Palladium nanoparticles on amino-modified silica-catalyzed C–C bond formation with carbonyl insertion

Article abstract of DOI:10.1007/s13738-021-02171-6

Abstract: A practical and heterogeneously catalyzed Stille, homo-coupling, and Suzuki carbonylation reaction has been reported using Pd nanoparticles supported on amino-vinyl silica-functionalized magnetic carbon nanotube (CNT@Fe₃O₄@SiO₂-Pd) for the efficient synthesis of symmetrical and unsymmetrical diaryl ketones from aryl iodides. A wide variety of symmetrical and unsymmetrical diaryl ketones were obtained in high yields under CO gas-free conditions using Mo(CO)₆ as an efficient carbonyl source. Considering the atom economy of Ph₃SnCl, less than an equimolar amount can be applied in Stille transformation, which is of great importance due to the toxicity of organotin derivatives. Moreover, no phosphine ligand and external reducing agent were necessary in these coupling carbonylation reactions. This heterogeneous Pd catalyst offers high activity with very low palladium leaching. Finally, the catalyst can be reused and recycled for six steps without loss in activity, exhibiting good example of sustainable methodology. Graphic abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s13738-021-02171-6

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-021-02171-6
ORIGINAL PAPER
Palladium nanoparticles on amino‑modifed silica‑catalyzed C–C bond
formation with carbonyl insertion
Elham Etemadi‑Davan1 · Dariush Khalili1 · Ali Reza Banazadeh2 · Ghazal Sadri1 · Pourya Arshad1
Received: 27 September 2020 / Accepted: 2 January 2021
© Iranian Chemical Society 2021
Abstract
A practical and heterogeneously catalyzed Stille, homo-coupling, and Suzuki carbonylation reaction has been reported using
Pd nanoparticles supported on amino-vinyl silica-functionalized magnetic carbon nanotube (CNT@Fe3O4@SiO2-Pd) for
the efcient synthesis of symmetrical and unsymmetrical diaryl ketones from aryl iodides. A wide variety of symmetrical
and unsymmetrical diaryl ketones were obtained in high yields under CO gas-free conditions using Mo(CO)6 as an ef-
cient carbonyl source. Considering the atom economy of Ph3SnCl, less than an equimolar amount can be applied in Stille
transformation, which is of great importance due to the toxicity of organotin derivatives. Moreover, no phosphine ligand
and external reducing agent were necessary in these coupling carbonylation reactions. This heterogeneous Pd catalyst ofers
high activity with very low palladium leaching. Finally, the catalyst can be reused and recycled for six steps without loss in
activity, exhibiting good example of sustainable methodology.
Graphic abstract
Supplementary information The online version of this article
(https://doi.org/10.1007/s13738-021-02171-6) contains
supplementary material, which is available to authorized users.
Extended author information available on the last page of the article
Vol.:(0123456789)
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Keywords Stille reaction · Homo-coupling carbonylation · Suzuki carbonylation · Diaryl Ketones · Phosphine-free ·
Heterogeneous catalysis
with gaseous CO, applying other alternatives such as metal
carbonyls is desirable.
Introduction
Besides, the chemistry of symmetrical diaryl ketones via
carbonylation is still underdeveloped. Performing this reac-
tion has been described with R-M [21, 22] (ArHgCl, Ar4Sn)
and R-X [23, 24] (Ar2I+: diaryliodonium) in the presence of
Pd catalyst and gaseous CO in which oxidative and reductive
conditions were required, respectively (Scheme 1: a′, b′). Uti-
lizing reducing and oxidative reagents under harsh conditions
for the preparation of the starting materials is the obstacle that
renders these reactions more practical. Recently, the Pd/hetero-
geneous P(III) catalytic system and Cr(CO)6 as a solid metal
carbonyl source were employed to construct symmetrical dia-
ryl ketone from aryl iodides (Scheme 1: c′) [25–28]. Another
methodology for the preparation of diaryl ketones is palla-
dium-catalyzed oxidative carbonylation of nontoxic boronic
acid derivatives (Scheme 1: d′) [29]. Moreover, non-catalytic
systems in the presence of unstable Co2(CO)8 and highly toxic
Ni(CO)4 were also used, which sufers from the production
of toxic side products (Scheme 1, e′) [30, 31]. Additionally,
ultrafast carbonylation of aryl iodides using Co2(CO)8 under
microwave irradiation was also reported (Scheme 1, f′) [32].
From the perspective of isolation challenges, the ideal solution
to overcome this issue is to immobilize the homogeneous Pd
catalyst onto various solid supports [11–14]. In this regard,
carbon nanotubes (CNTs) due to their large specifc surface
area, porous structure, strong adsorption capacity, and high
chemical and mechanical stability have been of great research
interest as a promising Pd support [33, 34]. However, the ten-
dency of the nanocatalysts to aggregate reduces the available
surface area, which might limit using of CNTs in the organic
Pd-catalyzed carbonylative cross-coupling reactions are one
of the attractive and straightforward routes for the formation
of multiple bonds in single step, which excludes the need
for multi-step reactions and isolation of the intermediates.
Unsymmetrical (A) and symmetrical (B) diaryl ketones as
value-added carbonylation products [1–4] are important
privileged intermediates present in many biologically active
natural products and can be obtained via Suzuki [1, 3, 5, 6]
or Stille carbonylation [5, 6] reactions (Scheme 1: a, b). A
variety of synthetic methods including Pd-catalyzed reac-
tions have been reported for the synthesis of symmetrical
ketones but not much have been reported for the unsym-
metrical ones. In this regard, homogeneous [7–10] and het-
erogeneous [11–14] Pd catalysts were used for carbonylation
cross-coupling reactions. The obvious difcult separation of
homogeneous catalysts made chemists to develop heteroge-
neous catalyst, although the former one has high selectivity
and give better yields. Magnetic heterogeneous Pd catalysts
have attracted much attention owing to the ease of separa-
tion by an external magnet [15, 16]. Organotin compounds
such as Me4Sn, Et4Sn, nPr3RSn, Bu4Sn, Bu3RSn (R: vinyl,
allyl, 1-naphthyl, 4-fuorophenyl, 3-pyridyl, phenyl) were
applied for the Stille transformation (Scheme 1, c, d) [17,
18]. The drawbacks encountered with the mentioned route
were the application of more than stoichiometric amounts of
organotin derivatives and gaseous CO (in most of the reac-
tions) albeit only very few protocols were reported in the
presence of Mo(CO)6 [19, 20]. Due to the toxicity and dif-
fculties in handling and running experiments in laboratory
Scheme 1 Diferent approaches
for the synthesis of unsymmetri-
cal and symmetrical ketones
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synthesis [35]. To conquer this issue, magnetic nanoparticles
coated with silica have been used to improve the chemical sta-
bility of the magnetite nanoparticles by shielding the magnetic
dipole interaction
EG (3 mL) at 110 °C. After the completion of the reac-
tion, an external magnet was used to separate the catalyst
from the cooled reaction mixture. Then, 10 mL of H2O was
added followed by extraction using EtOAc (3×10 mL). The
combined organic phases were dried over Na2SO4. Filtra-
tion of the crude mixture followed by evaporation of the
solvent and column chromatography on silica gel (n-hexane/
EtOAc) aforded the desired symmetrical diaryl ketones in
high yields.
with the silica shell [36, 37]. In continuation of our pre-
vious work [38], we herein use our previously synthesized
heterogeneous Pd catalyst (CNT@Fe3O4@SiO2-Pd) for
phosphine and ligand-free Stille, homo-coupling, and Suzuki
carbonylation of aryl iodides in the presence of magnetic Pd
catalyst with Mo(CO)6 as a solid source of carbon monoxide.
Sol–gel monomers containing amine functional groups are
known to coordinate more strongly with Pd ions to stabilize
the metal NPs in the silica matrix [39, 40]. Nevertheless,
external chemical reducing agents or reduction condition is
required to have more efcient metal ions reduction. Recent
reports in the literature afrm the potential application of
vinyl groups in the silica matrix to facilitate the reduction of
Pd ions and stabilize Pd in its zero oxidation state [41–44].
Hence, using a vinyl group in the structure of the catalyst
ofers the best option to decrease the need for an external
reducing agent. The present catalytic system exhibited
remarkable activity in carbonylation reactions and can be
easily recycled. The reactions proceeded smoothly without
any external reducing agent and phosphine ligands, yield-
ing a variety of symmetrical and unsymmetrical ketones in
good-to-high yields.
Results and discussion
Several research groups have demonstrated the efcient
routes for the synthesis of deposited Pd NPs on organically
modifed silica [43, 44]; however, the main disadvantage was
the low surface area of the catalysts. Taking into account
other groups research, our recent paper on Fe3O4@(A-V)-
silica-Pd MNPs synthesis, and also the properties of carbon
nanotubes (CNTs) as a suitable Pd support due to its large
surface area and high chemical and mechanical stability,
we decided to focus our eforts on studying the potential
application of CNT@Fe3O4@(A-V)-silica-Pd MNPs in car-
bonylative coupling reactions. Initially, CNTs were function-
alized with carboxyl groups under microwave irradiation,
which difers from traditional purifcation methods in taking
less time, the possibility of high sample throughput, and
fnally having control over amenable pressure and tempera-
ture [45, 46]. The functionalized CNTs were magnetized by
the addition of an alkaline solution of Fe2+ and Fe3+, which
subsequently coated with uniform silica shell over applying
tetraethyl orthosilicate (TEOS).
Experimental
General procedure for carbonylative Stille coupling
of aryl iodides with Mo(CO)6 using MCNTs@
(A‑V)‑silica‑Pd catalyst
Then, the silica layer was functionalized by adding a mix-
ture of vinyltriethoxysilane (VTEOS) and [3-(2-aminoethyl-
amino)propyl] trimethoxysilane (AEAPS) [47, 48]. At this
point, Pd precursor (10 ml of 5 mM PdCl2 in 1 mM H2SO4)
was added to deliver Pd NPs on functionalized silica shell
over MCNTs without the need for any external reducing
agent for reduction of Pd(II) to Pd(0) due to the capability
of the amino-vinyl-functionalized silica for the reduction
step [41, 42] (Scheme 2). The catalyst was completely char-
acterized by TEM, XRD, VSM, FTIR, and TGA analysis
(Supporting section).
MCNTs@(A-V)-silica-Pd (1.5% mol%) was added to a mix-
ture of aryl iodide (1 mmol), Mo(CO)6 (1 mmol), Cs2CO3
(1.5 mmol), Ph3SnCl (0.4 mmol) in DMF (3 mL) in a fask,
and the reaction was stirred at 100 °C for an appropriate
time under atmospheric pressure. Then, the reaction was
cooled down to room temperature followed by separation of
the catalyst by an external magnet. The mixture was washed
with 10 mL water, and the crude product was isolated using
EtOAc (3×10 mL). The organic phases were combined and
dried over Na2SO4, evaporated, and purifed by column chro-
matography on silica gel (n-hexane/EtOAc) to deliver the
desired ketone in high yields.
Performance of MCNTs@(A‑V)‑silica‑Pd in the Stille
carbonylation of aryl iodides
General procedure for carbonylative homo‑coupling
of aryl iodides with Mo(CO)6 using MCNTs@
(A‑V)‑silica‑Pd catalyst
Having synthesized and fully characterized the cata-
lyst, we wish to explore the Stille carbonylation of aryl
iodides. We initiated our research using 4-iodotoluene,
Ph3SnCl, [Pd], Cr(CO)6, and K2CO3 in DMF at 100 °C.
Fortunately, the reaction provides 4-methylbenzophenone
(2a) in 42% yield (Table 1, entry 1). A variety of bases
Aryl iodide (2 mmol) was added to a flask containing
a stirring mixture of MCNTs@(A-V)-silica-Pd catalyst
(1.5 mol %), K2CO3 (2.5 mmol), Mo(CO)6 (1 mmol), and
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Scheme 2 Synthesis of CNT@
Fe3O4@(A-V)-silica-Pd MNPs
Table 1 Optimization parameters for the reaction of 4-iodotoluene with Ph3SnCl
Entry
Solvent
Base
Metal carbonyl
Time (h)
2a %a
1
2
3
4
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
Toluene
PEG 400
EG
K2CO3
Et3N
KOAc
Cs2CO3
NaOH
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cr(CO)6
Cr(CO)6
Cr(CO)6
Cr(CO)6
Cr(CO)6
Cr(CO)6
Mo(CO)6
W(CO)6
Co2(CO)8
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
24
24
24
24
24
24
4.5
4.5
4.5
4.5
4.5
4.5
4.5
4.5
42
11
19
68
15
68
92
26
37
80
76
0
5
6b
7c
8
9
10d
11e
12
13
14
13
0
Reaction conditions: 4-iodotoluene (1 mmol), Ph3SnCl (0.4 mmol), metal carbonyl (1 mmol), base (1.2 mmol), [Pd] (1.5 mol %), and solvent
(3 mL) was used unless otherwise noted
aIsolated yields
b2 mol% of [Pd] were used
cBold value signifes the best reaction conditions
d1 mol% of [Pd] was used
eTemperature was 80 °C
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were tested substantially, and among them, Cs2CO3 gave
a relatively higher yield (entries 2–5). It is important to
note that increasing the amount of catalyst is not efective
(entry 6). Then, the choice of other metal carbonyls was
tested and higher yields were obtained upon treating with
Mo(CO)6 (entries 7–9). It was also found that decreasing
the amount of the [Pd] catalyst and temperature reduced
the yield of 2a to 80% and 76%, respectively. Other sol-
vents such as toluene, PEG-400, and ethylene glycol (EG)
were also checked in the presence of Mo(CO)6, but they
did not yield any signifcant amount of 2a (entries 10–14).
The substrate scope of aryl iodides was then investi-
gated under the aforementioned optimal reaction condition
(Table 3).
Performance of MCNTs@(A‑V)‑silica‑Pd nanocatalyst
in homo‑coupling carbonylation of aryl iodides
To extend the applicability of the catalyst, we decided to
scrutinize homo-coupling carbonylation of aryl iodides
(Table 2). To start with, we carried out the reaction of
4-iodotoluene (1a) with W(CO)6, Mo(CO)6, Cr(CO)6, and
Co(CO)8 with KOAc as the base in PEG 400 with 1.5 mol %
of our newly synthesized [Pd] catalyst. The outcome of
the reactions revealed the inefciency of W(CO)6 albeit
Mo(CO)6, Cr(CO)6, and Co(CO)8 delivered 4-methylbenzo-
phenone (3a) in 52%, 17%, and 25% yields, respectively. As
a result, Mo(CO)6 was selected as the carbonyl source for the
optimization reactions (entries 1–4). In the course of these
studies, several organic and inorganic bases were studied in
Table 2 Carbonylative homo-coupling reaction of 4-iodotoluene with Pd catalyst under diferent conditions
Entry
Solvent
Metal carbonyl
Base
Time (h)
3a (%)
1
2
3
4
5
6
7
8
PEG 400
PEG 400
PEG 400
PEG 400
PEG 400
PEG 400
PEG 400
PEG 400
PEG 400
PEG 400
EG
W(CO)6
KOAc
KOAc
KOAc
KOAc
NaOH
K2CO3
DABCO
nPr3N
Cs2CO3
Pyridine
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
12
12
12
12
12
12
12
12
12
12
8
8
8
8
8
8
7
7
7
0
52
17
25
12
61
18
8
55
10
80
66
49
58
42
26
80
86
78
0
Mo(CO)6
Cr(CO)6
Co(CO)8
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Cr(CO)6
Mo(CO)6
9
10
11
12
13
14
15
16
17a
18b,c
19
20d
DMF
Toluene
Dioxane
PEG 200
Diglyme
EG
EG
EG
EG
12
All the reactions were performed using 1-iodo-4-methylbenzene (2 mmol), M(CO)6 (1 mmol), base (1.2 mmol), [Pd] (1.5 mol %), and solvent
(3 mL) at 90 °C unless otherwise noted
aThe reaction was performed using 2 mol% Pd
bThe temperature was 110 °C
cBold value signifes the best reaction conditions
dBromobenzene was used instead of iodotoluene
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Table 3 Unsymmetrical and
symmetrical diaryl ketone
synthesis starting from aryl
iodides
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Table 3 (continued)
1H NMR and 13C NMR of all the products were taken and compared to the authentic samples [47, 48]
aIsolated yield
Scheme 3 Gram-scale synthesis
of symmetrical and unsym-
metrical diaryl ketones
PEG 400, which did not improve the yield of 3a greatly, and
it was found that K2CO3 is slightly better than KOAc (entries
5–10). Therefore, our efort was made to replace PEG 400
with other solvents using K2CO3 as the base. Exploration
of the impact of solvents modifed the yield of 3a to 80%
yield in ethylene glycol (EG) (entries 11–16). The yield
of 3a was not enhanced by further increasing the amount
of catalyst (entry 17). Thereafter, the reaction temperature
was further investigated; the obtained results indicated that
the yield of 3a was enhanced by raising the temperature to
110 °C (entry 18). Later, Cr(CO)6 was checked under this
optimized reaction conditions, and 3a was obtained in 78%
yield along with the formation of 4-methylbiphenyl as the
side product in 17% yield, which demonstrates the efciency
of Mo(CO)6 among the carbonyl sources giving less amount
of the competing uncarbonylated 4-methylbiphenyl as the
side product. Having established the reaction conditions for
4-iodotoluene (1a), we were delighted to perform the reac-
tion for other aryl electrophiles like bromobenzene under
the identical reaction condition; however, the reaction was
failed to react successfully.
meta-substituted analogs (Table 3, entries 1–4). Notably,
aryl iodide bearing a chloro group was also tolerated in this
method and delivered the corresponding products 2f and 3f
in good-to-excellent yields (entry 6).
Electron-defcient iodoarenes are known to be prone to
endure noncarbonylative coupling to biaryl by-products [49,
50]. It was found that lower yields were obtained when elec-
tron-withdrawing groups such as -NO2 and -COOEt groups
were present on aryl iodides (entries 7 and 8). Moreover,
reactions of bulky 1-iodonaphthalene also proceeded efec-
tively to furnish the desired products 2i and 3i in 77 and 74%
yields, respectively. As turnover numbers (TONs) and turno-
ver frequencies (TOFs) make heterogeneous catalysis very
cost efcient and usually represents the catalytic activity of
the catalyst, these two important factors were calculated for
Stille carbonylative reactions of triphenyltin chloride with
4-iodotoluene in the presence of nanomagnetic Pd catalyst.
This reaction produces relatively high TON (3.63×102; mol
product per mol [Pd]) and TOF (80.6 h−1).
Encouraged by the obtained results (Table 3), the gram-
scale application of our catalytic system was also tested in
Stille and homo-coupling carbonylation by starting from
10 mmol of 1-iodo-4-methylbenzene to furnish the desired
products 2a and 3a in 86 and 80% yield (Scheme 3).
In order to fnd out whether the palladium leaches out
from the solid catalyst to the solution during the reaction,
a hot fltration test was done for the Stille carbonylation of
4-iodotoluene with Ph3SnCl to achieve 2a as the product.
After 2 h, the catalyst was separated from the reaction mix-
ture using an external magnet under hot conditions, which
delivered 2a in 54% yield. Then, the fltrate was allowed
to react further, which revealed no further conversion of
With these novel fndings in hand, we study the scope of
Stille and homo-coupling carbonylation for variety of aryl
iodides in the presence of [Pd] catalyst (Table 3). As can
be seen from Table 3, MCNTs@(A-V)-silica-Pd catalyst is
an efective catalyst for the construction of both symmetri-
cal and unsymmetrical ketones in the presence of electron-
donating, electron-withdrawing, and steric-hindered aryl
iodides. High yields were obtained for iodobenzene sub-
stituted with electron-donating groups such as methyl and
methoxy at the para and meta position. However, para-
substituted substrates gave slightly higher yield than their
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Journal of the Iranian Chemical Society
recycling and recovery of them are a great concern from
the practical, economic, and environmental points of view.
Therefore, the recyclability of the catalyst was examined
for the preparation of 2a starting with 4-iodotoluene in the
presence of 1.5 mol % of the catalyst in DMF at 100 °C.
For the recycling experiment, the MCNTs@(A-V)-silica-Pd
catalyst was easily recovered from the reaction mixture with
an external magnet (Fig. 2a), and then, the separated cata-
lyst was in identical reaction conditions. Finally, recycling
experiments showed that the catalytic activity remained
almost unchanged after being reused for six consecutive
runs (Fig. 2b).
100
80
60
40
20
0
(a)
(b)
0
1
2
3
4
5
TIME
Fig. 1 a Time interval plot for Stille carbonylation of 4-iodotoluene
with Ph3SnCl over Pd magnetic nanocatalyst and b after removing
of the catalyst at 54% product formation. Yields were determined by
GC, with dodecane as an internal standard
To investigate the structure of the catalyst and the pres-
ence of pd nanoparticles on silica cores after Stille carbon-
ylation reaction, the TEM analysis of the catalyst after the
third run was taken, which is indicative of the preservation
of the shape of the catalyst (Fig. 3).
4-iodotoluene to 2a thereafter (Fig. 1). This observation
confrms that no appreciable leaching of palladium occurs
from the nanocatalyst under hot conditions.
After successful implementation of the Stille and
homo-coupling carbonylation of aryl iodides, we shifted
our attention to use our Pd catalyst in carbonylative
Suzuki reactions of aryl iodides with arylboronic acids.
In addition, ICP analysis showed a negligible amount of
Pd (less than 0.1%) metal in the solution. Since the cost
of transition metal-supported catalysts is often high, the
Fig. 2 a Photograph showing
the magnetic separation of the
catalyst. b The recyclability
results of MCNTs@(A-V)-
silica-Pd catalyst in the Stille
carbonylation of 4-iodotoluene
with Ph3SnCl
Fig. 3 a TEM image of
MCNTs@(A-V)-silica-Pd and
MCNTs@(A-V)-silica (inset)
nanocomposites. b TEM image
of the recycled catalyst after the
third run
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Journal of the Iranian Chemical Society
This reaction has received a great deal of attention as a
promising and powerful method for synthesizing diverse
biaryl ketones owing to the commercial availability of
stating materials and high atom economy [49, 51–54].
Having smoothly achieved the synthesis of biaryl ketones
through Stille and homo-coupling carbonylation of aryl
iodides, the Suzuki carbonylation reaction was explored
with iodotoluene and phenylboronic acid in the presence
of Mo(CO)6 under the same conditions as Stille coupling
except that K2CO3 and 90 °C were chosen as the more
proper condition. Because of the heterogeneous nature of
the magnetic catalyst, the reaction was performed for 8 h
to reach a maximum 94% conversion of iodotoluene. A
higher reaction temperature (> 90 °C) and longer reaction
time only resulted in the increase in the amount of biphe-
nyl as the by-product. This observation is mainly due to
the instability of ArCO-Pd-I at high temperature, which is
accompanied with the removal of the CO moiety [55, 56].
Unfortunately, our protocol does not provide satisfactory
yields in the case of aryl bromides or chlorides, which is
not unusual observation in Suzuki carbonylation reaction
[11, 57]. With this standard conditions in hand, carbon-
ylative Suzuki reactions were conducted on a variety of
commercially available aryl iodides (Table 4).
To check the merit of the present method, the results of
our catalytic system were compared with some reported
methods in the literature used in the synthesis of benzo-
phenone 2e (Table 5). It is evident that the catalytic activ-
ity, recyclability, and reaction conditions of the MCNTs@
(A-V)-silica-Pd is better or comparable than other catalytic
systems.
Based on the previous reports regarding the capabil-
ity of vinyl groups in the silica matrix to reduce Pd ions
[41, 42] and also XRD analysis (SI) which confirms the
presence of Pd (0) [38, 58], the following mechanism for
carbonylative Suzuki reactions was proposed (Scheme 4)
[59, 60].
Conclusions
In conclusion, the efficient carbonylative Stille, Suzuki,
and homo-coupling of aryl iodides were reported
using Mo(CO)6 as the solid metal carbonyl source and
MCNTs@(A-V)-silica-Pd as a heterogeneous and mag-
netic catalyst, which was prepared under phosphine-free
conditions due to the coordination of VTEOS and AEAPS
groups on silica to palladium. The catalyst was fully char-
acterized and used for the preparation of unsymmetri-
cal and symmetrical diaryl ketones in high yields with
high functional group tolerance. Moreover, in the Stille
carbonylation, 0.4 mmol of Ph3SnCl was used (less than
equimolar) with respect to aryl iodides (1 mmol), which
is an important issue due to the toxicity of organostan-
nanes. Besides, in the homo-coupling carbonylation, this
is the first report in which a heterogeneous magnetic cata-
lyst was applied. Hot filtration test and ICP analysis were
done which confirmed the heterogeneous nature of the
catalyst. Finally, the ease in separation of the catalyst
using an external magnet and its recyclability after six
executive runs without the loss in catalytic activity, not
required handling of gaseous CO and high-pressure reac-
tors are the advantages of the catalyst.
The iodoarenes featuring with the electron-donating group
such as -Me and -OMe at the para-position were prone to
deliver the carbonylation products 2a–b in excellent yields
(Table 4, entries 1 and 2). Meta-substituted iodobenzenes
were similarly found to be suitable substrates for this trans-
formation and gave the corresponding biaryl ketones in good
yields (entries 3 and 4). The reaction of aryl iodides bearing
electron-withdrawing groups such as –Cl, –NO2 and –COOEt
also proceeded well, giving the desired products 2f–h in
moderate-to-good yields under optimized reaction conditions
(entries 6–8). It is noteworthy that bulky 1-iodonaphthalene
could undergo the carbonylative cross-coupling reactions with
phenylboronic acid efectively, afording the desired product
2i in good yield (entry 9). The present protocol was also suc-
cessfully applied for the double carbonylation of 1,4-diiodo-
benzene, providing diketone 2j in 83% yield (entry 10).
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Journal of the Iranian Chemical Society
Table 4 Carbonylative Suzuki reactions of phenylboronic acid with aryl iodides 1a–i in the presence of nanomagnetic Pd catalyst
Reaction conditions: iodoarene (1.0 mmol), phenylboronic acid (1.1 mmol), M(CO)6 (1 mmol), base (1.1 mmol), [Pd] (1.5 mol %), solvent
(3.0 mL) at 90 °C
aIsolated yields
bUsing the corresponding aryl bromide and chloride
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Table 5 Comparison of the efciency of the present method with other systems for the synthesis of benzophenone 2e via homo-coupling carbon-
ylation and carbonylative Suzuki reactions in the presence of MCNTs@(A-V)-silica-Pd
Entry
System, conditions
Time
Yield (%)
Recyclability
References
1
2
3
4
5
6
7
8
9
CO, LiPdCl3-CuCI2, CH3CN, r.t.
1 h
1 h
2 h
24 h
2 h
2 min
4 h
10 h
10 h
29
61
78
76
83
78
96
94
81
–
–
–
–
–
–
9
4
6
[21]
[23]
[28]
[29]
[30, 31]
[32]
[1]
[6]
This work
CO, Ar2I+Br−, Pd(OAc)2, Zn, Acetone, r.t.
Cr(CO)6, PdCl2, P-ligand, KOAc, PEG, 90 °C
CO/O2, Pd(PPh3)2Cl2, CuCl, DMF, 80 °C
CO2CO8, PhHgBr, under N2, dry THF, r.t.
CO2CO8, Microwave, CH3CN, sealed tube
CO, Pd(OAc)2, K3PO4, tBuCOOH, PEG-400, r.t.
CO, PS-Pd-NHC, K2CO3, toluene, 100 °C,
Mo(CO)6, MCNTs@(A-V)-silica-Pd, K2CO3, DMF, 90 °C
Acknowledgements We gratefully acknowledge the fnancial support
of this study by Shiraz University Council.
Compliance with ethical standards
Conflict of interest The authors declare that there is no confict of in-
terest regarding the publication of this article.
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Authors and Afliations
Elham Etemadi‑Davan1 · Dariush Khalili1 · Ali Reza Banazadeh2 · Ghazal Sadri1 · Pourya Arshad1
1
* Elham Etemadi-Davan
Department of Chemistry, Shiraz University, Shiraz 71454,
etemadidavan@shirazu.ac.ir
Iran
2
* Dariush Khalili
Department of Chemistry and Biochemistry, Texas
Tech. University, Lubbock 79409, TX, USA
khalili@shirazu.ac.ir
1 3