An iron Schiff base complex loaded mesoporous silica nanoreactor as a catalyst for the synthesis of pyrazine-based heterocycles

An iron Schiff base complex was encapsulated in SBA-15 mesoporous silica to afford a Fe(III)-Schiff base/SBA-15 heterogeneous nanocatalyst for the synthesis of pyridopyrazine and quinoxaline heterocycles. These reactions proceeded in water with excellent yields. The catalyst was characterized by physico-chemical and spectroscopic methods and found to retain the characteristic channel structures of the SBA-15, allowing good accessibility of the encapsulated metal complex.     

Efficient solvent-free synthesis of pyridopyrazine and quinoxaline derivatives using copper-DiAmSar complex anchored on SBA-15 as a reusable catalyst

A catalytic system comprising mesoporous silica functionalized with Cu(II)-DiAmSar was synthe-sized. This was demonstrated as an efficient heterogeneous catalyst for the synthesis of biologically useful pyridopyrazine and quinoxaline heterocycles under solvent-free conditions. X-ray diffraction, transmission electron microscopy, N2 adsorption-desorption, Fourtier transformation infrared spectroscopy, and thermogravimetric analysis were used to characterize the catalyst and investi-gate the texture of SBA-15 during the grafting process.     

SBA-15锚定Cu(Ⅱ)-DiAmSar配合物催化剂上无溶剂高效合成吡啶并吡嗪和喹喔啉衍生物（英文）

A catalytic system comprising mesoporous silica functionalized with Cu(II)-DiAmSar was synthesized. This was demonstrated as an efficient heterogeneous catalyst for the synthesis of biologically useful pyridopyrazine and quinoxaline heterocycles under solvent-free conditions. X-ray diffraction, transmission electron microscopy, N2 adsorption-desorption, Fourtier transformation infrared spectroscopy, and thermogravimetric analysis were used to characterize the catalyst and investigate the texture of SBA-15 during the grafting process.     

Trisaminomethane–cobalt complex supported on Fe3O4 magnetic nanoparticles as an efficient recoverable nanocatalyst for oxidation of sulfides and C–S coupling reactions

In this work, trisaminomethane–cobalt complex immobilized onto the surface of Fe₃O₄ magnetic nanoparticles was successfully prepared via a simple and inexpensive procedure. The prepared nanocatalyst was considered a robust and clean nanoreactor catalyst for the oxidation and synthesis of sulfides under green conditions. This ecofriendly heterogeneous catalyst was characterized by Fourier transform infrared spectroscopy, X-ray diffractometry, energy-dispersive X-ray spectroscopy, inductively coupled plasma-atomic emission spectroscopy, thermogravimetric analysis, vibrating sample magnetometry, X-ray mapping, scanning electron microscopy, and transmission electron microscopy techniques. Use of green medium, easy separation and workup, excellent reusability of the nanocatalyst, and short reaction time are some outstanding advantages of this method.     

Efficient and green synthesis of dihydropyrimido[4,5-b]quinolinetriones using MWCNTs@TEPA/Co (II) as a novel and eco-friendly catalyst

A new heterogeneous nanocatalyst [MWCNTs@TEPA/Co (II)] was successfully prepared using multiwall carbon nanotubes (MWCNTs) as a suitable and efficient support for covalent anchoring of tetraethylene pentaamine (TEPA)/Co (II). The new heterogeneous catalyst was prepared through an easy and applicable method, and characterized by various techniques such as Fourier transform-infrared, thermogravimetric analysis, energy-dispersive X-ray spectroscopy, mapping, field emission-scanning electron microscopy, inductively coupled plasma-optical emission spectrometry and Brunauer−Emmett−Teller. Synthesized catalyst was used efficiently for the preparation of dihydropyrimido [4,5-b]quinolinetrione derivatives via the four-components reaction of barbituric acid, dimedone, aryl aldehyde and amines under thermal conditions. The nanostructure catalyst was easily recovered by filtration and reused several times without noticeable loss of its catalytic activity. Low amounts of catalyst (0.005 g), short reaction times and green conditions are some merits of the presented method.     

Functionalization of superparamagnetic Fe3O4@SiO2 nanoparticles with a Cu(II) binuclear Schiff base complex as an efficient and reusable nanomagnetic catalyst for N‐arylation of α‐amino acids and nitrogen‐containing heterocycles with aryl halides

Fe₃O₄@SiO₂ nanoparticles was functionalized with a binuclear Schiff base Cu(II)‐complex (Fe₃O₄@SiO₂/Schiff base‐Cu(II) NPs) and used as an effective magnetic hetereogeneous nanocatalyst for the N‐arylation of α‐amino acids and nitrogen‐containig heterocycles. The catalyst, Fe₃O₄@SiO₂/Schiff base‐Cu(II) NPs, was characterized by Fourier transform infrared (FTIR) and ultraviolet‐visible (UV‐vis) analyses step by step. Size, morphology, and size distribution of the nanocatalyst were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and dynamic light scatterings (DLS) analyses, respectively. The structure of Fe₃O₄ nanoparticles was checked by X‐ray diffraction (XRD) technique. Furthermore, the magnetic properties of the nanocatalyst were investigated by vibrating sample magnetometer (VSM) analysis. Loading content as well as leaching amounts of copper supported by the catalyst was measured by inductive coupled plasma (ICP) analysis. Also, thermal studies of the nanocatalyst was studied by thermal gravimetric analysis (TGA) instrument. X‐ray photoelectron spectroscopy (XPS) analysis of the catalyst revealed that the copper sites are in +2 oxidation state. The Fe₃O₄@SiO₂/Schiff base‐Cu(II) complex was found to be an effective catalyst for C–N cross‐coupling reactions, which high to excellent yields were achieved for α‐amino acids as well as N‐hetereocyclic compounds. Easy recoverability of the catalyst by an external magnet, reusability up to eight runs without significant loss of activity, and its well stability during the reaction are among the other highlights of this catalyst.     

Cr-free Co-Cu/SBA-15 catalysts for hydrogenation of biomass-derivedα-,β-unsaturated aldehyde to alcohol

Cr-free bi-metallic SBA-15-supported Co–Cu catalysts were examined in the conversion of bio-mass-derived α-, β-unsaturated aldehyde (furfural) to value-added chemical furfuryl alcohol (FOL). Co–Cu/SBA-15 catalysts with a fixed Cu loading of 10 wt% and varying Co loadings (2.5, 5, and 10 wt%) were prepared by the impregnation method. The catalysts were characterized by X-ray dif-fraction, N2 sorption, H2 temperature-programmed reduction, scanning electron microscopy, ener-gy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, CO chemi-sorption, and inductively coupled plasma mass spectrometry. The influence of different reaction parameters such as temperature, pressure, catalyst dosage, and furfural concentration on the cata-lyst performance was evaluated. Relative to catalysts supported on amorphous silica, the current SBA-15-supported Co–Cu catalysts displayed higher performance, attaining a furfural conversion of 99% and furfuryl alcohol selectivity of 80%. The catalytic reactions were conducted in a 100-mL autoclave at 170 °C and 2 MPa H2 pressure for 4 h.     

Fe3O4@SiO2 nanoparticles–functionalized Cu(II) Schiff base complex with an imidazolium moiety as an efficient and eco-friendly bifunctional magnetically recoverable catalyst for the Strecker synthesis in aqueous media at room temperature

Cu(II) Schiff base complex supported on Fe₃O₄@SiO₂ nanoparticles was employed as a magnetic nanocatalyst (nanocomposite) with a phase transfer functionality for the one-pot preparation of α-aminonitriles (Strecker reaction). The desired α-aminonitriles were obtained from the reaction of aromatic or aliphatic aldehydes, aniline or benzyl amine, NaCN, and 1.6 mol% of the catalyst in water at room temperature and good to excellent yields were obtained for all substrates. The catalyst was characterized analytically and instrumentally including Fourier-transform infrared spectroscopy, X-ray diffraction, thermogravimetric, nuclear magnetic resonance, energy-dispersive X-ray spectroscopy, inductively coupled plasma spectroscopy, vibrating-sample magnetometry analysis, dynamic light scattering, Brunauer–Emmett–Teller surface area, field emission scanning electron microscopy, and transmission electron microscopy analyses. The reaction mechanism was investigated, in which the performance of the catalyst as a phase transition factor seems to be probable. The catalyst showed high activity, high turnover frequency (TOF)s, significant selectivity, and fast performance toward the Strecker synthesis. The nanocatalyst can be readily and quickly separated from the reaction mixture with an external magnet and can be reused for at least seven successive reaction cycles without significant reduction in efficiency.     

L-lysine-Pd Complex Supported on Fe3O4 MNPs: a novel recoverable magnetic nanocatalyst for Suzuki C-C Cross-Coupling reaction

In this work, L-lysine-Pd Complex, immobilized onto the surface of Fe₃O₄ MNPs, was successfully prepared via simple and inexpensive procedure. The prepared nanocatalyst was considered as a robust and clean nano-reactor catalyst for the Suzuki and Heck C-C Cross-Coupling reactions in water as the green condition. This eco-friendly heterogeneous catalyst was characterized by Fourier transform infrared spectroscopy (FT-IR), X-Ray Diffractometer (XRD), energy-dispersive X-ray spectroscopy (EDS), inductively coupled plasma atomic emission spectroscopy (ICP), X-ray mapping, BET, thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) techniques. The use of a green medium, easy separation and workup, excellent reusability of the nanocatalyst and short reaction time are some outstanding advantages of this method.     

Copper Schiff base complex immobilized on magnetic graphene oxide: Efficient heterogeneous nanocatalyst for treating environmental pollutants and synthesis of chromenes

Herein, a new Cu(II) Schiff base complex was immobilized onto the magnetic graphene oxide surface through a stepwise procedure. The as-synthesized nanostructure (GO/Fe₃O₄/CuL) was characterized by various techniques including Fourier transform infrared (FT-IR), Raman spectroscopies, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), energy-dispersive X-ray (EDX) and inductively coupled plasma (ICP) spectroscopies, N₂ adsorption–desorption analysis, vibrating sample magnetometry (VSM), and X-ray diffraction (XRD). The catalytic activity of the synthesized nanocatalyst was examined in 4-nitrophenol (4-NP), Congo red (CR), and methylene blue (MB) reduction using NaBH₄ in an aqueous solution at room temperature. The reaction progress was monitored by UV–Vis spectroscopy. Also, the synthesized nanostructure was evaluated as an efficient catalyst for the synthesis of 2-amino-4H-benzopyrans via three-component reactions of 1-naphthol, malononitrile, and various aldehydes in ethanol/water at 50°C. The use of green solvents, the short reaction time, the high product yield, and easy separation from the reaction environment are the main benefits of this catalytic system. By covalent grafting of the complex on the graphene oxide surface, its catalytic performance significantly increased compared with graphene oxide; this is probably related to the chemical change of the graphene oxide surface. The results show the high chemical stability and the improved reusability of the synthesized nanocatalyst (six times) without significant loss in the catalytic activity of GO/Fe₃O₄/CuL nanocomposite.     

三丁基锡/SBA-15功能配合物的合成、表征及对Friedel-Crafts反应的选择性催化

将三丁基氯化锡与SBA-15介孔分子筛在N2气气氛中进行回流反应,得到有机锡无机配合物(C4H9)3Sn-O-SBA-15[Bu3SnS]。 利用X射线衍射(XRD)、透射电子显微镜(TEM)、氮气吸附脱附、固体核磁（NMR）和吡啶吸附脱附红外光谱分析(Py-IR)等方法对产物的组成、结构和性质进行了表征。 结果表明,产物Bu3SnS具有高度有序的六方介孔结构,与SBA-15相比,Bu3SnS比表面积、孔容和孔径变小,酸性增强。 Bu3SnS对苯甲醚Friedel-Crafts酰基化反应具有优异的催化性能,当反应温度为130 ℃,n（苯甲醚）∶n（苯甲酰氯）=1.0∶2.0,w（cat）=6%（相对于苯甲醚用量）,反应时间为5 h,苯甲醚的转化率达到76.0%,对甲氧基二苯酮（p-MBP）选择性达到97.8%。     

Guanine-La complex supported onto SBA-15: A novel efficient heterogeneous mesoporous nanocatalyst for one-pot,multi-component Tandem Knoevenagel condensation–Michael addition–cyclization Reactions

In this work, we present a simple, environmentally-friendly and economical route for the preparation of a novel lanthanum (III) organometallic complex immobilized onto a highly stable mesoporous silica SBA-15 (La-guanine@SBA-15) using an inexpensive and simple method and available materials. This mesoporous heterogenized complex was comprehensively characterized using FT-IR, XRD, EDS, ICP, MAP, SEM, TGA and BET techniques. The catalytic activity of this mesoporous material was studied in one-pot multi-component tandem Knoevenagel condensation–Michael addition–cyclization reactions in order to prepare a series of benzo [a] pyrano [2, 3-c] phenazine and 4,4′-(arylmethylene)-bis-(3-methyl-1-phenyl-1H-pyrazol-5-ols) derivatives under green conditions. This catalyst exhibited highly recoverable and recyclable features in consecutive reaction runs. Besides, the products were obtained in high yields and short reaction times. In this sense, simple preparation of the catalyst from the commercially available materials, simple operation, high catalytic activity, short reaction times, high yields and the use of green reaction conditions in the mentioned organic synthesis are the most significant advantages of this protocol. In addition, this nanocatalyst was easily recovered, using simple filtration, and reused several times without significant loss of its catalytic efficiency. Moreover, the leaching, heterogeneity and stability of La-guanine@SBA-15 were studied by hot filtration test and ICP technique. Finally, stability of the catalyst after recycling was confirmed by SEM and FT-IR techniques.     

CuI heterogenized on thiosemicarbazide modified‐multi walled carbon nanotubes (thiosemicarbazide‐MWCNTs‐CuI): Novel heterogeneous and reusable nanocatalyst in the C‐N Ullmann coupling reactions

Herein we described the synthesis of novel thiosemicarbazide‐MWCNTs‐CuI nanocatalyst by covalent grafting of thiosemicarbazide on carbon nanotubes surface and subsequent coordination with CuI catalyst. The formation of nanocatalyst was analyzed by Raman spectroscopy, energy dispersive spectroscopy (EDS), wavelength‐dispersive X‐ray spectroscopy (WDX) and ICP analysis. The morphology of the nanocatalyst was characterized using scanning and transmission electron microscopes (SEM and TEM). Additionally, the (thiosemicarbazide‐MWCNTs‐CuI) nanocatalyst was successfully employed in the N ‐arylation of indole, amines and imidazoles through intermolecular C(aryl)‐N bond formation from the corresponding aryl halides (Ar–I, Ar–Br, Ar–Cl) with amines through Ullmann‐type coupling reactions. Interestingly, the novel catalyst could be recovered and recycled five times.     

Synthesis, catalytic activity and phytotoxicity of a supported nickel(II) Schiff base complex

A supported Ni(II) complex has been synthesized and characterized by FTIR, UV–vis diffuse reflectance spectroscopy, thermogravimetric analysis and scanning electron microscopy. Its catalytic activity was evaluated for alkyne–azide coupling and benzothiazole synthesis. These reactions were found to require mild conditions, reaction times, and most importantly, could be carried out in aqueous medium. The catalyst could be easily recovered and reused five times without significant decrease in its activity. Leaching tests indicated that the catalyst is truly heterogeneous. The nickel complex was tested for its inhibition of germination of MTU 7029 seeds. Rice (MTU 7029, Oryza sativa) is a staple crop in southeast Asia.     

Synthesis and characterization of mesoporous organosilica supported palladium (SBA-Pr-NCQ-Pd) as an efficient nanocatalyst in the Mizoroki–Heck coupling reaction

In the present study, the modification of a mesoporous organosilica nanocomposite SBA-15 (Santa Barbara Amorphous 15) was carried out in two steps, first through the surface functionalization of SBA-Pr-NH₂ with 2-chloroquinoline-3-carbaldehyde to form SBA-Pr-NCQ, and then through a post-modification process with palladium ions. The target nanocompound structure of SBA-Pr-NCQ-Pd was characterized by different techniques (thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, Energy-dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy). The catalytic performance of the porous inorganic–organic hybrid nanocomposite (SBA-Pr-NCQ-Pd) in one of the most important carbon–carbon bond-forming processes, the Mizoroki–Heck coupling reaction of aryl halides and methacrylate in water/ethanol media, was examined. Compared to previous reports, this protocol afforded some advantages, such as high yields of products, short reaction times, catalyst stability without leaching, simple methodology, easy workup, and greener conditions. Also, the nanocatalyst can be easily separated from the reaction mixture and reused several times without a significant decrease in activity and promises economic as well as environmental benefits.     

Highly ordered mesoporous La(III)-substituted 5-oxopyrrolidine-2-carboxylic acid (Glp) immobilized on SBA-15 as a very efficient nanocatalyst for green aerobic oxidative coupling of thiols to disulfides

Selective aerobic oxidative coupling of thiols that are catalyzed by La(III)-substituted 5-oxopyrrolidine-2-carboxylic acid (Glp) immobilized on SBA-15 (SBA-15@Glp–La; SBA = Santa Barbara amorphous) was studied. Using SBA-15@Glp–La, the complete conversion was achieved at room temperature in the presence of air without producing any over-oxidized yields. SBA-15@Glp–La was prepared by post-grafting technique. 5-Oxopyrrolidine-2-carboxylic acid (Glp) condensation followed by La(III) impregnation caused this La(III)-grafted 5-oxopyrrolidine-2-carboxylic acid (Glp) to immobilize on SBA-15. This SBA-15@Glp–La catalyst shows excellent catalytic activity in the selective aerobic oxidative coupling of thiols. Effects of amount of the catalyst, polarity of the solvent, effects of substrate, and catalyst reusability were investigated. It has been observed that seven repetitive reaction cycles did not cause any appreciable loss in the catalytic activity of this catalyst. The catalyst characterization by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, thermal gravimetric analysis, transmission electron microscopy, inductively coupled plasma, elemental mapping, and N₂ adsorption–desorption is reported. The procedure developed is heterogeneous and environmentally benign.     

Pd–Schiff base complex supported on Fe3O4 magnetic nanoparticles: A new and highly efficient reusable catalyst for C–C bond formation in water

A protocol is introduced for the preparation of a new cage‐like Pd–Schiff base organometallic complex supported on Fe₃O₄ nanoparticles (Fe₃O₄@Schiff‐base‐Pd). The structure of the nanomagnetic catalyst was comprehensively characterized using Fourier transform infrared (FT‐IR) spectroscopy, X‐ray diffraction (XRD), energy‐dispersive X‐ray spectroscopy, Brunauer–Emmett–Teller measurements, scanning electron microscopy (SEM), transmission electron microscopy, X‐ray mapping, thermogravimetric analysis, vibrating sample magnetometry and inductively coupled plasma atomic emission spectroscopy. In the second stage, the catalytic activity of this catalyst was studied in the Suzuki and Heck cross‐coupling reactions in water as a green solvent. In this sense, simple preparation of the catalyst from commercially available materials, high catalytic activity, simple operation, short reaction times, high yields and use of green solvent are some advantages of this protocol. Finally, the nanocatalyst was easily recovered, using an external magnet, and reused several times without significant loss of its catalytic efficiency. In addition, the stability of the catalyst after recycling was confirmed using SEM, XRD and FT‐IR techniques.     

Synthesis and application of novel 1,2,3‐triazolylferrocene‐containing ionic liquid supported on Fe3O4 nanocatalyst in the synthesis of new pyran‐substituted Betti bases

A novel magnetic ferrocene‐labelled ionic liquid based on triazolium, [Fe₃O₄@SiO₂@Triazol‐Fc][HCO₃], has been synthesized and has been successfully introduced as a recyclable heterogeneous nanocatalyst. The catalytic activity of the novel magnetic nanoparticles was evaluated in the one‐pot three‐component synthesis of a wide variety of Betti bases. A simple, facile and highly efficient green method has been developed for the synthesis of kojic acid‐containing Betti base derivatives at room temperature. Additionally, this new protocol has notable advantages such as short reaction times, green reaction conditions, high yields and simple workup and purification steps. Also, the novel nanocatalyst could be easily recovered using an external magnetic field and reused for six consecutive reaction cycles without significant loss of activity. The newly synthesized nanocatalyst was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller measurements.     

Green synthesis of silver nanoparticles using Eucalyptus comadulensis leaves extract and its immobilization on magnetic nanocomposite (GO-Fe3O4/PAA/Ag) as a recoverable catalyst for degradation of organic dyes in water

The magnetically recyclable graphene oxide-Fe₃O₄/polyallylamine (PAA)/Ag nanocatalyst was prepared via a green route using Eucalyptus comadulensis leaves extract as both reducing and stabilizing agent. The catalytic activity of this nanocatalyst was investigated for the reduction reaction of methylene blue and methyl orange in the presence of NaBH₄ in aqueous medium at room temperature. The prepared nanocatalyst was characterized by different methods such as Fourier transformed infrared spectroscopy, X-ray diffraction, scanning electron microscopy–energy dispersive X–ray spectroscopy, thermogravimetric analysis, vibrating sample magnetometer, transmission electron microscopy, and UV–visible spectroscopy. The results show that graphene oxide/PAA/Ag nanocatalyst has good activity and recyclability, and can be reused several times without major loss of activity in the reduction process. The apparent rate constants of the methyl orange (MO) and methylene blue (MB) were calculated to be 0.077 s⁻¹ (3 mg of catalyst) and 0.15 s⁻¹ (2 mg of catalyst), respectively.     

Synthesis,characterization and heterogeneous catalytic application of a nickel(II) Schiff base complex immobilized on MWCNTs for the Hantzsch four-component condensation

A nickel(II) Schiff base complex immobilized on multi-wall carbon nanotubes (MWCNTs) surface as a highly efficient heterogeneous catalyst was synthesized and characterized by IR, X-ray diffraction patterns, scanning electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma, elemental analysis, and thermal gravimetric analysis. Then a facile and environmentally benign procedure was developed for synthesis of polyhydroquinoline derivatives via Hantzsch one-pot condensation reaction of aromatic aldehydes, 1,3-diones, ethyl acetoacetate, and ammonium acetate in the presence of above synthesized catalyst under solvent-free conditions. This protocol has the advantages of stability, easy availability, recyclability and eco-friendly nature of catalyst, simple experimental and work-up procedure, and also high to excellent yields. Considering the solvent-free condition and also temperature, time, and yield of the model reaction, the nanocatalyst reported here is among the best catalysts reported so far for synthesis of polyhydroquinolines.