Cross-coupling Reactions Of Aryl Bromides Research Articles

Palladium(II) and Platinum(II) Complexes Bearing ONS-Type Pincer Ligands: Synthesis, Characterization and Catalytic Investigations.

This work describes the synthesis of eight new Pd(II) and Pt(II) complexes with the general formula [M(TSC)Cl], where TSC represents the 4N-monosubstituted thiosemicarbazone derived from 2-acetylpyridine N-oxide with the substituents CH3 (H4MLO), C2H5 (H4ELO), phenyl (H4PLO) and (CH3)2 (H4DMLO). These complexes have been characterized by elemental analysis, molar conductivity, IR spectroscopy, 1H, 13C, 195Pt and ESI-MS. The complexes exhibit a square planar geometry around the metallic center coordinated by a thiosemicarbazone molecule acting as a donor ONS-type pincer ligand and by a chloride, as confirmed by the molecular structures of the complexes, [Pd(4ELO)Cl] (3) and [Pd(4PLO)Cl] (5), determined by single-crystal X-ray diffraction. The 195Pt NMR spectra of the complexes of formulae [Pt(4PLO)Cl] (6) and [Pt(4DMLO)Cl] (8) in DMSO show a single signal at -2420.4 ppm, confirming the absence of solvolysis products. Complexes 3 and 5 have been tested as catalysts in the Suzuki-Miyaura cross-coupling reactions of aryl bromides with phenylboronic acid, with yields of between 50 and 90.

Nickel-catalyzed C(sp2)-C(sp3) coupling via photoactive electron donor-acceptor complexes.

We have developed a novel Ni-catalyzed reductive cross-coupling reaction of aryl bromides and alkyl iodides via a photoactive electron donor-acceptor (EDA) complex. This photo-induced process enables the efficient construction of C(sp2)-C(sp3) bonds in the absence of an external photocatalyst. Electronically and structurally diverse aryl bromides, as well as secondary and primary alkyl iodides could undergo this transformation smoothly. Natural product derivatives were employed successfully, and UV-vis spectroscopy was utilized to gain mechanistic insight.

Pd nanoparticles supported in PDMAEMA-b-PLMA micelles: A superb catalytic platform for Suzuki-Miyaura cross-coupling in water

Pd nanoparticles (NPs) supported by micelles formed with poly(2-(dimethylamino)ethyl methacrylate)-b-poly(lauryl methacrylate) (Pd/PDMAEMA-b-PLMA) were prepared and employed as catalyst in the Suzuki-Miyaura cross-coupling reaction of aryl bromides with arylboronic acids in water. Most reactions proceeded with high efficiency at room temperature with only 0.05 mol% Pd loading in the absence of ligands, which afforded the desired functionalized biaryls in 73–98 % yields after 24 h. After reaction, Pd/PDMAEMA-b-PLMA retained in the aqueous phase was easily separated from the insoluble biaryl product and could be further reused two times without significant loss in catalytic efficiency. Characterization of the catalyst disclosed that sub-2 nm Pd NPs were embedded in the hydrophilic corona of polymeric micelles that served as nanoreactors in water.

Continuous Ligand-Free Catalysis Using a Hybrid Polymer Network Support.

Although the pharmaceutical and fine chemical industries primarily utilize batch homogeneous reactions to carry out chemical transformations, emerging platforms seek to improve existing shortcomings by designing effective heterogeneous catalysis systems in continuous flow reactors. In this work, we present a versatile network-supported palladium (Pd) catalyst using a hybrid polymer of poly(methylvinylether-alt-maleic anhydride) and branched polyethyleneimine for intensified continuous flow synthesis of complex organic compounds via heterogeneous Suzuki-Miyaura cross-coupling and nitroarene hydrogenation reactions. The hydrophilicity of the hybrid polymer network facilitates the reagent mass transfer throughout the bulk of the catalyst particles. Through rapid automated exploration of the continuous and discrete parameters, as well as substrate scope screening, we identified optimal hybrid network-supported Pd catalyst composition and process parameters for Suzuki-Miyaura cross-coupling reactions of aryl bromides with steady-state yields up to 92% with a nominal residence time of 20 min. The developed heterogeneous catalytic system exhibits high activity and mechanical stability with no detectable Pd leaching at reaction temperatures up to 95 °C. Additionally, the versatility of the hybrid network-supported Pd catalyst is demonstrated by successfully performing continuous nitroarene hydrogenation with short residence times (<5 min) at room temperature. Room temperature hydrogenation yields of >99% were achieved in under 2 min nominal residence times with no leaching and catalyst deactivation for more than 20 h continuous time on stream. This catalytic system shows its industrial utility with significantly improved reaction yields of challenging substrates and its utility of environmentally-friendly solvent mixtures, high reusability, scalable and cost-effective synthesis, and multi-reaction successes.

N,S-heterocyclic carbene containing benzothiazol-2-ylidene-Ru(II) and Pd(II) new complexes functionalized with butyl linked carbazole moiety: Synthesis, characterization and their catalytic efficiency and electropolymerizations

In contrast to the large number of polymeric N-heterocyclic carbenes (NHCs) there are relatively few examples of NHCs-containing conductive polymers. However, conducting polymers (CPs) could be excellent hosts for NHC compounds, as they can easily form polymer films electrochemically, and their optical & electrical properties can be easily tuned by electrochemically or changing bonding groups in their structure. In this work, the N,S-heterocyclic carbene (NHC) ligand precursor, N-(4-butylcarbazole)benzothiazolium bromide (1) was prepared by solvent-free alkylation of benzothiazole by 9-(4-bromobutyl)carbazole with high efficiency. The air- and moisture-stable new piano-stool Ru(II)-N,S-NHC (2) and PEPPSI type Pd(II)-N,S-NHC (3) complexes, were synthesized and characterized by 1H- and 13C NMR, FT-IR, UV–vis and ESI-MS spectroscopic methods and elemental analysis. Further confirmations of structural details for benzothiazolium salt (1) and its Ru(II)-N,S-NHC complex (2) were determined by X-ray single-crystal diffraction. The catalytic performance of the complexes (2 and 3) in transfer hydrogenation (TH) of acetophenone and Suzuki–Miyaura cross-coupling reactions of aryl bromides were also investigated, respectively. All compounds (1–3) were electrochemically polymerized and conducting polymer films with pendant carbene complex moieties were obtained. The electrical and optical properties of the resulting polymers were characterized via spectroelectrochemical studies.

Synthesis, photophysical properties and catalytic activity of Ƙ3-SCS pincer palladium (II) complex of N,N'-di-tert-butylbenzene-1,3-dicarbothioamide supported by DFT analysis

The title complex [PdCl(L)] (1), is obtained from the reaction of SCS pincer ligand HL (where, HL = N,N'-di-tert-butylbenzene-1,3-dicarbothioamide) with lithium tetrachloropalladate (II) in methanol. The compound 1 is characterized by elemental analysis, FTIR, 1H, and 13C NMR spectroscopy, UV–Vis spectroscopy, and X-ray crystallographic techniques. At room temperature, 1 emits luminescence light of wavelength 460 nm in the solid state upon excitation by UV light of wavelength 280 nm. The average emission lifetime indicates that, both the ligand and complex emission is fluorescence in nature and involves mainly ligand centers π-π* deexcitation. It also shows good catalytic activity towards Mizoroki-Heck and Suzuki-Miyaura cross-coupling reactions of aryl bromides with tert-butyl acrylate and p-tolylboronic acid respectively. For both type of reactions, >99% conversion of the substrates is found to occur for electronically activated p-nitro bromobenzene using 1 mol % of 1. Further, modern DFT calculations are performed to decipher the mechanistic insight on the preferable pathways of the Mizoroki-Heck cross-coupling reaction. Stepwise free energy of reactions for various probable reaction pathways suggest that the catalytic route has profound preference for Pd(0)-Pd(II) over Pd(II)-Pd(IV) pathway.

Suzuki–Miyaura Cross-Coupling Reaction with Potassium Aryltrifluoroborate in Pure Water Using Recyclable Nanoparticle Catalyst

AbstractThis paper describes the Suzuki–Miyaura cross-coupling reaction of aryl bromides with potassium aryltrifluoroborates in water catalyzed by linear polystyrene-stabilized PdO nanoparticles (PS-PdONPs). The reaction of aryl bromides having electron-withdrawing groups or electron-donating groups took place smoothly to give the corresponding coupling product in high yields. The catalyst recycles five times without significant loss of catalytic activity although a little bit increase in size of PdNPs was observed after the reaction.

Synthesis, characterization and catalytic activity of N-heterocyclic carbene ligated Schiff base palladacycles

A series of N-heterocyclic carbene (NHC) ligated Schiff base palladacycles were synthesized by the reaction of μ-acetato-bridged Schiff base palladacycles (PdL1-2) with imidazolium salts (a-c). The new NHC ligated palladacycles were fully characterized using 1H NMR, 13C NMR, infrared spectroscopy, MS analysis, and single-crystal X-ray diffraction for one complex (PdL1). Further exploration of the catalytic application of the palladacycles for Suzuki-Miyaura cross-coupling reactions of aryl bromides with phenylboronic acid was carried out. It was determined that the new dimeric imine-palladacycle (PdL2) exhibits the highest catalytic activity among the coupling compounds in this study.

A new PEPPSI type N-heterocyclic carbene palladium(II) complexes and its efficiency as a catalyst for Mizoroki-Heck cross-coupling reactions in water : Synthesis, Characterization and their antimicrobial and Cytotoxic activities

A series of novel benzimidazolium salts 2 and their new air and moisture stable PEPPSI type N-heterocyclic carbene palladium(II) complexes (PEPPSI: pyridine-enhanced pre-catalyst preparation, stabilisation, and initiation), were synthesized and characterized by means of 1H and 13C{1H} NMR, FTIR spectroscopic methods and elemental analysis was employed to catalyze the Mizoroki-Heck cross-coupling reactions of aryl bromides with styrene in water. To the best of our knowledge, this is the first report where a Pd-PEPPSI catalyst was successfully employed in aqueous-phase Mizoroki-Heck reaction. Good to excellent yields of cross-coupling products were obtained with a range of representative aryl bromides under relatively mild conditions. Moreever the antimicrobial activity of the PEPPSI type N-heterocyclic carbene palladium(II) complexes 3a-e varies with the nature of the ligands. Also, the IC50 values of both, complexes (3a-e) have been determined. In addition, the new PEPPSI type N-heterocyclic carbene palladium(II) complexes were screened for their cytotoxic activities. Complex 3b exhibited the highest antitumor effect with IC50 values 0.63 μg/mL and against MCF-7.

Nickel-Catalyzed Electrochemical Phosphorylation of Aryl Bromides.

A nickel-catalyzed electrochemical cross-coupling reaction of aryl bromides with dialkyl phosphites, ethyl phenylphosphinate, and diphenylphosphine oxide has been developed. This reaction utilizes a simple undivided cell with inexpensive carbon electrodes to synthesize aryl phosphonates, aryl phosphinates, and arylphosphine oxides at room temperature. This protocol provides a mild and efficient route for the construction of C-P bond in moderate to high yields with broad substrate scope.

Bioactive NHC-derived palladium complexes: synthesis, catalytic activity for the Suzuki-Miyaura coupling of aryl chlorides and bromides and their antibacterial activities

Pd(II)-bis(NHC) complexes (where NHC = N-heterocyclic carbene) bearing asymmetrically and symmetrically substituted NHC-ligand have been synthesized via deprotonation of 5,6-dimethylbenzimidazolium salts. The NHC precursors have been achieved via the two step N-alkylation of 5,6-dimethylbenzimidazole. The resultant salts were deprotonated with PdCl2 and K2CO3 in dry THF for 2(a–e). The obtained complexes were identified and characterized by 1H and 13C NMR, FT-IR, DART-TOF mass spectrometry and elemental analysis. These new Pd(II)-bis(NHC) complexes were applied as catalyst precursors for Suzuki-Miyaura cross-coupling reactions of aryl bromides and chlorides with phenylboronic acid to afford the corresponding products in good yields. This catalytic reaction was evaluated in the presence of KOtBu/toluene. The antibacterial activities of 2(a–e) were investigated against Gram (+)/(−) bacteria using the agar dilution procedure. The antibacterial activities of 2 vary with the nature of the ligands; MIC values of 2(a–e) were determined.

Preparation and characterization of PEPPSI-palladium N-heterocyclic carbene complexes using benzimidazolium salts catalyzed Suzuki–Miyaura cross coupling reaction and their antitumor and antimicrobial activities

New palladium complexes were efficiently synthesized from the reaction of benzimidazolium salts 2a–e, potassium carbonate (K2CO3) and palladium chloride (PdCl2) in pyridine (for 3a–e). The catalytic activity of these complexes in a catalytic system including palladium complexes and K2CO3 in DMF-H2O was evaluated in Suzuki–Miyaura cross-coupling reactions of aryl bromides and chlorides with phenylboronic acid. Our novel complexes show excellent catalytic activities with high turnover numbers (TON) and high turnover frequencies (TOF) (e.g. for the Suzuki–Miyaura reaction: TON up to 370 and TOF up to 123.3 h−1). Both benzimidazolium salts 2a–e and complexes 3 have been characterized using spectroscopic data and elemental analysis. The antimicrobial activity of the N-heterocyclic carbene palladium complexes 3a–e varies with the nature of the ligands. Also, the IC50 values of both, complexes (3a–e) and benzimidazoles 2a–e, have been determined. In addition, the new palladium complexes were screened for their antitumor activity. Complexes 3e and 3d exhibited the highest antitumor effect with IC50 values 6.85 μg/mL against MCF-7 and 10.75 μg/mL against T47D, respectively.

Synthesis of achiral NCN pincer Pt(II) and Pd(II) complexes and catalytic application in the Suzuki-Miyaura reaction

A series of platinum and palladium pincer complexes supported by achiral 1,3-bis(2′-imidazolinyl)benzene-based NCN ligands have been prepared via direct C2 metalation. Meanwhile, ligand precursor 3b and Pt(II) complex 4b were characterized by crystallographic studies, which reveals that the platinum atom in 4b adopts a distorted-square-planar geometry. The Pd(II) pincer complexes 5b was found to be an efficient catalyst for Suzuki cross-coupling reaction of aryl bromides and phenylboronic acid under air. In the presence of 0.5 mol% of Pd(II) 5b in DMF/K3PO4·3H2O for 8 h, the corresponding biaryl products could be obtained in 24–99% yields.

Dicyclohexylphosphino cyrhetrene: Synthesis, characterization and catalytic evaluation toward Suzuki-Miyaura cross-coupling reaction of aryl bromides and chlorides

Reaction of cyrhetrene ((η5-C5H5)Re(CO)3) with n-butyllithium (1.0equiv, −78°C) and then ClPCy2 (Cy=cyclohexyl) gives the new cyrhetrenyl-phosphino ligand (η5-C5H4PCy2)Re(CO)3 which was isolated as a pure sample in 86% yield and characterized by standard spectroscopic techniques (FT-IR, 1H, 13C and 31P NMR), MS, X-ray diffraction and Elemental Analysis). This rhenium containing cyrhetrenyl phosphine combined with Pd(OAc)2 (2:1mol ratio) resulted an efficient catalytic system for Suzuki couplings of aryl bromides and aryl chlorides with phenylboronic acid. The catalyst exhibits a high activity, with conversions of 100% after 20min.

Merrifield’s Resin-Supported Palladium–Bis(oxazoline) Complex-Catalyzed Cross-Coupling Reactions of Aryl Bromides and Aryl Chlorides

The catalytic activity and the recycling ability of palladium–bis(oxazoline) (Pd–BOX-M) complex supported on Merrifield’s resin have been investigated in Suzuki–Miyaura and Mizoroki–Heck cross-coupling reactions of aryl bromides and aryl chlorides. The supported palladium–bis(oxazoline) catalyst demonstrated exceptional catalytic activity and excellent recycling ability. The characterization of the recycled palladium catalyst reveals no significant change in its structure, oxidation state and the amount of loaded palladium. This confirms the excellent stability of the palladium-supported catalyst.

Synthesis and Catalytic Applications of a Triptycene-Based Monophosphine Ligand for Palladium-Mediated Organic Transformations.

1-Methoxy-8-(diphenylphosphino)triptycene (1), featuring high structural rigidity and steric bulkiness around the phosphine functionality, was synthesized as a new chiral monophosphine ligand for transition metal-catalyzed reactions. In the presence of 5–10 mol ppm (i.e., 0.0005–0.001 mol %) Pd(OAc)2 and 1 (2 equiv for Pd), Suzuki–Miyaura cross-coupling reactions of aryl bromides and arylboronic acids proceeded effectively under mild atmospheric conditions to give the corresponding biaryl compounds in a high yield. The single-crystal X-ray analysis of a Pd(II) complex of 1 revealed its coordination structure, in which two homochiral molecules form a dimer, suggesting that triptycene could provide a chiral environment for asymmetric organic transformations. In fact, optically active 1 obtained by optical resolution showed good enantioselectivity in the palladium-catalyzed asymmetric hydrosilylation of styrene, which represents, for the first time, the asymmetric catalytic activity of triptycene-based monophosphine ligands.

Graphene Oxide-Supported Oxime Palladacycles as Efficient Catalysts for the Suzuki–Miyaura Cross-Coupling Reaction of Aryl Bromides at Room Temperature under Aqueous Conditions

Palladacycles are highly efficient precatalysts in cross-coupling reactions whose immobilization on carbonaceous materials has been hardly studied. Herein, we report a detailed study on the synthesis and characterization of new oxime palladacycle-graphene oxide non-covalent materials along with their catalytic activity in the Suzuki–Miyaura reaction. Catalyst 1-GO, which has been fully characterized by ICP, XPS, TGA, and UV-Vis analyses has been demonstrated to be an efficient catalyst for the Suzuki–Miyaura coupling between aryl bromides and arylboronic acids using very low catalyst loadings (0.002 mol % of Pd) at room temperature under aqueous conditions.

A Palladium Catalyst System for the Efficient Cross-Coupling Reaction of Aryl Bromides and Chlorides with Phenylboronic Acid: Synthesis and Biological Activity Evaluation.

New benzimidazolium salts 1a–c and their palladium bis-N-heterocyclic carbene complexes 2a–c and palladium PEPPSI-type complexes 3a–c were designed, synthesized and structurally characterized by NMR (1H and 13C), IR, DART-TOF mass spectrometry and elemental analysis. Then these complexes 2–3 were employed in the Suzuki-Miyaura cross-coupling reaction of substituted arenes with phenylboronic acid under mild conditions in toluene and DMF/H2O (1/1) to afford functionalized biaryl derivatives in good to excellent yields. The antibacterial activity of palladium bis-N-heterocyclic carbene complexes 2a–c and palladium PEPPSI-type complexes 3a–c was measured by disc diffusion method against Gram positive and Gram negative bacteria. Compounds 2a, 2c and 3a–c exhibited potential antibacterial activity against four bacterial species among the five used indicator cells. The product 2b inhibits the growth of the all five tested microorganisms. Moreover, the antioxidant activity determination of these complexes 2–3, using 2.2-diphenyl-1-picrylhydrazyl (DPPH) as a reagent, showed that compounds 2a–c and 3b possess DPPH antiradical activity. The higher antioxidant activity was obtained from the product 2b which has radical scavenging activity comparable to that of the two used positive controls (gallic acid “GA“ and tutylatedhydroxytoluene “BHT“). Investigation of the anti-acetylcholinesterase activity of the studied complexes showed that compounds 2b, 3a, and 3b exhibited moderate activity at 100 μg/mL and product 2b is the most active.

Green synthesis of carbon quantum dots from vanillin for modification of magnetite nanoparticles and formation of palladium nanoparticles: Efficient catalyst for Suzuki reaction

In this report we prepared carbon quantum dots (CQD) from vanillin as an ecofriendly and naturally abundant compound for modification of magnetic nanoparticles (CQD@Fe3O4 NPs). This new magnetic solid has been used for complete reduction of PdCl2 with formation of stabilized palladium nanoparticles (Pd@CQD@Fe3O4 NPs) and characterized by SEM, TEM, EDX, solid UV, VSM, XPS, XRD, and N2 adsorption–desorption analyses. These magnetic supported Pd NPs have been used as an efficient catalyst for the Suzuki-Miyaura cross-coupling reactions of aryl bromides at room temperature in aqueous ethanol and of aryl chlorides at 120 °C in PEG200 under low catalyst loading in air. The heterogeneous catalyst can be easily recovered by an external magnet and reused for eight consecutive runs.

ChemInform Abstract: Indazolium Halides as Efficient Ligands for Pd‐Catalyzed Suzuki—Miyaura Cross‐Coupling of Aryl Bromides with Arylboronic Acids.

Abstract The indazolium halides containing various N -substituents have been conveniently prepared and applied in the palladium-catalyzed Suzuki–Miyaura cross-coupling reactions of aryl bromides with arylboronic acids at mild reaction conditions. The cross-coupling reaction provides the desired products in good to high yields. The ease of synthesis and the modularity, and the broad range of aryl bromides and arylboronic acids make this type of ligand attractive and promising for transition metal catalysis.