Regioselective Ortho‐C–H sulfenylation of free phenols catalyzed by Co(II)-immobilized on silica-coated magnetic nanoparticles

Article abstract of DOI:10.1016/j.mcat.2020.110772

Fe₃O₄?SiO₂-UT?Co^II is prepared by the silica-coated magnetic nanoparticles, urea-triazole, and CoCl₂. This organic-inorganic hybride composite showed a good to excellent catalytic activity toward regioselective ortho-sulfenylation of free phenols and naphthols using pivalic anhydride as a directing group, also K₂S₂O₈ and PPh₃ were employed as oxidant and additive respectively. The newly synthesized catalyst was fully characterized by using different techniques such as FT-IR, TGA, DTG, TEM, SEM, EDS, ICP and VSM analyses. The competitive price, accessibility and lower toxicity of cobalt compared to expensive transition metals using for C–H bond activation and functionalization constitute precious advantages for this method. Moreover, this heterogeneous catalyst could be magnetically recovered and reused without significant loss of its catalytic activity after five cycles.

Full text of DOI:10.1016/j.mcat.2020.110772

MolecularCatalysisxxx(xxxx)xxxx
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Regioselective Ortho‐CeH sulfenylation of free phenols catalyzed by Co(II)-
immobilized on silica-coated magnetic nanoparticles
Sepideh Khaefa,b, Abed Rostamic, Vahid Khakyzadehd,*, Mohammad Ali Zolfigolb,
Avat Arman Taherpoura, Meysam Yarieb
a Department of Organic Chemistry, Faculty of Chemistry, Razi University, Kermanshah, Iran
b Department of Organic Chemistry, Faculty of Chemistry, Bu Ali Sina University, Hamedan, Iran
c Vice Chancellor for Food and Drug, Kurdistan University of Medical Sciences, Sanandaj, Iran
d Department of Chemistry, K. N. Toosi University of Technology, P.O. Tehran, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords:
Fe3O4@SiO2-UT@CoII is prepared by the silica-coated magnetic nanoparticles, urea-triazole, and CoCl2. This
organic-inorganic hybride composite showed a good to excellent catalytic activity toward regioselective ortho-
sulfenylation of free phenols and naphthols using pivalic anhydride as a directing group, also K2S2O8 and PPh3
were employed as oxidant and additive respectively. The newly synthesized catalyst was fully characterized by
using different techniques such as FT-IR, TGA, DTG, TEM, SEM, EDS, ICP and VSM analyses. The competitive
price, accessibility and lower toxicity of cobalt compared to expensive transition metals using for CeH bond
activation and functionalization constitute precious advantages for this method. Moreover, this heterogeneous
catalyst could be magnetically recovered and reused without significant loss of its catalytic activity after five
cycles.
Regioselective
CeH sulfenylation
Phenol
2-sulfenylphenol
Cobalt (II)
Introduction
one of the most powerful protocols have attracted considerable atten-
tion [29,30]. Traditionally, aryl sulfenyl phenols have been synthesized
The CeH functionalization processes play an important role in or-
ganic chemistry by using transition metals due to its versatile and ef-
ficient applications in the synthesis of aryl-containing chemicals and
resolve the problems of prefunctionalization with halogens or reactivity
troubles with lighter halogens [1–5]. These processes can significantly
simplify the synthesis of pharmaceuticals, natural products, polymers,
and feedstock commodity chemicals [6–8]. Among CeH functionali-
zation processes, CeH functionalization of phenols is an essential be-
cause these compounds are common structural motifs found in many
bioactive natural products and medicine [9–12]. Typically, phenols are
modified with an appended directing group including silyl [13], acyl
[14], 2-pyridyl [15], carboxylate [16], silanol [17], carbamat [17],
pyridyl/pyrimidyl [18–24] and ester groups [25] in order to promote
regioselective ortho- CeH bond activation and overcomes their poor
directing abilities. However, noble transition metals such as palladium
and rhodium are essential in most cases.
from cross-coupling reaction of 2-halophenols with thiols in the pre-
sence of transition metals (Scheme 1, path A) [31–34]. Takaki and co-
workers have reported an alternative method for the sulfenylation of
phenols using a stoichiometric amount of FeCl3 under an oxygen at-
mosphere (Scheme 1, path B) [35]. Migita-type cross-coupling between
aryl halides and aryl thiols followed by selective hydroxylation of aryl
thioethers were applied for the synthesis of arylsulfenylphenols
(Scheme 1, path C) [36]. Cyclohexanone has been used as a substrate
for the synthesis of arylsulfenylphenols through successive dehy-
drogenation of two saturated carbon-carbon bonds of the six-membered
ring by using molecular oxygen as a hydrogen acceptor (Scheme 1,
path D) [37–39].
Numerous methods have been recently introduced for the sulfeny-
lation of 2-naphthols. At first, iodine was introduced as a catalyst by
Huang for the thiolation of aryl 2-naphthols with arylsulfonyl hy-
drazides via CeH bond functionalization (Scheme 1, path E) [40], Then
the application of iodine as a catalyst has been developed for the direct
sulfenylation of 2-naphthols with aryl thiols in DMSO solvent (Scheme
1, path F) [41]. Afterward, Xiao et al. reported the reaction of sodium
sulfinates with aryl 2-naphthols in the presence of iodine catalyst for
A derivative aryl sulfenyl phenols exist in a diversity of natural
products and medicines. For example; 2-sulfanylphenols were applied
as a drug for the treatment of cancer, HIV, heart disease, allergy, and
obesity [26–28]. Hence, regioselective ortho-sulfenylation of phenol as
⁎ Corresponding author.
E-mail address: v.khakyzadeh@kntu.ac.ir (V. Khakyzadeh).
https://doi.org/10.1016/j.mcat.2020.110772
Received 8 November 2019; Received in revised form 9 January 2020; Accepted 9 January 2020
2468-8231/©2020ElsevierB.V.Allrightsreserved.
Pleasecitethisarticleas:SepidehKhaef,etal.,MolecularCatalysis,https://doi.org/10.1016/j.mcat.2020.110772

S. Khaef, et al.
MolecularCatalysisxxx(xxxx)xxxx
Scheme 1. Previous strategies toward synthesis of aryl sulfenyl phenol/naphthol.
the synthesis of arylsulfenylnaphtols (Scheme 1, path G) [42]. Sulfe-
nylation of aryl 2-naphthols with iodohydrocarbons and sulfur powder
in the presence of a copper-based catalyst was performed for the
synthesis of arylsulfenylnaphtols (Scheme 1, Path H) [43].
dedicate a useful, clean and simple protocol for the synthesis of sulfe-
nylphenols/naphtols via Fe3O4@SiO2-UT@CoII catalyzed CHe bond
activation and subsequent functionalization of phenols/naphthols with
thiols in the presence of pivalic anhydride as a directing group, K2S2O8
and PPh3 as oxidant and additive respectively (Scheme 2, path v).
Employing heterogeneous catalysts has numerous advantages for
fine chemical synthesis. They can undoubtedly exhibit high specific
surface area to volume ratio, which heightens the contact between re-
actants and catalyst support and consequently raises the catalytic ac-
tivity and easily separate out of the reaction mixture [44–46]. In this
regard, magnetically separable catalysts have attracted a great deal of
attention. These elegant alternatives can improve the efficiency of the
catalyst separation from the reaction mixture upon reaction completion
by applying an external magnet [47–51]. Also, magnetic nanoparticles
(MNPs) can be applied as valuable structures for the immobilization of
both inorganic and organic catalytic active molecules [52–58]. Natural
and biochemical compounds like urea/thiourea can be used as a ligand
for MNPs. As a part of our continuous efforts for the synthesis of aryl
sulfides [59–67] and arylsulfenyphenols (Scheme 2, Path I) [68], we
Results and discussion
In the beginning, Fe3O4 nanoparticles were prepared by the
methods of previous works [69]. Then, the surface Fe3O4 nanoparticles
were modified by a layer of SiO2 through the reaction with tetra-
ethylorthosilicate (TEOS) [34]. In the Following step, 1 g of the Fe3O4@
SiO2 and urea-based ligand (5 mmol) in 80 ml of dry toluene were
refluxed under a nitrogen atmosphere for 24 h. The synthesized nano-
particles (Fe3O4@SiO2@ (CH2)3-Urea-Triazole) were separated and
washed thoroughly with n-hexane and air-dried. Finally, CoCl2.6H2O (5
mmol, 1.190 g) was added to a mixture of 1 g of the magnetic nano-
particles (Fe3O4@SiO2@ (CH2)3-Urea-Triazole) in ethanol and refluxed
Scheme 2. Strategies for the sulfenylation of ortho-phenols/naphthols situation and our work.
2

S. Khaef, et al.
MolecularCatalysisxxx(xxxx)xxxx
Scheme 3. Synthesis of Fe3O4@SiO2@ (CH2)3-Urea-Triazole@CoCl2.
for 24 h. Finally, the desired catalyst was separated and washed thor-
oughly with ethanol and air-dried (Scheme 3). The structure of catalyst
was fully identified by FT-IR, TGA, DTG, TEM, SEM, EDS, ICP, and VSM
analyses.
Fig. 1 investigated the FT-IR spectra of the applied materials for the
synthesis of the desired catalyst in a comparative mode. The peak ap-
peared at 1650 cm−1 can be described to the stretching vibration mode
of C]O that affirmed existence of urea moiety within the structure of
catalyst. The broad peak discerned at around 2900–3600 cm−1 can be
ascribed to the overlapping of NeH and un-coated OeH stretching
bands.
As depicted in Fig. 2, the EDX analysis verified all expected elements
which exist within the structure of the novel prepared magnetically
recoverable catalyst. These elements are iron, silicon, oxygen, carbon,
Fig. 2. EDX analysis of the novel prepared catalyst (Fe3O4@SiO2-UT@CoII).
nitrogen, and cobalt.
The morphology of the prepared catalyst was also investigated by
using SEM analysis. The resulting images illustrated in Fig. 3 (a–b)
shows the nanosized structure of the prepared catalyst. Particle size
distribution histogram based on SEM images is shown in Fig. 4. Ac-
cording to this histogram, the most particle sizes are 20−25 nm and the
average size of the catalyst particles is almost 22 nm. The average size
of the catalyst particles is almost 23 nm. Also, in order to study the
morphology and size of the catalyst in more detail, TEM analysis was
also used. The resulting images are portrayed in Fig. 3 (c–d). These
images confirmed the obtained data from SEM images and the core-
shell structure of nanoparticles.
The thermal behavior of the prepared catalyst was investigated by
using TG/DTG analyses. The resulting plots are illustrated in Fig. 5. The
weight loss from room temperature to around 150 °C is related to the
Fig. 1. FT-IR spectra of the ligand, Fe3O4 (A), Fe3O4@SiO2 (B), Fe3O4@
SiO2@(CH2)3-Urea-Triazole (C) and the Catalyst (Fe3O4@SiO2-UT@CoII).
3

S. Khaef, et al.
MolecularCatalysisxxx(xxxx)xxxx
Fig. 3. SEM images (low magnification (a)- high magnification (b)) and TEM images (high magnification c–d) of the novel prepared catalyst (Fe3O4@SiO2-UT@CoII).
desired catalyst were explored by VSM analysis. The resulting magnetic
curves were illustrated in Fig. 6. The achieved data indicated that the
modification of the surface of Fe3O4 nanoparticles leads to the reducing
of magnetic properties of each step. The data predict high magnetic
properties (around 27 emu/g) for desired catalyst which verified the
facile separation of the catalyst from the reaction mixture.
SEM of the catalyst after a cycle of reaction which shows in Fig. 7,
portrays that the average size of the catalyst particles remains almost 18
nm after the reaction.
The amount of Co species in the prepared catalyst was investigated
by inductively coupled plasma (ICP) analysis (Table 1). ICP data
showed that the Co content in Fe3O4@SiO2-UT@CoII compound was
2.77 × 10−4 mol gr−1 (row 1). ICP Mass analysis of recovered catalyst
Fig. 4. Particle size distribution histogram.
after a cycle of the reaction (row 2), revealed that Co leaching from the
surface of the catalyst was about 4.94 %, this means that synthesized
catalyst has stability in the reaction conditions.
To further study on the metal leaching of the synthesized catalyst,
hot filtration test was performed. The reaction of p-cresol with thio-
phenol was stopped after 10 h, and then the catalyst was separated by
an external magnet from the reaction mixture. While the solution was
still hot, the reaction mixture investigated by GC after 20 h. The results
indicated that the reaction didn’t progress after the separation of cat-
alyst.
evaporation of the physically absorbed solvent during the catalyst
preparation pathway. The catalyst shows high thermal stability up to
300 °C. At this stage the weight losses are beginning which related to
the decomposition of the organic-inorganic tags anchored to the surface
of Fe3O4@SiO2 nanoparticles. 80 % residual weight up to 600 °C shows
thermal stability of Fe3O4 and SiO2.
The magnetic properties of all prepared material in the way of the
4

S. Khaef, et al.
MolecularCatalysisxxx(xxxx)xxxx
Fig. 5. TG/DTG plots of the novel prepared catalyst (Fe3O4@SiO2-UT@CoII).
reaction (Table 2, entries 2–5). Among of them, Cs2CO3 was found to be
the most effective base for the above said reaction (Table 2, entry 5).
When the amount of catalyst was reduced, the yield of desired product
decreased (Table 2, entries 6). The reaction failed in the absence of a
catalyst (Table 2, entries 7). In order to study the effect of the solvents,
we have conducted the reaction in PEG200, DMF, CH3CN, and C2H4Cl2
(DCE), but none of them displayed positive effect on the yield of pro-
duct (Table 2, entries 8–11). No yield was observed when the reaction
was carried out under argon atmosphere (Table 2, entry 12). Employing
molecular O2 as an oxidant had not a good effect on the efficiency of
reaction (Table 2, entry 13). We used other oxidants for improving the
yield. When 5 mol % of K2S2O3 was added as oxidant to the reaction
mixture, the GC yield of desired product was obtained in 79 % (Table 2,
entry 14). Addition of AgCl as an oxidant to the model reaction mixture
was not effective (Table 2, entry 15). Various additives such as TBAB
(tetrabutylammonium
bromide),
TBAC
(tetrabutylammonium
chloride), LiBr and PPh3 were screened to boost the yield of reaction
(Table 2, entry 16–19). Surprisingly, the addition of PPh3 to the reac-
tion mixture caused a significantly enhanced yield, which might be due
to its strong coordination effect with cobalt (Table 2, entry 19). To show
the high activity of Fe3O4@SiO2-UT@CoII in ortho-regioselective sul-
fenylation of phenols and naphtols, CoFe2O4 MNPs and CoCl2 were also
tested as catalyst for the mentioned reaction (Table 2, entries 20–21)
that the lower yield was obtained in the presence of them.
Fig. 6. VSM curves Fe3O4 (A), Fe3O4@SiO2 (B), Fe3O4@SiO2@ (CH2)3-Urea-
Triazole (C), Catalyst: Fe3O4@SiO2@ (CH2)3-Urea-Triazole@CoCl2.
After preparation and characterization of the Fe3O4@SiO2-UT@CoII,
we centered on design and optimized a condition reaction for CeH
bond cleavage of phenols and subsequent CeS bond formation in a
simple and efficient condition (Table 2). Initially, a mixture of p-cresol
(1a), K2CO3, dimethyl sulfide (DMSO) (2 mL), and pivalic anhydride
were stirred at room temperature for 2 h. Then, one-pot synthesis of
sulfenylphenols/naphtols were investigated by adding thiophenol (2a),
oxidant, additive, base, Fe3O4@SiO2-UT@CoII in different reaction
conditions at 90 °C under air atmosphere. Toward this aim, the reaction
was performed in the presence of a catalytic amount of catalyst (0.06 g)
and K2CO3 as a base in DMSO solvent (Table2, entry 1). Under these
conditions, desired product was obtained in only 20 % yield. For im-
proving the yield of the reaction, we used different bases such as KOH,
NaOtBu, 1,4‐diazabicyclo[2.2.2]octane (DABCO) and Cs2CO3 in this
With the optimal conditions determined (Table 2, entry 19), the
efficiency and applicability of Fe3O4@SiO2-UT@CoII were explored for
the synthesis of 2-(arylthio) phenols derivatives via ortho-regioselective
sulfenylation of phenols with aryl thiols. The results are illustrated in
the Table 3. We noticed electron-donating groups on phenols drama-
tically promoted the reaction and gave 2-sulfenylphenols in high yields
due to the fact the electron-donating groups to increase the electron
density of the phenol ring (Table 3, 3b–3i), whereas electron-with-
drawing groups slightly inhibited the transformation and moderate to
low yields obtained in the reactions (3j-3b). There seems to be little
effect of the substituent position (ortho, meta or para) of the phenol ring
5

S. Khaef, et al.
MolecularCatalysisxxx(xxxx)xxxx
Fig. 7. SEM of the Fe3O4@SiO2-UT@CoII after a cycle of reaction.
Table 1
excellent yields. On the basis of the obtained results in the case of
electron-rich and electron-poor aryl thiols, it was found that in the
presence of electron-donating groups (4bb) the yield of reaction more
increased than electron-withdrawing ones (4bc and 4bd). We have also
investigated the possibility of synthesis of alkylthionaphtalen-2-ol using
the reaction of alkyl thiols with 2-naphtol. Aliphatic thiols including 1-
octanethiol, benzyl mercaptan, and cyclohexanethiol as sulfenylating
agents were also performed successfully under present reaction condi-
tions (4be-4bh).
ICP Mass analysis of the Fe3O4@SiO2-UT@CoII.
Row
Material
Object
Result (wt. %)
1
Fe3O4@SiO2-UT@CoII
Co
Co
1.6334
1.5527
2a
Fe3O4@SiO2-UT@CoII
a
(recovered catalyst).
on the reaction yield. For example, when the methyl was located at
ortho (3b), meta (3d) and para (3e) position on the phenol ring, the
corresponding products were obtained in 80 %, 83 %, and 95 % yields,
respectively. In contrast, the pH substituent on phenol ring at an ortho
(3c) and para (3 g) caused that the reaction yield partially decreased.
These obtained data may be due to the phenyl rings withdrawing effect.
Surprisingly, the compatibility of our catalyst with CeH bonds allows
us to carry out the chemoselective sulfenylation of halophenols such as
4-Cl (3 j), 4-Br (3k) and 4-F-phenol (3 l) with thiophenol without
changing CeX (halogen) bond. A strong electron-withdrawing group
(NeO2) on para position of phenol suppressed coupling reaction (3 m).
Likewise, aryl thiols containing electron-rich group (3n, 3q) showed
more reactivity than electron-poor group (3o, 3p, 3 r and 3 s). More-
over, dimethyl phenol smoothly participated in the coupling with 4-me-
thiophenol and furnished the corresponding products in excellent yield
(3 t).
Control experiments were carried out to gain preliminary insights
into the mechanism of the catalytic procedure. In this regard, we ex-
plore the roles of pivalic anhydride, O2, and catalyst on the path of
reaction. Under the standard conditions without the addition of pivalic
anhydride, phenol (1a) did not convert to the desired product (3a),
leaving the starting material intact and disulfide (4a) obtained in 10 %
yield (Scheme 4a).
The reaction of phenol ester (instead of the phenol/ pivalic system)
with thiophenol (2a) in the reaction, desired product (3a) obtained
with 73 % yield (Scheme 4b).
In the presence of N2 gas as without oxygen condition was not found
any product (Scheme 4c). Using disulfide (4a) instead of thiophenol
(2a), the product 3a was formed in only 5 % yield under the standard
reaction condition (Scheme 4d). In a control experiment in the absence
of phenol substrates, thiophenol (2a) underwent dimerization to afford
disulfide (4a) in 5 % yield (Scheme 4e).
To show more synthetic applicability of the described method,
generality, scop, limitations and approving the potentials of our catalyst
for the sulfenylation of phenols, we have investigated the possibility of
synthesis of aryl/alkyl sulfenylnaphtols using the reaction of aryl/alkyl
thiols with 1 and 2-naphtol under the optimized reaction conditions
(Table 2, entry 19).
According to our above control experiments and related references,
a plausible reaction pathway for the reaction of thiols with phenols and
naphtols in the presence of pivalic anhydride as directing group and
Fe3O4@SiO2-UT@CoII as a catalyst has been illustrated in Scheme 5. It
is known that phenol reacts with pivalic anhydride to produce phenolic
ester (I) [59–67]. Then, cobalt coordinate to oxygen atom (II) leading
to a directed ortho-metalation by a radical pathway and provide the key
intermediate III [14,59]. Intermediate III, furnishes the IV via ar-
omatization and Cobalt reduction in the presence of K2S2O8 (possible
reactions were proposed in the red circle). In continue, the intermediate
IV reacts with the thiol to generate V, which undergoes reductive
elimination and RS immigration gives VI. Finally, the desired product
The results in the Table 4 demonstrate that most of the aryl thiols
underwent smooth transformations to afford the corresponding 1-aryl
sulfenylnaphthol in good to excellent yields (3ba- 3bd). We further
tested the described method with naphthalen-2-ol under the optimized
reaction conditions. Encouragingly, the corresponding ar-
ylthiolnaphthalen-2-ol derivatives (4ba-4bd) were obtained in
6

S. Khaef, et al.
MolecularCatalysisxxx(xxxx)xxxx
Table 2
Optimization of catalyst, base, solvent, temperature, and additives.
Entry
Solvent
Base
Additive (5 mol %)
Oxidant (5 mol %)
GC Yield (%)
1
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
PEG
K2CO3
–
air
20
5
2
KOH
–
air
3
KOtBu
–
air
55
10
60
45b
0c
4
DABCO
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
–
air
5
–
air
6
–
air
7
–
air
8
–
air
0
9
DMF
–
air
38
0
10
11
12
13
14
15
16
17
18
19
20
21
CH3CN
C2H4Cl2
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
–
air
–
air
10
0d
–
Ar
–
O2
40e
79
45
90
87
80
95
60f
75g
–
K2S2O3
AgCl
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
–
TBAB
TBAC
LiBr
PPh3
PPh3
PPh3
[a]Condition: 1a (1 mmol), 2a (1.2 mmol), catalyst (0.06 g, 0.166 mmol), Cs2CO3 (3 mmol), DMSO (2 mL), K2S2O8 (5 mol %), PPh3 (5 mol %), 90 oC, 24 h.
b
c
d
e
f
g
The reaction carried out in the presence of 0.04 g of the catalyst.
Without catalyst.
Under argon atmosphier.
Under O2 atmosphier.
CoFe2O4 (0.04 g) was used.
CoCl2 (10 mol%) was used.
results from VI and release fresh catalyst for a new reaction cycle.
The reusability of the synthesized nanomagnetic catalyst was in-
vestigated for CeS bond coupling via CeH bond activation reaction of
p-cresol with thiophenol for five runs under the optimized reaction
conditions. The data are depicted in Fig. 8. After completion of each
run, ethyl acetate was added to the reaction mixture for dissolving the
desired product, unreacted starting materials and separation of het-
erogenous nanomegnetic catalyst. Then the catalyst was separated from
the reaction mixture by using an external magnet, repeatedly it was
washed with ethyl acetate, dried and reused in the next run. The ob-
tained data show that the performance of the catalyst smoothly de-
creases after five sequential runs.
synthesis of various kinds of sulfides. Development of described method
for cross-coupling of phenols and/or arenes with sulfur agents in other
useful transformations is under investigation in our laboratory.
Experimental section
General information
All the chemicals/reagents were purchased from E. Merck,
Germany. Organic extract were dried over anhydrous sodium sulphate.
Solvents were removed in a rotary evaporator under reduce pressure.
Silica gel (60–120 mesh size) was used for the column chromatography.
Reactions were monitored by TLC on silica gel 60 F254 (0.25 mm). 13C
NMR spectra were reported in ppm relative to residual CHCl3 (77.16
ppm) and DMSO (39.52 ppm) that were obtained with 1H-decoupling
and described in terms of chemical shift (δ in ppm). Data for 1H-NMR
are described as following: chemical shift (δ in ppm), multiplicity (s,
singlet; d, doublet; t, triplet; q, quartet; quin, quintet; sx, sextet; m,
multiplet; app, apparent; br, broad signal), coupling constant (Hz), in-
tegration. NMR data were given in University of Isfahan (Bruker-400
MHz) and Mashhad University of Medical Sciences (Bruker–ultrashield-
300 MHz). CHNS analyses were recorded on an Agilent Leco-932 CHNS
instrument (EI) at Kurdistan University.
Conclusion
In conclusion, we have developed Fe3O4@SiO2-UT@CoII as new
magnetically catalytic system for the synthesis of 2-arylsulfenylphenol
from free-phenols, aryl/alkyl sulfides, and pivalic anhydride as a di-
recting group via CHe bond activation. Significant advantages of the
introduced system are as follows: (i) A one-pot synthesis approach,
which offers a more straightforward and practical method and (ii) the
use of cheap, commercially available, easy-to-handle and chemically
stable starting substances and catalyst. More applications regarding the
introduced system are under development. We think that the present
work can open up a new and promising insight for designing and
7

S. Khaef, et al.
MolecularCatalysisxxx(xxxx)xxxx
Table 3
Ortho-regioselective sulfenylation of phenols with aryl thiols in the presence of catalytic
amounts of Fe3O4@SiO2-UT@CoII as a catalyst.a.
a
ROH (1 mmol), ArSH (1.2 mmol), catalyst (0.06 g), Cs2CO3 (3 mmol), DMSO (2 mL),
K2S2O8 (5 mol%), PPh3(5 mol%), 90 °C, 24 h [b] Isolated Yield.
General procedure for the preparation the urea based ligand
CoCl2.6H2O (5 mmol, 1.190 g) Fe3O4@SiO2@ (CH2)3-Urea-Triazole (1
g) in ethanol reflux. The product was obtained by centrifugation and
then washed with C2H5OH (20 mL × 3). Finally, the obtained product
was dried at 60 °C under vacuum for 10 h and stored in a desiccator
(Scheme 3).
To a round bottom flask (250 mL), a mixture of triethoxy(3-iso-
cyanatopropyl)silane (5 mmol, 1.236 mL) and 3-amino-1H-1,2,4 tria-
zole (5.2 mmol, 0.437 g) was added and stirred magnetically under
solvent-free conditions at 60 °C for 6 h. After completion of the reac-
tion, n-hexane (50 mL) was added to the mixture reaction and filtered.
Then, n-hexane was evaporated and desired urea based ligand was
obtained as a colorless viscose oil which characterized by FT-IR and
NMR spectra. (Scheme 3)
General procedure for synthesis of 2-(aryl thio) phenols
A mixture of phenol (1 mmol), Pivalic anhydride (1.2 mmol), K2CO3
(2 mmol) and DMSO (2 mL) was stirred at room temperature for
20–120 min. Then, catalyst (0.06 g), Cs2CO3 (3 mmol), PPh3 (5 mol %),
K2S2O8 (5 mol %), thiophenol (1.2 mmol) and DMSO (2 ml) were added
to the mixture which was stirred at 90 °C for 24 h. After complete
conversion of phenol (TLC), HCl aq. (4.0 ml, 1 M) was added to the
reaction mixture. After that, the reaction mixture was cooled to room
temperature and the product was extracted with ethyl acetate (2 × 10
mL), while the catalyst was recovered under the assistance of a magnet
and then washed with C2H5OH. The combined organic extracts were
dried over anhydrous Na2SO4, and the solvent and volatiles were re-
moved under vacuum to give the crude product. Further purification
was performed by column chromatography on silica gel eluting with n-
Hexane/Dichloromethane (Table 2).
General procedure for the preparation of Co(ll)-Immobilized silica- based
magnetic nano catalyst
In the beginning, Fe3O4 nano particles was prepared by the methods
of previous works.69 Then, the surface of Fe3O4 nano particles was
modified by
a layer of SiO2 through the reaction with tetra-
ethylorthosilicate (TEOS).69 In the Following step, 1 g of the Fe3O4@
SiO2 and urea based ligand (5 mmol) in 80 ml of dry toluene were
refluxed under a nitrogen atmosphere in a 150 ml round-bottom flask
under mechanical stirring (600 rpm) for 24 h. Then, synthesized na-
noparticles (Fe3O4@SiO2@ (CH2)3-Urea-Triazole) were thoroughly
washed with n-hexane, and dried under vacuum oven for 10 h. The
reaction system was stirred for another 24 h upon the addition
8

S. Khaef, et al.
MolecularCatalysisxxx(xxxx)xxxx
Table 4
Sulfenylation of 1 and 2-naphtol with aryl/alkyl thiols using Fe3O4@SiO2-UT@CoII as a catalyst.a.
a
ROH (1 mmol), RSH (1.2 mmol), catalyst (0.06 g), KOtBu (3 mmol), DMSO (2 mL), K2S2O8 (5 mol
%), PPh3(5 mol%), 90 °C, 24 h [b] Isolated Yield.
Scheme 4. Control experiment.
9

S. Khaef, et al.
MolecularCatalysisxxx(xxxx)xxxx
Scheme 5. Proposed catalytic cycle for ortho-regioselective sulfenylation of phenols and naphtols.
the ethical approval of all relevant bodies and that such approvals are
acknowledged within the manuscript.
Authorship
The International Committee of Medical Journal Editors (ICMJE)
recommends that authorship be based on the following four criteria:
1 Substantial contributions to the conception or design of the work; or
the acquisition, analysis, or interpretation of data for the work; AND
2 Drafting the work or revising it critically for important intellectual
content; AND
3 Final approval of the version to be published; AND
4 Agreement to be accountable for all aspects of the work in ensuring
that questions related to the accuracy or integrity of any part of the
work are appropriately investigated and resolved.
Fig. 8. Reusability of the synthesized catalyst Fe3O4@SiO2-UT@CoII for five
reaction cycles.
Funding
All those designated as authors should meet all four criteria for
authorship, and all who meet the four criteria should be identified as
authors. For more information on authorship, please see http://www.
icmje.org/recommendations/browse/roles-and-responsibilities/
defining-the-role-of-authors-and-contributors.html#two.
All listed authors meet the ICMJE criteria. We attest that all authors
contributed significantly to the creation of this manuscript, each having
fulfilled criteria as established by the ICMJE
Funding was received for this work.
Intellectual property
We confirm that we have given due consideration to the protection
of intellectual property associated with this work and that there are no
impediments to publication, including the timing of publication, with
respect to intellectual property. In so doing we confirm that we have
followed the regulations of our institutions concerning intellectual
property.
We confirm that the manuscript has been read and approved by all
named authors.
We confirm that the order of authors listed in the manuscript has
been approved by all named authors.
Research ethics
Declaration of Competing Interest
We further confirm that any aspect of the work covered in this
manuscript that has involved human patients has been conducted with
No conflict of interest exists.
10

S. Khaef, et al.
MolecularCatalysisxxx(xxxx)xxxx
Acknowledgements
[28] G. Smith, G. Mikkelsen, J. Eskildsen, C. Bundgaard, Bioorg. Med. Chem. Lett. 16
(2006) 3981.
[29] H. Tian, C. Zhu, H. Yanga, H. Fu, Chem. Commun. 50 (2014) 8875.
[30] S.K.R. Parumala, R.K. Peddinti, Green Chem. 17 (2015) 4068.
[31] K. Swapna, S.N. Murthy, M.T. Jyothi, Y.V.D. Nageswar, Org. Biomol. Chem. 9
(2011) 5989.
We thank Bu-Ali Sina University, K. N. Toosi University of
Technology and Iran National Science Foundation (INSF) (Grant num-
bers: 98001912 and 95819785) for financial support to our research
group.
[32] M.-T. Lan, W.-Y. Wu, S.-H. Huang, K.-L. Luo, F.-Y. Tsai, RSC Adv. 1 (2011) 1751.
[33] Y. Feng, H. Wang, F. Sun, Y. Li, X. Fu, K. Jin, Tetrahedron 65 (2009) 9737.
[34] N. Taniguchi, J. Org. Chem. 69 (2004) 6904.
[35] K. Komeyama, K. Aihara, T. Kashihara, K. Takaki, Chem. Lett. 40 (2011) 1254.
[36] R. Xu, J.-P. Wan, H. Mao, Y. Pan, J. Am. Chem. Soc. 132 (2010) 15531.
[37] Y. Izawa, D. Pun, S.S. Stahl, Science 333 (2011) 209.
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mcat.2020.110772.
[38] T. Diao, S.S. Stahl, J. Am. Chem. Soc. 133 (2011) 14566.
[39] W. Ge, X. Zhu, Y. Wei, Adv. Synth. Catal. 355 (2013) 3014.
[40] X. Kang, R. Yan, G. Yu, X. Pang, X. Liu, X. Li, L. Xiang, G. Huang, J. Org. Chem. 79
(2014) 10605.
References
[41] S.K.R. Parumala, R.K. Peddinti, Green Chem. 17 (2015) 4068.
[42] F.H. Xiao, S.Q. Chen, J.X. Tian, H.W. Huang, Y.J. Liu, G.-J. Deng, Green Chem. 18
(2016) 1538.
[1] Q. Fan, S. Werner, J. Tschakert, D. Ebeling, A. Schirmeisen, G. Hilt, W. Hieringer,
J.M. Gottfried, J. Am. Chem. Soc. 140 (2018) 7526.
[43] F. Xiao, S. Chen, C. Li, H. Huang, G.J. Deng, Adv. Synth. Catal. 358 (2016) 3881.
[44] M.A. Zolfigol, V. Khakyzadeh, A.R. Moosavi-Zare, A. Rostami, A. Zare, N. Iranpoor,
M.H. Beyzavie, R. Luque, Green Chem. 15 (2013) 2132.
[2] D.S. Kim, W.J. Park, C.H. Jun, Chem. Rev. 117 (2017) 8977.
[3] P.B. Arockiam, C. Bruneau, P.H. Dixneuf, Chem. Rev. 112 (2012) 5879.
[4] M.T. Mihai, G.R. Genov, R.J. Phipps, Chem. Soc. Rev. 47 (2018) 149.
[5] S. Santoro, S.I. Kozhushkov, L. Ackermann, L. Vaccaro, Green Chem. 18 (2016)
3471.
[45] N. Koukabi, E. Kolvari, A. Khazaei, M.A. Zolfigol, B. Shirmardi-Shaghasemi,
H.R. Khavasi, Chem. Commun. 47 (2011) 9230.
[46] N. Koukabi, E. Kolvari, A. Khazaei, M.A. Zolfigol, B. Shirmardi-Shaghasemi,
B. Fasahati, Adv. Synth. Catal. 354 (2012) 2001.
[6] J. Wencel-Delord, F. Glorius, Nat. Chem. 5 (2013) 369.
[7] J. Yamaguchi, A.D. Yamaguchi, K. Itami, Angew. Chem. Int. Ed. 51 (2012) 8960.
[8] D.J. Schipper, K. Fagnou, Chem. Mater. 23 (2011) 1594.
[9] J.-L. Dai, N.-Q. Shao, J. Zhang, R.-P. Jia, D.-H. Wang, J. Am. Chem. Soc. 139 (2017)
12393.
[47] E. Rafiee, S. Eavani, Green Chem. 13 (2011) 2116.
[48] M.B. Gawande, P.S. Brancoa, R.S. Varma, Chem. Soc. Rev. 42 (2013) 3371.
[49] D. Wang, C. Deraedt, J. Ruiz, D. Astruc, Acc. Chem. Res. 48 (2015) 1871.
[50] W. Xie, C. Zhang, LWT-Food Sci Technol. 93 (2018) 71.
[51] M. Bilal, Y. Zhao, T. Rasheed, H.M.N. Iqbal, Int. J. Biol. 120 (2018) 2530.
[52] M. Choi, K. Na, J. Kim, Y. Sakamoto, O. Terasaki, R. Ryoo, Nature 416 (2009) 246.
[53] E. Nikolla, Y.R. Leshkov, M. Moliner, M.E. Davis, ACS Catal. 1 (2011) 408.
[54] S. Shayles, V. Schunemann, W.R. Thiel, Angew. Chem. Int. Ed. 49 (2010) 3428.
[55] D. Wang, D. Astruc, Chem. Rev. 114 (2014) 6949.
[10] P. Su, C. Fan, H. Yu, W. Wang, X. Jia, Q. Rao, C. Fu, D. Zhang, B. Huang, C. Pan,
A. Zheng, Y. Sun, Mol. Catal. 475 (2019) 110460.
[11] D.C. Fabry, M.A. Ronge, J. Zoller, M. Rueping, Angew. Chem. Int. Ed. 54 (2015)
2801.
[12] B. Xiao, T.-J. Gong, Z.-J. Liu, J.-H. Liu, D.-F. Luo, J. Xu, L. Liu, J. Am. Chem. Soc.
133 (2011) 9250.
[56] Z. Fathi, E. Doustkhah, S. Rostamnia, F. Darvishi, A. Ghodsi, Y. Ide, Int. J. Biol.
Macromol. 117 (2018) 218.
[13] C. Ma, P. Fang, T.-S. Mei, ACS Catal. 8 (2018) 7179.
[14] Y. Hua, P. Asgari, T. Avullala, J. Jeon, J. Am. Chem. Soc. 138 (2016) 7982.
[15] A. John, K.M. Nicholas, J. Org. Chem. 77 (2012) 5600.
[16] T.-J. Gong, B. Xiao, Z.-J. Liu, J. Wan, J. Xu, D.-F. Luo, Y. Fu, L. Liu, Org. Lett. 13
(2011) 3235.
[57] E. Doustkhah, M. Heidarizadeh, S. Rostamnia, A. Hassankhani, B. Kazemi, X. Liu,
Mater. Lett. 216 (2018) 139.
[58] A. Baghban, M. Heidarizadeh, E. Doustkhah, S. Rostamnia, P.F. Rezaei, Int. J. Biol.
Macromol. 103 (2017) 1194.
[59] V. Khakyzadeh, A. Rostami, H. Veisi, B. Shirmardi Shaghasemi, E. Reimhult,
R. Luque, Y. Xia, S. Darvishi, Org. Biomol. Chem. 17 (2019) 4491.
[60] A. Rostami, A. Rostami, A. Ghaderi, M.A. Zolfigol, RSC Adv. 5 (2015) 37060.
[61] A. Rostami, A. Rostami, A. Ghaderi, J. Org. Chem. 17 (2015) 8694.
[62] A. Rostami, A. Rostami, N. Iranpoor, M.A. Zolfigol, Tetrahedron Lett. 57 (2016)
192.
[17] H.-X. Dai, G. Li, X.-G. Zhang, A.F. Stepan, J.-Q. Yu, J. Am. Chem. Soc. 135 (2013)
7567.
[18] Y. Wang, V. Gevorgyan, Angew. Chem. Int. Ed. 54 (2015) 2255.
[19] C. Huang, B. Chattopadhyay, V. Gevorgyan, A. Silanol, J. Am. Chem. Soc. 133
(2011) 12406.
[20] T. Kazutaka, H. Yoshihiro, K. Susumu, H. Koji, M. Masahiro, ACS Catal. 9 (2019)
5336.
[63] K. Amiri, A. Rostami, A. Rostami, New J. Chem. 40 (2016) 7522.
[64] N. Iranpoor, H. Firouzabadi, E. Etemadi-Davan, A. Rostami, A. Nematollahi, J.
Organomet. Chem. 740 (2013) 123.
[21] C. Huang, N. Ghavtadze, B. Chattopadhyay, V. Gevorgyan, J. Am. Chem. Soc. 133
(2011) 17630.
[65] A. Rostami, A. Rostami, A. Ghaderi, M. Gholinejad, S. Gheisarzadeh, Synthesis 49
(2017) 5025.
[22] M. Parasram, V.O. Iaroshenko, V. Gevorgyan, J. Am. Chem. Soc. 136 (2014) 17926.
[23] L. Ackermann, E. Diers, A. Manvar, Org. Lett. 14 (2012) 1154.
[24] X. Zhao, C.S. Yeung, V.M. Dong, J. Am. Chem. Soc. 132 (2010) 5837.
[25] B. Xiao, Y.T.-J. Fu, G. Xu, J.-J.J.Y. Dai, L. Liu, J. Am. Chem. Soc. 132 (2010) 468.
[26] J.A. Fernández-Salas, A.P. Pulis, D.J. Procter, Chem. Commun. 52 (2016) 12364.
[27] C.M. Grombein, Q. Hu, R. Heim, S. Rau, C. Zimmer, R.W. Hartmann, Eur. J. Med.
Chem. 89 (2015) 597.
[66] K. Amiri, A. Rostami, S. samadi, A. Rostami, Catal. Commun. 86 (2016) 108.
[67] B. Atashkar, M.A. Zolfigol, S. Mallakpour, Molecular Catal. 452 (2018) 192.
[68] A. Rostami, V. khakyzadeh, M.A. Zolfigol, A. Rostami, Mol. Catal. 452 (2018) 260.
[69] M.A. Zolfigol, R. Ayazi-Nasrabadi, S. Baghery, Appl. Organomet. Chem. 30 (2016)
500.
11