Reaction Of Phenylboronic Acid Research Articles

Direct conversion of lignin to functionalized diaryl ethers via oxidative cross-coupling

Efficient valorization of lignin, a sustainable source of functionalized aromatic products, would reduce dependence on fossil-derived feedstocks. Oxidative depolymerization is frequently applied to lignin to generate phenolic monomers. However, due to the instability of phenolic intermediates, repolymerization and dearylation reactions lead to low selectivity and product yields. Here, a highly efficient strategy to extract the aromatic monomers from lignin affording functionalized diaryl ethers using oxidative cross-coupling reactions is described, which overcomes the limitations of oxidative methods and affords high-value specialty chemicals. Reaction of phenylboronic acids with lignin converts the reactive phenolic intermediates into stable diaryl ether products in near-theoretical maximum yields (92% for beech lignin and 95% for poplar lignin based on the content of β−O−4 linkages). This strategy suppresses side reactions typically encountered in oxidative depolymerization reactions of lignin and provides a new approach for the direct transformation of lignin into valuable functionalized diaryl ethers, including key intermediates in pharmaceutical and natural product synthesis.

Novel hybrid phosphinite-theophylline ligands and their Pd(II) complexes. Synthesis, characterization and catalytic evaluation in Suzuki-Miyaura couplings

Two Pd(II) complexes bearing bidentated [R’2(OR)P^P(OR)R’2] (OR = 7-(2,3-dihydroxypropyl)theophylline and R’ = Ph for (1) and R’ = iPr for (2)) ligands were synthesized and fully characterized, including the unequivocal determination of their molecular structures by single crystal X-ray diffraction analysis. Thus confirming the coordination of the phosphinite-theophylline ligand to the Pd(II) center in a chelate manner. Exploration of these compounds as catalysts in Suzuki-Miyaura Couplings revealed complex (2) to be the best of the pair of complexes in the formation of CC bonds in the reactions of phenylboronic acid and a series of para-substituted bromobenzenes under mild reaction conditions (50 °C, 50 W, 5 min, and 0.05 mol % of catalyst), achieving yields of > 99 %.

Synthetic and DFT Modeling Studies on Suzuki–Miyaura Reactions of 4,5-Dibromo-2-methylpyridazin-3(2H)-one with Ferrocene Boronates, Accompanied by Hydrodebromination and a Novel Bridge-Forming Annulation In Vitro Cytotoxic Activity of the Ferrocenyl–Pyridazinone Products

This paper presented the efficiency of different Pd-based catalytic systems in a series of SM reactions of 4,5-dibromo-2-methylpyridazin-3(2H)-one with ferroceneboronic acid, ferrocene-1,1′-diboronoc acid, and its bis-pinacol ester. In addition to the disubstituted product, these transformations afford substantial amounts of isomeric 4- and 5-ferrocenyl-2-methylpyridazin-3(2H)-ones, and a unique asymmetric bi-pyridazinone-bridged ferrocenophane with a screwed molecular architecture. The reactions of phenylboronic acid, conducted under the conditions, are proven to be the most reductive in the conversions of ferroceneboronic acid, and produce 2-methyl-4,5-diphenylpyridazin-3(2H)-one as single product, supporting our view about solvent-mediated hydrodehalogenations that are supposed to proceed via the assistance of the ferrocenyl group present in the reaction mixture, or attached to the bromo-pyridazinone scaffold, which is constructed in the first SM coupling of the heterocyclic precursor. A comparative DFT modelling study on the structures and possible transformations of relevant bromo-, ferrocene- and phenyl-containing carbopalladated intermediate pairs was carried out, providing reasonable mechanisms suitable to account for the apparently surprising regioselectivity of the alternative hydrodebromination processes, and for the formation of the ferrocenophane product. Supporting the results of DFT modelling studies, the implication of DMF as a hydrogen transfer agent in the hydrodebromination reactions is evidenced by deuterium labelling experiments using the solvent mixtures DMF-d7–H2O (4:1) and DMF–D2O (4:1). The organometallic products display antiproliferative effects on human malignant cell lines.

A rapid construction of new boron heterocycles and evaluation of photophysical properties of iminoboronates.

A green and efficient method for the synthesis of oxadiazaborole, dioxazaborinine, and oxadiazaborinine from the reactions of phenylboronic acid with amidoxime, α-hydroxyl oxime and α-hydroxyl hydrazone, respectively, is described. The reactions were performed under catalyst-free and mild conditions. All products can be rapidly purified by filtration and washing. In addition, a set of iminoboronates were prepared following a one-pot multicomponent reaction procedure using α-hydroxyl hydrazone, salicylaldehyde and boronic acid derivatives as starting materials and their photophysical properties were assessed. Then, cross-coupling reactions can be carried out smoothly on some target compounds, which may help develop new boron masking strategies.

Efficient synthetic method of β-fluorocinnamate by arylboronic acids and ethyl 3,3,3-trifluoropropionate under palladium-catalyzed conditions

A convenient and efficient method for synthesizing β-fluorocinnamate and derivatives is reported. Palladium (II) catalysis was employed in β-F elimination and coupling reaction of phenylboronic acid and ethyl 3,3,3-trifluoropropionate with a high yield and E-selectivity. The reaction was conducted under mild conditions and could be widely adapted to boronic acid substrates.

Rh-catalyzed 1,4-addition reactions of arylboronic acids accelerated by co-immobilized tertiary amine in silica mesopores

Mesoporous silica-supported Rh complex catalysts were prepared by simple silane-coupling, followed by complexation, and characterized by FT-IR, SEM, Rh K-edge XAFS, and elemental analysis. Local structures of the Rh complexes in each sample were almost similar to those of a nonporous silica-supported diaminorhodium complex. Co-immobilization of a tertiary amine on the same silica surface induced slight changes to the Rh complex structure in the case of the support with smaller pores. The prepared catalysts showed high activity for the 1,4-addition reaction of phenylboronic acids. Co-immobilization of the tertiary amine increased the reaction rate by more than 7-fold, with turnover number of nearly 8500. The catalytic performance achieved with this novel system is with much higher than that reported previously with a nonporous silica-supported catalyst. The mesoporous silica-supported Rh complex-tertiary amine showed a wide substrate scope, including unsaturated ketones and nitriles. This co-immobilized tertiary amine may activate phenylboronic acid to enhance its reactivity in the transmetalation step with Rh-OH species.

PEPPSI-Pd-NHC catalyzed Suzuki-Miyaura cross-coupling reactions in aqueous media

A series of unsymmetrical 1,3-disubstituted benzimidazolium chlorides were synthesized as N-heterocyclic carbene (NHC) precursors. These compounds were used to synthesize of the PEPPSI-type palladium NHC complexes. The structures of all compounds were characterized by 1H NMR, 13C NMR, FT-IR spectroscopy and elemental analyses. The catalytic activity of the PEPPSI-type palladium–NHC complexes has been evaluated with respect to the Suzuki-Miyaura cross-coupling reactions of phenyl boronic acid with various aryl halides in aqueous media.

Nano CoCuFe2O4‐catalyzed coupling reaction of arylboronic acid with amines and thiols: An atom‐economic and ligand‐free route to access unsymmetrical amines and sulfides

An efficient protocol was developed for the nano CoCuFe2O4‐catalyzed C‐N and C‐S bond formation. By this catalytic system, both amine and sulfide‐based structural motifs were formed efficiently in aryl halide‐free route. The amination reaction of phenyl boronic acid with various types of amines was conducted under ligand‐free conditions, in ethanol as a green solvent at 60°C. Unsymmetrical diaryl/aryl alkyl sulfide synthesis via the coupling reaction of arylboronic acids with thiols was also conducted. The nano cobalt‐copper ferrite was used as a heterogenous efficient, inexpensive, magnetically separable and recyclable catalyst that can be used for several cycles.

Cu@Fe3O4-TiO2-L-dopa: A novel and magnetic catalyst for the Chan-Lam cross-coupling reaction in ligand free conditions

A novel and magnetic Cu(0) catalyst (Cu@Fe3O4-TiO2-L-dopa) has been prepared and characterized with different techniques, such as SEM, HR-TEM, ICP-AES, XRD, FTIR, EDX, CHN analysis, VSM and TGA studies. TiO2 nanoparticles were proved to be efficient in stabilizing magnetite nanoparticles, thus preventing their agglomeration. It has been also observed that grafting of Fe3O4-TiO2 with L-dopa reduces the leaching of Cu(0) nanoparticles. The synthesized catalyst showed excellent catalytic activity for the Chan-Lam cross-coupling reaction of phenyl boronic acid with different substituted anilines in ligand-free conditions, and was found to be recyclable up to 6 runs without loss of significant activity.

Palladium(II) Complexes of Monodentate Phosphine Ligands and Their Application as Catalyst in Suzuki-Miyaura C-C Coupling Reaction at Room Temperature

A series of palladium(II) complexes from monodentate phosphine ligands (1a-4a) were successfully prepared and characterized with 1H, 31P, 13C NMR, and HRMS techniques. These pre-catalysts were applied for the Suzuki-Miyaura C-C coupling reaction of phenylboronic acid with bromobenzene and the influence of the base and solvent on the performance of the pre-catalysts was investigated. Sterically hindered and electronically deactivated aryl bromides as well as activated ones gave the corresponding coupling products in good to excellent yields at room temperature.

Synthesis, characterization, and application of palladium complexes containing bis(aminophosphine) ligands

Two palladium complexes containing bis(aminophosphine) ligands have been prepared and characterized. Their solid structures were determined by X-ray single crystal diffraction studies. They were successfully employed in the Suzuki coupling reactions of phenylboronic acid and various aryl chlorides.

Synthesis of Cyclic and Cage Borosilicates Based on Boronic Acids and Acetoxysilylalkoxides. Experimental and Computational Studies of the Stability Difference of Six- and Eight-Membered Rings.

A series of borosilicates was synthesized, where the structure of the borosilicate core was easily modulated using two strategies: blocking of condensation sites and controlling the stoichiometry of the reaction. Thus, on the one hand, the condensation of phenylboronic or 3-hydroxyphenylboronic acid with diacetoxysilylalkoxide [(tBuO)(Ph3CO)Si(OAc)2] led to the formation of borosilicates (tBuO)(Ph3CO)Si{(μ-O)BPh}2(μ-O) (1), [{(tBuO)(Ph3CO)Si(μ-O)BPh(μ-O)}2] (2), and [{(tBuO)(Ph3CO)Si(μ-O)B(3-HOPh)(μ-O)}2] (3) with a cyclic inorganic B2SiO3 or B2Si2O4 core, respectively. On the other hand, the reaction of phenylboronic acid with triacetoxysilylalkoxide (Ph3CO)Si(OAc)3 in 3:2 ratio resulted in the formation of a cagelike structure [{(Ph3CO)Si(μ-O)2BPh(μ-O)}2] (4) with B4Si4O10 core, while the reaction of the boronic acid with silicon tetraacetate generated an unusual 1,3-bis(acetate)-1,3-diphenyldiboraxane PhB(μ-O)(μ-O,O'-OAc)2BPh (5). Additionally, compound 1 was used to evaluate the possibility to form N→B donor-acceptor bond between the boron atom in the borosilicates and a nitrogen donor. Thus, coordination of 1 with piperazine yielded a tricyclic [{(tBuO)(Ph3CO)Si(OBPh)2(μ-O)}2·C4H10N2] compound 6 with two borosilicate rings bridged by a piperazine molecule. Finally, the processes involved in the formation of the six- and eight-membered rings (B2SiO3 and B2Si2O4) in compounds 1 and 2 were explored using solution 1H NMR studies and density functional theory calculations. These molecules represent to the best of our knowledge first examples of cyclic molecular borosilicates containing SiO4 units.

Suzuki-Miyaura C-C Coupling Reactions Catalyzed by Supported Pd Nanoparticles for the Preparation of Fluorinated Biphenyl Derivatives

Heterogeneous recyclable catalysts in Suzuki-Miyaura C-C coupling reactions are of great interest in green chemistry as reusable alternatives to homogeneous Pd complexes. Considering the interesting properties of fluorinated compounds for the pharmaceutical industry, as precursors of novel materials, and also as components of liquid crystalline media, this present study describes the preparation of different fluorinated biphenyl derivatives by Suzuki-Miyaura coupling reactions catalyzed by a heterogeneous system (G-COOH-Pd-10) based on Pd nanoparticles supported onto COOH-modified graphene. The catalytic activity of the hybrid material G-COOH-Pd-10 has been tested in Suzuki-Miyaura C–C coupling reactions observing excellent versatility and good conversion rates in the reactions of phenylboronic acid, 4-vinylphenylboronic acid, 4-carboxyphenylboronic acid, and 4-fluorophenylboronic acid with 1-bromo-4-fluorobenzene. In addition, the influence of the arylbromide has been studied by carrying out reactions of 4-fluorophenylboronic acid with 1-bromo-2-fluorobenzene, 1-bromo-3-fluorobenzene, 1-bromo-4-fluorobenzene, 2-bromo-5-fluorotoluene, and 2-bromo-4-fluorotoluene. Finally, catalyst recyclability tests show a good degree of reusability of the system based on G-COOH-Pd-10 as the decrease in catalytic activity after five consecutive catalytic cycles in the reaction of 1-bromo-4-fluorobenzene with 4-florophenylboronic acid at 48 hours of reaction is lower than 8% while in the case of reactions at three hours the recyclability of the systems is much lower.

New tetrahedral boron heterobicycles: Cyclocondensation of phenylboronic acid with β-keto butanoic acid N-acyl hydrazones

A series of 4-phenyl-2-aryl-8-methyl-6-oxo-7-phenylhydrazo-2H,4H,6H,7H,8H[1,3,4,2]-oxadiazaborolo[2,3-b][1,3,2]oxazaborines were prepared in high yields via the reaction of phenylboronic acid with various N-acylhydrazones of 3-keto-2-(2′-phenylhydrazono) butanoic acid in the presence of 4Å molecular sieves. These derivatives represent a novel class of zwitterionic, tetrahedral boron heterocycles. Single crystal X-ray analysis of a representative boron containing product is reported.

Biaryl formation via Suzuki and Stille coupling reactions using palladium nanoparticle/polymeric N‐heterocyclic carbene grafted silica as recyclable and efficient catalyst

Palladium nanoparticles supported on polymeric N‐heterocyclic carbene grafted silica as an efficient organic–inorganic hybrid catalyst is introduced. Pd0 nanoparticle formation, which is stabilized by the polymeric N‐heterocyclic carbene ligands and ionic liquid units, was confirmed using X‐ray photoelectron spectroscopy. Scanning electron microscopy images showed microparticles of modified silica while transmission electron microscopy images displayed a fine distribution of Pd nanoparticles. The modified structure was applied successfully in biaryl formation via Suzuki and Stille coupling reactions. Various biaryls were generated through the reaction of phenylboronic acid or tetraphenyltin with a variety of haloarenes via cross‐coupling reactions. This catalyst showed promising activity after being recycled several times. Copyright © 2016 John Wiley & Sons, Ltd.

Ruthenium Hydride Complex Supported on Gold Nanoparticle Cored Triazine Dendrimers for C–C Coupling Reactions

In this work, the unusual ability of a ruthenium hydride catalyst, [RuHCl(PPh3)3CO], supported on gold nanoparticle cored triazine dendrimers in the Suzuki–Miyaura cross-coupling reaction and also in the synthesis of diaryl ketones is reported. [Ru-H@AuNPs-TD] was characterized by Fourier transform infrared spectroscopy, CHNS, TEM, SEM, ICP, and TGA analyses. The ruthenium hydride catalyst was used as a heterogeneous catalyst for the C–C coupling reactions of aryl halides with phenylboronic acids, and the biphenyl derivatives were produced in good to excellent yields. On the other hand, this catalytic system was applied for synthesis of diaryl ketones by the reaction of phenylboronic acids with substituted benzaldehydes. Moreover, this catalyst can be well-dispersed in the reaction medium, conveniently separated from the reaction mixture, and reused several times without significant loss of its activity.

An environmental catalyst derived from biological waste materials for green synthesis of biaryls via Suzuki coupling reactions

Synthesis of bio-macromolecular supported catalysts has gained much recent attention due to their greener nature. Among the biopolymers, chitosan is widely used as a support material due to its high affinity for metal ions. In this study, chitosan-Ulva sp. (green alga) composite microbeads were prepared as a support material for palladium catalyst. Ulva sp. particles were incorporated into chitosan matrix to enhance the interaction with palladium ions. The catalytic performance of chitosan-Ulva supported Pd(II) catalyst was investigated in the synthesis of biaryls via the Suzuki coupling reaction. All the experiments were conducted without using any solvent under the microwave irradiation, which is also considered as a green technique. This green catalyst exhibited high selectivity and efficiency in the reactions of phenyl boronic acid with different aryl halides in only 4min at low temperature (50°C). Excellent TON and TOF values were achieved for the catalyst; 4950 and 75000. In addition, the catalyst did not lose its activity even after 8 cycles. It showed high thermal stability (216.8°C) and durability in presence of oxygen. This green catalyst has a potential to be used in pharmacology, medicine and cosmetics.

ChemInform Abstract: Suzuki Cross‐Coupling in Aqueous Media.

AbstractA simple and efficient procedure for the Suzuki reaction of phenyl boronic acid or potassium phenyltrifluoroborate with aryl bromides and aryl iodides is reported The reaction can be conducted in pure water or aqueous media.

Synthesis, Characterization, Crystal Structures, and Catalytic C–C Coupling and Hydrosilylation Reactions of Palladium(II) Complexes Derived from CNC Pincer‐Type N‐Heterocyclic Carbenes

AbstractA series of pyridine linker containing bis(benz)imidazolium salts serving as precursors to CNC pincer‐type N‐heterocyclic carbene (NHC) ligands were prepared by successive N‐alkylation of the azole core. Binuclear NHC complexes of silver(I) were synthesized by in situ deprotonation of the corresponding (benz)imidazolium salt with silver(I) oxide in acetonitrile at elevated temperature in the dark. Subsequently, pincer‐type palladium(II)–NHC complexes were prepared by transmetalation using silver(I)–NHC complexes in acetonitrile at elevated temperatures. All compounds were fully characterized by elemental analysis, FTIR spectroscopy, and 1H and 13C NMR spectroscopy. X‐ray diffraction studies on single crystals of three compounds confirmed the distorted square‐planar geometry around the palladium(II) center. All complexes are monomeric in nature, and the bis‐NHC ligand chelates in the CNC mode. The effective catalytic potentials of the palladium complexes were demonstrated by their high activities in aqueous‐phase Suzuki–Miyaura and Heck–Mizoroki cross‐coupling reactions of phenylboronic acid and n‐butyl acrylate with a range of functionalized bromobenzene derivatives. The former coupling reaction afforded biphenyls in yields of 71–99 %, whereas the latter reaction evidenced low yields of the n‐butyl cinnamates. Further, all the palladium complexes were studied for their potential in a catalytic hydrosilylation reaction.

N‐methyliminodiacetic acid as a simple and highly efficient ligand for palladium‐catalyzed Suzuki–Miyaura cross‐coupling of aryl chlorides

A simple, air‐stable, inexpensive and easily prepared molecule, N‐methyliminodiacetic acid (MIDA), is reported as a ligand for palladium‐catalyzed Suzuki–Miyaura cross‐coupling reaction of phenylboronic acid with aryl chlorides. The yield of the corresponding Suzuki coupling reaction is up to around 90% at both high temperature of 80°C and room temperature under ambient atmosphere. Copyright © 2015 John Wiley & Sons, Ltd.