Size-Selective Homocoupling of Arylboronic Acids Mediated by a Copper-Based Metal–Organic-Framework

Copper-based metal–organic-frameworks with open metal sites have received increasing research interest as heterogeneous catalysts for various organic transformations. A copper-based metal organic framework (1) built with L-NO₂ ligand (L-NO₂?=?4,4′-dicarboxy-4″-nitrotriphenylamine) was selected for catalyzing aerobic homocoupling of arylboronic acid toward biaryl products given its structural robustness and 1-D channels lined with rich open metal sites. The experimental results show that MOF (1) exhibits pronounced size selectivity over arylboronic acid molecules, which is only effective for short arylboronic acid molecules (e.g. phenylboronic acid, p-methylphenylboronic acid and p-fluorophenylboronic acid), giving the corresponding biaryl products in good yields. Moreover, MOF (1) also demonstrates a good recyclability which only shows a small decay in the catalytic performance after five repeated runs.

     

Palladium(II)‐Catalyzed 1,4‐Addition of Arylboronic Acids to β‐Arylenones for Enantioselective Synthesis of 4‐Aryl‐4H‐chromenes

The enantioselective 1,4‐addition of arylboronic acids to β‐arylenones to give β‐diaryl ketones was carried out at 0–25 °C in the presence of a dicationic palladium(II) catalyst, [Pd(S,S‐chiraphos)(PhCN)₂](SbF₆)₂. Addition of a silver salt such as silver tetrafluoroborate [AgBF₄] or silver hexafluoroantimonate [AgSbF₆] (5–10 mol %) was effective to achieve high enantioselectivities at low temperatures (92–99 % ee) and to reduce the catalyst loading to 0.05 mol %. The protocol provided a simple access to 4‐aryl‐4H‐chromenes. Optically active chromenes were synthesized with up to 99 % ee via dehydration of the 1,4‐adducts between arylboronic acids and β‐(2‐hydroxyaryl)‐α,β‐unsaturated ketones.     

Highly regioselective palladium-catalyzed direct cross-coupling of imidazo[1,2-a]pyridines with arylboronic acids

A highly regioselective method for the palladium-catalyzed direct cross-coupling of imidazo[1,2-a]pyridines with arylboronic acids has been developed by using O₂ as oxidant. This process can be applied to a wide range of imidazo[1,2-a]pyridines and arylboronic acids with excellent C-3-regioselectivity. It provides a new way for developing CC bond-forming processes of multisubstituted imidazo[1,2-a]pyridines, which are common structural motifs in natural products and pharmaceuticals.     

Aerobic Ligand‐Free Suzuki Coupling Reaction of Aryl Chlorides Catalyzed by In Situ Generated Palladium Nanoparticles at Room Temperature

An aerobic, ligand‐free Suzuki coupling reaction catalyzed by in situ generated palladium nanoparticles in polyethylene glycol with an average molecular weight of 400 Da (PEG‐400) at room temperature has been developed. This catalytic system is a very simple and highly active protocol for the Suzuki coupling of aryl chlorides with arylboronic acids, which proceed smoothly in excellent yields in short times using low catalyst loadings. Control experiments demonstrated that the Suzuki reaction catalyzed by the in situ generated palladium nanoparticles can be carried out much quicker than that using the preprepared particles under the same conditions. The formation of palladium nanoparticles in PEG‐400 was promoted by arylboronic acids.     

Rhodium Containing Magnetic Nanoparticles: Effective Catalysts for Hydrogenation and the 1,4-Addition of Boronic Acids

New efficient rhodium catalysts supported on superparamagnetic iron oxide nanoparticles (NPs) have been prepared using a novel method involving sulfonated triphenylphosphine ligands. They successfully promote the hydrogenation of olefins as well as the addition of arylboronic acids to dimethyl itaconate (ItMe₂) in water for up to 10 recycles. The catalysts were stable towards leaching of the metal complexes and were readily recovered by applying an external magnetic field.     

Ligandless palladium supported on SiO2–TiO2 as effective catalyst for Suzuki reaction

TiO₂–SiO₂ mixed oxides were prepared by the homogeneous precipitation method, and the supports were characterized by XRD, IR and BET. Ligandless palladium supported on SiO₂–TiO₂ was prepared by the deposition–precipitation method and used as recoverable catalyst for Suzuki reactions. The results revealed that the supported catalyst Pd/SiO₂–TiO₂ exhibited excellent catalytic activity for the coupling of aryl bromides with arylboronic acid, and also exhibited moderate catalytic activity for the coupling of aryl chlorides. The catalyst was recycled by simple filtration and reused without further disposal, no significant Pd leaching and loss of catalytic activity was observed except the first reuse.     

Suzuki–Miyaura Reactions of Aryl Chloride Derivatives with Arylboronic Acids using Mesoporous Silica‐Supported Aryldicyclohexylphosphine

The Suzuki–Miyaura reactions using mesoporous‐supported aryldicyclohexylphosphine as ligand have been investigated. The catalysts were based on SBA‐15 type mesoporous silica which was transformed in a four‐step synthesis leading to a phosphine‐containing hybrid material The most productive catalytic system studied was generated in situ from this material and the homogeneous palladium complex, Pd(OAc)₂. Other catalytic systems were studied for comparison [homogeneous cataysts, a “preformed” catalyst obtained by reaction of PdCl₂(PhCN)₂ and the phosphine‐containing material]. Variations involving the solvent system, the substrate aryl chloride and the arylboronic acid reactant were also studied. For both in situ and preformed catalyst systems, high conversions and yields are obtained for activated aryl chlorides. Success of the reaction for unactivated aryl chlorides was limited to the catalyst formed in situ. The catalyst formed in situ was also shown to be reactive under aqueous reaction conditions in the cross‐coupling of 1‐(4‐chlorophenyl)ethanone with phenylboronic acid.     

A Reusable Polymer-Anchored Palladium(II) Schiff Base Complex Catalyst for the Suzuki Cross-Coupling,Heck and Cyanation Reactions

A new polymer-anchored Pd(II) complex has been synthesized, characterized and its catalytic activity was investigated for the Suzuki cross-coupling reaction between aryl halides and arylboronic acid in the presence of K₂CO₃ as a base, for Heck olefination of aryl halides with alkenes, and for cyanation reaction of aryl iodides with K₄Fe(CN)₆ in presence of Et₃N as base. The key features of the catalyst include rapid reactions with excellent conversion without the use of phosphine ligands and total stability under the reactions conditions. The catalyst was recovered by simple filtration and reused five-times without significant loss of catalytic activity.     

Palladium‐Catalyzed Heck‐Type Reactions of Allylic Esters with Arylboronic Acids or Potassium Aryltrifluoroborates

A selective and general route to (E)‐1,3‐diaryl‐prop‐1‐enes and (E)‐3‐arylallyl acetates has been developed by palladium‐catalyzed Heck‐type reactions of allylic esters with arylboronic acids or potassium aryltrifluoroborates. The present method selectively proceeds including β‐OAc elimination or β‐H elimination on the basis of the boronic acids. Whereas a variety of allylic esters were reacted with arylboronic acids, palladium(II) acetate [Pd(OAc)₂], tetra(n‐butyl)ammonium chloride [(n‐Bu)₄NCl] and postassium dihydrogen phosphate (KH₂PO₄) to afford the corresponding diarylation products in moderate to good yields, treatment of allylic esters with potassium aryltrifluoroborates furnished the corresponding monoarylation products.     

Accurate determination of temperature dependent full matrix parameters of piezoelectric materials using only one sample

It is of great importance to accurately determine the full matrix parameters of the piezoelectric materials using as few samples as possible. Here we performed a simple and widely applicable method to accurately determine the full matrix parameters of [001]_C-poled K(Ta,Nb)O₃ single crystal. Only one sample was used throughout the experiment procedure, which eliminated inconsistency from multi-sample testing. We also improved the accuracy of results by inversing the impedance spectra of two inequivalent crystallographic directions, [001]_C and [010]_C. Based on this technique, variation of full matrix parameters with temperature were obtained using one sample. This work is of great significance for the characterization of novel piezoelectric materials and the evaluation of the performance of piezoelectric devices at various temperature.     

Palladium‐Catalyzed Hydroxymethylation of Aryl‐ and Heteroarylboronic Acids using Aqueous Formaldehyde

Cyclometallated NHC palladium complexes prepared from palladium(II) acetate [Pd(OAc)₂] and unsymmetrical 1,3‐diarylimidazolinium salts catalyzed the hydroxymethylation of (hetero)arylboronic acids using an excess amount of formalin to afford (hetero)arylmethanols in good to satisfactory yields.

     

A self-assembled supramolecular solid for catalytic application

A 1,8-naphthalenecarboxylic anhydride-4,5-dicarboxylate (L) bridged copper(II) dimeric molecular module [Cu₂L₂(DMF)₂(H₂O)₂] (1) can self-organize into a solid-state supramolecular architecture. The combination of the multitopic contact sites of hydrogen bonds coupled with two bulky aromatic cores promoted the molecule to self-link into a solid-state supramolecular architecture, which was almost insoluble in water and common organic solvents. Solid 1 can heterogeneously catalyze the cross-coupling of arylboronic acids with imidazole in the absence of a base or additive to generate the corresponding coupling products in excellent yields in methanol at 50 °C, which can be recovered and recycled by a simple filtration and was used for six consecutive cycles with consistent activity.     

Highly Efficient and Reusable Polyaniline‐Supported Palladium Catalysts for Open‐Air Oxidative Heck Reactions under Base‐ and Ligand‐Free Conditions

Oxidative Heck reactions of arylboronic acids and alkenes are carried out in the presence of polyaniline‐supported palladium catalysts using air as a co‐oxidant to afford the Heck products with excellent yields and selectivities under base‐ and ligand‐free conditions. The catalyst was recovered by simple filtration and used for several cycles with consistent activity.     

Generation of Arylated Quinones by Iron‐Catalyzed Oxidative Arylation of Phenols: Formal Synthesis of Phellodonin,Sarcodonin ε, Leucomelone and Betulinan A

Biologically and pharmaceutically relevant arylated quinones (Quin‐Ar) have been synthesized via direct C H arylation of a variety of phenols using arylboronic acids. An inexpensive, environmentally friendly iron catalyst, ferric sulphate, Fe₂(SO₄)₃, was employed in this operationally simple and efficient method.

     

Functionalized cellulose‐supported triphenylphosphine and its application in Suzuki cross‐coupling reactions

A new heterogeneous cellulose tagged triphenylphosphine (Cell‐OPPh₃) was synthesized and subsequently coordinated with Pd(OAc)₂ to form a cellulose‐supported triphenylphosphine palladium complex (Cell‐OPPh₃‐Pd). Cell‐OPPh₃ and the corresponding palladium complex were fully characterized by TGA, SEM, TEM, and NMR analysis. Results of catalytic activity experiments indicate that the Cell‐OPPh₃‐Pd complex can efficiently catalyze Suzuki–Miyaura cross‐coupling reactions of aryl halides with arylboronic acids at mild reaction conditions. The coupling products can be obtained in good to excellent yields (up to 98%). The work‐up procedure is simple and the catalyst could be easily recovered by filtration, and then reused in next run. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41427.     

High-throughput enzyme kinetics using microarrays

We report a microanalytical method to study enzyme kinetics. The technique involves immobilizing horseradish peroxidase on a poly-L-lysine (PLL)-coated glass slide in a microarray format, followed by applying substrate solution onto the enzyme microarray. Enzyme molecules are immobilized on the PLL-coated glass slide through electrostatic interactions, and no further modification of the enzyme or glass slide is needed. In situ detection of the products generated on the enzyme spots is made possible by monitoring the light intensity of each spot using a scientific-grade charged-coupled device (CCD). Reactions of substrate solutions of various types and concentrations can be carried out sequentially on one enzyme microarray. To account for the loss of enzyme from washing in between runs, a standard substrate solution is used for calibration. Substantially reduced amounts of substrate solution are consumed for each reaction on each enzyme spot. The Michaelis constant K_m obtained by using this method is comparable to the result for homogeneous solutions. Absorbance detection allows universal monitoring, and no chemical modification of the substrate is needed. High-throughput studies of native enzyme kinetics for multiple enzymes are therefore possible in a simple, rapid, and low-cost manner.     

Synthesis of Benzimidazole‐Substituted Arylboronic Acids via Aerobic Oxidation of 1,2‐Arylenediamines and Formyl‐Substituted Aryl MIDA Boronates using Potassium Iodide as a Catalyst

A highly efficient protocol for the synthesis of benzimidazole‐substituted arylboronic acids was developed via aerobic oxidative cyclization of 1,2‐aryldiamines and formyl‐substituted aryl MIDA (N‐methyliminodiacetic acid) boronates using potassium iodide as a nucleophilic catalyst. Furthermore, a one‐pot protocol for the synthesis of benzimidazole‐substituted arylboronic acids from 1,2‐phenylenediamines and formyl‐substituted arylboronic acids was developed without the isolation of any intermediates. The resulting boronic acids were further subjected to Suzuki–Miyaura coupling reactions without isolation, leading to diaryl‐substituted benzimidazoles with only one separation step.

     

Green synthesis of Ag/ZnO nanohybrid using sodium alginate gelation method

Mesoporous Ag/ZnO nanohybrid material has been successfully synthesized using simple and green route via sodium alginate media. The as-synthetized nanomaterial was structurally characterized using various techniques such as X-ray powder diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA) and N₂ adsorption-desorption measurements (BET). The Ag/ZnO nanoparticles were quasi-spherical, crystalline with a size ranging from 40 to 50 nm. In addition, characterization results confirmed that calcined Ag/ZnO nanomaterial sample was stable and mainly consisting of both hexagonal ZnO and cubic silver nanoparticles.     

High-turnover aminopyridine-based Pd-catalysts for Suzuki–Miyaura reaction in aqueous media

A high-turnover catalytic system based on commercially available aminopyridines (L) and PdCl₂ has been developed for Suzuki–Miyaura reaction in aqueous media. Reactions of arylboronic acids with a wide range of aryl iodides, bromides and chlorides proceeded in the presence of these catalysts for a short time in aqueous media to afford the cross-coupling products in high yields. Furthermore, this protocol allows tolerating a wide range of functional groups.     

A simple and effective copper catalyst for the conversion of arylboronic acids to aryl iodides at room temperature

Simple Cu(NO₃)₂·3H₂O was demonstrated to be of ability to catalyze the conversion of arylboronic acids to aryl iodides at room temperature. Compared with the previous copper-catalyzed method, the present procedure avoids the use of the ligand, the oxidant as well as the heating condition.