Ultrasonic accelerated coupling reaction using magnetically recyclable bis (propyl molononitril) Ni complex nanocatalyst: A novel, green and efficient synthesis of biphenyl derivatives

Article abstract of DOI:10.1016/j.ultsonch.2018.06.001

A novel, green and rapid sonochemical research to preparation of the biphenyls was carried out through the coupling reaction between various aryl halides and phenylboronic acid by using bis(propyl malononitrile) Ni (0) complex (NiFe₂O₄@SiO₂-BPMN-Ni) as an efficient nano catalyst. The catalyst can be recycled via an external magnet and reused several times without considerable loss of its catalytic activity. Compare to the previous works, this procedure has advantages such as easy workup, high yields of products, environmentally benign and short reaction times. The novel nickel catalyst prepared and characterized by FT-IR, XRD, SEM, EDX, TGA and VSM techniques.

Full text of DOI:10.1016/j.ultsonch.2018.06.001

Accepted Manuscript
Ultrasonic accelerated coupling reaction using magnetically recyclable bis
(propyl molononitril) Ni complex nanocatalyst: a novel, green and efficient
synthesis of biphenyl derivatives
Fatemeh Kiani, Hossein Naeimi
PII:
S1350-4177(18)30261-X
DOI:
https://doi.org/10.1016/j.ultsonch.2018.06.001
ULTSON 4199
Reference:
Ultrasonics Sonochemistry
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Accepted Date:
17 February 2018
30 May 2018
1 June 2018
Please cite this article as: F. Kiani, H. Naeimi, Ultrasonic accelerated coupling reaction using magnetically recyclable
bis (propyl molononitril) Ni complex nanocatalyst: a novel, green and efficient synthesis of biphenyl derivatives,
Ultrasonics Sonochemistry (2018), doi: https://doi.org/10.1016/j.ultsonch.2018.06.001
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Ultrasonic accelerated coupling reaction using magnetically recyclable bis
(propyl molononitril) Ni complex nanocatalyst: a novel, green and efficient
synthesis of biphenyl derivatives
Fatemeh Kiani, Hossein Naeimi*
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, 87317, I.R. Iran.
Fax: +98-03155511121; Tel: +98-03155912388; E-mail: Naeimi@kashanu.ac.ir.
Abstract:
A novel, green and rapid sonochemical research to preparation of the biphenyls was carried out
through the coupling reaction between various aryl halides and phenylboronic acid by using
bis(propyl malononitrile) Ni (0) complex (NiFe2O4@SiO2-BPMN-Ni) as an efficient nano
catalyst. The catalyst can be recycled via an external magnet and reused several times without
considerable loss of its catalytic activity. Compare to the previous works, this procedure has
advantages such as easy workup, high yields of products, environmentally benign and short
reaction times. The novel nickel catalyst prepared and characterized by FT-IR, XRD,
SEM, EDX, TGA and VSM techniques.
Keywords: Heterogonous catalyst, Coupling reaction, Ultrasound irradiation, Biphenyls, Nickel
ferrite.
1

1. Introduction
At present, researchers know that the chemical effects of ultrasound irradiation are various and
include considerable improvements in both stoichiometric and catalytic chemical reactions [1].
The cavitation phenomenon is driving force for sonochemistry, therefore a common requirement
is that the reaction should be carried out in the liquid phase [2]. When liquid are affected by
ultrasound irradiation, expansive and compressive acoustic waves makes alternately bubbles and
develops the bubbles oscillate. In proper conditions, a bubble can overgrow and finally detonate,
releasing the energy accumulated within the bubble in a very short time (with a heating and
cooling rate of >1010 K s-1) [3]. The quick implosion of these bubbles in the liquids produces
localized hot spots. The high local temperature and pressures provide desirable conditions for
doing a large number of reactions [4]. Compared to traditional procedures which provides
thermal energy in the macro environment, ultrasound irradiation is capable to activate many
chemical organic reactions via providing the activation energy in micro system [5, 6]. Hence, an
extensive diversity of chemical reactions can be carried out in shorter reaction times with higher
yields and milder conditions under ultrasound irradiation compared to conventional methods [4].
Furthermore reduce of side products [7, 8], saving costs and energy, nontoxic and
environmentally friendly solvent, are other advantages of sonochemistry [9, 10].
In recent years, magnetic nanoparticles have received significant attention due to their various
applications in immobilize enzymes, bioactive polymers, transition metal catalysts and
organocatalysts [11-13]. The surface of magnetic nanoparticles can be functionalized easily
through proper surface modifications to enable the loading of a diversity of desirable
functionalities [14].
2

Biaryl compounds have extensive application in many fields of organic chemistry. Suzuki and
co-workers [15] first in 1979 reported one of the most applied procedure for the forming of
carbon–carbon bonds involves Pd-catalyzed reactions between aryl halides and diverse
organoboron compounds in the presence of a base, and it is usually referred to as the Suzuki
coupling reaction [16]. Biaryl compounds has been applied to many fields, including natural
compounds, bioactive products, UV absorbers, numerous polymers, agrochemicals and
pharmaceutical intermediates, antioxidants, fine chemicals syntheses, and industrial applications
[17]. Previously, the phosphine ligands have been applied to stabilize active palladium
intermediates, and great effects have been reported for Pd-catalysed carbon–carbon coupling
reactions. However, the oxygen and water sensitivity, expensive, toxicity and unrecoverable of
these classes of ligands, prevents their usage in a diversity of synthetic applications [18].
Although using a Pd catalyst to develop the carbon-carbon cross coupling reaction is an
appropriate and green procedure, it also has many drawbacks, such as the requirements of
directing the group on the substrate to promote selectivity and low yields of products. Thus, the
development of a novel method is still a notable aim for the coupling reactions. The advantages
of this method are such as; mild, rapid, aerobic ligand less-based procedures using low catalyst
loading, cheaper and environmentally friendly catalysts accessible, phosphine-free catalytic
systems to overcome these difficulties. Nowadays, cross-coupling reactions catalyzed by other
metals have been greatly prevalenced because these metals are accessible, cost-effective, and
environmentally safe catalysts able to catalyze impressively the C-C coupling reactions [19-25].
3

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
13
NMR and C NMR spectra were recorded on Bruker Avance-400 MHz spectrometers in the
presence of tetramethylsilane as internal standard. A BANDELIN ultrasonic HD 3200 with
probe model KE 76, with the diameter of 6 mm, was used to produce ultrasonic irradiation and
homogenizing the reaction mixture. Transducer and probe converts electrical waves to
mechanical vibrations and is consisted of backing, piezoelectric, matching, booster and Horn.
Therefore, the induced frequency of probe to the reaction mixture is equal to 20 kHz. By
changing the power of Tip the cavitations rate is displaced so that the Tip frequency under
various amounts of power is constant. A thermal method was used for the calibration of
ultrasonic power. 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). Scanning electron microscope (SEM) of nanoparticles and
catalysts were recorded on a FESEM Hitachi S4160. 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
4

determination of the substrates and reaction monitoring were accomplished by TLC on silica-gel
polygram SILG/UV 254 plates (from Merck Company).
2.2. Catalyst preparation
2.3. 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 [26]. 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
untill the pH of 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 80 ºC 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 15 min at 2000 rpm and then dried overnight at above 80 ºC. The
acquired substance was then grinded into a fine powder and then calcined for 10 h at 600
ºC.
2.4. 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 [27]. 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 N2 atmosphere condition, 4 mL of tetraethoxysilane (TEOS) and 2 mL of
5

ammonia were added into NiFe2O4 MNPs suspension in turn under vigorous stirring. The
reaction system was kept at 35 ºC for 6 h. Consequently, the black precipitates, NiFe2O4@SiO2
o
MNPs, were washed with deionized water and ethanol for 3 times and dried at 80 C for 10h.
2.5. General procedure for functionalization of NiFe2O4@SiO2 MNPs surfaces
To our knowledge, the surface of silica nanoparticles can be easily functionalized through the
treatment with 3-iodopropyltriethoxysilane (3-IPTES). With vigorously stirring, 400 µL of 3-
IPTES 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 subsequently with toluene, dichloromethane, and methanol, and dried under reduced
pressure at 80 ºC 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) was
carried out by their reduction in the presence of NaBH4 as reducing agent, in absolute ethanol as
the solvent system.
2.6. 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 (8 mol% Ni) and Water/ EtOH
(1:1) (4 ml) and the reaction mixture was irradiated in ultrasonic apparatus. 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
6

chromatography on silica gel using n-hexane or different mixtures of n-hexane, ethyl acetate as
the eluents to afford the highly pure products (Table 4). The obtained pure products were
characterized by physical methods and the IR, 1H NMR and 13C NMR spectra.
2.7. Spectral data for biphenyl derivatives:
1, 1'-Biphenyl. White solid; m.p=70-72°C (Lit. [28] 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. [28] 80-82°C). IR (KBr)/ ν
1
(cm-1); 1247, 1178, 1120, 10354, 833, 762, 697. H 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. [28] 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).
4-Nitro-1, 1'-biphenyl. Pale yellow solid; m.p=112-114°C (Lit. [29] 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. [28] 113-115°C). IR
1
(KBr)/ ν (cm-1); 698, 748, 856, 1113, 1186, 1283, 1719. H 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).
7

1-((1, 1'-Biphenyl)-4-yl) ethan-1-one. White solid, m.p=115-117°C; (Lit. [30] 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. [31] 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. [32] 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. [29]). 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. [29]). 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. [32] 90-92°C). IR (KBr)/ ν (cm-11480, 1459, 1381,
1037, 837, 744. 1H NMR (400 MHz, CDCl3) δ: 7.35 (m, 2H), 7.44 (m, 4H), 7.60 (m, 8H).
8

1-Phenylnaphthalene. Colorless oil; (Lit. [33]). IR (KBr)/ ν (cm-1); 3056, 2957, 1593, 1487,
1
1072, 1022, 910, 801, 778. H NMR (400 MHz, CDCl3) δ: 7.48(m, 3H), 7.55 (m, 6H), 7.91 (d,
J= 8.0 Hz, 1H), 7.96 (d, J= 7.6 Hz, 2H).
3. Results and discussion
Nickel ferrite nanoparticles were prepared by using co-precipitation procedure, according to the
procedure reported in the literature [26]. 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 characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra,
scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), vibrating
sample magnetometer (VSM), and also, thermo-gravimetric analysis (TGA) techniques.
Scheme 1. Synthesis of the NiFe2O4@BPMN-Ni (0) catalyst.
9

3.1 Characterization results of NiFe2O4@ 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
equation, the average particle sizes of the as-synthesized nano NiFe2O4 were calculated and the
results show that the nano NiFe2O4 was obtained with an average diameter of 30 nm.
Fig. 1. The X-ray diffraction patterns of calcinated NiFe2O4.
Figure 2 shows the FT-IR spectrum of NiFe2O4 NPs, NiFe2O4@SiO2, NiFe2O4@SiO2-
(CH2)3–I and NiFe2O4@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 2920 cm-1 shows the presence of trace
amounts of CO2. 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
10

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-(CH2)3-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 CH2. These described peaks confirmed that NiFe2O4@SiO2-(CH2)3-I is prepared.
The FT-IR spectrum of NiFe2O4@BPMN showed absorption bands at 2225 cm−1; cyano, 2910
cm−1 (C–H).
11

Fig. 2. FT-IR spectrum of a) NiFe2O4 NPs, b) NiFe2O4@SiO2, c) NiFe2O4@SiO2-(CH2)3–I and d) NiFe2O4@BPMN.
Figure 3 shows the SEM image of NiFe2O4 and final catalyst, in that the spherical
morphology with an average diameter of about 50 nm for NiFe2O4 and 60 nm for catalyst was
observed. Elemental analysis was also performed. The results show that the nanoparticles have a
uniform size and spherical shape respectively as shown in Figure 3A and 3B.
12

Fig. 3. SEM images of (A) NiFe2O4 nanoparticles and (B) NiFe2O4@BPMN-Ni
Figure 4 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.
(a)
13

(b)
Fig.4. EDX spectrum of the (a) NiFe2O4 nanoparticles and (b) NiFe2O4@BPMN-Ni
Magnetic properties of NiFe2O4 nanoparticles and NiFe2O4@BPMN were investigated with
VSM at room temperature (Figure 5). 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 to 10
emug-1. Furthermore, this consequence shows that the magnetization property reduces via
coating and functionalization. Therefore these results confirm that the catalysts can be simply
separated and recycled by an external magnetic field.
14

Fig. 5. The VSM curve of NiFe2O4 nanoparticles and NiFe2O4@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 6. 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@BPMN 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.
15

Fig. 6. TGA curve of NiFe2O4@BPMN-Ni.
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 the effect of ultrasound irradiation and the results are listed in Tables
1, 2 and 3. At first, we 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@BPMN-Ni is the most effective catalyst for the sonochemically
preparation of biphenyl derivatives. Therefore, NiFe2O4@BPMN-Ni complex was used for
further investigations. Then several solvents such as DMF, EtOH, CH3CN, DMSO 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 8 mol% of the NiFe2O4@BPMN-Ni
catalyst, the yield developed sharply to 93% (Table 1, entry 9).
16

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 7).
Table 1.Optimization of solvent and catalytic system for the formation of biphenyl derivativesa.
Entry
Solvent
DMF
Catalytic system (mol %)
NiFe2O4@ BPMN-Au (10%)
NiFe2O4@ BPMN-Co (10%)
NiFe2O4@ BPMN - Ni (10%)
NiFe2O4@ BPMN - Fe (10%)
NiFe2O4@ BPMN - Ru (10%)
NiFe2O4@ BPMN - Ni (10%)
Yield b (%)
74
65
89
1
2
3
4
DMF
DMF
DMF
42
35
DMF
5
6
CH3CN
78
H2O / EtOH (1:1) NiFe2O4@ BPMN - Ni (10%)
7
8
93
82
DMSO
NiFe2O4@ BPMN - Ni (10%)
93
88
9
H2O / EtOH (1:1)
H2O / EtOH (1:1)
NiFe2O4@ BPMN - Ni (8%)
NiFe2O4@ BPMN - Ni (6%)
10
a Reactions conditions: aryl halide (1 mmol), phenylboronic acid (1.2 mmol),NaHCO3 (2 mmol), b Isolated yield
17

Table 2. Optimization of reaction in the presence of different bases a
Entry
Solvent
Base
K3PO4
NEt3
Base amount
Yield b
65
(mmol)
H2O / EtOH (1:1)
H2O / EtOH (1:1)
H2O / EtOH (1:1)
H2O / EtOH (1:1)
H2O / EtOH (1:1)
H2O / EtOH (1:1)
H2O / EtOH (1:1)
H2O / EtOH (1:1)
2
1
2
3
4
5
6
7
8
2
2
67
K2CO3
KOH
99
2
76
NaHCO3
Na2CO3
K2CO3
K2CO3
2
89
2
72
1.5
1
99
94
a Reactions conditions: aryl halide (1 mmol), phenylboronic acid (1.2 mmol), Ultrasonic irradiation (50 W), H2O /
EtOH (1:1) NiFe2O4@ BPMN - Ni (8%), b Isolated yield.
In next step of this research, the power of the ultrasonic irradiation was optimized. The
coupling reaction was performed under different powers of ultrasound irradiation. It was found
that the appropriate and effective power of ultrasound for this reaction to be 55 watt (Table 3,
entry 5).
Table 3. Study of the ultrasonic irradiation effect on the Suzuki cross-coupling a
Entry
Power (w)
Time (min)
Yield (%)b
1
2
3
4
5
silent
35
120
50
46
41
35
-
58
76
82
91
40
45
50
18

6
7
55
60
28
28
99
99
a Reactions conditions: aryl halide (1 mmol), phenylboronic acid (1.2 mmol), NiFe2O4@ BPMN - Ni (8%) 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 8 mol% of NiFe2O4@BPMN-Ni
catalyst and 3 mmol K2CO3 with water as solvent under ultrasonic irradiation 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 times under ultrasound irradiation.
Scheme 2. Suzuki-Miyaura cross-coupling using the NiFe2O4@BPMN–Ni complex.
Table 4. Suzuki-Miyaura cross-coupling of aryl halides and phenylboronic acid catalyzed by NiFe2O4@BPMN-Ni a
Entry
1
Aryl halide
Product
Time (min)
28
Yieldb (%)
99
2
51
90
19

3
4
25
50
97
93
5
6
37
40
95
97
7
8
43
37
96
97
9
35
25
98
98
10
11
12
38
35
95
97
20

13
14
48
73
98
90
15
16
50
80
92
82
a Reaction conditions: aryl halide (1 mmol), phenylboronic acid (1.2 mmol), NiFe2O4@BPMN-Ni (8%) and K2CO3
(1.5 mmol), b Isolated yield.
When the reaction was performed under ultrasonic irradiation to give excellent yields of
products in very short reaction times. Ultrasonic irradiation differs from traditional energy
sources. Ultrasound improvements the organic reactions in a solution via increase the number of
active cavitation bubbles and the size of the individual bubbles, both of which are expected to
result in higher maximum collapse temperature and accelerated respective reaction.
In order to illustrate the merit of this proposed research, we compared the obtained results with
the recently reported works. For this purpose, the reactions of iodobenzene and phenylboronic
acid using 8 mol% of Ni complex in water under ultrasonic irradiation in the presence of 3 mmol
of K2CO3 were chosen as a model reaction and the comparison was performed on the basis of
reaction conditions, reaction time and obtained yields (Table 5). The properties of this research
which make it exclusiveness than the other previously reported procedures, are mild reaction
condition, environmentally benign, simple recycle of the nano catalyst by an external magnet,
reusability of the catalyst for seven times without considerable loss of catalytic activity, excellent
yields of biphenyls and very short reaction times.
21

Table 5. Comparison the reaction results of 4-methoxy-1, 1'-biphenyl in this research and various reports in the
literature.
Entry
1
Reaction Condition
Time
Yield (%) a
97
ref
NiFe2O4@ BPMN-Ni (0).
US/55W
40 (min)
This work
Pd-Ni alloy,
2
3
4
5
12 (h)
3 (h)
4 (h)
4 (h)
92
92
92
93
[34]
[35]
[36]
[37]
100ºC
S-S-Pd,
20KHz (US)
PAPT-stablized gold
nanoparticles, 80ºC
Ni (0)/MWCNTs,
K3PO4, 100 ºC
a Isolated yield.
3.3. The proposed reaction mechanism
The proposed mechanism for the formation of biphenyl derivatives is demonstrated in Scheme 2.
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). This coupling reaction is efficiently performed on the high
nanoparticle surface and also by the cavitation phenomenon of ultrasound irradiation. 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 their carbon and halogen atoms. Thus the notable
roles of NiFe2O4@BPMN-Ni nanocatalyst are activation of aryl halides and efficient
development of the reaction on its high surface area.
22

Scheme 3. Proposed mechanism for Suzuki reaction
3.4. Catalyst Reusability
The recyclability of the NiFe2O4@BPMN-Ni complex as a heterogeneous catalyst was
investigated in the coupling of iodobenzene and phenylboronic acid using 8 mol% of catalyst in
water under ultrasonic irradiation in the presence of 3 mmol of K2CO3. After 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 seven cycles, the catalyst was demonstrated approximately the
same activity and leaded to the corresponding product in high yields (Figure 7).
23

Fig. 7. Reusability of catalyst for the synthesis of biphenyl.
4. Conclusion
In the current study an advanced, convenient and mild procedure introduced for the
synthesis of biphenyl compounds through condensation of phenylboronic acid and aryl halides
using highly efficient and magnetically recyclable nanocatalyst under ultrasound irradiation. This
novel sonochemically approach provides several advantages including green process, mild
reaction conditions, easy recoverability and reusability up to seven times for the nanocatalyst,
excellent yields of various biphenyl derivatives and short reaction times.
Acknowledgments
The authors are grateful to University of Kashan for supporting this work by Grant No.
159148/83.
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Graphical abstract:
Ultrasonic accelerated coupling reaction using magnetically recyclable bis(propyl
molononitril) Ni complex nanocatalyst: a novel, green and efficient synthesis of biphenyl
derivatives
27