Parisa Moradia and
Maryam Hajjami*b
aDepartment of Chemistry, Faculty of Science, Ilam University, P. O. Box 69315516, Ilam, Iran
bDepartment of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University, 6517838683, Hamedan, Iran. E-mail: mhajjami@yahoo.com; m.hajjami@basu.ac.ir
First published on 27th July 2021
Catalyst species are an important class of materials in chemistry, industry, medicine, and biotechnology. Moreover, waste recycling is an important process in green chemistry and is economically efficient. Herein, magnetic graphene oxide was synthesized using nickel magnetic nanoparticles and further applied as a novel support for the fabrication of a copper catalyst. The catalytic activity of supported copper on magnetic graphene oxide (Cu–ninhydrin@GO–Ni MNPs) was investigated as a selective, practical, and reusable nanocatalyst in the synthesis of diaryl ethers and biphenyls. Some of the obtained products were identified by NMR spectroscopy. This nanocatalyst has been characterized by atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM), wavelength dispersive X-ray spectroscopy (WDX), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and vibrating sample magnetometer (VSM) techniques. The results obtained from SEM shown that this catalyst has a nanosheet structure. Also, XRD and FT-IR analysis show that the structure of graphene oxide and nickel magnetic nanoparticles is stable during the modification of the nanoparticles and synthesis of the catalyst. The VSM curve of the catalyst shows that this catalyst can be recovered using an external magnet; therefore, it can be reused several times without a significant loss of its catalytic efficiency. The heterogeneity and stability of this nanocatalyst during organic reactions was confirmed by the hot filtration test and AAS technique.
It is worthy to note that C–C or C–O coupling reactions are usually performed in the presence of palladium-containing catalysts,18,31 which are very expensive. Meanwhile, Cu-containing catalysts are of interest because of their non-toxicity and cost-effective preparation methods.4 Therefore, herein, we have synthesized magnetic nickel-graphene oxide nanosheets as a support to fabricate the copper catalyst (Cu–ninhydrin@GO–Ni MNPs), and subsequently its catalytic application was studied in the C–C and C–O coupling reactions for the synthesis of diaryl ethers and biphenyls.
Scheme 3 Immobilization of copper on magnetic graphene oxide for the preparation of Cu–ninhydrin@GO–Ni MNPs. |
The elemental composition of Cu–ninhydrin@GO–Ni MNPs was qualitatively determined using EDS analysis (Fig. 2). As expected according to Scheme 3, the obtained results from EDS show that this catalyst is composed of a combination of C, O, Si, N, Ni, and Cu elements.
Also, the obtained results from EDS were confirmed by WDX analysis. The elemental composition distribution of this catalyst was investigated using WDX qualitative analysis. As shown in Fig. 3, all the elements are homogeneously distributed within the structure of this catalyst.
Fig. 3 Elemental mapping of (a) carbon, (b) oxygen, (c) silica, (d) nitrogen, (e) nickel, and (f) copper for Cu–ninhydrin@GO–Ni MNPs. |
Moreover, the exact amount of copper that was loaded on the modified GO–Ni MNPs was calculated by AAS analysis. According to the obtained results from AAS analysis, there is 0.71 × 10−3 mol of copper per gram of Cu–ninhydrin@GO–Ni.
The FT-IR spectra for Ni magnetic nanoparticles (Ni MNPs), graphene oxide nanosheets (GO), magnetic graphene oxide by Ni MNPs (GO–Ni MNPs), and Cu–ninhydrin@GO–Ni MNPs are shown in Fig. 4 and Table 1. The surface of GO is covered by a high density of hydroxyl groups, which appears as a strong band above 3000 cm−1 (Table 1, entry 1) in the FT-IR spectrum.41 The characteristic stretching peak for C–OH groups (Table 1, entry 2) on the surface of GO emerged at 1224 cm−1.42 The bending and stretching vibration of the C–H bonds are present at 878 and 2958 cm−1 in the FT-IR spectra (Table 1, entry 3).24 The bands at 1624 cm−1 and 1714 cm−1 correspond to the vibration of the CC bonds in the skeletal network of GO (Table 1, entry 4) and CO (Table 1, entry 5) bonds, respectively.43,44 The bands at about 462, 800, 1040, and 1082 cm−1 (Table 1, entries 6 and 7) correspond to the vibrations of Si–O–Si and Si–O–C.43 The bands at 1250, 1205, and 1050–1125 cm−1 (Table 1, entries 8–10) are attributed to the vibration of C–O–C, epoxide, and C–O groups attached to GO, respectively.43,45,46 The peak at 1199 cm−1 is attributed to the stretching vibration of the carboxyl C–O bonds.46 The vibration of the CN bonds is present at 1625 cm−147 in the FT-IR spectrum of the catalyst (Table 1, entry 12).
Fig. 4 FT-IR spectra of (a) Ni magnetic nanoparticles (Ni MNPs), (b) graphene oxide nanosheets (GO), (c) magnetic graphene oxide by Ni MNPs (GO–Ni MNPs), and (d) Cu–ninhydrin@GO–Ni MNPs. |
Entry | Functional group | Absorption (cm−1) | Reference |
---|---|---|---|
1 | O–H bonds | >3000 | 41 |
2 | C–OH bonds | 1224 | 42 |
3 | C–H bonds | 878, 2958 | 24 |
4 | CC bonds | 1624 | 43 |
5 | CO bonds | 1714 | 44 |
6 | Si–O–Si bonds | 462, 800 | 43 |
7 | Si–O–C bonds | 1040, 1082 | 43 |
8 | C–O–C bonds | 1250 | 45 |
9 | Epoxides | 1205 | 43 |
10 | Alkoxy C–O bonds | 1050–1125 | 46 |
11 | Carboxyl C–O | 1199 | 46 |
12 | CN bonds | 1625 | 47 |
The magnetic properties of Ni MNPs and Cu–ninhydrin@GO–Ni MNPs were studied by a VSM magnetometer at room temperature (Fig. 5). As shown in Fig. 5, Ni MNPs have a good magnetization value of about 45.71 emu g−1. As expected, Cu–ninhydrin@GO–Ni MNPs showed a lower magnetic value than the Ni MNPs, which was found to 10.06 emu g−1. The decrease in the magnetic value of the catalyst compared to that of the Ni MNPs is due to the shielding of the magnetic property by GO and the organic moieties on its surface. The VSM curve of Cu–ninhydrin@GO–Ni MNPs confirmed that this catalyst can be isolated by an external magnet.
In order to indicate the stabilization of the organic groups on the surface of GO–Ni MNPs, thermogravimetric analysis (TGA) of Cu–ninhydrin@GO–Ni MNPs was performed over air flow and a heating ramp of 10 °C min−1 in the temperature range of 30–800 °C. The TGA curve of Cu–ninhydrin@GO–Ni MNPs is indicated in Fig. 6, which indicates the various mass losses from this catalyst at different temperatures. The first is indicated at low temperatures between 25–100 °C, which corresponds to 4% weight loss. This mass loss is attributed to the evaporation of adsorbed solvents.48,49 The second weight loss, which is about 18%, is observed between 100 and 250 °C, which is attributed to the decomposition of thermally less stable and labile oxygen-containing functional groups (hydroxyl, epoxy, and carboxylic acid).21,50 The third weight loss at about 300 °C corresponds to the more stable oxygen-containing functionalities and the bulk pyrolysis of the carbon skeleton.51,52 The fourth weight loss, which shows a major decrease in the mass of about 31% in the temperature range of 250–450 °C, is attributed to the decomposition of supported organic moieties and the copper complex on the surface if GO–Ni MNPs,21,31 which can be possibly related to the strong chemical interaction between GO–Ni MNPs and the organic groups.
The structure of the synthesized materials was characterized by XRD using a PW1730 instrument from Philips company having CuKα (λ = 1.540598 Å) radiation at 40 kV and 30 mA with 2θ = 9–90°. The normal XRD patterns of Ni MNPs, GO, GO–Ni MNPs, and Cu–ninhydrin@GO–Ni MNPs are shown in Fig. 7. The normal XRD pattern of Ni MNPs reveals three characteristic peaks at 2θ values of 44.55°, 52.25°, and 76.10°, which correspond to the Miller indices (1 1 1), (2 0 0), and (2 2 0), respectively. These reflections confirm a face-centered cubic structure (FCC) of Ni MNPs.53–55 Also, these reflections and peak intensity broadening confirms the formation of Ni nanoparticles.56,57 The strong peaks confirmed that Ni MNPs have a pure and highly crystalline structure.56 The normal XRD pattern of graphene oxide nanosheets reveals characteristic peak at the 2θ value of 10.70° (0 0 2).21 Also, the several weak peaks of 2θ, which are observed at 2θ = 20–30° correspond to the labile oxygen-containing functional groups.58 These less thermally stable oxygen-containing functionalities were observed in the TGA curve as a weight loss between 100 and 250 °C. There are no peaks corresponding to Ni MNPs in the XRD spectrum of GO. The XRD pattern of the GO–Ni MNPs is combined of both diffractions from Ni MNPs and graphene oxide nanosheets, which reveals the successful preparation of GO–Ni MNPs. Also, all the reflections and their positions have remained in the XRD pattern of the Cu–ninhydrin@GO–Ni MNPs after the modification of the nanoparticles and the fabrication of the catalyst, which confirms the crystalline stability of Ni MNPs and graphene oxide nanosheets during the preparation of the catalyst.
Scheme 4 Carbon–carbon coupling reaction of PhB(OH)2 with aryl halides in the presence of Cu–ninhydrin@GO–Ni MNPs. |
Entry | Amount of catalyst (mg) | Solvent | Base | Temperature (°C) | Time (min) | Yield (%) |
---|---|---|---|---|---|---|
1 | — | H2O | Na2CO3 | 80 | 360 | N.R. |
2 | 20 | H2O | Na2CO3 | 80 | 120 | 93 |
3 | 30 | H2O | Na2CO3 | 80 | 50 | 97 |
4 | 40 | H2O | Na2CO3 | 80 | 40 | 96 |
5 | 30 | PEG | Na2CO3 | 80 | 50 | 18 |
6 | 30 | DMSO | Na2CO3 | 80 | 50 | 40 |
7 | 30 | 1,4-Dioxane | Na2CO3 | 80 | 50 | Trace |
8 | 30 | DMF | Na2CO3 | 80 | 50 | 52 |
9 | 30 | H2O | KOH | 80 | 50 | 48 |
10 | 30 | H2O | NaOCH3 | 80 | 50 | 36 |
11 | 30 | H2O | Et3N | 80 | 50 | 58 |
12 | 30 | H2O | K2CO3 | 80 | 50 | 79 |
13 | 30 | H2O | Na2CO3 | 60 | 50 | 43 |
After obtaining the optimal conditions for the coupling reaction of iodobenzene with PhB(OH)2, the scope of the catalytic activity of Cu–ninhydrin@GO–Ni MNPs was extended to the coupling of other aryl halides with PhB(OH)2. Therefore, various aryl iodides, aryl bromides, and aryl chlorides were investigated in the cross-coupling reaction with PhB(OH)2 in the presence of Cu–ninhydrin@GO–Ni MNPs (Table 3). All the products were isolated in excellent yields and high TOF values in short reaction times. However, the coupling of aryl iodide with PhB(OH)2 is easier and faster than aryl chloride or aryl bromide in the presence of this catalyst. For example, the highest TOF value was obtained for iodobenzene. In the other hand, the lowest TOF value was obtained for chlorobenzene. Therefore, the order of reactivity of aryl halides is aryl iodides > aryl bromides > aryl chlorides. Also, the effect of the electronic nature of the functional groups on the aromatic ring of the aryl halides was investigated by various electron-donating or electron-withdrawing groups. For example, the highest TOF value or a shorter reaction time was obtained for the cross coupling of 4-bromophenol with PhB(OH)2 in the presence of Cu–ninhydrin@GO–Ni MNPs. Meanwhile, the lowest TOF value or a longer reaction time was obtained for the cross coupling of 4-nitrobromobenzene with PhB(OH)2 in the presence of Cu–ninhydrin@GO–Ni MNPs. As shown in Table 3, the reactivity of para-functionalized bromobenzenes can be sorted as 4-OH > H > 4-NO2. Therefore, aryl halides bearing an electron-donating group are faster than aryl halides bearing an electron-withdrawing group in the C–C coupling reaction in the presence of Cu–ninhydrin@GO–Ni MNPs. In order to extend the scope of this procedure, the coupling of a sample of aryl halide containing fused ring compounds with PhB(OH)2 (Table 3, entry 9) was investigated in the presence of Cu–ninhydrin@GO–Ni MNPs, which has a high TOF value and excellent yield of the obtained products were observed in carbon–carbon coupling reactions.
The selectivity of Cu–ninhydrin@GO–Ni MNPs was confirmed for the coupling of 1-bromo-4-chlorobenzene with PhB(OH)2 (Table 3, entry 5). As mentioned, the cross-coupling of aryl bromides is faster than that of aryl chlorides. Therefore, the chloro functional group was not coupled with PhB(OH)2 and pure 4-chloro-1,1′-biphenyl was formed as the only product (Scheme 5).
The catalytic cycle for the cross-coupling reaction of aryl halides with PhB(OH)2 in the presence of Cu–ninhydrin@GO–Ni MNPs is outlined in Scheme 6.31,64 In the first step, oxidative addition gives intermediate I. Then, the reaction of the base with PhB(OH)2 as a Lewis acid produces PhB(OH)3, which, after a transmetallation step, gives intermediate II. Finally, the products were formed after the reduction elimination step and the catalyst was regenerated simultaneously to continue the catalytic cycle. According to this mechanism, non-polar solvents are not capable of solvation of polar intermediates and also the base is insoluble in these solvents. Therefore, non-polar solvents are not suitable for the Suzuki reaction. But the polar solvents have the ability to dissolve the base and can also the dissolve the polar intermediates. Therefore, the polar solvents lead to an increase in the Suzuki reaction rate. Protic solvents provide better conditions for the Suzuki reaction than aprotic solvents. The obtained results in Table 2 show a good agreement with the mechanism of C–C coupling reaction.
Scheme 6 The catalytic cycle for the cross-coupling reaction of aryl halides with PhB(OH)2 in the presence of Cu–ninhydrin@GO–Ni MNPs. |
The catalytic activity of Cu–ninhydrin@GO–Ni MNPs was also investigated for the synthesis of di-aryl ethers through the C–O coupling reaction of aryl halides with phenol (Scheme 7). The optimal conditions for the synthesis of ethers were obtained in the coupling reaction of iodobenzene with phenol as the model reaction (Table 4) under different conditions. At first, different amounts of the catalyst were investigated. As shown in Table 4 (entry 1), the model reaction did not occur in the absence of the catalyst even until 6 h. Meanwhile, the reaction rate and product yields were increased with an increase in the amount of the catalyst. Eventually, 30 mg (2.12 mol%) of the catalyst was selected as the optimal amount of Cu–ninhydrin@GO–Ni MNPs (Table 4, entry 2). In the second step, the model reaction was tested in several solvents in the presence of a constant amount of the catalyst (30 mg, 2.12 mol%). Therefore, polar protic solvents (such as PEG and H2O) and polar aprotic solvents (such as DMSO and DMF) were examined in the model reaction. As shown in Table 4, acceptable results were obtained in aprotic solvents. Finally, DMSO was selected as the optimal solvent. In continuation, the effect of the several inorganic and organic bases was examined in the model reaction in DMSO and in the presence of 30 mg of the catalyst. Alkali hydroxides as the base gives better results than other bases in terms of the reaction time and the TOF values. Therefore, potassium hydroxide was selected as the optimal base (Table 4, entry 2). In the final step, the reaction temperature decreased from 130 to 100 °C, whose reaction yield reduced from 98% to 67% within 120 min (Table 4, entry 13). Based on the abovementioned studies, the optimal conditions for the synthesis of ethers were obtained in DMSO as the solvent at 130 °C in the presence of 30 mg (2.12 mol%) of Cu–ninhydrin@GO–Ni MNPs using potassium hydroxide as the base (Table 4, entry 2).
Scheme 7 C–O coupling reaction of phenol with aryl halides in the presence of Cu–ninhydrin@GO–Ni MNPs. |
Entry | Amount of catalyst (mg) | Solvent | Base | Temperature (°C) | Time (min) | Yield (%) |
---|---|---|---|---|---|---|
1 | — | DMSO | KOH | 130 | 300 | N.R. |
2 | 30 | DMSO | KOH | 130 | 120 | 98 |
3 | 20 | DMSO | KOH | 130 | 160 | 90 |
4 | 35 | DMSO | KOH | 130 | 105 | 93 |
5 | 30 | PEG | KOH | 130 | 120 | 48 |
6 | 30 | DMF | KOH | 130 | 120 | 72 |
7 | 30 | H2O | KOH | Reflux | 120 | 35 |
8 | 30 | DMSO | Na2CO3 | 130 | 120 | 20 |
9 | 30 | DMSO | NaHCO3 | 130 | 120 | 27 |
10 | 30 | DMSO | Et3N | 130 | 120 | 55 |
11 | 30 | DMSO | NaOCH3 | 130 | 120 | 31 |
12 | 30 | DMSO | NaOH | 130 | 120 | 74 |
13 | 30 | DMSO | KOH | 100 | 120 | 67 |
The obtained conditions for the coupling reaction of iodobenzene with phenol were extended to the coupling of other aryl halides including aryl iodides, aryl bromides, and aryl chlorides (Table 5). All the products were obtained with high TOF values and good yields in short reaction times. Similar to the Suzuki reaction in the presence of Cu–ninhydrin@GO–Ni MNPs, the reactivity of aryl iodide in the C–O coupling reaction is higher than that of aryl chloride or aryl bromide. As shown in Table 5, it only takes 2 hours for the coupling of iodobenzene with phenol to complete (Table 5, entry 1), while it takes 8 and 12 hours for bromobenzenes and chlorobenzene to complete the reaction, respectively (Table 5, entries 3 and 8). Therefore, the order of reactivity of aryl halides in the synthesis of ethers in the presence of Cu–ninhydrin@GO–Ni MNPs is aryl iodides > aryl bromides > aryl chlorides. Therefore, this catalyst can selectively couple aryl iodides or aryl bromides compared to aryl chlorides (Table 5, entry 7). In order to extend the scope of this procedure, the coupling of 1-bromonaphthalene with phenol (Table 5, entry 9) was examined in the presence of Cu–ninhydrin@GO–Ni MNPs, in which the corresponding ether was obtained in excellent yield.
A cyclic mechanism for the synthesis of diaryl ethers in the presence of Cu–ninhydrin@GO–Ni MNPs is outlined in Scheme 8. The cyclic mechanism includes the oxidative addition, transmetallation, and reduction elimination steps, which lead to the formation of diaryl ethers from the coupling of aryl halides with phenol and the regeneration of the catalyst to continue the catalytic cycle.59
Scheme 8 The catalytic cycle for the C–O coupling of aryl halides with phenol in the presence of Cu–ninhydrin@GO–Ni MNPs. |
The natural heterogeneity of Cu–ninhydrin@GO–Ni MNPs was studied by the hot filtration test and AAS analysis.60 Initially, the coupling reaction of 4-nitrobromobenzene with PhB(OH)2 in the presence of this catalyst was performed under the optimized conditions. This reaction was stopped after 130 min, in which 61% of 4-nitro-1,1′-biphenyl was obtained as the product at this time. In order to evaluate the copper leaching, the exact amount of copper was calculated in the filtered solution by AAS after removing the catalyst by an external magnet. In this analysis, the concentration of copper in the filtered solution was found to be 0.000003 mol L−1. Therefore, copper leaching is negligible during the reaction. This means that Cu–ninhydrin@GO–Ni MNPs is heterogeneous in nature and the described reactions take place under heterogeneous conditions. To confirm these results, the reaction of 4-nitrobromobenzene with PhB(OH)2 was repeated. Halfway through the completion of the reaction, the reaction stopped and the reaction solution was allowed to proceed in the absence of catalyst. In this stage, 65% of 4-nitro-1,1′-biphenyl was obtained as the product. These experiments confirm that the leaching of copper did not occur. Also, in order to clearly show the catalytic properties, the recycled catalyst in half time of the reaction was reused in the same reaction, in which 90% of the product was obtained after 270 min. Due to the heterogeneous nature of this catalyst, it can be recovered and reused several times. The recoverability of the catalyst is an importance factor for the evaluability of the catalyst applications. Therefore, reusing Cu–ninhydrin@GO–Ni MNPs was examined in the synthesis of both diaryl ethers and biphenyls. In order to investigate this issue, the coupling of 1-bromo-4-chlorobenzene with PhB(OH)2 and also the coupling of iodobenzene with phenol in the presence of Cu–ninhydrin@GO–Ni MNPs were selected as the model reactions. At first, each of the reaction was started under the optimized condition, which can be found in Tables 2 (entry 3) and 4 (entry 2). After the completion of each reaction, the catalyst was recovered by the assistance of an external magnet. Then, to study the reusability of this catalyst, the catalytic activity of the recovered catalyst was evaluated in the next reaction again. The obtained results are summarized in Fig. 8. As shown in Fig. 8, this catalyst can be reused for atleast 8 runs consecutive in C–C or C–O coupling reactions.
Fig. 8 Recyclability of Cu–ninhydrin@GO–Ni MNPs in the coupling of ((a) red line) 1-bromo-4-chlorobenzene with PhB(OH)2 and ((b) green line) iodobenzene with phenol. |
In order to show the efficiency of Cu–ninhydrin@GO–Ni MNPs, the obtained results from the coupling of iodobenzene or chlorobenzene with PhB(OH)2 in the presence of this catalyst were compared with the previous methods (Table 6). As shown in Table 5, the products were obtained in higher yield in a shorter time than the other catalysts. Also, palladium catalysts were employed as the catalyst in some of the methods, which is very expensive and more toxic than the copper catalyst. In addition, the Suzuki reaction was carried out in water as the solvent in the presence of Cu–ninhydrin@GO–Ni MNPs; meanwhile, toxic, expensive, and organic solvents were used in other works. Also, the Suzuki reaction was reported in the presence of homogeneous catalysts, which cannot be recovered and reused. On the other hand, Cu–ninhydrin@GO–Ni MNPs can be recovered by an external magnet and recycled for several runs in C–C coupling reactions without a significant loss of its catalytic activity.
Entry | Catalyst (mol%) | Aryl halide | Condition | Time (h) | Yield (%) | TOF (h−1) | Ref. |
---|---|---|---|---|---|---|---|
1 | Pd(eao)2 (2 mol%) | Chlorobenzene | NaHCO3, PEG400/H2O, 80 °C | 360 | 34 | 2.8 | 61 |
2 | Pd NPs@Fe3O4–lignin | Chlorobenzene | K2CO3, EtOH:H2O, 90 °C | 270 | 81 | — | 62 |
3 | Pd@COF-QA (1.7 mol%) | Chlorobenzene | TEA, H2O, 50 °C | 360 | 99 | 9.7 | 63 |
4 | Cross-linked poly(ITC-HPTPy)–Pd (0.23 mol%) | Chlorobenzene | K2CO3, EtOH:H2O, 80 °C | 600 | 96 | 41 | 64 |
5 | Pd(dba)2 (2.5 mol%) | Chlorobenzene | Click-triazole, NaOtBu, toluene, 100 °C | 18 | 80 | 1.8 | 65 |
6 | Pd–isatin–boehmite (1.48 mol%) | Chlorobenzene | K2CO3, PEG, 80 °C | 250 | 87 | 14 | 66 |
7 | Pd(0)TBA@biochar (0.715 mol%) | Chlorobenzene | Na2CO3, PEG, 80 °C | 25 | 89 | 5 | 67 |
8 | Pd-imi-CC@MCM-41/Fe3O4 (1.5 mol%) | Chlorobenzene | Na2CO3, PEG, 80 °C | 24 | 89 | 2.5 | 68 |
9 | HMS–CPTMS–Cy–Pd | Chlorobenzene | K2CO3, PEG, 100 °C | 300 | 84 | 12.9 | 69 |
10 | Cu–MPAMP@Fe3O4 | Iodobenzene | Na2CO3, PEG, 80 °C | 100 | 97 | 51 | 70 |
11 | Pd/Au NPs (4 mol%) | Iodobenzene | EtOH/H2O, K2CO3, 80 °C | 24 | 88 | 0.9 | 71 |
12 | Pd NP (1 mol%) | Iodobenzene | H2O, KOH, 100 °C | 12 | 95 | 7.9 | 72 |
13 | Copper powder (10 mol%) | Iodobenzene | K2CO3, PEG, 110 °C | 12 | 99 | 0.8 | 73 |
14 | Cu–C (10 mol%) | Iodobenzene | H2O, K2CO3, 50 °C | 3.3 | 96 | 2.9 | 74 |
15 | Cu–C (20 mol%) | Chlorobenzene | H2O, K2CO3, 50 °C | 240 | 15 | 0.2 | 74 |
16 | Cu–ninhydrin@GO–Ni MNPs (2.12 mol%) | Chlorobenzene | N2CO3, H2O, 80 °C | 240 | 90 | 10.61 | This work |
17 | Cu–ninhydrin@GO–Ni MNPs (2.12 mol%) | Iodobenzene | N2CO3, H2O, 80 °C | 50 | 97 | 54.90 | This work |
Footnote |
† Electronic supplementary information (ESI) available. See DOI: 10.1039/d1ra03578a |
This journal is © The Royal Society of Chemistry 2021 |