An efficient heterogeneous Cu-grafted mesoporous organosilicas nanocatalyst for two and three component C-S coupling reactions

Article abstract of DOI:10.1166/jnn.2013.7574

Furfural-imine functionalized mesoporous organosilica material has been synthesized by postsynthesis surface functionalization of 2D-hexagnoal mesoporous SBA-15 with organosilane precursor 3-aminopropyltriethoxy-silane (APTES) followed by Schiff-base condensation with furfural. On the other hand, furfural-imine functionalized MCM-41 has been synthesized by Schiff-base condensation of furfural and 3-aminopropyltriethoxy-silane (APTES) followed by its hydrothermal co-condensation with tetraethylorthosilicate (TEOS) in the presence of a cationic surfactant CTAB. Subsequent reaction of the imine-functionalized mesoporous organosilicas with Cu(OAc)₂ in absolute ethanol produced Cu(II)-grafted mesoporous nanocatalysts 1 and 2, respectively. Powder XRD, HR TEM, FE SEM, N₂ sorption and EPR experimental tolls are employed to characterize these Cu-grafted furfural-imine functionalized nanocatalysts. Cu-grafted MCM-41 (1) showed very good catalytic efficiency for the coupling of aryl bromides and thiophenol under aerobic conditions to produce different thioethers. On the other hand, Cu-anchored mesoporous SBA-15 nanocatalyst (2) exhibited high catalytic activity for one-pot three component coupling of different aryl halides with thiourea and benzyl bromide in aqueous medium to produce different aryl alkyl thioethers in very good yields. Both Cu-grafted mesoporous nanocatalysts can be efficiently reused for several reaction cycles. Copyright

Full text of DOI:10.1166/jnn.2013.7574

Copyright © 2013 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 13, 4883–4895, 2013
An Efficient Heterogeneous Cu-Grafted Mesoporous
Organosilicas Nanocatalyst for Two and Three
Component C—S Coupling Reactions
John Mondal1, Noor Salam2, and Asim Bhaumik1ꢀ∗
1Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur 700032, India
2Department of Chemistry, University of Kalyani, Kalyani, Nadia 741235, W.B., India
Furfural-imine functionalized mesoporous organosilica material has been synthesized by post-
synthesis surface functionalization of 2D-hexagnoal mesoporous SBA-15 with organosilane pre-
cursor 3-aminopropyltriethoxy-silane (APTES) followed by Schiff-base condensation with furfural.
On the other hand, furfural-imine functionalized MCM-41 has been synthesized by Schiff-base
condensation of furfural and 3-aminopropyltriethoxy-silane (APTES) followed by its hydrothermal
co-condensation with tetraethylorthosilicate (TEOS) in the presence of a cationic surfactant CTAB.
Subsequent reaction of the imine-functionalized mesoporous organosilicas with Cu(OAc)2 in abso-
lute ethanol produced Cu(II)-grafted mesoporous nanocatalysts 1 and 2, respectively. Powder XRD,
HR TEM, FE SEM, N2 sorption and EPR experimental tolls are employed to characterize these
Cu-grafted furfural-imine functionalized nanocatalysts. Cu-grafted MCM-41 (1) showed very good
catalytic efficiency for the coupling of aryl bromides and thiophenol under aerobic conditions to
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produce different thioethers. On the other hand, Cu-anchored mesoporous SBA-15 nanocatalyst
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(2) exhibited high catalytic activity for one-pot three component coupling of different aryl halides
Copyright: American Scientific Publishers
with thiourea and benzyl bromide in aqueous medium to produce different aryl alkyl thioethers in
very good yields. Both Cu-grafted mesoporous nanocatalysts can be efficiently reused for several
reaction cycles.
Keywords: Aryl Alkyl Thoethers, Cu-Grafting, C S Bond Formation, 2 and 3 Component
Coupling Reactions, Furfural Imine Functionalized Mesoporous Organosilica.
1. INTRODUCTION
well as in the energy conversions.9 From the past one
decade it is believed that copper, in the nanoform pro-
vides fascinating catalytic activity in various organic trans-
formations. Due to the low cost of copper compared
to Au, Ag, Pd, Pt, Ru and Rh, Cu-containing com-
pounds/materials has attracted particular attention as cat-
alyst for various organic reactions.10ꢀ11 The size and
shape of these nanocatalysts became an important aspect
in catalyst design, which provides a highly active cat-
alyst surface, increasing the reaction rates and decreas-
ing the consumption of the catalyst.12ꢀ13 Furthermore,
Cu-grafted functionalized heterogeneous catalysts provide
the advantages of simplified isolation of the product, easy
recovery, enhanced stability and recyclability of the cata-
lysts over their respective homogeneous counterpart. Thus,
researchers are keener for the development of heteroge-
neous catalysts with the long catalyst life and reusability
for several cycles minimizing E factor.14ꢀ15 Many organic
transformations can be performed by employing hetero-
geneous copper catalysts such as supported CuNPs,16
Over a decade of extensive research nanomaterials have
emerged as one of the most useful and promising
materials because of their unique surface properties,
which are widely different from their corresponding bulk
systems.1ꢀ2 Due to their versatile potentials, nanomateri-
als are employed extensively in numerous frontline areas
such as electronic, optical, catalytic, coating, medical, sen-
sor applications, etc.3 High surface-to-volume ratio and
unique 1-, 2- or 3-dimentional morphological features
make the metal grafted nanoparticles more attractive cat-
alysts compared to the catalysts based on the respective
bulk materials.4ꢀ5 Further, different types of organic and
inorganic reactions catalyzed by self-assembled nanopar-
ticles are gaining increasing importance in recent times.6
Currently Cu/CuO nanoparticles have attracted a con-
siderable awareness in the field of catalysis7ꢀ8 and as
∗Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2013, Vol. 13, No. 7
1533-4880/2013/13/4883/013
doi:10.1166/jnn.2013.7574
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An Efficient Heterogeneous Cu-Grafted Mesoporous Organosilicas Nanocatalyst
Mondal et al.
nanostructured CuO materials,17 Cu/C,18 Cu/CuO,19 het-
ero bimetallic Cu–Ni/C20 and Cu/AlO(OH).21 One major
drawback in the heterogenization of Cu at the surface of
functionalized nanomaterials is that the nanoparticles have
the tendency to leach out irreversibly from its heteroge-
neous support, preventing long-lived recyclable use of the
nanocatalyst. This feature is sensitive to the ligand envi-
ronment of the copper ions, which strongly affect the dis-
persion of the copper species in the solid surface. So many
important factors such as the chemical nature of the sup-
port to entrap the copper nanoparticles, its acid-base func-
tionality (i.e., donar sites such as O, N, S atoms etc.) as
well as the location of copper nanoparticles into the chan-
nel of porous system play crucial role in catalyst life and
stability of the Cu-grafted nanocatalysts.23
In the last two decades considerable research work have
been devoted to synthesize mesoporous materials with tun-
able pore size distribution that can be used as a suitable
host matrix for anchoring metal/metal oxide species due to
their exceptionally high surface area, higher hydrothermal
and mechanical stability.24ꢀ25 Among them, SBA-15 type
silicas with the large mesopore can be synthesized using
poly (alkylene oxide) triblock copolymers as a structure
directing agent.26–28 The size, shape and connectivity of the
existing pores into the mesoporous materials can be tuned
through some chemical reactions in such a way that can
stabilize metal/metal oxide nanoparticles via anchoring of
be leached out from the mesopores during the reaction
conditions.
In this context it is pertinent to mention that C
S
bond formation reaction becomes an indispensable tool
in organic synthesis today and its importance is felt in
designing diverse array of target molecules ranging from
biological to pharmaceutical interestes35 as well as for the
development of new molecular precursor in the materi-
als science.36ꢀ37 A large variety of aryl sulfides can be
employed as drugs for the treatment of diabetes, inflam-
mation, Alzheimer’s and Parkinson’s disease,38 cancer39
and HIV disease.34 In this context, transition metal cat-
alyzed C S cross coupling40–43 reactions have been stud-
ied to a less extent compared to C C, C N and C
O
cross coupling reactions. Favorable S S oxidative cou-
pling reaction resulting in the undesired formation of
disulfides and simultaneous deactivation of metal catalyst
as organic sulfur compounds are effective metal binders,
make the C S cross coupling reaction quite inauspicious.
C
S cross-coupling has been performed with the use of
several transition metal catalysts such as palladium,44ꢀ45
nickel,46 copper,41 cobalt,42 iron,47 and indium48 etc. The
catalytic system associated with the palladium catalysts
for performing C S cross coupling reaction has been
employed to a limited extent due to the high cost, air
sensitivity of palladium salts and the use of environmen-
tally harmful organophosphorous ligands. Further, turn
over numbers (TON) for the Ni and Co catalysts in these
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the functional groups on the external surface and as well
as into the pores. The properties of these mesoporous sil-
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reactions are low. Due to the low cost and easy avail-
ability of copper salts it has the potential to be used
for the large scale catalytic process but the problems
associated with these catalysts are high reaction temper-
ature, long reaction time and severe reaction conditions.
So the copper containing heterogeneous catalyst must be
designed in such a way that will be inexpensive, non-
air sensitive and recyclable. C S cross coupling reaction
can be performed through the catalytic reaction of aryl
halides with thiophenol in the presence of a base. But
the direct use of volatile and foul-smelling thiols, which
hinders environmental and safety problems and limits the
use of this method for large scale operation. In this con-
text two interesting protocols have been developed for the
Copyright: American Scientific Publishers
ica supported nanocomposites can be controlled not only
by using the desired active ligands, which can encapsulate
the nanoparticles strongly but also dispersion of uniform
metal/metal oxide nanoparticles with the preservation of
the porous host structure. In recent times, two different
synthetic strategies are employed for the preparation of
Cu-grafted functionalized mesoporous silicas. Well dis-
persed CuO nanoparticles can be efficiently prepared by
“direct synthetic” method, which is industrially more prac-
ticable as it is relatively easy and convenient to han-
dle. CuO loaded mesoporous silicas like MCM-41 and
MCM-48 have been designed by using this strategy.29–31
Synthesis of Cu-rich functionalized mesoporous material
without the distortion of the pore ordering of the sup-
port becomes a tedious job as copper salts have the ten-
dency to leach out in acidic medium. Today considerable
efforts have been devoted for the synthesis of Cu(II)-rich
SBA-15 and KIT-6 materials by tuning “direct synthetic”
method.32 Post synthetic strategies are also be applied for
the synthesis of highly dispersed Cu nanoparticles sup-
ported over ordered mesoporous materials as host.33 Very
recently, some attempts have been made to design meso-
porous composite nanomaterials through the grafting of
metal ions on preliminary functionalized silica surface.34
Mesoporous silica has been functionalized in such a way
that the active metal ion can bind tightly with silica inside
the cavity present at the mesopore surface so that it cannot
C
S bond formation reactions catalyzed by Cu-grafted
nanocatalysts. One is the one-pot Michael addition reac-
tion via an odourless process involving in situ genera-
tion of S-alkylisothiouronium salts in water49 and another
one is one-pot thioetherification of aryl halides using
thiourea (free from the foul smell of thiols).50 In these
processes thiourea has been used instead of thiol and
thiourea undergoes reaction with the aryl halides to gen-
erate thiol moiety in situ and makes the catalytic pro-
cess free from foul smell. Thus, designing an efficient and
environmentally friendly Cu nanocatalyst for C S cross
coupling reaction without using foul smell thiol is highly
desirable to address these environmental and industrial
concerns.
4884
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Mondal et al.
An Efficient Heterogeneous Cu-Grafted Mesoporous Organosilicas Nanocatalyst
Herein, we report the synthesis and detailed characteriza-
tions of two Cu-grafted mesoporous nanocatalyst employ-
ing both “in-situ grafting” and “post grafting” methods.
Fufural-imine functionalized mesoporous material has been
synthesized by Schiff-base condensation of furfural and
3-aminopropyltriethoxy-silane (APTES) followed by its
hydrothermal co-condensation with tetraethylorthosilicate
(TEOS) in the presence of a cationic surfactant CTAB.
This mesoporous nanoparticles was functionalized by reac-
tion with Cu(OAc)2 to obtain Cu-grafted MCM-41 (1),
which acts as efficient catalyst for the C S cross cou-
pling reaction in DMF to yield different value added
sulfides. In another case “post grafting” method has
been applied to synthesize Cu-grafted SBA-15 nanocata-
lyst (2). This heterogeneous catalyst was developed by sur-
face functionalization with 3-aminopropyl-triethoxysilane
(APTES) followed by Schiff-base condensation with fur-
fural. This functionalized SBA-15 material was treated
with Cu(OAc)2 to provide Cu-grafted SBA-15 nanocatalyst
(2), which catalyzes one-pot three component thioetheri-
fication reaction of aryl halides with benzyl bromide and
thiourea in aqueous medium in the presence of K2CO3
base.
of the gel at 12.0. The resulting gel was left under stir-
ring for another 12 h at room temperature and then it was
autoclaved at 353 K for 72 h under static condition. After
72 h it was cooled at room temperature and filtered to offer
yellow colored solid. The template CTAB was removed
from as-synthesized sample by extracting the solid mass
for three times with ethanolic solution of HCl at room
temperature and this sample has been designated as (B).
2.1.3. Synthesis of Cu-Grafted Mesoporous MCM-41
Nanocatalyst (1)
Furfural-imine functionalized mesoporous silica B (1 g)
was diapersed in ethanol (20 ml) solution through contin-
uous stirring at room temperature for 30 min. Then cop-
per (II) acetate (0.2 g) was added into the mixture and the
stirring was continued at the room temperature to obtain
a homogeneous blue colored solution. It was refluxed for
about 8 h at 363 K. The color of the mesoporous material
was slowly changed from yellow to light green and no fur-
ther color change occurred on further reflux. The reaction
mixture was cooled at room temperature and the resulting
light green colored mesoporous solid was isolated through
filtration under suction. After washing several times with
ethanol it was dried under vacuum. The light green colored
mesoporous material was designated as Cu-grafted meso-
2. EXPERIMENTAL DETAILS
porous MCM-41 nanocatalyst 1. The outline for the prepa-
2.1. Synthesis of DCeul-iGverareftdedbMy PesuobploisrohuinsgMTCeMch-4n1ology to: Rice University, Fondren Library
ration of this furfural-imine functionalized Cu nanocatalyst
Copyright: American Sicsieshnotiwfinc iPnuSbclhisehmeers1.
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Nanocatalyst (1)
2.1.1. Synthesis of Schiff Base Ligand (A)
2.2. Synthesis of Cu-Grafted Mesoporous SBA-15
Nanocatalyst (2)
A solution of APTES (0.01 mol, 2.21 g, Aldrich) in dry
ethanol (5 ml) was added dropwise into the furfural solu-
tion (0.01 mol, 0.9609 g taken in dry ethanol 20 ml) over
20 min under vigorous stirring condition. After the com-
plete addition of organic ligand the reaction mixture was
refluxed for about 8 h. Then reaction mixture was allowed
to cool at room temp and excess solvent was evaporated to
dryness, leaving behind a dark brown colored viscous gel.
This dark brown colored viscous liquid was designated as
2.2.1. Synthesis of 3-Aminopropyl Functionalized
SBA-15
Calcined mesoporous silica SBA-15 was synthesized by
the reported procedure as described before.27 0.18 g of 3-
aminopropyltriethoxysilane (3-APTES) was added into the
calcined SBA-15 (0.1 g) dispersed into CHCl3 (10 mL)
1
(A) and it was characterized by H and 13C NMR.
2.1.2. Synthesis of Furfural Functionalized Mesoporous
Organic Hybrid Silica (B)
In a typical synthesis procedure structure directing agent
CTAB (Loba Chemie, 0.0075 mol, 2.73 g) was added in an
aqueous solution of tartaric acid (0.6 g in 20 g H2O) and
the resulting mixture was allowed to stirr for about 30 min.
After the solution becomes clear, dark brown color viscous
gel (A) (1.35 g) in 5 mL ethanol was added dropwise into
the surfactant solution and the resulting mixture was stirred
for about 2 h. Then 5.245 g TEOS (0.025 mol) was added
in the previous solution and it was stirred for about 2 h
to obtain a brown colored viscous gel. After that TMAOH
solution was added dropwise into the gel to make the pH
Scheme 1. Synthesis of Cu-F-MCM-41 nanocatalyst (1).
J. Nanosci. Nanotechnol. 13, 4883–4895, 2013
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An Efficient Heterogeneous Cu-Grafted Mesoporous Organosilicas Nanocatalyst
Mondal et al.
and the mixture was stirred at room temperature under N2
atmosphere for about 12 h. The resulting white solid was
isolated by filtration from the reaction mixture, washed
with chloroform followed by dichloromethane and finally
dried in air. The white colored solid was designated as I.
2.2.2. Synthesis of Furfural-Imine Functionalized
Mesoporous SBA-15 (D)
A solution of furfural (0.00081 mol, 0.077 g) taken in
methanol (5 ml) was added dropwise into the 3-APTES
functionalized SBA-15 material I dispersed into methanol
(15 ml) under vigorous stirring condition at room tem-
perature. After the complete addition of furfural the reac-
tion mixture was refluxed for about 6 h at 333 K. After
10–15 minutes the color of the reaction mixture was
changed into deep yellow and no further color change
occurred on further reflux after 6 h. The reaction mixture
was cooled at room temperature and the final yellow prod-
uct was filtered by repeatedly washing with hot methanol to
remove the unreacted aldehyde. The yellow colored mate-
rial was dried in air and was designated as (D).
Scheme 2. Synthesis of Cu-F-SBA-15 nanocatalyst (2).
with the addition of 2 ml water and catalyst was sep-
arated by simple filtration. The filtrate was diluted with
EtOAc (20 ml) and it was extracted with EtOAc with the
addition of 10% aqueous NaOH solution for several times
to remove the solvent DMF. The combined organic layer
was washed with water and brine solution. Then the com-
bined organic layer was dried over anhydrous Na2SO4 and
evaporated to dryness to offer the crude product diphenyl
2.2.3. Synthesis of Cu-Grafted Mesoporous SBA-15
Nanocatalyst (2)
sulfide as colorless oil. The isolated crude product was
1
characterized by H and 13C NMR respectively. The C
S
Dried furfural-imine functionalized mesoporous SBA-15
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coupling reaction between thiophenol with aryl bromides
over catalyst 1 is shown in the Scheme 3.
(D) (1 g) was dispersed in the absolute ethanol (20 ml).
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Then 0.2 g of copper (II) acetate was added into the pre-
Copyright: American Scientific Publishers
vious reaction mixture. Then the resulting reaction mix-
ture was kept under refluxing condition for about 8 h at
363 K. The color of the mesoporous material was slowly
changed from deep yellow to light green and no fur-
ther color change occurred on further reflux. The reaction
mixture was cooled at room temperature and the result-
ing mesoporous material was filtered through suction and
thoroughly washed with ethanol. After washing it was
dried at the room temperature. The light green colored
mesoporous material has been designated as Cu-grafted
mesoporous SBA-15 nanocatalyst (2). The outline for the
preparation of this Cu-grafted SBA-15 nanocatalyst is
shown in Scheme 2.
2.3.2. One-Pot Three Component Thioetherification in
Aqueous Medium
At first K2CO3 (552 mg, 4 mmol) and thiourea (91 mg,
1.2 mmol) were dissolved in 5 ml water. Then aryl halide
(1 mmol), benzyl bromide (188 mg, 1.1 mmol) and Cu-
grafted SBA-15 nanocatalyst (2) (25 mg) were added into
the previous aqueous solution and the resulting mixture
was heated at 373 K in an oil bath for the desired reac-
tion time. Progress of the reaction was monitored using
TLC. After completion of the reaction, the reaction mix-
ture was cooled to room temperature and it was extracted
with EtOAc. The combined organic layer was washed with
water to remove excess unreacted thiourea and then fol-
lowed by brine solution. Then the combined organic layer
was dried over anhydrous Na2SO4 and evaporated to dry-
ness to offer the preferred aryl alkyl thioethers as colorless
oil. The isolated crude product was characterized by 1H
and 13C NMR respectively. The reaction pathway for the
2.3. Catalytic Testing Procedure
2.3.1. Two Component C S Coupling Reaction of Aryl
Bromides with Thiophenol
A solution of bromobenzene (204 mg, 1 mmol), thiophe-
nol (121 mg, 1.1 mmol) and K2CO3 (276 mg, 2 mmol)
in 3 ml DMF was stirred at room temperature for 1 h.
Then Cu-grafted MCM-41 nanocatalyst 1 (20 mg) was
added into the reaction mixture and it was heated at 383 K
in an oil bath under aerobic condition. The progress of
the reaction was monitored by TLC. After a period of
time the reaction mixture was allowed to cool, quenched
Scheme 3.
C
S coupling reaction of bromobenzene with thiophenol
over Cu-F-MCM-41 nanocatalyst (1).
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Mondal et al.
An Efficient Heterogeneous Cu-Grafted Mesoporous Organosilicas Nanocatalyst
Fig. 1. Small angle powder XRD pattern of Cu-F-SBA-15 nanocata-
lyst (a) and reused nanocatalyst after catalytic reaction (b).
Scheme 4. One pot thioetherification reaction of aryl halides using
thiourea and benzyl bromide over Cu-F-SBA-15 nanocatalyst (2) in aque-
ous medium.
corresponding to 110 and 200 planes have been decreased
from that before Cu-loading. This considerable decrease in
the peak intensities on grafting of Cu at the surface could
be attributed to the lowering of local order. The PXRD
pattern of this material after six repetitive reaction cycles
is shown in Figure 1(b). From this pattern it is clear that
the Cu-nanocatalyst retains its mesoporous structure after
repeated recycles. The wide angle XRD pattern of the Cu
grafted SBA-15 nanocatalyst suggests that new orthorhom-
bic phase has been generated on the pore wall (Fig. 2(a)).
This nanocatalyst retains its nanostructures and crystalline
phase after catalytic recycling (Fig. 2(b)).
one-pot thioetherification reaction of aryl halide by using
thiourea and benzyl bromide over catalyst (2) in aqueous
medium is shown in the Scheme 4.
2.4. Characterization Techniques
Powder X-ray diffraction patterns are recorded on a Bruker
D-8 Advance SWAX diffractometer operated at 40 kV
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voltages and 40 mA current. The instrument has been cal-
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ibrated with a standard silicon sample, using Ni-filtered
Copyright: American Scientific Publishers
Cu Kꢁ (ꢁ = 0ꢂ15406 nm) radiation. Nitrogen adsorp-
tion/desorption isotherms were obtained using a Quan-
tachrome Autosorb 1 C at 77 K. Prior to gas adsorption, all
the samples were degassed for 10 h at 423 K. A JEOL JEM
6700F field emission scanning electron microscope is used
for the determination of morphology of the particles. High
resolution transmittance electron microscopic (HR TEM)
images were recorded in a Jeol JEM 2010 transmission
electron microscope. Cu loading in the sample was esti-
mated by using a Perkin-Elmer Optima 2100 DV Induc-
tive Coupled Plasma Atomic Emission Spectroscopy (ICP-
AES). 1H and 13C NMR experiments were carried out on a
Bruker DPX-300 NMR spectrometer. EPR measurements
were performed on a Bruker EMX EPR spectrometer at X-
band frequency (9.46 GHz) at liquid nitrogen temperature
(77 K).
N2 adsorption/desorption isotherms of the Cu-grafted
SBA-15 nanocatalyst and its reused form are shown in
the Figure 3. Both these samples showed typical type IV
isotherms with very large hysteresis loops in the 0.5 to
0.8 P/P range. The isotherms account for the relatively
ꢀ
ordered mesopore and the hysteresis loop is the charac-
teristic for the large tubular pores of SBA-15. The BET
surface areas for the Cu-grafted SBA-15 nanocatalyst and
3. RESULTS AND DISCUSSION
3.1. Characterisation of Catalysts
The small-angle powder X-ray diffraction (SAXRD) pat-
tern of Cu-grafted SBA-15 nanocatalyst (2) showed a sin-
gle intense peak (2ꢃ = 0ꢂ9) corresponding 100 (strong)
plane (Fig. 1(a)). This result suggests that the mesophase
has been preserved on grafting of Cu at the functional-
ized SBA-15 surface. But the intensities of the other peaks
Fig. 2. Wide angle powder XRD patterns of Cu-F-SBA-15 nanocata-
lysts: fresh (a) and reused (b).
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An Efficient Heterogeneous Cu-Grafted Mesoporous Organosilicas Nanocatalyst
Mondal et al.
observed here clearly suggests that there is no change
in the surface nanostructure and mesophase of the Cu-F-
SBA-15 material during the course of reaction.51
TEM images of the Cu-F-SBA-15 nanocatalyst are
shown in the Figure 4. Figure 4(A) clearly advocates that
the honeycomb-like hexagonally ordered mesopores hav-
ing dimensions 4.0–4.6 nm are arranged in the respec-
tive Cu nanocatalyst.52 The FFT diffractogram (inset of
Fig. 4(A)) predicts that the 2D-hexagonal pore channels
are present in the Cu-F-SBA-15 nanocatalyst. The black
colored spots present in the Figures 4(A) and (B) are
due to the chelation of furfural-grafted imine ligand with
Cu2+ ion and these black color Cu nanoclusters are uni-
formly distributed throughout the sample. Figure 4(C) clar-
ifies that the material has rod shaped particle morphology,
which is due to the chelation of the imine ligand with Cu+2
ion and as a result the growth of the nanocluster occurs in
the 1D way leading to the growth of the 1D nanorod. The
pore dimensions and distribution of the Cu nanoclusters
remains same in the reused catalyst (Fig. 4(D)).53
Fig. 3. N2 adsorption/desorption isotherms of Cu-F-SBA-15 nanocata-
lyst: fresh (a) and reused (b). Pore size distributions estimated through
NLDFT method is shown in the inset.
reused catalyst (Figs. 3(a) and (b)) are 118 m2 g−1 and
107 m2
g
−1, respectively and their corresponding pore
size dimensions (calculated by the NLDFT method and
shown in the inset of the Fig. 3) are 5.5 nm and 5.1 nm,
respectively. A small decrease in the BET surface area
The EPR spectra of the Cu-F-SBA-15 nanocatalyst
are shown in the Figure 5. EPR spectrum of Cu-F-
SBA-15 nanocatalyst displayed four splitting patterns
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Copyright: American Scientific Publishers
Fig. 4. HR TEM images of Cu-F-SBA-15 nanocatalyst (A), FFT pattern is shown in the inset), (B) and (C). TEM image of reused catalyst (D) after
sixth catalytic cycles.
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Mondal et al.
An Efficient Heterogeneous Cu-Grafted Mesoporous Organosilicas Nanocatalyst
Fig. 5. EPR spectrum of Cu-F-SBA-15 nanocatalyst: fresh (a) and
reused (b).
(mI = −3/2ꢀ −1/2ꢀ +1/2ꢀ +3/2) in the low-field
region (Fig. 5(a)) for the parallel component due to the
hyperfine interaction between the unpaired electron and
the nuclear spin of copper (I = 3/2). But the signals
for the perpendicular component (g = 2ꢂ06) remain un-
⊥
resolved. These are the characteristics signals typical for
isolated Cu2+ cations in the axial symmetry. EPR spec-
trum of Cu-F-SBA-15 nanocatalyst (Fig. 5(a)) showed:
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g = 2ꢂ26 and A = 172 G, which could provide us the
ꢁ
ꢁ
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information that the Cu(II) ions are arranged in the dis-
Copyright: American Scientific Publishers
torted square planar geometry. Therefore large pore of
Cu-F-SBA-15 nanocatalyst (4.6 nm) offers a confinement
effect to change a flexible geometry from square pyrami-
dal to a more distorted pattern. In the EPR spectrum of the
reused catalyst (Fig. 5(b)) the four splitting patterns and
the g , g and A values remain unaltered, suggesting that
Fig. 6. FE SEM images of Cu-F-SBA-15 nanocatalyst (A) and reused
Cu-F-SBA-15 nanocatalyst (B).
⊥
ꢁ
ꢁ
there is no change in the geometry and the environment of
large nanorods. The FE SEM image (Fig. 6(B)) of the
reused Cu-F-SBA-15 nanocatalyst suggests that the rod
shape morphology has been preserved after the catalysis.56
the catalyst during the course of the reaction.54
The FE SEM images of Cu-F-SBA-15 nanocatalyst and
reused catalyst are shown in the Figure 6. The FE SEM
image of the Cu-F-SBA-15 nanocatalyst (Fig. 6(A)) pre-
dicts us that this material has nanorod shape morphology.
Due to the strong coordinating ability of furfural-imine
functionalized SBA-15 it can form a complex with the
Cu+2 ion. As a result spherical nanoparticles coordi-
nate with the Cu+2 ion and leads to the growth of the
nanoparticles in 1D direction, resulting in the formation
of nanorods. We are quite aware about the fact that imine
functionalized ligand molecules also behaved as the cap-
ping agents that can selectively adsorbed onto the lateral
surfaces of the 1D Cu nanostructures causing complete
inhibition of lateral growth of the nuclei. As a result this
growth of the product continues along the c-axis in the
direction of 001 plane.55 Thus, our imine functionalized
silica served not only as the coordinating agent but also
as capping ligand, which played a crucial role for the 1D
growth of the spherical nanoparticles for the formation of
3.2. Catalytic Evaluations
C
S coupling reaction of different aryl bromides with
thiophenol in DMF (Scheme 3) was explored over the
Cu-F-MCM-41 nanocatalyst (1) to produce different sub-
stituted aryl thioether in excellent yields for various
electron donating and electron withdrawing compounds
1
(Table I). All these products are characterized by H and
13C NMR spectroscopy.57 The C S coupling reaction was
completed within 8–10 h for all the aryl bromides and
the turn over frequencies are moderately high (Table I).
It was found that 0.02 g is the optimum amount of
Cu-F-MCM-41 nanocatalyst required to perform this C
S
coupling reaction. The increase of catalyst amount does
not improve the yield of the products any further, whereas
decreasing the amount of catalyst leads to decrease in
the product yield. Under optimized reaction conditions for
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An Efficient Heterogeneous Cu-Grafted Mesoporous Organosilicas Nanocatalyst
Mondal et al.
Table I.
C
S coupling reaction of aryl bromides with thiophenol over Cu-F-MCM-41 nanocatalyst under aerobic conditions.a
Yieldb (%)
Entry
Aryl bromides
Br
Time (h)
Product
S
TON
37.9
1
2
8
82
H3CO
OHC
H3CO
S
Br
8
88
40.7
OHC
Br
3
4
5
10
8
86
85
85
39.8
39.3
39.3
S
NC
NC
Br
S
HO2C
HO2C
S
9
Br
H3COC
H3COC
Br
6
7
10
84
38.8
37.9
S
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82
OHC
Br
S
OHC
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Copyright: American Scientific Publishers
O2N
O2N
S
8
9
11
78
36.1
34.7
Br
NH2
S
H3C
NH2
10
75
Br
CH3
CHO
S
10
8
82
37.9
Br
CHO
d
H3CO
H3CO
11
8
58
26.8
9.2
Br
Br
S
S
H3CO
H3CO
e
12
16
2 0
Notes: aReaction conditions: aryl bromide (1 mmol, bromobenzene, 157 mg, entry 1), thiophenol (1.1 mmol, 121 mg), K2CO3 (2 mmol, 276 mg), DMF (3 ml), reaction
temperature: 110 ꢀC (oil bath), Cu-F-MCM-41 nanocatalyst (1): 20 mg; bIsolated yield of the product, cTurn over number (TON) = moles of substrate converted per mole
of active site; dReaction conditions: 4-bromoanisole (1 mmol, 187 mg), thiophenol (1.1 mmol, 121 mg), K2CO3 (2 mmol, 276 mg), DMF (3 ml), reaction temperature:
333 K (oil bath), Cu-F-MCM-41 nanocatalyst: 20 mg; eReaction conditions: 4-bromoanisole (1 mmol, 187 mg), thiophenol (1.1 mmol, 121 mg), K2CO3 (2 mmol, 276 mg),
DMF (3 ml), reaction temperature: 298 K (room temperature), Cu-F-MCM-41 nanocatalyst: 20 mg.
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An Efficient Heterogeneous Cu-Grafted Mesoporous Organosilicas Nanocatalyst
the C S coupling reaction the time taken and the prod-
uct yield obtained are listed in the Table I. The aldehy-
des with both electron donating (Table I, entries 2 and 9)
and electron withdrawing groups (Table I, entries 3, 4,
5, 6, 7, 8 and 10) participated in the C S coupling
reaction with equal efficiency. Thus, the nature and posi-
tion of substitution in the aromatic ring did not affect
the reactions much. The meta-substituted aromatic alde-
hyde (Table I, entry 7) as well as sterically hindered
ortho-substituted aromatic aldehydes (Table I, entries 9
and 10), both undergo arylthiolation very smoothly. Ortho-
substituted bromo benzene bearing –NH2 moiety in the
aromatic ring was compatible in this coupling reaction
without any reaction with the –NH2 group (Table I, entry
9). The C S coupling reaction can be performed with the
several sensitive functional groups attached with the aro-
matic ring (Table I, entries 3, 4, 7, 8 and 10). The reaction
was conducted by taking 4-bromoanisole and thiophenol
in the presence of Cu-F-MCM-41 nanocatalyst at 333 K
and 298 K temperature, providing yield 58% and 40%
respectively (Table I, entries 11 and 12). From these above
results we can conclude that the Cu-F-MCM-41 nanocat-
alyst is highly reactive at elevated temperature and 383 K
is the optimum temperature required for the promotion of
too. This data clearly suggests that the Cu nanoclusters
present at the catalyst surface play a crucial role to conduct
this C S coupling reaction. We have performed the C
S
coupling reaction in DMF solvent for bromobenzene and
thiophenol by using the homogeneous Cu-catalyst such as
Cu(OAc)2 ·H2O (Table II, entry 4). But the homogeneous
phase Cu catalyst Cu(OAc)2 ·H2O showed much lower cat-
alytic activity than our Cu-F-MCM-41 nanocatalyst. When
Cu(OAc)2 · H2O was used as a catalyst in the C S cou-
pling reaction of iodobenzene and thiophenol then only
35% yield of the product was obtained (Table II, entry 5).
Similarly, when Cu(OAc)2 ·H2O is used as catalyst at room
temperature (298 K) in DMF no product was observed
(Table II, entry 6). When Cu nanoparticle was anchored
with the simple MCM-41 silica through simple impregna-
tion, resulting catalyst showed only 45% product yield of
the coupling product (Table II, entry 7). This experimen-
tal data predicts us that furfural-imine functionalized Cu
nanocatalyst showed best results in terms of product yield
and reaction rate compared to simple MCM-41 anchored
Cu nanopraticles for this two component C S coupling
reaction.58 So functionalization with the organic ligand is
more important to anchor Cu nanoparticles strongly with
a uniform distribution at the mouth of the mesopores for
the promotion of two component C S coupling reaction.
With this sequence various bis-thioethers were achieved
as illustrated in Scheme 3. This coupling reaction pro-
C
S coupling reaction. In order to understand the ori-
gin of catalytic activity in the Cu nanoclusters grafted
into the functionalized MCM-41 silica, a control experi-
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vides enormous scope for an easy access to a library
of bisthioethers and will have much potential in organic
ment for the C S coupling reaction was performed by
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taking bromobenzene and thiophenol in absence of any
catalyst in DMF solvent at 383 K (Table II, entry 1).
Under this condition no reaction occurs and the starting
components remain unreacted. We have also carried out
the reaction in the presence of pure mesoporous silica
MCM-41 (Table II, entry 2) and furfural-imine function-
alized MCM-41 (Table II, entry 3) for bromobenzene and
thiophenol in DMF at 383 K. However, no correspond-
ing diphenyl sulfide was obtained under these conditions
Copyright: American Scientific Publishers
synthesis such as for the synthesis of poly-(p-phenylene
sulfide) polymers. ICP-AES analysis revealed that the Cu
content of this catalyst was 1.08 mmol g−1. The TONs for
various unsymmetrical diarylsulfides over catalyst 1 are
listed in the Table I (varies between 37.9–9.2).
One-pot thioetherification (Scheme 4) of different aryl
halides (chloro and bromo substituted arenes) using benzyl
bromide in the presence of thiourea in aqueous medium
at 100 ꢀC over Cu-F-SBA-15 nanocatalyst (2) gave dif-
ferent aryl alkyl substituted thioethers in good yields.
The reaction condition for this one-pot thioetherifica-
tion reaction was optimized with the reaction of ben-
zyl bromide (1.1 mmol, 188 mg), thiourea (1.2 mmol,
91 mg), bromobenzene (1 mmol, 157 mg) in the pres-
ence of K2CO3 base (4 mmol, 552 mg) over Cu-F-SBA-15
nanocatalyst (25 mg) in H2O under aerobic condition.
The reaction proceeded smoothly and gave phenyl benzyl
thioether with 82% yield.59 We have studied the exposure
of the reaction by applying various functional group sub-
stituted bromo- and chloro-arenes. Electron withdrawing
functional groups such as –NO2, –CHO, –COCH3, –CN
attached with the bromo- and chloro-arenes participated in
the C S coupling reaction very smoothly. Electron donat-
ing substituents such as –OCH3, –CH3, –OH, –NH2 on the
aromatic ring were compatible for this reaction and gave
uniformly high yield under this reaction condition. Hetero-
cyclic bromo compound (bromo pyrazole) underwent this
Table II. Screening of different catalyst sources for the C S cou-
pling reaction of aryl bromide with thiophenol over Cu-F-MCM-41
nanocatalyst.a
Entry
Catalyst
Time (h)
Yield (%)
1
2
3
4
5
6
7
No catalyst
MCM-41
15
15
15
15
15
10
15
0ꢂ0
0ꢂ0
0ꢂ0
25ꢂ0
35ꢂ0
0ꢂ0
Furfural-MCM-41
Cu(OAc)2 ·H2O
Cu(OAc)2 ·H2Ob
Cu(OAc)2 ·H2Oc
MCM-41 supported Cu nano
45ꢂ0
Notes: aReaction conditions: bromobenzene (1 mmol, 157 mg), thiophenol (1.1
mmol, 121 mg), K2CO3 (2 mmol, 276 mg), DMF (3 ml), reaction temperature:
110 ꢀC (oil bath), catalyst: 20 mg; bReaction conditions: iodobenzene (1 mmol,
204 mg), thiophenol (1.1 mmol, 121 mg), K2CO3 (2 mmol, 276 mg), DMF
(3 ml), reaction temperature: 110 ꢀC (oil bath), catalyst: Cu(OAc)2 · H2O, 20 mg;
cReaction conditions: bromobenzene (1 mmol, 157 mg), thiophenol (1.1 mmol,
121 mg), K2CO3 (2 mmol, 276 mg), DMF (3 ml), reaction temperature: 25 ꢀC
(room temperature), catalyst: Cu(OAc)2 ·H2O (20 mg).
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An Efficient Heterogeneous Cu-Grafted Mesoporous Organosilicas Nanocatalyst
Mondal et al.
Table III. Effect of bases for one-pot thioetherification reaction of
bromobenzene with benzyl bromide and thiourea over Cu-F-SBA-15
nanocatalyst.a
Entry
Base
Yield (%)b
1
2
3
4
5
K2CO3
Na2CO3
KOH
NaOH
Pyridine
82
75
60
60
50
Notes: aReaction conditions: aryl bromide (1 mmol, bromobenzene, 157 mg ),
thiourea (1.2 mmol, 91 mg), benzyl bromide (1.1 mmol, 188 mg), base (4 mmol),
H2O (5 ml), reaction temperature: 100 ꢀC (oil bath), Cu-F-SBA-15 nanocatalyst:
25 mg; bIsolated yield of the product.
Scheme 6. One pot thioetherification reaction of 3, 5-dibromosalicylic
acid using thiourea and benzyl bromide over Cu-F-SBA-15
nanocatalyst (2).
yield in the DMF solvent. Water has not been used here
as a solvent as the reaction for this paricular compound is
very poor in water solvent. We have introduced a compar-
ison data of our Cu-grafted nanocatalysts with the previ-
ously reported catalysts in the Table IV. From this Table IV
it is clear that our Cu-grafted mesoporous nanocatalysts
are more efficient than the other catalysts for performing
the C S coupling and thioetherification reactions.
one-pot thioetherification reaction with equal efficiency.
–NH2 substituted chloro compound did not undergo sub-
stitution reaction with benzyl bromide in the presence
of K2CO3 base under the reaction condition. The Cu con-
tent of the fresh catalyst was 0.986 mmol g−1, as measured
by ICP-AES analysis. A control experiment was conducted
by using bromobenzene, benzyl bromide and thiourea but
no corresponding product was obtained. In order to clarify
the fact that the catalytic activity generated from the Cu
sites we have performed the reaction in presence of SBA-
15 and furfural-SBA15 under optimized reaction condition
but here also no yield of the product was obtained. The
homogeneous phase Cu(OAc) ·H O was used as a catalyst
AAS analysis was carried out to estimate the Cu content
for the both nanocatalysts in the fresh form and after the
catalysis. After the completion of respective C S coupling
and thioetherification reaction the product was filtered off
and washed with acetone and then the filtrate was evapo-
rated to dryness. 30 wt% of nitric acid was added to the fil-
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2
IP: 115.127.33.132 On: Sun, 11 Oct 2015 15:39:32
for this thioetherification reaction but only 45% product
trate, and the resulting sample adjusted to 5 wt% nitric acid
was isolated.60 The reaction has been performed in a large-
Copyright: American Scientific Publishers
was applied to characterize the Cu leaching. Cu content in
the filtrate was analyzed by using a Shimadzu AA-6300
atomic absorption spectrophotometer. Atomic absorption
spectrometric analysis of the liquid phase suggested the
absence of any detectable amount of Cu in the filtrate solu-
tion and that filtrate remains complete colorless. We have
verified our results through ICP-AES analysis for both
scale by taking 1-bromo-4-nitrobenzene in the 10 mmol
scale. Here also desired product benzyl 4-nitrophenyl sul-
fide was obtained in 86% yield. We have tested the scope
of thioetherification reaction by employing different bases
considering the reaction of bromobenzene with benzyl bro-
mide and thiourea in aqueous medium (Table III). Various
bases such as pyridine, Na2CO3 and K2CO3 provided the
thioethers in moderate to excellent yields (Table III, entries
5, 2 and 1). When NaOH and KOH were used as the base
for this thietherification reaction then both of them pro-
vide same yield (Table III, entries 3 and 4). 1, 4-dibromo
benzene also undergoes double thioetherification reaction
in the presence of benzyl bromide and thiourea under
optimized conditions with the corresponding yield 75%
(Scheme 5). Similarly 3,5-dibromosalicylic acid undergoes
one pot thioetherification reaction to produce bis thioether
derivative in DMF solvent (Scheme 6). It produces 72%
Table IV. Comparison of Cu-grafted nanocatalysts with the reported
previous catalysts.
Catalyst
Solvent
NMP
Time (h) Yield (%) Reference
CuI (2.5 mol %)
No reusability
CuO nanoparticle
Cu/SiO2
CuI and Phen
CuO nanopowder
CoCl2 ·6H2O/ cationic
2,2ꢂ-bipyridyl system
Cu2O
16
92a, 60b
[58]
DMSO
DMSO
Toluene
Ionic liquid
H2O
10
11
3
95a, 37c
83c
[61]
[62]
[43]
[40]
[42]
67.2a
2
99d, 27e
24a, 48c 85a, 72c
DMSO
iPrOH
24d
22
61c
90
[63]
[64]
CuI in
Ethylene glycol
NiO-ZrO2
CuI
H2O
Wet PEG 200
24
24f
62a
80
[25]
[59]
Notes: aReaction was carried out with iodobenzene; bReaction was carried out
in aqueous medium; cRecation was carried out with bromobenzene; dReaction
was performed with Cs2CO3 base; eReaction was performed with K2CO3 base;
f Thioetherificarion reaction was carried out.
Scheme 5. One pot thioetherification reaction of 1,4-dibromobenzene
using thiourea and benzyl bromide over Cu-F-SBA-15 nanocatalyst (2)
in aqueous medium.
4892
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Mondal et al.
An Efficient Heterogeneous Cu-Grafted Mesoporous Organosilicas Nanocatalyst
the reused nanocatalysts. After 6th reaction cycle the Cu
content has been slightly decreased to 0.99 mmol g−1
and 0.979 mmol g−1 for the both catalysts Cu-F-MCM-41
nanocatalyst and Cu-F-SBA-15 nanocatalyst, respectively
(this decrease is within the experimental error of chem-
ical analysis). This result clearly signifies that Cu sites
have been covalently anchored with the organic functional
groups inside the backbone of silica unit, which indicates
no leaching of Cu occurs from the backbone of meso-
porous catalyst during course of reaction under optimized
condition.
Scheme 7. Three phase test for
Cu-F-MCM-41 nanocatalyst.
C
S coupling reaction over
Hot filtration test was carried out under optimized reac-
tion condition to understand the heterogeneity of our cat-
alytic systems. For the two component C S coupling
reaction 4-bromo anisole (1 mmol, 187 mg), thiophenol
(1.1 mmol, 121 mg), K2CO3 (2 mmol, 276 mg) and Cu-F-
MCM-41 nanocatalyst (25 mg) in 5 ml DMF was heated
at 383 K for 4 h. Also for the typical thioetherifica-
tion reaction 4-bromo anisole (1 mmol, 187 mg), K2CO3
(4 mmol, 552 mg), thiourea (1.2 mmol, 91 mg), benzyl
bromide (1.1 mmol, 188 mg) and Cu-F-SBA-15 nanocat-
alystꢀ (25 mg) in 5 ml of H2O was heated to refluxed at
100 C for 6 h. After a certain time (time included previ-
ously i.e., 4 h and 6 h) both the reaction were stopped. The
Cu-catalysts were filtered off (from the hot reaction mix-
ture) after 4 h and 6 h, respectively. GC and 1H NMR data
benzyl 4-methoxyphenyl sulfide product confirms that
4-bromoacetophenone did not take part in the thioetherifi-
cation reaction. Absence of any Cu leaching to the solution
confirms that anchored p-bromoacetophenone did not take
part in the thioetherification reaction. Had the copper from
Cu-F-SBA-15 nanocatalyst being leached to the solution,
the product that could have been obtained would be benzyl
4-formyl sulfide instead of benzyl 4-methoxyphenyl sul-
fide. Thus, this three-phase test provides further evidence
that the reaction is truly heterogeneous in nature and there
is no leaching of copper during the course of reaction.
The same procedure was followed for the Cu-F-MCM-41
nanocatalyst for the two component C S coupling reac-
tion. The three phase test reaction scheme was provided in
the Scheme 7.
In order to establish recyclability of the nanocatalysts
the C S coupling reaction (4-bromoanisole and thiophe-
nol) and one-pot thioetherification (4-bromo anisole, ben-
zyl bromide and thiourea) were performed under optimized
reaction conditions. These two reactions were taken as the
representative case. After the reaction was over, the cata-
lyst was separated from the reaction mixture by filtration,
washed with copious amount of water followed by diethyl
ether. Then the recovered catalysts were dried at room
temperature for 6 h and used for further six additional
reaction cycles. In all cases Cu-F-MCM-41 and Cu-F-
SBA-15 nanocatalysts exhibited consistent catalytic activ-
ity, establishing high recycling efficiency of the catalyst
and no significant loss of catalytic activity (Fig. 7).
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suggests that the 50% conversion was achieved after the
IP: 115.127.33.132 On: Sun, 11 Oct 2015 15:39:32
scheduled time. Then both reactions were continued with
Copyright: American Scientific Publishers
the respective filtrate for another 4 h and 6 h at the same
respective reaction temperature. Absolutely no increase in
product conversion was achieved beyond 50%. It is further
noted that copper is also not detected (AAS) in the liquid
phase after the completion of the reactions and the filtrates
remain completely colorless.
In order to verify heterogeneous nature of the nanocata-
lysts a three phase test was performed. In this experiment
a desired amount of amino-functionalized silica (AFS) was
refluxed with p-bromoacetophenone in dry ethanol under
nitrogen atmosphere for 5 h. Then the mixture was cooled
to room temperature and filtered via repeatedly washing
with ethanol to remove unreacted p-bromoacetophenone.
The material was air dried to obtain the PBA-AFS. Then
a mixture of 4-bromo anisole (1 mmol, 187 mg), K2CO3
(4 mmol, 552 mg), thiourea (91 mg, 1.2 mmol), benzyl
bromide (188 mg, 1.1 mmol) was heated at 100 ꢀC for
12 h in presence of Cu-F-SBA-15 nanocatalyst (25 mg)
and PBA-PS material. Resulting mixture was then cooled
to room temperature, extracted with EtOAc. The combined
organic layer was washed with water and brine solution.
Then the combined organic layer was dried over anhy-
drous Na2SO4 and evaporated to dryness. The product
was analyzed by 1H NMR, which showed the com-
pound was benzyl 4-methoxyphenyl sulfide. The obtained
solid residue was digested refluxing with 2MHCl and
the solution was extracted with Et2O. The obtained
Fig. 7. Recyclic efficiency of the Cu-F-MCM-41 and Cu-F-SBA-15
nanocatalysts. Series 1 = C
S
coupling reaction and Series 2 =
Thioetherification reaction.
J. Nanosci. Nanotechnol. 13, 4883–4895, 2013
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An Efficient Heterogeneous Cu-Grafted Mesoporous Organosilicas Nanocatalyst
Mondal et al.
4. CONCLUSIONS
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Cu-F-MCM-41 nanocatalyst catalyzed the C S coupling
reaction very efficiently under aerobic condition to offer
different bis-thioethers. Also another novel protocol for
one-pot thioetherification reaction of different bromo-and
chloroarenes with thiourea and benzyl bromide in the
presence of K2CO3 in aqueous medium was achieved by
Cu-F-SBA-15 nanocatalyst under aerobic condition to pro-
vide some value added aryl alkyl thioether. This one-pot
thioetherification procedure is free from the direct use
of volatile, foul-smelling thiols to the address industrial
and environmental concerns. Both the nanocatalysts are
inexpensive, non-air sensitive, robust and heterogeneous
in nature. Both the nanocatalysts can be separated from
the reaction mixture easily and recycled for several times
without significant loss of catalytic activity. The catalytic
activity for these Cu-grafted heterogeneous nanocatalysts
for the synthesis of thioethers via two and three compo-
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Acknowledgments: John Mondal and Noor Salam
thank CSIR, New Delhi and University Grant Commission
Delivered by Publishing Technology to: Rice University, Fondren Library
(UGC) for their respective senior and junior research fel-
lowships. Asim Bhaumik wishes to thank DST Unit on
Nanoscience for instrumental support.
IP: 115.127.33.132 On: Sun, 11 Oct 2015 15:39:32
33. Q. H. Zhang, W. P. Deng, and Y. Wang, Chem. Commun. 47, 9275
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3-Phenylsulfanylbenzaldehyde (Table I, entry 7): 1H NMR
(500 MHz, CDCl3ꢄ ꢅ 9.92 (s, 1H), 7.98 (s, 1H), 7ꢂ786–7ꢂ771 (d, J =
7ꢂ5 Hz, 2H), 7ꢂ49–7ꢂ371 (m, 3H), 7ꢂ322–7ꢂ186 (m, 3H); 13C NMR
(500 MHz, CDCl3ꢄ ꢅ 191.5, 138.0, 137.2, 136.9, 135.2, 132.2, 131.0,
129.1, 128.3, 127.6, 127.1.
4-Phenylsulfanylnitrobenzene (Table I, entry 8): 1H NMR
(500 MHz, CDCl3ꢄ ꢅ7ꢂ987–7ꢂ970 (d, J = 8ꢂ5 Hz, 2H), 7ꢂ495–7ꢂ476
(d, J = 7ꢂ5 Hz, 2H), 7ꢂ440–7ꢂ394 (m, 3H), 7ꢂ120–7ꢂ102 (d, J = 9 Hz,
2H); 13C NMR (500 MHz, CDCl3ꢄ ꢅ 148.2, 145.2, 136.8, 132.4,
130.3, 128.9, 127.3, 123.8.
4-methyl-2-phenylsulfanylaniline (Table I, entry 9): 1H NMR
(500 MHz, CDCl3ꢄ ꢅ7ꢂ522–7ꢂ507 (d, J = 7ꢂ5 Hz, 2H), 7ꢂ454–
7ꢂ7ꢂ175 (m, 4H), 6ꢂ914–6ꢂ896 (d, J = 9 Hz, 1H), 6ꢂ650–6ꢂ636 (d,
J = 7 Hz), 3.914 (s, 2H), 2.234 (s, 3H); 13C NMR (500 MHz,
CDCl3ꢄ ꢅ 141.4, 136.8, 132.4, 130.9, 129.1, 128.9, 127.4, 126.9,
115.8, 20.9.
56. J. Wang, W. J. Wang, B. Song, R. Wu, J. Li, Y. F. Sun, Y. F. Zheng,
and J. K. Jian, J. Nanosci. Nanotechnol. 10, 3131 (2010).
57. 1H and 13C NMR chemical shifts for different coupling products
reported in Table I
2-Phenylsulfanylbenzaldehyde (Table I, entry 10): 1H NMR
(500 MHz, CDCl3ꢄ ꢅ 10.2 (s, 1H), 7ꢂ846–7ꢂ828 (d, J = 9 Hz, 1H),
7.442–7.426 (d, J = 8 Hz, 1H), 7ꢂ377–7ꢂ311 (m, 6H), 7ꢂ161–7ꢂ035
(m, 1H); 13C NMR (500 MHz, CDCl3ꢄ ꢅ 191.1, 141.3, 136.8, 135.1,
133.9, 132.9, 131.6, 129.6, 128.9, 128.3, 127.3.
Di phenyl sulfide (Table I, entry 1): 1H NMR (300 MHz,
CDCl3ꢄ ꢅ = 7ꢂ519–7.109 (5H, m); 13C NMR (300 MHz, CDCl3ꢄ ꢅ =
137ꢂ6, 131.1, 129.2, 124.9.
4-Phenylsulfanylanisole (Table II, entry 2): 1H NMR (300 MHz,
CDCl3ꢄ ꢅ 3.78 (s, 3H), 6.98 (d, J = 8ꢂ7 Hz, 2H), 7.17−−7ꢂ21 (m,
5H), 7.40 (d, J = 9ꢂ0 Hz, 2H); 13C NMR (75 MHz, CDCl3ꢄ ꢅ 55.2,
115.0, 124.2, 125.7, 128.2, 128.9, 135.3, 138.6, 159.8.
4-Phenylsulfanylbenzaldehyde (Table I, entry 3): 1H NMR
(500 MHz, CDCl3ꢄ ꢅ 9.82 (s, 1H), 7ꢂ658–7.641 (d, J = 8ꢂ5 Hz, 2H),
7ꢂ590–7.577 (d, J = 6ꢂ5 Hz, 2H), 7ꢂ446–7.426 (d, J = 10 Hz, 2H),
7ꢂ22–7.15 (m, 3H); 13C NMR (500 MHz, CDCl3ꢄ ꢅ 190.7, 146.9,
136.8, 134.1, 132.2, 131.2, 130.8, 129.6, 127.3.
Di benzyl phenyl disulfide (Scheme 5): 1H NMR (300 MHz,
CDCl3ꢄ
ꢅ
7.11-7.28 (m, 14H), 3.49 (4H, s); 13C NMR
(300 MHz, CDCl3ꢄ ꢅ 137.7, 132.6, 128.9, 127.9, 126.8, 126.3,
42.6.
Di benzyl 2-hydroxy-1-carboxy phenyl disulfide (Scheme 6): 1H
NMR (300 MHz, CDCl3ꢄ ꢅ7ꢂ62–7ꢂ54 (t, 1H), 7ꢂ49−7ꢂ7ꢂ42 (m, 1H),
7ꢂ37–7ꢂ13 (m, 10H), 3.89 (s, 4H); 13C NMR (300 MHz, CDCl3ꢄ ꢅ
171.0, 153.4, 137.2, 129.6, 129.2, 128.6, 128.1, 127.6, 127.4, 125.6,
43.1
4-Phenylsulfanylbenzonitrile (Table I, entry 4): 1H NMR
(500 MHz, CDCl3ꢄ ꢅ 7.31–7.38 (m, 4H), 7.20 (d, 2H), 7.06–6.96
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Delivered by Publishing Technology to: Rice University, Fondren Library
(m, 3H); 13C NMR (500 MHz, CDCl3ꢄ ꢅ 142.1, 135.7, 132.8, 131.9,
IP: 115.127.33.132 On: Sun, 13152O, 1c1t92(2001105). 15:39:32
131.2, 129.4, 127.3, 117.8, 111.2.
Copyright: American S6c0i.enV.tiPfioclshPetutibwalirs, hJ.,e-Mrs. Basset, and D. Astruc, ChemSusChem 5, 6
4-Phenylsulfanylbenzoicacid (Table I, entry 5): 1H NMR
(500 MHz, CDCl3ꢄ ꢅ 7.52–7.51 ꢆdꢀJ = 8 Hz, 4H), 7.312–7ꢂ302
(t, J = 7 Hz, 4H), 7ꢂ240–7ꢂ225 (t, J = 7ꢂ5 Hz, 1H); 13C NMR
(500 MHz, CDCl3ꢄ ꢅ 171.0, 137.0, 129.0, 127.5, 127.1.
(2012).
61. L. Rout, T. K. Sen, and T. Punniyamurthy, Angew. Chem. 119, 5679
(2007).
4-Phenylsulfanylacetophenone (Table I, entry 6): 1H NMR
(500 MHz, CDCl3ꢄ ꢅ7ꢂ665–7ꢂ648 (d, J = 8ꢂ5 Hz, 2H), 7ꢂ350–7ꢂ335
(d, J = 7ꢂ5 Hz, 2H), 7ꢂ241–7ꢂ228 (d, J = 6ꢂ5 Hz, 2H), 7ꢂ061–7ꢂ006
(m, 3H); 13C NMR (500 MHz, CDCl3ꢄ ꢅ 196.9, 145.9, 135.7, 134.0,
131.9, 131.3, 129.6, 129.5, 126.8, 29.6.
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64. F. Y. Kwong and S. L. Buchwald, Org. Lett. 4, 3517 (2002).
Received: 17 October 2012. Accepted: 14 February 2013.
J. Nanosci. Nanotechnol. 13, 4883–4895, 2013
4895