Covalent attachment of 3-(aminomethyl)pyridine to graphene oxide: a new stabilizer for the synthesis of a palladium thin film at the oil–water interface as an effective catalyst for the Suzuki–Miyaura reaction

Abstract

This study describes the oxidation of graphite to graphene oxide (GO), followed by its covalent functionalization with 3-(aminomethyl)pyridine (3-ampy). A thin film was produced based on the reduction of the organopalladium(II) complex, [PdCl₂(cod)] (cod = 1,5-cyclooctadiene), at the toluene–water interface, in which the N group of the pyridine ring in 3-ampy helps in the uniform distribution of the Pd(0) nanoparticles (NPs) and also holds the particles strongly together during catalytic runs. The Pd/3-ampy-reduced-GO (rGO) nanohybrid was characterized using Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, energy dispersive X-ray analysis (EDAX), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The covalent functionalization reactions of GO include the formation of covalent bonds between the NH₂ functional group of 3-ampy and the epoxy group. Our studies show that the Pd/3-ampy-rGO nanohybrid is suitable for the Suzuki–Miyaura carbon–carbon coupling reaction. Compared to classical reactions, this method consistently has the advantages of well-dispersed Pd(0) NPs over the support, short reaction times, low catalyst loading, high yields and reusability of the catalyst without considerable loss of catalytic activity and a facile and low-cost method for the preparation of the catalysts. The Pd/3-ampy-rGO nanohybrid thin film showed highly improved catalytic activity toward aryl chloride derivatives as compared with other catalysts that have been reported.

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Introduction

Carbon–carbon cross coupling is one of the most powerful tools in the synthesis of many drugs, natural products, industrially important starting materials and for the construction of carbon-based molecules and materials.¹ The Suzuki–Miyaura cross-coupling reaction, in which organo-boron compounds (mainly organoboronic acids) couple with organic halides (or triflates) in the presence of a Pd catalyst and a base, is one of the most efficient methods for the construction of C–C bonds.²

Graphene oxide (GO) and functionalized GO are widely used as excellent carbon supports for catalysts to achieve the desired activity and stability. For example, it has been reported that graphene/GO-supported metal or metal oxide nanoparticles (NPs) could improve the performance of catalysts in the oxygen reduction reaction (ORR), hydrogen evolution reaction, oxygen evolution reaction, and carbon–carbon coupling reaction.³ Theoretical calculations have shown that the interaction between a metal and graphene changes the Fermi level of both the metal and graphene, which plays an important role in enhancing the catalytic activity.⁴ Thus, it is of great interest to prepare graphene/GO-based metal NPs with excellent catalytic activity. Palladium is an important metal for catalyzing many organic reactions such as the Suzuki, Heck, and Stille coupling reactions. In recent years, there has been a growing interest to prepare Pd nanostructures with morphological control.⁵ Organic amine groups containing N act as a linker, where they covalently bind with Pd NPs through Pd–N bonds. Depositing Pd NPs on such a functionalized support, which contains nitrogen atoms, appears to be a promising way for the formulation of a stable catalyst.⁶ Currently, two approaches are widely used to synthesize graphene/GO-supported metal NPs, i.e., an in situ growth method and an ex situ assembly method.⁷ The ex situ assembly approach usually needs the surface modification of the NPs and/or graphene/GO so that they can bind together through noncovalent interactions or chemical bonding.

Recently, the use of the liquid–liquid interface as a medium for the preparation of ultrathin films of metals, chalcogenides and oxides was demonstrated.⁸ The most important advantages of this assembly strategy are its significant simplicity and the universality found in almost all of the related low dimensional nanostructures. The quality of the films is generally better than that of films fabricated by other methods.⁹ In recent years, the application of organometallic complexes has appeared as an important alternative route for the synthesis of nanomaterials.¹⁰ We have reported the effect of different organoplatinum(II) and organopalladium(II) complexes on the morphology and size of Pt NPs and Pt–Pd NPs alloys at the oil–water interface in the absence of a stabilizer.^9,11 Recently, we synthesized Pd/reduced-GO (rGO) and Pd free stabilizer NPs and investigated the application of thin films obtained from an oil–water interface in the Suzuki–Miyaura reaction for the first time, which exhibited high catalytic activity.^2b Moreover, the application of Fe₃O₄ NPs, Pd/aminoclay NPs and Pd/Fe₃O₄/rGO nanohybrid were investigated as efficient catalysts for C–C bond formation.^2c,12

In this study, GO functionalized with 3-ampy was used as a substrate to prepare Pd NPs. This strategy is an easy and inexpensive method for the fabrication of NP thin films and only a beaker and syringe are required for a high-quality thin film, which can be easily produced in a short time. Transmission electron microscopy confirmed that the nanometer-sized Pd particles were well distributed on the 3-ampy-GO substrate. The Pd/3-ampy-rGO nanohybrid functioned as an efficient catalyst for Suzuki–Miyaura reactions for the formation of carbon–carbon bonds. High electron density groups on Pd nanocatalysts increase the rate of oxidative addition, which is the rate determining step of the catalytic cycle, and just as we expect, the C–C coupling reaction with the Pd/3-ampy-rGO nanohybrid is faster and occurs in less time than Pd/rGO nanocatalysts.

Experimental

All the chemical compounds were purchased from Merck Company. The complex [PdCl₂(cod)] (cod = cis,cis-1,5-cyclooctadiene) was synthesized using a reported procedure.¹³ Powder X-ray diffraction patterns (XRD) were obtained using a Bruker AXS (D8, Advance) instrument employing the reflection Bragg–Brentano geometry with Cu-Kα radiation. The qualitative and quantitative elemental composition of the treated samples were acquired by energy dispersive X-ray analysis (EDAX, model Seron AIS 2300, Korea). Transmission electron microscopy (TEM) images were obtained with a Philips CM-10 microscope operated at 100 kV. Raman spectra were recorded from 4250 cm⁻¹ to 100 cm⁻¹ on a high resolution dispersive Raman Thermonicolet (LabRAM HR UV/Vis/NIR, Electrooptics). The loading amount of palladium was determined using an ICP analyzer (Varian, Vista-Pro). FT-IR spectra were obtained with a Jasco FT/IR-680 plus spectrometer. ¹H NMR spectra were obtained using a Bruker 400 MHz ultra-shield spectrometer with CDCl₃ as the solvent and TMS as the internal standard.

Preparation of 3-ampy-GO

GO was synthesized from natural graphite flakes by a modified Hummers method.¹⁴ 0.01 g of GO was dispersed in distilled water and placed in a sonic bath for 10 min. Finally, a mixture containing 3-ampy (0.01 mmol) and 0.01 g NaOH in water was added. The reaction mixture was heated under a reflux at 80 °C for 24 h, after which the mixture was centrifuged and black crystals were separated, washed with ethanol and water and air-dried (Scheme 1).

Scheme 1 Schematic illustration of the preparation of 3-ampy-GO.

Preparation of Pd/3-ampy-rGO nanohybrid thin film at the oil–water interface

1 mM [PdCl₂(cod)] complex in toluene (25 ml) was sonicated for 15 min to prepare a yellow color solution. This solution was allowed to come in contact with distilled water (25 ml) containing 3-ampy-GO (10 mg) in a beaker (100 ml). Once the two layers were stabilized, an appropriate volume of aqueous solution of NaBH₄ (10 ml, 0.1 M) was injected into the aqueous layer using a syringe with minimal disturbance to the toluene layer. The onset of reduction was marked by the coloration of the liquid–liquid interface. With the passage of time, the color became more vivid, and finally resulted in a film at the liquid–liquid interface. The aqueous and organic layers below and above the film were, however, transparent.

General procedure for Suzuki–Miyaura coupling reaction

Arylhalide (0.5 mmol) and phenylboronic acid (0.75 mmol) were added to a flask containing the Pd/3-ampy-rGO catalyst (0.004 mol% of Pd) and K₂CO₃ (1 mmol) in 6 ml of EtOH/H₂O (1 : 1). The reaction was carried out at 80 °C. After the completion of the reaction (monitored by TLC), the reaction mixture was cooled to room temperature, and then dichloromethane (5 × 10 ml) was added to the reaction vessel and the solid catalyst was separated. The organic phase was separated and dried over anhydrous MgSO₄. The evaporation of the solvent gave the pure desired product. Characterization of these compounds was established by comparison of their FT-IR and ¹H NMR spectra with those of authentic samples, the details of which are given in the ESI.† The turnover number (TON (= mol of product/mol of catalyst)) and turnover frequency (TOF (= TON/time (h))) were calculated on the basis of the amount of biaryl product formed.

Results and discussion

Physicochemical characterization of the catalyst

In this study, the synthesis of a Pd/3-ampy-rGO nanohybrid thin film, which involves the chemical reduction of the [PdCl₂(cod)] complex at the oil–water interface with NaBH₄, is demonstrated. The FT-IR spectra of GO, 3-ampy-GO and Pd/3-ampy-rGO are shown in Fig. 1. The results from FT-IR spectroscopy revealed that the characteristic band of the carboxyl group in GO appears at ca. 1729 cm⁻¹ (C=O stretching) (Fig. 1a). The C–O vibrations of the epoxy groups in GO appear at ca. 1226 cm⁻¹.^2c,15 As shown in Fig. 1b, the peaks at 2865 and 2927 cm⁻¹ correspond to the symmetric ν_s CH₂ and asymmetric ν_as CH₂ of 3-ampy, respectively. Because the GO sheet contains reactive epoxy groups, its exposure to amine groups would lead to a ring opening reaction of the reactive three-membered epoxide ring, thus creating new C–N bonds and –OH functional groups. The increase of the peak intensities at 1575 and 1199 cm⁻¹ corresponds to the stretching of the new NH bending and C–N vibration, respectively. Amine groups did not react with the carboxylic acid groups of GO through the amidation process because the amide ν NH vibration, expected at 3300 cm⁻¹, is not present and the 1650–1750 cm⁻¹ region does not show a strong ν C=O band. The absorption band at around 1700 cm⁻¹ is attributed to carboxyl groups. However, the corresponding absorption (Fig. 1b) at this range is not observable, which is likely due to the overlapping the absorption of graphene sheets in this region.^2c,16 The FT-IR result in Fig. 1c shows that the Pd/3-ampy-rGO nanohybrid is formed via a charge-transfer interaction between 3-ampy and palladium, which demonstrates that the donation of an electron lone pair on the N group of pyridine ring in the 3-ampy into an unoccupied orbital of the palladium NP surface is responsible for the electron transfer and interaction of the Pd(II) complex with 3-ampy-GO.^8b,17 For 3-ampy-GO, absorption bands appear at 2915 cm⁻¹ and 2852 cm⁻¹, which is attributed to CH₂; a stronger absorption band appears at 1571 cm⁻¹, which is assigned to NH; and an absorption band appears at 1220 cm⁻¹, which is assigned to CN (Fig. 1c). Compared with the 3-ampy-GO reference, the absorption of 3-ampy in Pd/3-ampy-rGO nanohybrid is shifted.

Fig. 1 (a) FT-IR spectra of GO, (b) 3-ampy-GO, and (c) Pd/3-ampy-rGO.

Raman spectroscopy has been widely used to probe the structural and electronic characteristics of graphite materials, thus providing useful information on the defects (D band) and in plane vibration of sp² carbon atoms (G band). Fig. 2 shows the Raman spectra of GO and Pd/3-ampy-rGO. The prominent D peak appears from the structural imperfections created by the attachment of hydroxyl and epoxide groups on the carbon basal plane.¹⁸ The Raman spectra in Fig. 2 show characteristic peaks located at 1350 and 1592 cm⁻¹, which correspond to the D and G bands of graphene sheets, respectively. As shown in Fig. 2b, the Raman spectrum of amine-functionalized GO also exhibits fundamental vibrations that are similar to graphene oxide at 1598 and 1356 cm⁻¹. The Raman spectrum of 3-ampy-GO exhibits a higher relative D/G intensity ratio (1.45) compared to GO (0.95), which implies the decreased size of the sp² domains upon the localized chemical reduction of GO by 3-ampy.^16,18,19 Typically, Raman spectroscopy is used for the determination of exfoliation yield.²⁰ The G band of GO observed at 1592 cm⁻¹ shifted to 1598 cm⁻¹ after 3-ampy functionalization, which indicates the better exfoliation of graphene layers.¹⁹

Fig. 2 (a) Raman spectra of GO and (b) 3-ampy-GO.

The XRD pattern of graphite is displayed in Fig. 3. The intense peak centered at 26.3° corresponds to the (002) plane of graphite.²¹ Fig. 4a shows an SEM image and Fig. 4b shows the XRD pattern of the bulk GO in the dry state. In the XRD pattern (Fig. 4b), the clear diffraction band centered at 2θ = ∼10° corresponds to the (002) plane of GO.^2b The XRD pattern of 3-ampy-GO is shown in Fig. 5a. The first peak located at 2θ = 12.44 (002) is attributable to GO, which shifted to higher 2θ values (about 2°) compared to the XRD of GO, and the weak and broad peak at the 2θ value of 25.55° (002) confirms the GO intercalation with 3-ampy after the additional ring-opening reaction due to the amine groups of 3-ampy and the oxidation of graphite, which means that this peak is attributed to rGO. These findings allow us to confirm the successful conjugation of 3-ampy onto the GO surface. After chemical reduction by sodium borohydride to produce the rGO-supported catalyst, the sharp diffraction peak of GO at 10° disappeared in the XRD pattern, which implies the partial removal of the oxygen functional groups. The other characteristic peaks exhibit the face-centered-cubic (fcc) lattice structure of Pd, which correspond to the (111), (200), (220), (311) and (222) planes and indicate the presence of Pd(0) (Fig. 5b).^11b The composition of the Pd/3-ampy-rGO nanohybrid was further examined by energy dispersive X-ray analysis (EDAX), where the Pd and C elements were observed (Fig. 6). The palladium loading of the catalyst, which was obtained using inductively coupled plasma (ICP), was 2.1 μg.

Fig. 3 XRD pattern of graphite.

Fig. 4 (a) SEM image of GO and (b) XRD pattern of GO.

Fig. 5 (a) XRD pattern of 3-ampy-GO. (b) XRD pattern of the Pd/3-ampy-rGO nanohybrid thin film deposited on glass.

Fig. 6 EDAX spectrum of the Pd/3-ampy-rGO nanohybrid.

Fig. 7 shows the TEM images of the palladium NPs adhered on 3-ampy-GO sheets. The reduction of the Pd particles was further studied using TEM to obtain the distribution of the metal NPs on the functionalized GO (Fig. 7a and b). Spherical Pd NPs with a size of around 5–6 nm are well-dispersed on the support (Fig. 7c), which is quite consistent with the data obtained from the XRD analysis. Usually, small size NPs have the tendency to aggregate, and this phenomenon occurred exactly in the case of the Pd/3-ampy-rGO nanohybrid. It is believed that the presence of the organic amine moiety on the GO surface facilitated the dispersion of the Pd(0) NPs on the GO surface through coordination and it acts as a stabilizing agent.²²

Fig. 7 (a and b) TEM image of Pd/3-ampy-rGO nanohybrid and (c) histogram of particle size distribution.

Catalytic evaluation

Carbon–carbon bond formation is one of the most fundamental reactions for the construction of molecular frameworks in organic chemistry. Therefore, in this study, we studied the role of the prepared catalyst toward the Suzuki–Miyaura coupling reaction in the presence of the EtOH/H₂O (1 : 1) solvent (Table 1).

Table 1 Suzuki–Miyaura cross-coupling of aryl halides with phenylboronic acid catalyzed by the Pd/3-ampy-rGO nanohybrid

#	Substrate	Product	Time (min)	Yield^a (%)	TON^b	TOF^b (h^−1)
a Isolated yields.b See Experimental section for the calculation of TONs and TOFs.
1	C6H5I	1a	10	>99	24 750	148 500
2	C6H5Br	1a	20	95	23 750	71 250
3	4-MeC6H4Br	1b	60	87	21 750	21 750
4	4-MeOC6H4Br	1c	150	80	20 000	8000
5	C6H5Cl	1a	30	85	21 250	42 500
6	4-NO2C6H4Cl	1d	15	72	18 000	72 000
7	4-CNC6H4Cl	1e	15	76	19 000	76 000
8	C5H4NCl	1f	240	86	21 500	5375

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Solvent plays an important role in improving the reactivity of this type of coupling reaction. Therefore, we carried out rigorous investigations to define the best solvent for the Suzuki–Miyaura coupling reaction. Low yields were achieved with H₂O solvent, while the EtOH/H₂O solvent gave excellent yields. We examined the effect of the Pd/3-ampy-rGO nanohybrid system in the EtOH/H₂O solvent and interestingly an excellent yield of the product was obtained. As shown in Table 1, the Suzuki–Miyaura reaction of phenylboronic acid with selected aryl halides in the presence of the Pd/3-ampy-rGO nanohybrid as a palladium catalyst and aryl chlorides affords very high yields.

Normally, the catalytic cycle of the present reactions includes three steps: (1) oxidative addition, (2) transmetalation, and (3) reductive elimination.²³ K₂CO₃ was used as the base to optimize the conditions of the reaction. Usually, the activity of aryl halides decreases in the order of I > Br > Cl and electron-deficient aryl halides are generally more active than electron-rich ones.^22b Bromobenzene is faster than 4-bromotoluene in the cross-coupling reaction because CH₃ is an electron donor group and it reduces the oxidative addition step speed (Table 1, entries 2 and 3). Chlorobenzene is slower than 1-chloro-4-nitrobenzene due to the fact that the NO₂ group is electron-withdrawing and weakens the C(sp²)–Cl bond and increases the speed of oxidative addition (Table 1, entries 5 and 6). Thus, the oxidative addition step is generally considered as the rate-determining step (RDS). In the oxidative addition step, Pd(0) acts as a nucleophile and preferentially attacks the most electron-deficient position. It should be noted that the Pd/3-ampy-rGO nanohybrid behaved as a very good catalyst toward the Suzuki–Miyaura coupling reaction. The Pd/3-ampy-rGO catalyst, compared to other catalysts with graphene substrates and due to the presence of amine groups, exhibited a faster oxidative addition. As mentioned, the functionalized GO with the 3-ampy donation of a lone pair of electrons from the N group of the pyridine ring in the 3-ampy to Pd NPs improves the reactivity of the catalyst compared to Pd/rGO. Moreover, the N group of the pyridine ring in 3-ampy stabilizes the Pd(0) NPs and helps to increase their activity and stability. It should be noticed that we have compared the activity of Pd/3-ampy-rGO with Pd/rGO in the Suzuki–Miyaura reaction of bromobenzene and phenylboronic acid in the presence of the EtOH/H₂O (1 : 1) solvent at 80 °C. As shown in Table 2, a higher TOF and higher yield are seen for the Pd/3-ampy-rGO catalyst and more activity is established for the Pd/3-ampy-rGO catalyst.

Table 2 Suzuki–Miyaura reaction between bromobenzene and phenylboronic acid in the presence of Pd/rGO NPs and Pd/3-ampy-rGO nanohybrid in the EtOH/H₂O (1 : 1) solvent at 80 °C

#	Catalyst	Time (min)	Yield (%)	TON	TOF (h^−1)	Ref.
1	Pd/rGO	30	87	111	222	2b
2	Pd/3-ampy-rGO	20	95	23 750	71 250	This work

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When the Suzuki–Miyaura reaction of phenylboronic acid with bromobenzene was completed, the Pd/3-ampy-rGO nanohybrid could be easily separated from the reaction mixture. Centrifugation was applied to separate the catalyst from the reaction mixture, which was then washed with water and diethylether. The recovered catalysts were dried and checked using XRD analysis. As shown in Table 3, the catalyst showed excellent catalytic activity even after 8 times of recycling and its activity remained almost unaltered.

Table 3 Recycling result of the coupling reaction of phenylboronic acid with bromobenzene

Run	1st	2nd	3rd	4th	5th	6th	7th	8th
Yield (%)	89	88	90	86	88	88	86	87

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The TON and TOF, which are a measure of the efficiency of a catalyst, totally depend on the Pd concentration, which reflects the structural development of the supported palladium. Fox et al. reported that the Suzuki coupling reaction over a Pd-NP-cored G-3 dendrimer catalyst gives TON = 23 300 and TOF = 1942 h⁻¹.²⁴ Hou et al. reported that the Suzuki coupling reaction over a Pd–Ni/RGO catalyst gave TON = 9687.5 and TOF = 38 750 h⁻¹.²⁵ In the current study using Pd/3-ampy-rGO as a catalyst, a higher TON [23 750] and TOF [71 250 h⁻¹] were observed for the Suzuki–Miyaura reaction of phenylboronic acid with bromobenzene. The TON and TOF have been recorded in the presence of different Pd-based catalysts,^24,25 but unfortunately none of the studies reported on the reaction in the presence of aryl chlorides.^24–31 Pd/3-ampy-rGO can react with aryl chlorides to give high yields of the products.

We compared our results with those of the noble metal based catalysts reported in the past few years for the Suzuki–Miyaura coupling reaction, taking the reactions of chlorobenzene and 1-chloro-4-nitrobenzene with phenylboronic acid for Suzuki–Miyaura coupling as two examples (Table 4).^26–31 Although some of them can also obtain high yields, the following factors make our catalyst superior to the others for these reactions. (i) well-dispersed Pd(0) NPs over the support are strongly bound with the N moiety of the pyridine ring in 3-ampy, which offers excellent repeatability without loss of catalytic activity, (ii) the catalyst was prepared by a facile and low-cost method, (iii) good results were obtained in short reaction times using a low catalyst loading, and (iv) large TON for the catalyst indicates that the catalyst is stable and very long-lived.

Table 4 Study of the efficacy of the present system compared with previous reports

#	G	Catalyst	Solvent	Base	Temp (°C)	Time (h)	Yield (%)	Ref.
a Poly(2-aminothiophenol) supported gold NPs (0.05 mol).b Pd(OAc)2 (1f)2, (1f): 1,1,3,3-tetramethyl-2-n-butylguanidine (2 mol%).c Pd(OAc)2 (1g)2, (1g): 1,1,3,3-tetramethyl-2-sec-butylguanidine (2 mol%), TBAB (0.1 equiv.) as the additive.d Pd(OAc)2 (0.4 mol%).e NAP-Mg–Pd(0) (3 mol%).f Pd-Schiff base@MWCNTs (0.2 mol%).g Pd/Fe3O4/rGO nanohybrid (0.36 mol%).h PdFS NP thin film (0.48 mol%).i Pd/rGO NP thin film (0.48 mol%).j Na2[PdCl4] (0.5 mol%).
1	H	Au^a	H2O	NaOH	80	4	87	26
2	H	Pd(OAc)2 (1f)2^b	H2O : EtOH = 3 : 2	K2CO3	80	48	33	27
3	H	Pd(OAc)2 (1g)2^c	H2O : EtOH = 3 : 2	K2CO3	80	10	73	27
4	H	Pd(OAc)2^d	H2O	Na2CO3	150–170	5 min	45	28
5	H	NAP-Mg–Pd(0)^e	DMA	K3PO4	130	2–6	65	29
6	H	Pd(II)-MWCNTs^f	H2O : DMF = 1 : 1	K2CO3	65	7	53	30
7	H	Pd/Fe3O4/rGO^g	H2O	K2CO3	80	2.5	85	2c
8	H	PdFS^h	H2O	K2CO3	80	4	75	2b
9	H	Pd/rGO^i	H2O	K2CO3	80	3	80	2b
10	H	Pd/3-ampy-rGO	EtOH : H2O = 1 : 1	K2CO3	80	30 min	85	This work
11	NO2	Pd(OAc)2 (1f)2^b	H2O : EtOH = 3 : 2	K2CO3	R.T	10	67	27
12	NO2	Na2[PdCl4]^j	H2O–DMSO	KF, K3PO4	80	18	90	31
13	NO2	NAP-Mg–Pd(0)^e	DMA	K3PO4	130	2–6	90	29
14	NO2	Pd/Fe3O4/rGO	H2O	K2CO3	80	1.5	78	2c
15	NO2	PdFS^h	H2O	K2CO3	80	2.5	70	2b
16	NO2	Pd/rGO^i	H2O	K2CO3	80	1.5	74	2b
17	NO2	Pd/3-ampy-rGO	EtOH : H2O = 1 : 1	K2CO3	80	15 min	72	This work

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Conclusion

In summary, we demonstrated a simple approach for the synthesis of a Pd/3-ampy-rGO nanohybrid using a simple three-step method. This nanometal has well-dispersed 5–6 nm sized Pd(0) NPs on its surface, which act as the active site for the Suzuki–Miyaura C–C coupling reactions. The N group of the pyridine ring in 3-ampy shows high affinity for the Pd(0) NPs, thus making it durable for eight times repetitive use with consistent catalytic activity. Furthermore, the Pd/3-ampy-rGO nanohybrid behaved as a very good catalyst toward aryl chloride derivatives.

Acknowledgements

We thank the Yasouj University Research Council and Iranian Nanotechnology Initiative Council for their support.

References

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c5ra07171b

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