Inorganic–organic hybrid nano magnetic based nickel complex as a novel, efficient and reusable nanocomposite for the synthesis of biphenyl compounds in green condition

Article abstract of DOI:10.1016/j.poly.2018.11.070

The carbon–carbon cross coupling reactions through transition-metal-catalyzed processes has been significantly developed for their important synthetic applications. A novel and fantastic nickel-based catalyst supported on bis (propyl malononitrile) (NiFe₂O₄@SiO₂-BPMN-Ni) was easily prepared and evaluated as heterogeneous nanocatalyst in Suzuki cross coupling reaction of various aryl halides and phenylboronic acid. The catalyst prepared and characterized by using fourier transform infrared (FT-IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), thermo gravimetric analysis (TGA) and vibrating sample magnetometer (VSM) techniques. Compare to the previous works, this procedure have advantages such as easy workup, high yields of products, environmentally benign and short reaction times. The catalyst can be separated by external magnet and reused six times without any significant loss of activity which is an additional sustainable characteristic of this method. The products have been confirmed by spectroscopic and physical data such as; IR, ¹H NMR, and melting point.

Full text of DOI:10.1016/j.poly.2018.11.070

Accepted Manuscript
Inorganic–organic hybrid nano magnetic based nickel complex as a novel, ef-
ficient and reusable nanocomposite for the synthesis of biphenyl compounds in
green condition
Hossein Naeimi, Fatemeh Kiani
PII:
S0277-5387(18)30826-X
https://doi.org/10.1016/j.poly.2018.11.070
POLY 13638
DOI:
Reference:
Polyhedron
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5 August 2018
12 November 2018
14 November 2018
Please cite this article as: H. Naeimi, F. Kiani, Inorganic–organic hybrid nano magnetic based nickel complex as a
novel, efficient and reusable nanocomposite for the synthesis of biphenyl compounds in green condition,
Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.2018.11.070
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Inorganic–organic hybrid nano magnetic based nickel complex as a novel,
efficient and reusable nanocomposite for the synthesis of biphenyl compounds
in green condition
Hossein Naeimi*, Fatemeh Kiani
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, 87317,
I.R. Iran. Fax: +98-03155912397; Tel: +98-03155912388; E-mail: Naeimi@kashanu.ac.ir.
Abstract:
The carbon-carbon cross coupling reactions through transition-metal-catalyzed processes has
been significantly developed for their important synthetic applications. A novel and fantastic
nickel-based catalyst supported on bis (propyl malononitrile) (NiFe2O4@SiO2-BPMN-Ni) was
easily prepared and evaluated as heterogeneous nanocatalyst in Suzuki cross coupling reaction of
various aryl halides and phenylboronic acid. The catalyst prepared and characterized by
using fourier transform infrared (FT-IR), powder X-ray diffraction (XRD), scanning
electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), thermo
gravimetric analysis (TGA) and vibrating sample magnetometer (VSM) techniques.
Compare to the previous works, this procedure have advantages such as easy workup,
high yields of products, environmentally benign and short reaction times. The catalyst
can be separated by external magnet and reused six times without any significant loss of
activity which is an additional sustainable characteristic of this method. The products
1
have been confirmed by spectroscopic and physical data such as; IR, H NMR, and
melting point.
Keywords: Heterogonous catalyst, Coupling reaction, Biphenyls, Nickel ferrite, Green
syntheses.
1

1. Introduction
The ability to construct new bonds is important in chemical synthesis. A widely used approach is
the metal catalysed cross-coupling of two simple molecules to create a more complex product. In
particular the Suzuki-Miyaura reaction, which involves cross-coupling between a sp2-hybridized
boronic acid and a sp2-hybridized halide, is robust and highly tolerant of varying the reaction
partners. [1] The transition metals-catalyzed Suzuki-Miyaura reaction including the arylboronic
acids and aryl halides gives a very significant and clean approach for the formation of a biaryl
compound, which creates a partial structure in many of the industrially significant syntheses
involving functional polymers, fine chemicals and pharmaceuticals [2-6], because of its
demonstrated reliability, its functional group compatibility, and the low cost and ease of handling
of a wide variety of commercially available boron-based reagents. It is also the premier cross-
coupling process and has been widely applied in organic [3], medicinal and materials [7]
chemistry.
Owing to the growing tendency to avoid perilous materials in organic reaction Suzuki–Miyaura,
between coupling reactions, is the most superior [8, 9]. Water as a solvent is especially attractive
since it is nonpoisonous, available, cheap, and can be simply separated from organic substances.
In addition, boronic acids are non-toxic and stable towards air and moisture.
Besides, the ligands applied for providing catalytic systems for the less reactive substrates are
commonly air and/or water-sensitive, expensive and often not accessible commercially. For these
applied and economic reasons, as well as environmental considerations, the application of
heterogeneous catalysts systems is so extremely considerable and several investigations
addressed the analysis of the catalytic activity of these species. In addition, the possibility of
recycling and reusability of the solid catalyst is a vital topic in view of a presumptive scale-up of
the catalytic process from the industrial point of view [10].
Commonly, catalysts are separated into two categories: homogeneous systems and
heterogeneous systems. Although the reported useful effects with homogeneous system,
problems associated with the separation and recyclability of the expensive catalyst, limit their
use in synthetic and industrial applications. Therefore, it is necessary to develop supported
catalysts that can quickly be recycled from the reaction system and reused. Thus, in order to
overcome these drawbacks, many researches on developing effective procedures for metal
2

complexes on several different solid supports, such as clays[11], activated carbon[12], micro
porous polymers[13], and magnetic nanoparticles[14] have been performed. In recent years,
magnetic nanoparticles have received significant attention due to their various applications in
immobilize enzymes, bioactive polymers, transition metal catalysts and organocatalysts [15-17].
The surface of magnetic nanoparticles can be functionalized easily through proper surface
modifications to enable the loading of a diversity of desirable functionalities [18].
In continuation of ongoing our research toward catalytic reactions [19-21], herein, we studied a
thermal method that provides the efficient and simple preparation of biphenyls from
phenylboronic acid and aryl halides derivatives using magnetically recyclable NiFe2O4@SiO2-
BPMN-Ni complex as heterogeneous catalyst.
2. Experiment
2.1. Materials and Apparatus
All organic materials were purchased commercially from Sigma–Aldrich and Merck and were
used without further purification.
1
FT-IR measurements were recorded on Magna 550 apparatus using with KBr plates. The H
NMR and 13C NMR spectra were recorded on Bruker Avance-400 MHz spectrometers in the
presence of tetramethylsilane as internal standard. Nanostructures were characterized using a
Holland Philips Xpert X-ray powder diffraction (XRD) diffractometer (Cu Kα, radiation, λ =
0.154056 nm), at a scanning speed of 2°/min from 10º to 100° (2θ). FE-SEM and elemental
analysis were carried out using a Jeol SEM instrument (VEGA/TESCAN) combined with an
INCA instrument for energy-dispersive X-ray spectroscopy (EDX), with a scanning electron
electrode at 15 kV. Transmission electron microscopy (TEM) analyses were performed using a
JEOL-JEN 2010 transmission electron microscope operated at an accelerating voltage of 200 kV.
Thermo gravimetric analysis (TGA) was performed on a mettler TA4000 system TG-50 at a
heating rate of 10 K min-1 under N2 atmosphere. The magnetic properties of nanoparticles have
been measured with a vibrating sample magnetometer (VSM, PPMS-9T) at 300 K in Iran
(Kashan University). Melting points was obtained with a Yanagimoto micro melting point
apparatus and are uncorrected. The purity determination of the substrates and reaction
3

monitoring were accomplished by TLC on silica-gel polygram SILG/UV 254 plates (from Merck
Company).
2.2. Catalyst preparation
2.2.1. General procedure for preparation of NiFe2O4 nanoparticles
Nickel ferrite nanoparticles (NiFe2O4) were synthesized by co-precipitation procedure,
according to the reported method in the literature [22]. 3M solution of sodium hydroxide
was added drop wise to salt solutions of 0.4M ferric chloride (FeCl3.6H2O) and 0.2M
nickel chloride (NiCl2.6H2O). The pH of the solution was constantly monitored as the
NaOH solution was added slowly. The reactants were stirred using a magnetic stirrer till
pH of the solution was close to 13. Finally, 3 drops of oleic acid (as a surfactant) were
added to the solution. The liquid-precipitate mixture was then brought to a reaction
temperature of 80ºC and stirred for 40 min. The solutions were centrifuged and the
precipitate was washed several times with double distilled water and ethanol to remove
unwanted impurities and the excess surfactant from the synthesized sample. The sample
was centrifuged for 15min at 2000 rpm and then dried overnight at above 80ºC. The
acquired substance was then grinded into a fine powder and then calcined for 10 h at
600ºC.
2.2.2. General procedure for preparation of nano-NiFe2O4@SiO2 core-shell
The core-shell NiFe2O4@SiO2 nanoparticles were obtained by a Stober method with minor
modifications [23]. Generally, 100 mL of 75% ethanol/water solution containing the above
obtained NiFe2O4 MNPs were transferred into a three-neck flask. After ultrasonic mixing for 10
min, under the condition of N2 atmosphere, 4 mL of tetraethoxysilane (TEOS) and 2 mL of
ammonia were added into NiFe2O4 MNPs suspension in turn under vigorous stirring. The
reaction system was kept at 35ºC for 6 h. Consequently, the black precipitates, NiFe2O4@SiO2
MNPs, were washed with deionized water and ethanol for 3 times and dried at 80oC for 10h.
2.2.3. General procedure for functionalization of NiFe2O4@SiO2 MNPs surfaces
To our knowledge, the surface of silica nanoparticles can be easily functionalized through 3-
iodopropyltriethoxysilane. With vigorously stirring, 400 µL of 3-Iodopropyltrimethoxysilane and
600 µL of ammonia were added slowly to 10 mL of NiFe2O4@SiO2 MNPs solution suspended in
dry toluene. The solution was refluxed for 24 h under an inert atmosphere, filtered and washed
4

subsequently with toluene, dichloromethane, and methanol, and dried under reduced pressure at
80ºC for 10 h. A mixture of 3-Iodopropyl functionalized MNPs was added to a suspension of
K2CO3 (5 mmol) and malononitrile (5 mmol) in acetonitrile (30 ml). The mixture was refluxed
for 48 h. Subsequently, the immobilization of metals (Ni, Co, Au, Fe and Ru) were carried out by
their reduction in the presence of NaBH4 as reducing agent, in absolute ethanol as the solvent
system.
2.3. General procedure for the Suzuki-Miyaura coupling reaction
A vial equipped with a magnetic stirrer bar and a condenser was charged with aryl halide (1
mmol), phenylboronic acid (1.2 mmol), K2CO3 (2 mmol), catalyst (12 mg Ni complex) and
Water/ EtOH (1:1) (4 ml) and the reaction mixture was heated in 100°C. The reaction progress
was followed using thin layer chromatography. After completion of the reaction, the mixture was
cooled to room temperature, the catalyst was separated by an external magnet, and the product
was extracted with ethyl acetate (15 ml) and dried over anhydrous MgSO4. The resulting solution
was evaporated under vacuum to give the crude product. The separation of product by column
chromatography on silica gel using n-hexane or different mixtures of n-hexane, ethyl acetate as
the eluents to afford the highly pure product (Table 4). The obtained pure products were
characterized by melting points and IR and 1H NMR spectra.
2.4. Spectral data for biphenyl derivatives:
1, 1'-Biphenyl. White solid; m.p=70-72°C (Lit.[24] 68-70°C). IR (KBr)/ ν (cm-1); 3058, 1433,
1072, 902, 729, 696. 1H NMR (400 MHz, CDCl3) δ: 7.35 (t, J = 7.1 Hz, 2H), 7.44 (t, J= 7.4 Hz,
4H), 7.60 (d, J= 7.3 Hz, 4H).
4-Methoxy-1, 1'-biphenyl. light yellow solid; m.p=78-80°C (Lit.[24] 80-82°C). IR (KBr)/
ν (cm-1); 1247, 1178, 1120, 10354, 833, 762, 697. 1H NMR (400 MHz, CDCl3) δ: 3.86 (s,
3H); 6.98-7.00 (d, J= 8.4 Hz, 2H); 7.47-7.43(t, J= 7.2 Hz, 1H), 7.60-7.55(t, J= 7.4 Hz,
2H), 7.60-7.55(t, J= 8.2 Hz, 4H).
(1, 1'-Biphenyl)-4-carbonitrile. White solid; m.p=80-82°C (Lit.[24] 84-86°C). IR (KBr)/ ν (cm-
1
1); 844, 769, 722, 697. H NMR (400 MHz, CDCl3) δ: 7.42 (t, J = 7.2 Hz, 1H), 7.55 (t, J = 7.6
Hz, 2H), 7.60 (d, J = 7.2 Hz, 2H), 7.66-7.74 (m, 4H).
5

4-Nitro-1, 1'-biphenyl. Pale yellow solid; m.p=112-114°C (Lit.[25] 113-115°C). IR (KBr)/ ν
1
(cm-1); 3077, 1599, 1520, 1345, 1122, 854, 740, 696. H NMR (400 MHz, CDCl3) δ: 7.46-7.48
(m, 1H), 7.50-7.52 (m, 2H), 7.61-7.66 (m, 2H), 7.69-7.49 (m, 2H), 8.29-8.31 (m, 2H).
Methyl (1, 1'-biphenyl)-4-carboxylate. White solid; m.p=110-112°C (Lit.[24] 113-115°C). IR
(KBr)/ ν (cm-1); 698, 748, 856, 1113, 1186, 1283, 1719. 1H NMR (400 MHz, CDCl3) δ: 3.88 (s,
3H), 7.14(d, J= 7.2 Hz, 1H), 7.32-7.38 (t, J= 7.4 Hz, 2H), 7.43-7.50 (m, 4H), 7.84 (d, J= 8.2 Hz,
2H).
1-((1, 1'-Biphenyl)-4-yl) ethan-1-one. White solid, m.p=115-117°C; (Lit.[26] 117-119°C). IR
1
(KBr)/ ν (cm-1); 3031, 1681, 1600, 1359, 1263, 960, 842, 766. H NMR (400 MHz, CDCl3) δ:
2.67 (s, 3H); 7.42 (t, J = 7.2 Hz, 3H), 7.53 (d, J = 7.2 Hz, 2H), 7.56 (d, J= 8.4 Hz, 2H), 8.02 (d,
J= 8.4 Hz, 2H).
(1, 1'-Biphenyl)-4-carbaldehyde. White solid; m.p=61-63°C (Lit.[27] 62-65 °C). IR (KBr)/ ν
(cm-1); 2958, 2859, 1727, 1602, 1460, 846, 697. 1H NMR (400 MHz, CDCl3) δ: = 7.23 (t, J = 7.0
Hz, 1H), 7.44 (t, J = 7.0 Hz, 2H), 7.51 (d, J= 7.9 Hz, 2H), 7.66 (d, J = 7.7 Hz, 2H), 7.93 (d, J =
7.7 Hz, 2H), 10.05(s, 1H).
4-Methyl-1, 1'-biphenyl. White solid; m.p=40-42°C (Lit.[28] 41-43°C). IR (KBr)/ ν (cm-1);
3027, 2926, 2859, 1599, 1567, 1522, 1456, 1381, 1340, 1072, 823, 749, 698, 481. 1H NMR (400
MHz, CDCl3) δ: 2.41 (s, 3H), 7.36-7.38 (m, 2H), 7.44-7.47 (m, 1H), 7.50-7.52 (m, 2H), 7.60-
7.62 (m, 2H), 7.67-7.72 (m, 2H).
3-Methyl-1, 1'-biphenyl. Colorless liquid; (Lit.[25]). IR (KBr)/ ν (cm-1); 3054, 3023, 2958,
1
2858, 1636, 1579, 1460, 1381, 1270, 1072, 882, 737, 727, 698, 617, 543. H NMR (400 MHz,
CDCl3) δ: = 2.43 (s, 3H), 7.24 (d, J = 8 Hz, 1H) 7.36 (d, J = 8.0 Hz, 2H), 7.49 (m, 4H), 7.60 (q, J
= 8.0 Hz, 2H).
3-Chloro-1, 1'-biphenyl. Colorless transparent liquid; (Lit.[25]). IR (KBr)/ ν (cm-1); 3049, 3023,
1
2914, 1375, 1489, 1457, 1418, 1122, 1068, 1040, 1015, 775, 747, 689. H NMR (400 MHz,
CDCl3) δ: 7.35-7.39 (m, 3H), 7.52-7.56 (m, 3H), 7.70-7.72 (m, 3H).
p-Terphenyl. White solid; m.p=88-90°C (Lit.[28] 90-92°C). IR (KBr)/ ν (cm-1); 1480, 1459,
1381, 1037, 837, 744. 1H NMR (400 MHz, CDCl3) δ: 7.35 (m, 2H), 7.44 (m, 4H), 7.60 (m, 8H).
6

3. Results and discussion
Nickel ferrite nanoparticles were prepared by using co-precipitation procedure, according to the
procedure reported in the literature [22]. The synthetic pathway for preparation of the catalyst is
shown in Scheme 1. In order to characterize the catalyst structure, the synthesized nano catalyst
was analyzed using XRD, FT-IR, SEM, EDX, VSM, and also, TGA techniques.
Scheme 1.Synthesis of the catalyst NiFe2O4@SiO2-BPMN-Ni(0).
3.1 Characterization results of NiFe2O4@SiO2-BPMN-Ni
The powder XRD pattern of the nickel ferrite nanoparticles is shown in Figure 1. All of the
characteristics peaks of NiFe2O4 are present in the diffraction pattern and the diffraction peaks
match with standard XRD pattern (JCPDS file no. 03-0875). According to the Debye–Scherrer
7

equation, the average particle sizes of the as-synthesized nano NiFe2O4 were calculated and the
results show that nano NiFe2O4 was obtained with an average diameter of 35 nm.
Fig. 1. XRD patterns of (a) NiFe2O4, (b) NiFe2O4@SiO2-BPMN-Ni (0)
Figure 2 shows the FT-IR spectrum of NiFe2O4 NPs, NiFe2O4@SiO2, and NiFe2O4@SiO2-
BPMN in the range 400–4000 cm-1. The spectrum presents characteristic bands at 3415, 2920,
1620, 597 and 421 cm-1. The bands at 3415 and 1620 cm-1 can be assigned to the stretching
modes of absorbed water. The band at 597 cm-1 is attributed to the vibration of Fe–O bonds. The
characteristic band at 421 cm-1 can be assigned to metal vibrations of Ni–O bonds. In all three
spectra, the revealed peaks of NiFe2O4 were observed at 421–601 cm−1, which could be
attributed to the characteristic absorption of Fe–O and Ni–O bonds. In NiFe2O4@SiO2 spectrum,
NiFe2O4@SiO2–NH2 spectrum and final catalyst spectrum the intense peaks at 1091, 1095, 1096
cm−1 was derived from the Si–O–Si stretching vibrations. These peaks proved that SiO2 has
coated the surface of NiFe2O4. In NiFe2O4@SiO2–I spectrum, the characterized peaks at 591
cm−1 could be attributed to the C–I stretching vibrations. Moreover, the peak at 2945 cm−1 is
related to stretching vibration of CH2, the peak at 1466 cm−1 is related to bending vibration of
8

CH2. These described peaks confirmed that NiFe2O4@SiO2–I NPs are prepared. The FT-IR
spectrum of NiFe2O4@SiO2-BPMN showed absorption bands at 2225 cm−1, cyano, 2910 cm−1
(C–H).
Fig. 2. FT-IR spectrum of a) NiFe2O4 NPs, b) NiFe2O4@SiO2, c) NiFe2O4@SiO2-(CH2)3–I and d) NiFe2O4@SiO2-
BPMN.
Figure 3 shows the SEM image of NiFe2O4 and final catalyst, in that the spherical
morphology with an average diameter of about 35 nm for NiFe2O4 and 60 nm for catalyst was
observed. Elemental analysis was also performed by SEM. The results show that the
nanoparticles have a uniform size and spherical shape respectively as shown in Figure 3A, 3B.
9

Fig. 3. SEM images of (A) NiFe2O4 nanoparticles and (B) NiFe2O4@SiO2-BPMN-Ni.
10

To further confirm the morphology of synthesized nanoparticles, transmission electron
microscopy (TEM) was used. Figure 4 shows the SEM image of NiFe2O4@SiO2-BPMN-Ni,
indicating the size distribution of the uniformly dispersed nanoparticles. Moreover, TEM
analysis presented the nanoparticle size as 50 ± 5 nm.
Fig. 4. TEM image of NiFe2O4@SiO2-BPMN-Ni
Figure 5 shows the EDX spectra of NiFe2O4 and Ni complex supported on NiFe2O4
nanoparticles. The results showed the presence of C, N, O, Si, Cl, Fe, and Ni in the composites,
which confirmed that the Ni complex was loaded into NiFe2O4 nanoparticles.
11

(a)
(b)
Fig.5. EDX spectrum of (a) NiFe2O4 nanoparticles and
(b) NiFe2O4@SiO2-BPMN-Ni
Moreover, the loading of Ni in NiFe2O4@SiO2-BPMN-Ni(0) was determined using
inductively coupled plasma atomic emission spectroscopy (ICP-AES) and was obtained 25.14
wt%. Magnetic properties of NiFe2O4 nanoparticles, NiFe2O4@SiO2 and NiFe2O4@SiO2-
BPMN-Ni were investigated by VSM at room temperature and shown in Figure 6. Magnetization
of samples could be completely saturated at high fields of up to 1.0 T and the saturation
magnetization of samples decreased from 35 (NiFe2O4) to 25 (NiFe2O4@SiO2) and then 10
(NiFe2O4@SiO2-BPMN-Ni) emug-1. Furthermore, these consequence shows that the
magnetization property reduces via coating and functionalization and the main difference
12

happened for the magnetism of NiFe2O4@SiO2 after bonding to BPMN-Ni. Therefore these
results confirm that the catalysts can be simply separated and recycled by an external magnetic
field.
Fig. 6. The vibrating sample magnetism curves of a) NiFe2O4 nanoparticles, b) NiFe2O4@SiO2 and c) NiFe2O4@
SiO2-BPMN-Ni.
The thermal stability of the magnetic nanocatalyst was investigated using thermogravimetric
analysis (TGA) to confirm the presence of various groups on the surface of the NPs and the
related curves are displayed in Figure S1 (Supporting information). The initial small weight loss
from the catalyst below 200 °C which could be assigned to the loss of bound water or physically
adsorbed solvent. The weight loss observed (30%) at 250–650°C in TGA curve of
NiFe2O4@SiO2-BPMN-Ni is mainly related to the decomposition of organic groups grafted to
the NiFe2O4 surface. These results show that catalyst is stable up to 250°C and can be used in
organic synthesis.
3.2. Investigation of catalyst activity
To investigate the catalytic efficiency of the nanocatalyst and to characterize optimal
conditions for Suzuki-Miyaura coupling reaction, iodobenzene and phenylboronic acid was
selected as model reagents and were studied under different factors such as type and amount of
catalyst, solvent, bases and temperature and the results are listed in Tables 1, 2 and 3. At first, we
13

investigated performance of the several metals in Suzuki-Miyaura reaction. After screening a
various catalyst containing Ni, Co, Au, Fe and Ru complex, it has been found that the
NiFe2O4@SiO2-BPMN-Ni is the most effective catalyst for the preparation of biphenyl
derivatives. Therefore, NiFe2O4@SiO2-BPMN-Ni complex was used for further investigations.
Then several solvents such as DMF, Dioxane, CH3CN, DMSO, NMP and H2O/ EtOH (1:1) were
checked. The examination of solvent was displayed that H2O/EtOH (1:1) was the best solvent for
the coupling reaction of phenylboronic acid and aryl halide compounds (Table 1, entry 9).
Afterwards, the activity of the catalyst in different amounts on the reaction was studied. The
reviews showed that in the presence of 12 mg of the NiFe2O4@SiO2-BPMN-Ni catalyst, the
yield developed sharply to 93% (Table 1, entry 11).
In continues, to obtain the appropriate base for the reaction, we examined diverse bases,
among the different bases screened, K2CO3 was found to be the excellent base for this reaction
(Table 2, entry 9).
Table 1. Optimization of solvent and catalytic system for the formation of biphenyl derivatives.a.
Entry
Solvent
DMF
Catalytic system (mg)
Yield b (%)
1
2
3
4
5
6
7
8
22
88
15
37
43
62
75
78
NiFe2O4@SiO2-BPMN-Fe (15)
NiFe2O4@SiO2-BPMN-Ni (15)
NiFe2O4@SiO2-BPMN-Ru (15)
NiFe2O4@SiO2-BPMN-Au (15)
NiFe2O4@SiO2-BPMN-Co (15)
NiFe2O4@SiO2-BPMN-Ni (15)
NiFe2O4@SiO2-BPMN-Ni (15)
NiFe2O4@SiO2-BPMN-Ni (15)
DMF
DMF
DMF
DMF
DMSO
Dioxane
NMP
14

9
H2O / EtOH (1:1)
CH3CN
91
55
91
85
NiFe2O4@SiO2-BPMN-Ni (15)
NiFe2O4@SiO2-BPMN-Ni (15)
NiFe2O4@SiO2-BPMN-Ni (12)
NiFe2O4@SiO2-BPMN-Ni (10)
10
11
12
H2O / EtOH (1:1)
H2O / EtOH (1:1)
a Reactions conditions: aryl halide (1 mmol), phenylboronic acid (1.2 mmol),NaHCO3 (2 mmol), b Isolated yield.
Table 2. Optimization in the presence of different bases a
Base amount
Entry
Solvent
Base
Yield b
(mmol)
1
2
3
4
5
6
H2O / EtOH (1:1)
H2O / EtOH (1:1)
H2O / EtOH (1:1)
H2O / EtOH (1:1)
H2O / EtOH (1:1)
H2O / EtOH (1:1)
NaHCO3
Na2CO3
KOH
2
2
2
2
2
2
91
75
76
97
55
70
K2CO3
K3PO4
NEt3
H2O / EtOH (1:1)
H2O / EtOH (1:1)
H2O / EtOH (1:1)
H2O / EtOH (1:1)
7
8
NaOH
NaOAC
K2CO3
K2CO3
2
2
63
70
97
85
9
1.5
1
10
a Reactions conditions: aryl halide (1 mmol), phenylboronic acid (1.2 mmol), 120°C, H2O / EtOH (1:1)
NiFe2O4@SiO2-BPMN-Ni (12 mg), b Isolated yield.
In next step of this research, the reaction was carried out at different temperatures. The
effective temperature was found to be 100°C. (Table 3, entry 5).
15

Table 3. Study of the effect of different temperatures on the Suzuki cross-coupling a
Entry
Temp. (°C)
Time (min)
Yield (%)b
1
2
3
4
5
6
Room temperature
180
130
115
100
85
-
70
80
67
78
89
97
97
90
100
110
85
a Reactions conditions: aryl halide (1 mmol), phenylboronic acid (1.2 mmol), NiFe2O4@SiO2-BPMN-Ni (12 mg)
and K2CO3 (1.5 mmol) in Water/ EtOH (1:1), b Isolated yield.
With the optimal reaction condition in hands, a broad range of structurally diverse aryl
halides were reacted with phenylboronic acid in the presence of 12 mg of NiFe2O4@SiO2-
BPMN-Ni catalyst and 3 mmol K2CO3 and the results are showed in Table 4. As shown in Table
4, in the presence of Ni nanocatalyst, excellent product yields were achieved in shorter reaction
time and excellent yield.
Table 4. Suzuki-Miyaura cross-coupling of aryl halides and phenylboronic acid in the presence of
NiFe2O4@SiO2-BPMN-Ni a
Entry
Aryl halide
Product
Time (min)
Yieldb (%)
16

1
2
1a
1k
1j
2a
2k
2j
85
140
70
97
89
94
92
92
94
94
95
96
92
94
95
87
89
80
3
4
1f
2f
125
105
100
95
5
1e
1b
1g
1h
1c
1i
2e
2b
2g
2h
2c
2i
6
7
8
100
65
9
10
11
12
13
14
15
105
90
1o
1d
1m
1i
2o
2d
2m
2i
135
160
140
190
1n
2n
a Reactions conditions: aryl halide (1 mmol), phenylboronic acid (1.2 mmol), NiFe2O4@SiO2-BPMN-Ni (12 mg)
and K2CO3 (1.5 mmol), b Isolated yield.
3.3. The proposed reaction mechanism
The proposed mechanism for the formation of biphenyl derivatives is demonstrated in Scheme 2,
[29, 30]. Actually, the catalytic cycle consists of three steps: (1) oxidative addition, (2)
transmetalation, and (3) reductive elimination. The oxidative addition step is generally
considered as the rate-determining step (RDS) (Scheme 2). Although the two steps for oxidative
addition and reductive elimination are reasonably well understood, less is known about the
transmetalation with the aid of base. Available information indicates that there are three
processes, for transferring the organic group on the boron atom to R-Ni-X. The addition of bases
exerts a remarkable accelerating effect on the transmetalation between R-Ni-X and
organoboronic acids. This coupling reaction is efficiently performed on the high nanoparticle
surface. As shown in the steps, it is highly probable that the aryl halide compounds have been
activated, through placing Ni complex in nano catalyst between the atoms of carbon and halogen
17

in aryl halide. Thus the notable roles NiFe2O4@SiO2-BPMN-Ni nanocatalyst are activation of
aryl halides and efficient development of the reaction on its high surface area.
Scheme 3. Proposed mechanism for Suzuki reaction by NiFe2O4@SiO2-BPMN-Ni as catalyst
3.4. Catalyst Reusability
The recyclability of the NiFe2O4@SiO2-BPMN-Ni complex as a heterogeneous catalyst was
investigated in the coupling of iodobenzene and phenylboronic acid using 12 mg of catalyst in
water at 100°C in the presence of 3 mmol of K2CO3. After the completion of the reaction, the
catalytic system was separated from the reaction mixture using an external magnet and the
residual catalyst was washed with ethanol several times, dried and reused in subsequent
reactions. As can be seen after six cycles, the catalyst was demonstrated approximately the same
activity and leaded to the corresponding product in high yields (Figure 7).
18

Fig. 7. Reusability of catalyst for the synthesis of biphenyl.
4. Conclusion
In conclusions, we reported a novel and fantastic nickel-based catalyst supported on bis (propyl
malononitrile) as heterogeneous nanocatalyst in Suzuki reaction. The provided nanocatalyst
catalyzed the preparation of biphenyl compounds in high yields and short reaction times under
green conditions. The products can be easily separated from the reaction mixture by an external
magnet. Furthermore, the catalyst was simply recycled and reused six cycles without a
significant loss of activity. At last, it was concluded that the heterogenized catalyst has important
advantages including non‐toxic, easy separation of products, small amount of catalyst used,
facilely recyclable and reusable, which provides a green and effective method for synthesis of
biphenyl compounds.
Acknowledgments
The authors are grateful to University of Kashan for supporting this work by Grant No.
159148/78.
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Graphical abstract
:
Inorganic–organic hybrid nano magnetic based nickel complex as a novel,
efficient and reusable nanocomposite for the synthesis of biphenyl compounds