Preparation and characterization of Cu supported on 2-(1H-benzo[d]imidazol-2-yl)aniline-functionalized Fe3O4 nanoparticles as a novel magnetic catalyst for Ullmann and Suzuki cross-coupling reactions

Article abstract of DOI:10.1002/aoc.5820

Copper supported on 2-(1H-benzo[d]imidazol-2-yl)aniline (BIA)-functionalized Fe₃O₄ nanoparticles (Cu-BIA-Si-Fe₃O₄) as a novel magnetic catalyst was designed and used for the synthesis of new products via Ullmann and Suzuki cross-coupling reactions. The Ullmann reaction was performed by mixing arylboronic acid with aniline derivatives in dimethylsulfoxide solvent. Also, diaryls were synthesized via Suzuki C–C reactions between aryl halides and phenylboronic acid in the same solvent. The prepared materials and catalyst were characterized with various analytical techniques. The Cu-BIA-Si-Fe₃O₄ catalyst demonstrated catalytic efficiency with good to excellent yields for both types of reactions in comparison with commercial palladium catalysts. Also, the catalyst could be recovered by a simple filtration and retained its activity even after several cycles.

Full text of DOI:10.1002/aoc.5820

Received: 29 February 2020
DOI: 10.1002/aoc.5820
Revised: 20 April 2020
Accepted: 28 April 2020
F U L L P A P E R
Preparation and characterization of Cu supported on
-(1H-benzo[d]imidazol-2-yl)aniline-functionalized Fe O
2
3
4
nanoparticles as a novel magnetic catalyst for Ullmann and
Suzuki cross-coupling reactions
1
1
2
3
Liang Danqing | Jin Ming | Li Li | Majid Mohammadnia
1
Department of Institute of Physical
Copper supported on 2-(1H-benzo[d]imidazol-2-yl)aniline (BIA)-functionalized
Education, Shijiazhuang University,
Shijiazhuang, China
Fe O4 nanoparticles (Cu-BIA-Si-Fe O ) as a novel magnetic catalyst was
3
3 4
2
Department of Mechanical and Electrical
designed and used for the synthesis of new products via Ullmann and Suzuki
cross-coupling reactions. The Ullmann reaction was performed by mixing
arylboronic acid with aniline derivatives in dimethylsulfoxide solvent. Also,
diaryls were synthesized via Suzuki C–C reactions between aryl halides and
phenylboronic acid in the same solvent. The prepared materials and catalyst
were characterized with various analytical techniques. The Cu-BIA-Si-Fe O
College, Shijiazhuang University,
Shijiazhuang, China
3
Young Researcher and Elite Club,
Department of Chemistry, Bojnord
Branch, Islamic Azad University,
Bojnourd, Iran
3
4
Correspondence
catalyst demonstrated catalytic efficiency with good to excellent yields for both
types of reactions in comparison with commercial palladium catalysts. Also,
the catalyst could be recovered by a simple filtration and retained its activity
even after several cycles.
Liang Danqing, Department of Institute of
Physical Education, Shijiazhuang
University, Shijiazhuang, China.
Email: zhanghap85@163.com
K E Y W O R D S
coupling reaction, Cu nanoparticles, Schiff base, Suzuki reaction, Ullmann reaction
1
| INTRODUCTION
conjugating organic or inorganic materials onto the
surface of MNPs. All of these constructed catalysts can be
In recent years, with the development of nanotechnology,
nanomaterial-based catalysts have been used as impor-
tant heterogeneous catalysts in the synthesis of various
quickly separated using an external magnet and
recycled.
[
6,7]
These days, transition metal-catalyzed cross-coupling
reactions have become an important and well-known
method for the formation of C& C, C& N and C& S
bonds via combination of electrophilic and nucleophilic
segments. In fact, the construction of C& C, C& N and
C& S bonds is vital for the preparation of a diversity of
[1,2]
organic compounds.
One of these nanomaterials are
magnetic nanoparticles (MNPs) with exceptional charac-
teristics such as good eco-friendliness and biodegradabil-
ity, efficiency, easy accessibility, low or no toxicity and
high specific surface area for increasing catalyst loading
capacity and noticeable sustainability of heterogeneous
[
8]
biologically active and organic compounds. The forma-
tion of C& N bond is an important key reaction having
wide applications in the synthesis of organic functional
molecules. Usually, C& N bonds are constructed using
copper- and palladium-catalyzed amination of aryl
[3,4]
supports for preparation of various catalysts.
These
characteristics of MNPs comfortably cause them to be
[5]
good, enhanced catalyst candidates. Appropriate sur-
face modification of MNPs is vital to make them biocom-
patible and biodegradable. Generally, the coating method
is the most common surface modification approach for
[
9]
halides as well as arylboronic acids. Transition metal-
mediated C& N bond formation is a fundamental
Appl Organomet Chem. 2020;e5820.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
1 of 18
https://doi.org/10.1002/aoc.5820

2
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DANQING ET AL.
transformation that allows the preparation of noteworthy
amine products like diarylamines or diphenylamines via
functional groups and metal nanoparticles (e.g. Pd, Si or
Cu) is significant.
In the work reported here, first was constructed a
new, efficient, biodegradable and biocompatible hetero-
geneous recoverable functionalized catalyst consisting of
Cu supported on 2-(1H-benzo[d]imidazol-2-yl)aniline
[
39]
[10,11]
coupling reactions.
Also, to form C& C bonds in
biaryl or diphenyl compounds, the most significant pro-
cedure is through transition metal-catalyzed Suzuki
cross-coupling reactions between an aryl electrophile and
aryl nucleophile or aryl halides and phenylboronic
(BIA)-functionalized Fe O4 magnetic nanoparticles
3
[12]
acid.
(Cu-BIA-Si-Fe O ). Then, the prepared catalyst was
3
4
Diaryls are a valuable class of organic compounds
with wide applicability in the polymer and life science
employed for Suzuki coupling reactions between aryl
halides and phenylboronic acid and Ullmann coupling
reactions between arylboronic acid and anilines
(Scheme 1). The Cu-BIA-Si-Fe O catalyst was character-
ized using various techniques such as Fourier transform
infrared (FT-IR) spectroscopy, X-ray diffraction (XRD),
scanning electron microscopy (SEM), transmission elec-
tron microscopy (TEM), thermogravimetric analysis
(TGA), vibrating sample magnetometry (VSM), energy-
dispersive X-ray (EDX) analysis and inductively coupled
plasma atomic emission spectrometry (ICP-AES)
(Scheme 1).
[13,14]
industries as well the chemical industry.
A num-
ber of them display substantial special biological and
3
4
[15–17]
pharmacological activities.
Due to their signifi-
cance, development of efficient methods for their syn-
thesis is still a challenging and active area of research
and they have captured the interests of researchers for
a long time. Among the various protocols reported to
date, those involving copper-based catalysts are the
most general pathways for the generation of these
compounds. Common ways to synthesize these com-
pounds are via Pd- or Cu-catalyzed Ullmann coupling
[18–20]
and Suzuki cross-coupling.
Among Pd- or Cu-
catalyzed Ullmann reactions, Pd-catalyzed C& C and
C& N bond formations are prospering to certain
expanse and Cu-based catalysts are more favorable
because of cheap raw materials, simple and easy per-
2 | RESULTS AND DISCUSSION
2.1 | Characterization of prepared
Cu-BIA-Si-Fe O MNPs
3
4
[21,22]
formances and low toxicity.
Also, Pd- or Cu-catalyzed Ullmann and Suzuki reac-
tions are generally carried out with high catalyst load-
2.1.1 | FT-IR spectroscopic analysis
[23]
[24]
ings
or need high temperatures
which prevent their
The FT-IR spectra of Fe O , Fe O –ClSi, BIA-Si-Fe O
3
4
3
4
3 4
application for the preparation of complex mole-
and Cu-BIA-Si-Fe O4 are illustrated in Figure 1. The
3
[17,25]
−1
cules.
Many researchers have demonstrated that
bands at 586 and 447 cm were attributed to Fe& O
stretching and that at 3409 cm− corresponded to OH
groups on the magnetic surface of MNPs. Also, in the FT-
IR spectrum of Fe O –ClSi, the absorption band at
1
specific additives, which certainly operate as copper
ligands, improve reaction rates and allow the couplings
to be performed at more moderate temperatures, in the
presence of decreased amounts of copper or with a larger
substrate area. Recently, many new and unique ligands
have appeared and been introduced such as
3
4
1037 cm− is assigned to the Si& O groups. In the FT-IR
1
[
26]
1
,10-phenanthroline and its derivatives,
ethylene
[27]
[28]
glycol,
N,N-dimethylglycine,
diethylsalicylamide,
amino acids,
aminoarenethiolate,
[29]
[30]
[32]
[34]
oxime-type and Schiff base ligands,
thiophene-2-carboxylate,
ethylene glycol diacetate,
phosphine ligands,
[31]
[33]
bidentate phosphines,
(S)-2,2,6,6-tetramethylheptane-
2-aminopyrimidine-4,6-diol,
[35]
[36]
[37]
3
,5-dione,
pho-
[38]
sphazene P4-tBu base
and so on.
Despite remarkable developments in the heteroge-
neous recoverable copper-catalyzed Ullmann reaction,
these days the reusability of the catalyst support is
attracting much attention. Hence, application of an
efficient alternative to conventional heterogeneous cata-
lyst supports like functionalized MNPs with a range of
chemical materials including types of metal complexes,
SCHEME 1 Ullmann and Suzuki cross-coupling reactions
catalyzed by Cu-BIA-Si-Fe O
3 4

DANQING ET AL.
3 of 18
FIGURE 1 FT-IR spectra
of Fe
Fe
3
O
4
, Fe
3 4
O –ClSi, BIA-Si-
3
O
4
and Cu-BIA-Si-Fe O
3 4
spectrum of BIA-Si-Fe O , new bands were observed at
3
4
1
622 and 1410 cm−1 assigned to the C&d N and C& H
(
aromatic) stretching vibrations, respectively. The charac-
−
1
teristic bands at 2860 and 2919 cm are assigned to the
symmetric and asymmetric stretching of C& H bonds in
1H-benzo[d]imidazol-2-amine and propyl group unit of
BIA-Si-Fe O MNPs. These bands confirmed that 1H-
3
4
benzo[d]imidazol-2-amine had been successfully reacted
with amino present in the structure of BIA-Si-Fe O . The
3
4
N& H stretching peak of the amide group in BIA-Si-
−
1
Fe O appeared at 3427 cm . In addition, in the FT-IR
3
4
spectrum of Cu-BIA-Si-Fe O , the intensity of the adsorp-
3
4
−1
tion band at 629 cm that is assigned to the bending
vibration of C& H in pyridine heterocyclic ring is
reduced after formation of BIA-Si-Fe O complex with
3
4
FIGURE 2 XRD patterns of Fe
Si-Fe nanoparticles
3
O
4
nanoparticles and Cu-BIA-
Cu. Therefore, the data obtained from FT-IR spectros-
copy can indicate the existence of the nanomagnetic par-
ticles, heterocyclic moiety and Cu in the structure of
Cu-BIA-Si-Fe O MNPs (Figure 1).
3 4
O
displayed in Figure 2. It can be seen that the Fe O
3 4
3
4
obtained has a highly crystalline cubic spinel structure
which agrees with the standard Fe O (cubic phase) XRD
3
4
2
.1.2 | XRD analysis
pattern (PDF no. 88-0866). The patterns indicate a
crystalline structure with peaks at 2θ = 30.2 , 35.30 , 43.
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
XRD is employed as an experimental method for
determining the atomic and molecular structure of a
crystal, in which the crystalline structure causes a beam
of incident X-ray to diffract in many special directions.
The powder XRD patterns of two samples, Fe O4
3 , 53.65 , 57.3 and 62.8 corresponding to (220), (311),
(400), (422), (511) and (440), indicative of the cubic spinel
structure of Fe O MNPs. Also, in the XRD pattern of
3
4
[
34]
Cu-BIA-Si-Fe O nanoparticles (Figure 2), the peaks at
3 4
ꢀ
ꢀ
ꢀ
2θ = 42.87 , 50.26 and 74.56 are assigned to (111),
3
nanoparticles and Cu-BIA-Si-Fe O4 nanoparticles, are
(200), (220), (220), (311), (400), (422), (511) and (440),
3

4
of 18
DANQING ET AL.
indicative of the cubic spinel structure of Cu-BIA-Si-
revealed that the Cu-BIA-Si-Fe O nanoparticles contain
3
4
[40]
Fe O .
Hence, according to the results obtained from
about 13.62% of organic material (volatile components
3
4
ꢀ
XRD analysis, one can confirm the presence of Cu on
disappearing up to a temperature of about 100 C were
organic group moiety in the Cu-BIA-Si-Fe O4
neglected) (Figure 4). The composition ratio of the cata-
lyst can be evaluated from the residual mass percentage.
As exhibited in Figure 4, the first weight loss stage at
3
nanoparticles. The average Fe O and Cu-BIA-Si-Fe O
3 4
3
4
core diameters were calculated to be about 10 and
1.5 nm from the XRD results using Scherrer's equation,
ꢀ
1
almost 120 C (0.42%) was assigned to the evaporation of
D = kλ/βcos θ, where k is a constant (generally consid-
ered as 0.94), λ is the wavelength of Cu Ka (1.54 Å), β is
the corrected diffraction line full width at half-maximum
and θ is Bragg's angle.
adsorbed water molecules. The second weight loss at
120–330 C (5.77%) can be attributed to loss of 1H-
ꢀ
benzo[d]imidazol-2-amine group. The final weight loss at
ꢀ
330–600 C (7.85%) was attributed to propyl group.
According to the obtained results, the good connecting of
Cu-BIA-Si on the Fe O nanoparticles is asserted. The
3
4
2.1.3 | EDX analysis
amount of adsorbed organic compounds calculated using
Equation 1 is 0.5 mmol g :
−1
The EDX analysis of Cu-BIA-Si-Fe O4 is shown in
3
Figure 3. As can be seen, Cu-BIA-Si-Fe O is composed
Organic compounds ðmmolÞ
ð1Þ
3
4
of the expected elements in the structure of the catalyst
including C, O, N, Fe, Cu and Cl, indicating that Cu has
been correctly grafted to BIA-Si-Fe O .
=
ðweight loss=100 × Mw organic compoundsÞ × 1000
3
4
= 0:5 mmol
2.1.4 | ICP-AES analysis
2.1.6 | TEM analysis
ICP-AES analysis was used to indicate the same Cu con-
centration on the Cu-BIA-Si-Fe O as catalyst. In addi-
Morphologies of the synthesized Cu-BIA-Si-Fe O
3 4
nanoparticles were investigated using TEM as shown in
Figure 5. Particles are observed to have a spherical
morphology. Average particle size is estimated at about
14 nm from the TEM micrographs, which is in very
good agreement with the crystallite size estimated from
XRD at 11.5 nm. As shown in Figure 5, a basically
core–shell structure (dark-colored core for Fe O
3
4
tion, the absence of palladium metal in the reaction
solvent demonstrated no metal leaching into the reaction
mixture. ICP-AES analysis indicated the weight percent-
age of Cu to be 10% in Cu-BIA-Si-Fe O MNPs.
3
4
3
4
2.1.5 | Thermogravimetric analysis
nanoparticles and light-colored shell for organic group)
was obtained. This is an indication of nearly single
Information about the loading of Fe O nanoparticles
crystalline
character
of
the
Cu-BIA-Si-Fe O
3 4
3
4
with organic groups was obtained using TGA. The results
nanoparticles.
FIGURE 3 EDX spectrum of Cu-BIA-Si-
Fe
3 4
O

DANQING ET AL.
5 of 18
FIGURE 4 TGA diagram of Cu-
BIA-Si-Fe O
3 4
3 4
FIGURE 6 SEM image of Cu-BIA-Si-Fe O nanoparticles
3 4
FIGURE 5 TEM micrograph of Cu-BIA-Si-Fe O
nanoparticles
2.1.8 | Magnetic properties of catalyst
VSM was used for characterizing the magnetic properties
of Fe O , Fe O –ClSi, BIA-Si-Fe O and Cu-BIA-Si-Fe O
3
4
3
4
3
4
3 4
2
.1.7 | SEM analysis
at 300 K (Figure 7). The magnetization curves for these
nanoparticles show no hysteresis in their magnetizations.
As can be seen in Figure 7, the saturation magnetization
values for Fe O , Fe O –ClSi, BIA-Si-Fe O and Cu-BIA-
SEM is a primary tool for determining the size
distribution, particle shape, surface morphology and
fundamental physical properties. An SEM image of the
Cu-BIA-Si-Fe O nanoparticles is shown in Figure 6. The
3
4
3
4
3 4
−1
Si-Fe O were 73.8, 62.2, 58.7 and 48.6 emu g , respec-
3
4
tively. A small decrease of the saturation magnetization
of Cu-BIA-Si-Fe O was observed because of the grafting
3
4
SEM image of Cu-BIA-Si-Fe O displayed a sphere like
3
4
3 4
structure. It was seen to have individual crystallite sizes
in the range of 20 nm.
of Cu on the surface of BIA-Si-Fe O nanoparticles. In
3 4
other words, the differences in magnetization are due to

6
of 18
DANQING ET AL.
FIGURE 7 Room temperature
magnetization curves of Fe , Fe
BIA-Si-Fe and Cu-BIA-Si-Fe
3
O
4
3 4
O –ClSi,
3
O
4
3 4
O
the different coating layers and their thicknesses on the
surface of MNPs. In any case, the prepared magnetic cat-
alyst has excellent magnetic characteristics and can be
easily separated from reaction media completely using an
external magnetic field.
different amounts of the catalyst (0.5, 1, 1.5 and 2 mol%)
at several temperatures with various solvents. As evident
from Table 1, the optimized reaction conditions are the
use of Cu-BIA-Si-Fe O (1.5 mol%) using 1 mmol of
3
4
ꢀ
K CO as the base at 80 C in DMSO (4 ml).
2
3
Next, to prepare diaryls, Suzuki cross-coupling reac-
tions of aryl halide derivatives and phenylboronic acid
derivatives under optimum conditions were used. A wide
range of substituted and structurally diverse aryl halides
and phenylboronic acids were employed and the
corresponding products were prepared in good to excel-
lent yields (Table 2).
2
.2 | Catalytic application of Cu-BIA-Si-
Fe O nanoparticles
3
4
To find optimum conditions, the reaction of aryl halide
and phenylboronic acid for the synthesis of diaryl in the
presence of Cu-BIA-Si-Fe O as novel catalyst was used
The proposed mechanism for the coupling of aryl
halides and boronic acids is depicted in Scheme 2. The
3
4
as a model reaction. The reaction was carried out with
TABLE 1
3 4
Optimization of conditions for preparation of biphenyl in the presence of different amounts of Cu-BIA-Si-Fe O as catalyst
using 1 mmol of K
2
CO
3
as base at various temperatures
ꢀ
[a]
TOF (h−1
7
Entry
Solvent
CH CN
Amount of catalyst (mol%)
Temperature ( C)
Time (h)
Yield (%)
70
TON
70
)
1
2
3
4
5
6
7
8
9
3
1
1
70
110
100
60
10
4
DMF
75
75
18.75
40
DMSO
1
2
80
80
CH
3
OH
1
10
12
4
65
65
6.5
H
2
O
1
100
50
40
40
3.33
—
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
0.5
1
—
—
50
4
Trace
Trace
28
—
—
1.5
2
50
4
—
—
50
4
14
3.5
1
1
1
1
1
1
0
1
2
3
4
5
0.5
1
80
3
46
92
30.66
17
80
3
51
51
1.5
2
80
2
95
63.3
48
31.65
24
80
2
96
No catalyst
CuCl –DMSO
—
100
80
24
4
No reaction
70
—
—
2
2
35
8.75
a
Yields refer to isolated products.

DANQING ET AL.
7 of 18

8
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DANQING ET AL.

DANQING ET AL.
9 of 18
reaction is initiated by nucleophilic coordination of
amine with Cu(II) of the Cu-BIA-Si-Fe O4 catalyst
3
resulting in (A), which undergoes transmetalation with
boronic acid to furnish coupled Cu(II) complex (B).
Oxidation of (B) in turn affords complex (C) involving Cu
as Cu(III). Complex (C) on reductive elimination fur-
nishes the final C& C coupled product (D) and regener-
ates the Cu(I) catalyst which is further oxidized to
Cu(II) in the presence of air. There is an added advantage
of the magnetically separable heterogeneous catalyst in
that it can be easily recovered after completion of the
reaction without any significant loss (Scheme 2).
The most significant advantage of a heterogeneous
solid catalyst in organic reactions is its recoverability and
reusability. Hence, the recoverability and reusability of
the catalyst were studied using the selected model
reaction of aryl bromide and phenylboronic acid in
DMSO (Table 2, entry 1). The reaction mixture was
cooled to room temperature when the reaction was com-
pleted. After that, the catalyst was recovered using a mag-
netic field, washed with deionized water and ethanol,
and dried for the next run. According to the results, the
catalyst has good activity, reusability and stability in the
reaction media and can be reused five times without any
loss of its activity (Figure 8).
FIGURE 8 Recycling of Cu-BIA-Si-Fe O for preparation of of
diaryls
3
4
Encouraged by the satisfactory results for the synthe-
sis of diaryls, we decided to broaden the study of the cata-
lytic activity of Cu-BIA-Si-Fe O4 in the synthesis of
3
diphenylamine derivatives. The reaction conditions were
optimized starting from aniline (1 mmol) and phe-
nylboronic acid (1.2 mmol) catalyzed by various amounts
of the catalyst (0.5, 1, 1.5 and 2 mol%) with various tem-
peratures and solvents. As a result, the optimized reac-
tion conditions for the reaction of aniline and
phenylboronic acid are the use of Cu-BIA-Si-Fe O
3
4
ꢀ
In order to compare the catalyst of the present work
with several results reported in the literature, some of the
results for the preparation of diaryls are summarized in
Table 3. The obtained results indicated that Cu-BIA-Si-
Fe O is a better catalyst because of the short reaction
(1.5 mol%) and KF (0.2 mmol) in DMSO (4 ml) at 100 C
(Table 4).
The applicability of the prepared catalyst in the syn-
thesis of diarylamines was studied under the optimum
reaction conditions. The reported results in Table 5 indi-
cate that anilines and phenylboronic acid derivatives
3
4
times and good yields of products.
SCHEME 2 Suggested mechanism for
synthesis of diaryls via Suzuki C& C reactions
3 4
in presence of Cu-BIA-Si-Fe O nanocatalyst

10 of 18
DANQING ET AL.
TABLE 3
3 4
Comparison of Cu-BIA-Si-Fe O with other catalysts inSuzuki reaction for synthesis of diaryls
[a]
Entry Catalyst
Conditions
Time (h) Yield (%)
[
48]
1
Palladium N-heterocyclic carbene (0.02 mmol),
CO (1.2 eq)
Pd(OAc) /LHX (15 mol%)
i-PrOH (4 ml), r.t.
6
98
K
2
3
ꢀ
[49]
[50]
2
3
4
2
DMF/H
DMF/H
2
2
O (2 mmol), 50 C
3
7
3
93
95
98
ꢀ
Aminomethyldiphosphine–Pd(II) (1.2 mmol)
O (3/3 ml), 80 C
[
[
[
51]
52]
53]
Pd (1.0 mol)
K
3
PO
4
.3H
2
O (1.5 mmol), H
2
O/ethanol
ꢀ
(
2 ml), 80 C
5
6
Cross-linked poly(ITC-HPTPy)-Pd (0.23 mol%)
K
2
CO
3
(1.5 mmol), H
2
O/ethanol (3 ml),
2
98
78
ꢀ
80 C
CuCl
2
0
(10 mol%),
DCM (1.0 ml), Cs
2
CO
3
(2.0 equiv), r.t.
24
0
4
,4 -di-tert-butyl-2,2 -bipyridine (10 mol%)
Hercynite@L-methionine-Pd (0.1 mol%)
GO/Fe /Pd nanocomposite (0.36 mol)
ꢀ
[54]
7
8
K
K
2
2
CO
3
(3 mmol), ethanol (3 ml), 80 C
1.5
10
80
80
[55]
3
O
4
CO
3
(3 mmol), H
2
O/ethanol (3 ml),
ꢀ
80 C
ꢀ
[56]
[57]
9
1
1
Cu(II)–β-cyclodextrin (0.1 eq)
DMF, 90 C
10
14
2
80
94
ꢀ
0
1
Cu-PAR (0.05 g, 0.0129 mmol)
KOH (1 mmol), DMSO, 120 C
ꢀ
Cu-BIA-Si-Fe
3
O
4
(1.5 mol%)
K
2
CO
3
(1 mmol), DMSO, 80 C
95 (present work)
a
Yields refer to isolated pure products.
with both electron-withdrawing and electron-releasing
groups reacted efficiently and afforded products in excel-
lent yields.
A proposed mechanism for the reaction is shown in
Scheme 3. First, the coupling of aromatic amines and
boronic acids is as depicted in Scheme 1. The reaction is
initiated by nucleophilic coordination of amine with
aniline and phenylboronic acid in DMSO (Table 5,
entry 1). The results demonstrated that Cu-BIA-Si-Fe O
is a sustainable catalyst in reaction media and can be
reused four times with no significant loss of its catalytic
activity (Figure 9).
3
4
The recycled Cu-BIA-Si-Fe O4 catalyst (after four
3
recycles) was characterized using FT-IR spectroscopy,
SEM, EDX analysis, TGA and TEM, as shown in
Figures 10–14.
Cu(II) of the Cu-BIA-Si-Fe O4 catalyst resulting (A),
3
which undergoes transmetalation with boronic acid to
furnish coupled Cu(II) complex (B). Oxidation of (B) in
turn affords complex (C) involving Cu as Cu(III). Com-
plex (C) on reductive elimination furnishes the final
C& N coupled product (D) and regenerates
Cu(I) catalyst which is further oxidized to Cu(II) in the
presence of air. There is an added advantage of the mag-
netically separable heterogeneous catalyst in that it can
be easily recovered after completion of the reaction with-
out any significant loss (Scheme 3).
To investigate the activity and efficiency of the cat-
alyst in comparison with catalysts reported in the liter-
ature for the synthesis of diphenylamine derivatives,
the reaction of boronic acid with aniline was evaluated
as a representative example and conducted in the
presence of different catalysts. The results exhibited
that these methods are comparable to some previously
reported methods in terms of reaction times and yields
The FT-IR spectrum of recovered Cu-BIA-Si-Fe O is
3
4
illustrated in Figure 10. The peaks at around 2930 and
−
1
2852 cm , for asymmetric and symmetric vibrations of
C& H stretching, can be obviously observed. The
absorption peaks at 1630 and 1450 cm− correspond to
the asymmetric and symmetric stretching vibration of
C& N and C& H (aromatic) of organic moiety. The
absorption bands at 586 and 447 cm− were attributed to
Fe& O stretching and that at 3443 cm− corresponded to
OH groups on magnetic surface of Fe O . Therefore, the
1
1
1
3
4
data obtained from FT-IR spectroscopy indicate the exis-
tence of the nanomagnetic particles, heterocyclic moiety
and Cu in the structure of Cu-BIA-Si-Fe O MNPs
3
4
(Figure 10).
Morphologies
of
recovered
Cu-BIA-Si-Fe O
3 4
nanoparticles were investigated using TEM as shown in
Figure 11. Particles are observed to have spherical
morphology. Average particle size is estimated at about
14 nm from the TEM micrographs. Also, an SEM image
of the recovered Cu-BIA-Si-Fe O nanoparticles is shown
(
Table 6).
The recoverability and reusability of the prepared cat-
alyst were studied using the selected model reaction of
3
4

DANQING ET AL.
TABLE 4
11 of 18
Optimization of reaction conditions for synthesis of diarylamine
Amount of
catalyst (mol%) Base
Temperature
( C)
Time
(h)
Yield
TOF
TON (h−1
)
ꢀ
[a]
Entry Solvent
(%)
70
75
97
65
40
97
75
1
2
3
4
5
6
7
CH
3
CN
2
KF (1 mmol)
70
110
100
60
10
4
35
3.5
DMF
2
KF (1 mmol)
KF (1 mmol)
KF (1 mmol)
KF (1 mmol)
KF (1 mmol)
DABCO
37.5
9.37
DMSO
2
2.5
10
12
2.5
3
48.5 19.4
CH
3
OH
2
32.5
20
3.25
1.66
H
2
O
2
100
100
100
DMSO
DMSO
1.5
1.5
64.6 25.84
50 16.66
(
1 mmol)
8
9
1
1
1
1
1
1
1
1
1
1
2
2
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
No catalyst
1.5
1.5
0.5
1
Et
3
N (1 mmol)
100
100
75
2.5
2.5
5
82
79
20
40
65
75
65
85
97
97
96
96
54.6 21.84
52.6 21.04
NaOH (1 mmol)
KF (1 mmol)
KF (1 mmol)
KF (1 mmol)
KF (1 mmol)
KF (1 mmol)
KF (1 mmol)
KF (1 mmol)
KF (1 mmol)
KF (0.5 mmol)
KF (0.2 mmol)
KF (1 mmol)
KF (1 mmol)
0
1
2
3
4
5
6
7
8
9
0
1
40
8
75
5
40
8
1.5
2
75
5
43.3
37.5
8.66
8.33
43.33
28.33
75
4.5
3
0.5
1
100
100
100
100
100
100
100
100
130
85
3
1.5
2
2.5
2.5
2.5
2.5
24
4
64.6 25.84
64.6 25.84
1.5
1.5
2
64
64
—
39
25.6
25.6
—
No reaction
78
CuCl
2
–DMSO
2
9.75
a
Yields refer to isolated products.
in Figure 12. The SEM image of Cu-BIA-Si-Fe O showed
a sphere-like structure.
efficiency. It should be noted that there was low Cu
leaching (about 9.7%) during the reaction and the catalyst
showed high stability even after four cycles.
3
4
The TGA curve of the recovered nanoparticles shows
the mass loss of the organic functional group as it decom-
poses upon heating. The curve shows a weight loss of
ꢀ
about 13.4% from 680 C, resulting from the decomposi-
3 | EXPERIMENTAL
tion of functional groups grafted to the MNP surface
(
Figure 13).
As can be seen from the FT-IR analysis, the structure
of the Cu-BIA-Si-Fe O catalyst has not changed and,
3.1 | Chemicals and apparatus
Powder XRD of the prepared catalyst was performed
using a Philips PW 1830 X-ray diffractometer with a Cu
3
4
according to SEM analysis, the catalyst particles are
spherical. Also, the size of the recycled catalyst particles
is similar to those of the newly synthesized particles from
the TEM analysis, and EDX analysis has also not changed
ꢀ
Kα source (λ = 1.5418 Å) in the Bragg angle range 10–80
ꢀ
at 25 C. FT-IR spectra were obtained using a FT-IR spec-
−
1
trometer (Vector 22, Bruker) in the range 400–4,000 cm
(
Figure14). Therefore, based on the obtained results, the
at room temperature. SEM analysis was conducted using
a VEGA//TESCAN KYKY-EM 3200 microscope (acceler-
ation voltage of 26 kV). TEM experiments were con-
ducted with a Philips EM 208 electron microscope. EDX
analysis of the catalyst was conducted with a VEGA3
XUM/TESCAN. TGA was performed with a Stanton Red
Cu-BIA-Si-Fe O4 catalyst has not changed after four
recycles and its activity is similar to that of the newly
prepared catalyst.
3
The results demonstrated that the Cu-BIA-Si-Fe O4
3
catalyst could be reused four times without losing its

12 of 18
DANQING ET AL.
TABLE 5
3 4
Synthesis of diarylamines in the presence of Cu-BIA-Si-Fe O as catalyst
ꢀ
Melting point ( C)
[a]
Entry
Boronic acid
Aniline
Time (h)
Yield (%)
TON (%)
Found
Reported
[
58]
1
2.5
96
64
53–54
52–54
[
11]
2
3
4
2
97
95
95
64.6
63.3
63.3
64–66
91–92
84–85
65–66
[
8]
2.5
2.5
90
[
58]
85–87
[
8]
5
6
2
98
95
65.3
63.3
137
135–136
135–136
[
8]
2.5
136–137
[
59]
7
8
9
2
96
95
97
64
80–82
136–137
91–92
81–83
[
60]
2
63.3
64.6
135–137
[
8]
2.5
90

DANQING ET AL.
13 of 18
TABLE 5 (Continued)
ꢀ
Melting point ( C)
[a]
Entry
Boronic acid
Aniline
Time (h)
Yield (%)
TON (%)
Found
Reported
[
58]
1
0
2
98
65.3
72–74
73–75
[
8]
1
1
2.5
95
63.3
79–80
80–81
a
Yields refer to the isolated products.
SCHEME 3 Suggested mechanism for N-
arylation reactions in presence of Cu-BIA-Si-
3 4
Fe O nanocatalyst
TABLE 6
Comparison of results for present catalyst with those for other reported catalysts in the synthesis of diphenylamine
[
a]
Entry
Catalyst
Cu –β-CD (0.01 mmol), K
Cu(OAc) (5–20 mol %), myristic acid (10–40 mol%)
CuFAP (100 mg)
Cu-BIA-Si-Fe
Conditions
Time (h)
Yield (%)
ꢀ
[61]
1
2
3
4
2
2
CO
3
(3 equiv.)
DMF (1 ml), 90 C
Toluene (2 ml), r.t.
Methanol (4 ml), r.t.
48
24
3
90
[
[
62]
63]
2
92
90
ꢀ
3
O
4
(1.5 mol%), KF (0.2 mmol)
DMSO (4 ml), 100 C
2.5
96 (present work)
a
Isolated yield.
Craft STA-780 (London, UK). NMR spectra were
performed with a Bruker DRX-400 AVANCE instrument
Magnetic measurements were carried out using a VSM
instrument (MDK, model 7400). The metal loading was
determined using ICP-AES. Melting points were
evaluated with an Electrothermal 9100 apparatus.
1
13
(300.1 MHz for H, 75.4 MHz for C). The spectra were
obtained with samples in DMSO-d6 as a solvent.

14 of 18
DANQING ET AL.
3
3
.2 | General procedures
.2.1 | Preparation of Fe O MNPs
3
4
FeCl ꢁ6H O (2 mol) and FeCl ꢁ4H O (1 mol) were added
3
2
2
2
to 100 ml of deionized water and then sonicated to
dissolve all salts entirely. Afterwards, 10 ml of 25%
NH OH was added quickly into the reaction mixture in
4
one portion under nitrogen atmosphere at room
temperature followed by vigorous stirring for about
25 min with a magnetic stirrer. The black precipitate was
washed with deionized water four times (Scheme 4).
FIGURE 9 Reusability of the catalyst
FIGURE 10 FT-IR spectrum of
Cu-BIA-Si-Fe
four recycles
3 4
O nanoparticles after
FIGURE 11 TEM analysis of Cu-BIA-Si-Fe
3
O
4
nanoparticles
3 4
FIGURE 12 SEM analysis of Cu-BIA-Si-Fe O nanoparticles
after four recycles
after four recycles

DANQING ET AL.
15 of 18
3 4
FIGURE 13 TGA of Cu-BIA-Si-Fe O
nanoparticles after four recycles
After that, 2.5 ml of 3-chloropropyltrimethoxysilane was
added under reflux condition and stirred for 3.5 h with a
mechanical stirrer. The obtained precipitate was filtered
off with an external magnet and washed twice with etha-
ꢀ
nol and dried overnight in an oven at 85 C to afford
Fe O4
nanoparticles
coated
with
3
3-chloropropyltriethoxysilane (Scheme 5).
3
.2.3 | Preparation of BIA-Si-Fe O4
3
nanoparticles
First, 1.5 g of Fe O nanoparticles was added to 150 ml of
3
4
FIGURE 14 EDX analysis of Cu-BIA-Si-Fe
after four recycles
3
O
4
nanoparticles
ethanol and placed in an ultrasonic apparatus for 30 min.
Then 1 g of 1H-benzo[d]imidazol-2-amine was added
under reflux conditions and stirred vigorously with a
mechanical stirrer for 8 h. The obtained precipitate was
filtered off with an external magnet, rinsed with ethanol
several times and placed in an oven for 24 h to dry to
afford the product of 1H-benzo[d]imidazol-2-amine-
coated iron oxide nanoparticles (Scheme 6).
3
3
.2.2 | Preparation of
-chloropropyltrimethoxysilane-
functionalized Fe O nanoparticles
3
4
(
Fe O –ClPSi)
3
4
Initially, 1.5 g of Fe O MNPs was added to 100 ml of eth-
3
4
anol and placed in an ultrasonic apparatus for 25 min.
SCHEME 4 Preparation of Fe
3
O
4
nanoparticles
3 4
SCHEME 5 Preparation of Fe O –ClPSi nanoparticles

16 of 18
DANQING ET AL.
SCHEME 6 Preparation of BIA-Si-
Fe nanoparticles
3 4
O
3
.2.4 | Preparation of Cu-BIA-Si-Fe O4
(d, J = 8.8 Hz, 2H ), 7.01 (d, J = 8.8 Hz, 2H ), 7.19–7.31
3
Ar
Ar
13
nanoparticles
(m, 4HAr). C NMR (100 MHz, DMSO-d , δ, ppm): 54.8,
6
1
19.2, 126.0, 127.7, 129.4, 129.6, 131.4, 139.9, 159.7.
0
1
To prepare Cu-BIA-Si-Fe O nanoparticles, the obtained
4-Methoxy-4 -ethylbiphenyl (Table 2, entry 3):
H
3
4
BIA-Si-Fe O (0.5 g) was dispersed in 50 ml of ethanol by
NMR (400 MHz, DMSO-d , δ, ppm): 1.20 (t, J = 8.4 Hz,
3
4
6
sonication for 30 min, and then 0.045 g of CuCl was
3HCH3), 2.27 (q, J = 8.4 Hz, 2H CH ), 3.61 (s, 3H, OCH ),
2
2
3
added to the mixture. A brown suspension was formed
after refluxing with vigorous stirring for 8 h. The catalyst
6.81–6.85 (m, 2H ), 6.94–7.00 (m, 2H ), 7.07–7.11 (m,
Ar
Ar
13
4H ). C NMR (100 MHz, DMSO-d , δ, ppm): 18.8, 28.4,
Ar
6
(
Cu-BIA-Si-Fe O ) was separated from the solution using
51.8, 118.0, 123.6, 123.7, 126.4, 126.5, 130.5, 134.4, 160.0.
3
4
an external magnet, washed with deionized water several
times and dried in an oven overnight (Scheme 7). The
whole synthesis was performed under nitrogen flow.
3.2.6 | General procedure for N-arylation
reactions
3
.2.5 | General procedure for synthesis of
A mixture of phenylboronic acid (1 mmol), aromatic
amine (1.2 mmol) and 0.12 g (0.2 mmol) of KF in DMSO
diaryls via Suzuki coupling reactions
(
4 ml) was added to Cu-BIA-Si-Fe O (1.5 mol%) under
3 4
ꢀ
To synthesize diaryls via Suzuki coupling reactions, aryl
halide (1 mmol), phenylboronic acid (1 mmol)
and1 mmol of K CO as the base were mixed with each
other in DMSO (2.5 ml) in the presence of Cu-BIA-Si-
Fe O (1.5 mol%) as catalyst. The reaction mixture was
stirred vigorously at 80 C for various times according to
each substrate. After reaction, the solid catalyst was fil-
tered and washed several times with deionized water and
absolute ether and kept for reuse in a subsequent run
under the same reaction conditions. The filtrate was
extracted with ethyl acetate (3 × 5 ml), washed with
nitrogen atmosphere at 100 C for 2 h with vigorous stir-
ring. Then, after completion of the reaction, the catalyst
was separated using an external magnet and washed with
dry CH Cl three times and checked for its reusability.
2
3
2
2
The solvent of the reaction mixture was evaporated using
a rotary evaporator and then ethyl acetate and water were
added to the residue. The organic layer was dried over
3
4
ꢀ
anhydrous MgSO . The solvent was evaporated under
4
reduced pressure and the crude product was purified by
column chromatography using ethyl acetate–n-hexane.
Selected spectral data for a two known products are
deionized water, dried with anhydrous MgSO , filtered
given below:
4
1
and the solvent was evaporated and the final product
purified and prepared by preparative TLC (eluent: petro-
leum ether–ethyl acetate, 20/1) and the obtained product
yield evaluated.
Diphenylamine (Table 5, entry 1):
(400.13 MHz, DMSO, δ, ppm): 5.60 (s, 1H, N-H),
H
NMR
7.12–1.15 (m, 2H ), 7.22–7.27 (m, 4 H ) ppm, 7.38 (d,
Ar
Ar
13
4 H ). C NMR (100.6 MHz, DMSO, δ, ppm): 119.9,
Ar
Two known and reported synthesized compounds are
121.0, 123.7, 136.3.
4-Methyl-N-phenylaniline (Table 5, entry 3): H NMR
(400.13 MHz, DMSO, δ, ppm): 2.30 (s, 3H, CH ), 5.60 (s,
1
described with their characterization data below:
1
4
-Methoxybiphenyl (Table 2, entry 1): H NMR
3
(
400 MHz, DMSO-d , δ, ppm): 3.61 (s, 3H, OCH ), 6.90
1H, N& H), 7.09–7.20 (m, 2H), 7.21–7.27 (m, 3H), 7.42
6
3
SCHEME 7 Preparation of Cu-BIA-Si-
Fe nanoparticles
3 4
O

DANQING ET AL.
17 of 18
1
3
(
(
1
d, J = 2.0 Hz, 2H), 7.56 (d, J = 2.0 Hz, 2H). C NMR
100.6 MHz, DMSO, δ, ppm): 19.0, 122.2, 123.0, 123.7,
23.9, 127.4, 131.5, 135.3, 135.9.
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054.
7
[
4
| CONCLUSIONS
3
[
[
[
18] A. Y. Cheng, J. C. Hsieh, Tetrahedron Lett. 2012, 53, 71.
19] J. Lindley, Tetrahedron 1984, 40, 1433.
20] J. C. Henrim, P. C. Pascal, H. Samy, F. S. Jean, T. A. Marc,
Org. Lett. 2004, 6, 913.
A new and efficient catalyst consisting of copper
supported on 2-(1H-benzo[d]imidazol-2-yl)aniline-
functionalized Fe O4 nanoparticles (Cu-BIA-Si-Fe O )
has been developed as a highly active, stable and recover-
able heterogeneous catalyst for the preparations of diaryl
and diarylamines via Suzuki C& C reactions and
Ullmann coupling reactions between aryl halides with
phenylboronic acid and boronic acid with aniline deriva-
tives. The catalyst could be reused for several sequential
cycles with no effective loss of its activity.
3
3 4
[21] J. K. Huang, Y. Chen, J. H. Chan, L. R. Mike, D. L. Robert,
M. F. Margaret, Synlett 2011, 10, 1419.
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The author acknowledges the Beijing, Tianjin and Hebei
Governments under the Background of Service-oriented
Government Construction for support of this work.
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SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of this
article.
2
02000007
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