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Green synthesis of water-dispersable palladium nanoparticles and their catalytic application in the ligand- and copper-free Sonogashira coupling reaction under aerobic conditions
Accepted Manuscript Title: Green synthesis of water-dispersable palladium nanoparticles and their catalytic application in the ligand- and copper-free Sonogashira coupling reaction under aerobic conditions Author: Mahmoud Nasrollahzadeh Mehdi Maham Mohammad Mostafa Tohidi PII: DOI: Reference:
S1381-1169(14)00142-3 http://dx.doi.org/doi:10.1016/j.molcata.2014.04.004 MOLCAA 9066
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date: Revised date: Accepted date:
26-2-2014 3-4-2014 4-4-2014
Please cite this article as: M. Nasrollahzadeh, M. Maham, M.M. Tohidi, Green synthesis of water-dispersable palladium nanoparticles and their catalytic application in the ligand- and copper-free Sonogashira coupling reaction under aerobic conditions, Journal of Molecular Catalysis A: Chemical (2014), http://dx.doi.org/10.1016/j.molcata.2014.04.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Green synthesis of water-dispersable palladium nanoparticles and their catalytic application in the ligand- and copper-free Sonogashira coupling reaction under
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aerobic conditions Mahmoud Nasrollahzadeh,*,a Mehdi Mahamb and Mohammad Mostafa Tohidia a
Department of Chemistry, Faculty of Science, University of Qom, Qom 3716146611, Iran
b
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Department of Chemistry, Aliabad Katoul Branch, Islamic Azad University, Aliabad Katoul, Iran
us
ABSTRACT
Pd nanoparticles were prepared from PdCl2 by green method and were characterized with UV-Vis, XRD and
an
TEM methods. Catalytic studies indicated that Pd nanoparticles exhibited high activity for ligand-, amine- and copper-free Sonogashira coupling between aryl iodides and terminal alkynes under mild and aerobic conditions. This method has the advantages of high yields, simple methodology and easy work up. More importantly, the
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catalyst exhibits high catalytic activity, superior cycling stability and excellent substrate applicability.
1. Introduction
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Keywords: Palladium; Sonogashira; Copper-free; Ligand-free; Water
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The Sonogashira coupling reaction of terminal alkynes with aryl or vinyl halides provides a powerful and versatile method for C(sp)-C(sp2) bond formation, which has been widely applied to diverse areas such as heterocycles natural product synthesis, pharmaceuticals, biologically active molecules and material science [13].
The Sonogashira reaction usually proceeds in the presence of a homogeneous palladium catalyst, a copper salt as a co-catalyst, toxic phosphine ligands and a stoichiometric amount of base in an organic solvent such as an amine, benzene, THF, or DMF under inert conditions, which were economically and environmentally malignant [4,5].
*
Corresponding author. Tel.: +98 25 32103595; Fax: +98 25 32850953.
E-mail address: [email protected] (M. Nasrollahzadeh). 1
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However, most of traditional Pd-catalyzed reactions suffer from different drawbacks such as harsh reaction conditions, tedious work-ups, long reaction times, inert atmosphere conditions, use of toxic polar solvents and expensive ligands, environmental pollution caused by formation of side products and low yields of the products that restrict their usage in practical applications [4,5]. In Sonogashira coupling reaction, copper salts usually
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play an important role in assisting tansmetalation by the in situ generation of copper acetylide. However, it can also induce a Glaser-type oxidative homocoupling of the terminal acetylene to yield a diyne as a side reaction
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[4,5]. In addition, amines, such as triethylamine and piperidine, required in most Sonogashira reactions, have a bad smell and add to the environmental burden.
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The use of aqueous media in metal-catalyzed reactions have received considerable attention because waterbased synthetic processes are inherently safer (water is non-toxic and non-flammable) as well as being
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inexpensive. Moreover, the products can be isolated easily by extraction. Several examples of Pd-catalyzed Sonogashira reactions in aqueous media have been reported; however, many of these reactions are carried out in
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an aqueous-organic and in some case, special phosphine ligands and copper salts are required in order to reach high reaction efficiency [6-8]. In addition, among various catalysts for the Sonogashira coupling reactions,
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homogeneous palladium catalysts have been widely investigated, while less expensive heterogeneous palladium catalysts received scanter attention [9]. Thus, the use of ligand-free heterogeneous palladium catalysts is often
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desirable from the perspective of process development due to their easy handling, simple recovery, and
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recycling. Therefore, it is desirable to develop a mild, highly efficient and environmentally benign method for the ligand-, copper- and amine-free Sonogashira coupling reaction under heterogeneous conditions. Palladium (Pd) has widely been paid attention during the past few years due to its application potential as the homogeneous or heterogeneous catalyst for the carbon-carbon coupling reactions [10-14]. The problem with homogeneous catalysis is the difficulty to separate the catalyst from the reaction mixture and the impossibility to reuse it in consecutive reactions. However, heterogeneous catalysts allow a more easy separation from the reaction mixture. Since catalysis takes place on metal surface, nanoparticles (NPs) are much more reactive than the particulate metal counterpart due to their small sizes and large surface areas. So, heterogeneous catalysts are more and more used in the form of nanoparticles. There are several methods for the synthesis of palladium nanoparticles using toxic and expensive chemicals. Thus, environmentally benign production methods of Pd nanocatalysts without the use of harsh, toxic reducing agents (eg, hydrazine hydrate, sodium borohydride, dimethylformamide, ethylene glycol, and so on), and 2
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expensive chemicals are very desirable. Recently, extensive research effort has been made in utilizing various biological systems such as bacteria, fungus and plant extracts for the green synthesis of metal nanoparticles [15,16]. Green synthesis of NPs has several advantages over chemical synthesis, such as simplicity, very mild reaction conditions, and use of nontoxic solvents such as water, elimination of toxic and dangerous materials
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and cost effectiveness as well as compatibility for biomedical and pharmaceutical applications [17-21]. Also, in this method there is no need to use high pressure, energy, temperature and toxic chemicals. Despite the
materials for the synthesis of nanoparticles is yet to be fully explored [22,23].
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availability of methods for the green synthesis of Pd NPs by various plants the potential of gums as biological
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Gums are naturally occurring polysaccharide components in plants, which are fundamentally economical and easily available. They have assorted applications as thickeners, food emulsifiers, viscosifiers, sweeteners, and so
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on in confectionery, and as binders and drug release modifiers in pharmaceutical dosage forms [24]. In continuation of our efforts to develop environmentally friendly synthetic methodologies [25-33], we now
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wish to report a new and rapid protocol for the preparation of Pd NPs by using Sour cherry tree gum (Figure 1) as a reducing and stabilizing agent and their application as novel and stable heterogeneous catalysts for the
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copper- and phosphine-free Sonogashira coupling reaction in water under aerobic conditions (Scheme 1).
Figure 1. Image of Sour Cherry tree Gum.
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ArI +
R
Pd NPs K2CO3, H2O, 60 oC
Ar
R
Scheme 1. Sonogashira coupling in water
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2. Experimental 2.1. Instruments and reagents
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All reagents were purchased from the Merck and Aldrich chemical companies and used without further purification. Products were characterized by comparison of their physical and spectral data with authentic
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samples. Sour Cherry tree gum was obtained from the Bande Pay area, (city of Babol, province of Mazandaran, Iran). The NMR spectra were recorded in DMSO. 1H NMR spectra were recorded on a Bruker Avance DRX
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300 MHz instruments. The chemical shifts (δ) are reported in ppm relative to the TMS as an internal standard and J values are given in Hz. 13C NMR spectra were recorded at 75 Hz. FT-IR (KBr) spectra were recorded on a Perkin-Elmer 781 spectrophotometer. Melting points were taken in open capillary tubes with a BUCHI 510
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melting point apparatus and were uncorrected. TLC was performed on silica gel polygram SIL G/UV 254 plates. Transmission electron microscopy (TEM) was recorded on a JEOL JSM 100CX. XRD was recorded on a
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Bruker D8 XRD instrument SWAX.
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2.2. Preparation of palladium nanoparticles
Sour Cherry tree Gum was powdered in a Prestige high-speed mechanical blender. Then, 1.0% (w/v) of
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homogenous gum stock solution was prepared by adding this powder to reagent bottle containing ultra-pure water and stirring overnight at room temperature. Then this solution was centrifuged to remove the insoluble materials and the supernatant was used for all the experiments. In a typical synthesis of Pd NPs, 10 mL of the gum solution prepared above was added dropwise to 30 mL of 0.001 M aqueous solution of PdCl2 with constant stirring at 80 °C. Reduction of palladium ions (PdII) to palladium (Pdo) was completed around 30 min (as monitored by UV-Vis and FT-IR spectra of the solution). The color of the reaction mixtures gradually changed from transparent yellow to dark brown in 30 min at 80 °C indicating the formation of palladium nanoparticles. Then the colored solution of palladium nanoparticles was centrifuged at 6000 rpm for 30 min to completely dispersing. 2.3. General procedure for Sonogashira coupling reaction
4
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The freshly prepared solution of palladium in water (2 mol%) was added to the aryl iodide (1 mmol), alkyne (1.2 mmol), and K2CO3 (2 mmol) in a 25 mL flask and the mixture was vigorously stirred at 60 ºC for the appropriate times under aerobic conditions. After completion (as monitored by TLC), the reaction mixture was cooled and the organic layer was extracted with EtOAc, washed with water, dried over MgSO4, filtered and
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evaporated under reduced pressure. The residue was purified by column chromatography. The purity of the compounds was checked by 1H NMR and yields are based on aryl iodide. All the products are known and the
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spectroscopic data (FT-IR and NMR) and melting points were consistent with those reported in the literature [6-
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9]. 3. Results and discussion 3.1. Reduction of PdII to Pdo
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Reduction kinetics plays a key role in controlling the nucleation and growth of nanoparticles. In this work, we have employed Sour cherry tree gum as a reducing agent. To date, the reduction mechanism of palladium
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with Sour cherry tree gum has not been thoroughly investigated. Gums from plants may act both as reducing and capping agents in nanoparticle synthesis. PdII ions were reduced to their zero-valent states in water solution at
3.2. Characterization of catalyst
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70 ºC, and under aerobic conditions.
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The stable Pd NPs obtained were fully characterized by UV-Vis, TEM and XRD, and their behavior as
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catalyst was tested for the Sonogashira coupling reaction in water. 3.2.1. UV-Vis analysis
The progression of the reaction, formation and stability of palladium nanoparticles were controlled by UVVis spectroscopy (Figure 2). The yellow color of the PdII solution (λmax 415 nm) immediately changed into dark brown indicating reduction of PdII to Pdo and formation of Pd NPs as characterized by UV-Vis spectrum [34]. The synthesized palladium nanoparticles by the this method are quite stable and no obvious variance in the shape, position and symmetry of the absorption peak is observed even after two months which indicates that the as-prepared palladium nanoparticles can remain stable. The results suggested that Sour cherry tree gum plays an important role in the reduction and stabilization of palladium to palladium nanoparticles.
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Figure 2. UV-Vis absorbance spectra of Pd nanoparticles.
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3.2.2. X-Ray powder diffraction analysis
Phase investigation of the crystallized product was performed by XRD and the powder diffraction pattern of
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Pd NPs is presented in Figure 3. The presence of palladium was confirmed with powder XRD measurements. The XRD analysis of NPs dried powders indicated a crystalline structure with peaks at 20.0˚, 28.8˚, 40.0˚, 46.0˚,
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50.5˚ and 66.7˚, values found also by other authors in Pd NPs synthesized in the presence of a variety of
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size is found to be 11 nm.
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stabilizing agents [35]. The particles size can be found by applying Sherrer’s equation and the average particles
Figure 3. XRD pattern of Pd nanoparticles.
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3.2.3. Transmission electron microscopy (TEM) of Pd NPs The size and shape of the products were examined by transmission electron microscopy (TEM). Figure 4 shows TEM images of the as-produced palladium nanosphere. The products are of spherical morphology and have very narrow diameter distributions. Figure 5 shows the size distribution histogram of the nanoparticles.
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The particle sizes distributed in the range of 2.5-15 nm, with an average particle size of 5 ± 2 nm synthesized.
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Figure 4. TEM images of Pd nanoparticles.
Figure 5. Particle size distribution histogram.
3.3. Evaluation of the catalytic activity of Pd nanoparticles through the Sonogashira coupling reaction In most of transition metal catalyzed reactions, ligands play a key role. Various ligands such as phosphine and nonphosphine for palladium catalyzed coupling reactions are described in the literature. Most of these 7
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ligands are air and moisture sensitive, difficult to prepare, and expensive. Thus, catalysis under ligand-free conditions is an area of high importance. In this work, the prepared Pd NPs were used as a catalyst in the copper- and ligand-free Sonogashira coupling reaction. For optimization of the reaction conditions, we chose the reaction of 1.0 mmol of p-iodoanisole with 1.2
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mmol of phenylacetylene in the presence of 2.0 mol% of Pd NPs and 4.0 mL of water as the model reaction, and the effects of the bases were examined. As shown in Table 1, the reaction was influenced significantly by the
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base employed and the best result obtained in the case of K2CO3 (Table 1, entry 5). Increasing the amount of catalyst showed no substantial improvement in the yield. No surfactant, ligand or organic co-solvent was
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required. Since no copper salt used, the undesired formation of Glaser-type oxidative homocoupling product, a
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diyne, was also avoided.
Table 1.
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Copper-free Sonogashira reaction of phenylacetylene with p-iodoanisole in the presence of different basesa Entry
KOH
21
DMAP
0
NaOH
20
Na2CO3
78
5
K2CO3
91
6
K3PO4
79
3
Ac ce p
4
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2
a
Yield (%)b
d
1
Base
Reaction conditions: p-iodoanisole (1.0 mmol), phenylacetylene (1.2 mmol), Pd NPs (2.0 mol%), base (2.0
mmol), water (4.0 mL), 60 °C, 5 h. b
Isolated Yield.
Next, using the optimized procedure, a variety of aryl iodides possessing both electron-releasing and electron-withdrawing groups were employed. As indicated in Table 2, it is evident that our method is reasonably general and can be applied to several kinds of aryl iodides. In all cases the reaction gives the corresponding products in good to excellent yields under the reaction conditions.
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Table 2. Sonogashira coupling reaction of different aryl iodides with terminal alkynesa
5
7
8
F3C
I
10
a
2
I
O 2N
I
MeO
I
O 2N
I
93
94
2
93
3
88
3
87
OH
2
91
OH
5
91
4
92
OH
I
MeO
91
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I
OH
Ac ce p
9
89
5
I
O 2N
6
5
an
4
Me
Yield b (%)
5
I
M
3
MeO
d
2
I
Time (h)
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1
Alkyne
cr
Aryl iodide
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Entry
Me OH Me
Reaction conditions: aryliodide (1.0 mmol), phenylacetylene (1.2 mmol), Pd NPs (2.0 mol%), K2CO3 (2.0
mmol), water (4.0 mL), 60 °C. b
Yields are after work-up.
3.4. Catalyst recyclability The reusability of the catalysts is one of the most important benefits and makes them useful for commercial applications. The recycling potential of Pd NPs catalyst was studied by model Sonogashira coupling reaction for 9
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p-iodoanisole with phenylacetylene in three consecutive cycles under similar reaction conditions. The fact that water is an excellent solvent for the Pd NPs, but not for the reagents and products, allows an easy extraction/separation procedure from the reaction mixture. Thus, after each run, the reaction mixture was centrifuged at 10,000 rpm at room temperature for 15 min and filtered. Then the residue was washed with ethyl
ip t
acetate and reused. The catalytic activity did not decrease considerably after three catalytic cycles (Figure 6). This test clearly demonstrates the stability of catalyst over multiple runs and supporting its stability over
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extended duration.
+ C6H5C
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I
Yield %
CH
First Run
MeO
an
First Recycle
Pd NPs
Second Recycle
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Third Recycle
96 % 95 % 93 % 92 %
OMe
C
d
C6H5C
Ac ce p
4. Conclusions
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Figure 6. Reusability of Pd NPs for Sonogashira coupling reaction.
In conclusion, Sonogashira coupling reaction under moderate conditions can be achieved in water in the presence of Pd NPs generated by Sour Cherry tree gum as reductant. This method proved to be highly efficient and green for the following reasons: (i) the use of a green a renewable reagent such as Sour Cherry tree gum provides a great advantage in terms of safety, economy, and sustainability, (ii) using water as the solvent to conduct the Sonogashira reaction is very environmentally friendly and is an important component of green chemistry, (iii) the convenient preparation, high efficiency and reusability of the catalyst, (iv) low catalyst loading, high yields and a simple work-up procedure, and (v) elimination of dangerous and toxic reagents, ligands and organic solvents. The synthesized Pd NPs by this method are quite stable and can be kept under inert atmosphere for several months.
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Acknowledgments We gratefully acknowledge the Iranian Nano Council and University of Qom for the support of this work.
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[3] E. Negishi, L. Anastasia, Chem. Rev. 103 (2003) 1979.
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[12] A. Molnar, Chem. Rev. 111 (2011) 2251. [13] N. Selander, K. J. Szabo, Chem. Rev. 111 (2011) 2048. [14] L. Xiu, Z. Lin, Chem. Soc. Rev. 35 (2010) 1692. [15] Y. Konishi, K. Ohno, N. Saitoh, T. Nomura, S. Nagamine, H. Hishida, Y. Takahashi, T. Uruga, J. Biotechnol. 128 (2007) 648.
[16] M. Rai, A. Yadav, A. Cade, Critic. Rev. Biotechnol. 28 (2008) 277. [17] S. S. Shankar, A. Ahmad, M. Sastry, Biotechnol. Prog. 19 (2003) 1627. [18] S. P. Dubey, M. Lahtinen, M. Sillanpa, Process Biochem. 45 (2010) 1065. [19] D. Philip, Spectrochim. Acta, Part A 73 (2009) 374. [20] J. Kesharwani, J. K. Yoon, J.; Hwang, M. Rai, J. Bionanosci. 3 (2009) 1.
[21] V. K. Sharma, R. A. Yngard, Y. Lin, Adv. Colloid Interface Sci. 145 (2009) 83. [22] L. Jia, Q. Zhang, Nanotechnol 20 (2009) 385601. 11
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[23] X. Yang, Q. Li, H. Wang, J. Huang, L. Lin, W. Wang, et al. J. Nanopart. Res. 12 (2009) 589. [24] V. Rana, P. Rai, A. K. Tiwary, R. S. Singh, J. F. Kennedy, C. J. Knill, Carbohydr Polym. 83 (2011) 1031. [25] M. Nasrollahzadeh, A. Ehsani, A. Rostami-Vartouni, Ultrason. Sonochem. 21 (2014) 275.
[27] A. Ehsani, B. Jaleh, M. Nasrollahzadeh, J. Power. Sources 257 (2014) 300.
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[26] P. Fakhri, B. Jaleh, M. Nasrollahzadeh, J. Mol. Catal. A: Chem. 383-384 (2014) 17.
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[28] D. Habibi, M. Nasrollahzadeh, L. Mehrabi, S. Mostafaee, Monatsh. Chem. 144 (2013) 725. [29] D. Habibi, M. Nasrollahzadeh, H. Sahebekhtiari, J. Mol. Catal. A: Chem. 378 (2013) 148.
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[30] D. Habibi, H. Sahebekhtiari, M. Nasrollahzadeh, and A. Taghipour, Lett. Org. Chem. 10 (2013) 209. [31] D. Habibi, S. Heydari, M. Nasrollahzadeh, J. Chem. Res. 36 (2012) 573.
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[33] M. Nasrollahzadeh, A. Ehsani, M. Maham, Synlett 25 (2014) 505.
[34] Y. Li, X. M. Hong, D. M. Collard, M. A. El-Sayed, Org. Lett. 2 (2000) 2385.
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[35] T. Teranishi, M. Miyake, Chem. Mater. 10 (1998) 594.
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Scheme caption
ArI +
R
Pd NPs K2CO3, H2O, 60 oC
Ar
R
Ac ce p
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M
an
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cr
Scheme 1. Sonogashira coupling in water
ip t
Scheme 1. Sonogashira coupling in water.
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Figure captions Figure 1. Image of Sour Cherry tree Gum.
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Figure 2. UV-Vis absorbance spectra of Pd nanoparticles. Figure 3. XRD pattern of Pd nanoparticles.
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Figure 4. TEM images of Pd nanoparticles.
Ac ce p
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Figure 6. Reusability of Pd NPs for Sonogashira coupling reaction.
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Figure 5. Particle size distribution histogram.
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Ac ce p
te
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Figure 1. Image of Sour Cherry tree Gum.
Figure 2. UV-Vis absorbance spectra of Pd nanoparticles.
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Ac ce p
te
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Figure 3. XRD pattern of Pd nanoparticles.
Figure 4. TEM images of Pd nanoparticles.
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Figure 5. Particle size distribution histogram.
I + C6H5C
CH
First Run
M
MeO
te
d
Pd NPs
Second Recycle Third Recycle
96 % 95 % 93 % 92 %
OMe
C
Ac ce p
C6H5C
First Recycle
Yield %
Figure 6. Reusability of Pd NPs for Sonogashira coupling reaction.
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Table captions Table 1. Copper-free Sonogashira reaction of phenylacetylene with p-iodoanisole in the presence of different
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Table 2. Sonogashira coupling reaction of different aryl iodides with terminal alkynes.
ip t
bases.
Table 1.
Yield (%)b
Base
1
KOH
2
DMAP
0
3
NaOH
20
4
Na2CO3
78
K2CO3
91
K3PO4
79
M
an
Entry
5
21
d
6
Reaction conditions: p-iodoanisole (1.0 mmol), phenylacetylene (1.2 mmol), Pd NPs (2.0 mol%), base (2.0
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a
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Copper-free Sonogashira reaction of phenylacetylene with p-iodoanisole in the presence of different basesa
mmol), water (4.0 mL), 60 °C, 5 h. Isolated Yield.
Ac ce p
b
18
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Table 2. Sonogashira coupling reaction of different aryl iodides with terminal alkynesa
5
7
8
F3C
I
10
a
2
I
O 2N
I
MeO
I
O 2N
I
93
94
2
93
3
88
3
87
OH
2
91
OH
5
91
4
92
OH
I
MeO
91
us
I
OH
Ac ce p
9
89
5
I
O 2N
6
5
an
4
Me
Yield b (%)
5
I
M
3
MeO
d
2
I
Time (h)
ip t
1
Alkyne
cr
Aryl iodide
te
Entry
Me OH Me
Reaction conditions: aryliodide (1.0 mmol), phenylacetylene (1.2 mmol), Pd NPs (2.0 mol%), K2CO3 (2.0
mmol), water (4.0 mL), 60 °C. b
Yields are after work-up.
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Abbreviations XRD: X-ray Powder Diffraction TEM: Transmission electron microscopy
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FT-IR spectroscopy: Fourier transform infrared spectroscopy
Ac ce p
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NMR: Nuclear Magnetic Resonance
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Graphical Abstract Green synthesis of water-dispersable palladium nanoparticles and their catalytic
ip t
application in the ligand- and copper-free Sonogashira coupling reaction under aerobic conditions
cr
Mahmoud Nasrollahzadeh,* Mehdi Maham and Mohammad Mostafa Tohidi
+ RC
CH
an
R'
us
I
M
Pd NPs
R'
Ac ce p
te
d
RC
C
*
Corresponding author. Tel.: +98 25 32103595; Fax: +98 25 32850953.
E-mail address: [email protected] (M. Nasrollahzadeh). 21
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Highlights: Green synthesis of Pd nanoparticles. Sonogashira coupling reactions of different aryl iodides using Pd nanoparticles in
ip t
water.
Catalyst was characterized using the powder XRD, TEM and UV-Vis.
Ac ce p
te
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M
an
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cr
Catalyst can be easily recovered and reused.
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S1381-1169(14)00142-3 http://dx.doi.org/doi:10.1016/j.molcata.2014.04.004 MOLCAA 9066
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date: Revised date: Accepted date:
26-2-2014 3-4-2014 4-4-2014
Please cite this article as: M. Nasrollahzadeh, M. Maham, M.M. Tohidi, Green synthesis of water-dispersable palladium nanoparticles and their catalytic application in the ligand- and copper-free Sonogashira coupling reaction under aerobic conditions, Journal of Molecular Catalysis A: Chemical (2014), http://dx.doi.org/10.1016/j.molcata.2014.04.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Green synthesis of water-dispersable palladium nanoparticles and their catalytic application in the ligand- and copper-free Sonogashira coupling reaction under
ip t
aerobic conditions Mahmoud Nasrollahzadeh,*,a Mehdi Mahamb and Mohammad Mostafa Tohidia a
Department of Chemistry, Faculty of Science, University of Qom, Qom 3716146611, Iran
b
cr
Department of Chemistry, Aliabad Katoul Branch, Islamic Azad University, Aliabad Katoul, Iran
us
ABSTRACT
Pd nanoparticles were prepared from PdCl2 by green method and were characterized with UV-Vis, XRD and
an
TEM methods. Catalytic studies indicated that Pd nanoparticles exhibited high activity for ligand-, amine- and copper-free Sonogashira coupling between aryl iodides and terminal alkynes under mild and aerobic conditions. This method has the advantages of high yields, simple methodology and easy work up. More importantly, the
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catalyst exhibits high catalytic activity, superior cycling stability and excellent substrate applicability.
1. Introduction
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Keywords: Palladium; Sonogashira; Copper-free; Ligand-free; Water
Ac ce p
The Sonogashira coupling reaction of terminal alkynes with aryl or vinyl halides provides a powerful and versatile method for C(sp)-C(sp2) bond formation, which has been widely applied to diverse areas such as heterocycles natural product synthesis, pharmaceuticals, biologically active molecules and material science [13].
The Sonogashira reaction usually proceeds in the presence of a homogeneous palladium catalyst, a copper salt as a co-catalyst, toxic phosphine ligands and a stoichiometric amount of base in an organic solvent such as an amine, benzene, THF, or DMF under inert conditions, which were economically and environmentally malignant [4,5].
*
Corresponding author. Tel.: +98 25 32103595; Fax: +98 25 32850953.
E-mail address: [email protected] (M. Nasrollahzadeh). 1
Page 1 of 22
However, most of traditional Pd-catalyzed reactions suffer from different drawbacks such as harsh reaction conditions, tedious work-ups, long reaction times, inert atmosphere conditions, use of toxic polar solvents and expensive ligands, environmental pollution caused by formation of side products and low yields of the products that restrict their usage in practical applications [4,5]. In Sonogashira coupling reaction, copper salts usually
ip t
play an important role in assisting tansmetalation by the in situ generation of copper acetylide. However, it can also induce a Glaser-type oxidative homocoupling of the terminal acetylene to yield a diyne as a side reaction
cr
[4,5]. In addition, amines, such as triethylamine and piperidine, required in most Sonogashira reactions, have a bad smell and add to the environmental burden.
us
The use of aqueous media in metal-catalyzed reactions have received considerable attention because waterbased synthetic processes are inherently safer (water is non-toxic and non-flammable) as well as being
an
inexpensive. Moreover, the products can be isolated easily by extraction. Several examples of Pd-catalyzed Sonogashira reactions in aqueous media have been reported; however, many of these reactions are carried out in
M
an aqueous-organic and in some case, special phosphine ligands and copper salts are required in order to reach high reaction efficiency [6-8]. In addition, among various catalysts for the Sonogashira coupling reactions,
d
homogeneous palladium catalysts have been widely investigated, while less expensive heterogeneous palladium catalysts received scanter attention [9]. Thus, the use of ligand-free heterogeneous palladium catalysts is often
te
desirable from the perspective of process development due to their easy handling, simple recovery, and
Ac ce p
recycling. Therefore, it is desirable to develop a mild, highly efficient and environmentally benign method for the ligand-, copper- and amine-free Sonogashira coupling reaction under heterogeneous conditions. Palladium (Pd) has widely been paid attention during the past few years due to its application potential as the homogeneous or heterogeneous catalyst for the carbon-carbon coupling reactions [10-14]. The problem with homogeneous catalysis is the difficulty to separate the catalyst from the reaction mixture and the impossibility to reuse it in consecutive reactions. However, heterogeneous catalysts allow a more easy separation from the reaction mixture. Since catalysis takes place on metal surface, nanoparticles (NPs) are much more reactive than the particulate metal counterpart due to their small sizes and large surface areas. So, heterogeneous catalysts are more and more used in the form of nanoparticles. There are several methods for the synthesis of palladium nanoparticles using toxic and expensive chemicals. Thus, environmentally benign production methods of Pd nanocatalysts without the use of harsh, toxic reducing agents (eg, hydrazine hydrate, sodium borohydride, dimethylformamide, ethylene glycol, and so on), and 2
Page 2 of 22
expensive chemicals are very desirable. Recently, extensive research effort has been made in utilizing various biological systems such as bacteria, fungus and plant extracts for the green synthesis of metal nanoparticles [15,16]. Green synthesis of NPs has several advantages over chemical synthesis, such as simplicity, very mild reaction conditions, and use of nontoxic solvents such as water, elimination of toxic and dangerous materials
ip t
and cost effectiveness as well as compatibility for biomedical and pharmaceutical applications [17-21]. Also, in this method there is no need to use high pressure, energy, temperature and toxic chemicals. Despite the
materials for the synthesis of nanoparticles is yet to be fully explored [22,23].
cr
availability of methods for the green synthesis of Pd NPs by various plants the potential of gums as biological
us
Gums are naturally occurring polysaccharide components in plants, which are fundamentally economical and easily available. They have assorted applications as thickeners, food emulsifiers, viscosifiers, sweeteners, and so
an
on in confectionery, and as binders and drug release modifiers in pharmaceutical dosage forms [24]. In continuation of our efforts to develop environmentally friendly synthetic methodologies [25-33], we now
M
wish to report a new and rapid protocol for the preparation of Pd NPs by using Sour cherry tree gum (Figure 1) as a reducing and stabilizing agent and their application as novel and stable heterogeneous catalysts for the
Ac ce p
te
d
copper- and phosphine-free Sonogashira coupling reaction in water under aerobic conditions (Scheme 1).
Figure 1. Image of Sour Cherry tree Gum.
3
Page 3 of 22
ArI +
R
Pd NPs K2CO3, H2O, 60 oC
Ar
R
Scheme 1. Sonogashira coupling in water
ip t
2. Experimental 2.1. Instruments and reagents
cr
All reagents were purchased from the Merck and Aldrich chemical companies and used without further purification. Products were characterized by comparison of their physical and spectral data with authentic
us
samples. Sour Cherry tree gum was obtained from the Bande Pay area, (city of Babol, province of Mazandaran, Iran). The NMR spectra were recorded in DMSO. 1H NMR spectra were recorded on a Bruker Avance DRX
an
300 MHz instruments. The chemical shifts (δ) are reported in ppm relative to the TMS as an internal standard and J values are given in Hz. 13C NMR spectra were recorded at 75 Hz. FT-IR (KBr) spectra were recorded on a Perkin-Elmer 781 spectrophotometer. Melting points were taken in open capillary tubes with a BUCHI 510
M
melting point apparatus and were uncorrected. TLC was performed on silica gel polygram SIL G/UV 254 plates. Transmission electron microscopy (TEM) was recorded on a JEOL JSM 100CX. XRD was recorded on a
d
Bruker D8 XRD instrument SWAX.
te
2.2. Preparation of palladium nanoparticles
Sour Cherry tree Gum was powdered in a Prestige high-speed mechanical blender. Then, 1.0% (w/v) of
Ac ce p
homogenous gum stock solution was prepared by adding this powder to reagent bottle containing ultra-pure water and stirring overnight at room temperature. Then this solution was centrifuged to remove the insoluble materials and the supernatant was used for all the experiments. In a typical synthesis of Pd NPs, 10 mL of the gum solution prepared above was added dropwise to 30 mL of 0.001 M aqueous solution of PdCl2 with constant stirring at 80 °C. Reduction of palladium ions (PdII) to palladium (Pdo) was completed around 30 min (as monitored by UV-Vis and FT-IR spectra of the solution). The color of the reaction mixtures gradually changed from transparent yellow to dark brown in 30 min at 80 °C indicating the formation of palladium nanoparticles. Then the colored solution of palladium nanoparticles was centrifuged at 6000 rpm for 30 min to completely dispersing. 2.3. General procedure for Sonogashira coupling reaction
4
Page 4 of 22
The freshly prepared solution of palladium in water (2 mol%) was added to the aryl iodide (1 mmol), alkyne (1.2 mmol), and K2CO3 (2 mmol) in a 25 mL flask and the mixture was vigorously stirred at 60 ºC for the appropriate times under aerobic conditions. After completion (as monitored by TLC), the reaction mixture was cooled and the organic layer was extracted with EtOAc, washed with water, dried over MgSO4, filtered and
ip t
evaporated under reduced pressure. The residue was purified by column chromatography. The purity of the compounds was checked by 1H NMR and yields are based on aryl iodide. All the products are known and the
cr
spectroscopic data (FT-IR and NMR) and melting points were consistent with those reported in the literature [6-
us
9]. 3. Results and discussion 3.1. Reduction of PdII to Pdo
an
Reduction kinetics plays a key role in controlling the nucleation and growth of nanoparticles. In this work, we have employed Sour cherry tree gum as a reducing agent. To date, the reduction mechanism of palladium
M
with Sour cherry tree gum has not been thoroughly investigated. Gums from plants may act both as reducing and capping agents in nanoparticle synthesis. PdII ions were reduced to their zero-valent states in water solution at
3.2. Characterization of catalyst
d
70 ºC, and under aerobic conditions.
te
The stable Pd NPs obtained were fully characterized by UV-Vis, TEM and XRD, and their behavior as
Ac ce p
catalyst was tested for the Sonogashira coupling reaction in water. 3.2.1. UV-Vis analysis
The progression of the reaction, formation and stability of palladium nanoparticles were controlled by UVVis spectroscopy (Figure 2). The yellow color of the PdII solution (λmax 415 nm) immediately changed into dark brown indicating reduction of PdII to Pdo and formation of Pd NPs as characterized by UV-Vis spectrum [34]. The synthesized palladium nanoparticles by the this method are quite stable and no obvious variance in the shape, position and symmetry of the absorption peak is observed even after two months which indicates that the as-prepared palladium nanoparticles can remain stable. The results suggested that Sour cherry tree gum plays an important role in the reduction and stabilization of palladium to palladium nanoparticles.
5
Page 5 of 22
ip t cr us
Figure 2. UV-Vis absorbance spectra of Pd nanoparticles.
an
3.2.2. X-Ray powder diffraction analysis
Phase investigation of the crystallized product was performed by XRD and the powder diffraction pattern of
M
Pd NPs is presented in Figure 3. The presence of palladium was confirmed with powder XRD measurements. The XRD analysis of NPs dried powders indicated a crystalline structure with peaks at 20.0˚, 28.8˚, 40.0˚, 46.0˚,
d
50.5˚ and 66.7˚, values found also by other authors in Pd NPs synthesized in the presence of a variety of
Ac ce p
size is found to be 11 nm.
te
stabilizing agents [35]. The particles size can be found by applying Sherrer’s equation and the average particles
Figure 3. XRD pattern of Pd nanoparticles.
6
Page 6 of 22
3.2.3. Transmission electron microscopy (TEM) of Pd NPs The size and shape of the products were examined by transmission electron microscopy (TEM). Figure 4 shows TEM images of the as-produced palladium nanosphere. The products are of spherical morphology and have very narrow diameter distributions. Figure 5 shows the size distribution histogram of the nanoparticles.
M
an
us
cr
ip t
The particle sizes distributed in the range of 2.5-15 nm, with an average particle size of 5 ± 2 nm synthesized.
Ac ce p
te
d
Figure 4. TEM images of Pd nanoparticles.
Figure 5. Particle size distribution histogram.
3.3. Evaluation of the catalytic activity of Pd nanoparticles through the Sonogashira coupling reaction In most of transition metal catalyzed reactions, ligands play a key role. Various ligands such as phosphine and nonphosphine for palladium catalyzed coupling reactions are described in the literature. Most of these 7
Page 7 of 22
ligands are air and moisture sensitive, difficult to prepare, and expensive. Thus, catalysis under ligand-free conditions is an area of high importance. In this work, the prepared Pd NPs were used as a catalyst in the copper- and ligand-free Sonogashira coupling reaction. For optimization of the reaction conditions, we chose the reaction of 1.0 mmol of p-iodoanisole with 1.2
ip t
mmol of phenylacetylene in the presence of 2.0 mol% of Pd NPs and 4.0 mL of water as the model reaction, and the effects of the bases were examined. As shown in Table 1, the reaction was influenced significantly by the
cr
base employed and the best result obtained in the case of K2CO3 (Table 1, entry 5). Increasing the amount of catalyst showed no substantial improvement in the yield. No surfactant, ligand or organic co-solvent was
us
required. Since no copper salt used, the undesired formation of Glaser-type oxidative homocoupling product, a
an
diyne, was also avoided.
Table 1.
M
Copper-free Sonogashira reaction of phenylacetylene with p-iodoanisole in the presence of different basesa Entry
KOH
21
DMAP
0
NaOH
20
Na2CO3
78
5
K2CO3
91
6
K3PO4
79
3
Ac ce p
4
te
2
a
Yield (%)b
d
1
Base
Reaction conditions: p-iodoanisole (1.0 mmol), phenylacetylene (1.2 mmol), Pd NPs (2.0 mol%), base (2.0
mmol), water (4.0 mL), 60 °C, 5 h. b
Isolated Yield.
Next, using the optimized procedure, a variety of aryl iodides possessing both electron-releasing and electron-withdrawing groups were employed. As indicated in Table 2, it is evident that our method is reasonably general and can be applied to several kinds of aryl iodides. In all cases the reaction gives the corresponding products in good to excellent yields under the reaction conditions.
8
Page 8 of 22
Table 2. Sonogashira coupling reaction of different aryl iodides with terminal alkynesa
5
7
8
F3C
I
10
a
2
I
O 2N
I
MeO
I
O 2N
I
93
94
2
93
3
88
3
87
OH
2
91
OH
5
91
4
92
OH
I
MeO
91
us
I
OH
Ac ce p
9
89
5
I
O 2N
6
5
an
4
Me
Yield b (%)
5
I
M
3
MeO
d
2
I
Time (h)
ip t
1
Alkyne
cr
Aryl iodide
te
Entry
Me OH Me
Reaction conditions: aryliodide (1.0 mmol), phenylacetylene (1.2 mmol), Pd NPs (2.0 mol%), K2CO3 (2.0
mmol), water (4.0 mL), 60 °C. b
Yields are after work-up.
3.4. Catalyst recyclability The reusability of the catalysts is one of the most important benefits and makes them useful for commercial applications. The recycling potential of Pd NPs catalyst was studied by model Sonogashira coupling reaction for 9
Page 9 of 22
p-iodoanisole with phenylacetylene in three consecutive cycles under similar reaction conditions. The fact that water is an excellent solvent for the Pd NPs, but not for the reagents and products, allows an easy extraction/separation procedure from the reaction mixture. Thus, after each run, the reaction mixture was centrifuged at 10,000 rpm at room temperature for 15 min and filtered. Then the residue was washed with ethyl
ip t
acetate and reused. The catalytic activity did not decrease considerably after three catalytic cycles (Figure 6). This test clearly demonstrates the stability of catalyst over multiple runs and supporting its stability over
cr
extended duration.
+ C6H5C
us
I
Yield %
CH
First Run
MeO
an
First Recycle
Pd NPs
Second Recycle
M
Third Recycle
96 % 95 % 93 % 92 %
OMe
C
d
C6H5C
Ac ce p
4. Conclusions
te
Figure 6. Reusability of Pd NPs for Sonogashira coupling reaction.
In conclusion, Sonogashira coupling reaction under moderate conditions can be achieved in water in the presence of Pd NPs generated by Sour Cherry tree gum as reductant. This method proved to be highly efficient and green for the following reasons: (i) the use of a green a renewable reagent such as Sour Cherry tree gum provides a great advantage in terms of safety, economy, and sustainability, (ii) using water as the solvent to conduct the Sonogashira reaction is very environmentally friendly and is an important component of green chemistry, (iii) the convenient preparation, high efficiency and reusability of the catalyst, (iv) low catalyst loading, high yields and a simple work-up procedure, and (v) elimination of dangerous and toxic reagents, ligands and organic solvents. The synthesized Pd NPs by this method are quite stable and can be kept under inert atmosphere for several months.
10
Page 10 of 22
Acknowledgments We gratefully acknowledge the Iranian Nano Council and University of Qom for the support of this work.
[1] K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron Lett. (1975) 4467. [2] T. A. Kamali, D. Habibi, M. Nasrollahzadeh, Synlett (2009) 2601.
cr
[3] E. Negishi, L. Anastasia, Chem. Rev. 103 (2003) 1979.
ip t
References
[4] K. Sonogashira, in: B.M. Trost, I. Fleming (Eds.), Comprehensive Organic Synthesis, vol. 3,
us
Pergamon, New York, 1991.
[5] S. Shylesh, V. Schunemann, W. R. Thiel, Angew. Chem., Int. Ed. 49 (2010) 3428.
an
[6] C. Yi, R. Hua, Catal. Commun. 7 (2006) 377.
[7] H. F. Chow, C. W. Wan, K. H. Low, Y. Y. Yeung, J. Org. Chem. 66 (2001) 1910.
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[8] A. Corma, H. Garciá, A. Primo, J. Catal. 241 (2006) 123.
[9] B. Liang, M. Dai, J. Chen, Z. Yang, J. Org. Chem. 70 (2005) 391.
d
[10] M. Lamblin, L. Nassar-Hardy, J.-C. Hierso, E. Fouquet, F.-X. Felpin, Adv. Synth. Catal. 325 (2010) 33.
te
[11] R. Narayanan, Molecules 15 (2010) 2124.
Ac ce p
[12] A. Molnar, Chem. Rev. 111 (2011) 2251. [13] N. Selander, K. J. Szabo, Chem. Rev. 111 (2011) 2048. [14] L. Xiu, Z. Lin, Chem. Soc. Rev. 35 (2010) 1692. [15] Y. Konishi, K. Ohno, N. Saitoh, T. Nomura, S. Nagamine, H. Hishida, Y. Takahashi, T. Uruga, J. Biotechnol. 128 (2007) 648.
[16] M. Rai, A. Yadav, A. Cade, Critic. Rev. Biotechnol. 28 (2008) 277. [17] S. S. Shankar, A. Ahmad, M. Sastry, Biotechnol. Prog. 19 (2003) 1627. [18] S. P. Dubey, M. Lahtinen, M. Sillanpa, Process Biochem. 45 (2010) 1065. [19] D. Philip, Spectrochim. Acta, Part A 73 (2009) 374. [20] J. Kesharwani, J. K. Yoon, J.; Hwang, M. Rai, J. Bionanosci. 3 (2009) 1.
[21] V. K. Sharma, R. A. Yngard, Y. Lin, Adv. Colloid Interface Sci. 145 (2009) 83. [22] L. Jia, Q. Zhang, Nanotechnol 20 (2009) 385601. 11
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[23] X. Yang, Q. Li, H. Wang, J. Huang, L. Lin, W. Wang, et al. J. Nanopart. Res. 12 (2009) 589. [24] V. Rana, P. Rai, A. K. Tiwary, R. S. Singh, J. F. Kennedy, C. J. Knill, Carbohydr Polym. 83 (2011) 1031. [25] M. Nasrollahzadeh, A. Ehsani, A. Rostami-Vartouni, Ultrason. Sonochem. 21 (2014) 275.
[27] A. Ehsani, B. Jaleh, M. Nasrollahzadeh, J. Power. Sources 257 (2014) 300.
ip t
[26] P. Fakhri, B. Jaleh, M. Nasrollahzadeh, J. Mol. Catal. A: Chem. 383-384 (2014) 17.
cr
[28] D. Habibi, M. Nasrollahzadeh, L. Mehrabi, S. Mostafaee, Monatsh. Chem. 144 (2013) 725. [29] D. Habibi, M. Nasrollahzadeh, H. Sahebekhtiari, J. Mol. Catal. A: Chem. 378 (2013) 148.
us
[30] D. Habibi, H. Sahebekhtiari, M. Nasrollahzadeh, and A. Taghipour, Lett. Org. Chem. 10 (2013) 209. [31] D. Habibi, S. Heydari, M. Nasrollahzadeh, J. Chem. Res. 36 (2012) 573.
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[32] M. Nasrollahzadeh, A. Rostami-Vartooni, A. Ehsani, M. Moghadam, J. Mol. Catal. A: Chem. 387 (2014) 123.
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[33] M. Nasrollahzadeh, A. Ehsani, M. Maham, Synlett 25 (2014) 505.
[34] Y. Li, X. M. Hong, D. M. Collard, M. A. El-Sayed, Org. Lett. 2 (2000) 2385.
Ac ce p
te
d
[35] T. Teranishi, M. Miyake, Chem. Mater. 10 (1998) 594.
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Scheme caption
ArI +
R
Pd NPs K2CO3, H2O, 60 oC
Ar
R
Ac ce p
te
d
M
an
us
cr
Scheme 1. Sonogashira coupling in water
ip t
Scheme 1. Sonogashira coupling in water.
13
Page 13 of 22
Figure captions Figure 1. Image of Sour Cherry tree Gum.
ip t
Figure 2. UV-Vis absorbance spectra of Pd nanoparticles. Figure 3. XRD pattern of Pd nanoparticles.
cr
Figure 4. TEM images of Pd nanoparticles.
Ac ce p
te
d
M
an
Figure 6. Reusability of Pd NPs for Sonogashira coupling reaction.
us
Figure 5. Particle size distribution histogram.
14
Page 14 of 22
ip t cr us
Ac ce p
te
d
M
an
Figure 1. Image of Sour Cherry tree Gum.
Figure 2. UV-Vis absorbance spectra of Pd nanoparticles.
15
Page 15 of 22
ip t cr us
Ac ce p
te
d
M
an
Figure 3. XRD pattern of Pd nanoparticles.
Figure 4. TEM images of Pd nanoparticles.
16
Page 16 of 22
ip t cr us
an
Figure 5. Particle size distribution histogram.
I + C6H5C
CH
First Run
M
MeO
te
d
Pd NPs
Second Recycle Third Recycle
96 % 95 % 93 % 92 %
OMe
C
Ac ce p
C6H5C
First Recycle
Yield %
Figure 6. Reusability of Pd NPs for Sonogashira coupling reaction.
17
Page 17 of 22
Table captions Table 1. Copper-free Sonogashira reaction of phenylacetylene with p-iodoanisole in the presence of different
cr
Table 2. Sonogashira coupling reaction of different aryl iodides with terminal alkynes.
ip t
bases.
Table 1.
Yield (%)b
Base
1
KOH
2
DMAP
0
3
NaOH
20
4
Na2CO3
78
K2CO3
91
K3PO4
79
M
an
Entry
5
21
d
6
Reaction conditions: p-iodoanisole (1.0 mmol), phenylacetylene (1.2 mmol), Pd NPs (2.0 mol%), base (2.0
te
a
us
Copper-free Sonogashira reaction of phenylacetylene with p-iodoanisole in the presence of different basesa
mmol), water (4.0 mL), 60 °C, 5 h. Isolated Yield.
Ac ce p
b
18
Page 18 of 22
Table 2. Sonogashira coupling reaction of different aryl iodides with terminal alkynesa
5
7
8
F3C
I
10
a
2
I
O 2N
I
MeO
I
O 2N
I
93
94
2
93
3
88
3
87
OH
2
91
OH
5
91
4
92
OH
I
MeO
91
us
I
OH
Ac ce p
9
89
5
I
O 2N
6
5
an
4
Me
Yield b (%)
5
I
M
3
MeO
d
2
I
Time (h)
ip t
1
Alkyne
cr
Aryl iodide
te
Entry
Me OH Me
Reaction conditions: aryliodide (1.0 mmol), phenylacetylene (1.2 mmol), Pd NPs (2.0 mol%), K2CO3 (2.0
mmol), water (4.0 mL), 60 °C. b
Yields are after work-up.
19
Page 19 of 22
Abbreviations XRD: X-ray Powder Diffraction TEM: Transmission electron microscopy
ip t
FT-IR spectroscopy: Fourier transform infrared spectroscopy
Ac ce p
te
d
M
an
us
cr
NMR: Nuclear Magnetic Resonance
20
Page 20 of 22
Graphical Abstract Green synthesis of water-dispersable palladium nanoparticles and their catalytic
ip t
application in the ligand- and copper-free Sonogashira coupling reaction under aerobic conditions
cr
Mahmoud Nasrollahzadeh,* Mehdi Maham and Mohammad Mostafa Tohidi
+ RC
CH
an
R'
us
I
M
Pd NPs
R'
Ac ce p
te
d
RC
C
*
Corresponding author. Tel.: +98 25 32103595; Fax: +98 25 32850953.
E-mail address: [email protected] (M. Nasrollahzadeh). 21
Page 21 of 22
Highlights: Green synthesis of Pd nanoparticles. Sonogashira coupling reactions of different aryl iodides using Pd nanoparticles in
ip t
water.
Catalyst was characterized using the powder XRD, TEM and UV-Vis.
Ac ce p
te
d
M
an
us
cr
Catalyst can be easily recovered and reused.
22
Page 22 of 22