Magnetically Separable Pd Catalyst for Carbonylative Sonogashira Coupling Reactions for the Synthesis of α,β-Alkynyl Ketones

Catalytic system having an organotellurium ligand on graphene oxide: immobilization of Pd(0) nanoparticles and application in heterogeneous catalysis of cross-coupling reactions

First heterogeneous catalytic system, having a covalently linked hybrid bidentate organotellurium ligand [i.e., PhTe-CH2-CH2-NH2] on the surface of graphene oxide, has been synthesized with immobilized and stabilized Pd(0) nanoparticles. To the best of our knowledge, it is the first such catalytic system in which a heterogenized organotellurium ligand has been used. It has been well-characterized using different physicochemical characterization techniques viz. P-XRD, XPS, HR-TEM, EELS, FE-SEM, EDX, TGA, BET surface area analysis, FT-IR spectroscopy, and Raman spectroscopy. The Pd content of the final system has been quantified using ICP-OES. Its applications have been explored in Suzuki-Miyaura C-C cross coupling and C-O cross coupling reactions. Hot filtration experiments corroborate the heterogeneous nature of the catalysis. It is recyclable for up to five reaction cycles in Suzuki-Miyaura and C-O cross coupling with marginal loss in performance. It also catalyzes the reactions of chloroarenes such as chlorobenzene, 4-chloroaniline, 1-chloro-4-nitrobenzene, 4-chloroacetophenone, 4-chlorobenzophenone for Suzuki coupling, and 1-chloro-4-nitrobenzene, 4-chlorobenzonitrile, chlorobenzene, and 4-chlorotoluene for C-O coupling. P-XRD, FE-SEM, and EDX study reveals that the catalytic system retains its structural originality and functionality after recycling.

Magnetically separable Pd-iron-oxides composites as highly efficient and recyclable catalysts for ultra-rapid degradation and debromination of polybrominated diphenyl ethers

When precious nano-metals are used as environmental catalysts, it is important to tune the particle sizes and the reusability of the nano-metals for achieving their highly efficient catalytic performance at a low cost. In the present work, magnetic iron oxides (FeOx-Y) nanoparticles were pre-prepared as supports of nano-metals, where Y represented the mole percentage of Fe(III) in the total iron (Y ≥ 50 %). FeOx-Y (support), PdCl42- (Pd source) and NaBH4 (reducing agent) were added into the organic pollutant solution containing 2,2',4,4'-tetrabromodiphenyl ether (BDE47). After the NaBH4 was added, the followed reaction realized not only the rapid in-situ preparation of a Pd-loaded FeOx-Y composite catalyst (Pd-FeOx-Y), but also the ultra-fast and complete debromination of BDE47 within 30 s. Comparing the case without adding FeOx-Y, the debromination efficiency of BDE47 was much promoted in the presence of FeOx-Y. The support-induced enhancing effect on the catalytic ability of Pd nanoparticles was improved by increasing the Fe(III) content in the support, being attributed to the much more hydroxyl groups on the support surface. Considering both the catalytic and recovery abilities of Pd-FeOx-Y, Pd-FeOx-75 was the optimal choice because it could be magnetically recovered and re-used for multiple cycles with high catalytic activities. The presently developed "catalyst preparation-pollutant degradation" one-pot system could be applied to conduct complete debromination of all the PBDEs.

Recent advances in the application of alkynes in multicomponent reactions

Alkynes have two active positions to carry out chemical reactions: C[triple bond, length as m-dash]C and C-H. These two positions are involved and activated in different reactions using different reagents. In this study, we investigated the reactions of alkynes that are involved in multi-component reactions through the C-C and C-H positions and examined the progress and gaps of each reaction by carefully studying the mechanism of the reactions. Firstly, we investigated and analyzed the reactions involving the C[triple bond, length as m-dash]C position of alkynes, including the reactions between derivatives of alkynes with RN3, sulfur compounds (RSO2R', DMSO, S8, DABCO(SO2)2 and DABSO), barbituric acids, aldehydes and amines, COOH, α-diazoesters or ketones, and isocyanides. Then, we examined and analyzed the important reactions involving the C-H position of alkynes and the progress and gaps in these reactions, including the reaction between alkyne derivatives with amines and aldehydes for the synthesis of propargylamines, the reaction between alkynes with CO2 and the reaction between alkynes with CO.

Recent advances in the application of magnetic nanocatalysts in multicomponent reactions

Recently, the preparation and applications of magnetic nanostructures have attracted increasing attention in nanocatalysis studies, and magnetic nanoparticle (MNP) functionalized catalysts have been applied in important reactions such as Suzuki-Miyaura and Heck couplings. The modified nanocomposites demonstrate significant catalytic efficiency and excellent benefits in the context of catalyst recovery methods. This review discusses the recent modified magnetic nanocomposites in the field of catalytic applications along with the synthetic processes that are usually employed.

Al-Hussain S, E. A. Zaki M, H. Asghar B, A. Muhammad Z. Synthesis of spiropyrazoles under organic and nonorganic catalysis

Abstract:

Spiropyrazoles display many biological biological activities such as antitumor, vasodilation, analgesic, phosphodiesterase inhibitors, aldosterone antagonistic, anabolic, androgenic, anti-inflammatory, progestational and salt-retaining activities and they also exert neuroprotection in dopaminergic cell death. Many efforts have been made to obtain these derivatives with high yield and excellent regio-, diastereo- and enantioselectivities. Most of the spiroprazole synthesis methods were proceeded in good to excellent yield in the presence of organic catalysts as for examples squaramide, NHC pre-catalyst, pyrrole derivatives, bis-oxazoline, DMAP, DABCO, thiourea derivatives, DBU, acetic acid and quinoline catalysts. In addition, the inorganic and organo-metallic catalysts have been proven their efficiency in synthesis of various types of spiro-pyrazoles in excellent yield. Thus, in this review we have compiled all citations for the synthesis of spiropyrazoles in the presence of various types of catalysts such as organic, inorganic, and metalorganic catalysts in the range 2020 to 2012. This review article is a useful compilation for researchers interested in the synthesis of spiropyrazole derivatives and will assist them in selecting appropriate catalysts for preparation of their spiropyrazoles.

Straightforward Stereoselective Synthesis of Seven-Membered Oxa-Bridged Rings through In Situ Generated Cycloheptenol Derivatives

An iodine-mediated stereoselective synthesis of seven-membered oxa-bridged rings via in situ generated cycloheptenols was reported. This process was realized through the combination of C-C σ-bond cleavage and C-O bond-forming reactions in a one-pot fashion from simple and easily accessible raw materials. The formation of carbon radicals initiated by I₂ was the key to the reaction.

Supported Palladium Catalyzed Carbonylative Coupling Reactions using Carbon Monoxide as C1 Source

The carbonylative reactions of aryl halides, boronic acids, amines, activated alkene and alkynes under CO and supported palladium catalyzed conditions are very popular reactions for the synthesis of bioactive molecules, pharmaceuticals, polymers, peptides, intermediates and fine chemicals synthesis. Due to cost effectiveness and easy handling of recyclable supported palladium catalyst, it became more popular among researchers either working in academic institute or industry. In recent years, irrespective of poisoning effect of CO with palladium as major limitation, several advancements have been done through surface selection, designing and condition improvement to achieve high yield in the area of carbonylative coupling reactions. We hope this review will be helpful as a ready reference of last 20 years in the field of CO insertion reactions using diverse range of supported palladium catalysts under carbon monoxide or its sources as C1 source.

Magnetically Isolable Pt0/Co3O4 Nanocatalysts: Outstanding Catalytic Activity and High Reusability in Hydrolytic Dehydrogenation of Ammonia Borane

The development of a new platinum nanocatalyst to maximize the catalytic efficiency of the precious noble metal catalyst in releasing hydrogen from ammonia borane (AB) is reported. Platinum(0) nanoparticles are impregnated on a reducible cobalt(II,III) oxide surface, forming magnetically isolable Pt⁰/Co₃O₄ nanocatalysts, which have (i) superb catalytic activity providing a record turnover frequency (TOF) of 4366 min^-1 for hydrogen evolution from the hydrolysis of AB at room temperature and (ii) excellent reusability, retaining the complete catalytic activity even after the 10th run of hydrolysis reaction. The outstanding activity and stability of the catalyst can be ascribed to the strong interaction between the platinum(0) nanoparticles and reducible cobalt oxide, which is supported by the results of XPS analysis. Pt⁰/Co₃O₄ exhibits the highest TOF among the reported platinum-nanocatalysts developed for hydrogen generation from the hydrolysis of AB.

Cobalt ferrite supported platinum nanoparticles: Superb catalytic activity and outstanding reusability in hydrogen generation from the hydrolysis of ammonia borane

In this work, platinum(0) nanoparticles are deposited on the surface of magnetic cobalt ferrite forming magnetically separable Pt⁰/CoFe₂O₄ nanoparticles, which are efficient catalysts in H₂ generation from the hydrolysis of ammonia borane. Catalytic activity of Pt⁰/CoFe₂O₄ nanoparticles decreases with the increasing platinum loading, parallel to the average particle size. Pt⁰/CoFe₂O₄ (0.23% wt. Pt) nanoparticles have an average diameter of 2.30 ± 0.47 nm and show an extraordinary turnover frequency of 3628 min^-1 in releasing 3.0 equivalent H₂ per mole of ammonia borane from the hydrolysis at 25.0 °C. Moreover, the magnetically separable Pt⁰/CoFe₂O₄ nanoparticles possess high reusability retaining 100% of their initial catalytic activity even after ten runs of hydrolysis. The superb catalytic activity and outstanding reusability make the Pt⁰/CoFe₂O₄ nanoparticles very attractive catalysts for the hydrogen generation systems in portable and stationary fuel cell applications.

Oxidative Condensation of Furfural with Ethanol Using Pd-Based Catalysts: Influence of the Support

PdO nanoparticles were deposited on several supports (β-zeolite, Al2O3, Fe2O3, MgO, and SiO2), which displayed different crystallinity, textural properties, and amount of acid and basic sites. These catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption–desorption isotherms at −196 °C, NH3 and CO2 thermoprogrammed desorption analyses (NH3- and CO2-TPD, and X-ray photoelectron spectroscopy (XPS). Pd-based catalysts were tested in the oxidative condensation of furfural with ethanol to obtain value-added chemicals. The catalytic results revealed high conversion values, although the presence of a high proportion of carbonaceous deposits, mainly in the case of the PdO supported on β-zeolite and Al2O3, is also noteworthy. The presence of basic sites led to a beneficial effect on the catalytic behavior, since the formation of carbonaceous deposits was minimized. Thus, the 2Pd-MgO (2 wt.% Pd) catalyst reached the highest yield of furan-2-acrolein (70%) after 3 h of reaction at 170 °C. This better catalytic performance can be explained by the high basicity of MgO, used as support, together with the large amount of available PdO, as inferred from XPS.

Palladium(II) on 4 Å Molecular Sieves: A Simple and Reusable Catalyst for the Preparation of Ynones

Abstract

Pd2+ on 4 Å molecular sieves support has been prepared and investigated. The catalyst has successfully been used in the reaction of acyl chlorides and terminal alkynes yielding ynones. The catalyst can be reused without significant loss of activity.

Graphic Abstract

The highly efficient and selective dicarbonylation of acetylene catalysed by palladium nanosheets supported on activated carbon

An ultrathin Pd nanosheet-supported heterogeneous catalyst, Pd_CO/AC, with exposed (111) crystal plane was synthesized, and it shows superior catalytic reactivity (∼43.8%) and selectivity (∼99.0%) for the dicarbonylation of acetylene and CO.

Catalysis with magnetically retrievable and recyclable nanoparticles layered with Pd(0) for C–C/C–O coupling in water

Nanoparticles layered with palladium(0) were prepared from nano-sized magnetic Fe₃O₄ by coating it with silica and then reacting sequentially with phenylselenyl chloride under an N₂ atmosphere and palladium(ii) chloride in water. The resulting Fe₃O₄@SiO₂@SePh@Pd(0) NPs are magnetically retrievable and the first example of NPs in which the outermost layer of Pd(0) is mainly held by selenium. The weight percentage of Pd in the NPs was found to be 1.96 by ICP-AES. The NPs were authenticated via TEM, SEM-EDX, XPS, and powder XRD and found to be efficient as catalysts for the C–O and C–C (Suzuki–Miyaura) coupling reactions of ArBr/Cl in water. The oxidation state of Pd in the NPs having size distribution from ∼12 to 18 nm was inferred as zero by XPS. They can be recycled more than seven times. The main features of the proposed protocols are their mild reaction conditions, simplicity, and efficiency as the catalyst can be separated easily from the reaction mixture by an external magnet and reused for a new reaction cycle. The optimum loading (in mol% of Pd) was found to be 0.1–1.0 and 0.01–1.0 for O-arylation and Suzuki–Miyaura coupling, respectively. For ArCl, the required amount of NPs was more as compared to that needed for ArBr. The nature of catalysis is largely heterogeneous.

Fe₃O₄@SiO₂@SePh@Pd(0) (Pd, 1.96%) as the first example of NPs having a Pd(0) layer held by selenium can execute C–C/C–O coupling in 2–6 h (80 °C).

Aminophosphine Palladium Pincer-Catalyzed Carbonylative Sonogashira and Suzuki-Miyaura Cross-Coupling with High Catalytic Turnovers

This work documents the first palladium pincer complex-catalyzed carbonylative Sonogashira (CS) and carbonylative Suzuki-Miyaura (CSM) cross-coupling. Compared to previous protocols, which employ hazardous and toxic solvents, the aminophosphine pincer complex {[C₆H₃-2,6-(NHP{piperidinyl}₂)₂]Pd(Cl)} (III) catalyzes both the cross-coupling reactions in propylene carbonate, an eco-friendly and sustainable polar aprotic solvent. Advantageously, employing III allows the CS cross-coupling to be carried out at a palladium loading of 10^-4 mol % and the CSM cross-coupling to be carried out at 10^-6 mol %, thus resulting in catalytic turnovers of 10⁵ and 10⁷, respectively. Relative comparison of the pincer complex with conventional palladium precursors Pd(OAc)₂ and PdCl₂(PPh₃)₂ shows the efficiency and robustness of the pincer complex in effecting higher catalytic activity at low palladium loadings.

Superparamagnetic nanoparticle-catalyzed coupling of 2-amino pyridines/pyrimidines with trans-chalcones

An aerobic coupling of 2-aminopyrimidines or 2-aminopyridines with trans-chalcones to afford aroylimidazo[1,2-a]pyrimidines and aroylimidazo[1,2-a]pyridines is reported. Reactions proceed in the presence of CuFe₂O₄ superparamagnetic nanoparticle catalyst, two equivalents of iodine, oxygen oxidant, and 1,4-dioxane solvent. The catalyst is superior to many common copper or iron complexes. Copper ferrite could be easily separated by magnetic decantation and reused up to 5 times without a major loss of activity. The method described here marks a rare example of using a simple, heterogeneous catalyst for synthesis of fused heterocycles. To our best knowledge, aroylimidazo[1,2-a]pyrimidines and aroylimidazo[1,2-a]pyridines were not previously synthesized using this protocol.

An aerobic coupling of 2-aminopyrimidines or 2-aminopyridines with trans-chalcones to afford aroylimidazo[1,2-a]pyrimidines and aroylimidazo[1,2-a]pyridines is reported.

Reusable Catalyst for Transfer Hydrogenation of Aldehydes and Ketones Designed by Anchoring Palladium as Nanoparticles on Graphene Oxide Functionalized with Selenated Amine

The treatment of graphene oxide with ClCH₂COOH, thionyl chloride, and 2-(phenylselenyl)ethylamine successively has resulted in functionalization of its surface with selenated ethylamine molecules which may act as chelating (Se, N) ligands. The graphene oxide grafted with (Se, N) donor sites (GO-Se) on treatment with Na₂PdCl₄ and NaOH gave GO-Se anchored with Pd(0) nanoparticles (NPs) (GO-Se-Pd). The X-ray diffraction (powder), FT-IR, XPS, Raman spectroscopy, thermogravimetric analysis (TGA), and electron microscopic techniques (SEM and HR-TEM) authenticated the formation of GO-Se-Pd. The distribution of Pd(0) NPs of size ∼1-3 nm on GO-Se was found nearly uniform. The transfer hydrogenation of carbonyl compounds (aldehydes/ketones) with 2-propanol was catalyzed with GO-Se-Pd. The catalyst equivalent to 0.25 mol % of Pd was sufficient to convert aldehydes and ketones to alcohols in good yield (nearly quantitative for some substrates) and found somewhat more efficient for aldehydes than ketones. The reusability of GO-Se-Pd studied for transfer hydrogenation of 4-anisaldehyde to the corresponding alcohol can be understood by ∼96% conversion even in the sixth catalytic run. Flame AAS analysis of GO-Se-Pd revealed negligible leaching of Pd even after the sixth catalytic reaction cycle. Hot filtration experiments suggested the heterogeneous nature of the catalyst.

Palladium-catalyzed carbonylative Sonogashira coupling of aryl diazonium salts with formic acid as the CO source: the effect of 1,3-butadiene

An efficient carbonylative cross-coupling of aryl diazonium salts with terminal alkynes using formic acid as the CO source has been developed. And 1,3-butadiene was found to play a crucial role in this transformation.