Pd-containing IL-based ordered nanostructured organosilica: A powerful and recoverable catalyst for Sonogashira reaction

Article abstract of DOI:10.1016/j.tetlet.2020.152481

An IL-based ordered nanostructured organosilica supported palladium (Pd@ONO-IL) is synthesized and characterized. The Pd@ONO-IL was used as powerful nanocatalyst in the Sonogashira reaction that the corresponding products were obtained in high yield. The

Full text of DOI:10.1016/j.tetlet.2020.152481

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Pd-containing IL-based ordered nanostructured organosilica: A powerful and
recoverable catalyst for sonogashira reaction
Masoumeh Shaker, Dawood Elhamifar
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https://doi.org/10.1016/j.tetlet.2020.152481
TETL 152481
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Tetrahedron Letters
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Please cite this article as: Shaker, M., Elhamifar, D., Pd-containing IL-based ordered nanostructured organosilica:
A powerful and recoverable catalyst for sonogashira reaction, Tetrahedron Letters (2020), doi: https://doi.org/
10.1016/j.tetlet.2020.152481
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Graphical Abstract
Pd-containing IL-based ordered nanostructured organosilica:
A powerful and recoverable catalyst for Sonogashira reaction
Masoumeh Shaker and Dawood Elhamifar

1
Tetrahedron Letters
journal homepage: www.elsevier.com
Pd-containing IL-based ordered nanostructured organosilica: A powerful and
recoverable catalyst for Sonogashira reaction
Masoumeh Shaker and Dawood Elhamifar
Department of Chemistry, Yasouj University, Yasouj, 75918-74831, Iran
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
An IL-based ordered nanostructured organosilica supported palladium (Pd@ONO-IL) is
synthesized and characterized. The Pd@ONO-IL was used as powerful nanocatalyst in the
Sonogashira reaction that the corresponding products were obtained in high yield. The study
also showed high recoverability and reusability of Pd@ONO-IL without significant loss in
activity and durability.
Available online
Keywords:
Ordered nanostructure organosilica
Ionic-liquid
Palladium
Sonogashira cross-coupling reaction
nanocatalyst
The formation of Csp-Csp2 bond is a key step in the synthesis
of aryl alkynes and conjugated enynes, which are widely used in
the fabrication of natural products, pharmaceutical molecules and
agricultural chemicals. The Pd-catalyzed Sonogashira reaction
between aryl/vinyl halides and terminal alkynes is an effective
method to form Csp-Csp2 bond.1-4 Palladium, in both metallic and
complex forms, plays the role of a powerful catalyst in coupling
reactions. Over the past 40 years, finding powerful and electron-
rich ligands to create active Pd-complexes for coupling processes
has attracted the attention of many researchers.5-12 In recent years,
ionic liquids, as suitable ligands, have received a lot of attention
for the formation of palladium complex as well as control of Pd-
activity. In particular, supported ionic liquids (SILs) on the inert
supports have been more investigated. SILs are prepared via the
physical or chemical immobilization of ionic liquids on various
surfaces such as alumina, magnetic nanoparticles, metal oxides,
carbon nanotubes, silica and aerogel or xerogel structures.13-18 It
should be noted that during the immobilization of ionic liquid,
not only the unique properties of ILs and supports are preserved,
but also new important features are created. For example, the
rate of hydrophobicity and hydrophilicity of these supports can
be adjusted by changing the alkyl groups attached to the ionic
liquid. In recent years, SILs have been successfully used as
effective adsorbent, superconductor, fuel cell, stationary phase in
ionic liquids seem to be able to overcome these limitations due to
creation of a suitable reaction medium and well immobilization
of desired catalysts.23-26 Although a wide range of supports have
been used to synthesize supported ionic liquids, ordered
mesoporous silica have been able to play a more prominent role
in this field due to tunable their pore size, easy surface
modification and high adsorption capacity.27-29 Some of the
recently synthesized IL-containing nanomaterials supported
catalysts are WO42-@PMO-IL,30 PMO-IL-SO3H,31 MMSR-IL-
PA,32 Fe-MCM-41-IL,33 and Cu@PMO-IL.34 The periodic
mesoporous organosilicas based on alkyl-imidazolium units are
the most important supports in this field. In addition to successful
immobilization of various anions, imidazolium units have good
ability to form N-heterocyclic carbenes (NHCs) ligands to
stabilize metal species.30-34
In view of the above and according to our experience in the
field of synthesis and application of new heterogeneous catalysts,
herein, an IL-based ordered nanostructured organosilica
supported palladium (Pd@ONO-IL) is synthesized and
36
characterized (Scheme 1).35, The FT-IR of the Pd@ONO-IL
showed absorption bands at 1475 cm-1 (for C=C stretching), 1633
cm-1 (for C=N stretching), 2926 cm-1 (for aliphatic C-H
stretching) and 3171 cm-1 (for unsaturated C-H stretching),
respectively (Supporting Information, Figure 1S). TG analysis
showed three weight losses. The first one (lower than 150 °C) is
attributed to the removal of adsorbed water and alcoholic
solvents. The second weight loss between 160 and 280 °C is due
to the removal of the remained surfactant template. The three and
main weight loss from 300 to 600 °C is assigned to the removal
of incorporated ionic liquid groups into the material framework
electrochemistry and support to immobilize
a variety of
catalysts.19-22 In the catalytic processes, self-assembly and
deactivation of active catalytic sites based on transition metals,
non-recoverability of catalysts as well as inability to separate the
product from the reaction mixture are important challenges
between chemists. According to the recent studies, supported
———
 Corresponding author. Tel.: +98-743-322-3048; fax: +98-743-322-3048; e-mail: d.elhamifar@yu.ac.ir

2
Tetrahedron Letters
(Supporting Information, Figure 2S). This confirm high thermal
pattern of the Pd@ONO-IL showed a peak with high intensity
centered at 2 theta about 1.1° confirming an ordered hexagonal
mesostructure for the material (Supporting Information, Figure
4S). Also, the SEM image showed the uniform rope-like particles
for the Pd@ONO-IL (Supporting Information, Figure 5S).37 It
should be noted that formation of Pd–NHC complex in
imidazolium-based ionic liquids are known to be responsible for
superior catalytic reactivity.35, 38 The catalytic application of this
nanocatalyst was then investigated in the Sonogashira reaction
(Scheme 1).
stability of the designed catalyst. The EDX spectrum showed the
presence of Pd, Si, C, N and O elements in the material
(Supporting Information, Figure 3S). In fact, the results of TG,
EDX and FT-IR analyses confirmed the successful incorporation
and/or immobilization and high stability of ionic liquid and
palladium moieties into/onto the material framework. The
loading of palladium was calculated using Pd-content obtained
from ICP-OES and EDX analyses. The results of these two
techniques were in good agreement with each other and showed a
loading of 0.15 mmol g-1 for palladium. The low angle PXRD
Scheme 1. Synthesis of Pd@ONO-IL and its catalytic application in the Sonogashira reaction
To achieve optimal conditions, the reaction between
iodobenzene, phenylacetylene and piperidine (as a base for
activation of phenylacetylene) in the presence of Pd@ONO-IL
was chosen as a test reaction (Scheme 2, Table 1). In the first
step, the effect of catalyst amount was investigated in the reaction
progress. As shown, the reaction gives the best result in the
presence of 0.01 g of Pd@ONO-IL catalyst (Table 1, entries 1–
4). The temperature screening showed that 70 °C is the best
(Table 1, entry 3). Then, the effect of solvent was investigated
that the best result was obtained in DMF (Table 1, entry 3 vs.
entries 7 and 8). The superiority of DMF over other solvents is
due to its desirable dissolution, which is actually provided by a
desirable and successful interaction with the substrate.39 Finally,
to prove whether the CuI co-catalyst has a positive effect on the
Sonogashira reaction, the reaction was examined in the presence
of CuI. As shown in Table 1 (entry 9), where CuI is used as co-
catalyst, the yield is decreased. This observation is due to the fact
that CuI leads to the symmetric coupling of phenylacetylenes to
form by-alkynes, which is known as Glaser coupling.40, 41 Based
on these results, the use of 0.01 g (0.15 mol%) of Pd@ONO-IL
catalyst at 70 °C and DMF solvent were selected as the optimal
conditions.
research and according to the possible therapeutic value of
compounds containing alkyne, thiophene and pyrimidine, we
studied the synthesis of 5-methyl-4-(phenylethynyl)thieno[2,3-
d]pyrimidine as an active pharmaceutical ingredient42 in the
presence of Pd@ONO-IL catalyst (Table 2, entry 7).
Scheme 2. Model reaction to optimize conditions
Table 1. Effects of catalyst amount, temperature and solventa
Catalyst amount (g)
[mol%]
T
Yield
(%)b
Entry
Solvent
(°C)
1
2
---
70
70
70
70
25
50
70
70
70
DMF
---
63
94
95
25
52
64
57
59
0.005 [0.075]
0.01 [0.15]
0.015 [0.22]
0.01 [0.15]
0.01 [0.15]
0.01 [0.15]
0.01 [0.15]
0.01 [0.15]
DMF
3c
4
DMF
DMF
After optimization the reaction conditions, different aryl
halide derivatives were used as substrate to evaluate the effect of
Pd@ONO-IL catalyst in the preparation of different aryl alkyne
products (Table 2). As shown, although aryl iodides and aryl
bromides do not differ significantly in reaction yield, the reaction
time to reach the target product is longer for aryl bromides.
However, the required time for aryl chlorides is longer than other
aryl halides. It should also be noted that aryl halides bearing
electron withdrawing substations were more active than other
substrates. It was also found that Pd@ONO-IL has high TOF for
products derived from iodobenzene and aryl halides bearing
electron withdrawing substations. As further development of this
5
DMF
6
DMF
Toluene
7
8
Xylene (isomeric mixture)
DMF
9d
a Conditions reaction: Phenylacetylene (1 mmol), Ph-I (1 mmol), piperidine
b
c
(1.5 mmol), solvent (4 mL) and 120 min. Isolated yields. Optimum
conditions. d CuI was co-catalyst.

3
The recyclability study also showed that the Pd@ONO-IL can
be recovered and reused for four times without significant loss in
activity and durability (Figure 1).
To confirm the chemical and structural stability of the
nanocatalyst during 4 runs of reuse, the recycled nanocatalyst
was characterized by ICP, EDX and FT-IR techniques. The
similarity of the FT-IR spectrum of recovered nanocatalyst
(Supporting Information, Figure 6S) with the FT-IR of fresh
nanocatalyst confirms the high stability of the catalyst after
recovery stages. Also, the EDX analysis of the recovered catalyst
(Supporting Information, Figure 7S) demonstrated the signals of
Si, C, N, O and Pd elements in a pattern the same as its fresh
parent proving high stability of the catalyst after several steps of
recovery and reuse. According to EDX and ICP analyses, the
amount of Pd-leaching on the Pd@ONO-IL was negligible under
applied conditions.
Figure 1. Recyclability of Pd@ONO-IL nanocatalyst
To show the nature of catalyst, a leaching test was done in the
cross-coupling of iodobenzene and phenylacetylene as a model
test. To do this, after the progress of about 40% of the cross-
coupling process, the catalyst was removed by filtration and the
progress of the catalyst-free filtrate was then monitored.
Interestingly, after 1 h, no significant progress in the reaction was
observed. This result confirms that the catalyst is heterogeneous
in nature and no leaching of active palladium species performs
during the reaction process.
Next, a comparison was done between the performance of the
Pd@ONO-IL catalyst and some of the catalysts used recently in
the Sonogashira reaction (Table 3). As can be seen, in a general,
Pd@ONO-IL is a catalyst with higher efficiency, stability,
durability and TOF than other catalysts.
Table 2. Sonogashira reaction using Pd@ONO-ILa
Entry
Aryl halide
Product
Time (min)
120
Yield (%)b
94
TOF (h-1)c
313.3
1
2
3
4
5
6
195
440
165
240
210
90
54
93
82
82
184.6
49
225.4
136.6
156.1
7d
540
72
53.3
a Conditions reaction: Phenylacetylene (1 mmol), aryl halide (1 mmol), piperidine (1.5 mmol), DMF (4 mL), catalyst (0.01 g, [0.15 mol%]) and 70 °C. b Isolated
yields. c Turnover frequency [all TOFs were calculated by this equation: Yield (%) / Cat. (mol %) * Time (h)].d Supporting Information, Scheme 1S.
Table 3. Comparative study of the efficiency of our catalyst with that of previously reported catalytic systems in Sonogashira
coupling reaction
Time
(h)
Catalyst
Conditions
Recovery times
Yield (%)
TOF (h-1)
10.9
Ref.
Cat. (0.03 g), 120 ºC, DMF, Hexamine,
N2 atm.
43
Pd-LHMS-3
14
4
80
44
45
Pd(0)/MCoS-1
Ru/Al2O3
Cat. (0.02 g), 80 ºC, H2O, Et3N
6
5
2
94
85
78.3
0.7
Cat. (5 mol %), 90 ºC, CH3CN, Et3N
24
Cat. (0.01 g, [0.15 mol%]), 70 ºC, DMF,
piperidine
Pd@ONO-IL
2
4
94
313.3
This work

4
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of ionic liquid, palladium and piperidine moieties in the designed
Sonogashira reaction (Supporting Information, Scheme 2S).46
Watanabe, M.; Thomas, M. L.; Zhang, S.; Ueno, K.;
Yasuda, T.; Dokko, K. Chem. Rev. 2017, 117, 7190-7239.
In conclusion, the preparation, characterization and catalytic
application of a nanostructured Pd@ONO-IL catalyst were
developed. This catalyst was prepared by the immobilization of
Pd salt on ONO-IL. The EDX, FT-IR, TGA and ICP-OES
analyses confirmed the successful incorporation/immobilization
of IL and palladium species into/onto prepared material. The
catalytic application of Pd@ONO-IL was studied in the
Sonogashira reaction of aryl halides and phenylacetylene. The
results showed high performance as well as high recyclability
and durability of Pd@ONO-IL under applied conditions.
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5
Highlights
1. Preparation
nanostructured
an
IL-based
organosilica
ordered
supported
palladium (Pd@ONO-IL)
2. Characterization of Pd@ONO-IL using
TGA, IR, PXRD, SEM and EDX analyses
3. Catalytic application of Pd@ONO-IL in the
Sonogashira reaction
4. Recoverability, reusability and durability of
Pd@ONO-IL under applied conditions