C-C and C-H coupling reactions by Fe3O4/KCC-1/APTPOSS supported palladium-salen-bridged ionic networks as a reusable catalyst

Article abstract of DOI:10.1039/c8ra00485d

This study investigates the potential application of an efficient, easily recoverable and reusable magnetically separable Fe₃O₄/KCC-1/APTPOSS nanoparticle-supported salen/Pd(ii) catalyst for C-C and C-H cross-couplings. The Fe₃O₄/KCC-1/APTPOSS/salen/Pd(ii) MNPs were thoroughly characterized by using TEM, FE-SEM, TGA, XRD, VSM, FT-IR, ICP-MS, and BET. This observation was exploited in the direct and selective chemical reaction of 2-acetyl-benzaldehyde with cyclopentadiene for the synthesis of pentafulvene. The recycled catalyst has been analyzed by ICP-MS showing only minor changes in the morphology after the reaction, thus confirming the robustness of the catalyst.

Full text of DOI:10.1039/c8ra00485d

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PAPER
C–C and C–H coupling reactions by Fe O /KCC-1/
3
4
APTPOSS supported palladium-salen-bridged ionic
networks as a reusable catalyst
Cite this: RSC Adv., 2018, 8, 8761
a
b
b
Asadollah Hassankhani,* Seyed Mohsen Sadeghzadeh
and Rahele Zhiani
This study investigates the potential application of an efficient, easily recoverable and reusable magnetically
separable Fe /KCC-1/APTPOSS nanoparticle-supported salen/Pd(II) catalyst for C–C and C–H cross-
couplings. The Fe /KCC-1/APTPOSS/salen/Pd(II) MNPs were thoroughly characterized by using TEM,
3 4
O
3 4
O
Received 17th January 2018
Accepted 20th February 2018
FE-SEM, TGA, XRD, VSM, FT-IR, ICP-MS, and BET. This observation was exploited in the direct and
selective chemical reaction of 2-acetyl-benzaldehyde with cyclopentadiene for the synthesis of
pentafulvene. The recycled catalyst has been analyzed by ICP-MS showing only minor changes in the
morphology after the reaction, thus confirming the robustness of the catalyst.
DOI: 10.1039/c8ra00485d
rsc.li/rsc-advances
recyclable and easy to separate from the reaction solution using
Introduction
21,22
a magnet.
Lately, organometallic ionic complexes (OICs)
Schiff bases are a signicant class of ligands and have been have emerged as very marvelous catalysts because they can be
studied heavily. Much effort has been made to investigate the created from readily available and highly tailorable metal and
23,24
sustainability of Schiff-base type ligands for coupling reactions. ligand forerunners for multifunctional integration.
Many
The half-salen Pd(II) complexes were found to act as effectual researchers have showned OICs that contain a Lewis acidic
ꢀ
catalysts in coupling reactions. Many heterogenized systems metal center and a nucleophilic halogen anion (X ) portion as
have been based by supporting the salen Pd(II) complexes on highly impressive bifunctional catalysts for the coupling reac-
some supports, such as silica, and magnetite nanoparticles for tion between carbon dioxide and other organic compound
reuse of the catalysts. However, most of the catalytic systems under co-catalyst free circumstances owing to the cooperative
2
5–27
suffer from rough reaction conditions and disappointing cata- effects of the catalytic functional groups.
lytic efficiency.
Having this point
1
–10
in mind, we envisioned a way in which the preface of Lewis acid
ꢀ
Morphology-controlled nanomaterials such as silica play (metal center) active sites to a halogen anion (X ) based ionic
a decisive role in the development of technologies for address- polymer could provide highly active, recyclable catalysts for the
ing challenges in the elds of wellness, environment, and synthesis of heterocyclic compounds. In continued our
energy. Mesoporous silica materials discovery such as MCM-41 research, we've replaced the organic groups with silica groups.
and SBA-15, a notable increase in the design. It was synthesis of Our study illustrated that the APTPOSS was a powerful and
nanosilica with different sizes, shapes, morphologies, and highly efficient support for the strength of the catalyst structure.
tissue properties has been observed in lately years. KCC-1 is Our goal was to enhance the strength of the catalyst structure by
dendritic brous nanosilica as one notable invention that have this replacement. This catalyst support via obstruction of Fe
a unique brous morphology, unlike the tubular porous struc- KCC-1 by APTPOSS (Fe /KCC-1/APTPOSS). In fact, Fe
3
O
4
/
/
3 4
O
3
O
4
ture of various customary silica materials. It has a high surface KCC-1/APTPOSS is a nano labyrinth to hold the structure. We
area with improved accessibility to the internal surface, tunable believe that this unique property will be very useful for the
pore size and pore volume, controllable particle size, and, design of silica-supported catalysts, for which the accessibility
11–20
importantly, improved stability.
of active sites can be increased signicantly. Herein, we report
In recent years, magnetic nanoparticles of iron oxide (Fe
3
O
4
)
the design and synthesis of a novel bifunctional complex
have been widely used as a heterogeneous catalyst in organic composed of the cross-linked Fe
reactions because they are cheap, available, low toxicity, a substrate with the N,N -bis({4-dimethylamino}salicylidene)
ethylenediamino palladium(II) (salen-Pd(II)) Schiff base outer
3
O
4
/KCC-1/APTPOSS as
0
shell to serve as a catalyst for the synthesis pentafulvene
a
Department of New Materials, Institute of Science and High Technology and
(Scheme 1). It is noteworthy that this is the rst report on the
Environmental Sciences, Graduate University of Advanced Technology, PO Box
synthesis of magnetic nanoparticles that can be reused up to ten
times without signicant loss of catalytic activity.
7
6315-117, Kerman, Iran. E-mail: ahassankhani@gmail.com
b
Young Researchers and Elite Club, Neyshabur Branch, Islamic Azad University,
Neyshabur, Iran
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3 2
concentrated ammonia aqueous solution (NH $H O), followed
by the addition of 0.20 g of tetraethyl orthosilicate (TEOS). Aer
Experimental
Materials and methods
vigorous stirring for 24 h, the nal suspension was repeatedly
ꢁ
Chemical materials were purchased from Fluka and Merck in washed, ltered for several times and dried at 60 C in the air.
high purity. Melting points were determined in open capillaries
using an Electrothermal 9100 apparatus and are uncorrected. General procedure for the preparation of Fe O /SiO /KCC-1
3
4
2
FTIR spectra were recorded on a VERTEX 70 spectrometer MNPs
Bruker) in the transmission mode in spectroscopic grade KBr
(
3 4 2
Fe O /SiO (0.25 g) was dispersed in an aqueous solution (30
pellets for all the powders. The particle size and structure of
nano particle was observed by using a Philips CM10 trans-
mission electron microscope operating at 100 kV. Powder X-ray
diffraction data were obtained using Bruker D8 Advance model
with Cu ka radiation. The thermogravimetric analysis (TGA) was
carried out on a NETZSCH STA449F3 at a heating rate of
mL) containing urea (0.3 g) to form solution A under ultra-
sonication for 1 h. Cetylpyridinium bromide (CPB) (0.5 g) was
added to 0.75 mL of n-pentanol and 30 mL cyclohexane to from
solution B. Solution A was added to solution B under stirring at
room temperature. Then 1.25 g TEOS was added drop wise to
the abovementioned solution. The resulting mixture was
continually stirred for 1 h at room temperature and then placed
ꢁ
ꢀ1
1
13
10
C min under nitrogen. H and C NMR spectra were
recorded on a BRUKER DRX-300 AVANCE spectrometer at
00.13 and 75.46 MHz, BRUKER DRX-400 AVANCE spectrom-
ꢁ
into a 120 C environment for 5 h, thus inciting the reaction.
Aer the reaction was completed, the mixture was allowed to
3
eter at 400.22 and 100.63 MHz, respectively. Elemental analyses
for C, H, and N were performed using a Heraeus CHN–O-Rapid
analyzer. The purity determination of the products and reaction
monitoring were accomplished by TLC on silica gel polygram
SILG/UV 254 plates. Mass spectra were recorded on Shimadzu
GCMS-QP5050 Mass Spectrometer.
3 4 2
cool to room temperature, and the Fe O /SiO /KCC-1 core–shell
microspheres were isolated by strong magnetic suction, then
washed with deionized water and acetone, and dried overnight
ꢁ
in a drying oven at 40 C. This material was then calcined at
ꢁ
5
50 C for 5 h in air.
Preparation of octakis[3-(3-aminopropyltriethoxysilane)propyl]
octasilsesquioxane (APTPOSS). 3-Aminopropyltriethoxysilane (20
mmol) and ClPOSS (2 mmol) were transferred to a reaction vessel
under nitrogen atmosphere and the reaction solution was stirred
General procedure for the preparation of Fe
The synthesis procedure is illustrated as follows: (1) 0.01 mol
FeCl $4H O and 0.03 mol FeCl $6H O were dissolved in to
00 mL distilled water, followed by the addition of polyethylene
glycol (PEG) (1.0 g, MW 6000). (2) Sodium hydroxide (NaOH)
was added to the solution and the pH value was controlled in
3 4
O MNPs
ꢁ
at 100 C for 2 days. Then the mixture was cooled to room
2
2
3
2
temperature and the solution was ltered and washed with
2
28
methanol and acetone.
the range 12 # pH # 13. (3) 5 mL of hydrazine hydrate General procedure for the preparation of Fe
$H
O, 80% concentration) was added to the above APTPOSS MNPs
3 4
O /KCC-1/
(N
2
H
4
2
suspension. The reaction was continued for about 24 h at room
temperature. During this period, the pH value was adjusted by
NaOH and kept in the range 12 # pH # 13. The black Fe O NPs
3 4
3 4
Fe O /KCC-1 MNPs (2 mmol) and THF (20 mL) were mixed
together in a beaker, and then NaH (20 mmol) was dispersed in
to the mixture by ultrasonication. APTPOSS (0.5 g) was added at
were then rinsed several times with ionized water.
ꢁ
room temperature and stirred for another 16 h at 60 C. The
General procedure for the preparation of Fe
.02 mol of Fe MNPs were dispersed in a mixture of 80 mL of
ethanol, 20 mL of deionized water and 2.0 mL of 28 wt%
3 4 2
O /SiO MNPs
0
3 4
O
3 4
3 4
Scheme 1 Synthesis of pentafulvene in the presence of Fe O /KCC-1/ Scheme 2 Schematic illustration of the synthesis for Fe O /KCC-1/
APTPOSS/salen/Pd(II) MNPs.
APTPOSS/salen/Pd(II) MNPs.
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cooled to room temperature. Aer 48 h, the precipitated yellow
crystals were separated by ltration, washed with ethanol, and
ꢁ
dried at 80 C for 12 h to give the salen ligand.
General procedure for the preparation of Fe
APTPOSS/3-bromopropyl MNPs
3 4
O /KCC-1/
Under nitrogen atmosphere, 2 mL of 3-bromopropyltrimethox-
ysilane is added to 5.0 g of Fe /KCC-1/APTPOSS in suspension
3 4
O
with 50 mL of freshly distilled toluene. Aer 24 h of reaction
under reux, the resulting solid was separated using a magnet,
washed thoroughly with toluene, ethanol, and then subjected to
toluene Soxhlet extraction. The functionalized Fe O /KCC-1 is
3
4
ꢁ

nally dried in vacuum at 70 C.
General procedure for the preparation of Fe
APTPOSS/salen MNPs
3 4
O /KCC-1/
The salen ligand (0.41 g) was dissolved in toluene (5 mL) and
methanol (5 mL), respectively. The two solutions were
combined and the reaction mixture was vigorously stirred at
ꢁ
6
0 C for 24 h then Fe O /KCC-1/APTPOSS/3-bromopropyl (0.6
3
4
ꢁ
g) was added. Aer stirring at 60 C for 24 h, the brown solid was
separated by external magnet, washed with ethanol, and dried
ꢁ
under vacuum at 60 C for 24 h to afford Fe
3
O
4
/KCC-1/APTPOSS/
salen.
General procedure for the preparation of Fe O /KCC-1/
3
4
APTPOSS/salen/Pd(II) MNPs
A mixture of Fe O /KCC-1/APTPOSS/salen (0.45 g), PdCl (CH -
3
4
2
3
CN)
2
(0.5 g), and Et
3
N (0.8 mL) in methanol (10 mL) was
degassed with N
2
and reuxed for 4 h. Aer cooling to room
temperature, the precipitate was ltered and washed with
methanol (10 mL ꢂ 3) and ether (10 mL ꢂ 3) to get a powder.
The nal particle was separated from the solution by external
magnet, washed three times with water to remove any ions
present, and dried under vacuum.
General procedure for the synthesis of pentafulvene
A mixture of 2-acetyl-benzaldehyde (10 mmol), cyclopentadiene
(
70 mmol), and nano Fe
/KCC-1/APTPOSS/salen/Pd(II) (6 mg) and DMF (20 mL) were stirred at room temperature for
/KCC-1/salen/Pd(II) MNPs after ten the 3 h. Upon completion, the progress of the reaction was
3 4
O /KCC-1/APTPOSS/salen/Pd(II) MNPs
3 4 3 4
Fig. 1 TEM images of Fe O /KCC-1 MNPs (a); fresh Fe O /KCC-1/
APTPOSS/salen/Pd(II) MNPs (b); Fe
MNPs after ten reuses (c); Fe
reuses (d); FE-SEM images of Fe
KCC-1/APTPOSS/salen/Pd(II) MNPs (f); Fe
3 4
O
3 4
O
3
O
4
/KCC-1 MNPs (e); fresh Fe
/KCC-1/APTPOSS/salen/
3 4
O /KCC-1/salen/Pd(II) MNPs after
3 4
O /
monitored by TLC when the reaction was completed, the nano
KCC-1/salen/Pd(II) NPs were separated by external magnet. The
solvent was removed under reduced pressure, and the residue
was puried by ash column chromatography over silica gel
3 4
O
Pd(II) MNPs after ten reuses (g); Fe
ten reuses (h).
(EtOAc/hexanes, 1 : 5) to yield the desired pentafulvene.
resultant products were collected and washed with ethanol and
deionized water in sequence, and then dried under vacuum at
Results and discussion
ꢁ
60 C for 2 h for further use.
The salen–Pd Schiff base was covalently attached onto the
surface of Fe O /KCC-1/APTPOSS by a nucleophilic reaction,
which resulted in dual catalytically active centers with a syner-
3
4
General procedure for the preparation of salen
Diethylamine (0.30 g) was added to a solution of 4-(dieth- gistic effect to greatly enhance the catalytic productivity.
ylamino)salicylaldehyde (2.00 g) in ethanol (30 mL). The reac- Furthermore, the catalyst can be easily recovered from the
tion mixture was heated at reux for 24 h then the mixture was reaction mixture by centrifugation for steady reuse (Scheme 2).
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KCC-1/APTPOSS possesses a core of Fe
3
O
4
particle, nonporous
silica layer and silica bres. The as-prepared magnetic core–
shell brous silica material Fe O /KCC-1 with brous structure
3
4
was uniform and monodispersed. Also, TEM and FE-SEM
images of highly textured Fe /KCC-1 samples, where the
3 4
O
samples have spheres of uniform size with diameters of
ꢃ300 nm and a wrinkled radial structure (Fig. 1a and e). A close
inspection of these images shows that wrinkled bers (with
thicknesses of ꢃ8.5 nm) grow out from the center of the spheres
and are arranged radially in three dimensions. Also, the over-
lapping of the wrinkled radial structure forms cone-shaped
open pores. The TEM and FE-SEM images shows that the
entire sphere is solid and composed of bers. Furthermore, this
open hierarchical channel structure and bers are more easily
for the mass transfer of reactants and increase the accessibility
3 4
of active sites. The FE-SEM and TEM images of Fe O /KCC-1/
Fig. 2 XRD analysis of (a) Fe
3
O
4
, (b) Fe O
3 4
/KCC-1, and (c) Fe
O
3 4
/KCC- salen/Pd(II) MNPs showed that aer modication the
1
/APTPOSS/salen/Pd(II) MNPs.
morphology of Fe O /KCC-1 is not change (Fig. 1b and f). To
3
4
assess the exact impact of the presence of APTPOSS in the
catalyst, the Fe O /KCC-1/APTPOSS/salen/Pd(II) compared with
3
4
3 4
Fe O /KCC-1/salen/Pd(II) MNPs. To further understand this
issue, compared FE-SEM and TEM images of used catalyst with
those of the fresh catalyst. Comparison of FE-SEM and TEM
images of used catalyst with those of the fresh catalyst showed
that the morphology and structure of Fe
3 4
O /KCC-1/APTPOSS/
salen/Pd(II) and Fe O /KCC-1/salen/Pd(II) MNPs remained intact
3
4
aer ten recoveries. Fig. 1d and h shows degradation of
structure of Fe O /KCC-1/salen/Pd(II) MNPs in the reuse
3
4
process. Its ber structure has been destroyed. But, the func-
tionalization of the Fe /KCC-1/APTPOSS/salen/Pd(II) MNPs
does not result in the change of the morphology (Fig. 1c and g).
These study proves, this stable on structure of Fe /KCC-1/
3 4
O
3 4
O
APTPOSS/salen/Pd(II) MNPs were due to the presence of APT-
POSS in the catalyst structure. APTPOSS can be a strong scaf-
fold in KCC-1 structure.
3 4
Fig. 3 TGA diagram of Fe O /KCC-1/APTPOSS/salen/Pd(II) MNPs.
The powder X-ray diffraction patterns of Fe O , Fe O /KCC-1,
3
4
3 4
3 4
and Fe O /KCC-1/APTPOSS/salen/Pd(II) MNPs are shown in
Fig. 2. As can be observed, all samples possess the typical
diffraction peaks at (220), (311), (400), (422), (511) and (440),
3 4
which are in good agreement with the data for standard Fe O
sample, as reported in the JCPDS card (no. 19-0629) (Fig. 2a).
Besides the peak of iron oxide, the XRD pattern of Fe O /KCC-1/
3
4
APTPOSS core–shell nanoparticles presented a broad feature-
less XRD peak at low diffraction angle, which corresponded to
the amorphous silica (Fig. 2b). Fig. 2c shows a typical XRD
pattern of the Fe
was no change in it.
To conrm the thermal stability of the Fe
3 4
O /KCC-1/APTPOSS/salen/Pd(II) MNPs. There
3 4
O /KCC-1/APT-
POSS/salen/Pd(II) MNPs, the thermogravimetric analysis of this
material was performed at temperatures ranging from room
ꢁ
ꢁ
temperature to 700 C (Fig. 3). The weight loss below 250 C was
ascribed to the elimination of the physisorbed and chem-
Fig. 4 Adsorption–desorption isotherms of Fe
salen/Pd(II) MNPs.
O
3 4
/KCC-1/APTPOSS/
isorbed solvent on the surface of the silica material. About
ꢁ
1
1.6% of the weight loss, in the temperature range 250–450 C,
The morphology and structure of the Fe
3
O
4
/KCC-1/APTPOSS
was due to the organic group derivatives.
3 4
The N adsorption–desorption isotherms of Fe O /KCC-1/
APTPOSS/salen/Pd(II) MNPs showed characteristic type IV
3 4
and Fe O /KCC-1/APTPOSS/salen/Pd(II) MNPs are further char-
2
acterized by TEM and FE-SEM. As shown in Fig. 1a, the Fe
3 4
O /
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3 4 3 4
Table 1 Structural parameters of Fe O /KCC-1 and Fe O /KCC-1/
APTPOSS/salen/Pd(II) MNPs materials determined from nitrogen sorp-
tion experiments
S
BET
V
a
D
BJH
(nm)
2
ꢀ1
3
ꢀ1
Catalysts
(m g
)
(cm g
)
Fe
Fe
3
O
O
4
4
/KCC-1
427
311
1.23
0.98
14.51
11.16
3
/KCC-1/APTPOSS/salen/Pd(II)
curve (Fig. 4), which is consistent with literature reports on
standard brous silica spheres. As for Fe /KCC-1, the BET
surface area, total pore volume, and BJH pore diameter are
3 4
O
Fig. 6 Magnetic separation ability of Fe
obtained as 427 m g , 1.23 cm g , and 14.51 nm respec- Pd(II) MNPs.
O
3 4
/KCC-1/APTPOSS/salen/
2
ꢀ1
3
ꢀ1
tively, whereas the corresponding parameters of Fe
3
O
4
/KCC-1/
2
ꢀ1
APTPOSS/salen/Pd(II) MNPs have decreased to 311 m g , 0.98
3
ꢀ1
cm
g , and 11.16 nm. The nitrogen sorption analysis of
In addition, as seen in Fig. 6, by putting a magnet nearby the
reaction mixture balloons can be seen the magnetic separation
ability of catalyst. The magnet will attract the magnetic nano-
particles towards itself, and when the external magnet is
removed, the catalyst will scatter in the solution with little
shake.
Fe O /KCC-1/salen/Pd(II) MNPs also conrms a regular and
uniform mesostructure with a decrease in surface area, pore
diameter and pore volume parameters in comparison with
3
4
3 4
that of pristine Fe O /KCC-1. With the functionalization by
salen/Pd–Si, the corresponding pore volumes are drastically
reduced. This could be ascribed to increased loading with the
sensing probe, which occupies a large volume inside the silica
spheres (Fig. 4 and Table 1).
The magnetic properties of the nanoparticles were charac-
terized using a vibrating sample magnetometer (VSM). The
magnetization curves of the obtained nanocomposite registered
at 300 K show nearly no residual magnetism is detected (Fig. 5),
which means that the nanocomposite exhibited the para-
magnetic characteristics. Magnetic measurement shows that
FT-IR spectroscopy was employed to determine the surface
modication of the synthesized catalyst (Fig. 7). The Si–O–Si
ꢀ
1
symmetric and asymmetric stretching vibrations at 793 cm
ꢀ
1
ꢀ1
and 1091 cm and the O–H stretching vibration at 3430 cm
were observed for the Fe O /KCC-1 (Fig. 7a). The bands
3
4
ꢀ
1
observed at 3121 and 2929 cm are assigned to C–H stretching
of aromatic and aliphatic moieties. Moreover, the signals
ꢀ1
cleared at 1462 and 1632 cm are, respectively, attributed to
C]C and C]N. (Fig. 7b). These results indicated that the salen
had been successfully introduced onto the surface of Fe O /
pure Fe O , and Fe O /KCC-1/APTPOSS/salen/Pd(II) have satu-
3
4
3 4
3
4
ꢀ
1
ration magnetization values of 55.1, and 22.4 emu g respec-
tively. These nanocomposites with paramagnetic characteristics
and high magnetization values can quickly respond to the
external magnetic eld and quickly redisperse once the external
magnetic eld is removed. The result reveals that the nano-
composite exhibit good magnetic responsible, which suggests
a potential application for targeting and separation.
KCC-1.
To optimize reaction conditions for the Fe
3 4
O /KCC-1/APT-
POSS/salen/Pd(II) MNPs catalyst system, the effects of various
reaction parameters were investigated. We examined the effect
of solvent on the synthesis of pentafulvene using the Fe O /
3
4
3 4 3 4
Fig. 7 FTIR spectra of (a) Fe O /KCC-1 MNPs, (b) Fe O /KCC-1/
Fig. 5 Room-temperature magnetization curves of the nano catalysis. APTPOSS/salen/Pd(II) MNPs.
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Table 2 The effect of solvent and temperature for synthesis of
a
pentafulvene
ꢁ
b
Entry
Solvent
Temp. ( C)
Yield (%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMSO
Dioxane
Reux
130
110
90
70
50
80
85
92
92
92
92
92
74
82
69
77
82
74
69
77
21
17
15
10
29
21
32
18
—
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
Fig. 9 Effect of increasing amount of Fe
Pd(II) NPs on yield of pentafulvene.
3
O
4
/KCC-1/APTPOSS/salen/
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
CH
CH
3
CN
Cl
2
2
EtOAc
THF
Toluene
CHCl
n-Hexane
Benzene
the crucial role of temperature in the synthesis of pentafulvene
in the presence of Fe /KCC-1/APTPOSS/salen/Pd(II) MNPs as
3
3 4
O
a catalyst. Results clearly indicated that the catalytic activity is
sensitive to reaction temperature. The yield decreased when the
CCl
Cyclohexane
4
ꢁ
temperature reached 130 C. The best temperature for this
reaction was at room temperature (Table 2, entry 1–7).
The inuence of time on this reaction is exhibited in Fig. 8. It
is obvious that the pentafulvene yield increased up to 92% for
2
H O
EtOH
i-PrOH
MeOH
180 min. Whereas further increase in the time don't resulted in
Solvent-free
a slight decrease in the product yield. Therefore, the optimal
time for synthesis of pentafulvene is 180 min.
a
Reaction
conditions:
2-acetyl-benzaldehyde
(10
mmol),
cyclopentadiene (70 mmol), and nano Fe O /KCC-1/APTPOSS/salen/
Pd(II) MNPs (6 mg), and solvent (10 mL), 3 h. GC yields [%].
3 4
b
The amount of catalyst is another important factor in
current reaction for the synthesis of pentafulvene (Fig. 9). As
shown in Fig. 9, in the absence of the catalyst no product was
obtained. When 1–5 mg of catalyst was elaborated on sample
reaction, moderate yields of product was obtained. The best
result was achieved when the model reaction was carried out
in the presence of 6 mg of catalyst. A rise in the catalyst
amount showed no upgrading in the model reaction.
KCC-1/APTPOSS/salen/Pd(II) MNPs (Table 2). Solvent does affect
on catalysts performance. n-Hexane, benzene, CCl
hexane, an non-polar solvent, gave pentafulvene a lower yield
Table 2, entry 16–19). Also, i-PrOH, MeOH, EtOH, and H O,
protic polar solvents, gave also pentafulvene in low yields (Table
, entry 20–23). The reaction was do better in aprotic polar
solvent. CH CN, THF, CH Cl , THF, toluene, dioxane, CHCl ,
4
, or cyclo-
(
2
For further investigation the efficiency of the catalyst,
different control experiments were performed and the obtained
information is shown in Table 3. Initially, a standard reaction
was carried out using Fe O /KCC-1/APTPOSS showed that any
2
3
2
2
3
EtOAc, and DMSO gave pentafulvene in good yields (Table 2,
entries 4–12). In this study, it was found that DMF is a more
efficient (Table 2, entry 7) over other solvents. A solvent that
stabilizes one of two competing transition states that control
the selectivity should enhance the selectivity of the product
obtained via the stabilized transition state. We also investigated
3
4
amount of the desired product was not formed aer 60 min of
reaction time (Table 3, entries 1). Also, when Fe /KCC-1/
APTPOSS/salen was used as the catalyst, a reaction was not
observed (Table 3, entries 2). The salen could not give the
satisfactory catalytic activity under mild reactions. Based on
3 4
O
a
Table 3 Influence of different catalysts for synthesis of pentafulvene
b
Entry
Catalyst
KCC-1
Yield (%)
1
2
3
4
5
6
7
—
—
92
53
74
80
83
Fe
Fe
3
O
O
4
/KCC-1/APTPOSS
/KCC-1/APTPOSS/salen/Pd(II)
3
4
2
Nano-SiO /salen/Pd(II)
MCM-41/salen/Pd(II)
SBA-15/salen/Pd(II)
Salen/Pd(II)
a
Reaction conditions: 2-acetyl-benzaldehyde (10 mmol), cyclopentadiene
b
(70 mmol), and catalyst (6 mg), at room temperature for 3 h. Isolated
yield.
Fig. 8 Effect of time on yield of pentafulvene.
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Table 4 Reaction of various 2-acetyl-benzaldehydes with cyclo-
pentadiene in the presence of Fe
MNPs
O
3 4
/KCC-1/APTPOSS/salen/Pd(II)
a
b
Entry
1
2-Acetyl-benzaldehyde
Product
Yield (%)
92
2
3
94
89
Fig. 10 Time-dependent correlation of the palladium leaching in
model reaction.
investigations because of its high reactivity, high selectivity and
easy separation. Also, the activity and selectivity of nano-catalyst
can be manipulated by tailoring chemical and physical prop-
erties like size, shape, composition and morphology. To assess
the exact impact of the presence of KCC-1 in the catalyst, the
4
5
87
90
Fe
1/salen/Pd(II), SBA-15/salen/Pd(II), and nano-SiO
When nano-SiO /salen/Pd(II), MCM-41/salen/Pd(II) or SBA-15/
3
O
4
/KCC-1/APTPOSS/salen/Pd(II) MNPs compared with MCM-
4
2
/salen/Pd(II).
2
salen/Pd(II) was used as the catalyst, the yield of the desired
product was average to good, but the yield for Fe O /KCC-1/
3
4
APTPOSS/salen/Pd(II) MNPs was excellent. Non-negligible
activity of the silica was attributed to its shape, composition
and morphology. Besides, the large space between bers can
signicantly increase the accessibility of the active sites of
the KCC-1. That is why, the KCC-1 was more effective than nano-
6
91
2
SiO , MCM-41, and SBA-15 (Table 3, entries 3–6). As a result,
KCC-1 NPs were used in the subsequent investigations because
of its high reactivity, high selectivity and easy separation
(
Table 3).
a
Reaction
conditions:
2-acetyl-benzaldehyde
(10
mmol),
To examine the scope of the catalytic properties of the
cyclopentadiene (70 mmol), and catalyst (6 mg), at room temperature
for 3 h. Isolated yields (%).
b
catalyst for synthesis of pentafulvene, various types of 2-acetyl-
benzaldehydes was reacted with cyclopentadiene in the pres-
3 4
ence of a catalytic amount of Fe O /KCC-1/APTPOSS/salen/Pd(II)
these disappointing results, we continued the studies to MNPs. Furthermore, electron rich and electron poor 2-acetyl-
improve the yield of the product by added the Pd(II). Notably, benzaldehydes react smoothly with cyclopentadiene in similar
there was difference in the reaction yields when reaction was reaction conditions. The electron rich allylarene show good
carried out using Fe
3 4
O /KCC-1/APTPOSS/salen/Pd(II) NPs and
salen/Pd(II) catalyst (Table 3, entries 3 and 7). These results
+
ꢀ
showed catalytic properties of N Cl in this structure. These
+
ꢀ
results indicate that both of Pd(II) and ionic structure (N Cl ) in
this catalyst will maximize the catalyst performance. Also, salen/
Pd(II) is not recoverable and reusable for the next runs. These
observations show that the reaction cycle is mainly catalyzed by
3 4
Pd(II) species complexed on the Fe O /KCC-1/APTPOSS/salen
nanostructure. The nano-sized particles increase the exposed
surface area of the active site of the catalyst, thereby enhancing
the contact between reactants and catalyst dramatically and
mimicking the homogeneous catalysts. As a result, Fe
3 4
O /KCC-
1
/APTPOSS/salen/Pd(II) MNPs was used in the subsequent
Fig. 11 The reusability of catalysts for synthesis of pentafulvene.
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Table 5 The loading amount of Pd(II) in Fe
O
3 4
/KCC-1/APTPOSS/
salen/Pd(II) MNPs
Entry
Catalyst
wt%
1.7
1
2
Fe
Fe
3
3
O
O
4
/KCC-1/APTPOSS/salen/Pd(II)
/KCC-1/APTPOSS/salen/Pd(II) aer ten reuses
4
1.6
completion of reaction, the catalyst was separated by ltration,
washed with methanol and dried at the pump. The recovered
catalyst was reused for ten consecutive cycles without any
signicant loss in catalytic activity (Fig. 11). This lack of
reduction in catalyst performance can be attributed to the
simple and stability of the catalyst structure. Comparison of
FT-IR spectra of used catalyst with those of the fresh catalyst
showed that the structure of salen remained intact aer ten
recoveries (Fig. 12). Also, the loading amount of salen in the
3 4
Fig. 12 FTIR spectra of Fe O /KCC-1/APTPOSS/salen/Pd(II) MNPs
after ten reuses.
reactivity (90–94% yield) for the formation of the corresponding
products in the C–C and C–H coupling reaction under similar
reaction conditions. The relative reactivity of 2-acetyl-
benzaldehydes towards the Pd(II) centre decreases in the
order: MeO > Me (Table 4, entry 3 and 4). As shown in Table 4,
C–C and C–H coupling reaction of cyclopentadiene with uoro-
3 4 3 4
fresh Fe O /KCC-1/APTPOSS/salen/Pd(II) and Fe O /KCC-1/
APTPOSS/salen/Pd(II) aer ten reuses as determined by TGA.
The amount of salen in Fe O /KCC-1/APTPOSS/salen/Pd(II)
3
4
3 4
aer ten reuses was almost equal to the fresh Fe O /KCC-1/
APTPOSS/salen/Pd(II) (Fig. 13). Also, the contents of Pd(II) in
catalyst before and aer reaction were 1.7% and 1.6%
respectively, determined by ICP-MS. These indicate that most
of Pd(II) species leaching into solution are recaptured onto the
2-acetyl-benzaldehyde proceeds smoothly under mild reaction
conditions giving the reaction condition in excellent yields
(Table 4, entries 2).
For further investigation the possibility of the heterogeneous

bers of KCC-1 aer completion of the reaction (Table 5).
nature of Fe
3 4
O /KCC-1/APTPOSS/salen/Pd(II) MNPs, a kinetic
study was performed. For this purpose, copper leaching was
study for synthesis of pentafulvene under the optimized reac- Conclusions
tion condition. To determine the Pd(II) concentration in solu-
tion, ve samples of the reaction mixture were taken during the
3 4
In the present study Fe O /KCC-1/APTPOSS/salen/Pd(II) MNPs
was synthesized and characterized as an environmentally-
friendly nanocatalyst for the synthesis of pentafulvenes with
various electronically diverse substrates. The experimental
results displayed the core–shell structure of the synthesized
catalyst with a mean size range of 250–300 nm. In addition, the
catalyst was easily recoverable and reusable. Subsequently, high
yields in short reaction times were achieved without the need
for an expensive catalyst as well as excellent reusability for at
least ten times in the corresponding reaction without a reduc-
tion in catalytic activity.
reaction. The samples were analyzed by ICP-MS as well as the
yield of the reaction was monitored by GC. The results were
described in Fig. 10. No obvious leaching was observed,
according to the ICP-MS data. According to the obtained results,
the conclusion could be derived that the heterogenous palla-
dium species aren't the catalyst promoter in this reaction.
It is important to note that the heterogeneous property of
3 4
Fe O /KCC-1/APTPOSS/salen/Pd(II) MNPs facilitates its effi-
cient recovery from the reaction mixture during work-up
procedure. The activity of the recycled catalyst was also
examined under the optimized conditions. Aer the
Conflicts of interest
There are no conicts to declare.
Acknowledgements
This research was funded by a grant (No. 96/1650) from the
Institute for Science and High Technology and Environmental
Sciences, Graduate University of Advanced Technology,
Kerman, Iran.
Notes and references
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Fig. 13 TGA image of Fe O /KCC-1/APTPOSS/salen/Pd(II) MNPs after
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8768 | RSC Adv., 2018, 8, 8761–8769
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Paper
RSC Advances
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