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 C12H10ÀxClx. 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 Â 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 À 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 À 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 À 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.