Highly Efficient and Magnetically Recoverable Niobium Nanocatalyst for the Multicomponent Biginelli Reaction

Synthesis of novel benzopyrimido[4,5-d]azoninone analogs catalyzed by biosynthesized Ag-TiO2 core/shell magnetic nanocatalyst and assessment of their antioxidant activity

The present work reported the synthesis of novel benzopyrimido[4,5-d]azoninone analogs using a biosynthesized Ag-TiO2 core/shell magnetic nanocatalyst. Accordingly, three-component one-pot reactions of benzoazonine-dione with thiourea and aryl aldehyde derivatives under nanocatalytic and optimized conditions afforded reasonable to brilliant yields of the target products (57-91%). The nanocatalyst was synthesized by a facile method using turmeric ethanol extract as a reducing and chelating agent. The synthesized nanocatalyst was verified by FT-IR, XRD, zeta potential, EDX, SEM, and TEM. The nanocatalyst presented remarkable catalytic activity for the synthesis of the target products. The procedure provided biosynthesis of the nanocatalyst, accessible reagents, high yields and rates of the reactions, nanocatalyst recyclability, and ease of product isolation and purification. The novel products were characterized by FT-IR, 1H-NMR, 13C-NMR, mass spectra, and 2D NMR analysis (COSY, NOESY, HMQC & HSQC) spectral analyses. The antioxidant activity was assessed by DPPH and phosphomolybdate assays, in which the compounds exhibited excellent potency. Overall, this approach could be used to develop new and sustainable methods for the synthesis of antioxidants and other biologically active molecules.

Experimental and computational insights into the mechanism of the copper(i)-catalysed sulfonylative Suzuki-Miyaura reaction

A mechanistic study into the copper(i)-catalysed sulfonylative Suzuki-Miyaura reaction, incorporating sulfur dioxide, is described. Utilising spectroscopic and computational techniques, an exploration into the individual components of the competing catalytic cycles is delineated, including identification of the resting state catalyst, transmetalation of arylboronic acid onto copper(i), the sulfur dioxide insertion process, and the oxidative addition of aryl halide to Cu^I. Studies also investigated prominent side-reactions which were uncovered, including a competing copper(ii)-catalysed mechanism. This led to an additional proposed and connected Cu^I/Cu^II/Cu^III catalytic cycle to account for by-product formation.

Pyrazole-based lamellarin O analogues: synthesis, biological evaluation and structure-activity relationships

A library of pyrazole-based lamellarin O analogues was synthesized from easily accessible 3(5)-aryl-1H-pyrazole-5(3)-carboxylates which were subsequently modified by bromination, N-alkylation and Pd-catalysed Suzuki cross-coupling reactions. Synthesized ethyl and methyl 3,4-diaryl-1-(2-aryl-2-oxoethyl)-1H-pyrazole-5-carboxylates were evaluated for their physicochemical property profiles and in vitro cytotoxicity against three human colorectal cancer cell lines HCT116, HT29, and SW480. The most active compounds inhibited cell proliferation in a low micromolar range. Selected ethyl 3,4-diaryl-1-(2-aryl-2-oxoethyl)-1H-pyrazole-5-carboxylates were further investigated for their mode of action. Results of combined viability staining via Calcein AM/Hoechst/PI and fluorescence-activated cell sorting data indicated that cell death was triggered in a non-necrotic manner mediated by mainly G2/M-phase arrest.

Palladium nanoparticles-confined pore-engineered urethane-linked thiol-functionalized covalent organic frameworks: a high-performance catalyst for the Suzuki Miyaura cross-coupling reaction

Covalent organic frameworks (COFs) are potential templates for the synthesis of nanomaterials owing to the versatility of their structure. Most of the reported COFs comprise imine linkages. Herein, we report for the first time the synthesis of a urethane-linked COF (UCOF) using monoformylphloroglucinol and 1,4-phenylene diisocyanate as monomers. Furthermore, the UCOF was functionalized with cysteamine to introduce free dangling thiol groups into the cavity. The latter played a critical role in fixing the active metal efficiently and facilitating the confined growth of small metal nanoparticles (∼4-6 nm) with a high surface area leading to a pore-engineered heterogeneous Pd catalyst (PdNPs@UCOF-SH). The COF and Pd catalyst were characterized using various analytical techniques such as CP-MAS NMR, FTIR, PXRD, BET, FEG-SEM, HRTEM, XPS, TGA, and ICP-AES. The as-prepared UCOF-SH-supported Pd nanoparticles showed excellent catalytic activity in the Suzuki Miyaura cross-coupling reaction under mild conditions with low catalyst loading and eco-friendly solvents. The scope was extended to various aryl boronic acids and aryl halides (I, Br, and Cl). The halo-substituted and non-halo biaryl derivatives were obtained in good to excellent yields, within a shorter reaction time, avoiding the homocoupling of aryl boronic acid. The pore-engineered COF-derived catalyst is selective and easily recycled up to 10 runs without significant loss of catalytic activity. This reveals the robust nature of the PdNPs@UCOF-SH catalyst and the sustainability of the process which opens a new frontier for several catalytic applications.

Real-time visualization of the Suzuki reaction using surface enhanced Raman spectroscopy and a moveable magnetic nanoparticle film

Utilizing a moveable Fe₃O₄@Au film, an operando SERS strategy was developed successfully for visualizing Suzuki reaction processes. The feasibility and generality were verified by using the reaction of 3-bromopyridine and phenylboronic acid as a probe.

Towards depeptidized aminoboronic acid derivatives through the use of borylated iminium ions

Herein, we use α-boryl iminium intermediates to access progressively depeptidized branched β-aminoboronic acids that are functionalized with biologically relevant heterocycles. We investigate the interaction of these novel compounds with carbohydrates under physiological conditions and demonstrate their potential as synthetic building blocks.

Catalytic Approaches to Multicomponent Reactions: A Critical Review and Perspectives on the Roles of Catalysis

In this review, we comprehensively describe catalyzed multicomponent reactions (MCRs) and the multiple roles of catalysis combined with key parameters to perform these transformations. Besides improving yields and shortening reaction times, catalysis is vital to achieving greener protocols and to furthering the MCR field of research. Considering that MCRs typically have two or more possible reaction pathways to explain the transformation, catalysis is essential for selecting a reaction route and avoiding byproduct formation. Key parameters, such as temperature, catalyst amounts and reagent quantities, were analyzed. Solvent effects, which are likely the most neglected topic in MCRs, as well as their combined roles with catalysis, are critically discussed. Stereocontrolled MCRs, rarely observed without the presence of a catalytic system, are also presented and discussed in this review. Perspectives on the use of catalytic systems for improved and greener MCRs are finally presented.

Transmetalation of boronic acids and their derivatives: mechanistic elucidation and relevance to catalysis

The Suzuki-Miyaura reaction (the cross-coupling reaction of boronic acids with organic halides catalysed by Pd complexes) has been recognised as a useful synthetic organic reaction that forms a C(sp²)-C(sp²) bond. The catalytic cycle of the reaction involves the transmetalation of aryl- and alkenylboronic acids with Pd(II) complexes. It migrates the aryl and alkenyl groups of boronic acid to Pd and produces a Pd-C bond. Many studies have investigated the mechanism of transmetalation. They elucidated the mechanism of the organometallic reaction and its role as a fundamental step in catalytic reactions. This perspective reviews studies on the transmetalation of aryl- and alkenylboronic acids with Pd(II) complexes. Emphasis was laid on the structures and chemical properties of the intermediate Pd complexes and the effects of OH^- on the pathways of the catalytic Suzuki-Miyaura reaction. The reactions of arylboronic acids with Rh(I)-OH complexes were investigated, which are relevant to the mechanism of Rh-catalysed addition of aryl boronic acids to enones and aldehydes. Recent studies on the transmetalation of boronic acids with other late transition metals such as Fe(II), Co(I), Pt(II), Au(III), and Au(I) are presented with the related catalytic reactions and their utilisation in the synthesis of aromatic molecules and π-conjugated materials.

Synthesis of dihydropyrimidinones via multicomponent reaction route over acid functionalized Metal-Organic framework catalysts

Multi component reactions over heterogeneous solid acid catalysts are extremely important owing to easy separation, amenable recycling, and prospective scaling up of the process. Here, we are reporting the synthesis of biologically important dihydropyrimidinones over postsynthetic modified Cr-based metal-organic framework materials as heterogeneous catalysts containing the bifunctional Lewis and Brønsted acid sites. Cr-based metal-organic frameworks contained coordinatively unsaturated metal sites as inherent Lewis acid sites, whereas postsynthetic modifications introduced the Brønsted acid sites in the framework. A direct one pot synthesis route was employed to produce the pristine MOF in pure aqueous medium without using any additives. The bulk structure, morphology, surface and bonding properties of the synthesized materials were thoroughly characterized with powder XRD, FTIR, XPS, FE-SEM, TGA, and N₂ sorption isotherms. A qualitative evolution of acid strength was carried out over the functionalized MOFs. Among the post synthetic functionalized materials, carboxylic acid functionalized framework exhibited a very high yield of dihydropyrimidinones under solvent less moderate reaction conditions. The catalyst also demonstrated a robust recyclability and wide substrate scope. Comparative study showed a very high catalytic activity of the postsynthetic modified MOFs in comparison to the reported literature. The reaction condition was optimized by varying parameters like solvent, temperature, reaction duration and catalyst loadings. The mechanistic studies indicated the involvement of both the Lewis and Brønsted sites acid sites of the catalysts in the multicomponent reaction.

Phosphotungstic acid impregnated niobium coated superparamagnetic iron oxide nanoparticles as recyclable catalyst for selective isomerization of terpenes

Conversion efficiency as high as 80-100% and 50% selectivity for camphene and limonene was achieved with low production of polymeric byproducts (18-28%), easy recovery with a magnet and reuse for up to five cycles maintaining similar activity and distribution of products, using a new magnetically recyclable catalyst based on niobium oxide coated on superparamagnetic iron oxide nanoparticles (SPION) impregnated with phosphotungstic acid (HPW). The catalyst was demonstrated to be effective in the selective conversion of alpha and beta-pinenes into valuable terpenes, under ultrasonic probe activation and with toluene as solvent. A unique synergic effect between the components generating more active and selective catalytic sites was demonstrated, indicating that the SPION covered with 30 wt% of Nb2O5 gives the best performance when impregnated with HPW as co-catalyst. The materials were fully characterized by XRD, EDX, XPS, TEM, BET, VSM and FTIR.

C(acyl)–C(sp2) and C(sp2)–C(sp2) Suzuki–Miyaura cross-coupling reactions using nitrile-functionalized NHC palladium complexes

Application of N-heterocyclic carbene (NHC) palladium complexes has been successful for the modulation of C–C coupling reactions. For this purpose, a series of azolium salts (1a–f) including benzothiazolium, benzimidazolium, and imidazolium, bearing a CN-substituted benzyl moiety, and their (NHC)₂PdBr₂ (2a–c) and PEPPSI-type palladium (3b–f) complexes have been systematically prepared to catalyse acylative Suzuki–Miyaura coupling reaction of acyl chlorides with arylboronic acids to form benzophenone derivatives in the presence of potassium carbonate as a base and to catalyse the traditional Suzuki–Miyaura coupling reaction of bromobenzene with arylboronic acids to form biaryls. All the synthesized compounds were fully characterized by Fourier Transform Infrared (FTIR), and ¹H and ¹³C NMR spectroscopies. X-ray diffraction studies on single crystals of 3c, 3e and 3f prove the square planar geometry. Scanning Electron Microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), metal mapping analyses and thermal gravimetric analysis (TGA) were performed to get further insights into the mechanism of the Suzuki–Miyaura cross coupling reactions. Mechanistic studies have revealed that the stability and coordination of the complexes by the CN group are achieved by the removal of pyridine from the complex in catalytic cycles. The presence of the CN group in the (NHC)Pd complexes significantly increased the catalytic activities for both reactions.

Nitrile-functionalized Pd(ii) complexes have evaluated for the Suzuki–Miyaura cross-coupling reactions. The highest TON value was reached for the acylative Suzuki–Miyaura cross-coupling reaction of acyl chlorides with phenylboronic acids.

Green Approach for Visible-Light-Induced Direct Functionalization of 2-Methylquinolines

A transition metal- and oxidant-free visible light-photoinduced protocol for direct functionalization of 2-methylquinolines has been developed. This protocol enabled the C-H functionalization of substituted 2-methylquinolines with diacetyl or ethyl pyruvate, under environmentally friendly conditions. A mechanistic investigation based on density functional theory (DFT) calculations provided details about the origins of reactivity and selectivity.

Niobium Oxides as Heterogeneous Catalysts for Biginelli Multicomponent Reaction

This study reports a simple, reusable, and recoverable niobium-based heterogeneous catalysts for Biginelli multicomponent reactions. Different methods of catalysts preparation were investigated. For this purpose, HY-340 (Nb₂O₅·nH₂O) and Nb₂O₅ were chemically and/or thermally treated and investigated as catalysts for dihydropyrimidinones (DHPMs) production. The catalysts were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, temperature-programmed desorption of NH₃, adsorption/desorption of N₂ at -196 °C, and thermogravimetric and differential thermal analysis. The characterization results showed that niobium oxides have the potential to be used as catalysts because of high crystallinity and large surface area. Among the tested catalysts, Nb₂O₅ chemically treated (Nb₂O₅/T) showed the best catalytic performance. In the absence of solvents, 94% yield of DHPMs was achieved. Also, Nb₂O₅/T can be reused three times without a significant yield decrease. Additionally, a feasible reaction pathway was suggested based on the Knoevenagel mechanism for DHPM synthesis using niobium-based catalysts.

Striking dual functionality of a novel Pd@Eu-MOF nanocatalyst in C(sp2)-C(sp2) bond-forming and CO2 fixation reactions

Pd nanoparticles were immobilized on a highly porous, hydrothermally stable Eu-MOF via solution impregnation and H2 reduction to yield a novel Pd@Eu-MOF nanocatalyst. This composite was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), inductively coupled plasma optical emission spectroscopy (ICP-OES), powder X-ray diffraction (PXRD) and X-ray photoelectron spectroscopy (XPS). Unprecedentedly, the Pd@Eu-MOF nanocatalyst could be applied with excellent results in two strikingly different, mechanistically distinct, reactions i.e., Suzuki-Miyaura cross-coupling and cycloaddition of CO2 to a range of epoxides. Under the best reaction conditions, 98-99% yields have been attained in both catalytic processes. Moreover, in either case the heterogeneous catalyst was easily recovered and efficiently reused for more than four cycles, indicating its high stability and reproducibility. PXRD, TEM and XPS measurements on the recycled catalyst confirmed that it maintained its original structure and morphology; no Pd NP agglomeration was observed.

Isoniazid-functionalized Fe3O4 Magnetic Nanoparticles as a Green and Efficient Catalyst for the Synthesis of 3, 4-dihydropyrimidin-2(1H)-ones and their Sulfur Derivatives

BACKGROUND

A wide variety of dihydropyrimidins (DHPMs) exhibit pharmacological and biological activities. Herein, an efficient one-pot synthesis of some 3, 4-dihydropyrimidin-2(1H)-one derivatives is reported using Fe3O4 @SiO2-Pr-INH.

OBJECTIVE

Recently, several catalysts have been used to improve the Biginellis-reaction. However, some of these catalysts have imperfections. Herein, a convenient method for the synthesis of 3, 4-dihydropyrimidin- 2(1H)-ones and their sulfur derivatives using Fe3O4 @SiO2-Pr-INH is reported.

MATERIALS AND METHODS

Firstly, the catalyst was synthesized through a simple four-step method. The Fe3O4 MNPs were synthesized using the chemical co-precipitation method, coated with a layer of silica using TEOS, and then functionalized with CPTMS. Subsequently, a nucleophilic substitution of Cl by isoniazid resulted in the formation of the magnetic Fe3O4@SiO2-Pr-INH. After the preparation and characterization of Fe3O4@SiO2-Pr-INH, its catalytic activity was studied in the synthesis of 3, 4-dihydropyrimidin-2(1H)-one derivatives. Following the optimization of the reaction conditions, several 3, 4-dihydropyrimidin-2(1H)-one derivatives were synthesized by the reaction of ethyl acetoacetate or acetylacetone, thiourea or urea and aromatic aldehydes at 80 °C under solvent-free conditions.

RESULTS

Isoniazid-functionalized Fe3O4 magnetic nanoparticles (Fe3O4@SiO2-Pr-INH) were prepared using Fe3O4 with silica layer and their surface was modified with isoniazid. They were characterized successfully by infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and were used for the synthesis of some 3, 4-dihydropyrimidin-2(1H)-one derivatives as catalysts. Aromatic aldehydes with electron-donating or electron-withdrawing groups afforded 3, 4- dihydropyrimidin-2(1H)-ones and their sulfur derivatives in good to excellent yields in short reaction times.

CONCLUSION

Isoniazid-functionalized Fe3O4 magnetic nanoparticles (Fe3O4@SiO2-Pr-INH) were used as an efficient catalyst for Biginelli-type synthesis of 3, 4-dihydropyrimidin-2(1H)-ones and 3, 4-dihydropyrimidin- 2(1H)-thiones in good to excellent yields and short reaction times. It is noteworthy that this method has several advantages such as simple experimental procedures, the absence of solvent, environmentally benign process, stability and reusability of the catalyst.

Monolith catalyst design via 3D printing: a reusable support for modern palladium-catalyzed cross-coupling reactions

The use of an additive manufacturing procedure for the modification of catalytic structures is currently gaining popularity in the field of catalysis.

Concentrated solar radiation as a renewable heat source for a preparative-scale and solvent-free Biginelli reaction

Highly sustainable, economical, and faster Biginelli reaction has been established using concentrated solar radiation.

Greener synthesis of 1,2,3-triazoles using a copper(i)-exchanged magnetically recoverable β-zeolite as catalyst

A novel magnetically recoverable Cu(i)-exchanged β-zeolite catalyst was prepared, characterized and applied for the synthesis of 1,2,3-triazoles via the one-pot three-component reaction.

Selective ultrasonic assisted synthesis of iron oxide mesoporous structures based on sulfonated melamine formaldehyde and survey of nanorod/sphere, sphere and core/shell on their catalysts properties for the Biginelli reaction

Sulfonated melamine-formaldehyde including iron oxide nanoparticles were synthesized by sulfonation of melamine-formaldehyde and then Fe₃O₄ nanoparticles were bounded onto the surface of sulfonated melamine-formaldehyde (SMF). Two different iron oxide nanostructures including nanorods/spheres and nanospheres on sulfonated melamine-formaldehyde (SMF/Fe₃O₄) were obtained only by modifying the time of radiation from 4 to 8 h in our synthetic method. Furthermore core/shell (Fe₃O₄@SMF) was prepared by entrapping Fe₃O₄ magnetic nanoparticles as the core and sulfonated melamine-formaldehyde as the outer shell. The prepared components were characterized via, Fourier transform infrared spectroscopy (FT-IR), titration, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) analysis, Barret-Joyner-Halenda (BJH) analysis, vibrating sample magnetometer (VSM), energy-dispersive X-ray (EDX) spectroscopy, and thermal gravimetric analysis (TGA). According to obtained results, the synthesized products had a thermal stability near 180 °C, particle-size distribution around of 20-140 nm and surface area between 6 and 10 m²/g. In this study, vapor was used as a heat source. These effective and magnetically recoverable catalysts were employed for the synthesis of numerous 3,4-dihydropyrimidin-2(1H)-ones by utilizing aldehydes, ethylacetoacetate and urea. Functional easiness, excellent yields, short reaction time, the simplicity of work-up or filter, and thermal stability of these catalysts created them as appropriate heterogeneous systems and acceptable alternative to different heterogeneous catalysts.

Highly Efficient Synthesis of Substituted 3,4-Dihydropyrimidin-2-(1H)-ones (DHPMs) Catalyzed by Hf(OTf)₄: Mechanistic Insights into Reaction Pathways under Metal Lewis Acid Catalysis and Solvent-Free Conditions

In our studies on the catalytic activity of Group IVB transition metal Lewis acids, Hf(OTf)₄ was identified as a highly potent catalyst for "one-pot, three-component" Biginelli reaction. More importantly, it was found that solvent-free conditions, in contrast to solvent-based conditions, could dramatically promote the Hf(OTf)₄-catalyzed formation of 3,4-dihydro-pyrimidin-2-(1H)-ones. To provide a mechanistic explanation, we closely examined the catalytic effects of Hf(OTf)₄ on all three potential reaction pathways in both "sequential bimolecular condensations" and "one-pot, three-component" manners. The experimental results showed that the synergistic effects of solvent-free conditions and Hf(OTf)₄ catalysis not only drastically accelerate Biginelli reaction by enhancing the imine route and activating the enamine route but also avoid the formation of Knoevenagel adduct, which may lead to an undesired byproduct. In addition, ¹H-MMR tracing of the H-D exchange reaction of methyl acetoacetate in MeOH-d₄ indicated that Hf(IV) cation may significantly accelerate ketone-enol tautomerization and activate the β-ketone moiety, thereby contributing to the overall reaction rate.

Tuning the Biginelli reaction mechanism by the ionic liquid effect: the combined role of supported heteropolyacid derivatives and acidic strength

Herein, a combination of heteropolyacids and ionic liquids as a catalytic system was studied for the Biginelli multicomponent reaction; the positive ionic liquid effect associated with the acidic strength of zeolite-supported heteropolyacids made this combination an efficient catalytic system for the multicomponent synthesis of 3,4-dihydropyrimidin-2(1H)-one/thione derivatives. The acidic strength effect was evaluated, and a range was determined in which the reaction provided better results. The mechanism of the reaction was also investigated in the presence and absence of ionic liquids, and two features of paramount importance were revealed: the mechanism could be tuned to proceed through only one reaction path among three possibilities and the kinetics of the reaction was significantly faster in the presence of an ionic liquid.

Heteropolyacids and ionic liquid effect allowed tuning of the Biginelli reaction mechanism and synthesis of 3,4-dihydropyrimidin-2(1H)-one/thione derivatives in an efficient, recyclable fashion. The role of acidic strength and supported heteropolyacid is disclosed.

Synergistic effect of the Pd–Ni bimetal/carbon nanofiber composite catalyst in Suzuki coupling reaction

A novel Pd₁Ni₄ bimetal nanocomposite catalyst was prepared and showed better performance than their monometallic counterpart. What's more, the catalyst could be reused ten times without significant change in catalytic activity, which met the request of sustainable chemistry.

Palladium decorated on a new dendritic complex with nitrogen ligation grafted to graphene oxide: fabrication, characterization, and catalytic application

Immobilized Pd nanoparticles on a new ligand, namely, tris(pentaethylene-pentamine)triazine supported on graphene oxide (Pd_np-TPEPTA_(L)-GO) was introduced as a novel and robust heterogeneous catalyst for use in C–C bond formation reaction. The Pd_np-TPEPTA_(L)-GO catalyst was synthesized by complexation of Pd with TPEPTA as a ligand with high N-ligation sites that were supported on graphene oxide through 3-chloropropyltrimethoxysilane. The prepared catalyst was characterized using some microscopic and spectroscopic techniques. The TPEPTA_(L)-GO substrate is a 2D heterogeneous catalyst with a high specific surface area and a large amount of N-ligation sites. The Pd_np-TPEPTA_(L)-GO catalyst used in the C–C bond formation reaction between aryl or heteroaryl and phenylboronic acid derivatives was applied towards the synthesis of biaryl units in high isolated yields. Notably, a series of competing experiments were performed to establish the selectivity trends of the presented method. Also, this catalyst system was reusable at least six times without a significant decrease in its catalytic activity.

Immobilized Pd nanoparticles on a new ligand, namely, tris(pentaethylene-pentamine)triazine supported on graphene oxide (Pd_np-TPEPTA_(L)-GO) was introduced as a novel and robust heterogeneous catalyst for use in C–C bond formation reaction.

Nebivolol nanoparticles: a first catalytic use in Biginelli and Biginelli-like reactions

Herein, we report the catalytic activity of nebivolol nanoparticles a novel organocatalyst for the synthesis of DHPMs and DHPM-5-carboxamides. The nanoparticles are confirmed by DSC, TEM, AFM, and IR spectroscopy. The catalyst can be readily recovered and reused for the next four runs without any significant impact on the yields of the products. The products are fully characterized by FTIR, 1H NMR, 13C NMR, and distortionless enhanced polarization transfer (DEPT) NMR. The methodology adopted here offers several advantages such as solvent-free reaction, low loading of catalyst, short reaction times, and quantifiable yields.

Magnetic core-shell Carrageenan moss/Fe3O4: a polysaccharide-based metallic nanoparticles for synthesis of pyrimidinone derivatives via Biginelli reaction

Magnetically recoverable polysaccharide-based metallic nanoparticles Carrageenan moss/Fe3O4 (Fe3O4@CM) was tested for the synthesis of Pyrimidinone derivatives via Biginelli reaction under reflux conditions in Water. Interestingly, Fe3O4@CM prepared from unmodified Irish moss showed remarkable catalytic activity and recyclability. Low catalyst loading, simple reaction procedure, and using a green catalyst from a natural source are the important merits of this protocol.

Mechanistic Exploration of the Transmetalation and Reductive Elimination Events Involving PdIV -Abnormal NHC Complexes in Suzuki-Miyaura Coupling Reactions: A DFT Study

A comprehensive DFT (M06-L-D3(SMD)/BS2//M06-L/BS1 level) investigation has been carried out to explore in detail the mechanism of the transmetalation and reductive elimination reactions of abnormal N-heterocyclic carbene (aNHC) palladium(IV) complexes within the framework of Suzuki-Miyaura cross-coupling reactions. Emphasis was placed on the role of base and the effect of countercations on the critical transmetalation and reductive elimination events involving palladium(IV) complexes. Of the two competing roles of the base, the route involving boronate formation followed by halide exchange prevails over that of direct halide exchange for the intermediates [Pd^IV (aNHC)(OMe)₂ Cl]^- Na⁺ (pathway A), [Pd^IV (aNHC)(OMe)(Cl)₂ ]^- Na⁺ (pathway B), and [Pd^IV (aNHC)Cl₃ ]^- Na⁺ (pathway C) emanating from the oxidative addition reaction. The results of the calculations are in accordance with our previous theoretical findings of favorable energetics for palladium intermediates incorporating two coordinated methoxy groups. The negative role played by the countercation in the transmetalation step is mainly due to the overstabilization of the pre-transmetalation intermediate, which is in line with experimental kinetic results. The anionic complexes exhibit greater affinity for the transmetalation and reductive elimination reactions than the neutral variants.

P-arylation of aryl halides by an environmentally compatible method

In this paper, palladium–DABCO complex supported on magnetic nanoparticles was successfully used as a new magnetically recoverable heterogeneous catalyst for the synthesis of arylphosphonates via P-arylation of different types of aryl halides (aryl iodides/bromides/chlorides and benzene boronic acid/sulfonate), with phosphite esters (triethyl/triphenyl/tri-iso-propyl/diethyl/diphenyl/di-iso-propyl phosphite) in neat water without using any additive. The heterogeneous catalyst was easily isolated from the reaction mixture by an external magnet and reused five times without significant degradation in its activity.