Facile fabrication of magnetically separable palladium nanoparticles supported on modified kaolin as a highly active heterogeneous catalyst for Suzuki coupling reactions

Article abstract of DOI:10.1016/j.jpcs.2020.109566

In this study, Fe₃O₄ loaded Schiff base modified kaolin was prepared as a new support and palladium nanoparticles were anchored on it without any additional reducing agent (Pd NPs&at;Kao/Fe₃O₄/Pyr). Characterization studies demonstrated that Pd NPs&at;Kao/Fe₃O₄/Pyr was successfully designed and the size of particles was about 25 nm. Pd NPs&at;Kao/Fe₃O₄/Pyr was then utilized as catalyst in the preparation of biaryl compounds via Suzuki cross coupling reactions. Catalytic tests showed that Pd NPs&at;Kao/Fe₃O₄/Pyr acted as a highly active heterogeneous nanocatalyst in the coupling reaction of aryl iodides, bromides and chlorides containing different functional groups. Moreover, it was found that Pd NPs&at;Kao/Fe₃O₄/Pyr was successfully used in consecutive recycling tests and gave an 89percent yield even after ten runs. In addition to the high catalytic behavior and reusability, Pd NPs&at;Kao/Fe₃O₄/Pyr have some advantages such as i) capability of application for various halides containing different functional groups, ii) ease of purification of final product and iii) simple work-up.

Full text of DOI:10.1016/j.jpcs.2020.109566

Journal Pre-proof
Facile fabrication of magnetically separable palladium nanoparticles supported
on modified kaolin as a highly active heterogeneous catalyst for Suzuki coupling
reactions
Talat Baran, Mahmoud Nasrollahzadeh
PII:
S0022-3697(20)30944-6
https://doi.org/10.1016/j.jpcs.2020.109566
PCS 109566
DOI:
Reference:
To appear in: Journal of Physics and Chemistry of Solids
Received Date: 8 April 2020
Revised Date: 11 May 2020
Accepted Date: 16 May 2020
Please cite this article as: T. Baran, M. Nasrollahzadeh, Facile fabrication of magnetically separable
palladium nanoparticles supported on modified kaolin as a highly active heterogeneous catalyst
for Suzuki coupling reactions, Journal of Physics and Chemistry of Solids (2020), doi: https://
doi.org/10.1016/j.jpcs.2020.109566.
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Graphical Abstract
Facile fabrication of magnetically separable palladium nanoparticles supported on
modified kaolin as a highly active heterogeneous catalyst for Suzuki coupling reactions
Talat Baran and Mahmoud Nasrollahzadeh*
*Corresponding author. Tel.: +98 25 32103595; Fax: +98 25 32850953. E-mail address: mahmoudnasr81@gmail.com (M. Nasrollahzadeh)

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Facile fabrication of magnetically separable palladium nanoparticles supported on
modified kaolin as a highly active heterogeneous catalyst for Suzuki coupling reactions
Talat Barana and Mahmoud Nasrollahzadeh*
,b
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aDepartment of Chemistry, Faculty of Science and Letters, Aksaray University, 68100, Aksaray, Turkey
bDepartment of Chemistry, Faculty of Science, University of Qom, 3716146611, Qom, Iran
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Abstract
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In this study, Fe3O4 loaded Schiff base modified kaolin was prepared as a new support and
palladium nanoparticles were anchored on it without any additional reducing agent (Pd
NPs@Kao/Fe3O4/Pyr). Characterization studies demonstrated that Pd NPs@Kao/Fe3O4/Pyr
was successfully designed and the size of particles was about 25 nm. Pd NPs@Kao/Fe3O4/Pyr
was then utilized as catalyst in the preparation of biaryl compounds via Suzuki cross coupling
reactions. Catalytic tests showed that Pd NPs@Kao/Fe3O4/Pyr acted as a highly active
heterogeneous nanocatalyst in the coupling reaction of aryl iodides, bromides and chlorides
containing different functional groups. Moreover, it was found that Pd NPs@Kao/Fe3O4/Pyr
was successfully used in consecutive recycling tests and gave an 89% yield even after ten
runs. In addition to the high catalytic behavior and reusability, Pd NPs@Kao/Fe3O4/Pyr have
some advantages such as i) capability of application for various halides containing different
functional groups, ii) ease of purification of final product and iii) simple work-up.
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Keywords: Kaolin; Schiff base; Aryl halide; Suzuki; Palladium nanocatalyst
1. Introduction
*
Corresponding author
E-mail address: mahmoudnasr81@gmail.com (M. Nasrollahzadeh).
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Biaryls are valuable organic compounds, which form important structural parts of numerous
compounds such as herbicides, pharmaceuticals, and natural products [1]. Additionally,
biaryls are widely utilized in engineering materials such as molecular wires, conductive
polymers, and liquid crystals given their superior properties [2]. Therefore, the preparation of
these versatile compounds has recently gained extensive attention by researchers [3].
Transition metal based cross coupling reaction of aryl halides and organoboronic acids,
known as the Suzuki reaction, is one of the most important organic synthesis methods for the
formation of symmetrical or unsymmetrical biaryl compounds [4]. Additionally, Suzuki
coupling reactions have some advantages such as low toxicity of the starting materials, good
stability, mild reaction conditions and easy accessibility compared to other coupling reactions.
These properties make Suzuki reactions even more important in organic synthesis [5]. Suzuki
coupling reactions are usually carried out in the presence of homogeneous palladium
catalysts. However, these catalytic systems suffer from some disadvantages such as separation
and reusability [6]. These drawbacks cause process complexities and high costs. To solve
these problems, solid supported Pd(II) or Pd(0) heterogeneous catalysts have been considered
as alternatives due to their highly stability, activity, reusability and recoverability. However,
the disadvantage of heterogeneous catalysts is metal leaching, which leads to the decreased
reactivity and poor recycling performance of the catalyst due to the weak interaction of metal
with supports. Therefore, it is necessary to develop ideal supports, which can strongly interact
with metals as well as heterogeneous catalysts with high catalytic activity and reusability in
Suzuki reactions.
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The preparation of nano scaled transition metal nanoparticles (MNPs) with the
development of nano science has received much attention in the catalysis field due to the high
surface area and capability of such nanoparticles to conduct different catalytic reactions with
high catalytic performance [7,8]. Therefore, different MNPs have been designed and widely
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used as catalysts in numerous chemical reactions such as degradation of organic pollutants, C-
C coupling reactions, and aryl halide cyanation [9-11]. However, one of the most important
problems widely encountered in the synthesis of MNPs is the aggregation and leaching of
metals, which can adversely affect its catalytic property and reuse [12]. Therefore, there is a
need to prepare metallic nanocatalysts with high catalytic performance and longtime stability
in the catalytic systems. This can be solved by stabilizing metal nanoparticles on the right
type of support to help further improve their stability, catalytic activity and reusability.
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To date, different stabilizers such as biopolymers, carbon based materials, and metal
oxides have been used in the fabrication of MNPs [13-15]. Among the stabilizers used,
natural clays are promising materials compared to other support materials due to their
outstanding physicochemical properties, economic and environmental advantages [16, 17].
Kaolin, which is known as one of the most common clay minerals, is cheap, easily available,
eco-friendly and has high thermal and mechanical stability. These properties makes it a
significant candidate for nanocatalyst support [18, 19]. Therefore, kaolin or modified kaolin
derivatives can be prepared for the synthesis of different metallic nanoparticles such as Pd, Ag
and Au NPs and the catalytic performance or reusability of the MNPs prepared can be tested
in different catalytic reactions.
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In the light of our interest in the synthesis of nanoscale Pd NPs, in this study, a new
stabilizer featuring magnetic Schiff base modified kaolin was developed. Pd NPs were
decorated on the support in the absence of any reduction agents. The structure of Pd
NPs@Kao/Fe3O4/Pyr was characterized by FTIR, XRD, FE-SEM, EDS and TEM analyses
and it was found that the particle size of Pd NPs was as about 25 nm. Pd NPs@Kao/Fe3O4/Pyr
was then evaluated as a heterogeneous catalyst in the cross coupling reactions of aryl iodides,
bromides and chlorides to form the desired biaryl products in up to 98% yields. After the
Suzuki coupling reaction, Pd NPs@Kao/Fe3O4/Pyr was easily regenerated due to their
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magnetic nature and reused ten times with high reaction yields. Pd NPs@Kao/Fe3O4/Pyr was
shown to be an efficient and reusable catalyst in the synthesis of different biaryls with good
reaction yields.
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2. 2. Experimental
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2.1. Experimental information
Aryl halides, PdCl2, 3-aminopropyltriethoxysilane, pyrrole-2-carboxaldehyde, Cs2CO3,
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Na2CO3, K2CO3, KOH, NaOH, and toluene were purchased from Sigma Aldrich Chemical
Co. Kaolin was obtained from Turkey. FTIR spectra of Kao, Fe3O4 loaded kaolin,
Kao/Fe3O4/APTES, Kao/Fe3O4/Pyr and Pd NPs@Kao/Fe3O4/Pyr were recorded on a Perkin
Elmer Spectrum100 FTIR spectrophotometer. FE-SEM micrograms and EDS spectra of the
products were obtained using a QUANTA-FEG 250ESEM instrument. TEM images of Pd
NPs@Kao/Fe3O4/Pyr were obtained using a TEM JEOL JEM-2100 (UHR) instrument. XRD
patterns of Pd NPs@Kao/Fe3O4/Pyr were recorded using a Rigaku smart lab system (10-90°).
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2.2 Synthesis of Kao/Fe3O4/Pyr as stabilizer
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Firstly, Fe3O4 loaded kaolin was prepared as follows: FeSO4⋅7H2O (4.2ꢀg), FeCl3⋅6H2O
(6.1ꢀg) and kaolin were placed into 100 mL of water and the mixture obtained was stirred at
90ꢀ°C for 1 h. 10 mL of NH4OH solution was then transferred into the reaction media under
constant stirring and the resulting mixture was heated at 80ꢀ°C for another 1 h to obtain Fe3O4
loaded kaolin particles denoted as Kao/Fe3O4. 1.0 g of Kao/Fe3O4 was dispersed in 40 mL of
anhydrous toluene by ultrasonication for 30 min. at room temperature, followed by the
addition of 5 mL of 3-aminopropyltriethoxysilane into the reaction mixture, which was then
stirred 100 °C for 24 h to obtain APTES modified Kao/Fe3O4 (Kao/Fe3O4/APTES). Finally,
Schiff base modification was performed by stirring Kao/Fe3O4/APTES (1g) with pyrrole-2-
carboxaldehyde (2 g) in 30 mL of ethanol.
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2.3 Synthesis of Pd NPs@Kao/Fe3O4/Pyr
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Fabrication of palladium nanoparticles on the Kao/Fe3O4/Sch in the absence of any reducing
agents was achieved by stirring Kao/Fe3O4/Sch (0.5 g) and PdCl2 (0.1 g) in ethanol (20 mL) at
70ꢀ°C for 3 h. Pd NPs@Kao/Fe3O4/Pyr was then collected using an external magnet, rinsed
with water and dried to use in the cyanation reactions (Scheme 1).
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Scheme 1. Synthesis of Pd NPs@Kao/Fe3O4/Pyr
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2.4 General procedure for aryl halide cyanations
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The mixture containing Pd NPs@Kao/Fe3O4/Pyr (0.025 mol %), aryl halide (1 mmol),
Na2CO3 (3.5 mmol) and phenyl boronic acid (1.8ꢀmmol) was subjected to microwave
irradiation for 6 min. Upon the completion of the reaction, the mixture was extracted with
water: toluene (1:2) three times. The organic phase containing biaryls was evaporated and the
product was characterized by GC/MS analysis.
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3. Results and discussion
3.1 Characterization of Pd NPs@Kao/Fe3O4/Pyr
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Fig. 1 gives shows the FTIR spectra of Kao, Fe3O4 loaded kaolin, Kao/Fe3O4/APTES,
Kao/Fe3O4/Pyr and Pd NPs@Kao/Fe3O4/Pyr. The FTIR spectrum of kaolin displayed
characteristic bands at 3621-3690cm-1 (stretching vibrations of inner hydroxyl and outer
surface OH groups), 1112-1002 cm-1 (stretching of Si-O) and 912cm-1 (Al–OH stretching
vibrations) [20-23]. Following the fabrication of Fe3O4 loaded kaolin, the peaks of kaolin
shifted very slightly. Fe-O peaks, which appear at low wavenumbers (<600 cm−1), were not
detected due to the range of ATR-FTIR (4000–650 cm−1). To confirm the loading of Fe3O4 on
kaolin, XRD and EDS analyses were performed. After the treatment of Fe3O4 loaded kaolin
with APTES, new peaks were observed at 2930 and 2856cm-1 (stretching of aliphatic C-H),
1570 and 1481cm-1 (asymmetric and symmetric bending C-H), and 1387 cm-1(deformation of
the primary amine groups). These peaks confirmed the formation of silane modified magnetite
loaded kaolin [24, 25]. In the spectrum of Kao/Fe3O4/Pyr, a new peak is observed at 1660 cm-
1, indicating the formation of the Schiff base. It was observed that this imine vibration shifted
to 1638 cm−1 in the spectrum of Pd NPs@Kao/Fe3O4/Pyr, owing to the interaction of
palladium ions with the support.
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Fig. 1. FT-IR spectra of a) Kao, b) Fe3O4 loaded kaolin, c) Kao/Fe3O4/APTES, d)
Kao/Fe3O4/Pyr and e) Pd NPs@Kao/Fe3O4/Pyr.
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Surface characteristics of Kao, Fe3O4 loaded kaolin, Kao/Fe3O4/APTES,
Kao/Fe3O4/Pyr and Pd NPs@Kao/Fe3O4/Pyr were studied by FE-SEM and TEM analyses.
The FE-SEM image of indicated a layered surface morphology. After production of Fe3O4
loaded kaolin, its surface was covered with particles (Fig. 2 b). It was observed that the
number of particles on the surface of kaolin increased following the synthesis of
Kao/Fe3O4/APTES and Kao/Fe3O4/Pyr (Figs. 2c, d). In the case of Pd NPs@Kao/Fe3O4/Pyr,
the FE-SEM image indicated that the palladium nanoparticles were immobilized on
Kao/Fe3O4/ Pyr (Figs. 2e, f). In addition, the EDS analyses of Kao, Fe3O4 loaded kaolin,
Kao/Fe3O4/APTES and Pd NPs@Kao/Fe3O4/Pyr were carried out and the corresponding
spectra are shown in Fig. 3. In the EDS spectrum of Kao/Fe3O4, the appearance of the Fe
peaks in addition to the characteristic peaks of kaolin confirmed the formation of magnetic
kaolin. The EDS analysis of the catalyst showed extra Pd peaks, which also proved Pd NPs
formation (Fig. 3d). Moreover, the presence of Fe peaks in the spectrum of all the samples
showed that the designed stabilizer and catalyst retained their magnetic properties.
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Fig. 2. SEM images of a) Kao, b) Fe3O4 loaded kaolin, c) Kao/Fe3O4/APTES, d)
Kao/Fe3O4/Pyr and e, f) Pd NPs@Kao/Fe3O4/Pyr.
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Fig. 3. EDS spectra of a) Kao, b) Fe3O4 loaded kaolin, c) Kao/Fe3O4/APTES, d) Pd
NPs@Kao/Fe3O4/Pyr.
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To confirm the fabrication of Pd NPs, TEM analysis of Pd NPs@Kao/Fe3O4/Pyr was
performed and the TEM images also confirmed the fabrication Pd NPs on the Kao/Fe3O4/Pyr.
Moreover, it was found that the homogenously distributed Pd NPs were spherical and the
diameters of the particles of Pd NPs were about 25 nm (Fig. 4).
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Fig. 4. TEM micrograms of Pd NPs@Kao/Fe3O4/Pyr.
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Fig. 5 displays the XRD patterns of Pd NPs@Kao/Fe3O4/Pyr. In the XRD diagram of
Pd NPs@Kao/Fe3O4/Pyr, intense diffraction characteristic peaks of kaolin were observed at
12.42°, 20.93° and 26.70° [26, 27]. Additionally, typical Fe3O4 peaks also appeared at 30.25°,
35.61°, 43.40, 53.67°, 57.48° and 62.97° in the spectrum. These main peaks correspond to
(220), (311), (400), (422), (511) and (440) crystal planes of Fe3O4, respectively. The XRD
diagram also displayed new peaks at 40.02°, 46.69°, 68.14°, 83.32° and 86.52°, which can be
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attributed to (111), (200), (220), (311) and (222) planes of metallic Pd, verifying the
immobilization of Pd nanoparticles on the support.
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Fig. 5. XRD pattern of Pd NPs@Kao/Fe3O4/Pyr.
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3.2 Investigation of catalytic role of Pd NPs@Kao/Fe3O4/Pyr in Suzuki cross coupling
reactions
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Before the assessment of Pd NPs@Kao/Fe3O4/Pyr nanocatalyst in Suzuki cross coupling
reactions, the optimization reaction parameters were studied. To do this, the coupling reaction
of 4-NO2C6H4I catalyzed by Pd NPs@Kao/Fe3O4/Pyr was selected as the model reaction and
reaction parameters were investigated. In terms of green chemistry, no toxic organic solvents
were used during the catalytic tests and all the catalytic tests were performed under solvent
free conditions. The optimization experiments were conducted with respect to different
reaction parameters such as the amount of Pd NPs@Kao/Fe3O4/Pyr, reaction time and base
type. The details of the preliminary experiments performed and the isolated yields are
summarized in Table 1. Based on the control experiments, the optimum reaction conditions
were determined as the catalyst loading of 0.025 mol %, K2CO3 as the base, and reaction time
of 6ꢀmin. The scope of the Pd NPs@Kao/Fe3O4/Pyr substrate was then investigated in the
Suzuki cross coupling of a range of aryl iodides, bromides and chlorides. The results obtained
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are shown in Table 2. Entries 1-6 of Table 2 display that the Pd NPs@Kao/Fe3O4/Pyr
efficiently catalyzed the conversion of aryl iodides to the desired biaryls products with
excellent reaction yields. For example, the Suzuki cross coupling reactions of 4-MeOC6H4I
and 3-NO2C6H4I produced 96% and 95% yields, respectively. Cross coupling reactions of 4-
CH3C6H4I and 3-CH3C6H4I were catalyzed by Pd NPs@Kao/Fe3O4/Pyr with 87 and 82 %
yields, respectively. Afterwards, the coupling reaction of aryl bromides in the presence of Pd
NPs@Kao/Fe3O4/Pyr was investigated and good isolated yields were obtained. 4-CNC6H4Br
produced the expected biaryl in 97% yield. 4-NO2C6H4Br was coupled by Pd
NPs@Kao/Fe3O4/Pyr with 98% yield. In the next stage, the catalytic role of Pd
NPs@Kao/Fe3O4/Pyr in the coupling reaction of aryl chlorides under optimum reaction
conditions was also investigated and the nanoscale catalyst showed good performance in the
conversion of aryl chlorides to the desired biaryl compounds. 4-CNC6H4Cl was successfully
coupled in 76% yield by Pd NPs@Kao/Fe3O4/Pyr. These results showed that Pd
NPs@Kao/Fe3O4/Pyr is an effective nanocatalyst for the synthesis of biaryls containing
different functional groups. Moreover, to show the catalytic advantage of the catalyst
designed, the catalytic efficacy of Pd NPs@Kao/Fe3O4/Pyr was compared to other reported
catalysts in the Suzuki reaction of 4-CH3OC6H4I with PhB(OH)2 and the results are given in
Table 3. As observed in Table 3, the results show that Pd NPs@Kao/Fe3O4/Pyr is the most
effective catalyst in terms of reaction yield and time.
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Table 1. Optimization of reaction conditions for Suzuki cross coupling reaction of 4-
NO2C6H4I.
Entry
Catalyst mol (%)
0.025
Base
Cs2CO3
Cs2CO3
Cs2CO3
Na2CO3
KOH
Time (min)
Yield (%)
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5
4
6
6
6
6
86
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55
71
65
50
98
1
2
3
4
5
6
7
0.025
0.025
0.025
0.025
0.025
0.025
NaOH
K2CO3
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0.025
0.025
0.02
0.01
0.05
0.0
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
5
7
6
6
6
6
83
98
91
80
62
0
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10
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12
13
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Reaction conditions: p-NO2C6H4I (1.0 mmol), base (3.5 mmol), PhB(OH)2 (1. 8 mmol), 400 W and solvent-free
conditions.
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Table 2. Catalytic role of Pd NPs@Kao/Fe3O4/Pyr in Suzuki coupling reaction. a
Entry
Aryl halide (RC6H4X)
Yield (%)
TONb
TOFc (h-1)
R
X
I
1
2
3
4
5
6
7
8
9
10
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12
13
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16
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18
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20
4-CH3O
4-NO2
3-NO2
4-NH2
4-CH3
3-CH3
4-CH3O
3-CH3O
2-CH3O
4-NO2
3-NO2
4-CN
4-NH2
3-NH2
4-CH3
3-CH3
4-CH3O
3-NO2
4-CN
96
98
95
89
87
82
95
90
86
96
93
97
86
83
81
74
68
71
76
64
3840
3920
3800
3560
3480
3280
3800
3600
3440
3840
3720
3880
3440
3320
3240
2960
2720
2840
3040
2560
38400
39200
38000
35600
34800
32800
38000
36000
34400
38400
37200
38800
34400
33200
32400
29600
27200
28400
30400
25600
I
I
I
I
I
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
Cl
4-CH3
a
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Reaction conditions: Aryl halides (1.0 mmol), K2CO3 (3.5 mmol), PhB(OH)2 (1.8 mmol), Pd
NPs@Kao/Fe3O4/Pyr (0.025 mol%), 6 min, 400 W and solvent free conditions.
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b TON: Turnover number.
c TOF: Turnover frequency.
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Table 3. Comparison of catalytic behavior of Pd NPs@Kao/Fe3O4/Pyr with other reported
catalysts in the coupling reaction of 4-CH3OC6H4Br with PhB(OH)2.
Entry
Catalyst
Pd/ZnO
Pd NPs@biocomposite
Time
30 min
30 min
Yield (%)
Ref.
[28]
[29]
1
2
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13

3
4
5
cellulose Schiff base-Pd
Pd0.03/RPN
7 min
30 min
2 h
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98
67
[30]
[31]
[32]
Pd(II) Schiff base complexe
bearing bis-bidentate
monoanionic ligand
Pd NPs@Fe3O4-lignin
Fe3O4@SiO2-Pd
6
7
8
9
10
11
135 min
40 min
2 h
5 h
30 min
6 min
92
90
90
84
93
95
[33]
[34]
[35]
[36]
[37]
Pd-AcAc-Am-Fe3O4@SiO2
Pdo-Mont.
Nanoscale Pd/ZnO
Pd NPs@Kao/Fe3O4/Pyr
Present study
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3.3 Reusability of Pd NPs@Kao/Fe3O4/Pyr
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One of the most important features which distinguishes any catalyst is its high recoverability
and reusability in the catalytic systems. In this regard, the reusability of Pd
NPs@Kao/Fe3O4/Pyr in the coupling reaction of 4-NO2C6H4I with PhB(OH)2 was assessed.
Following the catalytic reaction, the Pd NPs@Kao/Fe3O4/Pyr catalyst used was easily
separated using an external magnet, regenerated by washing with water and dried to reuse in
the next run. This process was repeated after each run. The reusability tests revealed that Pd
NPs@Kao/Fe3O4/Pyr was a long lasting and stable catalyst by providing 89% yield after ten
successive runs (Fig. 6). The TEM images of recycled catalyst show no fundamental changes
in size of the particles and morphological specification of Pd NPs@Kao/Fe3O4/Pyr (Fig. 7).
Additionally, palladium leaching from the catalysts was checked by ICP analysis after the
recycling test and very low level leaching (1.1ꢀwt. %) was recorded due to the strong
interaction between Kao/Fe3O4/Pyr and Pd NPs.
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40
20
0
1
2
3
4
5
6
7
8
9
10
Runs
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Fig. 6. Reusability of Pd NPs@Kao/Fe3O4/Pyr.
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Fig. 7. TEM images of recycled Pd NPs@Kao/Fe3O4/Pyr.
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4. Conclusion
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In this work, magnetically separable, highly effective and eco-friendly palladium nanocatalyst
derived from Schiff base modified kaolin was prepared for the synthesis of various biaryls
and characterized by FTIR, FE-SEM, EDS, XRD and TEM. It was found that the palladium
particles of about 25 nm in size were homogeneously dispersed on Kao/Fe3O4/Pyr. Pd
NPs@Kao/Fe3O4/Pyr nanocatalyst showed excellent catalytic activity by producing the
desired biaryls with a yield of up to 98%. The Pd NPs@Kao/Fe3O4/Pyr showed not only good
catalytic performance, but also indicated high reusability in the Suzuki coupling reactions of
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aryl halides. The coupling reaction of 4-NO2H6C4I with PhB(OH)2 was successfully carried
out ten times by Pd NPs@Kao/Fe3O4/Pyr. Consequently, the results showed that Pd
NPs@Kao/Fe3O4/Pyr was useful nanocatalyst for Suzuki coupling reactions due to some
advantages such as high catalytic performance, high stability, relatively low cost, magnetic
recoverability and consequent high reusability.
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References
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357
18

Highlights:
‹
‹
‹
‹
Synthesis of Pd NPs on the Schiff base modified kaolin is presented.
Suzuki coupling reactions are performed using Pd NPs@Kao/Fe3O4/Pyr catalyst.
Characterization of catalyst accomplished by FT-IR, XRD, TEM, SEM, and EDS.
The catalyst can be recovered and reused ten times by magnetic separation without any
considerable changes in the catalytic activity.
1

In this work, magnetically separable, highly effective and eco-friendly palladium
nanocatalysts derived from Schiff base modified kaolin were prepared for the synthesis of
various biaryls and characterized by FTIR, FE-SEM, EDS, XRD and TEM. It was found that the
palladium particles of about 25 nm in size were homogeneously dispersed on Kao-Sch. Pd
NPs@Kao/Fe3O4/Pyr nanocatalyst showed excellent catalytic activity by producing the desired
biaryls with a yield of up to 98%. The Pd NPs@Kao/Fe3O4/Pyr showed not only good catalytic
performance, but also indicated high reusability in the Suzuki coupling reactions of aryl halides.
The coupling reaction of 4-NO2H6C4I with PhB(OH)2 was successfully carried out ten times by
Pd NPs@Kao/Fe3O4/Pyr. Consequently, the results showed that Pd NPs@Kao/Fe3O4/Pyr were
useful nanocatalyst for Suzuki coupling reactions due to some advantages such as high catalytic
performance, high stability, relatively low cost, magnetic recoverability and consequent high
reusability.

Declaration of interest: The authors declare no competing interest.