Ferrocene-based covalent organic framework-carbon nanotube hybrid modified with Cu(OAc)₂ as a robust catalyst for the preparation of tetrazoles

Abstract

The emergence of covalent organic framework-carbon nanotube hybrid composites (COF-CNT) has opened up a promising approach for the development of heterogeneous catalysis. In this research, a new ferrocene-based COF was wrapped onto the surface of a carbon nanotube and modified with Cu(OAc)₂ (denoted as FCOF-CNT-Cu(OAc)₂) for boosting the catalytic performance for the preparation of tetrazoles. Ferrocene segments played a decisive role in assisting Cu(OAc)₂ as catalytically active sites for the preparation of 5-substituted 1H-tetrazoles and acrylonitrile-linked tetrazoles. FCOF-CNT-Cu(OAc)₂ had a high specific surface area of 117 m² g⁻¹, which accelerated the catalytic process. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) analyses revealed that the catalyst was ordered with a tubular morphology and spherical COF grown on the outer surface of the CNT. This work presents FCOF-CNT-Cu(OAc)₂ as a superior catalyst toward the preparation of 5-substituted 1H-tetrazoles and acrylonitrile-linked tetrazole derivatives. Consequently, tetrazole derivatives were synthesized in short reaction times under green and mild reaction conditions.

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Introduction

COFs, as highly crystalline porous organic materials, are assembled with strong covalently bound building blocks, and they hold promises in diverse academic studies and offer broad practical applications such as in energy conversion and storage,^1,2 gas adsorption and separation,^3,4 sensing,⁵ drug delivery,⁶ electronic devices,⁷ semiconductors,⁸ and catalysis.⁹ The outstanding characteristics of COFs include large specific surface area, well-defined porosity, low density, convenient functionalization, post-modification ability, and high thermal, chemical, and physical stabilities, each of which is of immense importance in the context of the applications of these materials.^10,11 In the context of catalytic applications of COFs, these are fantastic candidates in most catalytic processes such as asymmetric synthesis and photocatalytic, oxidation, reduction, coupling, and multicomponent reactions.^12–15 Due to the adjustable functionality of cavities, well-defined porosities, and rich metal chelation sites, these materials are rational and versatile hosts for metal ions, nanoparticles, and metal clusters.^16,17 A huge variety of reactions, such as the aryl methanol oxidation-aldol reaction,¹⁸ click reaction-induced triazole synthesis,¹⁹ Suzuki–Miyaura cross-coupling reaction²⁰ and Betti reaction,²¹ have been facilitated by metal-ion-doped COFs. Cu(II)-coordinated COFs, because of their high activity, selectivity and ease of recovery and reusability, have a promising outlook and a decisive role in several catalytic reactions.^22–24

Copper ions, due to their high selectivity and activity, natural abundance, and low cost, have garnered significant interest in catalytic transformations such as organometallic catalysis, gas-phase catalysis and photocatalysis.^25,26 Hereof, Cu(OAc)₂ nanoparticles is a paradigm example of click chemistry and is regarded as one of the most important synthetic trends for the preparation of heterocyclic compounds such as tetrazoles. Due to its broad applicability, selectivity, and biocompatibility, Cu(OAc)₂ plays a decisive role in the click chemistry preparation of tetrazole families.^27,28

Recently, hybrid COFs such as COF-CNT,²⁹ COF-graphene oxide,³⁰ and COF-metal organic frameworks³¹ have been reported. Among these, COF-CNT can solve some drastic problems like metal guest colonization, poor stability, and weak effective interactions.³² Due to the strong π–π interactions between the COF layers and MVCNT, this complex can be a fantastic host for the decoration of metal ions as highly active catalytic centers.^33,34

Ferrocene, as an interesting and unique functional moiety, has a distinctive electron-rich sandwich-like structure, which has inherent catalytic activity and is stable under harsh reaction conditions such as high temperature and alkaline and acidic media.³⁵ In recent years, ferrocene derivatives have been exploited as privileged building components for the fabrication of COFs.^36,37 Due to the organic–inorganic characteristics of ferrocene-based COFs and their superior performance as catalysts, they have been ingeniously applied in several catalytic reactions such as photocatalytic,³⁸ electrocatalytic,³⁹ and Fenton-like⁴⁰ reactions.

Heterocyclic chemistry is the heart of organic chemistry, and its catalytic synthesis has gained wide attention.⁴¹ Chemicals containing tetrazoles are some of the most important and beneficial compounds belonging to the family of N-rich heterocycles, attracting burgeoning attention owing to their plethora of applications in functional materials, coordination chemistry, energetic materials, sensing, catalysis, and pharmaceuticals.^42–44 Several synthetic methodologies, such as 3 + 2 cycloaddition of nitriles and azides, cycloaddition of oximes and azides, and conversion of amides into tetrazole via the Mitsunobu reaction, have been reported for the preparation of tetrazoles.^45,46 In medicinal applications, tetrazole derivatives are known as anti-inflammatory, antibiotic, antihypertensive, antiallergic, antifungal, anti-HIV, and anticonvulsant agents and bioisosteres.^47–49 Among the tetrazole-bearing compounds, nitrile-linked tetrazoles have been neglected in the past century because of a lack of practical synthetic methods.⁵⁰ Therefore, development of suitable and applicable synthetic methodologies for these compounds requires great attention.

In this experimental study, considering our experience in porous materials, especially COFs,⁵¹ a new ferrocene-based COF was fabricated on the surface of MVCNT and modified with Cu(OAc)₂. This catalytic platform was engineered with a predetermined goal in mind. We envisioned that the synergistic effects of the ferrocene core, CNT, and Cu(OAc)₂ in FCOF-CNT-Cu(OAc)₂ would make it an ideal catalyst for the preparation of tetrazole-based compounds (Schemes 1 and 2).

Scheme 1 Schematic of the fabrication of FCOF-CNT-Cu(OAc)₂.

Scheme 2 Catalytic preparation of tetrazole derivatives using FCOF-CNT-Cu(OAc)₂.

Results and discussion

Structural investigation of FCOF-CNT-Cu(OAc)₂

FT-IR and XRD analyses were adopted to explore the successful construction of FCOF-CNT-Cu(OAc)₂. The FT-IR spectra of the starting materials and intermediates at different steps of the catalyst synthesis are illustrated in Fig. 1, with the corresponding functional groups indicated. The carbonyl and cyclopentadienyl groups of 1,1-diacetylferrocene appeared at 1661 and 1459 cm⁻¹, respectively. In the FT-IR spectrum of TAPT, the characteristic absorption bands at 1608 and 1503 cm⁻¹ corresponded to imine and aromatic groups, respectively. Moreover, the sharp peaks at 3465 and 3376 cm⁻¹ were related to the amine functional group. According to the FT-IR spectrum of FCOF-CNT, it was clear that the disappearance of the NH₂ bands in TAPT and carbonyl band in 1,1-diacetylferrocene was accompanied by the emergence of a C=N band at 1698 cm⁻¹, indicating a polycondensation reaction between TAPT and 1,1-diacetylferrocene.^52,53 In the FT-IR spectrum of Cu(OAc)₂·H₂O, the strong peak at about 1631 cm⁻¹ and the broad peak at about 3458 cm⁻¹ were attributed to the stretching vibration mode of the C=O of acetate groups and H₂O, respectively. After coordinating Cu²⁺, the main peaks in the FT-IR spectrum of FCOF-CNT did not change apparently.

Fig. 1 FT-IR spectra of FCOF-CNT-Cu(OAc)₂ and its intermediates.

XRD patterns of CNT, FCOF-CNT and FCOF-CNT-Cu(OAc)₂ presented in Fig. 2 were used to evaluate the crystalline structure of FCOF-CNT-Cu(OAc)₂. The XRD pattern of CNT showed distinctive peaks at 26.2°, 35.6°, 43.3°, 57.3° and 62.8°, belonging to the (002), (100), (101), (004) and (110) planes, respectively. Besides, the XRD pattern of FCOF-CNT and FCOF-CNT-Cu(OAc)₂ displayed similar diffraction signals to that of CNT, indicating that the crystallinity of the CNT was retained after FCOF was wrapped on its surface. In the XRD pattern of FCOF-CNT, the (100) plane of FCOF was observed at 8.3°, indicating that the crystalline structure of FCOF was retained.⁵⁴ The XRD pattern of FCOF-CNT-Cu(OAc)₂ had additional peaks at 6.9°, 13.7° and 32.3°, indicating the successful loading of Cu(OAc)₂ while preserving the crystallinity of FCOF-CNT (Fig. 2).

Fig. 2 XRD patterns of CNT, FCOF-CNT and FCOF-CNT-Cu(OAc)₂.

Morphology investigation of FCOF-CNT-Cu(OAc)₂

According to FE-SEM analysis, FCOF-CNT-Cu(OAc)₂ exhibited a tubular morphology with spherical COF growths on the outer surface of the CNT. As illustrated in Fig. 3a and b, the as-prepared CNT inherited a clean and regular nanotube structure with an average diameter of 40 nm, and its outer surface morphology was different from those of FCOF-CNT and FCOF-CNT-Cu(OAc)₂. The formation of spherical FCOF particles on the surface of CNT was observed in Fig. 3c–f, and the average diameter of FCOF-CNT-Cu(OAc)₂ was 70 nm, whose larger diameter and coarser surface can be attributed to the successful coating of FCOF on the surface of CNT. TEM analysis was used to further study the morphology of the catalyst. TEM images of FCOF-CNT and FCOF-CNT-Cu(OAc)₂ revealed the tubular morphology, in which the spherical FCOF was grown on the surface of CNT as core–shell structures (Fig. 4a–c). EDS analysis showed the predicted signals of C, N, O and Fe for FCOF-CNT and C, N, O, Cu and Fe for FCOF-CNT-Cu(OAc)₂ (Fig. 5). Mapping images revealed the uniform distribution of all the expected elements in both FCOF-CNT and FCOF-CNT-Cu(OAc)₂. Notably, the uniform distribution of Cu nanoparticles without any agglomeration was observed (Fig. 5).

Fig. 3 FE-SEM images of CNT (a, b), FCOF-CNT (c, d) and FCOF-CNT-Cu(OAc)₂ (e, f).

Fig. 4 TEM images of FCOF-CNT (a, b) and FCOF-CNT-Cu(OAc)₂ (c).

Fig. 5 EDS mapping results of FCOF-CNT (a) and FCOF-CNT-Cu(OAc)₂ (b).

Porosity evaluation of FCOF-CNT-Cu(OAc)₂

Porosity and surface area of FCOF-CNT and FCOF-CNT-Cu(OAc)₂ were investigated using the N₂ absorption–desorption isotherm and BET methods at 77 K. According to Fig. 6a and b, in the region of p/p₀ below 0.1, the N₂ adsorption of FCOF-CNT was significantly increased, whereas the N₂ adsorption of FCOF-CNT-Cu(OAc)₂ increased at a gentler rate. This indicated the presence of more micropores in FCOF-CNT than in FCOF-CNT-Cu(OAc)₂, which can be attributed to the occupation of micropores by Cu(OAc)₂. By increasing the p/p₀ to 0.9, we observed hysteresis loops for both the samples, indicating the presence of a mesoporous structure for both of them. Moreover, the obtained BET surface area of FCOF-CNT and FCOF-CNT-Cu(OAc)₂ were 441 and 117 m² g⁻¹, respectively. The Barrett–Joyner–Halenda (BJH) method was applied to show the pore size distributions in the samples. As illustrated in Fig. 6c and d, most of the pore radii for both FCOF-CNT and FCOF-CNT-Cu(OAc)₂ were less than 10 nm, indicating microporous and mesoporous structures.

Fig. 6 N₂ adsorption/desorption isotherms of FCOF-CNT (a) and FCOF-CNT-Cu(OAc)₂. (b) Pore size distribution of FCOF-CNT (c) and FCOF-CNT-Cu(OAc)₂. (d) TGA/DTG curves of FCOF-CNT and (e) FCOF-CNT-Cu(OAc)₂ (f).

Thermal stability analysis

TGA/DTG analysis with a heating rate of 10 °C min⁻¹ was used to check the thermal stability of the catalyst. The TGA curves of FCOF-CNT and FCOF-CNT-Cu(OAc)₂ show only a small weight loss of 4% at about 70 °C, which can be attributed to the trapped organic solvents, and another weight loss of 15% in the range of 200–400 °C may be ascribed to the removal of small portions of the organic layers and acetate groups of Cu(OAc)₂. In general, by increasing the temperature to 600 °C, approximately 20% of FCOF-CNT and FCOF-CNT-Cu(OAc)₂ was removed, confirming that both samples have excellent thermal stability (Fig. 6e and f).

Catalytic application of FCOF-CNT-Cu(OAc)₂

After precise characterization and analysis of FCOF-CNT-Cu(OAc)₂, we delved into its catalytic application for the preparation of tetrazoles. First of all, we tried to find the optimal reaction conditions for the preparation of 5-substituted 1H-tetrazoles and acrylonitrile-linked tetrazoles, separately. We chose the preparation of 1f molecule as a model reaction using 4-chlorobenzaldehyde oxime and sodium azide as the starting materials. The main parameters, such as the solvent and amount of the catalyst, were evaluated. Therefore, the model reaction was performed with different solvents, including CH₂Cl₂, water, n-hexane, EtOH, MeOH, and DMF, under reflux conditions or solvent-free conditions at 110 °C. We found that performing the reaction with CH₂Cl₂ gave a better yield than using other solvents or under solvent-free conditions. Moreover, in most reported papers the reflux within the DMF and DMSO solvents were selected for the preparation of tetrazoles,⁵⁵ but we used the reflux of CH₂Cl₂ as a milder reaction condition, which is a key point in green chemistry and has more importance in saving energy resources. In addition, different amounts of catalyst were used for the model reaction, and 20 mg of FCOF-CNT-Cu(OAc)₂ was selected as the optimum amount of catalyst. The results, including further details, are listed in Table 1. In a similar study, we realized that the optimized reaction conditions for the preparation of acrylonitrile-linked tetrazoles were using EtOH as the solvent under reflux conditions, and 15 mg FCOF-CNT-Cu(OAc)₂ was the optimum amount of catalyst (Table 2).

Table 1 Optimization of reaction conditions for the preparation of 1f molecule^a

Entry	Solvent	Temperature (°C)	Catalyst loading (mg)	Yield^b (%)
a Reaction conditions: 4-chlorobenzaldehyde oxime (2 mmol, 0.312 g), sodium azide (3 mmol, 0.195 g), 2 h. b Isolated yield.
1	CH2Cl2	Reflux	25	96
2	CH 2 Cl 2	Reflux	20	96
3	CH2Cl2	Reflux	15	80
4	CH2Cl2	Reflux	10	30
5	CH2Cl2	Reflux	—	—
6	Water	Reflux	20	—
7	n-Hexane	Reflux	20	20
8	EtOH	Reflux	20	40
9	DMF	Reflux	20	94
10	MeOH	Reflux	20	—
11	—	110	20	—

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Table 2 Optimization of reaction conditions for the preparation of 2b molecule^a

Entry	Solvent	Temperature (°C)	Catalyst loading (mg)	Yield^b (%)
a Reaction conditions: 4-chlorobenzaldehyde (2 mmol, 0.282 g), malononitrile (2.4 mmol, 0.158 g), sodium azide (3 mmol, 0.195 g), 2 h. b Isolated yield.
1	EtOH	Reflux	20	94
2	EtOH	Reflux	15	94
3	EtOH	Reflux	10	85
4	EtOH	Reflux	—	—
5	Water	Reflux	15	30
6	n-Hexane	Reflux	15	40
7	EtOAc	Reflux	15	70
8	CH2Cl2	Reflux	15	Trace
9	MeOH	Reflux	15	80
10	—	110	15	—

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With the optimum conditions and promising results in hand, a series of aldehydes and aldehyde oximes were subjected to the synthesis of acrylonitrile-linked tetrazoles and 5-substituted-1H-tetrazoles, respectively. Diverse electron-donating and electron-withdrawing substituted aldehydes and aldehyde oximes were applied, and good results were obtained. All derivatives were synthesized in short reaction times (2 h) with high yields (80–96% for 5-substituted-1H-tetrazoles and 72–94% for acrylonitrile-linked tetrazoles) (Tables 3 and 4). In another study, to verify the potential of FCOF-CNT-Cu(OAc)₂ as a highly active catalyst, we compared its activity with those of FCOF-CNT, CNT and Cu(OAc)₂ for the model reaction. The yield of 1f was found to be significantly decreased with FCOF-CNT, CNT and Cu(OAc)₂ as catalysts rather than FCOF-CNT-Cu(OAc)₂ (Table 5).

Table 3 Catalytic preparation of 5-substituted 1H-tetrazoles using the FCOF-CNT-Cu(OAc)₂ catalyst^a

a Reaction conditions: aldehyde oxime (2 mmol), sodium azide (3 mmol, 0.194 g), CH₂Cl₂, reflux, 40 °C, 2 h, catalyst (20 mg), reported yields are isolated yields.^56–64

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Table 4 Catalytic preparation of acrylonitrile-linked tetrazoles using the FCOF-CNT-Cu(OAc)₂ catalyst^a

a Reaction conditions: aldehyde (2 mmol), sodium azide (3 mmol, 0.195 g), malononitrile (2.4 mmol, 0.158 g), EtOH, reflux, 80 °C, 2 h, catalyst (15 mg), reported yields are isolated yields.^65–69

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Table 5 Comparison of the catalytic ability of FCOF-CNT-Cu(OAc)₂, FCOF-CNT, CNT and Cu(OAc)₂ for the preparation of 1f^a

Entry	Catalyst	Catalyst loading	Yield (%)
a Reaction conditions: 4-chlorobenzaldehyde oxime (2 mmol, 0.312 g), sodium azide (3 mmol, 0.195 g), 2 h, CH2Cl2, reflux, 40 °C.
1	FCOF-CNT-Cu(OAc) 2	20 mg	96
2	COF-CNT	20 mg	40
3	CNT	20 mg	20
4	Cu(OAc)2	10 mol%	30

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In addition, in a comparative study, the catalytic activity of FCOF-CNT-Cu(OAc)₂ and some of the reported homogeneous and heterogeneous catalysts was evaluated for the preparation of 1f molecule. According to the revealed results, FCOF-CNT-Cu(OAc)₂ exhibited a higher catalytic activity under milder reaction conditions than most of the reported catalysts. We note that the recyclability and reusability of FCOF-CNT-Cu(OAc)₂ is a crucial parameter that makes it more valuable than homogeneous catalysts (Table 6).

Table 6 Comparison of the catalytic ability of FCOF-CNT-Cu(OAc)₂ with some reported heterogeneous and homogeneous catalysts for the preparation of 1f

Entry	Catalyst	Time (h)	Yield (%)
1	FCOF-CNT-Cu(OAc) 2 , CH 2 Cl 2 , reflux, 40 °C, [this work]	2	96
2	Diphenyl phosphorazidate, toluene, reflux^49	16	89
3	25 mol% Cu(OAc)2, DMF, 120 °C (ref. 44)	12	90
4	CoY zeolite, DMF, 120 °C (ref. 48)	14	91
5	Pincer type Pd(II) complex, KOH, H2O/DMSO, 90 °C (ref. 70)	8	78
6	(η^6-p-cymene)Ruthenium(II), DMF, 140 °C (ref. 71)	8	93
7	CuSO4·5H2O, DMSO, 140 °C (ref. 55)	0.5	100
8	AgNO3, DMF, 120 °C (ref. 55)	5	80
9	Piperazinium hydrogensulfate, 100 °C (ref. 72)	2	93
10	Copper-coordinated-poly(α-amino acid)/magnetite graphene oxide, water, 70 °C (ref. 47)	1.41	92

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To examine the recovery and reusability of the catalyst, recycling tests with FCOF-CNT-Cu(OAc)₂ were conducted for the preparation of 2b under the optimal reaction conditions. After completing the reaction, CH₂Cl₂ was added to the flask and insoluble FCOF-CNT-Cu(OAc)₂ was separated from the reaction mixture via filtration, washed with CH₂Cl₂, dried at 100 °C and retained for the next run. The catalytic ability of FCOF-CNT-Cu(OAc)₂ was well preserved after six consecutive reaction cycles, and no significant loss in catalytic performance was observed (Scheme 3). The FE-SEM and EDS/mapping analyses results of the recovered catalyst are shown in Fig. 7 and 8.

Scheme 3 Recoverability and reusability of COF-CNT-Cu(OAc)₂.

Fig. 7 FE-SEM image of recovered COF-CNT-Cu(OAc)₂.

Fig. 8 EDS signals and mapping images of recovered COF-CNT-Cu(OAc)₂.

Inspired by a previous report,⁴⁴ we suggest a plausible mechanism for the preparation of tetrazoles (Scheme 4). First, the hydroxy group of the oxime is activated by the catalyst, which facilitates the nucleophilic attack and cycloaddition of NaN₃ across the C=N group. In the next step, the desired product is generated by removing H₂O, assisted by the catalyst, as well as hydrolysis by acid.

Scheme 4 Plausible mechanism for the preparation of 1f molecule.

Experimental section

In the Experimental section, the importance of a nonstoichiometric ratio of reactants in organic synthesis for delivering high yields of products was considered.⁷³

Materials and methods

In this research, all starting materials and reagents were purchased from Merck and Sigma-Aldrich companies and were applied without further purification. FT-IR spectra were recorded with an FT-IR spectrometer, PerkinElmer Spectrum 65 model. ¹H NMR spectra were performed on a Bruker spectrometer operating at 250 MHz, and ¹³C NMR spectra were performed at 62 MHz. FE-SEM analysis was performed with a TESCAN MIRA4 instrument, and TEM analysis was conducted with a ZEISS, EM10C-100 KV instrument. X-ray diffraction (XRD) analysis was performed with an X'Pert Pro instrument. N₂ adsorption/desorption isotherms were obtained using a BELSORP Mini model instrument. Thermogravimetric/derivative thermogravimetry analysis (TGA/DTG) (Mettler Toledo company, TGA2 model) was used to investigate the thermal stability of the catalyst.

General experimental procedure for the synthesis of FCOF-CNT-Cu(OAc)₂. The synthetic procedure for FCOF-CNT-Cu(OAc)₂ is shown in Scheme 1. 1,1-Diacetylferrocene (1.5 mmol, 0.405 g), tris(4-aminophenoxy)-1,3,5-triazine (TAPT) (1 mmol, 0.402 g), CNT (0.2 g) and DMSO (30 mL) were added to a round-bottom flask, and the reaction mixture was refluxed for 72 h at 140 °C under an N₂ atmosphere. After completing the reaction, the obtained FCOF-CNT was filtered and washed several times with MeOH and tetrahydrofuran (THF) and finally dried at 120 °C for 24 h. FCOF-CNT (0.5 g), Cu(OAc)₂·H₂O (0.75 mmol, 0.15 g), and 30 mL of dry ethanol were then stirred at room temperature for 4 h. The resulting product was washed with ethanol and placed in an oven at 120 °C for 12 h to remove any trapped solvents.
Synthesis of 5-substituted 1H-tetrazoles in the presence of FCOF-CNT-Cu(OAc)₂. Initially, to prepare the oxime derivatives, a mixture of aromatic aldehydes (2 mmol), pyridine (3 mmol, 0.237 g) as catalyst, and hydroxylamine hydrochloride (3 mmol, 0.208 g) and 10 mL of ethanol were poured into a round-bottomed flask and stirred at room temperature for 6 h. After that, the formed solids were washed by water to yield the desired pure product. In the next step, oxime derivatives (2 mmol), sodium azide (3 mmol, 0.195 g) and 20 mg FCOF-CNT-Cu(OAc)₂ as catalyst were added to 10 mL of CH₂Cl₂ and refluxed at 40 °C. After completion of the reaction, the catalyst was separated using a filtration method. After removing the solvent, 10 mL of 2 M hydrochloric acid was added to the reaction mixture, and the resulting precipitate was washed with water and EtOH to obtain the pure product.
Synthesis of acrylonitrile-linked tetrazole derivatives using FCOF-CNT-Cu(OAc)₂ catalyst. A mixture of aromatic aldehyde (2 mmol), sodium azide (3 mmol, 0.195 g), malononitrile (2.4 mmol, 0.158 g), FCOF-CNT-Cu(OAc)₂ (15 mg) and EtOH (10 mL) was added to a 10 mL round-bottomed flask and stirred at 80 °C. Upon completion of the reaction, 20 mL of CH₂Cl₂ was added to the flask and the insoluble catalyst was separated using filtration. The solvent was removed, and 10 mL of 2 M hydrochloric acid was added to the reaction mixture and the resulting precipitate was washed with water and cold EtOH to yield the pure acrylonitrile-linked tetrazole derivative.

Spectral data

5-(4-Nitrophenyl)-1H-tetrazole. M.p. = 213–215 °C, FT-IR (KBr, ν, cm⁻¹): 3447, 3219, 1552, 1515, 1339. ¹H NMR (250 MHz, DMSO-d₆) δ_ppm 8.41 (d, J = 7.5 Hz, 2H), 8.27 (d, J = 7.5 Hz, 2H). ¹³C NMR (63 MHz, DMSO-d₆) δ_ppm 149.1, 131.1, 128.7, 125.0.

5-(3-Nitrophenyl)-1H-tetrazole. M.p. = 248–250 °C, FT-IR (KBr, ν, cm⁻¹): 3159, 2955, 1602, 1574, 1321. ¹H NMR (250 MHz, DMSO-d₆) δ_ppm 9.82 (s, 1H), 7.69–7.32 (m, 2H), 6.89 (s, 1H). ¹³C NMR (63 MHz, DMSO-d₆) δ_ppm 160.1, 154.0, 132.4, 124.4, 120.8, 117.9.

5-(2,4-Dichlorophenyl)-1H-tetrazole. M.p. = 171–173 °C, FT-IR (KBr, ν, cm⁻¹): 3421, 2918, 1614, 1570, 1505. ¹H NMR (250 MHz, DMSO-d₆) δ_ppm 7.96 (s, 1H), 7.39 (broad peak, 2H). ¹³C NMR (63 MHz, DMSO-d₆) δ_ppm 141.5, 130.6, 127.8.

5-(4-Chlorophenyl)-1H-tetrazole. M.p. = 250–252 °C, FT-IR (KBr, ν, cm⁻¹): 3422, 3098, 1687, 1610. ¹H NMR (250 MHz, DMSO-d₆) δ_ppm 8.35 (s, 1H), 7.95 (s, 1H), 7.62 (s, 2H). ¹³C NMR (63 MHz, DMSO-d₆) δ_ppm 155.2, 136.3, 130.0, 129.3, 123.7.

3-(1H-Tetrazol-5-yl)phenol. M.p. = 222–225 °C, FT-IR (KBr, ν, cm⁻¹): 3193, 3053, 1603, 1574, 1472. ¹H NMR (250 MHz, DMSO-d₆) δ_ppm 9.81 (s, 1H), 7.30 (broad peak, 3H), 6.87 (s, 1H). ¹³C NMR (63 MHz, DMSO-d₆) δ_ppm 160.0, 132.3, 119.2, 118.6, 118.0.

5-(Naphthalen-2-yl)-1H-tetrazole. M.p. = 212–214 °C, FT-IR (KBr, ν, cm⁻¹): 3422, 3055, 1649, 1495. ¹H NMR (250 MHz, DMSO-d₆) δ_ppm 8.56–8.40 (m, 2H), 8.19–7.89 (m, 3H), 7.64–7.54 (m, 2H). ¹³C NMR (63 MHz, DMSO-d₆) δ_ppm 148.6, 134.7, 132.9, 132.7, 130.4, 129.4, 129.1, 128.3, 127.8, 124.9.

1,4-Di(1H-tetrazol-5-yl)benzene. M.p. = 240–242 °C, FT-IR (KBr, ν, cm⁻¹): 3358, 3088, 1660, 1434. ¹H NMR (250 MHz, DMSO-d₆) δ_ppm 8.14–7.94 (m, 4H).

(E)-3-(4-Chlorophenyl)-2-(1H-tetrazol-5-yl)acrylonitrile. M.p. = 160–162 °C, FT-IR (KBr, ν, cm⁻¹): 3452, 3154, 2230, 1586. ¹H NMR (250 MHz, DMSO-d₆) δ_ppm 8.67 (s, 1H), 8.10–7.88 (m, 2H), 7.66–7.51 (m, 2H). ¹³C NMR (63 MHz, DMSO-d₆) δ_ppm 147.3, 137.3, 131.9, 131.5, 129.8, 115.9, 98.4.

(E)-3-(2,3-Dichlorophenyl)-2-(1H-tetrazol-5-yl)acrylonitrile. M.p. = 158–160 °C, FT-IR (KBr, ν, cm⁻¹): 3422, 3141, 2233, 1610. ¹H NMR (250 MHz, DMSO-d₆) δ_ppm 8.57 (s, 1H), 8.00 (s, 1H), 7.84 (d, J = 7.5 Hz, 1H), 7.57 (s, 1H). ¹³C NMR (63 MHz, DMSO-d₆) δ_ppm 144.3, 133.8, 133.4, 133.2, 132.07, 130.0, 129.3, 128.9, 115.0, 103.7.

(E)-3-(4-Hydroxyphenyl)-2-(1H-tetrazol-5-yl)acrylonitrile. M.p. = 165–167 °C, FT-IR (KBr, ν, cm⁻¹): 3334, 3172, 2233, 1599. ¹H NMR (250 MHz, DMSO-d₆) δ_ppm 10.49 (s, 1H), 8.19–7.87 (m, 3H), 6.89 (s, 2H). ¹³C NMR (63 MHz, DMSO-d₆) δ_ppm 162.1, 148.9, 133.7, 132.9, 123.9, 117.5, 117.2, 92.4.

(E)-3-(Naphthalen-2-yl)-2-(1H-tetrazol-5-yl)acrylonitrile. M.p. = 158–160 °C, FT-IR (KBr, ν, cm⁻¹): 3422, 3141, 2233, 1610. ¹H NMR (250 MHz, DMSO-d₆) δ_ppm 8.57 (s, 1H), 8.00 (s, 1H), 7.84 (d, J = 7.5 Hz, 1H), 7.57 (s, 1H). ¹³C NMR (63 MHz, DMSO-d₆) δ_ppm 144.3, 133.8, 133.4, 133.2, 132.1, 130.0, 129.3, 128.9, 115.0, 103.7.

Conclusion

To summarize, a Cu(OAc)₂-loaded ferrocene-based COF-wrapped MVCNT was evaluated as a hybrid-reticular catalyst. Benefiting from the synergistic effect of ferrocene moiety, CNT and Cu(OAc)₂, FCOF-CNT-Cu(OAc)₂ exhibited a superior and appropriate catalytic performance in multi-component reactions. More importantly, FCOF-CNT-Cu(OAc)₂ exhibited an ordered and tubular morphology, high porosity and great stability. Accordingly, FCOF-CNT-Cu(OAc)₂ was successfully assessed for the preparation of 5-substituted 1H-tetrazoles and acrylonitrile-linked tetrazoles. The synthesized tetrazole derivatives were prepared in high yields under short reaction times and mild reaction conditions compared with previous reports. In addition, this catalyst showed acceptable recovery and reusability, whereby its activity was well preserved after six consecutive reaction cycles with no significant loss in its catalytic potential. This study provides an intense insight into the key role of hybrid reticular chemistry-based catalysis in organic transformations and can encourage chemists to develop new hybrid COFs.

Author contributions

Zahra Alishahi: writing – original draft, validation, methodology, investigation. Mohammad Ali Zolfigol: writing – review & editing, project administration, resources, supervision, funding acquisition, conceptualization, data curation. Morteza Torabi: writing – original draft, validation, methodology, investigation. Yanlong Gu: resources, data curation, methodology.

Conflicts of interest

The authors declare no competing interests.

Data availability

The data supporting this article have been included as part of the SI. See DOI: https://doi.org/10.1039/d5na00566c.

Acknowledgements

We thank the Bu-Ali Sina University and Iran National Science Foundation (INSF) (Grant Number: 4041905) for providing the financial support to our research group.

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