γ‐Fe 2 O 3 @Cu 3 Al‐LDH/HEPES a novel heterogeneous amphoteric catalyst for synthesis of annulated pyrazolo[3,4‐d]pyrimidines

Construction of a Dual-Functionalized Acid-Base Nanocatalyst via HEPES Buffer Functionalized on Fe3O4 as a Reusable Catalyst for Annulation Reactions

Herein, we present a highly efficient dual-functionalized acid-base nanocatalyst, denoted as Fe3O4@GLYMO-HEPES, featuring sulfuric acid and tertiary amines as its dual functional components. This catalyst is synthesized through the immobilization of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) as the source of these functionalities onto magnetite (Fe3O4) using 3-glycidoxypropyltriethoxysilane (GLYMO) as a linker. Characterization studies confirm the integrity of the Fe3O4 core, with the GLYMO-HEPES coating exhibiting no phase changes. Furthermore, Fe3O4@GLYMO-HEPES nanoparticles demonstrate a uniform size distribution without aggregation. Notably, the catalyst exhibits remarkable stability up to 200 °C and possesses a saturation magnetization value of 31.5 emu/g, facilitating easy recovery via magnetic separation. These findings underscore the potential of Fe3O4@GLYMO-HEPES as a versatile and recyclable nanocatalyst for various applications. Its catalytic ability was evaluated in the synthesis of various pyrano[2,3-c]pyrazoles and 2-amino-3-cyano-4H-chromenes through a tandem Knorr-Knoevenagel-Michael-Thorpe-Ziegler-type heterocyclization mechanism, using different aldehydes. A wide range of fused heterocycles was synthesized having good to excellent yields. The process is cost-effective, safe, sustainable, and scalable, and the catalyst can be reused up to five times. The prepared catalyst was found to be highly stable and heterogeneous and showed good recyclability.

An Fe3O4 supported O-phenylenediamine based tetraaza Schiff base-Cu(ii) complex as a novel nanomagnetic catalytic system for synthesis of pyrano[2,3-c]pyrazoles

In this research, we present a post-synthetic method for synthesizing a novel nanomagnetic Cu(II) Schiff base complex and investigate its efficiency in catalytic organic conversion reactions. Various spectroscopic analyses were employed to characterize the physiochemical characteristics of the resulting nanocomposite. The experimental results successfully demonstrate the catalytic application of the prepared Cu-complex in the preparation of pyrano[2,3-c]pyrazole heterocycles. This synthesis involved a one-pot three-component condensation reaction, wherein hydrazine hydrate, ethyl acetoacetate, malononitrile, and aromatic aldehydes were combined under reflux conditions using water as the solvent. Notably, the heterogenized complex exhibited exceptional catalytic performance, achieving remarkable conversion rates and selectivity, all accomplished using only 12 mg of the catalyst. Furthermore, thorough stability assessments of this catalyst were conducted through reusability and hot filtration tests, which confirmed its non-leaching properties and demonstrated excellent results over the course of five consecutive runs.

Nanomagnetic tetraaza (N4 donor) macrocyclic Schiff base complex of copper(ii): synthesis, characterizations, and its catalytic application in Click reactions

In this research, a novel nanomagnetic tetra-azamacrocyclic Schiff base complex of copper(ii) was produced via a post-synthetic surface modification of an Fe3O4 surface by a silane-coupling agent that contains acetylacetone functionalities at the end of its chain. Moreover, the target Cu complex that involves a tetradentate Schiff base ligand was obtained from a template reaction with o-phenylenediamine and Cu(NO3)2·3H2O. Furthermore, the prepared complex was nominated as [Fe3O4@TAM-Schiff-base-Cu(II)]. The Fourier-transform infrared (FT-IR) analysis indicates the presence of a Schiff-base-Cu complex in the catalyst. X-ray spectroscopy (EDS) and TGA analysis reveal that approximately 6-7% of the target catalyst comprises hydrocarbon moieties. The scanning electron microscope (SEM) and transmission electron microscopy (TEM) images demonstrate the presence of uniformly shaped particles, nearly spherical in nature, with sizes ranging from 9 to 18 nm. [Fe3O4@TAM-Schiff-base-Cu(II)] was applied as a catalyst for the click synthesis of a diverse range of 5-substituted-1H-tetrazoles in PEG-400 as a green medium. Regarding the electrical properties of the Cu(ii) complex, the presence of a tetra-aza (N4 donor) macrocyclic Schiff base as an N-rich ligand was reasonable - leading to its excellent capacity to catalyze these organic transformations. Finally, the high magnetization value (44.92 emu g-1) of [Fe3O4@TAM-Schiff-base-Cu(II)] enables its recycling at least four times without compromising the catalytic efficiency.

Synthesis of a bistriazolyl-phenanthroline-Cu(ii) complex immobilized on nanomagnetic iron oxide as a novel green catalyst for synthesis of imidazoles via annulation reactions

We designed and prepared a novel N-heterocycle-based nanocatalyst by a post synthetic method, namely the [Fe3O4@DAA-BTrzPhen-Cu(ii)] composite. In this method, bistriazolyl-phenanthroline groups were stepwise synthesized on an Fe3O4 substrate and used as a tetradentate nitrogenous ligand for coordinating to copper ions. The obtained nanocomposite was well characterized using FT-IR, PXRD, TGA, EDAX, ICP-OES, EDX-mapping, SEM, TEM, VSM and BET analyses, which confirm the formation of a thermostable crystalline spherical particle morphology with the particle size in the range of 17 nm to 25 nm and a magnetization value of 42 emu g-1. Also, the catalytic activity of [Fe3O4@DAA-BTrzPhen-Cu(ii)] as a novel and magnetically separable heterogeneous nanocatalyst was evaluated in preparing various tetrasubstituted imidazole derivatives from one-pot four-component condensation of anilines, aldehydes, 1,2-diketones and ammonium acetate, and favorable products were produced with excellent yields. The stability, low Cu leaching, and heterogenous nature of the nanocatalyst were confirmed by hot-filtration and leaching tests. The copper based nanocatalyst could be easily recovered by magnetic field separation and recycled at least 8 times in a row without noticeable loss in its catalytic activity.

SiO2-supported HClO4 catalyzed synthesis of (Z)-thiazolylhydrazonoindolin-2-ones and their electrochemical properties

In this paper, an environmentally benign silica-supported perchloric acid (HClO₄-SiO₂) catalyzed green FCDR strategy has been developed for the synthesis of (Z)-THIs (6) with high stereospecificity via an intramolecular hydrogen bond (IHB) directed approach, involving the reaction of methyl ketones (1), N-bromosuccinimide (NBS) (2), isatins (4) and thiosemicarbazide (5) in ethanol at reflux temperature for 45-60 min in one-pot. The reaction proceeds through the construction of C-Br (α-bromination), C-S & C-N (heterocyclization), and CN (condensation) bonds in one pot. The absolute structure of the compound (Z)-3-(2-(4-(4-bromophenyl)thiazol-2-yl)hydrazono)indolin-2-one (6e) has been confirmed by single-crystal XRD analysis. Further, the role of IHB on Z-configuration of the synthesized (Z)-THIs is proved by single-crystal XRD and ¹H NMR studies. Wide substrate scope, good functional group tolerance, scalability, improved safety since the method circumvents the use of highly lachrymatric α-bromoketones as starting materials, high product yields (up to 98%), short reaction times, reusable solid Brønsted acid catalyst (HClO₄-SiO₂), and products that do not require column chromatography purification are all attractive features of this FCDR strategy. Electrochemical properties of THIs (6) are examined by cyclic voltammetry. The HOMO and LUMO energy level of THIs, 6a, 6c, 6d, 6j, 6o-6v, 6y, and 6aa are comparable with the reported ambipolar materials, and the HOMO levels of other THIs, 6b, 6e-6i, 6n, 6w, 6x, 6z and 6 ab-6ae are similar with the most commonly used hole transporting materials (HTMs).

Ni(ii) immobilized on poly(guanidine-triazine-sulfonamide) (PGTSA/Ni): a mesoporous nanocatalyst for synthesis of imines

Mesoporous materials have been the subject of intense research regarding their unique structural and textural properties and successful applications in various fields. This study reports a novel approach for synthesizing a novel porous polymer stabilizer through condensation polymerization in which Fe₃O₄ magnetic nanoparticles (Fe₃O₄ MNPs) are used as hard templates. Using this method allowed the facile and fast removal of the template and mesopores formation following the Fe₃O₄ MNPs. Different techniques were performed to characterize the structure of the polymer. Based on the obtained results, the obtained mesoporous polymeric network was multi-layered and consisted of repeating units of sulfonamide, triazine, and guanidine as a novel heterogeneous multifunctional support. Afterward, the new nickel organometallic complex was supported on its inner surface using the porous poly sulfonamide triazine guanidine (PGTSA/Ni). In this process, the obtained PGTSA/Ni nanocomposite was used as a heterogeneous catalyst in the synthesis of imines from amines. Since this reaction has an acceptorless dehydrogenation pathway, the hydrogen gas is released as its by-product. The synthesized nanocatalyst was structurally confirmed using different characterization modalities, including FT-IR, SEM, XRD, EDX, TEM, elemental mapping, ICP-AES, BET, and TGA. In addition, all products were obtained in high turnover frequency (TOF) and turnover number (TON). The corresponding results revealed the high selectivity and activity of the prepared catalyst through these coupling reactions. Overall, the synthesized nanocatalyst is useable for eight cycles with no considerable catalytic efficiency loss.

Chlorosulfonic acid coated on porous organic polymer as a bifunctional catalyst for the one-pot three-component synthesis of 1,8-naphthyridines

The synthesis of six-membered oxygen- and nitrogen-containing heterocycles has been regarded as the most fundamental issue in organic chemistry and the chemical industry because these heterocycles are used in producing high-value products. In this study, an efficient, economic, sustainable, and green protocol for their multicomponent synthesis has been developed. The one-pot direct Knoevenagel condensation–Michael addition–cyclization sequences for the transformation of aromatic aldehydes, malononitrile, and 2-aminopyridine generate the corresponding 1,8-naphthyridines over a novel mesoporous bifunctional organocatalyst supported cholorosulfonic acid [poly(triazine-benzene sulfonamide)-SO₃H (PTBSA-SO₃H)] under ambient conditions. The catalyst was used for the formation of 1,8-naphthyridine derivatives for six runs. The current strategy provided a wider substrate range, and short reaction times.

Chlorosulfonic acid coated on porous organic polymer as a bifunctional catalyst for one-pot three-component synthesis of 1,8-naphthyridines