Synthesis of diaryl sulfides via nickel ferrite-catalysed C─S bond formation in green media

Article abstract of DOI:10.1002/aoc.4409

NiFe₂O₄ magnetic nanoparticles (MNPs) were synthesized, characterized and applied as an air-stable, inexpensive and magnetically separable nanocatalyst for the synthesis of structurally diverse sulfides. Efficient methodologies were developed for the synthesis of unsymmetric diaryl sulfides via odourless and one-pot reactions of triphenyltin chloride/S₈ or arylboronic acid/S₈ as thiolating agents with aryl halides or nitroarenes as starting materials in the presence of base (K₂CO₃ or NaOH) and NiFe₂O₄ MNPs as a catalyst in water or poly (ethylene glycol) as solvent at 80–110?°C. Free from ligand and the unpleasant smell of thiols and with the use of magnetically reusable nanocatalyst, green solvents and commercially available and cheap sulfur source and starting materials, these methods are more eco-friendly and practical than available protocols for the synthesis of sulfides.

Full text of DOI:10.1002/aoc.4409

Received: 18 December 2017
DOI: 10.1002/aoc.4409
Revised: 4 April 2018
Accepted: 10 April 2018
F U L L P A P E R
Synthesis of diaryl sulfides via nickel ferrite‐catalysed C─S
bond formation in green media
Shiva Farzin1 | Abdollah Rahimi1 | Kamran Amiri1 | Abed Rostami2 | Amin Rostami1,3
1 Department of Chemistry, Faculty of
NiFe2O4 magnetic nanoparticles (MNPs) were synthesized, characterized and
applied as an air‐stable, inexpensive and magnetically separable nanocatalyst
for the synthesis of structurally diverse sulfides. Efficient methodologies were
developed for the synthesis of unsymmetric diaryl sulfides via odourless and
one‐pot reactions of triphenyltin chloride/S8 or arylboronic acid/S8 as
thiolating agents with aryl halides or nitroarenes as starting materials in the
presence of base (K2CO3 or NaOH) and NiFe2O4 MNPs as a catalyst in water
or poly (ethylene glycol) as solvent at 80–110 °C. Free from ligand and the
unpleasant smell of thiols and with the use of magnetically reusable
nanocatalyst, green solvents and commercially available and cheap sulfur
source and starting materials, these methods are more eco‐friendly and practi-
cal than available protocols for the synthesis of sulfides.
Science, University of Kurdistan, 66177‐
15175 Sanandaj, Iran
2 Vice Chancellor for Food and Drug,
Kurdistan University of Medical Science,
Sanandaj, Iran
3 Research Centre of Nanotechnology,
University of Kurdistan, PO Box 416
Sanandaj, Iran
Correspondence
Amin Rostami, Department of Chemistry,
Faculty of Science, University of
Kurdistan, 66177‐15175 Sanandaj, Iran.
Email: a.rostami@uok.ac.ir
Funding information
University of Kurdistan
KEYWORDS
aryl halide, NiFe2O4 MNPs, nitroarene, S8, sulfide
1 | INTRODUCTION
these efforts have improved the reaction conditions, most
of these reported methods were performed under homo-
Thioetherification reactions are some of the most use-
ful chemical reactions in synthetic organic chemistry
due to the biological and pharmacological activities of
geneous and non‐recoverable reaction conditions. Over
the past few years, heterogeneous catalysts have attracted
the attention of researchers from both economic and
industrial points of view as compared to homogeneous
catalysts. However, these systems suffer from low activ-
ity, reproducibility and selectivity. In order to overcome
these problems, recently magnetic nanoparticles (MNPs)
have been introduced into the field of catalysis. These
couple the advantages of heterogeneous (easy separation
and excellent reusability) and homogeneous (high activ-
ity and reproducibility) systems, which make them
promising materials for practical and large‐scale
applications.[17]
products.[1,2]
Therefore,
protocols
leading
to
thioetherification of aromatic compounds, which are
efficient, cheap and practical, have attracted a great
deal of attention.[3]
Cross‐coupling reactions using transition metal cata-
lysts such as Cu, Pd, Fe, Ni, Co and In are powerful tools
for the construction of carbon–sulfur bonds.[4–10] The
major drawbacks of these protocols are using volatile,
less available, expensive and foul‐smelling thiols as sub-
strates that can lead to serious safety and environmental
problems. To overcome these drawbacks, various
persulfides (thiol surrogates) have been employed.[11–15]
Among sulfur sources, S8 due to its being commercially
available, of low cost, chemically stable, odourless and
easy to handle has been successfully used.[16] Although
NiFe2O4 MNPs are air‐stable, easily made, low‐cost
and bimetallic nanoparticles displaying very good cata-
lytic activity in various organic reactions.[18,19] Such prop-
erties can stem from synergetic electronic interactions
between two different metal atoms in an individual
Appl Organometal Chem. 2018;32:e4409.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4409

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FARZIN ET AL.
nanoparticle. These nanoparticles can be separated con-
veniently using an external magnetic field and reused
several times, which are the main benefits of these
systems.
2 | EXPERIMENTAL
2.1 | Materials and Instrumentation
All reagents and solvents used in this work were pur-
chased from commercial sources of Aldrich, Merck and
Fluka and used without further purification. Fourier
transform infrared (FT‐IR) spectroscopic analyses were
carried out with KBr discs using a VERTEX 70 (Bruker,
Germany) FT‐IR spectrophotometer. All reactions for
purity determination of products were monitored using
Very recently, we have reported odourless and
one‐pot methods for the synthesis of unsymmetric
sulfides using the reaction of arylboronic acid/S8 or
triphenyltin chloride/S8 system as a thiolating agent
with aryl/alkyl halides or nitroarenes in the presence
of copper salts as homogeneous catalysts.[20] Although
these protocols represent considerable progress in C─S
bond formation, recycling and reuse of the catalysts
under the homogeneous conditions are difficult and
large amounts of catalysts were lost during work‐up
of the reactions. Moreover, in some cases, toxic and
polar solvents, long reaction times and high reaction
temperatures are required for completion of the
reactions.
Herein, in continuation of our studies of the appli-
cation of magnetically reusable nanocatalysts in
organic synthesis[21] and the development of new syn-
thetic methodologies for the synthesis of sulfides,[20]
we report the application of NiFe2O4 MNPs as a highly
active recyclable heterogeneous magnetic nanocatalyst
for one‐pot thioetherification of nitroarenes or aryl
halides with triphenyltin chloride, arylboronic acids
or alkyl halides in the presence of S8 in green solvents.
TLC with gel 60 F254 plates. The H NMR and 13C NMR
1
spectra were recorded with a Bruker NMR spectrometer
at 250 and 62.5 MHz, respectively. Scanning electron
microscopy (SEM) images and energy‐dispersive X‐ray
(EDX) analysis of the MNPs were recorded using a
FESEM‐TESCAN MIRA3. Powder X‐ray diffraction
(XRD) patterns were collected with a Philips X'Pert Pro
diffractometer. The magnetic properties of the catalyst
were measured using alternating gradient force magne-
tometry (AGFM; Meghnatis Daghigh Caviar Co., Iran).
2.2 | Preparation of NiFe2O4 MNPs
NiFe2O4 MNPs were synthesized using a chemical co‐
precipitation technique similar to that of the litera-
ture,[22] using FeCl3 ⋅6H2O and NiCl2 ⋅6H2O in basic
TABLE 1 Optimization of reaction conditions for C─S bond formation reaction of iodobenzene and triphenyltin chloridea
Entry
Base
Solvent
Catalyst (mol%)
Temp. (°C)
GC yield (%)
1
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Morpholine
Et3N
H2O
29
25
40
60
60
60
60
60
60
60
60
60
60
30
2
H2O
29
60
3
H2O
29
100
80
4
H2O
21
5
H2O
None
29
—
b
6
H2O
—
7
DMSO
DMF
PEG400
H2O
29
80
8
29
100
85
9
29
10
11
12
29
—
—
H2O
29
c
K2CO3
H2O
29
—
aReaction conditions unless stated otherwise: iodobenzene (204 mg, 1 mmol), triphenyltin chloride (128 mg, 0.35 mmol), S8 (48 mg, 1.5 mmol), KF (174 mg, 3
mmol), NiFe2O4 MNPs (29 mol%), base (4 mmol), Bu4NOH (1 mmol) and solvent (2 ml) at 60°C.
bReaction performed in the absence of Bu4NOH.
cWithout KF.

FARZIN ET AL.
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solution as follows. In a two‐necked flask, FeCl3 ⋅6H2O
(2.160 g, 8 mmol) and NiCl2 ⋅6H2O (0.950 g, 4 mmol)
were dissolved in 75 ml of distilled water and stirred at
room temperate under a nitrogen atmosphere for
20 min. Thereafter, under very rapid mechanical stirring,
a solution of NaOH (3 g, 75 mmol) in water (15 ml) was
added slowly dropwise during 15 min and the resultant
mixture of brown precipitate heated to 90 °C for 5 h.
Subsequently, the reaction mixture was cooled to room
temperature, and the MNPs were separated by magnetic
decantation, washed with deionized water (4 × 5 ml) and
ethanol (2 × 5 ml) and dried under vacuum at room tem-
perature. Finally, the NiFe2O4 MNPs were calcined at
600 °C for 5 h.
2.3 | General Procedure for C─S Coupling
Reaction of Aryl Halides with Triphenyltin
Chloride
NiFe2O4 MNPs (29 mol%) were added to a mixture of aryl
halide (1 mmol), triphenyltin chloride (0.35 mmol), S8
(1.5 mmol), KF (3 mmol), Bu4NOH (1 mmol) and
K2CO3 (4 mmol) in water (2 ml). Then the mixture was
stirred for the appropriate time at 80 °C. The progress of
the reaction was monitored by TLC. After completion of
the reaction, the reaction mixture was cooled to room
temperature and the catalyst was separated using a
magnetic field. The reaction mixture was extracted using
a mixture (1:1) of Et2O and H2O (3 × 5 ml). The organic
TABLE 2 NiFe2O4 MNP‐catalysed synthesis of phenylaryl sulfides from triphenyltin chloride, S8 and aryl halides
Entry
ArX
Productb
Time (h)
Yield (%)
1
16
95
2
3
4
30
19
15
90
93
97
5
6
34
28
85c
94
7
30
90
8
9
25
18
87
75
10
11
16
32
94
92
aGeneral procedure: ArX (1 mmol), triphenyltin chloride (0.35 mmol), S8 (1.5 mmol), KF (3 mmol), K2CO3 (4 mmol), NiFe2O4 (29 mol%), Bu4NOH (1 mmol)
and H2O (2 ml), 60°C.
bAll products are known and were characterized by NMR spectra as compared with data reported in the literature.[20]
cReaction performed at 80°C.

4 of 12
FARZIN ET AL.
layer was dried over MgSO4 and then evaporated under
reduced pressure. The residue was purified by column
chromatography on silica gel using n‐hexane–EtOAc
(70:30), affording the desired products in good to excel-
lent yields.
2.5 | General Procedure for Synthesis of
Phenylaryl Sulfides using Triphenyltin
Chloride and Nitroarenes
A one‐necked flask was charged with NiFe2O4 MNPs
(15 mol%), potassium carbonate (4 mmol), S8 (1.5 mmol),
KF (3 mmol), nitroarene (1 mmol), triphenyltin chloride
(0.35 mmol) and 3 ml of poly (ethylene glycol)
(PEG200). The mixture was magnetically stirred and
heated at 110 °C for the appropriate reaction time. The
progress of the reaction was monitored by TLC. After
completion of the reaction, the reaction mixture was
cooled to room temperature, the catalyst was separated
using an external magnet and water (4 ml) was added.
The products were extracted with Et2O (3 × 5 ml) and
dried over anhydrous Na2SO4. Evaporation of the solvent
and purification by column chromatography on silica gel
(n‐hexane–EtOAc) gave the desired phenylaryl sulfides in
good to high yields.
2.4 | General Procedure for C─S Coupling
Reaction of Aryl Halides with Arylboronic
Acids
In a one‐necked flask, a mixture of aryl halide (1 mmol),
arylboronic acid (1.2 mmol), S8 (1.5 mmol), Bu4NOH
(1 mmol), NaOH (4 mmol) and NiFe2O4 MNPs
(29 mol%) in water (2 ml) was magnetically stirred for
the required time at 80 °C. The progress of the reaction
was monitored by TLC. Upon completion of the reaction,
the reaction mixture was cooled to room temperature, the
nanocatalyst was separated using an external magnet and
the reaction mixture was extracted using a mixture (1:1)
of Et2O and H2O (3 × 5 ml). The combined organic layer
was dried over anhydrous MgSO4 and then evaporated
under reduced pressure. The crude products were
purified by column chromatography on silica gel using
n‐hexane–EtOAc (70:30). The products were obtained in
good to excellent yields.
2.6 | General Procedure for Synthesis of
Unsymmetric Diaryl Sulfides using
Arylboronic Acids and Nitroarenes
A one‐necked flask was charged with NiFe2O4 MNPs
(20 mol%), sodium hydroxide (4.0 mmol), S8 (1.5 mmol),
TABLE 3 Optimization of reaction conditions for C─S coupling reaction of iodobenzene and phenylboronic acida
Entry
Base
Solvent
Catalyst (mol%)
Temp. (°C)
GC yield (%)
1
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
K2CO3
Et3N
H2O
29
29
29
None
21
29
29
29
29
29
29
29
29
29
40
60
80
80
80
80
80
80
80
80
80
80
80
80
40
2
H2O
50
3
H2O
100
—
4
H2O
5
H2O
75
6
DMSO
DMF
EtOH
PEG400
Toluene
H2O
90b
100b
50
7
8
9
95
10
11
12
13
14
80
b
—
H2O
70
—
60
H2O
KOH
H2O
aReaction conditions unless stated otherwise: iodobenzene (204 mg, 1 mmol), phenylboronic acid (146 mg, 1.1 mmol), S8 (48 mg, 1.5 mmol), NiFe2O4 MNPs (29
mol%), base (4 mmol), Bu4NOH (1 mmol) and solvent (2 ml).
bWithout Bu4NOH.

FARZIN ET AL.
5 of 12
TABLE 4 C─S bond formation of aryl halides with arylboronic acids using S8 catalysed by NiFe2O4 MNPsa
Entry
ArX
ArB (OH)2
Productb
Time (h)
Yield (%)
1
14
95
2
3
4
5
6
16
28
32
19
20
93
88
85
95
93
7
8
13
15
96
90
9
30
33
25
80c
70c
95
10
11
12
13
27
32
93
75
14
34
73
15
16
28
32
85
80
17
16
70
(Continues)

6 of 12
FARZIN ET AL.
TABLE 4 (Continued)
Entry
ArX
ArB (OH)2
Productb
Time (h)
Yield (%)
18
20
65
19
20
21
22
15
17
34
35
95
94
94
91
aGeneral procedure: ArX (1 mmol), arylboronic acid (1.2 mmol), S8 (1.5 mmol), NaOH (4 mmol), NiFe2O4 MNPs (29 mol%), H2O (2 ml) and Bu4NOH (1 mmol),
80°C.
bAll products are known and were characterized by NMR spectra as compared with data reported in the literature.[20]
cReaction performed at 100°C.
nitroarene (1 mmol), arylboronic acid (1.1 mmol) and
PEG200 (2 ml). The mixture was magnetically stirred
and heated at 110 °C for the appropriate reaction time.
The progress of the reaction was monitored by TLC. After
completion of the reaction, the reaction mixture was
cooled to room temperature, the catalyst was separated
using an external magnet and water (5 ml) was added.
The product was extracted with Et2O (3 × 5 ml) and dried
over anhydrous Na2SO4. Evaporation of the solvent and
purification by column chromatography on silica gel (n‐
hexane–EtOAc) gave the desired diaryl sulfides in good
to high yields.
triphenyltin chloride, the reaction of iodobenzene and
triphenyltin chloride in the presence of S8 as a sulfur
source, KF as sulfur activator, K2CO3 as base, Bu4NOH
as base and phase transfer agent and NiFe2O4 MNPs as
catalyst in water as solvent was selected as a model reac-
tion. The effect of temperature, amount of nanocatalyst,
solvent and base on the model reaction was investigated.
The reaction was conducted at various temperatures, with
60 °C giving the best yields; when the reaction tempera-
ture was decreased, the GC yield was decreased (Table 1,
entries 1–3). The results indicate that the reaction did not
proceed in the absence of NiFe2O4 (Table 1, entry 5), while
the reaction was efficiently carried out in the presence of
29 mol% of the catalyst (Table 1, entry 3). In addition to
3 | RESULTS AND DISCUSSION
NiFe2O4 MNPs were prepared using a co‐precipitation
method according to the procedure presented by
Aliahmad and Noori[22] and characterized using SEM,
XRD, FT‐IR, EDX and AGFM techniques. The results of
characterization are provided in the supporting informa-
tion (Figures S1–S5).
3.1 | NiFe2O4 MNP‐Catalysed Synthesis of
Sulfides through Cross‐Coupling Reactions
of Aryl Halides with Triphenyltin Chloride
or Arylboronic Acid in Presence of S8
FIGURE 1 Recyclability of NiFe2O4 MNPs in the reaction of
iodobenzene with (a) phenylboronic acid and (b) triphenyltin
chloride under optimized reaction conditions (Tables 2 and 4, entry 1)
In order to investigate the synthesis of phenylaryl sulfides
through cross‐coupling reactions of aryl halides with

FARZIN ET AL.
7 of 12
water,
various
solvents
such
as
PEG400,
(Table 1, entry 12). As is evident from Table 1, aryl halide
(1 mmol), triphenyltin chloride (0.35 mmol), K2CO3
(4 mmol), S8 (1.5 mmol), KF (3 mmol) as S8 activator and
Bu4NOH (1 mmol) in the presence of NiFe2O4 (29 mol%)
in water (2 ml) at 60 °C were found to be ideal reaction
conditions for the synthesis of phenylaryl sulfide.
Subsequently, a series of various phenylaryl sulfide
derivatives were synthesized successfully with the optimal
conditions in hand (Table 1, entry 3). The results
obtained for coupling reactions of various aryl halides
dimethylformamide (DMF) and dimethylsulfoxide
(DMSO) in the absence of phase transfer agent were inves-
tigated (Table 1, entries 6–9). It was observed that in addi-
tion to water, DMF is also a suitable solvent for this
reaction (Table 1, entry 8). Also, we found that the cou-
pling reaction failed in the absence of Bu4NOH in water
solvent (Table 1, entry 6). Organic bases such as
morpholine and Et3N were not effective (Table 1, entries
10 and 11). No product was observed in the absence of KF
TABLE 5 Optimization of reaction conditions for coupling reaction of 4‐nitroanisole with triphenyltin chloridea
Entry
Solvent
Base
Catalyst (mol%)
Temp. (°C)
GC yield (%)
1
2
3
4
5
6
7
DMF
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
20
110
110
110
110
110
110
100
100
100
—
PEG200
PEG200
PEG200
PEG200
PEG200
PEG200
20
None
5
45
10
77
15
100
80
15
aReaction conditions: 4‐nitroanisole (1 mmol), triphenyltin chloride (0.35 mmol), sulfur (1.5 mmol), NiFe2O4 (15 mol%), KF (3 mmol), K2CO3 (4 mmol) and
solvent (3 ml).
TABLE 6 Synthesis of phenylaryl sulfides from reaction of nitroarenes with triphenyltin chloride using S8 catalysed by NiFe2O4 MNPs in
PEG200a
Entry
ArNO2
Product
Time (h)
Isolated yield (%)
1
13
92
2
20
92
3
4
5
18
8
88
84
93
10
6
9
89
aGeneral procedure: nitroarene (1 mmol), triphenyltin chloride (0.35 mmol), S8 (1.5 mmol), NiFe2O4 (15 mol%), KF (3 mmol), K2CO3 (4 mmol), PEG200 (3 ml).

8 of 12
FARZIN ET AL.
with triphenyltin chloride are summarized in Table 2. It
was found that aryl halides with electron‐withdrawing
groups reacted more quickly than those with electron‐
releasing groups (Table 2, entries 4 and 5). The steric hin-
drance effect of aryl halides upon the rate of the reactions
and 9). No reaction occurred in the absence of Bu4NOH
in water (Table 3, entry 11). Various bases such as KOH,
K2CO3 and Et3N were also examined (Table 3, entries
12–14), and the best result was obtained using NaOH
(Table 3, entry 3).
was evident (Table 2, entries
6
and 7). The
Under the optimized conditions (Table 3, entry 3), the
cross‐coupling reaction of structurally diverse aryl halides
with arylboronic acids was studied (Table 4). The reac-
tions proceeded well to produce the corresponding diaryl
sulfides in moderate to excellent yields (Table 4).
Arylboronic acids containing electron‐donating groups
showed less reactivity (Table 4, entries 1–22).
To check the leaching of metal from the NiFe2O4
MNPs, a hot filtration test was performed for the synthe-
sis of diphenyl sulfide from iodobenzene, phenylboronic
acid and S8 in the presence of NiFe2O4 MNPs under opti-
mized reaction conditions. The catalyst was removed
using an external magnet from the reaction mixture after
3 h under hot conditions and the mixture was allowed to
react further for 14 h. The GC yield of the product at this
stage (3 h) was 50%. After 14 h, there was no significant
increase in the yield of the product. This study clearly
demonstrated that there was no significant amount of
leaching.
For many catalytic processes, the ability to easily recy-
cle the catalyst is highly desirable. Thus, the recovery and
recyclability of the NiFe2O4 MNPs were studied in the
carbon–sulfur coupling reaction of iodobenzene with
phenylboronic acid or triphenyltin chloride. After the
first run, the catalyst was separated easily with the appli-
cation of an external magnetic field, washed with diethyl
ether, dried under vacuum and subjected to the next run.
The recycled catalyst was used for five runs without any
significant loss of activity (Figure 1).
chemoselectivity of the presented protocol was investi-
gated for the reaction of 1‐bromo‐4‐chlorobenzene as a
dihalogenated aryl halide; the bromide showed more
reactivity (Table 2, entry 9). Aryl chlorides which are rel-
atively unreactive substrates were converted into the cor-
responding phenylaryl sulfides in excellent yields under
the same reaction conditions (Table 2, entries 10 and 11).
In continuation of our studies of thioetherification of
aryl halides by activating the C─X bond, we studied the
possibility of the synthesis of unsymmetric diaryl sulfides
using arylboronic acid as coupling partner in the pres-
ence of S8 and a catalytic amount of a NiFe2O4 MNPs.
For this aim, the reaction between iodobenzene and
phenylboronic acid in the presence S8 was selected as a
model reaction. We first conducted the reaction in the
presence of NiFe2O4 MNPs, S8, NaOH and Bu4NOH in
water at 40 °C. Under these conditions, the desired prod-
uct was obtained in 40% yield (Table 3, entry 1). By
increasing the reaction temperature to 80 °C, the com-
plete conversion of iodobenzene into the product was
observed (Table 3, entry 3). To investigate the effect of
the catalyst, the model reaction was performed in the
absence of NiFe2O4 MNPs, the result indicating that the
reaction did not proceed (Table 3, entry 4). Various
solvents such as PEG400, DMF, DMSO, toluene and
EtOH were investigated (Table 3, entries 6–10). It was
observed that DMF and PEG200 are also the most effec-
tive even in the absence of nBu4NOH (Table 3, entries 7
TABLE 7 Optimization of reaction conditions for reaction of nitrobenzene with phenylboronic acida
Entry
Solvent
Base
Catalyst (mol%)
Temp. (°C)
GC yield (%)
1
2
3
4
5
6
7
8
9
PEG200
DMF
NaOH
NaOH
Cs2CO3
NaOtBu
NaOH
NaOH
NaOH
NaOH
NaOH
20
20
20
20
None
5
110
110
110
110
110
110
110
110
100
100
100
15
PEG200
PEG
100
—
PEG200
PEG200
PEG200
PEG200
PEG200
55
10
15
20
79
85
75
aReaction conditions: nitrobenzene (1 mmol), phenylboronic acid (1.1 mmol), S8 (1.5 mmol), NiFe2O4 (20 mol%), base (4 mmol) and solvent (3 ml).

FARZIN ET AL.
9 of 12
a
TABLE 8 C─S bond formation of nitroarenes with arylboronic acid for synthesis of unsymmetric sulfides using S8 catalysed by NiFe2O4
Entry
ArNO2
ArB (OH)2
Product
Time (h)
Yield (%)
1
20
87
2
25
77
3
4
30
38
80
85
5
6
26
34
80
75
7
8
11
12
92
92
9
13
15
77b
88b
10
11
12
13
15
85b
85b
aReaction conditions: nitroarene (1 mmol), arylboronic acid (1.1 mmol), NiFe2O4 (20 mol%), S8 (1.5 mmol), NaOH (4 mmol), PEG200 (2 ml), 110 °C.
bReaction carried out in the presence of NaOtBu as base.

10 of 12
FARZIN ET AL.
(1.1 mmol) in the presence of 1.5 mmol of S8, 15 mol%
of NiFe2O4 MNPs and 4 mmol of NaOH in PEG200 at
110 °C. Under these conditions, the desired product
was obtained in a GC yield of 100% (Table 7, entry 1).
A similar result was observed when DMF was used
instead of PEG as solvent (Table 7, entry 2). Only 15%
of diphenyl sulfide was obtained when NaOH was
replaced with Cs2CO3 (Table 7, entry 3). NaOtBu was
also a suitable base for this reaction (Table 7, entry 4).
When the amount of NiFe2O4 MNPs was reduced, the
GC yield decreased (Table 7, entries 5–8). By decreasing
the reaction temperature to 100 °C, a lower yield was
obtained (Table 7, entry 9).
In order to generalize the scope of the reaction, differ-
ent types of nitroarenes bearing both electron‐donating
groups (Table 8, entries 3–6) and electron‐withdrawing
groups (Table 8, entries 7–12) were subjected to reaction
with arylboronic acid under the optimized reaction condi-
tions. The reactions proceeded well to produce the corre-
sponding diaryl sulfides in moderate to excellent yields. It
was observed that nitroarenes with electron‐withdrawing
groups show greater activities than those having electron‐
donating groups (Table 8, entries 2–12). Likewise,
arylboronic acids containing electron‐donating groups
showed less reactivity (Table 8, entries 1–12).
3.2 | Catalytic application of NiFe2O4
MNPs in Synthesis of Sulfides using
Reaction of Nitroarenes with Triphenyltin
Chloride or Arylboronic Acids in Presence
of S8
There are some disadvantages associated with the use of
aryl halides as coupling partners, which are generally
environmental pollutants and their preparation is often
laborious when parent aryl halides are used as starting
materials. Hence, recently, nitroarenes have been used as
an alternative electrophilic coupling partner for carbon–
carbon[23] and carbon–heteroatom bond formation.[24]
Very recently, we reported the synthesis of unsymmetric
sulfides from cross‐coupling reaction of triphenyltin chlo-
ride or arylboronic acids with nitroarenes in the presence
of S8 catalysed by Cu salts.[20c] Although that report repre-
sents considerable progress in the field of synthesis of sul-
fides, the main disadvantage of these methods is using
homogeneous catalysts that leads to contamination of
products with transition metal that is not favourable from
a synthetic point of view especially in medicinal synthesis.
In order to minimize catalyst contamination of products, a
good strategy is using NiFe2O4 MNPs as a magnetically
reusable heterogeneous catalyst.
The reaction of 4‐nitroanisole with triphenyltin chlo-
ride was chosen as a model reaction. Inspired by previous
results,[20c] we conducted the reaction in the presence of
S8/KF system as a source of sulfur, NiFe2O4 MNPs as a
catalyst and K2CO3 as a base in DMF at 110 °C. Under
these conditions, the desired product was obtained in
100% yield (Table 5, entry 1). PEG200 was also an effec-
tive solvent for the reaction (Table 5, entry 2). The
amount of catalyst was optimized (Table 5, entries 3–6).
The reaction failed in the absence of the catalyst
(Table 5, entry 3). When the reaction temperature was
decreased to 100 °C, the desired product was obtained
in a yield of 80% (Table 5, entry 7).
The recyclability of the catalyst was examined for the
cross‐coupling reaction of 4‐nitroanisole with triphenyltin
chloride under the aforementioned optimized reaction
conditions (Figure 2). As shown in Figure 2, the catalyst
can be recycled up to five times with little loss of activity.
Such slight loss may be due to the inherent tendency of
agglomeration of the MNPs in each exposure and poison-
ing of the catalyst after the fifth cycle.
To verify that the size and morphology of the nano-
particles were not altered during the process, SEM images
of the recovered MNPs were runned after the second
cycle (Figure 3a) and fifth cycle (Figure 3b). According
Under the optimized conditions (Table 5, entry 6), we
studied the coupling reaction of various nitroarenes with
triphenyltin chloride in the presence of KF/S8 and
NiFe2O4 MNPs (Table 6). As is evident, the expected
phenylaryl sulfides were obtained in good to high yields.
It was found that nitroarenes with electron‐withdrawing
groups reacted faster than those having electron‐releasing
groups (Table 6, entries 1–6).
In order to expand these methods, we became inter-
ested in studying the possibility for the synthesis of
unsymmetric diaryl sulfides using the reaction between
nitroarenes, arylboronic acid and S8 in the presence of a
catalytic amount of NiFe2O4 MNPs. Inspired by the suc-
cessful results discussed above, we conducted the reac-
tion of phenylboronic acid (1 mmol) and nitrobenzene
FIGURE 2 Recycling experiment of NiFe2O4 MNPs in the
reaction of 4‐nitroanisole with triphenyltin chloride under
optimized reaction conditions (Table 6, entry 2)

FARZIN ET AL.
11 of 12
SCHEME 1 Proposed mechanism
to those having electron‐donating groups) and based on
previous studies of application of NiFe2O4 as a source of
Ni (II) in organic reactions[18,19] and reported mecha-
nisms for C─S bond formation reactions using ArB
(OH)2/S8 as thiolating agent, ArNO2 as coupling partner
in cross‐coupling reactions and transition metal salts as
catalyst,[20,24] a mechanism is proposed as depicted in
Scheme 1. We believe that the reaction involves a hetero-
geneous process and the catalysis may occur on the sur-
face of the NiFe2O4 MNPs. It is hypothesized that S8
reacts with NaOH to produce sodium disulfide.[16a] Then,
stable NiS is formed from the reaction of sodium disulfide
with NiFe2O4 MNPs. In the next step, NiS reacts with
arylboronic acid via oxidative addition reaction to give
intermediate I which subsequently converts to intermedi-
ate II. Intermediate II reacts with nitroarene via C─N
bond cleavage to provide the key intermediate III. The
desired product may be obtained from reductive elimina-
tion of the key intermediate III.
4 | CONCLUSIONS
We have developed efficient, simple and mild methods
for C─S bond formation via cross‐coupling reaction of
aryl halides with arylboronic acid or triphenyltin chloride
in the presence of S8 as a sulfur surrogate and NiFe2O4
MNPs as magnetically reusable nanocatalyst in water as
a green solvent. Moreover, we synthesized unsymmetric
diaryl sulfides via cross‐coupling reaction of triphenyltin
chloride or arylboronic acid with nitroarenes as the effec-
tive starting materials using S8 and NiFe2O4 MNPs.
Important features of these procedures are as follows:
FIGURE 3 SEM images of recovered NiFe2O4 MNPs after (a)
second and (b) fifth runs of the C─S bond formation reaction in
the reaction of iodobenzene with triphenyltin chloride
1. The catalyst was easily prepared from commercially
available and cheap starting materials, rapidly sepa-
rated using an appropriate external magnet and
reused several times with little loss of activity.
2. Using a commercially available, inexpensive, easy‐
to‐handle and chemically stable sulfur source and
starting materials.
to these images, morphology and dispersity of the nano-
particles were unchanged during the process.
On the basis of our observations (no significant
amount of leaching and enhanced reactivity of
nitroarenes with electron‐withdrawing groups compared

12 of 12
FARZIN ET AL.
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ACKNOWLEDGEMENT
We gratefully acknowledge financial support of this
research by the University of Kurdistan.
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ORCID
Amin Rostami http://orcid.org/0000-0001-8195-8963
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SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of the
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How to cite this article: Farzin S, Rahimi A,
Amiri K, Rostami A, Rostami A. Synthesis of diaryl
sulfides via nickel ferrite‐catalysed C─S bond
formation in green media. Appl Organometal
Chem. 2018;32:e4409. https://doi.org/10.1002/
aoc.4409
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