The first report on the preparation of peptide nanofibers decorated with zirconium oxide nanoparticles applied as versatile catalyst for the amination of aryl halides and synthesis of biaryl and symmetrical sulfides

Article abstract of DOI:10.1039/c7nj00628d

We have reported the preparation of peptide nanofibers decorated with zirconium oxide nanoparticles for the first time as a novel, non-toxic, inexpensive and recyclable catalyst for the amination of aryl halides and synthesis of biaryl and symmetrical sulfides (via reaction of aryl halides with S₈ or 2-thiobarbituric acid as sulfur transfer reagents). The structure of the catalyst was studied by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), atomic absorption spectroscopy (AAS), UV-visible absorption and fluorescence spectroscopy.

Full text of DOI:10.1039/c7nj00628d

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Method
The First Report on the Preparation of Peptide Nanofibers
Decorated with Zirconium Oxide Nanoparticles: Applied as
Versatile Catalyst for the Amination of Aryl Halides, Synthesis of
Biaryl and Symmetrical Sulfides
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Arash Ghorbani-Choghamarani* and Zahra Taherinia
We have reported the preparation of peptide nanofibers decorated with zirconium oxide nanoparticles for the first time as
a novel, non-toxic, inexpensive and recyclable catalyst for the amination of aryl halides, synthesis of biaryl and synthesis of
symmetrical sulfides (via reaction of aryl halides with S8 or 2-thiobarbituric acid as sulfur transfer reagents). The structure
of the catalyst was studied by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM),
thermogravimetric analysis (TGA), atomic absorption spectroscopy (AAS), UV–visible absorption and Fluorescence
Spectroscopy.
catalyse coupling reaction by zirconium. Thus, it was highlighted
how to take advantage of its characteristic properties to perform
innovative and useful transformations.
Introduction
Transition metal-catalyzed cross-coupling reaction has become a
significant and well-known procedure for the formation of C-C, C-N
and C-S bonds via combination of electrophilic and nucleophilic
fragments. The formation of C-C, C-N and C-S bonds is very
important and powerful tools for the preparation of a variety of
biologically active, agrochemical and polymeric compounds.1 In
general, the catalysts that are chosen for cross coupling reactions
are almost palladium, nickel and copper complexes.2-6 These
reactions often require harsh reaction conditions such as high
temperature, high catalyst loading or specially designed phosphine
ligands. These reactions often require harsh reaction conditions
such as high temperature, high catalyst loading or specially
designed phosphine ligands. To overcome these limitations, much
attention has been paid to developing catalytic systems to minimize
the environmental impact (E-factor) of the processes and efficient
catalytic activity.
A great attention toward nanoparticles has been apparent in the
past decade because the high surface areas and their reactive
surfaces make them successful supports in catalysis cross-coupling
reactions.9 The mostly and newly used nano-sized supports are
boehmite,10 MCM-41,11 graphen oxide,12 Fe3O4,13 carbon
nanotube14 and nanofiber.15 In the recent years, nanofibers have
received considerable attention due to their environmentally
friendly properties, pharmaceutical properties, degradability
content, high specific surface area and high mechanical stability.
Therefore, nanofibers are very promising candidates for catalyst
supports. Nanofibers can be generated in numerous techniques
such as drawing,16 template synthesis,17 electrospinning18 and self-
assembly.19 Among these methods the self-assembling has gained
increasing attention. Sufficient binding sites on nanofibers surface
make them an ideal organic-based support for anchoring metal
nanoparticles or the parent precursor metal ions. Hence, as a part
of our research program directed toward the utility of peptide
nanofiber, we decided to prepare ZrO nanoparticles immobilized on
peptide nanofibers. This novel nanostructural material was applied
as an effective catalyst for the amination of aryl halides, synthesis
of biaryl and symmetrical sulfides.
Zirconium compounds have been successfully applied for various
reactions such as (1) carbon-carbon formation reactions, (2) carbon-
heteroatom formation reactions, (3) synthesis of heterocycles, (4)
one-pot multicomponent reactions, and (5) miscellaneous reactions
7. Also, Roozbeh and co-workers reported that Ni-poly (N-vinyl-2-
pyrrolidone)/TiO2-ZrO2 was an effective catalyst for coupling
8
reactions of aromatic halides with phenylboronic acid.
Result and discussion
Consequently, the key advances about zirconium-catalysed coupling
reactions are paid more attention by us due to its wide distribution,
low price and efficient catalytic activity. It is very difficult to directly
To the best of our knowledge, this is the first report for the green
synthesis of peptide nanofibers decorated with zirconium oxide
nanoparticles in aqueous solution. After converting of desired
peptide into nanofiber using self-assembly procedure (that is
Department of Chemistry, Ilam University, P.O. Box 69315516, Ilam, Iran. E-mail:
arashghch58@yahoo.com; a.ghorbani@ilam.ac.ir; Fax: +98 84 32227022; Tel:
+98 84 32227022
15
recently reported by our group),
ZrO nanoparticles was
immobilized on the surface of this nanostructural compound
(Scheme 1).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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DOI: 10.1039/C7NJ00628D
HO
O
C
HO
H
O
C
N
H
C
CH2
H
NH2
H2C
O
C
N
H
CH2
+
H2
C
H2
C
H
H2C
C
NH3
O
C
C
ZrO
NH2
CH H2C
CH2
N
ꢀ
H2
C
H2
C
H
C
H
C
H N
2
N
O
C
C
N
H
O
C
CH H2C
CH2
N
NH2
H
C
+
NH
O
H2
H2
C
H
H2N
HN
N
C
H
N
H
O
C
+
H
NH
H
H2
OH
H
OH
N
H2C
N
2H
O
+
ꢀO
OH
H
OH
N
H2C
N
C
C
O
O
C
ꢀO
OH
HO
C
C
H2
C
O
O
C
H2
C
H
O
NH2
CH
CH2
C
N
H
CH
CH2
C
N
NH2
HN
C
C
N
C
+
H2
C
N
H
C
H2
H
H2
ꢀ
OH
H
H2
H2
ZrO
OH
+
ꢀ
O
C
+
H2N
O
O
NH
ꢀ
H2N
O
NH
O
H
O
O
H-bonding interaction
H
O
+
O
OH
O
O
O
O
OH
OH
O
O
C
C
H
HO
H
H
HO
H
ZrOCl2.8H2O
N
H
C
CH2
N
bridging effect
H
C
CH2
N
C
H2C
N
C
H2C
O
C
ZrO
O
C
H2
C
H2
C
H
H2
H2
self- assembly
H
CH H2C
CH2
N
NH2
NH2
H
C
+HN
C
C
CH H2C
CH2
N
C
N
OH
H
C
C
N
H
C
HN
+
C
N
ꢀ
C
N
C
NH
H
H
H2
H
2H
+
OH
H
H2
H
O
H2
NH
+
N
O
H2C
N
H
O
O
ꢀO
OH
H
OH
N
H2C
N
C
C
O
O
C
OH
H2
C
C
C
O
O
O
C
H
CH
CH2
C
N
HO
H2
C
O
NH2
H
HN
C
N
H
C
CH
CH2
C
N
OH
H
+2
H2
H2
ZrO
HO
NH2
HN
C
C
N
C
ZrOCl2 addition
O
H
+
C
H2
H
H2
HO
+
H2N
NH
O
O
O
+
H2N
OH
NH
O
O
ꢀ
HO
O
OH
OH
O
HO
HO
OH
HO
Scheme 1. Schematic synthesis of ZrO nanoparticles supported on the peptide nanofibers
Characterization of supported ZrO nanoparticles on the peptide peptide nanofiber. However in the absence of metal ions, the
nanofiber
fluorescence of the peptide nanofiber is perhaps quenched by the
occurrence of a photoinduced electron transfer (PET) process
because of the presence of lone pairs of donor atoms in the ligand.
The complexation of zirconium ions with PNF probably prevents PET
process; therefore, the fluorescence intensity can significantly be
increase via this coordination. 22
To assess the coordination of ZrO with peptide nanofiber, we
performed FT-IR, UV Visible analysis, fluorescence spectroscopy,
SEM, TGA, and atomic absorption spectroscopy (AAS). In order to
study the binding mode of the peptide nanofiber to metal, the IR
spectrum of the free peptide nanofiber was compared with the
corresponding peptide nanofiber decorated with ZrO. The band at
1643ꢀcm−1 is characteristic of bending vibration of N–H group's in
the peptide. Reducing this frequency to 1636ꢀcm−1 is due to
coordination of nitrogen to zirconium20 (Figure 1). UV-Vis and
fluorescence properties of peptide nanofiber, metallic salt and
peptide nanofiber decorated with ZrO using water as solvent is
also presented in Figure 2. In the peptide nanofiber and ZrONP-PNF,
π-π* transitions of imine bond at 250-300 nm were studied. It can
be seen that the visible spectra of the ZrONP-PNF show higher
absorption than the free peptide nanofiber and alone metallic salt,
this fact can be illustrated because of the coordination of metal ion
to the peptide nanofiber. 21
The fluorescence properties of peptide nanofiber and ZrONP-PNF
were studied at room temperature in H2O (Fig. 3). It is interesting
that the ZrONP-PNF shows a higher intensity than that of the free
2 | J. Name., 2012, 00, 1-3
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ARTICLE
Fig. 1. FT-IR spectra of peptide powder (a) the peptide nanofiber solution (b) ZrO
nanoparticles supported on peptide nanofiber (c).
Fig. 2. UV-Visible absorption spectra for ZrOCl2.8H2O, peptide nanofiber and ZrONP-PNF
Fig 3. Fluorescence spectra of peptide nanofiber and ZrONP-PNF
SEM images of the zirconium oxide immobilized on the peptide
nanofibers. Fig 4 (b and c) show that nanofibers with preserved
morphology after the addition of ZrO, also (d and e) indicate the
distribution of zirconium oxide nanoparticles on the nanofiber
without agglomeration.
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Catalytic studies
After preparation and characterization of ZrO nanoparticles
supported on peptide nanofiber, catalytic activity of this compound
was investigated for the coupling reaction of aniline, ammonia,
phenyl boronic acid, S8, and 2- thiobarbituric with aryl halides. In
general, all reactions were very clean, and the desired products
were obtained in high yields under normal atmospheric conditions.
Initially, we examined coupling reactions of iodobenzene with S8 in
the presence of ZrO-woven nanofiber, and various parameters were
optimized to improve the reaction further. The results are
summarized in Table 1.
Table 1 Optimization of the reaction conditions for the C-S coupling using
iodobenzene and S8 as sulfur transfer agent.a
Fig. 4 (a) SEM image of the surface of the woven nanofibers (b, c, d and e) SEM image
of the surface of the woven nanofibers decorated with ZrO nanoparticles
Entry
Cat
(µl)
Solvent
Temp.
(ºC)
base
Time
(h)
Yield
(%)b
Atomic absorption spectroscopy (AAS) was employed to determine
the exact amount of ZrO immobilized on peptide nanofiber that was
1
2
200
200
DMSO
PEG
120
120
KOH
KOH
1.5
1.5
90
found to be 1.6× 10-4 mol g-1 The thermal behavior of ZrO
.
N.R
immobilized on peptide nanofiber was investigated by
thermogravimetric analysis from room temperature to 500 °C (TGA)
(Fig. 5). The first step from room temperature to 140 °C shows a
~4% weight loss due to loss of adsorbed water and organic solvents.
3
4
200
200
200
200
200
200
200
100
200
200
DMF
H2O
120
120
120
120
120
120
120
120
100
80
KOH
KOH
KOH
Et3N
KF
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
2
79
N.R
N.R
N.R
N.R
17
The second step between 140 and 240 °C shows a 12% weight loss
~
of the total solid catalyst. Differential thermogravimetric analysis
(DTA) of catalyst reveals that a peak at 160 °C, which is related to
the start a decomposition process; also this curve shows an
exothermic peak at 420 °C.
5
Toluene
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
6
7
8
K2CO3
Na2CO3
KOH
KOH
KOH
9
Trace
39
10
11
11
90
2
44
aReaction conditions: iodobenzene (1 mmol), S8 (1 mmol), ZrONP-PNF solution (µL),
base (4 mmol).
Fig. 5 TGA curve of ZrO immobilized on peptide nanofiber
4 | J. Name., 2012, 00, 1-3
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ARTICLE
According to the results shown in Table 1, it was found that the In order to investigate the selectivity of described method; the
base and solvent significantly affected the yield of the desired reaction of 1-bromo-4-chloro benzene as dihalogenated aryl halide
product. The best solvents for this system were found to be DMSO wit S8 was also investigated that the bromide showed more
and DMF (Table 1, entries 1, 3). Furthermore, among organic and reactivity (Table 2, entry 8). This selectivity allows remaining an
inorganic bases, KOH was effective base for this reaction. In active halide site for further functionalization.
addition, the reaction yield and reaction rate increased by rising the
reaction temperature and the amount of woven nanofiber
templated ZrO nanoparticles. It should be mentioned when we
examined the temperature of 120 °C, the yield did not change.
Table 2. Synthesis of symmetrical sulfides via reaction of S8 and aryl/alkyl
Increasing temperature of 120 °C decreases the reaction time,
but did not increase the yield of diphenyl sulfide (Table 1,
halides catalyzed by peptide nanofibers decorated with ZrO nanoparticles
(ZrONP-PNF) in DMSO.a
entry 1). Thus, we preferred to choose 100 °C. Finally, the best
results were obtained with iodobanzane (1 mmol), S8 (1 mmol), and
KOH (4 mmol) in the presence of catalytic amounts of woven
nanofiber ZrO (200 µl) in DMSO as solvent at 100 °C (Table 1). By
these optimal conditions we studied the coupling reaction of
different aryl halides including electron drawing and electron-
donating groups to produce the corresponding symmetrical sulfides
in moderate to excellent yields (results are summarized in Table 2).
Experimental results show that halide derivatives with different
functional groups, such as OCH3, CF3, Me, NO2 and etc. provide
good to excellent yields. As can be seen, aryl chlorides were not as
reactive as aryl bromides and iodides. In the case of aryl halide with
a free hydroxy group the reaction proceeded without the need of a
protecting group and the desired product was obtained in good
yield. It should be noted in some cases the product in the presence
of electron-with drawing substituent's has shorter reaction time
than electron-donating substituent's ones.
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aReaction conditions: aryl halides (1 mmol), S8 (1 mmol), ZrONP-PNF (200 µL), KOH (4
Mp (°C)
mmol) and DMSO (2 mL). bIsolated yield.
Time
(h)
Yield
(%)b
Entry
1
Ar-X
product
Oil 28
Oil 28
Oil 28
Oil29
Oil30
The proposed mechanism for the synthesis of sulfides on the basis
of previous reports23 has been depicted in Scheme 2. Initially S8
reacts with KOH to give potassium disulfide then peptide
nanofibers decorated with ZrO nanoparticle react with potassium
disulfide to give zirconium disulfide, which adds to aryl halide via
oxidative addition reaction to produce intermediate 1. Reductive
elimination then occurred to form intermediate. 2. After that, aryl
2
90
85
65
88
2
3
4
4
15
8
halide reacts with intermediate
2 by oxidative addition to
generate compound 3, which can undergo reductive elimination
to produce diphenyl sulfide and Zr (Scheme 2).
5
6
6.5
92
87
Oil31
7
Oil 32
7
9
85
Scheme 2. Proposed mechanisms for the synthesis of symmetrical sulfides via
reaction of aryl halides and S8 catalyzed by peptide nanofibers decorated with ZrO
nanoparticles.
Oil33
8
5
6.5
7.5
3
78
75
71
79
70
65
60
55
A second portion of this work involves the application of our
protocol to the synthesis of symmetrical sulfides from reaction of
aryl halide and 2- thiobarbituric acid as a novel sulfur transfer
reagent.
Oil 34
9
Iodobenzene and 2- thiobarbituric acid were chosen as model
substrates to optimize the reaction conditions, and several
parameters such as amount of catalyst, base, solvent, and
temperature under normal atmospheric conditions was screened
(Table 3).
Oil34
10
11
12
13
14
15
Oil 35
Table 3 Optimization of the reaction conditions for the C-S coupling using
Iodobenzene and 2- thiobarbituric acid as sulfur transfer agent.a
149ꢀ15036
149ꢀ15036
2
2.5
10
12
Entry
1
Cat
(µl)
300
Solvent
DMSO
Temp.
(ºC)
base
KOH
Yield (%)b
82
150-15337
150-15337
130
2
3
4
5
6
7
300
300
300
300
300
300
PEG
DMF
130
130
130
130
130
130
KOH
KOH
KOH
KOH
Et3N
K2CO3
N.R
17
H2O
N.R
N.R
N.R
N.R
156-15838
43-4639
Toluene
DMSO
DMSO
16
17
7
1
80
80
6 | J. Name., 2012, 00, 1-3
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Journal Name
ARTICLE
8
300
200
300
200
DMSO
DMSO
DMSO
DMSO
140
130
100
80
KOH
KOH
KOH
KOH
85
54
9
10
11
27
N.R
aReaction conditions: iodobenzene (1 mmol), 2- thiobarbituric acid (1 mmol), ZrONP-
PNF (µL), base (7 mmol). bIsolated yield. Reaction time: 24 h.
Firstly, the effect of solvents was investigated and it was
observed that the desired product was not obtained in PEG,
H2O and Toluene (Table 3, entries 2, 4 and 5). However, the
reaction readily proceeded in DMSO and DMF (Table 3).
Among various bases that was screened (e.g., KOH, K2CO3
and Et3N), KOH was the most effective one in DMSO. The
reaction when conducted at 100 °C, the observed yield was
very low (Table 3, entries 9). It should be mentioned when we
examined the temperature of 140 °C, the yield only increased
3 percent (Table 3, entries 8) in comparison with 130 °C
(small change in yield was observed). Thus, the ideal
temperature for the reaction was found to be 130 °C. Finally,
the amount of catalyst was also screened, and 300 µL of
woven nanofiber templated ZrO nanoparticles was found to
be optimal value, a lower yield and longer reaction time was
observed when the amount of the catalyst was decreased
(Table 3, entry 9).Under optimized conditions (Table 3), we
studied the coupling reaction of various aryl halides with 2-
thiobarbituric acid. This protocol efficiently cross coupled aryl
halides having electron withdrawing group (e.g., NO2, Cl and CF3)
with 2-thiobarbituric acid to produce the corresponding aryl
sulfides in excellent yields
whereas in the presence of electron
donating group (4-OMe) a slight decrease in the yield of the diaryl
sulfide (Table 4) was observed. It should be noted the coupling
reaction of 1-bromo-4-nitrobanzane, 1-chloro-4-nitrobenzene led to
the desired product without nitrobenzene converted to amino
benzene sulfides. This protocol was also applied for the cross-
coupling reaction between of 1-bromo-4-chlorobenzene as
dihalogenated aryl halide with 2-thiobarbituric acid to investigate
the selectivity of this procedure which the bromide showed more
reactivity than the chloride group (Table 4, entry 8).
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aReaction conditions: aryl halides (1 mmol), 2-thiobarbituric acid (1 mmol), ZrONP-PNF
(300 µL), KOH (7 mmol) and DMSO (2 mL). bIsolated yield. c, dThe reaction was carried
out for 4h.
Mp (°C)
Time
(h)
Yield
(%)b
Entry
1
Ar-X
product
24
24
24
24
Oil 28
Oil 28
Oil28
82
78
The mechanism of this reaction is suggested as outlined in Scheme
3. It is assumed that 2ꢀthiobarbituric acid reacts with KOH to
produce the potassium thiolate. Next, the aryl halid caused the
oxidative addition of zirconium to produce intermediate a.
The intermediate a reacts with the potassium thiolate to
produce intermediate b, which is transformed into thiol anion
in the presence of KOH, then thiol anion reacts with
intermediate a by oxidative addition to form compound c,
which undergoes reductive elimination to produce
corresponding sulfide and releases ZrO nanoparticles that
start another catalytic cycle.
2
3
23
70
Oil29
Oil30
4
5
50
72
24
24
Oil 31
6
7
Oil32
68
24
24
Scheme 3. Proposed mechanisms for the synthesis of symmetrical sulfides via reaction
of aryl halides and 2-thiobarbituric acid catalyzed by peptide nanofibers decorated with
ZrO nanoparticles.
Oil 33
Oil34
Oil 34
8
9
75
65
62
The reactivity of woven nanofiber templated ZrO nanocatalyst, also
examined for cross-coupling reaction between aryl halides and
aniline or aqueous ammonia. To identify optimum reaction
conditions, we first investigated the C-N cross-coupling of aniline
and iodobenzene in the presence of woven nanofiber templated ZrO
nanoparticles. Selected results from our screening experiments are
summarized in Table 5.
24
24
10
149ꢀ
Table 5 Optimization of the reaction conditions for the C-N cross coupling
15035
11
80
50
10
6
reaction using iodobenzen and aniline.a
149ꢀ
H
N
I
15036
ZrNPꢀPNF (Cat.)
12c
NH2
Solvent,
Base
15 h
150-
Entry
Cat
(µl)
300
Solvent
DMSO
PEG
Temp.
(ºC)
base
KOH
KOH
Yield (%)b
80
15336
13d
35
25
8
1
2
130
150-
300
300
300
130
130
130
N.R
15337
14
24
3
4
DMF
H2O
KOH
KOH
N.R
N.R
150-
15337
15
16
10
60
24
4
43-4639
8 | J. Name., 2012, 00, 1-3
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ARTICLE
Mp (°C)
Time
(h)
Entry
Ar-X
Amine
Product
Yield (%)b
5
6
7
8
9
300
300
300
200
300
DMSO
DMSO
DMSO
DMSO
DMSO
130
130
140
130
100
Et3N
-
N.R
N.R
76
15
18
80
78
5340
5340
1
KOH
KOH
KOH
77
2
3
18
14
9041
55
68
75
10
200
DMSO
80
KOH
19
Oil41
4c
5d
6e
7
aReaction conditions: iodobenzene (1 mmol), aniline (3 mmol), ZrONP-PNF
135-13641
135-13642
Oil43
(µL), base (4 mmol).
8
70
68
It was found that when the reaction proceeded at 80 °C, the
observed yield was very low and when the temperature was
increased to 130 °C, a yield of 90% could be obtained but
when we examined temperature 140, the yield significantly
decreased. The decrease is due to the composition of side
products, thus the ideal temperature for the reaction was
found to be 130 °C. Without base addition, the reaction in
DMSO proceeded ineffectively (Table 5, entry 6), whereas the
reactions in the presence of KOH in DMSO resulted in high
conversion of starting materials to diphenyl amine. Also the
influence of the amount of catalyst on the yield of the
product was evaluated. It was observed that 300 µL of woven
nanofiber templated ZrO nanoparticles was the optimum
value for this transformation.
Cl
10
18
O2
N
68
72
18
24
24
24
103-
10544
8
9
Oil45
NH2
70
45
NH3
NH3
NH3
56–5946
NH2
Eventually, the best result was achieved when the reaction
was pursued at 130 °C using 300 µL of woven nanofiber
templated ZrO nanoparticles in the presence of KOH in
DMSO.
10
11
MeO
69
146-
14847
Table 6. Synthesis of aniline derivatives via reaction of R-NH2
and aryl halides catalyzed by peptide nanofiber decorated
with ZrO nanoparticles (ZrONP-PNF) in DMSO.a
aReaction conditions: aryl halide (1 mmol), aniline (3 mmol), ZrONP-PNF (µL), KOH 4
mmol.
As shown in (Table 6), the expected products were obtained in
moderate to high yields. It was shown that aryl halides with
electron-withdrawing groups reacted more quickly than the aryl
halides with electron-releasing groups (Table 4, entries 4−6).
The proposed mechanism for this transformation has been
illustrated in Schemes 4 based of previous reports.24 Initially aryl
halide reacts with ZrO by oxidative addition to form intermediate
(a), then the intermediate (a) reacts with amine in the presence of
KOH to produce intermediate (b), then intermediate (b) via
reductive elimination afford to aniline or secondary amine and
releases zirconium oxide nanoparticle.
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Utilizing these conditions, various aryl halides reacted with
triphenyltin chloride and/or phenyl boronic acid to give the
corresponding biaryl. Importantly, aryl halide derivatives bearing
electron-donating as well as electron- withdrawing substituents
efficiently provided the desired products; also, iodobenzenes was
found to be
a more reactive substrate than bromo- and
chlorobenzenes.
Scheme 4. Proposed mechanism for the synthesis of secondary amine via reaction of R-
NH2 and aryl halides catalyzed by peptide nanofiber decorated with ZrO nanoparticles.
Table 8 Synthesis of biphenyles via reaction of triphenyltin chloride or
phenyl boronic acid with aryl halides catalyzed by peptide nanofiber
decorated with ZrO nanoparticles (ZrONP-PNF) in DMSO.a
Finally, the C-C cross-coupling reactions of triphenyltin chloride
and/or phenyl boronic acid with aryl halides were studied (Table 7).
Triphenyltin chloride and iodobenzene were used as model reaction,
and various parameters were optimized (Table 7).
Yield b (%)
80
Mp (°C)
Phenyl
reagent
Entry
1
Ar-X
product
63-6648
Table 7 Optimization of the reaction conditions for the C-C coupling using
iodobenzene and triphenyltin chloride.a
63-6648
86-9049
70
65
2
3
4
Entry
1
Cat
(µl)
400
Solvent
DMSO
Temp.
(ºC)
base
KOH
Yield (%)b
80
30-3250
110
50
85
2
3
4
5
6
7
8
9
400
400
400
400
400
400
300
300
PEG
DMF
110
110
110
110
110
130
110
80
KOH
KOH
N.R
N.R
N.R
N.R
N.R
70
Oil51
5
H2O
KOH
2751
65
55
DMSO
DMSO
DMSO
DMSO
DMSO
Na2CO3
K2CO3
KOH
6
7
44-4652
KOH
66
44-4652
69-7052
KOH
33
48
80
8
9
aReaction conditions: iodobenzene (1 mmol), phenyl boronic acid (1.2 mmol), ZrONP-
PNF (µL), base (3 mmol).
As shown in (Table 7), the nature of the base and solvent affects the
yield of the desired product. Among screened solvents and bases,
DMSO and KOH both gave the better yield compared with other
solvents and bases. The ideal temperature for the reaction was
found to be 110°C. When the reaction conducted at the
temperature of 130 for the identical amount of time, we faced a
decrease in yield. Therefore, we preferred to choose 110
temperature.
113-11553
78
10
113-11553
75
70
11
12
Oil 51
OMe
Also, the reaction yield and reaction rate increased via increasing
the amount of the catalyst.
10 | J. Name., 2012, 00, 1-3
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Journal Name
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ARTICLE
temperature. Then 20 mL of ethyl acetate was added to the
reaction mixture, which led to the precipitation of ZrONP-PNF. The
resulting precipitate was washed twice with ethyl acetate (2 x 10
mL), dried and applied for the next run. It was found that ZrONP-
PNF could be reused at least four times without a significant loss of
its catalytic activity.
Yield
(%)b
Mp (°C)
Phenylating
agent
Entry
Ar-X
product
113-115
68
53
13
14
113-
65
53
115
aReaction conditions: aryl halide (1 mmol), phenyl boronic acid (1.2 mmol), triphenyltin
chloride (0.5 mmol), ZrONP-PNF (400 µL), KOH (3 mmol), reaction time: 24 h.
The proposed mechanism for described-above cross-coupling
reaction has been outlined in Scheme 5. We hypothesize that aryl
halide reacts with zirconium to give intermediate A, followed by
trans metalation and reductive elimination to give the coupling
product and restore the catalytically active zirconium species.
Fig. 6 Catalyst recycling study for the synthesis of diphenyl sulfide.
Finally, in order to assess the present protocol with respect to other
reported methods for the synthesis of symmetrical sulfides via
reaction of aryl halides and alkyl halide with S8 the catalytic
performance of the zirconium oxide immobilized on the peptide
nanofiber was compared with some of the previously reported
catalysts (Table 9). This catalyst leads to good reaction time and
higher yield than the previously reported catalysts. More
importantly, compared with other catalysts, ZrONP-PNF is easily
prepared and can be reused at least four times without any
significant loss of its catalytic activity.
Table 9. Comparison of ZrONP-PNF for the synthesis of diphenyl sulfide via
reaction of S8 and iodobenzene with previously reported procedures.
Entry
1
Catalyst
Yield
(%)a
88
Time
(h)
Ref.
25
MCM-41-2N-CuI
24
2
3
5
6
7
Nano copper oxide
Copper oxide particles
CoI2 (dppe) /Zn
Indium
94
92
98
96
90
20
21
10
24
2
26
27
4
Scheme 5 Proposes mechanism for the synthesis biphenyl via reaction of triphenyltin
chloride or phenyl boronic acid with aryl halides catalyzed by peptide nanofibers
decorated with ZrO nanoparticles
5
ZrONP-PNF
This
work
There is an increasing pressure on chemical and pharmaceutical
industries to decrease chemical waste and advance the selectivity
and effectiveness of synthetic processes. For the development of
recoverable and recyclable catalysts, it is necessary to implement
green chemistry principles. In this aim, we investigated the
recoverability and reusability of the ZrO nanoparticle supported on
the peptide nanofiber for the synthesis of sulfides via reaction of
iodobenzene with S8 over four successive runs. Reaction was
performed in DMSO at 130 °C, using 1 mmol iodobenzene, 1 mmol
aIsolated yields.
Conclusions
In summary, we have described the first peptide nanofibers
decorated with zirconium oxide nanoparticles that catalyzed C-N, C-
S and C-C cross-coupling reactions under mild reaction conditions in
excellent yields. Peptide nanofibers can provide multiple functions
such as support, ligand and the high surface area for the
immobilization of ZrO nanoparticles, which is resulting the high
catalytic activity in described reactions. This new coupling reaction
S8 and KOH 4 mmol in the presence of ZrONP-PNF (200 μl), upon
completion of the reaction, the mixture was cooled down to room
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underlines the potential of using zirconium oxide nanoparticles as a
A round bottom flask was charged with of 1 mmol of 2-
very user-friendly, inexpensive and efficient catalyst for the cross thiobarbituric acid, aryl halide (1 mmol), KOH (7 mmol), solution
coupling of carbon-heteroatom and carbon-carbon bonds. In containing ZrO nanoparticle decorated on nanofibers (300 µL) and
addition, this nanocatalyst can be easily recovered and reused for DMSO (2 mL). Then reaction mixture was stirred at 130 °C. The
subsequent run for at least 4 times with less deterioration in its progress of reaction was monitored by TLC. After reaction
catalytic activity.
Experimental section
Materials
completion, the mixture was extracted with ethyl acetate (2×20
mL). The organic extract was washed twice with water and dried
over anhydrous Na2SO4, then filtered and the solvent was
evaporated to achieve corresponding sulfide. In order to obtain
high pure sulfide, the crude product was purified by preparative
TLC.
All reagents and solvents used in this work were purchased from
Sigma-Aldrich, Fluka or Merck Chemical Companies and used
without further purification.
General procedure for the synthesis of N-arylation
The reaction was conducted at 130 °C in DMSO (3 ml) with 3 mmol
of amine, 1 mmol of aryl halid, 4 mmol of KOH and 300 µL of a
solution containing ZrO nanoparticle decorated on nanofibers. The
progress of reaction was monitored by TLC. After reaction
completion, the mixture was cooled to room temperature and was
extracted with ethyl acetate (2 x 20 mL). The organic layer was
washed twice with water and dried with anhydrous Na2SO4, then
filtered and the solvent was evaporated to achieve corresponding
aryl amine. In order to obtain high pure aryl amine, the crude
product was purified by preparative TLC.
Instrumentation
NMR spectra were acquired on a Bruker Avance III 400 MHz.
Melting points were measured with an Electrothermal 9100
apparatus. The particles size and morphology were investigated by
a JEOL JEM-2010 scanning electron microscopy (SEM), on an
accelerating voltage of 200 kV. Varian Cary 300 Bio UV-Vis, Vertex
70
Fourier
transformed
infrared
and
Varian
Cary
spectrofluoremeter were used for UV-Vis, FT-IR and fluorescence
spectral analysis.
Preparation of peptide nanofiber (PNF)
Peptide nanofiber (PNF) has been prepared based on our newly
reported procedure.15
General procedure for the synthesis of biaryl
A round bottom flask was charged with an aryl halid (1 mmol),
phenyl boronic acid (1.2 mmol) or triphenyltin chloride (0.5 mmol),
KOH (3 mmol), ZrO nanoparticle supported on peptide nanofiber
(ZrONP-PNF) (400 µl) and DMSO (3 mL). The reaction mixture was
then stirred at 130°C under atmospheric conditions. Reaction
progress was monitored by TLC. Upon the reaction completion,
mixture was cooled down to room temperature, then filtered, and
extracted with ethyl acetate. The combined organic layer was dried
over Na2SO4, filtered, and purified by preparative tin layer
chromatography using n-hexane/ethyl acetate as eluent.
Synthesis of ZrO nanoparticle supported on the peptide
nanofiber (ZrONP-PNF)
Peptide 30.14 mg (0.04 mmol) was dissolved in 0.2 mL doubly
distilled water and 0.8 mL phosphate buffer solution (pH 8) was
added. Then 32 mg (0.31 mmol) of succinic anhydride was added
to the peptide solution. The solution was sonicated for a few
minutes. This mixture was stirred overnight at 80 °C. In the next
step ZrOCl2.8H2O (3.2 mg, 0.01 mmol) was added to reaction
mixture and stirred for 12 hour at 80 °C, to obtain ZrONP-PNF
quantitatively.
Selected spectral data
4, 4'-Dimethoxy diphenyl sulfide: 29
General procedure for the sulfides synthesis using S8
1H NMR (CDCl3, 400 MHz): δ= 7.36 (d, J = 6.8 Hz, 4H), 6.76 (d, J=7.2
Hz, 4H), 3.63 (s, 6H).
A round bottom flask was charged with of 1 mmol of S8, aryl halide
(1 mmol), KOH (4 mmol), 200 µL of the solution containing ZrO
nanoparticle decorated on nanofibers and DMSO (2 mL). Then the
reaction mixture was stirred at 100 °C. The progress of reaction was
monitored by TLC. After reaction completion, the mixture was
extracted with ethyl acetate (2×20 mL). The organic extract was
washed twice with water, and then dried with anhydrous Na2SO4,
filtered, and the solvent was evaporated to achieve corresponding
sulfide. In order to obtain high pure sulfide, the crude product was
purified by preparative TLC.
3, 3’-Dimethoxy diphenyl sulfide: 31
1H NMR (CDCl3, 400 MHz): δ= 7.76-7.73(m, 1H), 7.58-7.54(m, 1H),
7.4(d, J=6.4 Hz, 1H), 7.14(d, J=6 Hz, 1H), 4.26(s, 3H).
Bis(3-(Trifluoromethyl)phenyl)sulfane:32
1H NMR (CDCl3, 400 MHz): δ= 7.90-7.77(m, 4H), 7.58-7.40 (m, 4H);
MS (EI, m/z): 322.1.
4,4’-Dichloro diphenyl sulfide: 33
General procedure for the sulfides synthesis using 2-
thiobarbituric acid
12 | J. Name., 2012, 00, 1-3
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ARTICLE
1H NMR (CDCl3, 400 MHz): δ =7.57-7.56(m, 4H), 7.55-7.51(m, 4H).
4-Nitro-biphenyl: 53
Dip-tolyl sulfide: 34
1H NMR (400 MHz, DMSO): δ= 8.33 (d, J= 8.8 Hz, 2H), 8.08 (d, J = 8.8
Hz, 2H), 7.81 (d, J = 8.8 Hz, 2H), 7.57-7.47 (m, 3H). 13C NMR (100
MHz, DMSO): δ= 147.1, 147.1, 138.2, 129.7, 128.3, 127.8, 127.7,
124.5.
1H NMR (CDCl3, 400 MHz): δ= 7.37-7.35 (d, J = 6.4 Hz, 2H), 7.17-
7.15(d, J = 7.6 Hz, 2H), 2.37(s, 3H); MS (EI, m/z): 215.2.
Bis-(3-pyridyl) sulfide: 35
Authors thank the research facilities of Ilam University, Ilam, Iran,
for financial support of this research project.
1H NMR (CDCl3, 400 MHz): δ = 8.63(s, 1H), 8.57(d, J= 4, 1H), 7.73-
7.71(m, 1H), 7.36-7.32(m, 1H).
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