Abstract
At first, an organometallic catalyst namely, Pd-DPyE@MCM-41@MNP was prepared through magnetic (Fe3O4) nanoparticles-doped into channels of mesoporous silica MCM-41 and then, anchoring a novel complex composed of di(4-pyridyl)ethylene and palladium on the inner surface of the support. This immobilized catalyst was successfully identified via VSM, ICP-OES, TEM, FTIR, TGA, SEM, BET, XRD, EDX and elemental mapping analyses. After that, it was used as a versatile, heterogeneous, and magnetically reproducible catalyst in the generation of N,N′-alkylidene bisamides (1a-13a, 8–20 min, 90–98%, 50 °C, solvent-free) and Suzuki–Miyaura coupling (SMC) reaction derivatives (1b-26b, 10–140 min, 86–98%, 60 °C, PEG-400). The VSM plot of Pd-DPyE@MCM-41@MNP displays that this nanocatalyst can be easily recycled by applying an external magnetic field. In both synthetic paths, this nanocatalyst was reused at least seven times without palladium leaching and significantly reducing its catalytic performance. Also, stability and heterogeneous nature of catalyst were approved via ICP-OES technique and hot filtration test.
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Introduction
Nanocatalysts have gained significant attention in organic reactions due to their unique properties and enhanced catalytic performance compared to traditional catalysts1,2,3. They offer various applications and advantages in organic reactions, including increased activity, selectivity, and efficiency1,2,3. Their unique properties and versatility make them promising candidates for advancing various branches of organic chemistry and enabling more sustainable and efficient chemical processes1,2,3.
In recent years, organometallic catalysis has become a powerful tool in various chemical transformations3,4. In organometallic catalysis, the metal centers in the catalyst are crucial role in facilitating and controlling chemical reactions3,4. These metal centers can be transition metals like Pd, Pt, Ni, or non-transition metals such as Mg, Zn, etc. The organic ligands attached to the metal in the catalyst also contribute to its reactivity and selectivity5,6,7,8. Organometallic catalysis finds applications in various fields, including pharmaceuticals, agrochemicals, materials science, and more9,10,11,12. It enables the synthesis of complex and structurally diverse compounds that may be challenging to access through traditional organic synthesis methods. The use of support materials, such as MCM-41, is crucial in preparing organometallic catalysts. Using a support material like MCM-41 helps to enhance the stability of the catalyst13,14,15. The support acts as a protective matrix, preventing the aggregation or decomposition of the active metal species16. This stability allows for extended catalyst lifetimes and better control over catalytic reactions. In the realm of catalysis, the concept of a support material acting as a protective matrix refers to how the support physically surrounds and stabilizes the active metal species, shielding it from adverse conditions and interactions that could degrade its performance. This protective matrix helps maintain the integrity and activity of the catalyst. Zeolites, activated carbon, metal–organic frameworks (MOFs), silica supports, alumina supports, and MCM-41 are examples of supports acting as protective matrices in catalysis. In these examples, the supports function as protective matrices by encapsulating, stabilizing, and preventing the aggregation or degradation of active metal species, ultimately contributing to the efficiency and durability of the catalyst system17,18,19,20,21,22,23.
MCM-41 and other mesoporous supports have a high surface area and well-defined porous structure24,25,26. This feature provides many accessible active sites for the metal catalyst, increasing the overall catalytic activity. The high surface area also allows for better dispersion of metal complexes, ensuring greater reactant exposure and improving reaction rates. The incorporation of magnetic components into MCM-41 nanoparticles adds magnetic properties to the material, enabling the particles to respond to external magnetic fields16,24,25,26.
Organometallic catalysts are widely used in various organic transformations, including the generation of carbon–carbon, carbon–nitrogen, carbon–oxygen, and carbon–sulfur bonds16. The remarkable development in this field is due to the importance of such links in the framework of important pharmaceutical, chemical and industrial compounds16,27,28,29,30. In these transformations, palladium is a multipurpose catalyst, and its vital role in all kinds of coupling reactions, oxidation and reduction and multi-component or domino reactions is mentioned in the literature16,27,28,29,30. In this work, with the help of a palladium-based catalytic system, the pseudo three-component synthesis of N,N′-alkylidene bisamides and Suzuki–Miyaura Coupling (SMC) reaction derivatives has been investigated. N,N′-alkylidene bisamides, mainly produced via the condensation of aryl aldehydes (1 mmol) with primary amides (2 mmol), are versatile compounds with considerable potential in various fields31,32,33,34,35,36,37. Their diverse biological activities and synthetic accessibility make them attractive targets for medicinal and organic chemists, since they can exhibit diverse biological activities, including antimicrobial, antitumor, anti-inflammatory, and enzyme-inhibitory properties. Their activity is often linked to their ability to interact with specific protein targets, modulating biochemical pathways and cellular processes38,39,40,41,42,43,44. Besides, the SMC reaction is one of the most efficient and general organic transformations for producing herbicides, drugs, liquid crystals, polymers, catalyst ligands, natural products, and modern materials45,46. Conventionally, carbon–carbon coupling is performed in the presence of transition metal complexes comprising organic ligands in organic solvents at high temperatures47. Nevertheless, there are several problems on the way to produce these SMC derivatives. First and foremost, the organic solvents used may cause irreparable environmental challenges due to their noxiousness, and reactions performed under harsh temperature conditions certainly consume more energy48. In the second place, the most frequent catalytic systems are promoted for the carbon–carbon coupling reaction with homogeneous palladium complexes with ligands e.g., carbenes, dibenzylideneacetone, and phosphine, which are expensive to prepare and sensitive to humidity and air. Furthermore, reusing catalysts with such ligands is difficult and has harmful environmental consequences49,50. Long reaction times, use of high amounts of metal precursors, difficult separation and purification of products, low yields of products, hard work-up and lack of proper reproducibility of the catalysts used are other problems in this field51,52,53,54,55,56,57,58,59.
According to the above points, in this work, an organometallic catalyst based on palladium supported in the mesoporous channels of MCM-41 magnetic (Fe3O4) nanoparticles named Pd-DPyE@MCM-41@MNP was designed, produced, and identified. It was used for the rapid production of N,N′-alkylidene bisamides through the reaction of 1 mmol aldehydes with 2 mmol primary amides, and also the synthesis of SMC derivatives via the reaction of 1 mmol (hetero)aryl halides with 1 mmol benzeneboronic acid under eco-friendly and moderate conditions.
Experimental
Materials and devices
Explanations related to the specifications of raw materials and devices are provided in the supplementary material file.
Production of the nanocatalyst
At first, MCM-41@MNP substrates were produced through doping magnetic (Fe3O4) nanoparticles (MNPs) into the mesoporous channels of silica. To this end, nude MNPs were produced by chemical co-precipitation approach in a basic solution of Fe3+ and Fe2+ ions at 80 °C according to the procedure mentioned in the literature60. MNPs (2 g) were dispersed in 30 mL H2O via ultrasonication within 30 min, and then 150 mL EtOH was added to the resulting mixture and stirred at room ambient. Next, PEG (5.36 g), TEOS (2 mL) and 10 mL of ammonia solution (28 wt%) were added to the resulting suspension with stirring, and it was stirred at ambient temperature for 30 h until NMPs were coated with MCM-41. The acquired MCM-41@MNP was cleaned with distilled H2O and EtOH, and it was dried at 25 °C. Subsequently, MCM-41@MNP in a mixture of 30 mL deionized water, 20 mL ethanol, 0.15 g CTAB, and 0.6 mL ammonia solution was dispersed, and stirred for 30 min at 25 °C. Following, 0.4 g TEOS was slowly added to the resulting mixture and stirring was continued for another 5 h. The residual solids were cleaned with deionized water and ethanol, and dried at 80 °C under vacuum conditions (10 h). To eliminate the CTAB template, 5 mL hydrochloric acid (2 mol/L) and 100 mL EtOH were added to the acquired composite (0.1 g) and the resulting mixture was stirred at 25 °C for 24 h. The remaining products (i.e., MCM-41@MNP) were cleaned by a mixture of H2O and EtOH and separated via magnetic decantation.
The achieved MCM-41@MNP (1.5 g) was dispersed in 40 mL n-hexane via ultrasonication, then 2.5 mL CPTMS ((3-chloropropyl)trimethoxysilane) was added to this mixture, and stirred for 5 h in N2 at 40 °C. Then, the acquired nPr-Cl@MCM-41@MNP was cleaned with EtOH (4 × 5 mL), and isolated by magnetic decantation. At 50 °C, nPr-Cl@MCM-41@MNP was dried. At the next stage, 1 g of nPr-Cl@MCM-41@MNP was dispersed in 50 mL toluene through sonication for 20 min, and 2.5 mmol di(4-pyridyl)ethylene was added to the reaction mixture and stirred under reflux conditions in N2 for 12 h. Then, the acquired nanoparticles (DPyE@MCM-41@MNP) were cleaned with EtOH (3 × 5 mL) and dried at 50 °C after separation by magnetic decantation. The produced DPyE@MCM-41@MNP (1 g) in 25 mL toluene was dispersed using sonication (30 min), and 0.50 mmol Pd(OAc)2 was added to the mixture, and then stirred for 12 h at 80 °C. Next, the 0.6 mmol NaBH4 was added to the obtained mixture and stirred (2 h). In the last step, the final product (Pd(0)-DPyE@MCM-41@MNP) was detached via magnetic decantation, washed several times with ethanol and dried at ambient temperature (Scheme 1).
Production steps Pd-DPyE@MCM-41@MNP.
General path for the synthesis of N,N′-alkylidene bisamides catalyzed by Pd-DPyE@MCM-41@MNP
In the absence of a solvent at a temperature of 50 °C, a mixture containing 10 mg Pd-DPyE@MCM-41@MNP (2.5 mol%), 2 equivalent amide and 1 equivalent aldehyde were heated till the reaction was finished via TLC monitoring. Upon completion of the reaction, the cooled reaction mixture was diluted with 10 mL of ethanol, and the catalyst was isolated via simple filtration technique along with the utilization of an external magnetic field and was cleaned by ethanol (2 × 5 mL) and ethyl acetate (2 × 5 mL), and dried for use in the next run. Finally, to give pure products, the solvent was evaporated and the residue was recrystallized in ethanol (95%).
General route for SMC reaction catalyzed by Pd-DPyE@MCM-41@MNP
In a flask at a temperature of 60 °C in PEG-400 solvent (2 mL), a mixture of 6 mg Pd-DPyE@MCM-41@MNP (1.50 mol%), 1 equivalent aryl halide (or heteroaryl halide), 1 equivalent benzeneboronic acid and 3 equivalents sodium carbonate were stirred till the reaction was finished via TLC monitoring. Upon completion of the reaction, the catalyst was recovered by simple filtration technique along with the application of an external magnetic field. It was cleaned with ethanol (2 × 5 mL) and ethyl acetate (2 × 5 mL), and dried for employ in the next cycle. Then, the reaction mixture using diethyl ether and water (3 × 5 mL) was extracted and, organic layer with 1.5 g of Na2SO4 was dried. Finally, derivatives of SMC reaction were generated with suitable efficiency after evaporation of the solvent.
Ethics approval and consent to participate
The author’s declare that the paper is not be submitted simultaneously to another journal. The submitted work is original and has not been published elsewhere in any form or language, and the authors have no conflict of interest regarding this manuscript. The authors agree to participate in submitting our manuscript to this journal, and agree to the publication of our research data in this journal.
Results and discussion
As part of our continuing research effort to create novel synthetic techniques, after successfully fabricating the catalyst, we examined the surface morphology using SEM and TEM images (Figs. 1 and 2). The SEM images (Fig. 1a,b), of the synthesized Pd-DPyE@MCM-41@MNP showed that the catalyst was uniformly smaller than 60 nm in size. The majority of the particles share the same quasi-spherical form. Moreover, the particle size distribution of the Pd-DPyE@MCM-41@MNP revealed that these nanoparticles have a size in the range of 15–85 nm and a mean diameter of 53.16 nm (Fig. 1c).
The FE-SEM images (a, b) and particle size distribution (c) of Pd-DPyE@MCM-41@MNP.
The TEM images (a, b) of Pd-DPyE@MCM-41@MNP.
The TEM images of the Pd-DPyE@MCM-41@MNP nanoparticles demonstrated the formation of Pd nanoparticles with almost spherical shape on the modified MCM-41@MNP nanoparticles surfaces (Fig. 2a,b). The little black patches in the image might be ascribed to local Pd concentrations, most likely found in the channels (Supplementary Fig. S1).
Energy-dispersive X-ray spectroscopy (EDX) was used to analyze the presence of different elements in the produced sample. As demonstrated in Fig. 3, the presence of Pd, Fe, N, C, Si, O and Cl species in the EDX analysis of this synthesized catalyst supported the immobilization of Pd complex on MCM-41@MNP. Furthermore, the elemental mapping analysis confirms the findings of the EDS investigation. As illustrated in Fig. 4, the elemental mapping analysis revealed a homogenous distribution of all components. Also, the exact amount of Pd immobilized on DPyE@MCM-41@MNP per gram of the catalyst was achieved by inductively coupled plasma atomic emission spectroscopy (ICP-OES) and found to be 2.500 × 10−3 mol g−1.
EDX pattern of Pd-DPyE@MCM-41@MNP.
Elemental mapping images of Pd-DPyE@MCM-41@MNP.
In Fig. 5, the FT-IR spectra of MCM-41@MNP (a), nPr-Cl@MCM-41@MNP (b), DPyE@MCM-41@MNP (c), and Pd-DPyE@MCM-41@MNP (d), are shown, and the results are compiled in Table 1. According to these findings, the catalyst components are connected to each other and the desired skeleton is formed (i.e., Pd-DPyE@MCM-41@MNP). It should be noted that the palladium linking to DPyE@MCM-41@MNP was approved by the change of C=N vibration stretching in Pd-DPyE@MCM-41@MNP (1663 cm−1), to a lower wavenumber compared to DPyE@MCM-41@MNP (1669 cm−1), that is the cause for this shift is the coordination of palladium to DPyE onto functionalized MCM-41@MNP16,61.
FT-IR spectra of MCM-41@MNP (a), nPr-Cl@MCM-41@MNP (b), DPyE@MCM-41@MNP (c), and Pd-DPyE@MCM-41@MNP (d).
The magnetic characteristics of MCM-41@MNP and Pd-DPyE@MCM-41@MNP were studied using the VSM method. Pd-DPyE@MCM-41@MNP has a lower magnetic value than MCM-41@MNP, as seen in Fig. 6a,b. This is because organic molecules and complex palladium protect the MCM-41@MNP surface. However, its magnetic property was such that it was easily separated from the reaction mixture by magnetic decantation during the separation process.
Magnetic patterns of MCM-41@MNP (a) and Pd-DPyE@MCM-41@MNP (b).
The nitrogen adsorption-desorptions of MCM-41@MNP and Pd-DPyE@MCM-41@MNP are depicted in Fig. 7a,b. The samples have the form of type IV curves, which are typical of mesoporous materials (according to the IUPAC classification). For MCM-41@MNP and Pd-DPyE@MCM-41@MNP, the corresponding Brunauer–Emmett–Teller (BET) surface areas are 529.8 and 367.2 m2/g, respectively. Pd-DPyE@MCM-41@MNP has a smaller surface area than MCM-41@MNP. This can be conveniently attributed to grafting organic materials and anchoring Pd-complex onto MCM-41@MNP mesoporous channels. Table 2 provides an overview of the samples characteristics, which agrees with the literature62.
Nitrogen adsorption–desorption isotherms of MCM-41@MNP (a) and Pd-DPyE@MCM-41@MNP (b).
Figure 8 displays the TGA diagram of Pd-DPyE@MCM-41@MNP. This curve illustrates a little weight loss in the low-temperature region (below 200 °C) of exactly 6.11%. The elimination of solvents that have been adsorbed is reflected in this weight loss. Also, the catalyst TGA diagram revealed a 13.91% weight loss in the 200–600 °C range, which is associated with the immobilized organic layers on MCM-41@MNP.
TGA analysis of Pd-DPyE@MCM-41@MNP.
The wide-angle XRD spectra of MCM-41@MNP and Pd-DPyE@MCM-41@MNP in an extent of 2θ = 10–80° are depicted in Fig. 9a,b, respectively. In these spectra, the diffraction lines with Bragg angles at 62.72° (440), 57.01° (511), 52.88° (422), 43.22° (400), 35.23° (311), and 30.50° (220) represent the crystalline phase of iron magnetic nanoparticles63. The agreement of these findings with the standard pattern of MNPs indicates the fact that no change in the crystalline phase of MNPs occurred during the modification of MCM-41@MNPs. Moreover, the presence of a set of peaks with Bragg angles of 68.01° (220), 46.29° (200), and 40.09° (111) prove that Pd(0) was doped into the mesoporous channels of MCM-41@MNP (Fig. 9b)64. Meanwhile, the wide graph of 2θ at 20–29° degrees is correlated the silica framework in the catalyst body65.
The wide-angle XRD patterns of MCM-41@MNP (a) and Pd-DPyE@MCM-41@MNP (b).
Figure 10 displays the small angle XRD patterns of MCM-41@MNP (a) and Pd-DPyE@MCM-41@MNP (b) to reflect the mesoporous nature of the catalyst. In this figure, the pattern of MCM-41@MNPs demonstrated a fierce peak with Bragg angles at 2θ = 2.28°, that is associated with the uniformity of mesoporous channels of MCM-41. The mentioned reflection became weaker after the creation of organic substrates and the anchoring of palladium particles on the channels 66.
Small angle XRD patterns of MCM-41@MNP (a) and Pd-DPyE@MCM-41@MNP (b).
Evaluation of catalytic performance Pd-DPyE@MCM-41@MNP
In this section, the performance of palladium anchored organometallic catalyst on MCM-41@Fe3O4 substrate was evaluated in the synthesis of N,N′-alkylidene bisamide derivatives and then in the production of biphenyl derivatives through SMC reaction.
In the first part of this study, to evaluate the optimal conditions for the production of N,N′-alkylidene bisamide, the condensation of 1 equivalent 3-nitrobenzaldehyde and 2 equivalents benzamide was picked as the benchmark reaction (Scheme 2), and the impact of the nature of the solvent (using solvents e.g., H2O, Toluene, EtOH, THF, CH3CN, CHCl3 and EtOAc) (Table 3, entries 2–8), the type and amount of catalyst (by screening 5, 10 and 15 mg of Pd-DPyE@MCM-41@MNP, and also utilizing its components as catalyst) (Table 3, entries 11–13), and also the temperature (in the range of 25–130 °C) on its yield and time were systematically investigated. The findings were tabulated in Table 3. The comparison of the results revealed that the optimal state was obtained in solvent-free conditions using 10 mg of Pd-DPyE@MCM-41@MNP at 50 °C. It should be noted that the reaction failed under harsh circumstances in the absence of a catalyst at 130 °C (Table 3, entry 2).
Benchmark reaction for the production of N,N′-alkylidene bisamides.
Next, various derivatives of N,N′-alkylidene bisamides were fabricated via the condensation of acetamide (or benzamide) with aryl aldehydes in the best circumstances (Table 4, 1a-13a). As the data in Table 4 reflected, the desired structures were synthesized in short times (8–20 min) with high efficiency (90–98%), using a variety of benzaldehyde derivatives substituted in different positions with aromatic ring activating and aromatic ring deactivating groups. The findings confirmed the wide range and effective performance of Pd-DPyE@MCM-41@MNP to catalyze the aforementioned condensation.
Scheme 3 proposes a reasonable mechanism based on existing literature36. Pd-DPyE@MCM-41@MNP starts the process of activating aldehydes. Intermediate I is created by adding amides to an activated aldehyde and removing H2O. When a second amide molecule is added nucleophilically to activated intermediate I, symmetrical N,N′-alkylidine bisamide products are formed.
Possible mechanism of the synthesis of symmetrical N,N′-alkylidine bisamide.
In the second step of this study, in order to preliminary screening of the reaction, the SMC reaction of 1 equivalent 4-methoxy iodobenzene (4b) with 1 equivalent benzeneboronic acid was considered as a benchmark (Scheme 4), for optimizing the reaction factors e.g., base, solvent, amount of catalyst and temperature (Table 5). Monitoring the effects of temperature in the range of 25–70 °C in various solvents (including EtOH, PEG-400, CH3CN, DMF and DMSO) displayed that by taking into account the criteria of green chemistry in the discussion of energy adjustment, the optimal temperature for the reaction progress was 60 °C in PEG-400 (Table 5, entry 2 vs. entries 13–15); because at a temperature of 70 °C, the efficiency of the desired derivative did not increase clearly compared to the temperature of 60 °C, and also at ambient temperature and 50 °C, the yield of the desired product dropped clearly. In the continuation of the benchmark reaction screening using various kinds bases such as Na2CO3, NaHCO3, DABCO and KOH (Table 5, entries 2–5), it has shown that with the help of Na2CO3, the catalyst has the highest performance and the highest yield of the coupled product is obtained. Furthermore, additional experiments proved that the amount of 6 mg of catalyst was adequate to ensure a clean and complete transformation (Table 5, entry 2). Once the amount was decreased to 3 mg, the efficiency reduced to 79% in 50 min (Table 5, entry 7). On the other hand, utilizing 9 mg of catalyst did not considerably increase the efficiency (Table 5, entry 8). These observations showed that it is necessary to use the appropriate base and temperature for this catalytic transformation because the model reaction failed in the absence of each of these two factors (Table 5, entries 1 and 6). Examining the above observations led us to consider the use of 6 mg of catalyst at 60 °C with Na2CO3 base (3 mmol) in PEG solvent (2 mL) as the optimal mode (Table 5, entry 2).
Benchmark in SMC reaction.
By optimizing the reaction conditions, we developed the range of performance and activity of the DPyE@-MCM-41@MNP palladium-based organometallic catalyst in the SMC reaction using different (hetero)aryl bromides, iodides, and chlorides substituted with electron-releasing or electron-absorbing groups along with benzeneboronic acid (Table 6). The results presented in Table 6 demonstrate the catalyst's excellent efficiency in reactions involving aryl iodides and aryl bromides with both electron-donating and electron-accepting groups. As expected, reactions involving aryl chlorides resulted in the formation of corresponding biphenyls over a longer reaction period. However, the presence of para-substituents led to faster product formation compared to ortho-substituents, attributed to reduced steric hindrance (Table 6, Input 2b vs. 3b and entry 4b vs. 5b). Notably, the results of two reactions of 1-Bromo-4-chlorobenzene (Table 6, entry 17b), and 1-Chloro-4-iodobenzene (Table 6, entry 18b) with benzeneboronic acid, highlighted the catalyst’s selectivity in the SMC reaction with di-haloarenes; because the coupling occurred only with the bromo and iodo functional groups, and the chloro functional group remained untouched in both reactions.
Scheme 5 illustrates a possible mechanism for the Pd-DPyE@MCM-41@MNP SMC reaction. The first stage in the previously described procedure is the oxidative addition of copper to the aryl halide, resulting in the formation of the organocopper intermediate (II). Intermediate (III) is produced via transmetallation of (II). The catalytic cycle could proceed because the intermediate (III) was eliminated reductively, which led to the synthesis of the product and the regeneration of the catalyst 2.
Possible mechanism of the SMC reaction.
Reusability of catalyst
The ability of magnetic nanoparticles to be recovered and reused several times is one of its most significant features. In this regard, the catalyst was separated from the reaction mixture using an external magnet after the reaction was finished, it washed with EtOH and EtOAc. After drying at 60 °C, ready for the subsequent run. After recovery, we investigated the activity of Pd-DPyE@MCM-41@MNP during the synthesis of compounds (1a) and (1b). According to the findings, this magnetic nanocatalyst maintained its catalytic activity for at least seven runs when it was recovered and reused (Figs. 11 and 12).
Recyclability of Pd-DPyE@MCM-41@MNP in the synthesis of compound 1a.
Recyclability of Pd-DPyE@MCM-41@MNP in the synthesis of compound 1b.
Next, after the seventh recycling in production 1a and the ninth recycling in production 1b, the structure of the catalyst was evaluated separately by EDX (Figs. 13 and 14), FT-IR (Figs. 15 and 16) and SEM (Figs. 17 and 18) techniques. In both ways of recycling, the matching of the findings of these analyses with the corresponding spectra of the fresh catalyst sample showed that the structure and texture of the catalyst did not change significantly during repeated use, even in the last cycle. These results support the high reproducibility of our catalyst; however, the natural wastage (0.02–0.03%) of the catalyst during recycling and the aggregation of its particles has caused a slight decrease in its performance.
EDX pattern of consumed Pd-DPyE@MCM-41@MNP in the synthesis of compound 1a.
EDX pattern of consumed Pd-DPyE@MCM-41@MNP in the synthesis of compound 1b.
FT-IR pattern of consumed Pd-DPyE@MCM-41@MNP in the synthesis of compound 1a.
FT-IR pattern of consumed Pd-DPyE@MCM-41@MNP in the synthesis of compound 1b.
SEM micrograph of consumed Pd-DPyE@MCM-41@MNP in the synthesis of compound 1a.
SEM micrograph of consumed Pd-DPyE@MCM-41@MNP in the synthesis of compound 1b.
Leaching study of catalyst
Palladium washing from Pd-DPyE@MCM-41@MNP was examined through ICP-OES and a hot filtration procedure. Palladium concentrations of the fresh and reused catalysts were found to be 2.500 × 10−3 mol g−1 and 2.479 × 10−3 mol g−1, respectively, according to the ICP-OES analysis. These findings imply that this catalyst has minimal palladium leaching.
To address the variable nature of Pd-DPyE@MCM-41@MNP in the Suzuki–Miyaura coupling reaction, the hot filtration experiment was carried out in the coupling of iodobenzene and benzeneboronic acid. In this investigation, 53% of the product was produced in half the reaction time (5 min). After five minutes, the catalyst was separated and the reaction was resumed. After that, the catalyst-free reaction was carried out for a further five minutes by the filtrated solution. Consequently, only 56% of 1,1'-biphenyl was generated. These results reveal that there is no visible rise in product concentration that indicates a heterogeneous mechanism throughout the recycling process.
Comparison
The efficiency of Pd-DPyE@MCM-41@MNP was studied by comparing our results with the previously described techniques in the synthesis of 3a and 1b compounds. As indicated in Table 7, Pd-DPyE@MCM-41@MNP has good results than other catalysts. Furthermore, Pd-DPyE@MCM-41@MNP has various benefits, including stability, short reaction time, high yield, and ease of separation.
Conclusions
Briefly, Pd-DPyE@MCM-41@MNP as a retrievable, reusable heterogeneous organometallic nanocatalyst was prepared by immobilizing the Pd-DPyE complex on MCM-41@MNP support and characterized by a wide range of physicochemical parameters. Then, the catalytic power of Pd-DPyE@MCM-41@MNP in the preparing N,N′-alkylidene bisamides and SMC derivatives was assessed separately through (i) reaction of aldehydes (1 equivalent) with primary amides (2 equivalents) and, (ii) reaction between (hetero)aryl halides (1 equivalent) with benzeneboronic acid (1 equivalent) under benign and mild conditions. The findings reflected that this catalyst in both production routes successfully isolated the respective derivatives in short reaction times (8–20 min and 10–140 min, respectively) with excellent yields (90–98% and 86–98%, respectively). In addition, in routes (i) and (ii) catalysts were used in 7 and 9 consecutive runs, respectively, with an average yields of 95.28% to 92.11%, and the durability of the nanostructured skeleton was confirmed after recycling experiments with SEM and EDX techniques. Pd-DPyE@MCM-41@MNP has a high potential for catalytic conversion due to its simplicity of isolation, low cost, high efficiency, and high reproducibility/stability; consequently, its catalytic performance can be investigated in future research.
Data availability
The data that support the findings of this study are available on request from the corresponding author.
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Acknowledgements
The authors are grateful to acknowledge the Takin Shimi Sepanta Industries Co, Ilam, Iran.
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S.I.S.A: produced several N,N′-alkylidene bisamides products (1a-6a), and edited the paper. R.O.S: produced several Suzuki–Miyaura coupling derivatives (1b-9b). A.R.A: produced several N,N′-alkylidene bisamides products (7a-13a). N.F: produced several Suzuki–Miyaura coupling derivatives (10b-26b). M.A: Optimized reaction conditions for the synthesis N,N′-alkylidene bisamides. S.H.J.A: Optimized Suzuki–Miyaura coupling reaction conditions. A.A: determined the skeletonof the nanocatalyst via VSM, TEM, SEM, and FTIR analyses. M.A.J: determined the skeletonof the nanocatalyst by BET, EDS and elemental mapping analyses. S.B.A: determined the skeleton of the nanocatalyst through ICP, TGA and XRD analyses. M.S.G.N: fabricated the nanocatalyst, and wrote the paper. We have confirmed.
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Ibraheem Shelash Al-Hawary, S., Saleh, R.O., AlBajalan, A.R. et al. Synthesis of N,N′-alkylidene bisamides and Suzuki–Miyaura coupling reaction derivatives with Pd organometallic catalyst anchored to channels of mesoporous silica MCM-41. Sci Rep 14, 7688 (2024). https://doi.org/10.1038/s41598-024-58310-5
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DOI: https://doi.org/10.1038/s41598-024-58310-5
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