Efficient Heterogenization of Palladium by Citric Acid on the Magnetite

Journal of Organometallic Chemistry 883 (2019) 1e10

Contents lists available at ScienceDirect

Journal of Organometallic Chemistry

journal homepage: www.elsevier.com/locate/jorganchem

Efﬁcient heterogenization of palladium by citric acid on the magnetite nanoparticles surface (Nano-Fe3O4@CA-Pd), and its catalytic application in C-C coupling reactions

* Ehsan Ghonchepour, Mohammad Reza Islami , Ahmad Momeni Tikdari

Department of Chemistry, Shahid Bahonar University of Kerman, 22 Bahman Avenue, 76169, Kerman, Iran article info abstract

Article history: In this study, citric acid was used as a ligand for the heterogenization of palladium chloride on Fe3O4 Received 30 October 2018 nanoparticles surface as efﬁcient and recoverable green catalyst (Nano-Fe3O4@CA-Pd). The catalytic Received in revised form activity of this composite was tested in the Sonogashira and the Suzuki cross-coupling reactions. The 12 January 2019 structure of catalyst characterized using spectroscopic data, magnetic, and thermal techniques such as Accepted 14 January 2019 FT-IR, SEM, EDX, XRD, VSM, and TGA. Available online 16 January 2019 © 2019 Elsevier B.V. All rights reserved.

Keywords: Palladium Magnetic nanoparticles Heterogenization C-C coupling Green catalyst Suzuki reaction Sonogashira reaction

1. Introduction advantages of heterogeneous systems [5e7]. Magnetic-supported catalysts are a useful group of heteroge- Nowadays, attention to green chemistry is one of the main neous systems, in which the catalyst is separated using an external concerns of the world that should be especially followed as an magnetic field. Such catalysts could have longer lives, minimizing essential requirement. The catalyst is a key component of “green the change in activity and selectivity over homogeneous catalysts chemistry”, and one of the important challenges facing the in- [8,9]. Synthesis the surface properties of magnetic nanoparticles dustry now is the design and use of environmentally safe catalysts can be carried out using different methods: (a) covering with ox- [1,2]. A green catalyst must have many properties such as low ides, carbon, polymer or metallic layers; (b) the non-covalent preparation cost, high activity, high stability, great selectivity, easy approach with polymers or surfactants; and (c) the covalent and efficient recoverable and good recyclability [3]. Due to approach between hydroxyl groups on the nanoparticles surface improved efficacy, homogeneous catalysis has grabbed more and anchoring agents such as carboxylic acid, phosphoric acid and attention and affecting than heterogeneous approaches. Despite dopamine derivatives [8]. the toxicity and difficulty of separating homogeneous catalysts Citric acid (Fig. 1) is a weak natural organic acid with three along with the loss of catalyst activity after one run, these catalysts carboxylate groups, solid and soluble in water. It is a natural pre- have scarcely been utilized in the industry [4]. In recent years to servative, which is available in citrus fruits. The carboxylate groups avoid these problems, heterogeneous catalytic systems have been can join to metal oxide surface [10e12] and can form stable com- used extensively in various synthetic transformations. Straight- plexes with metal ions such as Pd and Cu [13,14]. forward experimental procedures, mild reaction conditions, The biaryls are one of the most important compounds in nature reusability of catalysts and minimal waste disposal, are the and they have become of special interest to researchers because some biaryl systems have biological activity and pharmaceutically useful. For example, Diflunisal (1, Fig. 2) has been shown analgesic fl * Corresponding author. and anti-in ammatory activity and in recent years the use of E-mail address: [email protected] (M.R. Islami). biphenyl derivatives has been developed in industry. For example, https://doi.org/10.1016/j.jorganchem.2019.01.008 0022-328X/© 2019 Elsevier B.V. All rights reserved. 2 E. Ghonchepour et al. / Journal of Organometallic Chemistry 883 (2019) 1e10

2.2. Synthesis of magnetic nanoparticles Nano-Fe3O4@CA-Pd

To prepare of magnetic catalyst (Nano-Fe3O4@CA-Pd), a mixture of 0.994 g (5.0 mmol) FeCl2.4H2O and 2.70 g (10.0 mmol) Fig. 1. Citric acid structure. FeCl3.6H2O salts dissolved in 100 ml of deionized water under intense stirring. An aqueous ammonia solution (30 ml) (25% w/w) was added to the stirring mixture to increase the reaction pH about 11. After 1 h, 10 ml solution of citric acid (0.2 M) was added drop- wise to this black suspension. The reaction mixture was continu- ously stirred for 1 h at room temperature and then refluxed for 1 h. The (Fe3O4@CA) were separated from the aqueous solution using an external magnet and washed with water in several times. In next section, 2.0 mmol (0.355 g) of PdCl2 and 3.0 mmol (0.317 g) of Na2CO3 were added to a solution of 0.50 g Fe3O4@CA in 50 ml Fig. 2. Structure of Diflunisal (1) and Polychlorinated biphenyl (2). methanol and stirring at room temperature for 24 h. Finally, nanoparticles were separated from the solution by magnetic decantation and washed several times with water, ethanol and polychlorinated biphenyl (PCB) (2, Fig. 2) is an organic chlorine diethyl ether respectively, before been dried in an oven overnight. compound with the formula C12H10xClx. Polychlorinated bi- fl phenyls are widely deployed as dielectric and coolant uids in 2.3. General procedure for suzuki coupling reaction in the presence electrical apparatus, carbonless copy paper and in heat transfer of Nano-Fe3O4@CA-Pd fluids [15,16]. Powerful synthetic method for the generation of biaryl in To a solution of arylhalide compound (1.0 mmol), phenylboronic organic chemistry is a C-C coupling reaction between arylhalids acid (1.0 mmol) and 2.0 mmol K2CO3 in 8 ml EtOH/H2O (1:1), was and arylboronic acid in the presence of a metal catalyst (Suzuki added 10 mg of Nano-Fe3O4@CA-Pd. The mixture was heated and reaction). For this reaction in the recent years, many alternative stirred at 75 C for 25 min. The progress of the reaction was homogeneous and heterogeneous catalyst systems have been re- monitored by TLC. After 25 min, the nanoparticles were separated ported such as Pd(OAc)2 [17], Pd(PPh3)4 [18], NiCl2(PPh3)2 [19], with an external magnet from the reaction mixture and washed Nanoparticles of Ni and NiO [14], thallium (I) Salts [20], Fe3O4 with deionized water and diethyl ether repeatedly. Water (50 ml) nanoparticle-ionic liquid [21], Natural DNA-Modified Graphene/Pd was then added to the reaction mixture and extracted with CH2Cl2 Nanoparticles [22], Fe3O4@EDTAePdCl2 [8], Ni@Pd/KCC-1 [23], Au/ (2 25 mL) and dried over Na2SO4. The solvent was removed under MPC, Pd/MPC [24], and PdNi/mCN [25]. reduced pressure to give the crude product. The residue was sub- Although acceptable results have been obtained in terms of jected to column chromatography using n-hexane as an eluent to fi short reaction times, conditions, and reaction ef ciency [26]. But in afford pure product. some method, there is drawbacks such as poor catalyst recyclability Biphenyl (Table 2, entry1). Yield 98%. mp 68e70 C. 1H NMR [17], tedious work-up and long reaction times [20]. Due to the 13 (400 MHz, CDCl3)d 7.66 (d, 4H), 7.50 (m, 4H), 7.40 (m, 2H). C NMR importance of green chemistry, we decided to synthesize the high (100 MHz, CDCl3) d: 127.25, 127.34, 128.84, and 141.31. catalytic activity of supported and heterogeneous catalysts with the 4-Methoxy-biphenyl (Table 2, entry 4). Yield 95%. mp 85e88 C. advantages of easy separation of magnetic nanoparticle. Here we 1 H NMR (400 MHz, CDCl3) d 7.62e7.55 (m, 4H), 7.46 (t, 2H, wish to report the preparation of palladium complex with citric J ¼ 7.7 Hz), 7.35 (t, 1H, J ¼ 7.3 Hz), 7.02 (d, 2H, J ¼ 8.5 Hz), 3.91 (s, 3H, acid that stabilized on the Fe3O4 nanoparticles (Nano-Fe3O4@CA- 13 OCH3). C NMR (100 MHz, CDCl3) d: 55.37, 114.24, 126.70, 126.78, Pd) and characterized and study of its catalytic activity for the Suzuki coupling reaction between aryl halide and phenylboronic acid. Table 1 Optimization of C-C coupling reaction conditions between phenylboronic acid and iodobenzene.a

2. Experimental Entry Catalyst Catalyst (mol%) Base Solvent Temp (C) Yieldb %

2.1. Chemicals, Instrumentation, and analysis 1L3 10 K2CO3 EtOH 25 68 2L3 10 K2CO3 EtOH 75 80 FT-IR spectra were obtained in the area 4000e400 cm 1 using a 3L3 10 Li2CO3 EtOH 75 75 4L 10 Na CO EtOH 75 75 Nicolet IR100 instrument with spectroscopic grade KBr. The images 3 2 3 5L3 10 K2CO3 H2O750 and EDX analyze of the catalyst were observed using Philips XL 30 6L3 10 K2CO3 EtOH/H2O 75 98 and S-4160 instruments with coated gold equipped with dispersive 2:1 X-ray spectroscopy capability. TGA was performed on a Thermal 7L3 10 K2CO3 EtOH/H2O 75 95 1:2 Analyzer with a heating rate of 10 C min 1 over a temperature 8L 10 K CO EtOH/H O 75 98 e ﬂ 3 2 3 2 region of 25 600 C under owing compressed nitrogen gas. 1:1

Powder X-ray diffraction (XRD) spectra were recorded at room 9L3 5K2CO3 EtOH/H2O 75 90 temperature by a Philips X-Pert 1710 diffractometer using Co Ka 1:1 (l ¼ 1.78897 Å) at a voltage of 40 kV and current of 40 mA and data 10 L1 10 K2CO3 EtOH/H2O 75 10 1:1 were collected from 10 to 90 (2q) with a scan speed of 0.02 s 1. 11 L2 10 K2CO3 EtOH/H2O 75 20 The magnetic properties of catalyst nanoparticles were obtained 1:1 with a vibrating alternating gradient force magnetometer. All sol- a Phenylboronic acid 1 mmol, iodobenzene 1.0 mmol, base 2.0 mmol, catalyst, vents and chemicals purchased and used without further solvent (8 mL), and 25 min. puriﬁcation. b Isolated yield. E. Ghonchepour et al. / Journal of Organometallic Chemistry 883 (2019) 1e10 3

1 Table 2 H NMR (400 MHz, CDCl3) d 8.06 (d, 2H, J ¼ 8.5 Hz), 7.71 (d, 2H, The substrates scope of the C-C coupling reaction between phenylboronic acid and ¼ ¼ ¼ a J 8.01 Hz), 7.65 (d, 2H, J 6.7 Hz), 7.50 (t, 2H, J 7.6 Hz), 7.43 (t, aryl halide by catalyzed by Nano-Fe3O4@CA-Pd. 1H, J ¼ 7.3 Hz), 2.67 (s, 3H, CH3). entry Ar-X product yieldb % Ref 4-Methyl-biphenyl (Table 2, entry 10). Yield 76%. mp 46e47 C. 1 1 98 [33] H NMR (400 MHz, CDCl3) d 7.63 (dd, 2H, J ¼ 8.0, 0.8 Hz), 7.56 (dd, 2H, J ¼ 8.0, 1.6 Hz), 7.48 (t, 2H, J ¼ 7.8 Hz), 7.38 (t, 1H, J ¼ 7.4 Hz), 7.31 (d, 2H, J ¼ 7.9 Hz), 2.45 (s, 3H, CH3). 2 90 [33] 4-Cl-biphenyl (Table 2, entry 12). Yield 98%. mp 76e78 C. 1H NMR (400 MHz, CDCl3) d 7.60e7.53 (m, 4H), 7.49e7.43 (m, 4H), 7.39 (t, 1H, J ¼ 7.3 Hz). 3 40 [33] 4-Nitro-biphenyl (Table 2, entry 13). Yield 95%. mp 111e113 C. 1 H NMR (400 MHz, CDCl3) d 8.32 (d, 2H, J ¼ 8.7 Hz), 7.76 (d, 2H, J ¼ 8.7 Hz), 7.65 (d, 2H, J ¼ 7.45 Hz), 7.55e7.46 (m, 3H). 4 95 [34] 4-Cyano-biphenyl (Table 2, entry 14). Yield 86%. mp 84e86 C. 1 H NMR (400 MHz, CDCl3) d 7.73 (m, 4H, J ¼ 18.0 Hz), 7.62 (d, 2H, J ¼ 8.0, 7.11 Hz), 7.52 (t, 2H, J ¼ 6.8 Hz), 7.46 (d, 1H, J ¼ 7.1 Hz). 5 98 [34]

2.4. General procedure for sonogashira coupling reaction in the 6 98 [34] presence of Fe3O4@CA-Pd

To a solution of aryl halide compound (1.0 mmol), phenylacetylene (1.5 mmol) and 2.0 mmol K CO in DMF (3 mL), was 7 65 [35] 2 3 added 10 mg of Fe3O4@CA-Pd. The mixture was heated and stirred at 90 C for 2 h. The progress of the reaction was monitored by TLC. After 2 h, the nanoparticles were separated with an external magnet from the reaction mixture and washed with deionized water and diethyl ether repeatedly. Water (50 ml) was then added to the 8 95 [34] reaction mixture and extracted with CH2Cl2 (2 25 mL) and dried over Na2SO4. The solvent was removed under reduced pressure to give the crude product. The residue was subjected to column chromatography using petroleum ether as an eluent to afford pure 9 trace [36] product. 1,2-Diphenylethyne (Table 4, entry 1). Yield 95%. 1H NMR 10 76 [37] (500 MHz, CDCl3) d 7.56 (dt, J ¼ 6.7, 1.6 Hz, 4H), 7.42e7.38 (m, 4H), 13 7.37 (d, J ¼ 1.9 Hz, 2H). C NMR (126 MHz, CDCl3) d 132.5, 131.6, 129.2, 128.4, 81.6 (see Table 5). 11 0 e 1-Nitro-4-(phenylethynyl0)benzene (Table 4, entry 4). Yield 1 95%. H NMR (500 MHz, CDCl3) d 8.25 (d, J ¼ 8.9 Hz, 2H), 7.69 (d, J ¼ 8.8 Hz, 2H), 7.62e7.56 (m, 2H), 7.43 (d, J ¼ 1.9 Hz, 2H), 7.41 (dd, 12 98 [38] 13 J ¼ 5.0, 1.8 Hz, 1H). C NMR (126 MHz, CDCl3) d 147.0, 132.3, 131.8, 130.3, 129.3, 128.5, 123.6, 122.1, 94.7, 87.5. 13 95 [35] 2-Fluoro-1-nitro-4-(phenylethynyl)benzene (Table 4, entry 5). 1 Yield 55%. H NMR (500 MHz, CDCl3) d 8.07 (dd, J ¼ 8.8, 7.8 Hz, 1H), 14 86 [39]

Table 3 Optimization of C-C coupling reaction conditions between 4-Iodonitrobenzene and a Phenylboronic acid 1.0 mmol, aryl halide 1.0 mmol, K2CO3 2 mmol, Nano- phenylacetylene.a Fe3O4@CA-Pd (10 mg), EtOH/H2O (1:1, 8 ml), and 25 min. b b Isolated yield. entry cat Solvent Base Temp ( C) Yield %

1 e DMF K2CO3 70 0 2 Nano-Fe O @CA-Pd DMF K CO 70 85 128.19, 128.77, 133.79, 140.86, and 159.18. 3 4 2 3 3 Nano-Fe3O4@CA-Pd DMF K2CO3 90 95 2-Methoxy-biphenyl (Table 2, entry 6). Yield 98%. A colorless 4 Nano-Fe3O4@CA-Pd DMF K2CO3 110 90 1 d ¼ oil. H NMR (400 MHz, CDCl3) 7.65 (d, 2H, J 7.39 Hz), 7.52 (t, 2H, 5 Nano-Fe3O4@CA-Pd DMF Na2CO3 90 85 J ¼ 7.39 Hz), 7.44e7.41 (m, 3H), 7.14 (t, 1H, J ¼ 7.3 Hz), 7.08 (d, 1H, 6 Nano-Fe3O4@CA-Pd DMF KOH 90 20 13 7 Nano-Fe3O4@CA-Pd DMF NaOH 90 45 J ¼ 8.2 Hz), 3.9 (s, 3H, OCH3). C NMR (100 MHz, CDCl3) d: 55.64, 8 Nano-Fe O @CA-Pd DMSO K CO 90 82 111.35, 120.98, 127.07, 128.14, 128.78, 129.71, 130.84, 131.04, 138.70, 3 4 2 3 9 Nano-Fe3O4@CA-Pd CH3CN K2CO3 90 60 156.59. 10 Nano-Fe3O4@CA-Pd EtOH K2CO3 90 90 c 1-Phenyl naphthalene (Table 2, entry 7). Yield 65%. A colorless 11 Nano-Fe3O4@CA-Pd DMF K2CO3 90 90 1 12 Nano-Fe O @CA-Pd DMF K CO 90 95d oil. H NMR (400 MHz, CDCl3) d 7.83 (d, 2H, J ¼ 8. 8 Hz), 7.78 (d, 1H, 3 4 2 3 13 J ¼ 9.0, 1.6 Hz), 7.47e7.39 (m, 6H), 7.37e7.33 (m, 3H). C NMR a Reaction conditions: 4-Iodonitrobenzene (1.0 mmol), phenylacetylene (2.0 mmol), base (2.0 mmol), solvent (3 ml), 2 h. (100 MHz, CDCl3) d: 125.58, 125.96, 126.22, 127.13, 127.42, 127.83, b Isolated yield. 128.45, 128.47, 129.05, 130.26, 131.80, 133.99, 140.43, 140.94. c e Phenylacetylene (1.0 mmol). 4-Acetylbiphenyl (Table 2, entry 8). Yield 95%. mp 116 119 C. d Phenylacetylene (1.5 mmol). 4 E. Ghonchepour et al. / Journal of Organometallic Chemistry 883 (2019) 1e10

Table 4 126.3, 121.6, 121.1, 120.9, 96.4, 86.4. The substrates scope of the C-C coupling reaction between phenylacetylene and a 1-Methoxy-4-(phenylethynyl)benzene (Table 4, entry 6). Yield various aryl halides by Nano-Fe3O4@CA-Pd as a catalyst. 1 80%. H NMR (500 MHz, CDCl3) d 7.57 (dd, J ¼ 8.1, 1.6 Hz, 2H), 7.39 entry Ar-X product yieldb % (dd, J ¼ 15.1, 8.1 Hz, 5H), 6.83e6.79 (m, 2H), 3.81 (s, 3H).13C NMR 1 95 (126 MHz, CDCl3) d 158.7, 132.5, 132.2, 129.2, 128.4, 121.8, 115.7, 112.8, 81.6, 73.9, 55.4. 1-Methyl-4-(phenylethynyl)benzene (Table 4, entry 8). Yield 1 2 65 85%. H NMR (500 MHz, CDCl3) d 7.63e7.53 (m, 3H), 7.48 (d, J ¼ 8.1 Hz, 2H), 7.41e7.34 (m, 4H), 7.19 (s, 1H), 2.41 (s, 3H). 13C NMR (126 MHz, CDCl3) d 138.4, 131.6, 131.5, 129.1, 128.3, 128.1, 123.5, 3 10 120.2, 89.6, 88.8, 21.5.

4 95 3. Results and discussion

Scheme 1 shows the synthetic pathway for Fe3O4@CA-Pd nanoparticles. 5 55

3.1. FT-IR spectra analyze of Nano-Fe3O4@CA-Pd 6 80 Fig. 3(aec) shows the FT-IR spectra of a) Fe3O4@CA, b) Fe3O4@CA-Pd, c) Fe3O4@CA-Pd (after the fifth run). The spectrum is 7 75 shown in Fig. 3(a) related to the raw Fe3O4@CA. Typical bands assigned to the Fe-O stretching vibration appeared at around 600e400 cm 1. The C¼O vibration (asymmetric stretching) of COOH group of CA [27] gives a strong band around 1710 cm 1 and 8 85 this peak in CA-MNP shifts to an intense band at about 1609 cm 1. This shift proves the binding of a CA radical to surface of Fe3O4 nanoparticles by chemisorptions of carboxylate (citrate) ions 9 55 [10,28]. In Fig. 3(b) IR spectrum for Pd-functionalized Fe3O4@CA showed, It is worth mentioning that in Pd-anchored mesoporous a Reaction conditions: aryl halide (1.0 mmol), phenylacetylene (1.5 mmol), K CO 2 3 Fe3O4@CA material, the C¼O stretching frequency is shifted to a (2.0 mmol), Fe3O4@CA-Pd (10 mg), DMF (3 ml), 90 C, and 2 h. lower wavelength at ~1572 cm 1 indicating that C¼O bond is co- b Isolated yield. ordinated to palladium. And finally, FT-IR spectra of the catalyst after five-run recycled depicted in Fig. 3(c) that indicate catalyst Table 5 activity after five-run were not observed any change. Comparison of the reaction of 4-Iodonitrobenzene with phenylacetylene in the Fig. 4 shows the final catalyst (Nano-Fe3O4@CA-Pd). The TGA presence of Nano- Fe3O4@CA-Pd and some previously reported catalysts. was recorded by heating the sample at a rate of 10 C min 1 and Catalyst Temp. (C) Time (h) Yield (%)[ref] showed that an endothermic peak at a lower temperature (lower MgO@PdCu 60 15 96 [41] than 100 C) can be ascribed to the removal of physically absorbed OxPdCy@clay 130 24 92 [42] water and CA molecules on the surface of Fe3O4 nanoparticles. Fe3O4@SiO2-NHC-Pd(II) 60 1.5 94 [43] There is a peak at 220e500 C that associated with an Pincer Cu-NHC Complexes 135 24 53 [44] exothermic DTA peak, accompanied by 8.9% weight loss in differ- a Nano- Fe3O4@CA-Pd 90 2 95 ential thermogravimetric curve, this peak is due to the complete a Present work. thermal decomposition of the complexes and the loss of their organic portion. Major weight loss at high temperatures is char- acteristic of chemisorbed materials and confirms that the citric acid 7.56 (dd, J ¼ 7.6, 1.8 Hz, 2H), 7.43 (d, J ¼ 1.5 Hz, 1H), 7.42 (d, group is chemically bound to the surface of the magnetic nano- J ¼ 1.4 Hz, 1H), 7.41 (q, J ¼ 1.4, 1.0 Hz, 2H), 7.39 (t, J ¼ 1.0 Hz, 1H).13C particles [12]. NMR (126 MHz, CDCl ) d 131.9, 129.6, 128.6, 127.6, 127.5, 126.3, 3 The catalyst, therefore, was stable up to 200 C, and confirmed

Scheme 1. Synthesis of Fe3O4@CA-Pd. E. Ghonchepour et al. / Journal of Organometallic Chemistry 883 (2019) 1e10 5

Fig. 3. FT-IR spectra of a) Fe3O4@CA, b) Nano-Fe3O4@CA-Pd, c) Nano-Fe3O4@CA-Pd (after the fifth run). that it could be safely used in organic reactions ranging from 25 to correspond to the (111), (220), (311), (400), (422), (511) and (440) 200 C, and TGA result reveals that the thermal stability of syn- reflections respectively. The magnetic XRD peaks match well with thesized Nano-Fe3O4@CAePd catalyst is maintained at a higher these peaks, which is in agreement with the standard pattern for temperature. Thus the FTIR and TGA results confirmed that Fe3O4 crystalline magnetite (Fe3O4) with an inverse spinel structure [29]. nanoparticles have been functionalized with citric acid during the The Fe3O4@CA-Pd XRD pattern indicates tree peaks around 40.37, course of synthesis. The amount of the metal supported onto the 46.94 and 68.36 correspond to the (111), (200), (220) reflections 0 Fe3O4@CA was determined by induced coupled plasma (ICP) anal- respectively, these peaks match well with Pd , which achieved with þ ysis and was 0.023 g of Pd per g of catalyst (0.2 mmol g 1). The TGA a reduction of Pd2 in the synthetic levels [30,31]. curves and ICP-AES results also confirm the successful supporting Superparamagnetic properties were studied for the Fe3O4@CA- of the Pd(0)eCA complex onto the magnetic surface. Pd in an applied magnetic field at ambient temperature with the The XRD pattern of two different stepwise synthetic pathway for field sweeping from 8000 to þ8000 Oersted (Fig. 6). Bare the preparation of the catalyst is shown in Fig. 5. The XRD pattern of nanocrystals of Fe3O4 have a high saturation magnetization of 73.7 1 Fe3O4@CA 5(a), Nano-Fe3O4@CA-Pd 5(b) have similar Diffraction emu g at room temperature [31], which in this catalyst de- peaks at around 30.41, 35.80, 43.42, 53.80, 57.40, 62.97 and 74.53 creases to 51 emu g 1 and hysteresis loop was not observed,

Fig. 4. Thermogravimetric analyze of Nano-Fe3O4@CA-Pd. 6 E. Ghonchepour et al. / Journal of Organometallic Chemistry 883 (2019) 1e10

Fig. 5. The XRD pattern of a) Fe3O4@CA, b) Fe3O4@CA-Pd.

Fig. 6. VSM curve of Nano-Fe3O4@CA-Pd. confirmed that catalyst is a superparamagnetic material. Satura- nanosized and they have a spherical shape with a rough surface and tion magnetization decreases as the particle size are reduced due a range diameter of 20e50 nm (Fig. 7(a)). Transmission electron to the enhancement of surface spin effects, and as particle size microscopy confirms the formation of single-phase Fe3O4 nano- decreases the coercivity vanishes and becomes a super- particles, with spherical morphology (Fig. 7(b)). In TEM image Pd paramagnetic state. The prepared catalyst dispersed in the solvent NPs is not clearly observable (or detectable) [32], but the ICP, XRD and subjected to an external magnetic field can immediately and EDX analysis confirm the presence of Pd NPs in catalyst gather nanoparticles, then with slight shaking can be promptly re- structure. dispersed. These results indicate that the particles display good The EDX spectrum of Nano-Fe3O4@CA-Pd catalyst is outlined in magnetic characteristics that could be useful when they are Fig. 8. These analyzes indicate that Pd coated in the catalyst applied as a magnetic catalyst. The nanoparticles exhibit high structure. The palladium content of the catalyst was found to be permeability in magnetization, which was sufficient for magnetic 0.85 mmol g 1 based on the EDX spectrum. separation using a conventional magnet. After characterization, the activity of the catalyst was tested in Fig. 7 shows the morphology of Nano-Fe3O4@CA-Pd taken by the C-C coupling reaction between phenylboronic acid and aryl scanning electron microscopy (SEM) and Transmission electron halide. First, we examined the reaction of phenylboronic acid with microscopy (TEM). These images confirm that the particles are iodobenzene under various conditions in order to establish the E. Ghonchepour et al. / Journal of Organometallic Chemistry 883 (2019) 1e10 7

optimal conditions. The results are summarized in Table 1. The first reaction was performed under the following conditions: phenylboronic acid 1.0 mmol (0.122 g), iodobenzene 1.0 mmol (0.204 g), potassium carbonate 2.0 mmol (K2CO3 0.276 g) as a base and EtOH (8 mL) in the presence of Nano-Fe3O4@CA-Pd (L3) (10 mg) at r.t. After 25 min of reaction time, the desired biphenyl was formed in 68% yield (Table 1, entry 1). To improve yield, the effect of temperature on the efficiency of the reaction was considered. Interestingly, the yield was increased up to 80% when temperature increased to 75 C(Table 1, entry 2). In the next section, the role of the different base was examined. The use of Li2CO3 and Na2CO3 instead of K2CO3 caused to reduce the yield of product to 75% (Table 1, entries 3, 4). In the next step, the effect of solvent on the efficiency of the reaction was considered. In the end, some solvents, as well as water, ethanol and difference percent mixture of ethanol and water, were examined. The maximum yield (98%) was obtained when the mixture of EtOH/H2O (2:1) and (1:1) was used as a solvent so, we chose eco-friendly and greener mixture EtOH/H2O (1:1) as optimal solvent (Table 1, entries 5e8). The effect of catalyst scanned with reducing the amount of the catalyst to 5 mg led to decrease yield to 90% (Table 2, entry 9). The use of Fe3O4 (L1) and Fe3O4@CA (L2) as a catalyst caused to decrease the efficiency of reaction to 10 and 20% respectively (Table 1, entries 10e11). According to Table 1, the optimal condition achieved with phenylboronic acid (1.0 mmol), aryl halide (1.0 mmol), K2CO3 (2.0 mmol) and a mixture of EtOH/H2O (1:1) as the solvent in the presence of Nano-Fe3O4@CA-Pd (L3)at25 Cin 25 min period. With the optimal conditions in hand (Scheme 2), we next studied the substrates scope of this reaction by screening the aryl halides. A variety of aryl halides were subjected under optimal conditions and the result are depicted in Table 2. All biphenyls products were known and characterized by melting point (mp), IR, 1Hand13C NMR data as well as by comparison of their physical data with those in the literature (Table 2,Column5). In the next section, the catalytic activity of Nano-Fe3O4@CA-Pd Fig. 7. SEM image of Nano-Fe3O4@CA-Pd (a), and TEM image of Nano-Fe3O4@CA-Pd for the Sonogashira coupling reaction different conditions was (b). investigated. For this purpose, the reaction of 4-Iodonitrobenzene with phenylacetylene under various conditions was examined in order to establish the optimal conditions. The results are

Fig. 8. EDX analyze of Nano-Fe3O4@CA-Pd. 8 E. Ghonchepour et al. / Journal of Organometallic Chemistry 883 (2019) 1e10

Scheme 2. The optimal condition for Suzuki reaction in presence of Nano-Fe3O4@CA-Pd.

reaction that the corresponding yield increased to 95% (Table 3, entries 11e12). With the optimal conditions determined (Scheme 3), the sub- strate scope of this reaction was next studied by screening the aryl halides. A variety of aryl halides were subjected to optimal conditions, and the results are shown in Table 4. Scheme 3. The optimal condition for Sonogashira coupling reaction in presence of All of the aryl halides were converted to the corresponding Nano-Fe3O4@CA-Pd. product in high yields. The corresponding products were known and characterized by IR, 1HNMR,and13C NMR data as well as by summarized in Table 3. the comparison of their physical data with those in the The first reaction was performed under the following condi- literature. tions: the mixture of 4-Iodonitrobenzene (1.0 mmol, 0.249 g) and The mechanism of the reaction is not entirely clear to us, but a phenylacetylene (2.0 mmol, 0.204 g) was reacted in the absence of a reasonable mechanism has been depicted in Scheme 4. The Suzuki catalyst and (2.0 mmol 0.276 g) potassium carbonate as base in cross-coupling reaction is an organic reaction in which an orga- 3 mL DMF at 70 C. After 2 h of reaction time, no product was found. nohalide reacts with an organoborane in the presence of palladium This result showed that the catalyst plays a vital role in this reaction catalyst and base to give a biaryl product. According to the accepted (Table 3, entry 1). In order to improve yield, 10 mg of Fe O @CA-Pd 3 4 principle, in the first stage an oxidative addition reaction (o.a.) was used. The yield was increased up to 85% (Table 3, entry 2). The occurs in which Ar-X (I) is attached to the catalyst, and forms an effect of temperature and base on the reaction efficiency was also organopalladium intermediate (II) through a Pd(0)ePd(II) catalytic checked. Interestingly, the yield was increased up to 95% when the cycle [40]. In the second step, the transmetalation (t.m.) has temperature was increased to 90 C and the yield decreased to 90% occurred with the borate V and the halide anion is replaced by R with 110 C(Table 3, entries 3e4). In addition, the role of different group on the palladium complex and the new intermediate (VII) is bases was examined; the use of Na CO , KOH, and NaOH instead of 2 3 formed. In the final step, reductive elimination reaction (r.e.) is K CO reduced the yield to 90% (Table 3, entries 5e7). Also, this 2 3 carried out and the final product (VIII) is formed. Also, at this stage, reaction scanned in the presences of different solvents such as the palladium catalyst is regenerated and can participate in the DMSO, acetonitrile, and ethanol that the respective yield was 82%, reaction cycle (Scheme 4). 60%, and 90% (Table 3, entries 8e10). This reaction shows that when The efficacy of the Nano-Fe3O4@CA-Pd nanoparticles was we use the one equivalent of phenylacetylene, the yield decreased compared with some previously reported catalysts through the to 90%. In the final reaction, we add 1.5 eq of phenylacetylene in a reaction of 4-Iodonitrobenzene with phenylacetylene (See Table 3).

Scheme 4. Proposed reaction mechanism. E. Ghonchepour et al. / Journal of Organometallic Chemistry 883 (2019) 1e10 9

Fig. 9. (a) Reaction mixture during stirring with magnetic bar; (b) Reaction environment after completion of reaction after separation of Nano-Fe3O4@CA-Pd using an external magnet; (c) Reusability of Fe3O4@CA-Pd in the Suzuki model reaction.

The advantages of the catalyst introduced here are short reaction shown in Fig. 10. These XRD patterns shows that the catalyst's time, easy separation of the catalyst, and its reusability. structure did not change after reaction. Reusability of the catalyst was tested in the Suzuki model reaction. After completion of the reaction in the first run, the catalyst was easily separated by using an external magnet (Fig. 9(a, b)). It 4. Conclusions was washed twice with ethyl acetate, dried at ambient temperature and immediately used in the next step. The reaction was repeated In this study, PdCl2 was converted to a heterogeneous catalyst by for up to five consecutive runs without significant change in cata- using Fe3O4 nanoparticles and was modified with citric acid (Nano- lyst activity and reaction efficiency (Fig. 9(c)). Pd leaching during Fe3O4@CA-Pd) and characterized as a magnetically separable the reaction process was scanned by ICP of the recycled catalyst. nanocatalyst. The catalytic activity of the prepared Nano- The result didn't show any change in Pd amount in catalyst struc- Fe3O4@CA-Pd was tested in Sonogashira and Suzuki cross-coupling ture after recovering from the reaction mixture. Also, the XRD reactions. Biphenyls and diphenylethynes were efficiently synthe- patterns of the recycled catalyst after Suzuki model reaction is sized in the presence of K2CO3 as a base with excellent yields and in short reaction times. Recovery of the catalyst was simple using a

Fig. 10. XRD patterns of nanocatalyst after using in reaction mixture. 10 E. Ghonchepour et al. / Journal of Organometallic Chemistry 883 (2019) 1e10 magnet, allowing its reuse without significant loss of its catalytic modified fibrous silica nanospheres as highly efficient and recoverable cata- activity. lyst for reduction of 4-nitrophenol and hydrodechlorination of 4- chlorophenol, Appl. Catal., B 162 (2015) 372e380. [24] Z. Dong, X. Le, Y. Liu, C. Dong, J. Ma, Metal organic framework derived mag- Acknowledgments netic porous carbon composite supported gold and palladium nanoparticles as highly efficient and recyclable catalysts for reduction of 4-nitrophenol and fi hydrodechlorination of 4-chlorophenol, J. Mater. Chem. 2 (44) (2014) We thank the Shahid Bahonar University of Kerman for nancial 18775e18785. support. [25] X. Cui, Y. Long, X. Zhou, G. Yu, J. Yang, M. Yuan, J. Ma, Z. Dong, Pd-doped Ni nanoparticle-modified N-doped carbon nanocatalyst with high Pd atom uti- lization for the transfer hydrogenation of nitroarenes, Green Chem. 20 (5) References (2018) 1121e1130. [26] N.E. Leadbeater, M. Marco, Ligand-free palladium catalysis of the Suzuki re- [1] P.J. Walsh, H. Li, C.A. de Parrodi, A green chemistry approach to asymmetric action in water using microwave heating, Org. Lett. 4 (17) (2002) 2973e2976. catalysis: solvent-free and highly concentrated reactions, Chem. Rev. 107 (6) [27] S. Nigam, K. Barick, D. Bahadur, Development of citrate-stabilized Fe 3 O 4 (2007) 2503e2545. nanoparticles: conjugation and release of doxorubicin for therapeutic appli- [2] P.T. Anastas, J.C. Warner, Principles of green chemistry, Green Chem.: Theor. cations, J. Magn. Magn Mater. 323 (2) (2011) 237e243. Pract. (1998) 29e56. [28] Q. Lan, C. Liu, F. Yang, S. Liu, J. Xu, D. Sun, Synthesis of bilayer oleic acid-coated [3] D. Wang, D. Astruc, Fast-growing field of magnetically recyclable nano- Fe 3 O 4 nanoparticles and their application in pH-responsive Pickering catalysts, Chem. Rev. 114 (14) (2014) 6949e6985. emulsions, J. Colloid Interface Sci. 310 (1) (2007) 260e269. [4] B. Cornils, W.A. Herrmann, Applied Homogeneous Catalysis with Organome- [29] B. Wang, Q. Wei, S. Qu, Synthesis and characterization of uniform and crys- tallic Compounds, VCH Weinheim etc, 1996. talline magnetite nanoparticles via oxidation-precipitation and modified co- [5] A.K. Gupta, M. Gupta, Synthesis and surface engineering of iron oxide nano- precipitation methods, Int J Electrochem Sci 8 (2013) 3786e3793. particles for biomedical applications, Biomaterials 26 (18) (2005) 3995e4021. [30] S. Navaladian, B. Viswanathan, T. Varadarajan, R. Viswanath, A rapid synthesis [6] A.R. Hajipour, S. Jajarmi, A novel and highly efficient polyaniline-functional- of oriented palladium nanoparticles by UV irradiation, Nanoscale Res. Lett. 4 ized multiwall carbon nanotube-supported cu (I) complex for Sonogashira (2) (2008) 181. coupling reactions of aryl halides with phenylacetylene, Appl. Organomet. [31] Z.-L. Wang, J.-M. Yan, H.-L. Wang, Y. Ping, Q. Jiang, Pd/C synthesized with citric Chem. 32 (2) (2018), e3992. acid: an efficient catalyst for hydrogen generation from formic acid/sodium [7] Q.X. Liu, D.X. Zhao, H. Wu, Z.X. Zhao, S.Z. Lv, Catalytic activities of NHC-PdCl2 formate, Sci. Rep. 2 (2012) 598. species based on functionalized tetradentate imidazolium salt in three types [32] E. Ghonchepour, M.R. Islami, B. Bananezhad, H. Mostafavi, A.M. Tikdari, Syn- of C-C coupling reactions, Appl. Organomet. Chem. (2018), e4429. thesis of recoverable palladium composite as an efficient catalyst for the [8] K. Azizi, E. Ghonchepour, M. Karimi, A. Heydari, Encapsulation of Pd (II) into reduction of nitroarene compounds and Suzuki cross-coupling reactions using superparamagnetic nanoparticles grafted with EDTA and their catalytic ac- sepiolite clay and magnetic nanoparticles (Fe3O4@ sepiolite-Pd2þ), CR CHIM tivity towards reduction of nitroarenes and SuzukieMiyaura coupling, Appl. (2018). Organomet. Chem. 29 (2015) 187e194. [33] W. Liu, H. Cao, H. Zhang, H. Zhang, K.H. Chung, C. He, H. Wang, F.Y. Kwong, [9] R. Liu, Y. Guo, G. Odusote, F. Qu, R.D. Priestley, Coreeshell Fe3O4 polydop- A. Lei, Organocatalysis in cross-coupling: DMEDA-catalyzed direct C H ary- amine nanoparticles serve multipurpose as drug carrier, catalyst support and lation of unactivated benzene, J. Am. Chem. Soc. 132 (47) (2010) carbon adsorbent, ACS Appl. Mater. Interfaces 5 (18) (2013) 9167e9171. 16737e16740. [10] M. Racuciu, D. Creanga, A. Airinei, Citric-acid-coated magnetite nanoparticles [34] D.-H. Lee, J.-H. Kim, B.-H. Jun, H. Kang, J. Park, Y.-S. Lee, Macroporous for biological applications, Eur. Phys. J. E 21 (2) (2006) 117e121. polystyrene-supported palladium catalyst containing a bulky N-heterocyclic [11] M.E. De Sousa, M.B. Fernandez van Raap, P.C. Rivas, P. Mendoza Zelis, carbene ligand for Suzuki reaction of aryl chlorides, Org. Lett. 10 (8) (2008) P. Girardin, G.A. Pasquevich, J.L. Alessandrini, D. Muraca, F.H. Sanchez, Stability 1609e1612. and relaxation mechanisms of citric acid coated magnetite nanoparticles for [35] C.-L. Sun, H. Li, D.-G. Yu, M. Yu, X. Zhou, X.-Y. Lu, K. Huang, S.-F. Zheng, B.-J. Li, magnetic hyperthermia, J. Phys. Chem. C 117 (10) (2013) 5436e5445. Z.-J. Shi, An efficient organocatalytic method for constructing biaryls through [12] E. Ghonchepour, A. Nakisa, A. Heydari, Citric acid coated magnetite nano- aromatic CeH activation, Nat. Chem. 2 (12) (2010) 1044e1049. particles: an efficient and reusable green catalyst for rapid acetylation of al- [36] Ü. Yılmaz, N. S¸ ireci, S. Deniz, H. Küçükbay, Synthesis and microwave-assisted cohols and phenols, Org. Chem. Res. 2 (1) (2016) 96e101. catalytic activity of novel bis-benzimidazole salts bearing furfuryl and thenyl [13] N. Sarlak, M. Adeli, M. Karimi, M. Bordbare, M. Farahmandnejad, Quantitative moieties in Heck and Suzuki cross-coupling reactions, Appl. Organomet. study on the interaction of Agþ and Pd 2þ with CNT-graft-PCA (polycitric Chem. 24 (5) (2010) 414e420. acid) in aqueous solution, J. Mol. Liq. 180 (2013) 39e44. [37] D. Zim, A.S. Gruber, G. Ebeling, J. Dupont, A.L. Monteiro, Sulfur-containing [14] B. Zhu, T. Fan, D. Zhang, Adsorption of copper ions from aqueous solution by palladacycles: efficient phosphine-free catalyst precursors for the Suzuki citric acid modified soybean straw, J. Hazard Mater. 153 (1) (2008) 300e308. cross-coupling reaction at room temperature, Org. Lett. 2 (18) (2000) [15] S.S. Gujral, S. Khatri, P. Riyal, V. Gahlot, Suzuki cross coupling reaction-A re- 2881e2884. view, Indo Global J. Pharmaceut. Sci. 2 (2012) 351e367. [38] L. Shen, S. Huang, Y. Nie, F. Lei, An efficient microwave-assisted Suzuki re- [16] K. Tempero, V. Cirillo, S. Steelman, Diflunisal: a review of pharmacokinetic and action using a new pyridine-pyrazole/Pd (II) species as catalyst in aqueous pharmacodynamic properties, drug interactions, and special tolerability media, Molecules 18 (2) (2013) 1602e1612. studies in humans, Br. J. Clin. Pharmacol. 4 (S1) (1977) 31Se36S. [39] M.E. Hanhan, C. Cetinkaya, M.P. Shaver, Effective binuclear Pd (II) complexes [17] J.P. Wolfe, S.L. Buchwald, A highly active catalyst for the room-temperature for Suzuki reactions in water, Appl. Organomet. Chem. 27 (10) (2013) amination and Suzuki coupling of aryl chlorides, Angew. Chem. Int. Ed. 38 (16) 570e577. (1999) 2413e2416. [40] F. Bellina, A. Carpita, R. Rossi, Palladium catalysts for the Suzuki cross-coupling [18] N. Miyaura, T. Yanagi, A. Suzuki, The palladium-catalyzed cross-coupling re- reaction: an overview of recent advances, Synthesis (15) (2004) 2419e2440, action of phenylboronic acid with haloarenes in the presence of bases, Synth. 2004. Commun. 11 (7) (1981) 513e519. [41] M. Gholinejad, M. Bahrami, C. Najera, B. Pullithadathil, Magnesium oxide [19] X. Bei, H.W. Turner, W.H. Weinberg, A.S. Guram, J.L. Petersen, Palladium/P, O- supported bimetallic Pd/Cu nanoparticles as an efficient catalyst for Sonoga- ligand-catalyzed Suzuki cross-coupling reactions of arylboronic acids and aryl shira reaction, J. Catal. 363 (2018) 81e91. chlorides. Isolation and structural characterization of (P, O)-Pd (dba) complex, [42] M. Gholinejad, N. Dasvarz, C. Najera, Novel oxime-palladacycle supported on J. Org. Chem. 64 (18) (1999) 6797e6803. clay composite as an efficient heterogeneous catalyst for Sonogashira reac- [20] M. Sato, N. Miyaura, A. Suzuki, Cross-coupling reaction of alkyl-or arylboronic tion, Inorg. Chim. Acta. 483 (2018) 262e270. acid esters with organic halides induced by thallium (I) salts and palladium- [43] M. Esmaeilpour, A.R. Sardarian, H. Firouzabadi, N-heterocyclic carbene-Pd (II) catalyst, Chem. Lett. 18 (8) (1989) 1405e1408. complex based on theophylline supported on Fe3O4@ SiO2 nanoparticles: [21] A. Taher, J.-B. Kim, J.-Y. Jung, W.-S. Ahn, M.-J. Jin, Highly active and magnet- highly active, durable and magnetically separable catalyst for green Suzuki- ically recoverable Pd-NHC catalyst immobilized on Fe3O4 nanoparticle-ionic Miyaura and Sonogashira-Hagihara coupling reactions, J. Organomet. Chem. liquid matrix for Suzuki reaction in water, Synlett (15) (2009) 2477e2482, 873 (2018) 22e34. 2009. [44] D. Domyati, R. Latifi, L. Tahsini, Sonogashira-type cross-coupling reactions [22] K. Qu, L. Wu, J. Ren, X. Qu, Natural DNA-modified graphene/Pd nanoparticles catalyzed by copper complexes of pincer N-heterocyclic carbenes, as highly active catalyst for formic acid electro-oxidation and for the Suzuki J. Organomet. Chem. 860 (2018) 98e105. reaction, ACS Appl. Mater. Interfaces 4 (9) (2012) 5001e5009. [23] Z. Dong, X. Le, C. Dong, W. Zhang, X. Li, J. Ma, Ni@ Pd coreeshell nanoparticles