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. 2024 Jul 29;14:17401. doi: 10.1038/s41598-024-68316-8

Fe3O4@SiO2@NTMPThio-Cu: a sustainable and eco-friendly approach for the synthesis of heterocycle derivatives using a novel dendrimer template nanocatalyst

Sahar Peiman 1, Behrooz Maleki 1,✉
PMCID: PMC11286752  PMID: 39075155

Abstract

In this research, Fe3O4@SiO2@NTMPThio-Cu was introduced as a novel and green heterogeneous nanocatalyst with a dendrimer template that is environmentally friendly and reusable based on Fe3O4@SiO2. In this way, magnetic silica nanoparticles were first modified with cyanuric chloride, followed by melamine and thiosemicarbazide, and ultimately, it’s decorated with the cost-effective metal copper. The synthesized nanocatalyst was characterized by various analyses such as FT-IR, XRD, SEM, TGA, and EDX. The efficiency of Fe3O4@SiO2@NTMPThio-Cu was measured in one-pot synthesis of xanthene and spirooxindole-pyran derivatives under mild solvent-free conditions. High efficiency, excellent yield of products, mild reaction conditions, simple operation, no use of toxic organic solvents, and reusability of this catalyst increase the attractiveness of this technique for large-scale environmentally friendly operations.

Keywords: Green chemistry, Magnetic nanoparticles, Dendrimer, Spirooxindole-pyran, Xanthene

Subject terms: Environmental sciences, Chemistry, Nanoscience and technology

Introduction

The emphasis on advanced and green chemistry in trendy organic synthesis has increased significantly in the past few years, such as not utilizing hazardous or harmful reagents and solvents, using recyclable and inexpensive catalysts, and avoiding inappropriate reaction conditions. Through the years, there has been a growing interest in the use of environmentally friendly reagents or solvents, acceptable atom economy, and optimizing organic synthesis conditions to minimize energy consumption1,2.

Today, one of the greatest challenges in the industry or organic developments is finding ways to utilize clean and sustainable chemical technologies to produce beneficial chemicals. Including methods to achieve this important goal is to use stable catalysts that work in the green chemistry. Researchers’ investigation indicates that the use of heterogeneous catalysts in chemical industrial processes has gained a special place. These catalysts are environmentally friendly and help produce sustainable fuels and many essential chemicals1,3–6.

Nanotechnology is one of the most important parts of modern scientific fields. Nanoscience allows scientists in various fields like medicine, engineering, and chemistry to achieve significant progress in line with their goals at the molecular and cellular levels. In recent years, due to their unique size and high surface area, magnetic nanoparticles have found special applications in industry and the biological sciences, such as gene therapy, drug delivery, information storage, sensors, etc7–9.

Magnetic nanoparticles have been considered due to special features such as low toxicity, compatibility with the environment, cheapness of the surface that can be changed with different groups, and easy magnetic removal10–16. Magnetic resonance imaging, gene therapy, biosensors, and cancer treatment can be mentioned among the applications of magnetic nanoparticles. However, being in an acidic environment and air (oxidizing) causes a change in magnetic properties, followed by a reduction in the absorption capacity and its application range15,17–19. Stabilization of magnetic nanoparticles with the help of magnetic core–shells, which have the advantages of a core and a wide range of shells, is a suitable solution to overcome this limitation, and has attracted much attention in studies20–22. Silica is one of the best reagents because its surface contains hydroxyl functional groups, which can connect with various linkers. In addition, this composition has high compatibility and good stability23.

Dendrimers, which are a type of branched polymer composed of repeating units that extend outward from a central core, have gained popularity. Significant attention because of their high geometric symmetry controllable, molecular weight, and well-defined molecular structure. In addition to their water solubility, multivalency, and entrapment of hydrophilic drug molecules, dendrimers have been referred to as polymeric drug delivery systems24,25.

Thiosemicarbazide is a beneficial structural component that has the potential to perform chemical functions in biologically active molecules, and further investigation of this structure can lead to the discovery of a basis for a novel type of therapeutic agent. Research shows that their derivatives have antibacterial, anti-tumor, antifungal, and anti-seizure activities. On the other hand, they are also considered good antioxidants (Fig. 1). They are a special group of organic compounds that is known not only for its diverse biological activities but also as a metal chelating and anti-corrosion agent26–29.

Figure 1.

Figure 1

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Some thiosemicarbazide structures have biological properties.

Xanthenes are heterocyclic compounds. This group of organic compounds has a vast array of biological and medicinal properties, including anti-cancer, photodynamic therapy, antibacterial, antiviral, and anti-inflammatory30–33. Another type of heterocyclic compound that has superior biological and medicinal properties is spirooxindole-pyran. Among these properties are anti-bacterial, anti-microbial, anti-cancer, anti-tumor, anti-allergy, antimicrobial, and anti-HIV34–37 (Fig. 2).

Figure 2.

Figure 2

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Biologically active compounds with xanthene and spirooxindole skeletons.

Based on our previous research on the synthesis of catalysts and their application38–45, herein we have developed a novel strategy for the synthesis of a recyclable dendrimer-templated catalyst containing thiosemicarbazide coordinated with inexpensive copper metal. Then, to show its capability, we used the above catalyst in the synthesis of xanthene and spirooxindole-pyran derivatives.

Experimental

All chemicals were purchased from Merck and Sigma Aldrich and used without purification. X-ray diffraction (XRD) patterns were obtained using the Philips PW-1830. The Electro thermal 9100 apparatus was used to determine of melting points. Magnetic analysis curves were recorded using the VSM model MDKB from Danesh Pajohan Kavir Co. Kashan, Iran. The FT-IR Spectra were detected using the Shimadzu IR-470 spectrophotometer. The 1H and 13C spectra of the products were recorded with a Bruker DRX 400-Avance spectrometer. TEM images were obtained by TEM Philips EM-208S. The SEM images were recorded via a SEM VEGA3. The EDS analysis was done using MAP, LINE SCAN. Termogravimetric analysis (TGA) was recorded with TGA STA6000.

Preparation of Fe3O4@SiO2@Pr-NH2

The synthetic steps of Fe3O4@SiO2 were followed according to previously reported literature10. 2.5 ml of APTES were added to 1 g of Fe3O4@SiO2 which was subjected to ultrasonic waves in 30 ml of dry toluene. 24 h were spent stirring the mixture under reflux conditions. Finally, it was collected using an external magnetic field, washed with toluene and dried.

Preparation of Fe3O4@SiO2@NH2-TCT

1 g of the nanoparticle from the previous step was subjected to ultrasonic waves in dry THF (40 ml). In the next step, cyanuric chloride (TCT) (0.5 g) and Et3N (3 mmol) were added to it and stirred for 6 h at a temperature of 0–5 °C under nitrogen gas. Finally, the nanoparticles were separated with the help of the magnetic field and washed several times with THF.

Preparation of Fe3O4@SiO2@NH2-TCT-Mel

1 g of Fe3O4@SiO2@NH2-TCT nanoparticles were dispersed in 40 ml of dry THF. Then, 8 mmol of melamine and 1 ml of Et3N were separately dissolved in dry THF and slowly added to the reaction container containing nanoparticles. The solution was mechanically stirred at 0–5 °C for 5 h and 8 h at room temperature under a nitrogen atmosphere. Fe3O4@SiO2@NH2-TCT-Mel as separated using the magnet, washed with THF, and then dried.

Preparation of Fe3O4@SiO2@NH2-TCT-Mel-PrBr

1 g of Fe3O4@SiO2@NH2-TCT-Mel nanoparticles were dispersed in 30 ml of dry toluene. Then 6 ml of 1,3-dibromopropane and 0.1 g sodium iodide were added in a nitrogen atmosphere and refluxed for 30 h. After finishing the reaction, it was separated with a magnet, washed with ethyl acetate, and then dried.

Preparation of Fe3O4@SiO2@NH2-TCT-Mel-Pr-thiosemicarbazide-Cu(II) (Fe3O4@SiO2@NTMPThio-Cu)

1 g Fe3O4@SiO2@NH2-TCT-Mel-Pr was suspended in 50 ml of dry toluene and sonicated for 30 min. Following this, 1 g of thiosemicarbazide was dissolved in it and refluxed for 24 h. Eventually, the desired Fe3O4@SiO2-Pr-Thiosemicarbazide was separated using a strong magnet and washed several times with EtOH to leave only the thiosemicarbazide that had chemically bonded with the magnetic substrate. In the next step, 1 g of the catalyst and 6 mmol of Cu(OAc)2 in 50 ml of EtOH were placed under reflux conditions and stirred for 24 h. Finally, after separating the catalyst, it was washed several times with EtOH (Scheme 1).

Scheme 1.

Scheme 1

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Preparation of Fe3O4@SiO2@NTMPThio-Cu catalyst.

General procedure for the synthesis of xanthenes

A mixture of dimedone (2 mmol), and/or β-naphthol (2 mmol), aromatic aldehyde (1 mmol), and 15 mg Fe3O4@SiO2@NTMPThio-Cu in the solvent-free conditions and was stirred for 10 min at 25 °C. Following the reaction's completion (follow up with help from TLC), EtOH /H2O (1:1) was added to the reaction medium, and the catalyst was collected by the magnetic field. The solid product recrystallized from EtOH (Scheme 2).

Scheme 2.

Scheme 2

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Preparation of xanthenes in the presence of Fe3O4@SiO2@NTMPThio-Cu.

General procedure for the synthesis of spirooxindole-pyran derivatives (10a–t)

1 mmol of isatins, 1 mmol of malononitrile, 1 mmol of 1,3-dicarbonyl compounds, and 15 mg of Fe3O4@SiO2@NTMPThio-Cu were stirred at 25 °C under solvent-free conditions. After completing the reaction (which was monitored by TLC), EtOH was added to the mixture. After separating the catalyst, the products were purified in EtOH (Scheme 3).

Scheme 3.

Scheme 3

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Preparation of spirooxindole-pyran derivatives in the presence of Fe3O4@SiO2@NTMPThio-Cu.

Spectral data for selected products

Compound (4a) δH (400 MHz, CDCl3): 1.04 (s, 6H), 1.15 (s, 6H), 2.21 and 2.27 (ABq, 4H), 2.49 (s, 4H), 4.74 (s, 1H), 7.21–7.28 (m, 4H). δC (100 MHz, CDCl3): 27.5, 29.5, 32.6, 32.4, 40.9, 50.6, 115.6, 128.2, 129.8, 132.0, 142.4, 162.5, 196.3.

Compound (4d) δH (400 MHz, CDCl3): 1.00 (s, 6H), 1.16 (s, 6H), 2.18 and 2.31 (ABq, 4H), 2.52 (s, 4H), 4.86 (s, 1H), 7.49 (d, 2H), 8.15 (d, 2H,). δC (100 MHz, CDCl3): 27.4, 30.0, 32.3, 32.6, 41.0, 50.6, 111.0, 114.6, 123.5, 130.1, 147.4, 151.5, 163.0, 196.2.

Compound (5a) δH (400 MHz, CDCl3): 6.51 (s, 1H), 7.14 (d, 2H), 7.44–7.53 (m, 6H), 7.61–7.65 (m, 2H), 7.84 (d, 2H), 8.57 (d, 2H), 8.34 (d, 2H). δC (100 MHz, CDCl3): δ 37.4, 116.8, 118.2, 122.5, 124.4, 126.9, 128.7, 128.9, 129.1, 129.5, 131.1, 131.3, 132.1, 143.5, 148.7.

Compound (5c) δH (400 MHz, CDCl3): 2.15 (s, 3H), 6.47 (s, 1H), 6.99 (d, 2H), 7.26–7.43 (m, 4H), 7.49 (d, 2H), 7.60 (t, 2H), 7.78 (d, 2H), 7.85 (d, 2H), 8.43 (d, 2H). 13C NMR (CDCl3): 20.8, 37.6, 117.4, 118.0, 122.7, 124.2, 126.7, 128.1, 128.7, 129.1, 131.0, 131.4, 135.8, 142.1, 148.6.

Compound (5f) δH (400 MHz, CDCl3): 6.545 (t, 1H), 7.27 (t, 1H), 7.40–7.84 (m, 12 H), 8.30 (d, 2H), 8.43 (s, 1H). 13C NMR (CDCl3): 37.6, 115.8, 118.1, 121.6, 122.0, 122.7, 124.5, 127.2, 129.0, 129.4, 129.5, 131.0, 134.2, 146.9, 148.1, 148.7.

Compound (6b) δH (400 MHz, CDCl3): 0.98 (s, 3H), 1.16 (s, 3H), 2.29 and 2.35 (2H), 2.60 (s,), 5.70 (s, 1H), 7.15–7.19 (m, 2H,), 7.30–7.33 (m, 2H), 7.35 (d, 1H), 7.40–7.44 (m, 1H), 7.45–7.49 (m, 1H), 7.80–7.83 (m, 2H), 7.92 (d, 1H). δC (100 MHz, CDCl3): 27.2, 29.4, 32.3, 34.2, 41.6, 51.0, 114.0, 117.0, 123.45, 124.9, 127.2, 128.4, 128.5, 128.6, 130.1, 129.9, 131.3, 131.6, 132.0, 143.2, 147.8, 164.0, 197.0.

Compound (6d) δH (400 MHz, CDCl3): δ 0.99 (s, 3H), 1.18 (s, 3H), 2.26 and 2.39 (ABq, 2H), 2.74 (s, 2H), 5.85 (s, 1H), 7.40 (d, 1H), 7.42–7.51 (m, 2H), 7.60 (d, 2H), 7.84–7.89 (m, 3H), 8.09 (d, 2H). 13C NMR (100 MHz, CDCl3): 27.1, 31.1, 34.3, 36.1, 42.4, 52.0, 114.0, 116.2, 118.2, 123.3, 125.8, 126.6, 128.5, 129.9, 129.9, 131.2, 131.4, 146.8, 152.0, 164.3, 197.0.

Compound (10a) δH (400 MHz, CDCl3): 1.00 (s, 3H), 1.04 (s, 3H), 2.14 (q, 2H), 2.54 (d, 2H), 6.78 (d, 1H), 6.88 (t, 1H), 6.97 (d, 1H), 7.15 (t, 1H), 7.24 (s, 2H), 10.41 (s, 1H). δC (100 MHz, CDCl3): 28.4, 29.0, 32.4, 47.2, 50.4, 57.9, 109.6, 111.2, 117.7, 122.1, 123.4, 128.6, 134.8, 142.4, 159.2, 164.5,178.5, 195.3.

Compound (10f) δH (400 MHz, DMSO): δ 3.05 (s, 3H), 3.7 (s, 3H), 6.83 (d, 1H), 7.22 (d, 2H), 7.29 (s, 1H), 7.66 (s, 2H), 10.66 (s, 1H). δC (100 MHz, CDCl3,): 28.11, 29.81, 48.07, 57.43, 86.96, 111.13, 117.17, 124.52, 126.24, 128.82, 136.16, 141.50, 150.13, 152.70, 158.64, 159.98, 177.85.

Compound (10m) δH (400 MHz, DMSO): 6.87 (d, 1H), 6.95 (t, 1H), 7.22 (d, 2H), 7.51 (t, 1H), 7.55 (t,1H), 7.67 (s, 1H), 7.76 (t, 1H), 7.95 (d, 1H), 10.7 (s, 1H). δC (100 MHz, CDCl3): 20.15, 27.22, 36.73, 47.61, 57.25, 111.01, 111.70, 123.92, 126.08, 128.50, 137.03, 141.38, 159.18, 167.053, 178.40, 195.71.

Compound (10o) δH (400 MHz, DMSO): 1.87–198 (m, 2H), 2.25 (t, 2H), 2.66 (t, 2H), 6.81 (d, 1H), 7.15 (s, 1 H), 7.20 (d, 1H), 7.31 (s, 2H), 10.57 (s, 1H). δC (100 MHz, CDCl3): 20.15, 27.22, 36.73, 47.61, 57.25, 111.01, 111.70, 123.92, 126.08, 128.50, 137.03, 141.38, 159.18, 167.053, 178.40, 195.71.

Compound (10l) δH (400 MHz, DMSO): δ 2.74 (s,1H), 2.89 (s,1H), 6.81 (d, 1H), 7.22 (d, 1H), 7.39 (s, 1H), 7.49 (s, 2H), 10.67 (s, 1H). δC (100 MHz, CDCl3): 47.47, 57.19, 91.42, 111.12, 117.20, 124.84, 126.36, 128.91, 135.51, 141.50, 153.59, 158.72, 159.75, 174.53 and 177.56.

Ethical approval

This work does not contain any studies with human participants or animals performed by any of the authors.

Results and discussions

A rational design aimed at preparing a novel high-performance and recyclable dendrimer-templated nanocatalyst containing thiosemicarbazide is brought up (Scheme 1). First, magnetic nanoparticles were synthesized using the co-precipitation method, then they were covered with a coating of silica to protect and achieve a modifiable surface with spherical morphology. In the following step, the surface was modified with APTES, and after that, 1, 3-dibromopropane, cyanuric chloride, melamine, and thiosemicarbazide were placed in the last step. Then Cu metal was placed in suitable conditions to perform the preparation of xanthene and spirooxindole-pyran derivative reactions.

Functional groups in the catalyst synthesis periods were checked using FT-IR spectroscopy (Fig. 3). The peak in the region of 589 cm−1 is caused by the stretching vibration of the Fe–O bond. The formation of a Si–O–Si network with two peaks in the regions of 955 and 1094 cm−1 was determined, which indicates the formation of the surface silanol group (Si–OH). The peak at 1634 cm−1 is attributed to the N–H bending bond. The sight of distinguishable peaks at 2890 and 2918 cm−1 are relevant to the symmetric and asymmetric vibrations of the C–H groups of propyl carbon chains, respectively, which appear after the immobilization of APTES on Fe3O4@SiO2 (Fe3O4@SiO2@Pr-NH2 spectrum). The stretching vibration mode of C–N and C=N in triazine rings in cyanuric chloride and melamine is observed in the range of 1397–1778 cm (Fe3O4@SiO2@NH2-TCT, and Fe3O4@SiO2@NH2-TCT-Mel spectrums). The 3418 and 3469 cm−1 bands are due to the asymmetric and symmetric stretching vibrations of the N–H bonds of melamine (Fe3O4@SiO2@NH2-TCT-Mel spectrum). The CH2–Br bond bending appears in the region of 1167 cm−1 (Fe3O4@SiO2@NH2-TCT-Mel-PrBr), which proves the bond between melamine and 1,3-dibromopropane. The disappearance of this peak in Fe3O4@SiO2@NH2-TCT-Mel-Pr-Thiosemicarbazide indicates the successful bonding between thiosemicarbazide and Fe3O4@SiO2@NH2-TCT-Mel-PrBr. On the other hand, effective performance of Fe3O4@SiO2@NH2-TCT-Mel-PrBr as a result of thiosemicarbazide covalent binding of carbazide with IR absorption bands of 3177, 3264, and 3370 cm−1 due to the presence of the free NH2 group, also, the presence of C=S and C–N stretching bonds at 1283 and 1620 cm−1 was shown respectively (Thiosemicarbazide and Fe3O4@SiO2@NH2-TCT-Mel-Pr-Thiosemicarbazide-Cu(II) spectrums). The shifting of the peaks from 1395, 1620, 1656, 1777, 3177, and 3370 cm−1 to 1381, 1592, 1646, 1737, 3118, and 3310 cm−1 respectively, indicates the stabilization of copper metal (Fe3O4@SiO2@NH2-TCT-Mel-Pr-Thiosemicarbazide-Cu(II) spectrum).

Figure 3.

Figure 3

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FT-IR synthesis steps of Fe3O4@SiO2@NTMPThio-Cu.

The crystallinity of Fe3O4@SiO2@NTMPThio-Cu synthesis was investigated using XRD analysis (Fig. 4). The similar peaks in the synthesized catalyst compared to Fe3O4 show that the nanoparticles are nicely crystallized and its crystalline phase did not change during the synthesis step (2θ = 30.2, 36.6, 43.5, 53.8, and 62.5 were attribute to (220), (311), (400), (422), (511), and (440) reflections).

Figure 4.

Figure 4

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XRD patterns of the Fe3O4 and Fe3O4@SiO2@NTMPThio-Cu.

The thermal stability of Fe3O4@SiO2@NH2-TCT and Fe3O4@SiO2@NTMPThio-Cu was investigated through TGA analysis. The samples exhibit slight weight loss (below 150 °C), which is attributed to the removal of physically absorbed water molecules from the surface. The decrease in weight percentage is 37% and 40% for Fe3O4@SiO2@NH2-TCT and Fe3O4@SiO2@NTMPThio-Cu, respectively, which is due to the separation of different groups of NH2-TCT and NH2-TCT-Mel-Pr-Thiosemicarbazide-Cu(II) immobilized on the surface, which indicates the successful modification of Fe3O4@SiO2 (Fig. 5).

Figure 5.

Figure 5

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TGA thermograms of (A) Fe3O4@SiO2@NH2-TCT and (B) Fe3O4@SiO2@NTMPThio-Cu.

TEM and FE-SEM morphological examination shows that magnetic nanoparticles. By placing the silica layer and immobilizing the ligands on the substrate, they have a spherical structure with an average particle size of 25.5 nm. TEM images of Fe3O4@SiO2@NTMPThio-Cu show that the black spherical nanoparticles of Fe3O4 are covered by a layer of SiO2 and NH2-TCT-Mel-Pr-Tiosemicarbazide-Cu(II) (Figs. 6 and 7).

Figure 6.

Figure 6

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FE-SEM images of Fe3O4@SiO2@NTMPThio-Cu.

Figure 7.

Figure 7

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TEM images of Fe3O4@SiO2@NTMPThio-Cu.

The magnetic behavior of Fe3O4@SiO2@NTMPThio-Cu was measured at ambient temperature using VSM analysis. The magnetic properties of the synthesized Fe3O4 nanoparticles are 67.93 emu/g, while the saturation magnetization of Fe3O4@SiO2@NTMPThio-Cu is 37.24 emu/g, which shows that the catalyst has maintained its magnetic behavior (Fig. 8).

Figure 8.

Figure 8

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VSM spectra of Fe3O4 and Fe3O4@SiO2@NTMPThio-Cu.

In this manuscript, we have sought to utilize the fundamental property of copper metal on a dendrimer. Considering the advantages of employing heterogeneous catalytic systems, the synthesis of these systems is of great importance. To achieve this goal, it was necessary to select a suitable support and ligands for the desired outcome. Nano silica presents itself as an appropriate option due to the presence of suitable functional groups on its surface. After that, cyanuric chloride, followed by melamine and thiosemicarbazide were used to produce dendrimer template multi-branched grafts. Lastly, the copper metal complex was formed with the aid of the atoms in thiosemicarbazide. Moreover, for the purpose of facilitating the separation and reusability of the catalyst, the nanocatalyst was magnetized. This allowed for easy separation from the reaction environment through the use of an external magnetic field, enabling reusability in subsequent steps.

The synthesis reaction of xanthenes, and spirooxindole-pyrans in the presence of Fe3O4@SiO2@NTMPThio-Cu was chosen to show the catalytic activity (Schemes 2 and 3).

To detect the optimal conditions for synthesizing xanthenes, the reaction of β-naphthol (2 mmol) with benzaldehyde (1 mmol) was investigated as a model reaction in the presence of the catalyst. Initially, the reaction was carried out various solvents, including CH3CN, CH2Cl2, H2O, EtOH, and solvent-free conditions. It was shown that showed that the reaction proceeded with a higher yield under solvent-free conditions (Table 1, entries 1–5). In the next step, we measured the temperature conditions. Raising the temperature up to 25 °C had no result in increasing the product yields. Therefore, the temperature of 25 °C was selected as the optimal temperature (Table 1, entries 5–7). In the next step, different amounts of the catalyst were evaluated to obtain the optimal amount; increasing to 30 mg did not affect the efficiency of the catalyst (Table 1, entry 5 and entries 8–11). The reaction in catalyst-free conditions was associated with a negligible yield (Table 1, entry 12).

Table 1.

Synthesis xanthenes using Fe3O4@SiO2@NTMPThio-Cu.

Entry Catalyst (mg) Solvent Temp (°C) Time (min) Yield (%)
1 Fe3O4@SiO2@NTMPThio-Cu (15) EtOH 25 12 85
2 Fe3O4@SiO2@NTMPThio-Cu (15) CH2Cl2 25 12 60
3 Fe3O4@SiO2@NTMPThio-Cu (15) CH3CN 25 12 75
4 Fe3O4@SiO2@NTMPThio-Cu (15) H2O 25 12 80
5 Fe3O4@SiO2@NTMPThio-Cu (15) Solvent-free 25 12 97
6 Fe3O4@SiO2@NTMPThio-Cu (15) Solvent-free 40 12 97
7 Fe3O4@SiO2@NTMPThio-Cu (15) Solvent-free 60 12 97
8 Fe3O4@SiO2@NTMPThio-Cu (10) Solvent-free 25 12 90
9 Fe3O4@SiO2@NTMPThio-Cu (20) Solvent-free 25 12 97
10 Fe3O4@SiO2@NTMPThio-Cu (25) Solvent-free 25 12 97
11 Fe3O4@SiO2@NTMPThio-Cu (30) Solvent-free 25 12 97
12 – Solvent-free 25 12 Trace
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Reaction conditions: 2 mmol β-naphthol, 1 mmol benzaldehyde, in the presence of Fe3O4@SiO2@NTMPThio-Cu.

Significant values are in [bold].

After determining the optimal conditions, the catalyst's performance was assessed. Employing the reaction of aryl aldehydes, β-naphthol, and dimedone for the synthesis of xanthene derivatives in the vicinity of Fe3O4@SiO2@NTMPThio-Cu (Table 2). The obtained outcomes in Table 2 indicate that aldehydes that contain electron-withdrawing groups produce products with higher yields in a shorter time. On the other hand, in the aldehydes with electron-donating groups, the observations made showed the reaction yield was somewhat lower after relatively longer times.

Table 2.

Synthesis of derivatives 4a–f, 5a–f and 6a–d by Fe3O4@SiO2@NTMPThio-Cu.

Entry Product Time (min) Yield (%) MP °C [Refs.]
1 graphic file with name 41598_2024_68316_Figa_HTML.gif 12 97 207–20846
2 graphic file with name 41598_2024_68316_Figb_HTML.gif 10 98 232–23346
3 graphic file with name 41598_2024_68316_Figc_HTML.gif 15 98 230–23246
4 graphic file with name 41598_2024_68316_Figd_HTML.gif 20 92 229–23047
5 graphic file with name 41598_2024_68316_Fige_HTML.gif 20 94 252–25346
6 graphic file with name 41598_2024_68316_Figf_HTML.gif 25 96 166–16846
7 graphic file with name 41598_2024_68316_Figg_HTML.gif 20 96 286–28746
8 graphic file with name 41598_2024_68316_Figh_HTML.gif 60 92 155–15748
9 graphic file with name 41598_2024_68316_Figi_HTML.gif 50 92 151–15248
10 graphic file with name 41598_2024_68316_Figj_HTML.gif 12 96 284–28546
11 graphic file with name 41598_2024_68316_Figk_HTML.gif 10 98 284–28546
12 graphic file with name 41598_2024_68316_Figl_HTML.gif 10 96 296–29846
13 graphic file with name 41598_2024_68316_Figm_HTML.gif 10 96 29649
14 graphic file with name 41598_2024_68316_Fign_HTML.gif 10 96 316–31846
15 graphic file with name 41598_2024_68316_Figo_HTML.gif 15 92 220–22150
16 graphic file with name 41598_2024_68316_Figp_HTML.gif 15 90 202–20446
17 graphic file with name 41598_2024_68316_Figq_HTML.gif 20 90 215–21646
18 graphic file with name 41598_2024_68316_Figr_HTML.gif 20 98 176–17746
19 graphic file with name 41598_2024_68316_Figs_HTML.gif 20 96 199–20151
20 graphic file with name 41598_2024_68316_Figt_HTML.gif 20 96 175–17646
21 graphic file with name 41598_2024_68316_Figu_HTML.gif 22 88 163–16546
22 graphic file with name 41598_2024_68316_Figv_HTML.gif 90 80 17152
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Reaction conditions: solvent-free conditions, aldehydes: dimedone or β-naphthol (1:2 or 2 mmol), 15 mg Fe3O4@SiO2@NTMPThio-Cu.

Following that, to determine the optimal conditions in the synthesis of spirooxindole-pyran derivatives, malonitrile (1 mmol), dimedone (1 mmol), and isatin (1 mmol) were selected as model reactions. First, the reaction in the adjacency of Fe3O4@SiO2@Mel-Rh-Cu was experimented with in different solvents, including CH3CN, THF, H2O, EtOH, and solvent-free conditions. According to the obtained data, the highest efficiency obtained in 4 min (98% yield) was achieved in solvent-free conditions (Table 3, entries 1–5). Furthermore, no significant change in the product yield was observed when the temperature was increased to 60 °C (Table 3, entries 5–7). In addition, raising the amount of the catalyst from 10 to 15 mg increased the yield from 92 to 98%, but the reaction yield did not change with a further increase in the amount of the catalyst (Table 3, entry 5, and entries 8–10). The model reaction was not efficient in the absence of the catalyst, and in the presence of Fe3O4@SiO2 and Fe3O4@SiO2@NH2-TCT-Mel, it was associated with a lower efficiency than the catalyst Fe3O4@SiO2@Mel-Rh-Cu (Table 3, entry 5, and entries 11–13).

Table 3.

Synthesis spirooxindole-pyran using Fe3O4@SiO2@NTMPThio-Cu.

Entry Catalyst (mg) Solvent Temp (°C) Time (min) Yield (%)
1 Fe3O4@SiO2@NTMPThio-Cu (15) EtOH 25 4 98
2 Fe3O4@SiO2@NTMPThio-Cu (15) THF 25 4 75
3 Fe3O4@SiO2@NTMPThio-Cu (15) CH3CN 25 4 65
4 Fe3O4@SiO2@NTMPThio-Cu (15) H2O 25 4 95
5 Fe3O4@SiO2@NTMPThio-Cu (15) Solvent-free 25 4 98
6 Fe3O4@SiO2@NTMPThio-Cu (15) Solvent-free 40 4 98
7 Fe3O4@SiO2@NTMPThio-Cu (15) Solvent-free 60 4 98
8 Fe3O4@SiO2@NTMPThio-Cu (10) Solvent-free 25 4 92
9 Fe3O4@SiO2@NTMPThio-Cu (20) Solvent-free 25 4 98
10 Fe3O4@SiO2@NTMPThio-Cu (25) Solvent-free 25 4 98
11 Fe3O4@SiO2 Solvent-free 25 4 30
12 Fe3O4@SiO2@NH2-TCT-Mel Solvent-free 25 4 88
13 – Solvent-free 25 4 –
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Reaction conditions: benzaldehyde (1 mmol), malononitrile (1 mmol) and isatin (1 mmol).

Significant values are in [bold].

To expand the reaction scope, we operated Fe3O4@SiO2@NTMPThio-Cu as a catalyst in the multicomponent reaction of, malononitrile, isatin derivatives, and 1,3-dicarbonyl compounds. The results showed that the products were achieved with excellent efficiency after a short period of reaction time (Table 4).

Table 4.

Synthesis spirooxindole-pyran by Fe3O4@SiO2@NTMPThio-Cua.

Entry Product Time (min) Yield (%) MP °C [Refs.]
1 graphic file with name 41598_2024_68316_Figw_HTML.gif 12 97 287–28853
2 graphic file with name 41598_2024_68316_Figx_HTML.gif 10 98 29053
3 graphic file with name 41598_2024_68316_Figy_HTML.gif 15 98 29754
4 graphic file with name 41598_2024_68316_Figz_HTML.gif 20 92 28554
5 graphic file with name 41598_2024_68316_Figaa_HTML.gif 20 94 229–23055
6 graphic file with name 41598_2024_68316_Figab_HTML.gif 25 96 22356
7 graphic file with name 41598_2024_68316_Figac_HTML.gif 20 96 30055
8 graphic file with name 41598_2024_68316_Figad_HTML.gif 12 96 294–29657
9 graphic file with name 41598_2024_68316_Figae_HTML.gif 10 98 25458
10 graphic file with name 41598_2024_68316_Figaf_HTML.gif 10 96 30659
11 graphic file with name 41598_2024_68316_Figag_HTML.gif 10 96 30560
12 graphic file with name 41598_2024_68316_Figah_HTML.gif 10 96 30060
13 graphic file with name 41598_2024_68316_Figai_HTML.gif 15 92 29758
14 graphic file with name 41598_2024_68316_Figaj_HTML.gif 15 90 29261
15 graphic file with name 41598_2024_68316_Figak_HTML.gif 20 90 225–22762
16 graphic file with name 41598_2024_68316_Figal_HTML.gif 20 98 26062
17 graphic file with name 41598_2024_68316_Figam_HTML.gif 20 96 27961
18 graphic file with name 41598_2024_68316_Figan_HTML.gif 20 96 275–27863
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In the previous literature, numerous catalysts have been used in the synthesis of xanthene and spirooxindole-pyran derivatives. In continuation, the performance of the synthesized catalyst was assessed by comparing it to other catalysts in model reactions (Table 5). As shown, Fe3O4@SiO2@NTMPThio-Cu gave the best yield in the shortest reaction time under solvent-free conditions at 25 °C.

Table 5.

Catalyst comparison of Fe3O4@SiO2@NTMPThio-Cu and other catalysts.

Sample Conditions Time Yield (%)
graphic file with name 41598_2024_68316_Figao_HTML.gif This research/solvent free/25 °C 12 min 98
Amberlyst-15/C2H4Cl2/Reflux64 2 93
Silica-supported HBF4/no solvent/125 °C65 h 98
SBA-15/SO3H/C2H4Cl2/85 °C66 30 min 95
Cellulose sulphate/no solvent/100–110 °C67 24 h 97
SiO2–Cl/no solvent/110 °C68 1 h 93
Potassium aluminum sulfate/H2O/110 °C69 3 h 90
H5PW10V2O40/no solvent/100 °C70 3 h 98
graphic file with name 41598_2024_68316_Figap_HTML.gif This research /solvent free/25 °C 4 min 98
L-proline/H2O/80 °C57 20 min 94
W6O19/MS/EtOH/80 °C71 120 min 95
NiO@g-C3N4/ETOH/80 °C72 20 min 95
Magnesia/H2O/80 °C73 120 min 95
PSGO-Fe3O4/H2O/80 °C74 120 min 96
Silica sulfuric acid NPs/EtOH/80 °C75 30 min 96
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The synthetic mechanism of xanthenes and spirooxindole-pyran derivatives is given in Schemes 4 and 5.

Scheme 4.

Scheme 4

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Synthetic mechanism of xanthene derivatives.

Scheme 5.

Scheme 5

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Synthetic mechanism of spirooxindole-pyran derivatives.

Synthetic mechanism of xanthene derivatives: At first, by activating the carbonyl group, the catalyst makes aldehydes more sensitive to nucleophilic attack by dimedone to form intermediate (A), in the next step, another molecule of dimedone is added by Michael to form intermediate (B). By eliminating H2O and intramolecular cyclization, it leads to the production of the desired product (Scheme 4).

The possible route for synthesizing spirooxindole-pyran in the presence of Fe3O4@SiO2@NTMPThio-Cu is shown in Scheme 5. First, carbonyl functional groups are activated by copper (II) ions in the catalyst, and condensation reactions are facilitated. The carbonyl group in isatin can be activated by Fe3O4@SiO2@NTMPThio-Cu, and nucleophilic attack by CH malononitrile acid group with knoevenagel condensation and intermediate (A) is obtained. Then, by the addition of Michael by dimedone and enolization, intermediate (B) is formed. Finally, the desired product is obtained by nucleophilic attack through oxygen to the nitrile group and tautomerization.

Recycling of catalyst

One of the major challenges faced by chemists involved in catalyst synthesis is to ensure that the catalysts can be reused. Therefore, researching about this great issue is inevitable. In this experiment, after separating the catalyst, we washed it with EtOH and dried it for reuse. Studies have shown that at least eight steps can be performed using this catalyst without much change in performance (Fig. 9). Also, for further study, FE-SEM image, FT-IR spectrum, and XRD patterns have been checked after 8 recycling cycles, which do not show any significant difference. (Fig. 10).

Figure 9.

Figure 9

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Recyclability of the catalyst in xanthene and spirooxindole-pyran synthesis model reaction.

Figure 10.

Figure 10

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FE-SEM, FTIR spectra, and XRD patterns after recycling.

Examination of the possible leaching of copper nanoparticles from the nanocatalyst on the model reactions was also analyzed. The consequences of ICP-OES analysis indicated that the amount of Cu leaching in the catalyst after 7 recycling steps is 4.5% by weight, which is very insignificant considering the loading of Cu in the fresh catalyst, which is 4.9% by weight. These evidences demonstrate the heterogeneous nature and suitable stability of the catalyst.

Conclusion

In order to create green nanocatalysts that are high-performing, environmentally friendly, reusable, and recyclable for a minimum of 8 consecutive cycles without a considerable loss of activity, we have successfully synthesized a novel and stable pseudo-dendrimeric magnetic core–shell catalyst. The catalyst was identified using different analytical methods. The performance of Fe3O4@SiO2@NTMPThio-Cu was investigated in the green synthesis of xanthene and spirooxindole-pyran derivatives. The above-developed method has several advantages, such as ease of magnetic separation, reusability, short reaction time, excellent product yield, mild reaction conditions, an easy working method, and the use of inexpensive copper metal.

Acknowledgements

This study was supported by a research grant (Number 33/38554) from the University of Mazandaran.

Author contributions

Writing: S.P.; B.M. Conceptualization: S.P.; B.M. Data curation: S.P.; B.M. Formal analysis: S.P.; B.M. Project administration: S.P.; B.M. Methodology: S.P.; B.M. Validation: S.P.; B.M. Review and editing: S.P.; B.M. All authors reviewed the manuscript.

Data availability

The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Competing interests

The authors declare no competing interests.

Footnotes

Publisher's note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

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