Ultrasound-accelerated synthesis of biphenyl compounds using novel Pd(0) nanoparticles immobilized on bio-composite

Accepted Manuscript Ultrasound-accelerated synthesis of biphenyl compounds using novel Pd(0) nanoparticles immobilized on bio-composite Talat Baran PII: DOI: Reference:

S1350-4177(18)30307-9 https://doi.org/10.1016/j.ultsonch.2018.03.017 ULTSON 4130

To appear in:

Ultrasonics Sonochemistry

Received Date: Revised Date: Accepted Date:

25 February 2018 17 March 2018 20 March 2018

Please cite this article as: T. Baran, Ultrasound-accelerated synthesis of biphenyl compounds using novel Pd(0) nanoparticles immobilized on bio-composite, Ultrasonics Sonochemistry (2018), doi: https://doi.org/10.1016/ j.ultsonch.2018.03.017

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Ultrasound-accelerated

synthesis

of

biphenyl

compounds

using

novel

Pd(0)

nanoparticles immobilized on bio-composite Talat Baran Aksaray University, Faculty of Science and Letters, Department of Chemistry, 68100 Aksaray, Turkey

Corresponding author: Address: Department of Chemistry, Faculty of Science and Letters, Aksaray University, Aksaray, Turkey, 68100 Tel.: +90 382 2882162; fax: +90 382 2882299. E-mail address: [email protected] (T. Baran)

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Abstract This study describes (i) an eco-friendly approach for design of Pd(0) nanoparticles on a natural composite, which is composed of carboxymethyl cellulose/agar polysaccharides (CMC/AG), without using any toxic reducing agents and (ii) development of ultrasound assisted simple protocol for synthesis of biphenyl compounds. Chemical characterization studies of Pd(0) nanoparticles (Pd NPs@CMC/AG) revealed that size of the particles were in the range of 37–55 nm. Catalytic performance of Pd NPs@CMC/AG was evaluated in synthesis of various biphenyl compounds by using the ultrasound-assisted method that was developed in this study. Pd NPs@CMC/AG exhibited excellent catalytic performance by producing high reaction yields. In addition, Pd NPs@CMC/AG was successfully used up to six reaction cycles without losing its catalytic activity, indicating high reproducibility of Pd NPs@CMC/AG. Additionally, compared to conventional the methods, new ultrasoundassisted synthesis technique that was followed in this study exhibited some advantages such as shorter reaction time, greener reaction conditions, higher yields and easier work-up. Keywords: carboxymethyl cellulose; agar; ultrasound; biphenyl

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1. Introduction Recently, metallic nanomaterials have attracted great attention because of their potential applications in electronics [1], optics materials [2], sensors [3] and biomedicine [4]. Metallic nanoparticles are also becoming increasingly important for catalytic systems [5-7]. Among noble metal nanoparticles such as Ag, Au and Pt, palladium nanoparticles (Pd NPs) are very promising materials and therefore they have been widely used in different areas such as fuel cell, hydrogenation, oxidation and cross-coupling reactions [8-10]. Especially, Pd NPs play a pivotal role in synthesis of biphenyl compounds [11, 12], which are commonly used in cosmetics, medicine and pharmacology [13, 14]. Nevertheless, Suzuki-Miyaura reactions have some drawbacks because they require use of excessive energy, longer reaction time and toxic organic solvents. Recently, non-conventional methods such as microwave irradiation, photo-activated processes, sunlight and ultrasonication have become very popular and they have been used in Suzuki-Miyaura reactions to overcome the problems addressed above. [15]. Among the non-conventional energy sources, ultrasonication one of the most powerful method and it has been widely utilized in catalytic systems since it offers high selectivity, low reaction time, mild conditions and operational simplicity [16-18]. Therefore, ultrasonication technique has great potential for synthesis of organic compounds in terms of lower use of excessive energy and formation of chemical waste. The material that serves as support for nanoparticles has great impact on size, shape, and distribution immobilized metallic nanoparticles on the surface [19]. These physical properties of metallic nanoparticles directly affect their catalytic activity in applications. Recently, researchers have reported production of different noble metal nanoparticles stabilized on different inorganic materials such as bentonite [20], graphene oxide [21], carbon nanotube [22] magnetic-materials [23] and mesoporous materials [24]. On the other hand, considering their high thermal durability, large surface area, biodegradability, eco-friendly 3

nature, cost effectiveness and abundance in nature, carbohydrate polymers are also noted as promising support materials for metal nanoparticles [25, 26]. Therefore, these superior materials or their composites should be used as stabilizer for immobilization different noble metallic particles and their activity should be explored in different catalytic reactions. In this study, novel palladium nanoparticles were immobilized on carboxymethyl cellulose/agar composite (CMC/AG) without using any toxic reducing agents. Structural characterization of Pd NPs@CMC/AG was performed with FT-IR, TGA, SEM-EDAX, XRD and ICP-OES analyses. SEM images showed that palladium particles had spherical morphology and the size of the particles varied in the range of 37–55 nm. Catalytic behavior of Pd NPs@CMC/AG was investigated in the Suzuki-Miyaura reaction under ultrasonic sonication in water at 60°C for 30 min. The tests showed that Pd NPs@CMC/AG had good activity in the synthesis of various biphenyl compounds via Suzuki-Miyaura reaction. Reproducibility of Pd NPs@CMC/AG was tested in coupling reaction and it was determined that it could be reused up to six runs with good reaction yields. Catalytic activity of Pd NPs@CMC/AG was also tested in conventional reflux-heating system as a comparison of ultrasonic method. The test revealed that the ultrasonication technique dramatically accelerated the Suzuki-Miyaura reactions and higher reaction yields were obtained compared to conventional heating system. 2. Material and methods 2.1 Materials Carboxymethyl cellulose (CMC) Agar (AG), PdCl2, Na2PdCl4, PdCl2(CH3CN)2, K2CO3, NaOH, KOH, Cs2CO3, phenyl boronic acid, aryl halides, ethanol, DMF and toluene were obtained from Sigma-Aldrich 2.2 Instrumentation 4

FT-IR spectra of the CMC/AG composite and Pd NPs@CMC/AG were obtained on a Perkin Elmer Spectrum 100 FT-IR spectrophotometer. Thermal and mechanical durability of CMC/AG composite and Pd NPs@CMC/AG were studied on EXSTAR S11 7300 (nitrogen atmosphere; 30–650°C heating range). The surface properties of CMC/AG composite and Pd NPs@CMC/AG were obtained on QUANTA-FEG 250 ESEM by coating with platinum. The analysis of Pd ion on the CMC/AG composite was determined using EDAX-Metek. X-ray diagram of Pd NPs@CMC/AG was recorded on a Rigaku smart lab system (at 40 kV, 30 mA, and 2θ with a scan angle of 10−80°). Palladium ion content of Pd NPs@CMC/AG was investigated by using Perkin Elmer Optima 2100 DV Inductively Coupled Plasma (ICP) Optical Emission Spectrometer (OES). The characterizations of biphenyl compounds were done on GC–MS Agilent GC-7890 A- MS 5975. VWR Ultrasonic Cleaner USC-TH 50Hz ultrasonic bath sonicator was used in the Suzuki-Miyaura cross coupling reactions. 2.3 Preparation of Pd NPs@CMC/AG 0.5 g of CMC was dissolved in 100 mL of water and then 0.5 g of AG was added to the reaction mixture and stirred for overnight at room temperature (RT) to form CMC/AG composite. Subsequently, solution of PdCl2 in water was added in the reaction media (0.2 g, 50 mL) and refluxed at 100°C for 5 h to ensure completely conversion of Pd(II) to Pd(0). After this time period, the colorless reaction solution turned into dark gray, confirming reduction Pd(II) to Pd(0). Then, the reaction mixture was cooled at RT and dark gray palladium nanoparticles was obtained by evaporating the solvent (Scheme 1).

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………………………………………..Scheme 1……………………………………….. 2.4 General procedure of C-C coupling reactions The mixture of 1.0 mmol aryl halides, 1.8 mmol phenyl boronic acid, 3.5 mmol base, 1x10-2 mmol Pd NPs@CMC/AG and 6 mL of water were sonicated at 60°C for 30 min. Formation of biphenyl compounds was followed by thin layer chromatography. After the coupling reactions, the reaction mixture was extracted with toluene. Organic phase, which containing biphenyl compounds, was separated with separation funnel and desired coupling products were obtained by evaporating of the solvent. 3. Results and discussion 3.1 Characterization studies Characterization of CMC/AG composite and Pd NPs@CMC/AG were performed with FT-IR, TGA, SEM-EDAX, XRD and ICP-OES analyses. Fig.1 demonstrates FT-IR spectra of CMC/AG composite and Pd NPs@CMC/AG. The FT-IR spectrum of the synthesized CMC/AG composite (Fig. 1a) showed prominent peaks at 3266, 2918, 1736, 1590, 1323 and 1039 cm−1, which were ascribed to the stretching of –OH group of AG, C–H stretching of AG, the stretching of C=O in the substituent group of the CMC, the stretching of asymmetric COO−, the stretching of symmetric COO−, –OH bending vibration and the stretching of C-O bond of ether (C-O-C) and alcohol in glucose units of CMC and AG, respectively [27, 28]. 6

FT-IR analysis of Pd NPs@CMC/AG showed that there were no dramatic changes in functional groups of CMC/AG composite following the stabilization of Pd NPs on the CMC/AG composite surface (Fig. 1b). However, it was observed that the functional group peaks of Pd NPs@CMC/AG shifted to higher wavenumber and the intensity of the peaks decreased compared to the spectrum of CMC/AG composite due to strongly bonding interactions between the functional groups of CMC/AG composite and palladium ions [29].

…………………………….………Figure 1…………………………… Thermal durability of CMC/AG composite and Pd NPs@CMC/AG was explored with TG/DTG and displayed in Fig 2.

Maximum thermal degradation temperature (Tmax) of

CMC/AG composite was found as 231.8°C from the thermogram (Fig. 2a). On the other hand, it was observed that Pd NPs@CMC/AG had slightly higher thermal stability (Tmax: 247.6°C) than CMC/AG composite because palladium particles, which were stabilized on composite, contributed to the thermal stability (Fig. 2b). This high thermal durability of Pd

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NPs@CMC/AG reveals that it is a desired catalyst for catalytic reactions which require high temperature.

…………………………….………Figure 2…………………………… SEM analysis was used to investigate CMC/AG composite and Pd NPs@CMC/AG surface morphology and their SEM micrographs are presented in Fig. 3. As can be seen in Fig. 3a, CMC/AG composite has very regular surface morphology like a film. In case of Pd NPs@CMC/AG (Fig. 3b,c), the formation of small sized spherical palladium nanoparticles are clearly seen. In addition, palladium nanoparticles had spherical morphology and the average sizes ranged from 37 to 55 nm. Furthermore, palladium nanoparticles were homogeneously dispersed on CMC/AG composite and no aggregation formation was observed in the SEM image of Pd NPs@CMC/AG. These results revealed a good interaction between designed CMC/AG composite and palladium ions. On the other hand, EDAX analysis was performed to determine elemental composition of Pd NPs@CMC/AG (Fig. 4). In the EDAX spectrum of Pd NPs@CMC/AG, palladium peaks were clearly observed, indicating nanoparticles was successfully prepared. Composition of palladium on CMC/AG composite was determined as 20.37 wt% using EDAX. Palladium content of nanoparticle was also investigated with ICP-OES and it was found to be 19.89 wt%. Determined very close

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palladium values showed that palladium nanoparticle was homogeneously dispersed on the surface of the fabricated CMC/AG composite.

…………………………….………Figure 3……………………………

…………………………….………Figure 4…………………………… Crystalline nature of Pd NPs@CMC/AG was investigated with powder XRD analysis and its pattern is given in Fig. 5. When XRD pattern was examined, three significant peaks were observed at 40.06°, 46.74° and 68.16° which were ascribed to (111), (200) and (220) crystallographic planes of palladium [30]. These peaks also showed the purity of palladium nanoparticle on the surface of CMC/AG composite. 9

…………………………….………Figure 5…………………………… 3.2 Catalytic activity experiments 3.2.1 Optimization studies Before the evaluation of the catalytic performance of Pd NPs@CMC/AG, operating conditions such as temperature, time, catalyst loading, base and solvent were investigated on the model coupling reaction using ultrasonic assisted method. The coupling reaction of paraiodide anisole and phenyl boronic acid was preferred as a model reaction. Influence of the reaction temperature on ultrasound assisted Suzuki-Miyaura coupling reaction was studied in the temperature range of 30-70°C. It was observed that the reaction yield increased with elevating the reaction temperature up to 60°C, but higher reaction temperature did not much contribute to the reaction yield; 30°C (45 %), 40°C (70%), 50°C (85%), 60°C (98%), 70°C (98%). Therefore, the ideal reaction temperature was recorded as 60°C. Suzuki-Miyaura reaction was also carried out at different reaction times under ultrasonic sonication to determine best reaction time. The reaction yield increased from 15% to 98% with increasing reaction times and the best reaction time was determined as 30 min according to the control 10

studies; 5 min (15 %), 10 min (23%), 15 min (41%), 20 min (65), 25 min (82), 30 min (98%). The effect of catalyst loading was also explored on ultrasound assisted model Suzuki-Miyaura coupling reaction using different amount of the catalyst. Catalyst loading of 1x10−2 mmol produced the best result; 98%. Base system is one of the most important parameters affecting the reaction yield in Suzuki-Miyaura coupling reactions. Four different inorganic bases (K2CO3 (98%), Cs2CO3 (75%), NaOH (51%) and KOH (42%)) were tested and K2CO3 was selected as base system because it worked efficiently compared to other bases. Additionally, model coupling reaction was performed in various solvents such as ethanol (70%), water (98%), DMF (40%) and toluene (35%) to determine the ideal solvent. The highest reaction yield was reached with water. Catalytic activity of Pd NPs@CMC/AG was tested against various Suzuki-Miyaura coupling reactions using determined operating conditions (K2CO3, 60°C, 30 min, 1×10−2 mmol catalyst, in water). 3.2.2 Catalytic behavior of Pd NPs@CMC/AG in Suzuki-Miyaura coupling reactions Catalytic performance of Pd NPs@CMC/AG was tested in the synthesis of biphenyl compounds which were obtained by coupling reactions of a series of aryl iodides, bromides and chloride with phenyl boronic acid under ultrasonic sonication (Table 1). Catalytic cross coupling reactions which containing aryl iodides as substrate showed excellent catalytic performance in the presence of Pd NPs@CMC/AG (Table 1, entry 1-6). For example, aryl bromide with para-substituted –OCH3 gave high reaction yield (%98). The coupling reaction of phenyl boronic acid and meta-NO2 substituted aryl iodide (electron-attracting group) produced reaction yield of 90%. In addition, it was observed that aryl iodides with electronrepelling groups had lower efficiency than electron attracting groups (Table 1, entry 4-6). Catalytic activity of Pd NPs@CMC/AG was also evaluated using different aryl bromides containing both electron-rich and electron-poor substituents and the high reaction yields were obtained. As seen in Table 1, OCH3-para-substituted aryl bromide gave excellent biphenyl 11

yield (94 %) in presence of Pd NPs@CMC/AG (entry 7-16). On the other hand, aryl bromides with -OCH3 at the meta and ortho-position showed slightly lower catalytic performance compared to the para-position due to steric hindrance effect (92% and 85%, respectively). Following the coupling reaction of para-substituted -NO2 and -CN aryl bromides produced also good reaction yields; 96%, 95%, respectively. Considering obtained results, the substrates versatility of Pd NPs@CMC/AG was also investigated using various aryl chlorides under the optimum conditions. When aryl chlorides are used as substrate, low reaction yields are generally obtained due to their poor reactivity in Suzuki-Miyaura coupling reactions. However, in this study, good results were obtained with aryl chlorides in presence of Pd NPs@CMC/AG (Table 1, entry 17-23). For example, the reaction yield reached to 77% when para-substituted -CN aryl chloride was used as substrate. On the other hand, low biphenyl yields were obtained with aryl chlorides bearing electron donor groups. For example, after the ultrasound assisted coupling reactions, yields of 43% and 54 % were produced with -meta and para-substituted-CH3 aryl chlorides. Characterizations of the biphenyl compounds were performed by GC/MS. Furthermore, model coupling reaction was carried out under conventional heating system (60°C, 5 h) in water to show performance of ultrasonication technique and the result is given in Table 1 (entry 24). The catalyst gave higher reaction yield with shorter reaction time using ultrasonic sonication than conventional heating system. This test revealed that ultrasonication technique is more suitable for Pd NPs@CMC/AG. In addition, the model coupling reaction was performed with all reactants except Pd NPs@CMC/AG under ultrasonic sonication and no biphenyl product was obtained. This result revealed that SuzukiMiyaura reaction could not be executed without Pd NPs@CMC/AG. Catalytic performance of different commercial palladium compounds such as PdCl2 , Na2PdCl4 and PdCl2(CH3CN)2 were investigated on the model reaction under the optimum 12

conditions to evaluate catalytic activity of Pd NPs@CMC/AG. It is clearly seen from Table 1, Pd NPs@CMC/AG had far better catalytic performance over commercial palladium compounds (Table 1, entry 25-27).

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Table 1. Catalytic activity of Pd NPs@CMC/AG in Suzuki-Miyaura coupling reaction

Entry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24a 25b 26c 27d

X I I I I I I Br Br Br Br Br Br Br Br Br Br Cl Cl Cl Cl Cl Cl Cl I I I I

R 4-OCH3 3-NO2 4-NH2 2-CH3 3-CH3 4-CH3 2-OCH3 3-OCH3 4-OCH3 4-CN 3-NO2 4-NO2 3-NH2 4-NH2 3-CH3 4-CH3 2-OCH3 3-OCH3 4-OCH3 3-NO2 4-CN 3-CH3 4-CH3 4-OCH3 4-OCH3 4-OCH3 4-OCH3

Yield 98 90 84 56 59 75 85 92 94 95 91 96 78 80 59 70 51 54 69 74 77 43 54 75 45 51 47

Reaction conditions: 1.0 mmol aryl halides, 1.2 mmol phenyl boronic acid, 3.5 mmol K 2CO3 and 1x10-2 mmol Pd NPs@CMC/AG, 60°C, 30 min under ultrasonic sonication a: 1.0 mmol aryl halides, 1.2 mmol phenyl boronic acid, 3.5 mmol K2CO3 and 1x10-2 mmol Pd NPs@CMC/AG under conventional heating (60°C, 5h) b: 1.0 mmol aryl halides, 1.2 mmol phenyl boronic acid, 3.5 mmol K2CO3 and 1x10-2 mmol PdCl2, 60°C, 30 min under ultrasonic sonication c: 1.0 mmol aryl halides, 1.2 mmol phenyl boronic acid, 3.5 mmol K2CO3 and 1x10-2 mmol Na2PdCl4, 60°C, 30 min under ultrasonic sonication d: 1.0 mmol aryl halides, 1.2 mmol phenyl boronic acid, 3.5 mmol K2CO3 and 1x10-2 mmol PdCl2(CH3CN)2, 60°C, 30 min under ultrasonic sonication

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3.2.3 Reproducibility of Pd NPs@CMC/AG Reproducibility of catalysts is an attractive property as it decreases the production cost, and this feature makes it useful for industrial applications [31]. At this point, reusability of the catalyst should be investigated in the catalytic reactions. In this study, reproducibility of Pd NPs@CMC/AG was explored as follows; following the ultrasound assisted coupling reaction, used Pd NPs@CMC/AG was recovered with centrifugation and reactivated by washing with hot ethanol. This regenerated process was repeated for each cycle and the same Pd NPs@CMC/AG was used in all reproducibility studies. Reproducibility of Pd NPs@CMC/AG was studied on specified model Suzuki-Miyaura reactions. This test showed that Pd NPs@CMC/AG could be reused even after 6 runs (Fig. 6). This result clearly indicated that Pd NPs@CMC/AG catalyst has practical recyclability.

…………………………….………Figure 6……………………………

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4. Conclusions In conclusion, Pd NPs have been successfully stabilized on prepared CMC/AG composite by using green and simple method. Structural characterization of Pd NPs@CMC/AG was performed with various analytic tools. These analyses showed that Pd NPs@CMC/AG has been successfully prepared. Catalytic behavior of Pd NPs@CMC/AG was tested in ultrasound-assisted Suzuki-Miyaura coupling reactions. It was found that aryl halides were converted to the desired biphenyl compounds with excellent reaction yields in the presence of Pd NPs@CMC/AG at only 30 min in water. Additionally, reproducibility test of Pd NPs@CMC/AG indicated that it could be reused for at least six successive reactions. It was observed that the ultrasonication technique dramatically accelerated the Suzuki-Miyaura coupling reaction in the presence of Pd NPs@CMC/AG compared to the conventional heating system. Consequently, both the designed catalyst and the developed ultrasound-assisted synthesis method provided some advantages such as highly efficiency, practicability, simplicity, inexpensiveness, and green approach for Suzuki-Miyaura coupling reactions.

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Figure and Scheme Captions Fig.1 FT-IR spectra of a) CMC/AG composite b) Pd NPs@CMC/AG Fig.2 TG/DTG curves of a) CMC/AG composite b) Pd NPs@CMC/AG Fig.3 SEM images of a) CMC/AG composite b-c) Pd NPs@CMC/AG Fig.4 EDAX spectra of Pd NPs@CMC/AG Fig.5 XRD diagram of Pd NPs@CMC/AG Fig.6 Reusability of Pd NPs@CMC/AG Scheme 1. Synthesis pathway of Pd NPs@CMC/AG

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Highlights Pd NPs was immobilized on CMC/AG composite using without any reduction agents Suzuki reactions were performed under ultrasonic sonication Pd NPs@CMC/AG showed good catalytic performance in water Pd NPs@CMC/AG reused for many times

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