Nano palladium supported on high-surface-area metal-organic framework MIL-101: An efficient catalyst for Sonogashira coupling of aryl and heteroaryl bromides with alkynes

Article abstract of DOI:10.1002/aoc.3277

Palladium nanoparticle-incorporated metal-organic framework MIL-101 (Pd/MIL-101) was successfully synthesized and characterized using X-ray diffraction, nitrogen physisorption, X-ray photoelectron, UV-visible and infrared spectroscopies, and transmission electron microscopy. The characterization techniques confirmed high porosity and high surface area of MIL-101 and high stability of nano-size palladium particles. Pd/MIL-101 nanocomposite was investigated for the Sonogashira cross-coupling reaction of aryl and heteroaryl bromides with various alkynes under copper-free conditions. The reusability of the catalyst was tested for up to four cycles without any significant loss in catalytic activity.

Full text of DOI:10.1002/aoc.3277

Full Paper
Received: 9 December 2014
Accepted: 19 December 2014
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.3277
Nano palladium supported on high-surface-
area metal–organic framework MIL-101: an
efficient catalyst for Sonogashira coupling of
aryl and heteroaryl bromides with alkynes
Manne Annapurna, T. Parsharamulu, P. Vishnuvardhan Reddy, M. Suresh,
Pravin R. Likhar and Mannepalli Lakshmi Kantam*
Palladium nanoparticle-incorporated metal–organic framework MIL-101 (Pd/MIL-101) was successfully synthesized and character-
ized using X-ray diffraction, nitrogen physisorption, X-ray photoelectron, UV–visible and infrared spectroscopies, and transmis-
sion electron microscopy. The characterization techniques confirmed high porosity and high surface area of MIL-101 and high
stability of nano-size palladium particles. Pd/MIL-101 nanocomposite was investigated for the Sonogashira cross-coupling reac-
tion of aryl and heteroaryl bromides with various alkynes under copper-free conditions. The reusability of the catalyst was tested
for up to four cycles without any significant loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web-site.
Keywords: palladium nanoparticles; metal–organic framework MIL-101; heterogeneous catalyst; Sonogashira coupling
mostly for aryl iodides.[28–33] Wang and co-workers have successfully
demonstrated that polyvinylpyrrolidone-supported palladium nano-
Introduction
The catalytic coupling of terminal alkynes with aryl and alkenyl bro-
mides (Sonogashira coupling) is one of the most powerful and versa-
tile routes for constructing arylalkynes and conjugated enynes.[1–5]
Functionalized alkynes/conjugated enynes are industrially very im-
portant intermediates for pharmaceuticals, natural products and ma-
terials with specialized optical and electronic properties.[6–12]
Although Sonogashira coupling is well established using several tran-
sition metal catalysts, the use of palladium complexes as catalysts has
been predominantly reported in the literature.[13–15] However,
palladium-catalysed homogeneous reactions on a large scale are
not economically and environmentally viable because these reac-
tions suffer drawbacks such as high cost of the palladium catalysts,
difficulty in separation of catalyst from product mixture which con-
tributes to metal contamination of the products, recyclability of the
catalyst and environmental pollution from heavy metal ions.[16–20]
In recent years, a lot of interest has been shown in the development
of heterogeneous catalysis due to its advantages in industrial applica-
tion, importantly, easy separation and feasibility of catalyst recycling.
Among various heterogeneous catalysts, metal nanoparticles, espe-
cially palladium nanoparticles, have been extensively used as catalysts
for various C–C coupling reactions.[21,22] However, these palladium
nanoparticles are often prone to aggregation without stabilizers or sup-
ports and lose their catalytic activity.[23] During the last decade, catalytic
systems involving palladium nanoparticles in ionic liquids,[24,25] or sup-
ported on various supports such as solid and layered materials,[26,27]
modified silica gel,[28] polymers,[29] polysilanes,[30] biopolymers,[31]
polysaccharides[32] and graphite oxide[33] have been successfully
applied to the Sonogashira coupling reaction of aryl halides. The
catalytic efficiency of the reported catalysts has been demonstrated
particles catalyse the Sonogashira coupling of aryl iodides and bro-
mides with various terminal alkynes under heterogeneous reaction
conditions.[34] Therefore, use of suitable supports that can stabilize pal-
ladium nanoparticles and can efficiently catalyse Sonogashira coupling
of aryl and heteroaryl bromides with alkynes will be a good strategy.
The development of a new synthetic protocol for the preparation of
1,2-diheteroarylalkynes or 1,2-arylheteroarylalkynes is still a challenge
in the field of heterogeneous catalysis.
The choice of support is an important criterion in heterogeneous
catalytic reactions, particularly for easy preparation and handling,
high surface area for the active metal sites, high pore volume and
pore size to allow entry of bulky substrate molecules, air and mois-
ture stability, thermal stability to high temperature and recoverable
and recyclable properties. In recent years, metal–organic frame-
works (MOFs) have emerged as a new class of hybrid porous mate-
rials assembled with metal cations and organic linkers.[35] MOFs are
promising materials for applications in catalysis, gas storage and
separation[36–38] due to their remarkable properties such as high
surface area, porosity, chemical tunability and thermal stability. Pal-
ladium nanoparticles supported on various MOFs have been used
as heterogeneous catalysts for versatile organic syntheses such as
selective aerobic oxidation of alcohols,[39] Heck,[40] Suzuki[41] and
*
Correspondence to: Mannepalli Lakshmi Kantam, Inorganic and Physical
Chemistry Division, CSIR-Indian Institute of Chemical Technology (CSIR-IICT),
Tarnaka, Hyderabad – 500007, India. E-mail: mlakshmi@iict.res.in
Inorganic and Physical Chemistry Division, CSIR-Indian Institute of Chemical
Technology (CSIR-IICT), Tarnaka, Hyderabad 500007, India
Appl. Organometal. Chem. (2015)
Copyright © 2015 John Wiley & Sons, Ltd.

M. Annapurna et al.
Sonogashira[42] cross-coupling reactions, and direct C–H bond
arylation of indoles with arylboronic acids.[43] The MOF Cr3(F,OH)
(H2O)2O[(O2C)–C6H4–(CO2)]3ÁnH2O (MIL-101) is an ideal support for
metal nanoparticles because it has a large surface area (Brunauer–
Emmett–Teller (BET), ca 4000 m2 gÀ1) and pore size (ca 30 Å). More-
over, MIL-101 possesses numerous potentially unsaturated chro-
mium sites (up to 3.0 mmol gÀ1), which can provide Lewis acid
sites for catalytic reactions after the removal of terminal water
molecules.[44]
We report here a successful preparation of palladium nanoparti-
cles supported on MIL-101 (Pd/MIL-101), its characterization and
catalytic applications. Pd/MIL-101 was found to be a highly efficient
heterogeneous catalyst for the Sonogashira coupling of aryl and
heteroaryl bromides with terminal alkynes.
spectroscopy, BET specific surface area and nitrogen physisorption.
ICP analysis reveals that the palladium loading in Pd/MIL-101 is 3.5
wt%. Low-angle XRD patterns indicate that the structure of MIL-101
is mostly preserved after incorporation of palladium nanoparticles.
In addition, the intensity of the diffraction peaks is well maintained
even after dispersion of palladium nanoparticles which reveals no
apparent loss of crystallinity (Fig. S1, supporting information). Fur-
thermore, the characteristic diffraction peak of palladium species
is undetectable in wide-angle XRD patterns of Pd/MIL-101 which
shows that the palladium nanoparticles are too small or the palla-
dium content in the sample is too low for detection. This result is
in good agreement with earlier reports (Fig. S2, supporting
information).[47]
Figure 1 shows the XPS spectra of Pd/MIL-101. The XPS spectra of
MIL-101 and Pd/MIL-101 suggest evidence of two palladium metal-
lic species with binding energies of two prominent peaks at 335.3
and 340.7 eV which are assigned to Pd 3d5/2 and Pd 3d3/2 bands, re-
spectively. These binding energies clearly suggest that the Pd spe-
cies in the catalyst is in the metallic state: Pd(0).[48] Though the
concentration of Pd(0) species in the Pd/MIL-101 catalyst is very
high, the appearance of Pd 3d5/2 and Pd 3d3/2 at 337.0 and 343.3
eV indicates traces of Pd2+ species present in the MIL-101 support.
To investigate the dispersion of palladium nanoparticles on the
MIL-101 support, a Pd/MIL-101 sample was examined using TEM.
The TEM images of the Pd/MIL-101 catalyst clearly show that the
palladium nanoparticles are highly dispersed on the MIL-101 sup-
port. The average size of palladium nanoparticles is found to be in
the range 3–4 nm for fresh Pd/MIL-101 catalyst and 4–5 nm for
used Pd/MIL-101 catalyst, which confirms that palladium nanopar-
ticles are well dispersed on the surface of MIL-101 (Fig. 2).
Results and Discussion
MIL-101 was synthesized and purified according to a procedure re-
ported by Férey and co-workers.[44,45] As can be seen from Fig. S1
(supporting information), the low-angle X-ray diffraction (XRD) pat-
tern of the as-synthesized MIL-101 is in good agreement with the
reported XRD pattern.[44–46] The incorporation of palladium nano-
particles was achieved by an impregnation method by addition of
MIL-101 into a solution of Pd(CH3COO)2 in tetrahydrofuran (THF).
The synthesized Pd/MIL-101 catalyst was thoroughly characterized
using analytical techniques such as inductively coupled plasma
(ICP), XRD, transmission electron microscopy (TEM), X-ray photo-
electron spectroscopy (XPS), UV–visible spectroscopy, FT-IR
Using nitrogen physisorption isotherm measurements, the BET
surface area and total pore volume of MIL-101 are calculated to
be 2575 m2 gÀ1 and 1.49 cm3 gÀ1, respectively. The BET surface area
and total pore volume for Pd/MIL-101 are decreased to 2098 m2
gÀ1 and 1.22 cm3 gÀ1, respectively. The appreciable decrease in
the BET surface area and pore volume after the impregnation of
palladium nanoparticles on the MIL-101 support indicates that
the palladium nanoparticles are highly dispersed and located at
the surface of MIL-101. The pore size distribution patterns are
shown using density functional theory (DFT) in Fig. S3 (see
supporting information), and textural parameters of the catalysts
are given in Table 1, which reveal that the average pore size for
MIL-101 decreases from 2.33 to 2.31 nm after the impregnation
of palladium nanoparticles on the surface of MIL-101.
FT-IR patterns of both catalysts are shown in Fig. S4 (see
supporting information). The stretching frequencies of (O–C–O)
near 1516 and 1401 cmÀ1 confirm the presence of dicarboxylate
groups within the framework. The stretching and bending vibra-
tional bands in the range 600–1600 cmÀ1 correspond to benzene
Figure 1. XPS spectra and binding energies of core electrons of as-
synthesized Pd/MIL-101.
Figure 2. TEM images of (A, B) fresh Pd/MIL-101 and (C) used Pd/MIL-101.
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Appl. Organometal. Chem. (2015)

Nano Pd/MIL-101-catalysed Sonogashira coupling reactions
Table 1. Textural parameters of MIL-101 and Pd/MIL-101
Column chromatographic separation affords 50% yield of the
cross-coupled product. A slight increase in the yield of the product
is observed on changing the solvent from DMF–H2O to DMF
(Table 2, entry 2). Also, it is noted that the yield of desired product
is increased on changing the reaction time from 3 to 6 h (Table 2,
entry 4). Solvent screening studies indicate that polar aprotic sol-
vents like DMF and N,N′-dimethylacetamide (DMA) are superior
for this reaction (Table 2, entries 2–10), whereas non-polar solvents
like toluene and o-xylene are not as effective (Table 2, entries 11
and 12). To determine the optimal reaction conditions, the impact
of various bases on the efficiency of this process was screened.
The most promising result is obtained with CH3COOK while other
bases like Cs2CO3 and K3PO4 give good yields, and bases like
LiOHÁH2O and CH3COONa give moderate yields. The addition of
tetrabutylammonium bromide does not significantly affect the
yield of coupled product (Table 2, entry 6). When the reaction is per-
formed under nitrogen atmosphere, the yield of the product re-
mains unaltered (Table 2, entry 7).
To investigate the further scope of Sonogashira reaction, we next
examined the reaction of phenylacetylene with a series of aryl bro-
mides, as summarized in Table 3. The reaction performed with the
more reactive aryl bromide 4-bromonitrobenzene affords the corre-
sponding coupled product in good yield under the optimized reac-
tion conditions (Table 3, 3a). Deactivated aryl bromides, for instance
bromobenzene, 4-bromotoluene and 4-bromoanisole, furnish the
desired products in good to moderate yields (Table 3, 3d–3f). An
ester-functionalized aromatic bromide also affords a good yield of
coupling product (Table 3, 3i). Electron-deficient aryl bromides
show good yields (96, 95, 91, 93, 83%) of corresponding desired
products in the coupling reaction (Table 3, 3b, 3c, 3g, 3h, 3j). It
should be noted that 1-bromonaphthalene and 9-
bromophenanthrene are sterically hindered substrates, but
Catalyst
Surface area
Average pore
size (nm)
Pore volume
b
(m2 gÀ1
)
(cm3 gÀ1
)
a
MIL-101
2575
2098
2.33
2.31
1.49
1.22
Pd/MIL-101
aBET surface area.
bTotal pore volume by single point method at a relative pressure of
0.99.
rings. The appearance of these bands in the spectrum of Pd/MIL-
101 confirms that there is no transformation or deformity of the
MIL-101 framework after incorporation of palladium nanoparticles
on MIL-101.[49]
Thermal stability of MIL-101 and Pd/MIL-101 was studied using
thermogravimetric analysis (TGA). The thermograms are shown in
Fig. S5 (see supporting information). The weight loss in the temper-
ature range 80–140 °C indicates the removal of crystalline water.
The weight loss in the range 300–450 °C indicates the removal of
OH/F groups from the frameworks or decomposition of the frame-
works for both MIL-101 and Pd/MIL-101 catalysts.[50]
UV–visible pattern of MIL-101 is shown in Fig. S6 (see supporting
information). The absorption bands at 447 and 599 nm indicate that
Cr(III) is present in distorted octahedral form. After the incorpora-
tion of palladium on MIL-101, there is no distinguishable change
observed in the UV–visible pattern of Pd/MIL-101.[51]
Initially, a reaction was performed with phenylacetylene (204 mg,
2.0 mmol) and 4-bromonitrobenzene (202 mg, 1.0 mmol), in the
presence of Pd/MIL-101 (3.5 wt%) catalyst and K2CO3 (276 mg, 2.0
mmol) as base in DMF–H2O (1:1) as solvent system at 130°C.
Table 2. Optimization studies for cross-coupling of phenylacetylene with 4-bromonitrobenzenea
Entry
Base (mmol)
Solvent
Time (h)
Yield (%)b
1
K2CO3 (2.0)
DMF–H2O
DMF
3
3
6
6
6
6
6
6
6
6
6
6
50c
60c
64
2
K2CO3 (2.0)
3
K2CO3 (2.0)
DMA
4
Cs2CO3 (1.0)
K3PO4 (1.0)
DMA
71
5
DMA
85
6
K3PO4 (1.0)
DMA
87d
83e
40
7
K3PO4 (1.0)
DMA
8
LiOHÁH2O (1.0)
CH3COONa (1.0)
CH3COOK (1.0)
CH3COOK (1.0)
CH3COOK (1.0)
DMA
9
DMA
65
10
11
12
DMA
90
Toluene
o-Xylene
—
—
aUnless otherwise stated, all reactions were performed using 4-bromonitrobenzene (1.0 mmol), phenylacetylene (2.0 mmol),
Pd/MIL-101 (Pd 3.5 wt%; 5 mg), base (1.0 mmol), in 3.0 ml of solvent at 130 °C for 6 h.
bIsolated yields.
cCatalyst loading 10 mg.
dTetrabutylammonium bromide used as additive.
eReaction performed under nitrogen atmosphere.
Appl. Organometal. Chem. (2015)
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M. Annapurna et al.
Table 3. Sonogashira coupling of various aryl bromides with
bromides 2-bromopyridine and 3-bromopyridine. Surprisingly both
these substrates couple with phenylacetylene and afford the re-
spective products in 70–80% yields (Table 3, 3m and 3n). The activ-
ity of Pd/MIL-101 was tested for the coupling of 2-bromoquinoline,
3-bromoquinoline, 4-bromoisoquinoline (Table 3, 3o–3q), 2-
bromothiophene and 3-bromothiophene (Table 3, 3r and 3s). All
heteroaryl bromides afford yields of the coupling products in the
coupling reaction under investigation. However, 3-bromofuran
does not afford desired product under the conditions used (Table 3,
3t). In a comparative study, a commercial Pd/C catalyst (5 wt% Pd
loading) was used under identical reaction conditions, and only
45% yield of the coupled product is obtained (Table 3, 3u). In some
reports Pd/C was used as catalyst in combination with PPh3 and CuI
as additives for the Sonogashira coupling reaction of aryl bromides
with phenylacetylene.[52] Recently, Shu’s group reported palladium
nanoparticles supported on MOF-5 as a heterogeneous catalyst for
Sonogashira coupling. However, this methodology was limited only
to aryl iodides with very high catalyst loading.[42]
phenylacetylene catalysed by Pd/MIL-101a
Entry
ArX
Product
Yield (%)b
1
p-O2N–C6H4–Br
p-NC–C6H4–Br
3a
3b
3c
3d
3e
3f
90
96
95
80
70
65
91
93
75
83
70
73
70
80
85
73
92
86
87
0
2
3
m-NC–C6H4–Br
4
C6H5–Br
5
p-Me–C6H4–Br
6
p-MeO–C6H4–Br
p-MeOC–C6H4–Br
m-MeOC–C6H4–Br
p-EtOOC–C6H4–Br
p-CF3–C6H4–Br
7
3g
3h
3i
8
9
10
11
12
13
14
15
16
17
18
19
20
21
3j
1-Bromonaphthalene
9-Bromophenanthrene
2-Bromopyridine
3-Bromopyridine
2-Bromoquinoline
3-Bromoquinoline
4-Bromoisoquinoline
2-Bromothiophene
3-Bromothiophene
3-Bromofuran
3k
3l
Encouraged by these results, we investigated the catalytic activ-
ity of Pd/MIL-101 for the Sonogashira coupling of aryl and
heteroaryl bromides with aromatic and heteroaromatic alkynes un-
der the optimized reaction conditions. The reactions of 3-
bromopyridine with 1-ethynyl-3-methylbenzene and 3-
ethynylthiophene furnish good yields of coupled products (Table 4,
3m
3n
3o
3p
3q
3r
entries
1 and 2). The coupling of bromobenzene with
heteroarylalkynes does not result in expected coupled product
(Table 4, entries 3 and 4).
3s
3t
The reusability of the Pd/MIL-101 catalyst was examined in
Sonogashira coupling. 4-Acetylbromobenzene (597 mg, 3.0 mmol)
or 4-bromonitrobenzene (606 mg, 3.0 mmol), and phenylacetylene
(612 mg, 6.0 mmol), CH3COOK (294 mg, 3.0 mmol) and 15 mg of
Pd/MIL-101 (3.5 wt%) catalyst were stirred in DMA for 6 h at
130 °C. After the completion of the reaction, the contents were cen-
trifuged to separate the solid catalyst from the reaction mixture.
The catalyst was then thoroughly washed with distilled water
followed by methanol and then dried in air. This catalyst was used
for other four reaction cycles without further purification (Fig. 3).
The yields are given in Table 5: no significant drop in the yields of
the product is observed. Further, we investigated the leaching of
palladium to verify the cause of the slight drop in yields in succes-
sive recycle runs. Fresh and reused catalyst (recovered from the first
cycle) were digested in a minimum volume of concentrated HCl
and diluted with double-distilled water to prepare standard volu-
metric solutions. The palladium content in both fresh and used cat-
alyst was analysed using ICP. It is observed that there is no loss of
palladium content in the used catalyst. We suspect that the reason
behind the slight drop in the yields in successive run might be the
p-O2N–C6H4–Br
3u
45c
aUnless otherwise stated, all reactions were performed using aryl
bromide (1.0 mmol), phenylacetylene (2.0 mmol), catalyst (Pd 3.5
wt%, 5 mg), CH3COOK (1.0 mmol), in 3.0 ml of DMA solvent at
130 °C for 6 h.
bYields of isolated product after purification by column
chromatography.
cPd/C (5 wt%) used as catalyst.
interestingly, both show yields of coupled products in coupling re-
action with phenylacetylene (Table 3, 3k and 3l). The optimized re-
action conditions of this protocol were extended to the heteroaryl
Table 4. Pd/MIL-101-catalysed Sonogashira coupling of aryl bromides
with arylalkynes and heteroarylalkynesa
Entry
Aryl halide
Alkyne
Yield (%)b
1
2
3
4
3-Bromopyridine 1-Ethynyl-3-methylbenzene
3-Bromopyridine 3-Ethynylthiophene
65
63
—
—
Bromobenzene
Bromobenzene
5-Ethynyl-1H-imidazole
2-Ethynylpyridine
aUnless otherwise stated, all reactions were performed using aryl and
heteroaryl bromides (1.0 mmol), aromatic and heteroaromatic
alkyne (2.0 mmol), catalyst (3.5 wt%, 5 mg), CH3COOK (1.0 mmol),
in 3.0 ml of DMA solvent at 130 °C for 6 h.
bIsolated yields.
Figure 3. Catalyst recyclability test.
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Appl. Organometal. Chem. (2015)

Nano Pd/MIL-101-catalysed Sonogashira coupling reactions
Table 5. Recyclability of Pd/MIL-101 catalysta
200–800 nm. Spectral-grade BaSO4 was taken as reference for the
reflectance spectra.
Substrate
Yield (%)b
3rd
1st
2nd
4th
5th
Synthesis of MIL-101
4-Acetylbromobenzene
4-Bromonitrobenzene
91
90
89
88
88
88
85
86
85
86
Cr-MIL-101 was prepared using the hydrothermal method with 1,4-
benzenedicarboxylic acid (0.166 g, 1.0 mmol), Cr(NO3)3Á9H2O (0.400
g, 1.0 mmol), hydrofluoric acid (0.020 g, 1.0 mmol) and water (265 g)
at 493 K for 8 h in a Teflon-lined autoclave. After cooling, the reac-
tion mixture was filtered using a large-pore fritted glass filter (G1) to
remove excess unreacted dicarboxylic acid. The product was sepa-
rated from water using Whatman filter paper. A significant amount
of unreacted benzenedicarboxylic acid was present within or out-
side the pores of MIL-101 and was removed using a solvo-thermal
method with ethanol (95% ethanol with 5% water) at 353 K for 24
h and 1 M NH4F solution at 343 K for 24 h.[45]
aReaction conditions: aryl bromide (3.0 mmol), phenylacetylene (6.0
mmol), catalyst (3.5 wt%, 5 mg), CH3COOK (3.0 mmol), in 9.0 ml of
solvent at 130 °C for 6 h.
bIsolated yields.
slight increase in the size of palladium nanoparticles which is ob-
served in the TEM study.
Synthesis of Pd/MIL-101
Conclusions
About 105.48 mg of palladium acetate was dissolved in 5.0 ml
of THF and was impregnated on the MIL-101 support. Drying
of the material was carried out at room temperature for 24 h
followed by reduction in hydrogen flow at 473 K for 2 h.[41]
The palladium loading on MIL-101 was estimated as 3.5 wt%
using ICP analysis.
We have developed a highly efficient heterogeneous catalyst sys-
tem, Pd/MIL-101, from MIL-101 and palladium nanoparticles for
the Sonogashira coupling reaction of aryl/heteroaryl bromides with
aryl/heteroaryl alkynes. Due to the high surface area, large pore size
and stability to air and moisture of MIL-101, Pd/MIL-101 acts as a
highly efficient catalyst and does not require external ligands. The
coupling reactions are performed using low loading of palladium
on MIL-101 under aerobic conditions. The catalyst is easily recover-
able after each reaction cycle and is reusable for up to four cycles
without significant loss of catalytic activity.
General Procedure for Sonogashira Coupling
In a typical reaction, a 25 ml oven-dried reaction vessel was charged
with Pd/MIL-101 (3.5 wt%, 5 mg), and aryl halide (1.0 mmol),
phenylacetylene (2.0 mmol), potassium acetate (98.1 mg, 1.0 mmol)
and DMA (2.0 ml) were added. The resulting solution was stirred at
130 °C for 6 h. The reaction was monitored using thin-layer chroma-
tography. At the end of the reaction, the mixture was cooled to
room temperature, diluted with EtOAc (20 ml) and washed with 1
N aqueous HCl and water. The combined organic phase was dried
over anhydrous Na2SO4. After removal of the solvent, the residue
was subjected to column chromatography with silica gel and a mix-
ture of hexane–ethyl acetate as eluent (50:1) to afford the
Sonogashira coupling product in high purity. All the products were
confirmed using 1H NMR, 13C NMR and mass spectroscopic
techniques.
Experimental
Materials and Instrumentation
All reagents were commercial-grade materials and were used with-
out further purification. All solvents were dried and distilled using
standard methods. Thin-layer chromatography was performed
using pre-coated silica gel 60-F254 plates. Purification of products
was carried out by column chromatography with commercial col-
umn chromatography grade silica gel (60–120 mesh) using a mix-
ture of ethyl acetate and hexane as eluting agent. All known
compounds were characterized and compared with literature re-
ports. 1H NMR and 13C NMR spectra were obtained as solutions in
CDCl3, with tetramethylsilane as the internal standard. ESI-MS was
carried out with an LCQ ion trap mass spectrometer equipped with
an ESI source. XRD patterns were recorded with a Rigaku Ultima-IV
X-ray diffractometer using Ni-filtered Cu Kα radiation (1.5406 Å) with
a scan speed of 2° minÀ1 over a range of 2θ = 10–80° at 40 kV and
30 mA. Nitrogen adsorption–desorption isotherms were obtained
at 77 K with a Quadrasorb SI Quantachrome instrument. Prior to
analysis, samples were evacuated at 150 °C for 12 h under vacuum.
The specific surface areas were calculated using the BET method
over a relative pressure range of 0.05 to 0.30. The pore size was cal-
culated using DFT. Total pore volume was taken using a single point
method at P/P0 = 0.99. FT-IR spectral analysis of the samples was
performed using a PerkinElmer Spectrum GX spectrometer with a
resolution of 4 cmÀ1 using KBr discs, in the range 400–4000
cmÀ1. TGA was used to determine thermal stability using a TGA
Q500A analyser with a heating rate of 10 °C minÀ1 in nitrogen flow.
UV–visible diffuse reflectance spectra of samples were recorded
with a Shimadzu spectrophotometer (UV-3600) in the range
Acknowledgments
M. Annapurna thanks UGC, New Delhi, India, for the award of a Se-
nior Research Fellowship (SRF). The authors thank Dr B. Sreedhar,
I&PC Division, CSIR-IICT, for carrying out detailed TEM analysis of
the Pd/MIL-101 catalyst.
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