Coupling Reactions Of Aryl Bromides Research Articles

Palladium/1,3-bis(ferrocenylmethy)imidazolinium chloride catalyst for Suzuki cross-coupling reactions

We describe here the first results of catalytic performance of in situ prepared [Pd(O2CCH3)2] / 1,3-bis(ferrocenylmethy)imidazolinium chloride involving a saturated imidazole ring were successfully employed to Suzuki cross-coupling reactions of different aryl bromides (bromobenzene, 2-bromobenzonitrile, 2-bromotoluene, p-bromobenzaldehyde, p-bromoacetophenone, p-bromoanisole, p-bromotoluene and p-bromobenzotrifluoride) with phenylboronic acid under the optimum conditions. Optimum conditions were choosed, as 24 h, 80 oC, K2CO3 as base, dioxane as solvent, 1,3-bis(ferrocenylmethy)imidazolinium chloride as auxiliary ligand. Under these optimum conditions, 2- bromobenzonitrile, p-bromoacetophenone and p- bromobenzaldehyde react with phenyl boronic acid in moderate yields 57%, 50%, and 46% respectively. Catalytic experiments showed that [Pd(O2CCH3)2] / 1,3-bis(ferrocenylmethy)imidazolinium chloride catalytic system was moderately effficent in the Suzuki cross coupling reaction of aryl bromides in dioxane.

Incorporating Domain Knowledge and Structure-Based Descriptors for Machine Learning: A Case Study of Pd-Catalyzed Sonogashira Reactions.

Machine learning has revolutionized information processing for large datasets across various fields. However, its limited interpretability poses a significant challenge when applied to chemistry. In this study, we developed a set of simple molecular representations to capture the structural information of ligands in palladium-catalyzed Sonogashira coupling reactions of aryl bromides. Drawing inspiration from human understanding of catalytic cycles, we used a graph neural network to extract structural details of the phosphine ligand, a major contributor to the overall activation energy. We combined these simple molecular representations with an electronic descriptor of aryl bromide as inputs for a fully connected neural network unit. The results allowed us to predict rate constants and gain mechanistic insights into the rate-limiting oxidative addition process using a relatively small dataset. This study highlights the importance of incorporating domain knowledge in machine learning and presents an alternative approach to data analysis.

Palladium(II) Pincer Complexes Derived From N,N’,N’’‐Tris(2‐thioanisyl)guanidine. Syntheses, Structural Aspects, Solution Behaviour and Suzuki‐Miyaura Coupling Reactions

AbstractGuanidine, [(ArNH)2C=NAr] (Ar=2‐(MeS)C6H4) was prepared in 70 % (method 1)/92 % (method 2) yields. Cyclopalladation of the guanidine with Pd(OC(O)R)2 (R=Me and tBu) afforded the CNS pincer complexes, [Pd{κ3(C,N,S)}(OC(O)R)] in 82 % and 75 % yields, respectively. [Pd{κ3(C,N,S)}(OC(O)R)] (R=Me and tBu) upon metathesis reaction with LiBr gave [Pd{κ3(C,N,S)}Br] in 67 % and 72 % yields, respectively. The reaction of [Pd{κ3(C,N,S)}Br] with AgBF4 in MeCN gave [Pd{κ3(C,N,S)}(MeCN)]BF4 in 82 % yield. The new compounds were characterised by elemental analysis, IR and NMR spectroscopies and mass spectrometry. Molecular structures of [(ArNH)2C=NAr] (Ar=2‐(MeS)C6H4) and [Pd{κ3(C,N,S)}(OC(O)tBu)] were determined by single crystal X‐ray diffraction while the solution behaviour of the former compound studied by VT 1H NMR spectroscopy. [Pd{κ3(C,N,S)}(OAc)] was used as a catalyst in Suzuki‐Miyaura coupling reactions of aryl bromides with aryl boronic acids.

Cover Feature: Pincer‐Type Mesoionic Carbene Nickel(II) Complexes: Synthesis, Properties, Reactions, and Catalytic Application to the Suzuki–Miyaura Coupling Reaction of Aryl Bromides (Eur. J. Inorg. Chem. 10/2022)

The Cover Feature shows an image of the final product of an elaborately designed pincer complex derived from triazolylidene, which has emerged through a long series of steps from the earth′s abundant nickel mines. The complex has interesting properties provided by the ligand with strong σ-donor and π-acceptor abilities, and bulky substituents. It is also active in the Suzuki-Miyaura coupling of aryl bromides. The crystals are called annabergite and are known to be a landmark in nickel mining. Like this crystal, the complex is expected to become one of the landmarks for the development of organonickel chemistry. More information can be found in the Research Article by K. Matsubara and co-workers.

Pincer‐Type Mesoionic Carbene Nickel(II) Complexes: Synthesis, Properties, Reactions, and Catalytic Application to the Suzuki–Miyaura Coupling Reaction of Aryl Bromides

AbstractTridentate pincer‐type triazolylidene nickel(II) complexes have been prepared and characterized. Despite increasing interest in the new series of mesoionic carbene (MIC) ligands in the field of homogeneous catalysis, pincer‐type MIC metal complexes have rarely been used as catalysts, and there are few studies on MIC nickel complexes. Herein, MIC nickel(II) halide complexes were synthesized from their silver analogues and fully characterized. An anion exchange reaction with silver tetrafluoroborate in acetonitrile gave a dicationic acetonitrile complex in good yield. A comparison of the structures and frontier orbitals between the MIC‐ and NHC‐nickel(II) chloride complexes has revealed that these complexes are comparable in nature. However, their use in the Suzuki–Miyaura (SM) cross‐coupling reaction of aryl bromides with phenylboronic acid requires different conditions to provide sufficient results.

Synthesis, crystal structure, and catalytic activity of bridged-bis(N-heterocyclic carbene) palladium(II) complexes in selective Mizoroki-Heck cross-coupling reactions

A series of three 1,3-propanediyl bridged bis(N-heterocyclic carbene)palladium(II) complexes (Pd-BNH1, Pd-BNH2, and Pd-BNH3), with + I effect order of the N-substituents of the ligand (isopropyl > benzyl > methoxyphenyl), was the subject of a spectroscopic, structural, computational and catalytic investigation. The bis(NHC)PdBr2 complexes were evaluated in Mizoroki-Heck coupling reactions of aryl bromides with styrene or acrylate derivatives and showed high catalytic efficiency to produce diarylethenes and cinnamic acid derivatives. The X-ray structure of the most active palladium complex Pd-BNH3 shows that the Pd(II) center is bonded to the two carbon atoms of the bis(N-heterocyclic carbene) and two bromide ligands in cis position, resulting in a distorted square planar geometry. The NMR data of Pd-BNH3 are consistent with a single chair-boat rigid conformer in solution with no dynamic behavior of the 8-membered ring palladacycle in the temperature range 25–120 °C. The catalytic activities of three Pd-bridged bis(NHC) complexes in the Mizoroki-Heck cross-coupling reactions were not found to have a direct correlation with +I effect order of the N-substituents of the ligand. However, a direct correlation was found between the DFT calculated absolute softness of the three complexes with their respective catalytic activity. The highest calculated softness, in the case of Pd-BNH3, is expected to favor the coordination steps of both the soft aryl bromides and alkenes in the Heck catalytic cycle.

Novel and efficient bridged bis(N‐heterocyclic carbene)palladium(II) catalysts for selective carbonylative Suzuki–Miyaura coupling reactions to biaryl ketones and biaryl diketones

Bridged N,N′‐substituted bisbenzimidazolium bromide salts (L1, L2, and L3) were synthesized and fully characterized. Reactions of palladium acetate with L1, L2, and L3 afforded corresponding new bridged bis(N‐heterocyclic carbene)palladium(II) complexes (C1, C2, and C3) in high yields. The X‐ray structure of complex C1 showed that the Pd(II) ion is bonded to the two carbon atoms of the bis(N‐heterocyclic carbene) and two bromido ligands are in the cis position, resulting in a distorted square planar geometry. The three Pd(NHC)2Br2 complexes C1, C2, and C3 were evaluated in carbonylative Suzuki–Miyaura coupling reactions of aryl boronic acids with aryl halides and displayed high catalytic activity with low catalyst loading. The coupling reactions of aryl bromides were selective towards the carbonylation product at higher carbon monoxide pressure.

The Hiyama Cross-Coupling Reaction at Parts Per Million Levels of Pd: In Situ Formation of Highly Active Spirosilicates in Glycol Solvents.

A palladium NNC-pincer complex at a 5 mol ppm loading efficiently catalyzed the Hiyama coupling reaction of aryl bromides with aryl(trialkoxy)silanes in propylene glycol to give the corresponding biaryls in excellent yields. This method was applied to the syntheses of adapalene and a biaryl-type liquid-crystalline compound, as well as to the derivatization of dextromethorphan and norfloxacin. ESI-MS and NMR analyses of the reaction mixture suggested the formation of pentacoordinate spirosilicate intermediates in situ. Preliminary theoretical studies revealed that the glycol-derived silicate intermediates formed in situ are quite reactive silicon reagents in the transmetalation step.

A well-designed sandwich-like MS/Pd@MS hollow nanosphere for Suzuki coupling reactions of aryl bromides and arylboronic acids

A hollow core-shell nanosphere with sandwiched Pd nanoparticles between two-layered mesoporous silica was designed through layer-by-layer assembly. The nanocomposite exhibited outstanding catalytic activity and thermal stability in Suzuki coupling reactions of aryl bromides and arylboronic acids. The conversion of bromobenzene was up to 82.8% in 1 h and 68.2% in 5 min, and the sandwich structure was well-kept after running five cycles, with few Pd NPs mass loss.

Efficient synthesis of 3-benzoyl Benzo[b]thiophenes and raloxifene via Mercury(II)-Catalyzed cyclization of 2-alkynylphenyl alkyl sulfoxides

The unique selective estrogen receptor modulator, Raloxifene (1), and antitubulin agent 2 were synthesized through the key intermediate, 4-methoxybenzyl 2-bromo-4-methoxyphenyl sulfoxide (6), respectively. It was found that compared with the o-sulfanyl aryl bromides, the sulfinyl group at ortho position accelerated the Sonogashira coupling reaction of aryl bromides. Thus, compound 6 was coupled with 3,4,5-trimethoxyphenyl acetylene, followed by mercury-catalyzed cyclization reaction afford compound 2 in 79% overall yield. Raloxifene (1) was prepared from compound 6 in four steps and 33% overall yield via coupling reaction with 1-trimethylsily-2-(4-tert-butyldimethylsiloxy)phenylethyne, mercury-catalyzed cyclization reaction, alkylation and demethylation.

Pd Nanoparticles Dispersed on ZrIV Organophosphonate: A Robust and Reusable Catalyst for Suzuki–Miyaura Cross‐Coupling Reactions

A mesoporous zirconium(IV) phosphonate was synthesized by the hydrothermal reaction of ZrOCl2·8H2O with a trisphosphonic acid ligand, mesityl‐1,3,5‐tris(methylenephosphonic acid). Treatment of the mesoporous ZrIV phosphonate framework with Pd(OAc)2 and subsequent reduction produced a nanocomposite where Pd nanoparticles of average size ca. 7–8 nm were found to be homogeneously and abundantly dispersed over the phosphonate framework. The composite acts as an efficient and reusable heterogeneous catalyst in the Suzuki–Miyaura cross coupling reaction of aryl bromides with aryl boronic acids.

Highly active and reusable hydrotalcite-supported Pd(0) catalyst for Suzuki coupling reactions of aryl bromides and chlorides

A palladium(0) nanocluster supported on hydrotalcite has been prepared and tested for the Suzuki coupling reaction. The prepared catalyst showed very efficient catalytic activity for cross coupling of iodo- and bromoarenes under very mild reaction conditions, affording >90% yield. Under the optimized reaction conditions, chloroarenenes also showed very good reactivity. Transmission electron microscopic imaging data showed the formation of very small Pd(0)-nanoclusters (d = 2.2 ± 0.5 nm) well dispersed on the support, which enhanced the activity and stability of the catalyst for the Suzuki cross-coupling reaction. This catalytic system offers an easy method of preparation with good activity and reusability up to five cycles.

The Palladium Acetate-Catalyzed Microwave-Assisted Hirao Reaction without an Added Phosphorus Ligand as a "Green" Protocol: A Quantum Chemical Study on the Mechanism.

It was proved by our experiments that on microwave irradiation, the mono‐ or bidentate phosphorus ligands generally applied in the palladium(II)‐catalyzed P–C coupling reaction of aryl bromides and dialkyl phosphites or secondary phosphine oxides may be substituted by the excess of the >P(O)H reagent that exists under a tautomeric equilibrium. Taking into account that the reduction of the palladium(II) salt and the ligation of the palladium(0) so formed requires 3 equivalents of the P‐species for the catalyst applied in a quantity of 5–10%, all together, 15–30% of the P‐reagent is necessary beyond its stoichiometric quantity. In the coupling reaction of diphenylphosphine oxide, it was possible to apply diethyl phosphite as the reducing agent and as the P‐ligand. The reactivities of the diethyl phosphite and diphenylphosphine oxide reagents were compared in a competitive reaction. The mechanism and the energetics of this new variation of the Hirao reaction of bromobenzene with Y2P(O)H reagents (Y=EtO and Ph) was explored by quantum chemical calculations. The first detailed study on simple reaction models justified our assumption that, under the conditions of the reaction, the trivalent form of the >P(O)H reagent may serve as the P‐ligand in the palladium(0) catalyst, and shed light on the fine mechanism of the reaction sequence. The existence of the earlier described bis(palladium complex) {[H(OPh2P)2PdOAc]2} was refuted by high level theoretical calculations. This kind of complex may be formed only with chloride anions instead of the acetate anion. The interaction of palladium acetate and Y2P(O)H may result in only the formation of the [(HO)Y2P]2Pd complex that is the active catalyst in the Hirao reaction. The new variation of the Hirao reaction is of a more general value, and represents the greenest protocol, as there is no need for the usual P‐ligands. Instead, the >P(O)H reagent should be used in an excess of up to 30%. Hence, the costs and environmental burdens may be decreased.

A straightforward synthesis of 4,5-dihalofunctionalized imidazol-2-ylidene/imidazolyl-metal complexes from trihaloimidazolium salts/imidazoles: Structure and catalytic studies

Backbone dihalofunctionalized imidazol-2-ylidene/imidazolyl-metal complexes (5−13) of group–10 metal ions were synthesized through a proficient and single step oxidative addition method using 2,4,5-trihaloimidazolium salts or imidazoles respectively. The donor property of 4,5-diiodofunctionalized imidazol-2-ylidene was described for the first time. The catalytic activity of palladium complexes containing imidazol-2-ylidene (6 and 7)/imidazolyl (10 and 11) groups towards Suzuki-Miyaura coupling reaction of aryl bromides was evaluated and compared with its unsubstituted counterpart. Besides, the investigation of reaction pathway in catalysis was carried out.

Bis‐benzimidazolium‐palladium system catalyzed Suzuki‐Miyaura coupling reaction of aryl bromides under mild conditions

Bis‐benzimidazolium salts were prepared successfully from commercially available and inexpensive o‐phenylenediamine through a series of simple reactions. The bis‐NHC‐Pd complexes prepared in situ can catalyze Suzuki‐Miyaura cross‐coupling reaction under very mild conditions in aqueous media with excellent yields. The efficiency of this reaction is demonstrated by its compatibility with a range of functional groups. Di‐ortho‐substituted biaryls could be accomplished in 89–99% yields. Moreover, the rigorous exclusion of air or moisture is not required in these transformations.

Microwave-Assisted Synthesis of Pd Nanoparticles and Catalysis Application for Suzuki Coupling Reactions

A facile and efficient method was developed for the synthesis of highly active palladium nanoparticles (PdNPs) by microwave-assisted chemical reduction. The PdNPs with different morphology were prepared with or without KBr (capping agent) using ethylene glycol (EG) and citric acid (CA) as reducing agent in the presence of polyvinylpyrrolidone (PVP), respectively. The as-prepared PdNPs were characterized by (UV-Visible Spectrophotometer) UV-Vis, transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. The results showed that the PdNPs reduced by EG without KBr (PdNPs-EG) has smaller particle size than other PdNPs. The remarkable catalytic activity of the PdNPs catalysts are obtained using a low amount of PdNPs (0.1 mmol‰) using K2CO3 as base and EtOH/H2O as solvent toward Suzuki coupling reactions of aryl bromides and phenylboronic acid for 15 min.

Application of Tripodal Linker Units to Immobilized Diphenylphosphine Palladium Complex Catalysts for Suzuki-Miyaura Coupling Reactions of Aryl Bromide: Effect of Immobilization Method of Phosphine Ligand on Catalytic Performance

A tripodal linker unit that tightly binds to a silica surface via three independent Si–O–Si bonds was applied to immobilize diphenylphosphino-palladium complex catalysts onto ordered mesoporous silica. The diphenylphosphino-functionalized silica materials were prepared by: (i) grafting the bromine-substituted tripodal linker unit onto mesoporous silica and a subsequent treatment with potassium diphenylphosphide (the “bottom-up” method), (ii) directly grafting pre-synthesized tripodal diphenylphosphino ligands onto silica (the “top-down” method). The catalytic properties were evaluated in the Suzuki-Miyaura coupling reaction of aryl bromides. The tripodally immobilized catalyst prepared via the “bottom-up” method showed lower leaching levels of palladium and phosphorus compared to catalyst prepared via the “top-down” method.

P(HEMA)-Pd(II) and p(HEMA-MAH)-Pd(II) Microspheres: Efficient, Recyclable and Ligand-Free Catalyst for Suzuki-Miyaura Cross-Coupling Reaction in Water

In this study, the authors report the synthesis and characterization of new poly(hydroxyethyl methacrylate) palladium(II) (p(HEMA)-Pd(II)) and poly(hydroxyethyl methacrylate-N-methacryloyl-(L)-histidine methyl ester) palladium(II), p(HEMA-MAH)-Pd(II) microsphere catalysts, and their catalysis in Suzuki-Miyaura coupling reactions of aryl bromides with phenylboronic acid in water. The microsphere catalysts were characterized by SEM, ICP-MS, FTIR, and diffuse-reflactance UV-visible spectroscopy. The p(HEMA)-Pd(II) and p(HEMA-MAH)-Pd(II) microsphere catalysts were active catalysts in Suzuki-Miyaura coupling reactions of arylbromides with phenylboronic acid affording biphenyls in high yield. Recycling experiments showed that the p(HEMA)-Pd(II) and p(HEMA-MAH)-Pd(II) microsphere catalysts could be used seven or ten times with essentially no loss in activity in the Suzuki-Miyaura coupling reactions.

ChemInform Abstract: Selective Cross‐Electrophile Coupling by Dual Catalysis

AbstractReview: 12 refs.

Selective Cross-Electrophile Coupling by Dual Catalysis.

Palladium and nickel: This Highlight summarizes recent developments in the area of dual-catalytic Ullman-type coupling reactions of aryl bromides and triflates: Weix and co-workers took advantage of the different selectivities and stabilities of palladium and nickel catalysts to favor the desired cross-coupling and suppress homocoupling.