A simple and green synthesis of diaryl sulfides catalyzed by an MCM-41-immobilized copper(I) complex in neat water

Article abstract of DOI:10.1016/j.jorganchem.2013.09.024

The heterogeneous carbon-sulfur bond formation reaction of aryl iodides with potassium thiocyanate was achieved in neat water at 130 C by using 5 mol% MCM-41-immobilized bidentate nitrogen/CuCl complex [MCM-41-2N-CuCl] as catalyst and Cs₂CO₃ as base, yielding a variety of diaryl sulfides in moderate to high yields. This heterogeneous copper catalyst can be easily prepared by a simple two-step procedure from commercially available and cheap reagents and recovered by a simple filtration and reused for 10 cycles without loss of catalytic activity.

Full text of DOI:10.1016/j.jorganchem.2013.09.024

Journal of Organometallic Chemistry 749 (2014) 55e60
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Note
A simple and green synthesis of diaryl sulfides catalyzed
by an MCM-41-immobilized copper(I) complex in neat water
,
a
b
a,
Mingzhong Cai b , Ruian Xiao , Tao Yan , Hong Zhao
*
*
a School of Chemistry and Chemical Engineering, Guangdong Pharmaceutical University, Guangzhou 510006, PR China
b Key Laboratory of Functional Small Organic Molecule, Ministry of Education and Department of Chemistry, Jiangxi Normal University, Nanchang 330022,
PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The heterogeneous carbonesulfur bond formation reaction of aryl iodides with potassium thiocyanate
was achieved in neat water at 130 ꢀC by using 5 mol% MCM-41-immobilized bidentate nitrogen/CuCl
complex [MCM-41-2NeCuCl] as catalyst and Cs2CO3 as base, yielding a variety of diaryl sulfides in
moderate to high yields. This heterogeneous copper catalyst can be easily prepared by a simple two-step
procedure from commercially available and cheap reagents and recovered by a simple filtration and
reused for 10 cycles without loss of catalytic activity.
Received 5 July 2013
Received in revised form
8 September 2013
Accepted 17 September 2013
Keywords:
Copper
Ó 2013 Elsevier B.V. All rights reserved.
Diaryl sulfide
Aryl iodide
Green chemistry
Heterogeneous catalysis
1. Introduction
nickel [25,26], cobalt [27], copper [28e32], and indium [33,34].
Among these methods, the copper-catalyzed cross-coupling is
Recently, increasing attention has been paid to the develop-
ment of environmentally benign organic transformations for the
construction of complex molecules [1e4]. The arylesulfur bonds
proverbially exist in many molecules that are of biological, phar-
maceutical and materials interest [5e11]. For example, diaryl sul-
fide functionalities have been found in numerous drugs with a
broad spectrum of therapeutic activities such as antidiabetes, anti-
inflammatory, anti-Alzheimer’s, anti-Parkinson’s, anticancer, and
anti-HIV [12,13]. Traditional methods for the synthesis of aryle
sulfur bonds often require harsh reactions. For instance, coupling
of copper thiolates with aryl halides take place in polar solvents
such as HMPA, and at elevated temperature around 200 ꢀC.
Reduction of aryl sulfones or aryl sulfoxides requires strong
reducing agents such as DIBAL-H or LiAlH4 [14e16]. The develop-
ment of efficient methods for the formation of arylesulfur bonds
has been a subject of interest in synthetic chemistry since Migita
first reported the palladium-catalyzed cross-coupling of aryl ha-
lides with thiols [17,18]. A wide range of transition metals was used
to catalyze this coupling reaction, including palladium [19e24],
highly attractive due to the relatively low cost and environmen-
tally negative influence of the process. Although these copper-
catalyzed cross-coupling reactions of aryl halides with thiols are
highly efficient, the problem with homogeneous catalysis is the
difficulty to separate the copper catalyst from the reaction mixture
and the impossibility to reuse it in consecutive reactions. In
addition, homogeneous catalysis might result in unacceptable
copper contamination of the desired isolated product, which is a
particularly significant drawback for its application in the phar-
maceutical industry. From the standpoint of environmentally
benign organic synthesis, the design of a green chemical method
for the formation of arylesulfur bonds is considered of high
practical value.
Over the last decade there has been an increasing interest in the
search for more sustainable chemical processes. In this context, the
use of nontoxic chemicals, renewable reagents and environmen-
tally friendly solvents, among which water is the most benign one,
is a most valuable feature for the design of a “green” chemical
protocol. Recently, the use of water as solvent in organic reactions
has attracted much attention due to the low cost, nontoxicity,
safety, availability, and greater chemo-selectivity compared with
organic solvents [35e38]. Carril et al. reported the S-arylation of
thiophenol derivatives with aryl halides leading to diaryl sulfides
catalyzed by a combination of a copper salt and a 1,2-diamine
* Corresponding authors. Fax: þ86 791 88120388, þ86 760 88207939.
E-mail addresses: caimzhong@163.com (M. Cai), zhaohong1001@sina.com
(H. Zhao).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.09.024

56
M. Cai et al. / Journal of Organometallic Chemistry 749 (2014) 55e60
derivative using exclusively water as the solvent, the water solu-
tion containing the copper complexes can be reused for only three
times [39]. Recently, Zhou et al. reported a highly efficient protocol
of CeS bond formation between aryl halides and potassium thio-
cyanate in water using 10 mol% CuCl2/1,10-phenanthroline as a
catalytic system and (n-Bu)4NF as a PTC, no the recovery and
reutilization of the aqueous medium containing the active catalyst
was described [40].
mixture was stirred for 24 h at 100 ꢀC. Then the solid was filtered
and washed by CHCl3 (2 ꢂ 20 mL), and dried in vacuum at 160 ꢀC for
5 h to obtain 3.474 g of hybrid material MCM-41-2N. The nitrogen
content was found to be 2.19 mmol/g by elemental analysis.
2.2.2. Preparation of MCM-41-2NeCuCl
In a small Schlenk tube, 1.0 g of MCM-41-2N was mixed with
0.1 g (1.0 mmol) of CuCl in 10 mL of dry DMF. The mixture was
stirred at room temperature for 7 h under an argon atmosphere.
The solid product was filtered by suction, washed with DMF and
acetone and dried at 60 ꢀC/26.7 Pa under Ar for 5 h to give 1.086 g of
a pale blue copper complex (MCM-41-2NeCuCl). The nitrogen and
copper content was found to be 1.77 mmol/g and 0.46 mmol/g,
respectively.
In spite of tremendous effort dedicated to the immobilization of
homogeneous palladium complexes over the last two decades
[41,42], very few examples of carbonecarbon bond or carbone
heteroatom bond formation reactions catalyzed by heterogeneous
copper catalysts have appeared [43e48]. So, the development of a
stable heterogeneous copper catalyst that allows for highly efficient
CeS bond formation reactions of a wide range of aryl halides is
worthwhile. Developments on the mesoporous material MCM-41
provided a new possible candidate for a solid support for immo-
bilization of homogeneous catalysts [49]. MCM-41 has a regular
pore diameter of ca. 5 nm and a specific surface area >700 m2 gꢁ1
[50]. Its large pore size allows passage of large molecules such as
organic reactants and metal complexes through the pores to reach
to the surface of the channel [51e53]. To date, some palladium and
rhodium complexes on functionalized MCM-41 support have been
prepared and successfully used in organic reactions [54e60]. Very
recently, we reported the synthesis of the first MCM-41-
immobilized bidentate nitrogen/CuI complex and found that it is
a highly efficient and recyclable heterogeneous catalyst for the
homo- and heterocoupling of terminal alkynes [46]. However, to
the best of our knowledge, no CeS bond formation reaction be-
tween aryl halides and potassium thiocyanate catalyzed by
immobilization of copper in MCM-41 has been described in the
open literature. In continuing our efforts to develop greener syn-
thetic pathways for organic transformations, herein we wish to
report an efficient, heterogeneous CeS bond formation reaction
between aryl iodides and potassium thiocyanate catalyzed by an
MCM-41-immobilized bidentate nitrogen/CuCl complex in neat
water.
2.3. General procedure for the synthesis of diaryl sulfides
To a resealable Schlenk tube, was added Cs2CO3 (2.0 mmol),
KSCN (1.5 mmol) and MCM-41-2NeCuCl (110 mg, 0.05 mmol), and
the reaction vessel was fitted with a rubber septum. The vessel was
evacuated and back-filled with argon and this evacuation/back-fill
procedure was repeated one additional time. The aryl iodide
(1.0 mmol) and water (3 mL) were then added under a stream of
argon. The reaction tube was quickly sealed and the contents were
stirred while heating in an oil bath at 130 ꢀC for 48 h. After
completion of the reaction, the reaction mixture was cooled to
room temperature, extracted with ethyl acetate (3 ꢂ 5 mL), and
filtered. The MCM-41-2NeCuCl complex was washed with distilled
water (2 ꢂ 5 mL), ethyl acetate (2 ꢂ 5 mL), and Et2O (2 ꢂ 5 mL) and
reused in the next run. The extract was concentrated under reduced
pressure and the residue was purified by flash column chroma-
tography on silica gel (petroleum/ethyl acetate ¼ 50:1 to 10:1) to
provide the desired product.
2.3.1. Diphenyl sulfide, 2a [40]
Colorless oil. 1H NMR (CDCl3, 400 MHz):
d
¼ 7.41e7.27 (m, 10H);
13C NMR (CDCl3, 100 MHz):
d
¼ 135.8, 131.1, 129.2, 127.1.
2. Experimental
2.3.2. Di-p-tolyl sulfide, 2b [40]
Colorless oil. 1H NMR (CDCl3, 400 MHz):
d
¼ 7.15 (d, J ¼ 8.0 Hz,
2.1. General remarks
4H), 7.01 (d, J ¼ 8.0 Hz, 4H), 2.24 (s, 6H); 13C NMR (CDCl3, 100 MHz):
d
¼ 136.9, 132.7, 131.1, 129.9, 21.1.
All chemicals were reagent grade and used as purchased. The
products were purified by flash chromatography on silica gel.
Mixture of EtOAc and hexane was generally used as eluent. All
coupling products were characterized by comparison of their
spectra and physical data with authentic samples. 1H NMR spectra
(400 MHz) were recorded on a Bruker Avance 400 MHz spec-
2.3.3. Di-o-tolyl sulfide, 2c [40]
White solid. 1H NMR(CDCl3, 400 MHz):
d
¼ 7.24 (d, J ¼ 8.4 Hz,
2H), 7.17 (t, J ¼ 7.2 Hz, 2H), 7.10 (t, J ¼ 7.2 Hz, 2H), 7.05 (d, J ¼ 7.6 Hz,
2H), 2.38 (s, 6H); 13C NMR (CDCl3, 100 MHz):
130.5, 127.1, 126.7, 20.4.
d
¼ 138.9, 134.3, 131.1,
trometer with TMS as an internal standard in CDCl3 as solvent. 13
C
NMR spectra (100 MHz) were recorded on a Bruker Avance
400 MHz spectrometer in CDCl3 as solvent. Copper content was
determined with inductively coupled plasma atom emission
Atomscan16 (ICP-AES, TJA Corporation). X-ray powder diffraction
was obtained on Damx-rA (Rigaka). Microanalyses were measured
by using a Yanaco MT-3 CHN microelemental analyzer. GC analysis
was performed on an SRI 8610C equipped with a fused silica
capillary column. The mesoporous material MCM-41 was easily
prepared according to a literature procedure [61].
2.3.4. 4,40-Dimethoxy diphenyl sulfide, 2d [62]
Colorless oil. 1H NMR (CDCl3, 400 MHz):
d
¼ 7.20 (d, J ¼ 8.8 Hz,
4H), 6.76 (d, J ¼ 8.8 Hz, 4H), 3.71 (s, 6H); 13C NMR (CDCl3, 100 MHz):
d
¼ 158.5, 132.2, 126.9, 114.3, 54.9.
2.3.5. 2,20-Dimethoxy diphenyl sulfide, 2e [40]
White solid. 1H NMR (CDCl3, 400 MHz):
d
¼ 7.27e7.22 (m, 2H),
7.05 (dd, J ¼ 1.6 Hz, J ¼ 7.6 Hz, 2H), 6.92e6.85 (m, 4H), 3.87 (s, 6H);
13C NMR (CDCl3, 100 MHz):
110.8, 55.9.
d
¼ 157.8, 132.0, 128.4, 122.6, 121.2,
2.2. Preparation of the catalyst
2.3.6. 3,30-Dimethoxy diphenyl sulfide, 2f [40]
White solid. 1H NMR (CDCl3, 400 MHz):
2.2.1. Preparation of MCM-41-2N
d
¼ 7.25 (t, J ¼ 8.0 Hz,
A
solution of 2.31
g
of 3-(2-aminoethylamino)propyl-
2H), 6.98 (d, J ¼ 8.0 Hz, 2H), 6.93 (s, 2H), 6.83e6.80 (m, 2H), 3.80 (s,
trimethoxysilane in 18 mL of dry chloroform was added to a sus-
pension of 2.2 g of the MCM-41 in 180 mL of dry toluene. The
6H); 13C NMR (CDCl3, 100 MHz):
113.0, 55.3.
d
¼ 160.1, 136.7, 130.1, 123.4, 116.3,

M. Cai et al. / Journal of Organometallic Chemistry 749 (2014) 55e60
57
Scheme 1. Preparation of MCM-41-2NeCuCl complex.
2.3.7. 4,40-Dichloro diphenyl sulfide, 2g [62]
3. Results and discussion
Colorless oil. 1H NMR (CDCl3, 400 MHz):
d
¼ 7.29e7.21 (m, 8H);
13C NMR (CDCl3, 100 MHz):
d
¼ 133.9, 133.5, 132.3, 129.5.
3.1. Synthesis and characterization of MCM-41-2NeCuCl
2.3.8. 4,40-Dibromo diphenyl sulfide, 2h [40]
The MCM-41-immobilized bidentate nitrogen/CuCl complex
(MCM-41-2NeCuCl) was very conveniently prepared starting from
commercially available and inexpensive 3-(2-aminoethylamino)
propyltrimethoxysilane and CuCl (Scheme 1). Firstly, the meso-
porous material MCM-41 reacted with 3-(2-aminoethylamino)
propyltrimethoxysilane in toluene at 100 ꢀC for 24 h to generate 3-
(2-aminoethylamino)propyl-functionalized MCM-41 (MCM-41-
2N). The latter was subsequently treated with CuCl in DMF at room
temperature for 7 h to generate the MCM-41-immobilized biden-
tate nitrogen/CuCl complex (MCM-41-2NeCuCl) as a pale blue
powder, the copper content of the complex was found to be
0.46 mmol/g according to the ICP-AES measurements. XRD patterns
of the parent MCM-41 and the modified materials MCM-41-2N,
MCM-41-2NeCuCl are displayed in Fig. 1. Small angle X-ray pow-
der diffraction of the parent MCM-41 gave peaks corresponding to
hexagonally ordered mesoporous phases. For MCM-41-2N and
MCM-41-2NeCuCl, the (100) reflection of the parent MCM-41 with
decreased intensity was remained after functionalization, while the
(110) and (200) reflections became weak and diffuse, which could
be due to contrast matching between the silicate framework and
organic moieties which are located inside the channels of MCM-41
White solid. 1H NMR (CDCl3, 400 MHz):
d
¼ 7.45 (d, J ¼ 8.4 Hz,
4H), 7.21 (d, J ¼ 8.4 Hz, 4H); 13C NMR (CDCl3, 100 MHz):
d
¼ 134.5,
132.6, 132.4, 121.5.
2.3.9. 4,40-Difluoro diphenyl sulfide, 2i [40]
Colorless oil. 1H NMR (CDCl3, 400 MHz):
d
¼ 7.24e7.20 (m, 4H),
6.92 (t, J ¼ 8.6 Hz, 4H); 13C NMR (CDCl3, 100 MHz):
d
¼ 162.2 (d,
1JCF ¼ 246.0 Hz),133.0 (d, 3JCF ¼ 8.0 Hz), 131.1 (d, 4JCF ¼ 3.0 Hz), 116.4
(d, 2JCF ¼ 22.0 Hz).
2.3.10. 4,40-Dinitro diphenyl sulfide, 2j [40]
Yellow solid. 1H NMR (CDCl3, 400 MHz):
d
¼ 8.14 (d, J ¼ 8.8 Hz,
4H), 7.42 (d, J ¼ 8.8 Hz, 4H); 13C NMR (CDCl3, 100 MHz):
d
¼ 141.7,
130.1, 125.1, 123.6.
2.3.11. 2,20-Dinitro diphenyl sulfide, 2k [40]
Yellow solid. 1H NMR (CDCl3, 400 MHz):
d
¼ 8.10 (d, J ¼ 8.0 Hz,
2H), 7.58e7.48 (m, 4H), 7.31 (d, J ¼ 8.0 Hz, 2H); 13C NMR (CDCl3,
100 MHz):
d
¼ 149.4, 133.8, 133.7, 131.5, 128.7, 125.5.
2.3.12. 3,30-Ditrifluoromethyl diphenyl sulfide, 2l
Colorless oil. 1H NMR (CDCl3, 400 MHz):
d
¼ 7.62 (s, 2H), 7.54 (d,
J ¼ 7.2 Hz, 2H), 7.51e7.44 (m, 4H); 13C NMR (CDCl3, 100 MHz):
2
d
¼
136.2, 134.2, 131.4 (q, JCF
¼
33.0 Hz), 129.9, 127.7(q,
3JCF ¼ 4.0 Hz), 124.4 (q, 3JCF ¼ 4.0 Hz),123.6 (q, 1JCF ¼ 271.0 Hz). Anal.
(100)
Calcd. for C14H8F6S: C, 52.18; H, 2.50. Found: C, 52.37; H, 2.31.
1
2.3.13. 4,40-Diacetyl diphenyl sulfide, 2m [40]
Yellow oil. 1H NMR (CDCl3, 400 MHz):
d
¼ 7.91 (dd, J ¼ 1.6,
6.8 Hz, 4H), 7.40 (dd, J ¼ 1.6, 6.8 Hz, 4H), 2.61 (s, 6H); 13C NMR
(CDCl3, 100 MHz):
d
¼ 197.1, 141.1, 135.9, 130.6, 129.3, 26.6.
2
3
2.3.14. Bis(3-pyridyl) sulfide 2n [40]
Colorless oil. 1H NMR(CDCl3, 400 MHz):
d
¼ 8.61 (s, 2H), 8.54e
8.52 (m, 2H), 7.67e7.65 (m, 2H), 7.29e7.25 (m, 2H); 13C NMR (CDCl3,
(110)
(200)
100 MHz):
d
¼ 151.7, 148.7, 138.7, 131.9, 124.2.
2.3.15. Bis(1-naphthyl) sulfide 2o [62]
1
2
3
4
5
6
White solid. 1H NMR (CDCl3, 400 MHz):
d
¼ 8.36e8.33 (m, 2H),
2 (degrees)
7.83e7.80 (m, 2H), 7.72e7.70 (m, 2H), 7.48e7.45 (m, 4H), 7.25e7.18
(m, 4H); 13C NMR (CDCl3, 100 MHz):
¼ 134.1, 132.6, 132.4, 129.9,
128.6, 128.0, 126.8, 126.4, 125.9, 125.1.
d
Fig. 1. XRD profiles of the parent MCM-41 (1), MCM-41-2N (2) and MCM-41-2NeCuCl
(3).

58
M. Cai et al. / Journal of Organometallic Chemistry 749 (2014) 55e60
Table 1
Table 2
Reaction condition screening for the coupling of iodobenzene with KSCN.a
Heterogeneous copper-catalyzed CeS coupling of different aryl iodides with po-
tassium thiocyanate.a
Entry
Base
Temp (ꢀC)
Time (h)
Yieldb (%)
Entry
Ar/I
Product
Yieldb (%)
1
2
3
4
5
6
7
8
Na2CO3
K2CO3
Cs2CO3
KHCO3
K3PO4
NaOAc
Et3N
Bu3N
130
130
130
130
130
130
130
130
130
130
130
120
100
140
130
130
130
130
130
130
130
48
48
48
48
48
48
48
48
48
48
48
60
72
48
24
60
72
30
48
48
48
47
59
88
42
50
68
60
66
69
54
61
81
65
86
71
86
65
87
89
61
72
1
2
3
4
5
6
7
8
Ph/I
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
2n
2o
88
86
75
78
69
84
82
81
85
83
70
86
84
61
65
4-CH3C6H4/I
2-CH3C6H4/I
4-CH3OC6H4/I
2-CH3OC6H4/I
3-CH3OC6H4/I
4-ClC6H4/I
4-BrC6H4/I
4-FC6H4/I
9
Piperidine
Pyridine
DBU
9
10
11
12
13
14
15
16
17c
18d
19e
20f
21g
10
11
12
13
14
15
4-O2NC6H4/I
2-O2NC6H4/I
3-CF3C6H4/I
4-CH3COC6H4/I
3-Pyridinyl/I
1-Naphthyl/I
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
a
Reaction conditions: aryl iodide (1.0 mmol), KSCN (1.5 mmol), MCM-41-2Ne
CuCl (110 mg, 0.05 mmol), Cs2CO3 (2.0 mmol), H2O (3.0 mL) at 130 ꢀC under Ar for
48 h.
b
Isolated yield.
a
Reaction conditions: iodobenzene (1.0 mmol), KSCN (1.5 mmol), copper catalyst
(110 mg, 0.05 mmol), base (2.0 mmol), H2O (3.0 mL) under Ar.
b
obtained when MCM-41-2NeCuBr or MCM-41-2NeCuI was used
as the catalyst (Table 1, entries 20 and 21). Therefore, the optimal
catalytic system involved the use of MCM-41-2NeCuCl (5 mol%),
Cs2CO3 (2 equiv) in neat water at 130 ꢀC under Ar for 48 h (Table 1,
entry 3).
Isolated yield.
Copper catalyst (55 mg, 0.025 mmol) was used.
Copper catalyst (220 mg, 0.1 mmol) was used.
(n-Bu)4NF (0.2 mmol) was used as a PTC.
c
d
e
f
MCM-41-2NeCuBr (117 mg, 0.05 mmol) was used.
g
MCM-41-2NeCuI (102 mg, 0.05 mmol) was used.
Then, a variety of aryl iodides were examined to explore the
scope of substrates under the optimized reaction conditions and
the results are listed in Table 2. As shown in Table 2, the CeS
coupling reactions of a variety of aryl iodides with KSCN proceeded
smoothly to afford the corresponding diaryl sulfides in moderate to
high yields. The electron nature of substituents seemed to have no
effect on the results, various electron-donating and electron-
withdrawing substituents such as eCH3, eOCH3, eBr, eCl, eF, e
CF3, eCOCH3 and eNO2 on aryl iodides were well tolerated. The
reactions of sterically hindered aryl iodides such as 2-iodotoluene,
2-iodoanisole, and 2-nitroiodobenzene with potassium thiocyanate
also provided good yields of the desired diaryl sulfides 2c, 2e and
2k under the optimized reaction conditions, respectively (Table 2,
entries 3, 5 and 11), although the effect of steric hindrance on the
reaction was observed. Moreover, high yields obtained in the
case of 4-chloroiodobenzene, 4-bromoiodobenzene and 4-
fluoroiodobenzene indicated that there was good chemo-
selectivity between iodide, bromide, chloride, and fluoride func-
tional groups (Table 2, entries 7e9). A heteroaryl iodide, such as 3-
iodopyridine, could also afford the desired diaryl sulfide 2n in 61%
yield (Table 2, entry 14). The bulky 1-iodonaphthalene also reacted
effectively with KSCN to give the corresponding product 2o in 65%
yield (Table 2, entry 15). The method provides a quite general route
for the synthesis of diaryl sulfides having various functionalities.
The results above prompted us to investigate the reaction of aryl
bromides with KSCN. However, aryl bromides were not reactive
under the optimized reaction conditions for aryl iodides and no
desired product was obtained.
[61,63]. These results indicated that the basic structure of the
parent MCM-41 was not damaged in the whole process of catalyst
preparation.
3.2. Heterogeneous CeS coupling reactions of aryl iodides with
potassium thiocyanate
In our initial screening experiments, iodobenzene and potas-
sium thiocyanate were selected as model substrates to optimize
the reaction conditions, and the results are summarized in Table 1.
At first, the base effect was examined, and a significant base effect
was observed. It is evident that good yields were obtained when
Cs2CO3, NaOAc, piperidine and Bu3N were used as the base
(Table 1, entries 3, 6, 8 and 9), whereas Na2CO3, K2CO3, KHCO3,
K3PO4, Et3N, pyridine, and DBU afforded low to moderate yields
(Table 1, entries 1, 2, 4, 5, 7, 10, 11), so Cs2CO3 was finally selected as
the base for the reaction. Our next studies focused on the effect of
reaction temperature and time on the model reaction. For the
temperatures tested [100, 120, 130, and 140 ꢀC], 130 ꢀC gave the
best result. It was found that the reaction was accomplished when
it was carried out in water at 130 ꢀC for 48 h. Finally, the amount of
supported copper catalyst was also screened, and 5.0 mol% loading
of copper was found to be optimal, a lower yield was observed
when the amount of the catalyst was decreased (Table 1, entry 17).
Increasing the amount of copper catalyst could shorten the reac-
tion time, but did not increase the yield of diphenyl sulfide (Table 1,
entry 18). The addition of (n-Bu)4NF (0.2 equiv) as a PTC also did
not enhance the yield (Table 1, entry 19). To verify the effect of the
anion of copper(I) salts on the reaction, we also prepared MCM-41-
2NeCuBr and MCM-41-2NeCuI from CuBr or CuI instead of CuCl
according to Scheme 1. It was found that lower yields were
3.3. Recycling of the catalyst
For a heterogeneous transition-metal catalyst, it is important
to examine its ease of separation, recoverability and reusability.

M. Cai et al. / Journal of Organometallic Chemistry 749 (2014) 55e60
59
Table 3
4. Conclusion
The CeS coupling reaction of iodobenzene with KSCN catalyzed by the recycled
catalyst.a
In summary, we have developed a novel, practical and envi-
ronmentally friendly access to diaryl sulfides through the reaction
of aryl iodides with KSCN by using an MCM-41-immobilized
bidentate nitrogen/CuCl complex [MCM-41-2NeCuCl] as catalyst
in neat water. One of the advantages derived from the use of such a
benign solvent as water are clear in terms of safety, cost and
innocuousness. Furthermore, the methodology is applicable to a
variety of aryl iodides. This heterogeneous copper catalyst can be
very conveniently prepared by a simple two-step procedure from
commercially available and cheap reagents. In addition, this
methodology offers the competitiveness of recyclability of the
catalyst without significant loss of catalytic activity, and the catalyst
could be easily recovered and reused for at least 10 cycles,
providing thereby environmental and economic advantages over
previously reported protocols and rendering this methodology
highly suitable for industrial application.
Cycle
Yieldb (%)
Cycle
Yieldb (%)
1
3
5
7
9
88
87
87
86
86
2
4
6
8
10
88
86
87
85
85
a
Reaction was carried out with iodobenzene (1 mmol), KSCN (1.5 mmol), MCM-
41-2NeCuCl (110 mg, 0.05 mmol), Cs2CO3 (2.0 mmol), H2O (3.0 mL) at 130 ꢀC under
Ar for 48 h.
b
Isolated yield.
We also investigated the recyclability of the MCM-41-2NeCuCl by
using the CeS coupling reaction of iodobenzene with KSCN. After
carrying out the reaction, the catalyst was separated by simple
filtration and washed with distilled water, ethyl acetate and
diethyl ether. After being air-dried, it can be reused directly
without further purification. The recovered copper catalyst was
used in the next run, and almost consistent activity was observed
for 10 consecutive cycles (Table 3, entries 1e10). Fig. 2 shows the
time course of the coupling reaction of iodobenzene with KSCN
using the fresh and the tenth recycled catalysts. As shown in
Fig. 2, for the tenth recycled catalyst, the induction period and the
reaction rate in the tenth run did not change significantly
compared with that of the fresh one, indicating that the catalytic
system is robust for this coupling reaction. In addition, copper
leaching in the immobilized catalyst was also determined. The
copper content of the catalyst was found by ICP analysis to be
0.45 mmol/g after ten consecutive runs, only 2% of copper had
been lost from the MCM-41 support. The high stability and
excellent reusability of the catalyst may result from the chelating
action of bidentate 2-aminoethylamino ligand on copper and the
mesoporous structure of the MCM-41 support. The result is
important from a practical point of view. The high catalytic ac-
tivity, excellent reusability and the easy accessibility of the MCM-
41-2NeCuCl make it a highly attractive heterogeneous copper
catalyst for the parallel solution phase synthesis of diverse li-
braries of compounds.
Acknowledgments
We thank the National Natural Science Foundation of China (No.
21272044) and Key Laboratory of Functional Small Organic Mole-
cule, Ministry of Education (No. KLFS-KF-201213) for financial
support.
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