ligands exhibit tridentate coordination to the metal center and occupy the meridional positions forming two chelate rings. The two Ni(II) POCOP pincer complexes with a fluorothiophenolate ligand reported herein, with formulas [Ni(SC6F4-4-H){C6H2-3-(C2H3O)-2,6-(OPiPr2)2}] (2) and [Ni(SC6F5){C6H2-3-(C2H3O)-2,6-(OPiPr2)2}] (3), are isostructural. Additionally, they are prepared in a facile manner from the chloride compound [NiCl{C6H2-3-(C2H3O)-2-6-(OPiPr2)2}] (1). The complexes exhibited slightly distorted square planar geometries around the metal. The fluorothiophenolate ligands are responsible of the C—H···F, C—F···π and C=O···πF interactions that contribute to stabilize the crystal structure arrays.

Magnetically Recoverable Nanoparticulate Catalysts for Cross-Coupling Reactions: The Dendritic Support Influences the Catalytic Performance.

Carbon-carbon cross-coupling reactions are among the most important synthetic tools for the preparation of pharmaceuticals and bioactive compounds. However, these reactions are normally carried out using copper, phosphines, and/or amines, which are poisonous for pharmaceuticals. The use of nanocomposite catalysts holds promise for facilitating these reactions and making them more environmentally friendly. In the present work, the PEGylated (PEG stands for poly(ethylene glycol) pyridylphenylene dendrons immobilized on silica loaded with magnetic nanoparticles have been successfully employed for the stabilization of Pd2+ complexes and Pd nanoparticles. The catalyst developed showed excellent catalytic activity in copper-free Sonogashira and Heck cross-coupling reactions. The reactions proceeded smoothly in green solvents at low palladium loading, resulting in high yields of cross-coupling products (from 80% to 97%) within short reaction times. The presence of magnetic nanoparticles allows easy magnetic separation for repeated use without a noticeable decrease of catalytic activity due to the strong stabilization of Pd species by rigid and bulky dendritic ligands. The PEG dendron periphery makes the catalyst hydrophilic and better suited for green solvents. The minor drop in activity upon the catalyst reuse is explained by the formation of Pd nanoparticles from the Pd2+ species during the catalytic reaction. The magnetic separation and reuse of the nanocomposite catalyst reduces the cost of target products as well as energy and material consumption and diminishes residual contamination by the catalyst. These factors as well as the absence of copper in the catalyst makeup pave the way for future applications of such catalysts in cross-coupling reactions.

Synthesis and characterization of mononuclear oxime-based palladacycles incorporating phosphorus ylides: application as a catalyst in Suzuki cross coupling reactions and their biological activities

The synthesis of mononuclear oxime-based palladacycles of the type [Pd{C,N-C6H4{C(Me)=NOH}-2}(Ph2PCH2CH2PPh2C(H)C(O)C6H4X)]ClO4(X = Cl (1), Br (2), NO2 (3), OCH3 (4)) is reported from the reactions of [Pd{C,N-C6H4{C(Me)=NOH}-2}(μ-Cl)]2 with phosphorus ylides in dichloromethane under reflux. The obtained compounds were characterized by FT-IR, NMR (1H, 13C{H} and 31P{H}) spectroscopic methods and elemental analysis. Splitting of the chloride bridge formed four new mononuclear oxime-based palladacycles incorporating bidentate phosphorus ylides (1-4). These palladacycles were applied for Suzuki-Miyaura cross-coupling reactions under aerobic conditions in EtOH/H2O solvent. Upon optimizing the reaction conditions, complex 3 was highly efficient to catalyze the cross-coupling of aryl halides with phenylboronic acids at a 0.44 mol % palladium loading. Also, the cytotoxic effects of 1-4 were evaluated by an MTT assay in three human carcinoma cell lines: HT29, A549, and 1321N1. The results indicate that these compounds had toxic effects and 4 has greater toxic activity with respect to the other complexes in all three cell lines. Thus, these compounds can be considered as efficient catalysts in cross-coupling reactions and as a cytotoxic agent.

Chasing C,C‐Palladacycles

AbstractThe different approaches for the synthesis of C,C‐palladacycles are reviewed in this manuscript. These species hold a bidentate ligand that chelates the Pd atom through two C‐donor moieties. Their relevance is closely related to the fact that they are intermediates in many palladium‐catalyzed transformations. Furthermore, some of them have been used as efficient catalyst in cross coupling reactions. The review is structured according to the different strategies that have been employed to achieve the synthesis of the C,C‐palladacycle derivatives, starting with those involving one elemental step (such as the oxidative addition of strained C−C bonds to Pd(0) or the transmetalation reactions between organometallic reagents and Pd(II) precursors), and continuing with more complex processes, where at least two elementary steps of Pd chemistry are involved (for example, carbometalation of alkenes followed by a C−H activation process). A final section highlights some aspects of synthetic methodologies based on Pd catalysis in which one or several C,C‐palladacyclic intermediates are involved.

Tetraorganylargentate(III) Complexes: Key Intermediates in Silver-Mediated Cross-Coupling Reactions

The use of silver as a catalyst in cross-coupling reactions remains underdeveloped. We show by means of electrospray-ionization mass spectrometry that the diorganylargentates LiAgR′2·Li(CN) (R′ = M...

Microwave-Assisted Synthesis of 2-Aryl and 2,5-Diarylthiophene Derivatives via Suzuki-Miyaura Cross-Coupling Using Novel Palladium Complex as a Catalyst

A novel phosphine-free pyrimidine-based palladium(II) complex have been synthesized from easily accessible starting materials and its ability to be a catalyst for cross-coupling reactions namely, Suzuki-Miyaura (SMC) has been investigated. The structure of the new formamidinyl pyrimidine-based complex has been elucidated by using spectroscopic as well as physical characterization techniques. The novel palladium(II) complex showed its applicability as a catalyst for SMC of 2-bromothiophene and 2,5-dibromothiophene with arylboronic acids under conventional and microwaves irradiation conditions. The developed catalytic system exhibited reasonable catalytic activity to obtain 2-aryl and 2,5-diarylthiophene derivatives using mild reaction conditions.

Synthesis and Characterization of a Tetradentate, N-Heterocyclic Carbene Copper(II) Complex and Its Use as a Chan–Evans–Lam Coupling Catalyst

Copper N-heterocyclic carbenes (NHCs) are an emerging area of focus for catalysis and other applications. Using a straightforward methodology, a new and highly modifiable tetradentate copper(II) NHC complex was generated and characterized using X-ray crystallography, UV–vis and EPR spectroscopy, cyclic voltammetry, and ESI-MS. This copper(II) NHC complex adopted a distorted 4-coordinate coordination mode and demonstrates a unique absorption spectrum for a copper(II) species, but more interestingly, its redox properties indicate that it can readily access all three common copper oxidation states under atmospheric conditions. The tetradentate copper(II) NHC complex was used to catalytically generate new C–N bonds from a series of phenylboronic acids and amines. Once this CEL methodology was refined, moderate to high yields were achieved using catalytic amounts of the copper(II) complex to couple phenylboronic acids to a series of aniline derivatives. Substituted phenylboronic acids and anilines had minimal impact on the catalytic capabilities of this copper complex; however, there is some indication that steric interactions between catalyst and substrates may have an impact on efficient catalysis. The straightforward synthesis of this framework and the utilization of an inexpensive, first-row transition metal center in this system highlight the usefulness of copper(II) NHCs as catalyst for cross-coupling reactions.

Thiosemicarbazone Complexes of Transition Metals as Catalysts for Cross-Coupling Reactions

Catalysis of cross-coupling reactions under phosphane-free conditions represents an important ongoing challenge. Although transition metal complexes based on the thiosemicarbazone unit have been known for a very long time, their use in homogeneous catalysis has been studied only relatively recently. In particular, reports of cross-coupling catalytic reactions with such complexes have appeared only in the last 15 years. This review provides a survey of the research in this area and a discussion of the prospects for future developments.

Core-shell iron oxide@cathecol-polymer@palladium/copper nanocomposites as efficient and sustainable catalysts in cross-coupling reactions

Magnetic core-shell Fe2O3@polymer-Pd/Cu nanocomposites (NCs) were developed as efficient and sustainable nanocatalysts for cross-coupling reactions. The designed NCs consisted of three components: i) a magnetic core (Fe2O3 nanoparticle), which allowed the recovery and reuse of the NCs, enhancing thus their attractiveness as green catalysts; ii) a catechol-based polymer coating, chosen because of its strong chelating ability towards metal ions, and its potential to be obtained from biomass (lignin depolymerization); and iii) catalytically active metal nanoparticles (Pd and Cu NPs) immobilized via in situ formation onto the polymeric shell. As-prepared Pd-based NCs successfully catalyzed Suzuki-Miyaura cross-coupling reactions, achieving yields between 87% and 97% in only 20–40 min depending on the aryl halides and boronic acid derivatives. Similarly, Cu-based NCs exhibited a quite good catalytic efficiency (> 80%) in the synthesis of propargylamines via A3 coupling reaction of phenylacetylene with various aldehydes and amines. Importantly, these NCs presented a good reusability, without significant decrease in efficiency after several cycles. However, the major advantage of the designed NCs is the lower Pd or Cu content (1.5 wt% and 2.6 wt%, respectively) as compared to most of the reported similar catalysts (between 3 – 6 wt% for Pd and > 5 wt% for Cu), which is a key challenge in view of developing cost-effective and environment-friendly catalysts while maintaining a high efficiency.

New Palladium(II)-Complex Based on Nitrogen Rich Ligand Efficient Precatalyst for C–C Cross-Coupling in Water Under Microwaves Irradiation

A new phosphine-free pyrimidylformamidine-based ligand and its palladium(II) complex has been synthesized from easily accesible staring materials and its ability to be a catalyst for cross-coupling reactions namely Suzuki–Miyaura (SMC) has been investigated. Firstly, the precatalyst was examined in cross-coupling of phenylboronic acid and p-bromoacetophenone which is selected due to its reactivity and as a low cost bromide that could be used for model cross-coupling reaction. The new palladium(II) complex showed high applicability as a precatalyst for SMC of aryl halides with various derivatives of boronic acid in water under conventional and microwaves irradiation conditions and the cross coupled products were obtained in excellent yields under mild reaction conditions.

Nb2O5 supported catalysts for cross-coupling reactions

Palladium and nickel supported on Nb2O5 were synthesized via wet impregnation method and tested for the Suzuki-Miyaura reaction. The catalysts were characterized by X-ray fluorescence, textural analysis, scanning and transmission electron microscopy, thermogravimetry/differential thermal analysis and X-ray diffraction. Palladium catalyst resulted in high isolated yields (91%). Satisfactory yields (48%) were achieved employing the nickel catalyst. Hot filtration experiments were performed to evaluate the reaction heterogeneity. The catalysts were submitted to consecutive reactions runs to assess recyclability. Deactivation was attributed to catalyst loss by filtration between cycles, minor leaching of the active phase and poisoning by inorganic species.

Comparison of the catalytic performances of bridged bi-metallic and non-bridged mono-metallic PEPPSI type palladium N-heterocyclic carbene complexes

Palladium-N-heterocyclic carbene complexes are widely investigated catalysts in cross-coupling reactions. However, studies about the catalytic activities of bridged bi-metallic complexes are quite rare. Therefore, in this study, anthracene-substituted one mono-metallic and one bridged bi-metallic PEPPSI-type Pd-NHC complexes were synthesized in order to compare their catalytic activities in Suzuki-Miyaura and Mizoroki-Heck reactions. Both complexes were fully characterized by 1H and 13C NMR, LC-MS, IR spectra and elemental analyses. The results of catalytic reactions clearly revealed that mono-metallic complex performs better catalytic activity than bi-metallic analogue in the use of same amount of palladium.

Efficient preparation and application of monodisperse palladium loaded graphene oxide as a reusable and effective heterogeneous catalyst for suzuki cross-coupling reaction

A homogeneously dispersed graphene oxide supported palladium nanomaterial (Pd@GO) has been successfully synthesized and used as a catalyst in cross-coupling reactions at room temperature. Various analytical techniques such as X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM) were used to characterize the monodisperse Pd@GO. Monodisperse Pd@GO nanomaterials were used for the cross-coupling reactions which brought together organic molecules with functional significance. This catalyst showed superior catalytic activity and stability for these coupling reactions. High product yields, short reaction times and mild reaction conditions, obtained by the using of developed catalysts. Importantly, the catalyst can be used at least five experiments successfully without losing its efficiency.

Isothiazoles in the Design and Synthesis of Biologically Active Substances and Ligands for Metal Complexes

The chemistry of isothiazoles is being intensively developed, which is evidenced by the wide range of selective transformations involving the isothiazole heterocycle and the high biological activity of its derivatives that can be used as effective new drugs and plant protection chemicals. Some representatives of isothiazoles have proven to be synergists of bioactive substances, which opens the way to lower the doses of drugs used and is especially important in cancer chemotherapy. In the framework of the present review, the accomplishments in the chemistry of isothiazoles over the past 18 years are examined, whilst current strategies for the synthesis of isothiazole-containing molecules and key directions of studies in this field of heterocyclic chemistry are discussed. Considerable attention is paid to chlorinated isothiazoles and strategies for their use in the synthesis of biologically active substances. In addition, a comprehensive review of existing literature in the field of metal complexes of isothiazoles is given, including the results and prospects for the practical use of isothiazole–metal complexes as catalysts for cross-coupling reactions in aqueous and aqueous–alcoholic media (‘green chemistry’).1 Introduction2 Synthesis by Ring-Forming Reactions2.1 Intramolecular Cyclization2.2 (4+1)-Heterocyclization2.3 (3+2)-Heterocyclization2.4 Syntheses by Ring Transformations3 Isothiazoles by Ring Functionalization Reactions: Nucleophilic Substitution, Cross-Coupling and Side-Chain Functionalization4 Selected Syntheses of Biologically Active Isothiazole Derivatives5 Isothiazoles in the Synthesis of Transition-Metal Complexes and in Metal-Complex Catalysis6 Conclusion

Sulfonated salicylidene thiadiazole complexes with Co (II) and Ni (II) ions as sustainable corrosion inhibitors and catalysts for cross coupling reaction

Condensation of 2,5‐dihydrazinyl thiadiazole with 5‐sodium sulfonate salicylaldehyde afforded dibasic tetradentate pincer N,O,O,N‐salicyldiene thiadiazole ligand (H2Sanp). The novel dipolar ligand formed para‐magnetic pincer complexes within Co (II) and Ni (II) ions (Co‐Sanp and Ni‐Sanp) under sustainable conditions. The water‐soluble ligand and its metal‐complexes were estimated by mass, IR and UV–Visible spectroscopy, EA (elemental analyses), TGA (Thermogravimetric analyses), magnetic susceptibility, and conductivity measurements. The catalytic reactivity of Co‐Sanp and Ni‐Sanp were evaluated in the Suzuki and Buchwald‐Hartwig cross coupling reaction in aqueous‐methanol binary mixtures. Both reactions of boronic acid or aryl amines with aryl halides gave high chemoselective yield of C―C or C―N product. The inhibition characteristics of H2Sanp and its Ni‐ and Co‐complexes were performed for the C‐steel corrosion in 1.0 M HCl using electrochemical measurements and surface analysis methods. These methods indicated that the synthesized compounds have served as efficient mixed‐type corrosion inhibitors and their adsorption on the steel surface obeyed isotherm model of Langmuir. Co‐Sanp inhibitor displays the best corrosion inhibition efficiency, and the capacity is up to 97.11% at of 250 mg L−1. Surface analysis confirms formation of protective layer on the C‐steel surface.

Functionalized Bis(triazolyl)phenylmethanol–palladium(II) Catalysts for Cross Coupling Reactions in Water

AbstractPdII‐bis(triazolyl)phenylmethanol complexes bearing different groups (i. e., H, OMe, OH, COOH) directly attached to the benzyl rings were explored as precatalysts for copper‐free Sonogashira and Suzuki–Miyaura coupling reactions in water. Crystal structures reveal a bidentate N,N binding mode of the bis(triazolyl) ligands affording a distorted square planar PdII complexes. With the exception of the phenol‐substituted bis(triazolyl) ligands, the other three Pd complexes exhibited high activities toward Suzuki–Miyaura coupling reactions. Transmission electron microscopy (TEM) study and PPh3 poisoning experiments confirm that bis(triazoly)‐stabilized Pd nanoparticles (Pd NPs) were generated in situ during the catalytic reactions and involved as one of the active catalytic species in the Suzuki–Miyaura cross coupling.

Circumventing Intrinsic Metal Reactivity: Radical Generation with Redox-Active Ligands.

Nickel complexes have gained sustained attention as efficient catalysts in cross-coupling reactions and co-catalysts in dual systems due to their ability to react with radical species. Central to this reactivity is nickel's propensity to shuttle through several accessible redox states from Ni0 to NiIV . Here, we report the catalytic generation of trifluoromethyl radicals from a nickel complex bearing redox-active iminosemiquinone ligands. This unprecedented reactivity is enabled through ligand-based oxidation performing electron transfer to an electrophilic CF3+ source while the nickel oxidation state is preserved. Additionally, extension of this reactivity to a copper complex bearing a single redox equivalent is reported, thus providing a unified reactivity scheme. These results open new pathways in radical chemistry with redox-active ligands.