Magnetically recoverable nanostructured Pd complex of dendrimeric type ligand on the MCM-41: Preparation, characterization and catalytic activity in the Heck reaction

Article abstract of DOI:10.1515/mgmc-2020-0023

A palladium complex of a dendrimer type ligand of aminoethylacrylamide immobilized onto the mesoporous channels of MCM-41 with magnetic core was prepared and characterized using various techniques such as XRD, TEM, BET, FT-IR, TGA, and VSM. The prepared nanostructured material was found as a magnetically recoverable catalyst for Heck reaction of aryl halides and vinylic C-H. The catalyst is easily recoverable with an external magnet and is reusable with different leaching amounts depending to loading of Pd. A hot filtration test was also performed and gave evidence that Palladium in heterogeneous samples can dissolve and then redeposit on the surface of the support material.

Full text of DOI:10.1515/mgmc-2020-0023

Main Group Met. Chem. 2020; 43: 184–199
Research Article
Open Access
Mohammad Abdollahi-Alibeik*, Najmeh Gharibpour and Zahra Ramazani
Magnetically recoverable nanostructured Pd
complex of dendrimeric type ligand on the
MCM-41: Preparation, characterization and
catalytic activity in the Heck reaction
complexes, while, these types of catalysts suffer from
https://doi.org/10.1515/mgmc-2020-0023
Received December 30, 2019; accepted September 12, 2020.
several disadvantageous associated with the separation
of the expensive palladium, reusability, instability at high
temperature and toxicity of phosphine ligands (Liu et al.,
2015). To overcome difficulties caused by homogeneous
catalysts, in recent decades, heterogeneous catalysts
have been developed. Among them, many heterogeneous
catalysts containing Palladium have been designed
and used in organic transformations (Tarahomi et al.,
2019; Veisi et al., 2015a). Recently, many heterogeneous
catalysts containing palladium which, Pd nanoparticles
or complexes are involved as active catalyst sites have
been used as catalyst in Heck reaction including polymer
supported Pd complex (Schwarz et al., 2000), modified
silica supported Pd complex (Clark et al., 2000), Pd
anchored to layered double hydroxide (Choudary et al.,
2002), Pd(II) salen complex covalently anchored to multi-
walled carbon nanotubes (Movassagh et al., 2015), Pd(0)-
complex supported on boehmite nanoparticles (Ghorbani-
Choghamarani et al., 2016), Pd(0)-S-methylisothiourea
grafted onto mesoporous MCM-41 (Noori et al., 2016),
Abstract: A palladium complex of a dendrimer type
ligand of aminoethylacrylamide immobilized onto the
mesoporous channels of MCM-41 with magnetic core was
prepared and characterized using various techniques such
as XRD, TEM, BET, FT-IR, TGA, and VSM. The prepared
nanostructured material was found as a magnetically
recoverable catalyst for Heck reaction of aryl halides and
vinylic C–H. The catalyst is easily recoverable with an
external magnet and is reusable with different leaching
amounts depending to loading of Pd. A hot filtration test
was also performed and gave evidence that Palladium in
heterogeneous samples can dissolve and then redeposit
on the surface of the support material.
Keywords: dendrimer ligand; palladium complex;
MCM-41; Fe3O4; Heck reaction; reusable catalyst
1 Introduction
ferromagnetic
nanoparticle-supported
palladium
complex (Bahrami et al., 2017), Pd salen complex@cpgo
(Ghabdian et al., 2018), Fe2O3@SiO2–(CH2)3–Pdtc–Pd
(Tashrifi et al., 2019) Pd nanoparticles inside the pores
of Zif-8 (Azad et al., 2019), Pd–ninhydrin immobilized on
magnetic nanoparticles (Hajjami and Shirvandi, 2020),
Bnps@SiO2(CH2)3NH-CC-Amp-Pd (0) (Khodamorady and
Bahrami, 2020), Palladium anchored on guanidine-
terminated magnetic dendrimer (Niknam et al., 2020),
Palladium complex supported on MCM-41 (Nikoorazm
et al., 2020). Among them, silica support is highly regarded
because of some advantages such as availability, excellent
stability and ability of robust anchoring of organic moiety
for providing catalyst site.
Palladium catalyzed Heck-type vinylation of aryl
halides is one of the most important and versatile tool
for carbon-carbon coupling reaction in the field of
synthetic organic chemistry including natural products,
pharmaceuticals, liquid crystals and heteroarenes
(Gruber-Woelfler et al., 2012). Generally, Heck reaction
is catalyzed by homogeneous palladium phosphine
* Corresponding author: Mohammad Abdollahi-Alibeik, Department
of Chemistry, Yazd University, Yazd 89158-13149, Iran;
e-mail: abdollahi@yazd.ac.ir, moabdollahi@gmail.com;
Tel: +98-35-31232659; Fax: +98-35-38210644
Najmeh Gharibpour and Zahra Ramazani, Department of Chemistry,
Yazd University, Yazd 89158-13149, Iran
Mesoporous silica, is a very widely used support,
due to bearing a very high surface area and uniform array
Open Access. © 2020 Abdollahi-Alibeik et al., published by De Gruyter.
Attribution alone 4.0 License.
This work is licensed under the Creative Commons

ꢀ
M. Abdollahi-Alibeik et al.: Magnetically recoverable nanostructured Pd complex of dendrimeric type ligand
ꢀ185
of hexagonal channels (Abdollahi-Alibeik and Heidari- nanoparticles on the ternary hybrid system of graphene
Torkabad, 2012; Abdollahi-Alibeik and Rezaeipoor- oxide, Fe3O4 nanoparticles, and pamam dendrimer
Anari, 2016; Hashemi-Uderji et al., 2018b). Moreover, (Tarahomi et al., 2019), Ce(IV) immobilized on halloysite
silanol groups on the surface of MCM-41 are useful for nanotube–functionalized dendrimer (Ataee-Kachouei
immobilization of organic modifiers (Abdollahi-Alibeik et al., 2020).
and Pouriayevali, 2011). Linkage of modifier with the
Although, these heterogeneous catalysts are
silanol groups onto the inner surface of hexagonal easily recoverable by simple filtration, however, some
channels can provide active catalytic sites and therefore nanoparticles may remain in the reaction media. To
hexagonal channels of MCM-41 can act as nanoreactor. overcome this problem many magnetically recoverable
Recently, a wide variety of transition metal complexes have catalysts have been improved (Abdollahi-Alibeik et al.,
been anchored on the surface of MCM-41 and have been 2015; Kazemi and Mohammadi, 2020). Due to coupling
applied as catalysts in various organic transformations with organic ligands such as dendrimeric type support and
(Chang et al., 2013; Gao et al., 2015).
inorganic compounds such as silica, Fe3O4 nanoparticles
Dendrimers are particularly well-suited for hosting has been used as magnetic core in the preparation
metal nanoparticles because the dendrimer templates of magnetic separable catalysts such as Palladium
are of fairly uniform composition and structure, and immobilized on amidoxime-functionalized magnetic
therefore they yield well-defined nanoparticle replicas Fe3O4 nanoparticles (Veisi et al., 2015b), multifunctional
(Crooks et al., 2001). Immobilizing of metal complex of magnetic core-shell dendritic mesoporous silica
denderimeric ligands on the solid supports is of practical nano spheres (Sun et al., 2016), magnetic iron oxide/
importance due to the ability of loading a large amounts phenylsulfonic acid (Elhamifar et al., 2018), magnetic
of metal ions on the surface of the support, as well as their mesoporous MCM-41 supported boric acid (Ramazani et
recoverability and reusability (Isfahani et al., 2013). Many al., 2019), Fe3O4-AMPD-Pd (Tamoradi et al., 2018), Fe3O4@
dendrimer functionalized solid support have been used FSM-16-SO3H (Hashemi-Uderji et al., 2018a) and pyridine-
as heterogeneous catalysts in organic reactions such as 2-carboimine copper(I) complex immobilized on Fe3O4@
SO3H-dendrimer functionalized magnetic nanoparticles MCM-41 (Moaddeli and Abdollahi-Alibeik, 2018).
(Maleki et al., 2019), HPA-dendrimer functionalized
However,duetoimportanceofrecoveryandreusability
magnetic nanoparticles (Jamshidi et al., 2018), magnetic of solid catalysts, improvement of new magnetically
multi-walled carbon nanotubes functionalized with recoverable catalytic system is also desirable.
polyamidoamine
(PAMAM)
dendrimers
(Adibian
In this research, our strategy is developing a
et al., 2020), dendritic chiral auxiliaries on silica (Chung heterogeneous catalyst by immobilizing a denderimeric
and Rhee, 2002; Gharibpour et al., 2017; Isfahani et al., type ligand on the surface of MCM-41 (MMNP, Scheme 1)
2013; Tarahomi et al., 2019). MCM-41-supported copper- with various loading amounts of palladium and
complexed dendrimer (Gharibpour et al., 2017), Pd application of metal complex in Heck reaction in order
Scheme 1:ꢀSteps of preparing the MMNP catalyst.

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186ꢀ
M. Abdollahi-Alibeik et al.: Magnetically recoverable nanostructured Pd complex of dendrimeric type ligand
to study of the catalytic activity and also leaching of Pd to the MNPs@MCM-41 spectrum (Figure 1a) confirms
(Scheme 2).
successful modification of MNPs@MCM-41 surface by
APTMS. The reaction between amino group of 3-amino-
propyltrimethoxysilane (APTMS) and terminal alkene
of ethyl acrylate has formed on the MNPs@MCM-41-NH2.
Formation of this bond was confirmed by FT-IR spectra of
MNPs@MCM-41-NH2 with a characteristic band at 1736 cm–1
(Figure 1c). After the formation of the amide group,
carbonyl peak of this group is appeared at 1653 cm–1
2 Result and discussion
2.1 The catalyst characterization
MCM-41withmagneticcore(MNPs)waspreparedaccording in MNPs@MCM-41-NE2-EDA spectrum (Figure 1d). This
tothepresentedmethodinScheme1,andfunctionalization carbonyl peak is shifted to 1657 cm–1 in the spectrum of
with dendrimer type ligand and then a complexation was palladium complex (Figure 1e). This result confirms
carried out according to presented method in Scheme 1.
To confirm successful functionalization of the synthesized
MNPs@MCM-41, the MMNP catalyst was characterized
using FT-IR spectroscopy in the range of 400-4000 cm−1
and the corresponding spectra are shown in Figure 1.
MNPs@MCM-41 shows characteristic peaks at 806, 1082
and 1240 cm–1 linked to stretching bands of Si–O–Si and
the peak at 461 cm–1 linked to bending Si–O–Si (Figure 1a).
In this spectrum, the characteristic peaks around 585 and
630 cm−1 can be assigned to Fe−O bands. The presence
of stretching and bending peaks of aliphatic C–H and
N–H bonds (the peaks at 2940, 1495, and 1560 cm–1) in the
MNPs@MCM-41-NH2 (Figure 1b) spectrum in comparison
Figure 1:ꢀFT-IR spectra of: (a) MNPs@MCM-41, (b) MNPs@MCM-
41-NH2, (c) MNPs@MCM-41-NE2, (d) MNPs@MCM-41-NE2-EDA, (e)
MMNP.
Scheme 2:ꢀHeck reaction in the presence of the MNNP catalyst.
Scheme 3:ꢀCatalyst preparation.

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M. Abdollahi-Alibeik et al.: Magnetically recoverable nanostructured Pd complex of dendrimeric type ligand
ꢀ187
formation of complex between Pd and amide ligand on of MCM-41 revealed three characteristic Bragg reflections
the MCM-41. peaksatlowanglepattern(2θ=2°-6°).Thepresenceofthese
The FT-IR spectra of reused catalyst after the first run to three Bragg reflexes can be indexed highly ordered pore
the third run were studied to investigate effect of possible system with a high porosity in a hexagonal mesoporous
leaching of Pd from ligand and also possible deformation structure of MCM-41, corresponding to d100, d110, and d200
of ligand (Figure 2). Results show that all of main peaks planes at 2θ = 2.4°, 4.0°, and 4.6°, respectively (Figure 3a).
of the ligand remained unchanged. The carbonyl peak On the other hand, an overall decreased intensity, some
in 1657 cm–1 is unchanged in all three spectra. This result broadened reflections of d100 and a decrease in 2θ based
confirms that there is not significant leaching of Pd from on the Bragg’s equation (an increase in the d-spacing)
the ligand.
are observed at low angle XRD pattern of MNPs@MCM-41
Low angle powder X-ray diffraction (XRD) patterns (Figure 3b) compared to pure MCM-41, which are due to
of all samples: pure MCM-41 (a), MNPs@MCM-41 (b) and the decrease in ordered structure degree of hexagonal
MMNP (c) were displayed in Figure 3. The XRD analysis mesostructures after incorporation of magnetic iron oxide
into the MCM-41 framework. At low angle XRD pattern
of MMNP (Figure 3c) compared to Fe3O4@MCM-41, the
organometallic functionalization of palladium complex
(a)
dendrimer reduces the intensity of d100, increases the
d-spacing and shifts it to the higher angle (2θ = 1.84°),
(b)
corresponded to blockage of the mesoporous channels
by palladium complex dendrimer. These changes often
observed in mesoporous silica materials.
(c)
High-angle powder X-ray diffraction (XRD) patterns of
all samples: MNPs (a), pure MCM-41 (b), MNPs@MCM-41
(c) and MMNP (d) were illustrated in Figure 4. There are
reflection peaks at 2θ = 30°, 36°, 43°, 57°, 63°, and 74° in
the XRD patterns of MMNP (Figure 4d), which is observed
at pure Fe3O4 (Figure 4a) and MNPs@MCM-41 (Figure 4c),
indexed to the pure stoichiometric Fe3O4 structure. The
low molar ratio of MNPs in the support (Si/Fe = 119/1)
caused low intensity MNPs peaks at XRD patterns. The
broad peak at the range of 2θ = 14°-31° is indicated to the
amorphous silica network.
4000
3500
3000
2500
Wavenumber(cm–1
2000
1500
1000
500
)
Figure 2:ꢀFT-IR spectra of the recycled catalyst after: (a) first run, (b)
second run, and (c) third run.
The transmission electron microscopy (TEM)
image of MMNP was shown in Figure 5. TEM image of
MMNP shows that the ordered hexagonal mesoporous
structure of MCM-41 channels is remained unchanged
Figure 3:ꢀLow angle XRD pattern of: (a) MCM-41, (b) MNPs@
MCM-41, and (c) MMNP.
Figure 4:ꢀHigh angle XRD pattern of: (a) MNPs, (b) MCM-41, (c)
MNPs@MCM-41, and (d) MMNP.

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188ꢀ
M. Abdollahi-Alibeik et al.: Magnetically recoverable nanostructured Pd complex of dendrimeric type ligand
after organometallic functionalization on the MMNP detected, zero coercivity and remanence on the loop of
(Figures 5a,b). The MNPs anchored onto the MCM-41 can magnetization, suggesting that both of MNPs@MCM-41
be detected in Fig 5c.
and MMNP exhibited a superparamagnetic feature.
The superparamagnetic behavior of FMNC was The magnetic saturation values of MNPs@MCM-41 and
confirmed by magnetization curves of MNPs@MCM-41 MMNP were 4.05 emu/g and 2.50 emu/g (Figures 6a,b),
and MMNP (Figure 6). The magnetic hysteresis loops respectively. There was some decrease in saturation
were accomplished by an applied magnetic field at room magnetization value after surface modification of MNPs@
temperature (300 K). There was no apparent hysteresis MCM-41 (MMNP, Figure 6b), in comparison with MNPs@
MCM-41 (Figure 6a), which confirms modified organic
matter on the MNPs@MCM-41 surface and relative low
mass ratio of MNPs in the MMNP sample. The isolation
of the MMNP was achieved using an external permanent
magnet beside the reactor wall, making the resumption
of the MMNP very straightforward, which is necessary for
magnetic separation (Figure 7).
The mesoporous structure of MNPs@MCM-41 was
confirmed by nitrogen adsorption–desorption isotherms.
In this isotherms a sharp inflection at p/p° = 0.2-0.4 is
related to the nitrogen capillary condensation in the
uniform mesopores, which confirms the mesoporous
structure of synthesized MNPs@MCM-41.
A sharper
hysteresis was observed at higher p/p° (p/p° > 0.8) related
to the nitrogen condensation within the formed voids by
nanoparticles (Figure 8a). Figure 8b shows the nitrogen
adsorption–desorption isotherms of the MMNP catalyst
that a mesoporous inflection was not observed at the
medium p/p° partial pressure region (p/p° = 0.2-0.4). This
means that organic maters occupied the inner voids of
the MMNP@MCM-41. According to the obtained results
from N2 sorption, the surface area (SBET), pore volume
(Vpore), and pore diameter (Dpore) of MMNP@MCM-41 are
783.24 m2/g, 1.00 cm³/g, and 7.4 nm, respectively. There
is some decrease amount of SBET and Vp in Table 2 which
identified cavities filling by organic matter.
Figure 5:ꢀTEM image of MMNP: (a) mesoporous channels of MCM-41,
(b) MNPs anchored onto MCM-41 and (c) A 28-nm magnetic core.
4
2
0
The thermal stability of the MMNP was studied by
thermogravimetric analysis (TGA). TGA measurement
was conducted by the heating of 47 mg MMNP sample in
(b)
(a)
-2
-4
-8000
-4000
0
4000
8000
Applied field (Oe)
Figure 6:ꢀMagnetization curves of: (a) MNPs@MCM-41 and (b)
MMNP.
Figure 7:ꢀIsolation of MMNP by employing an external field.

ꢀ
M. Abdollahi-Alibeik et al.: Magnetically recoverable nanostructured Pd complex of dendrimeric type ligand
ꢀ189
the range of 25-800°C (Figure 9). TGA curve presents two optimum conditions using various Pd loading, catalyst
exothermic peaks in the range of 25-280°C and 280-700°C. amount, solvents, bases, temperatures and the reacting
The exothermic peak at 25-280°C contains 7.4% weight loss components ratios.
which corresponded to the removal of physically adsorbed
The effect of the palladium loading on the catalytic
moisture and other solvents. The second exothermic peak activity of MMNP was studied by using the catalyst with
at 280-700°C contains 17% weight loss can be assigned to different loading amounts of Pd with mass ratios of
the decomposition of organometallic dendrimer on the ligand:PdCl2 = 100:5, 100:10, 100:15 and 100:20 in the Heck
surface of MMNP@MCM-41. According to the TGA curve, modelreactionforthreeruns(Table3). AsshowninTable3,
organometallic dendrimer on the MMNP@MCM-41 surface MMNP with loading mass ratio of ligand:PdCl2 = 100:10
can be thermally stable up to 280°C.
had the best catalytic behavior rather than other loading
mass ratios in terms of reaction time and palladium loss
percent after third runs. In the loading mass ratio of
ligand:PdCl2 = 100:5, the reaction was not complete at all,
so the palladium amount in this loading was not enough
2.2 Catalytic activity
The catalytic performance of MMNP catalyst was for this reaction (Table 3, entry 1). In 100:10 loading,
investigated in the reaction of p-bromonitrobenzene and the reaction time is 1.5 times in the second cycle, also
ethyl acrylate as a model reaction. The results summarized palladium loss percent after second cycle is about 9.4%,
in Tables 3 and 4. The reaction was carried out under the which is negligible compared to the fresh catalyst (Table 3,
entry 2). While for the 100:15 and 100:20 loading, the
reaction times are 8.4 and 14 times respectively in the
second cycle, and palladium loss percent after second
cycle is about 9.1 and 7.6%, respectively, compared to
the fresh catalyst (Table 3, entries 3 and 4). The reaction
times at 100:15 and 100:20 fresh catalysts were better
than 100:10, but the reaction times after second cycle
for 100:15 and 100:20 were worse than 100:10, while the
palladium loss for 100:15 and 100:20 after second cycle
were less than 100:10. These results suggest that a part
of palladium chloride used in the construction of 100:15
and 100:20, formed complexes at MMNP catalyst and
Table 1:ꢁd-spacing calculation of MCM-41, MNPs@MCM-41 and
MMNP.
Entry
Sample
MCM-41
2θ (°)
2.4
d-spacing (nm)*
Figure 8:ꢀN2 adsorption–desorption isotherms of: (a) MNPs@
MCM-41 and (b) MMNP.
1
2
3
3.8
5.1
4.8
MNPs@MCM-41
MMNP
1.72
1.84
* d100 = nλ/2sin θ, (n = 1, Fix λ (Cu kα) = 1.54 Å).
Table 2:ꢁTextural properties of MNPs@MCM-41 and MMNP samples.
b
c
Entry Sample
dp BJHa
(nm)
1.97
2.06
SBET
Vp
(m2/g)
783.2
175.7
(cm³/g)
1.00
1
2
MNPs@MCM-41
MMNP
0.49
a Pore diameter according to the maximum of the BJH desorption
pore size distribution.
b BET Surface Area.
Figure 9:ꢀThermogravimetric analysis of: (a) MMNP and (b)
magnification of MMNP thermogravimetric analysis.
c Single point adsorption total pore volume.

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190ꢀ
M. Abdollahi-Alibeik et al.: Magnetically recoverable nanostructured Pd complex of dendrimeric type ligand
Table 3:ꢁScreening of various catalyst loading in the Heck reaction.a
Entry
Ligand:PdCl2 mass ratio (mg) Reaction cycle
Pd mol% before reaction Pd mol% after reaction Time (min)
Yield (%)b
24
Fresh
0.1
0.06
0.03
0.02
0.82
0.79
0.77
0.84
0.81
0.80
0.90
0.88
0.85
Over night
1
100:5
100:10
100:15
100:20
1
0.06
0.03
0.85
0.82
0.79
0.88
0.84
0.81
0.92
0.90
0.88
Over night
24
2
Over night
60
20
Fresh
95
2
3
4
1
75
95
2
Fresh
1
90
91
25
95
90
97
2
210
10
91
Fresh
1
95
100
140
94
2
90
a The reaction was carried out with aryl halide (1 mmol), olefine (2.5 mmol), TEA (3 mmol), DMF (1 mL), and MMNP (20 mg) as catalyst at
130°C under an air atmosphere.
b Isolated yield.
the excess palladium chloride have been settled on the (TEA) gave a better result than inorganic bases (Na3PO4,
catalyst surface. So the Heck reaction in the presence of K3PO4 and K2CO3), whereas, there is no reaction progress
100:15 and 100:20 was done with palladium-complex and in the absence of base. Interesting results were obtained
free palladium particles at fresh catalyst and after the first by changing in the amount of base. The use of lower or
run, free palladium particles deactivated and still existed more than 3 mL TEA, caused weakening in the MMNP
on the catalyst surface so it seems less palladium loss catalytic activity (Table 4, entries 8 and 14-18). When the
in the loading mass ratios of ligand:PdCl2 = 100:15 and Heck reaction was accomplished at different temperatures
100:20 rather than 100:10 (Table 3, entries 2-4).
in the presence of MMNP, it was found that temperature
After selecting the best loading of palladium chloride at 130°C is the best. The Heck reaction in the absence of
on dendrimer ligand (ligand:PdCl2 = 100:10), the reaction the catalyst was not carried out at all. Notwithstanding,
was carried out under the optimum conditions using the amounts of 10 and 20 mg of MMNP showed good
various catalyst amount, solvents, bases, temperatures, results for the Heck reaction and 40 mg of the catalyst
and the reacting components ratios using model reaction had negative effect on the Heck reaction. At first it seemed
(p-bromonitrobenzene with ethyl acrylate as the model that 2 mg is the optimal amount of the catalyst, but was
reaction). ThesolventshadsignificanteffectsontheMMNP not enough for other derivatives, so finally; 10 mg MMNP
catalytic activity. Among the different polar and nonpolar (0.42 mol% palladium) was selected as the optimal
solvents (H2O, CH3CN, CH3CN:H2O, DMF, DMF:H2O, and amount of the catalyst (Table 4, entries 8 and 22-25).
toluene) or solvent-free condition; the polar solvent such The ethylacrylate usage in amount of 2, 2.5 and 3 mmol
as dimethylformamide (DMF) gave higher yield than (as an olefin) was studied in Heck reaction and as shown
nonpolar solvent such as toluene (Table 4, entries 2-9) and in Table 4 (entries 24, 30, and 31) the amount of 1:2.5 mmol
solvent-freeconditionwasnotappropriate(Table4,entry1). of aryl halide:olefin was the best reacting component
Amount of DMF also affected on the product yield. As ratio. More interestingly, reaction atmosphere changing
shown in Table 4 (entries 8 and 26-29), with decreasing from inert to air had better effect on MMNP catalytic
DMF amount from 4 mL to 0.5 mL, it was observed that activity (Table 4, entry 24 and 32).
the suitable amount of DMF is 1 mL. The bases (such as
To investigate the application of MMNP as catalyst
TEA, Na3PO4, K3PO4, and K2CO3) used in the Heck reaction in Heck reaction, a variety of olefins were coupled with
had great influences on the MMNP catalytic activity. different aryl halides in the presence of 10 mg MMNP
As shown in Table 4 (entries 8 and 10-13) the organic base (0.42 mol% palladium) using TEA as a base in DMF.

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M. Abdollahi-Alibeik et al.: Magnetically recoverable nanostructured Pd complex of dendrimeric type ligand
ꢀ191
Table 4:ꢁScreening of various parameters for the Heck reaction.
Entry
1
MMNP (mg:mol% Pd)
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
20:0.85
–
Solvent (mL)
–
H2O (1)b
Ethylacrylate (mmol)
Base (mmol)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
–
Temp (°C)
70
Time (h)
6
Yield (%)
0a
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.0
3.0
2.5
2
Reflux
Reflux
Reflux
90
24
4
5a
3
Toluene (1)
CH3CN (1)
CH3CN:H2O (2:1)
CH3CN:H2O (1:1)
CH3CN:H2O (1:2)
DMF (1)
30a
30a
45a
50a
50a
95b
20a
0a
97c
77c
67c
97c
81c
95c
93c
10a
93c
87c
90c
0a
97c
95c
90c
90c
93c
95c
87c
93c
95c
40d
4
24
7:30
6:30
6:30
1
5
6
90
7
90
8
130
90
9
DMF:H2O (1:1)
DMF (1)
24
24
24
24
24
2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
130
130
130
130
130
130
130
130
130
110
120
140
130
130
130
130
130
130
130
130
130
130
130
DMF (1)
Na3PO4 (3.0)
K3PO3 (3.0)
K2CO3 (3.0)
TEA (2.0)
TEA (2.5)
TEA (2.8)
TEA (3.5)
TEA (4.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
TEA (3.0)
DMF (1)
DMF (1)
DMF (1)
DMF (1)
1
DMF (1)
1:30
2
DMF (1)
DMF (1)
2
DMF (1)
24
3
DMF (1)
DMF (1)
1
DMF (1)
5
2:0.085
10:0.42
40:1.7
DMF (1)
3
DMF (1)
2:15
1
DMF (1)
10:0.42
10:0.42
10:0.42
10:0.42
10:0.42
10:0.42
10:0.42
DMF (4)
5
DMF (3)
3:30
2:30
1
DMF (1.5)
DMF (0.5)
DMF (1)
2:50
2:30
3
DMF (1)
DMF (1)
a Reaction progress with TLC (n-hexan:ethylacetate 80:20 as eluent) under air atmosphere.
b Reaction was carried out in the presence of 10 mol% SDS.
c Isolated yield, under air atmosphere .
d Reaction progress with TLC (n-hexan:ethylacetate 80:20 as eluent) under argon atmosphere.
These results are illustrated in Table 5. Aryl bromide with (Table 5, entries 6, 8 and 11). The order of activity for olefins
electron-donating groups has excellent yield compared is ethyl acrylate > acrylonitrile > styrene (Table 5, entries
with aryl bromide with electron-withdrawing groups and 1-7). The scope of the procedure was also investigated
their activity were NO2 > CHO > H > CH3 > OCH3 (Table 5, using aliphatic halides as starting material. Results show
entries 1, 4 and 8-10). Halobenzene activities were I > Br > Cl that alkyl halides react with olefins as well as aryl halides

ꢀ
192ꢀ
M. Abdollahi-Alibeik et al.: Magnetically recoverable nanostructured Pd complex of dendrimeric type ligand
Table 5:ꢁThe Heck reaction of various alkyl and aryl halides and olefins in the presence of MMNP as a catalyst.
Entry
1
Aryl halide (1)
Olefine (2)
Product (3)a
Time (h:min) Yield (%)b
2:15
95
98
91
90
91
2
3
4
5
6
24
2:15
1
3:15
0:30
98
Continued

ꢀ
M. Abdollahi-Alibeik et al.: Magnetically recoverable nanostructured Pd complex of dendrimeric type ligand
ꢀ193
Table 5:ꢁcontinued
Entry
Aryl halide (1)
Olefine (2)
Product (3)a
Time (h:min) Yield (%)b
7
1
98
8
9
12
90
24
60
65
10
11
36
15
No reac-
tion
12
13
14
15
3:30
4:45
4
90
95
90
6:30
90
Continued

ꢀ
194ꢀ
M. Abdollahi-Alibeik et al.: Magnetically recoverable nanostructured Pd complex of dendrimeric type ligand
Table 5:ꢁcontinued
Entry
16
Aryl halide (1)
Olefine (2)
Product (3)a
Time (h:min) Yield (%)b
93
7
a The reaction was carried out with aryl halide (1 mmol), olefine (2.5 mmol), TEA (3 mmol), DMF (1 mL) and MMNP (10 mg, 0.42 mol%
palladium) as catalyst at 130°C under an air atmosphere.
b Isolated yield.
and high yields of products have been achieved (Table 5, with the start of the reaction, the highest reaction rate
entries, 12-16). matches the highest palladium concentration in solution,
The reuse of the MMNP catalyst was investigated in and palladium is redeposited on the support again after
the Heck coupling reaction of p-bromonitrobenzene with the reaction is completed (Gnad et al., 2020; Heidenreich
ethyl acrylate as a model reaction. After completion of et al., 2002; Zhao et al., 2002). It has been confirmed that
the reaction (monitored by TLC; eluent: EtOAc:n-hexane, solid palladium catalysts act as reservoirs for active Pd
20:80) MMNP catalyst could be easily separated from species in solution and the dissolved Pd species tend to
reaction mixture using an external permanent magnet, readsorb onto the support after the reaction has been
washed with warm ethanol (3 × 3 mL) and dried at 100°C completed.
for 1 h, then reused in the model reaction at the same
In the present study, in order to investigate whether
reaction condition. The results of reusability study are the MMNP catalyzed Heck reaction takes place based on
demonstrated in Table 6. As shown in Table 6 (entries 1-3), the heterogeneous surface or due to Palladium leaching
it was found that there is a low increase in the reaction from MMNP, we accomplished hot filtration test to
time and low decrease in the product yield. These results differentiate between heterogeneous and homogeneous
suggest that the palladium leaching of MMNP catalyst activity based on the comparison of observed results
can be ignored. To confirm this issue, the Pd loading of before and after MMNP catalyst separation using an
the recovered catalyst after second cycle was determined external permanent magnet in the reaction temperature.
using atomic absorption spectroscopy and 0.38 mol% The reaction was interrupted at 30 min and then the
palladium was detected (Table 6, entry 3). Thus, 9.5% of filtrate was collected from the hot reaction mixture. The
Pd leaching (Table 6, the difference between entries 1 and reaction was then conducted for another 105 min using
3) is a reason for ignored deactivation of the catalyst after the filtrate in the absence of the solid catalyst. Results
the second cycle. It is noticeable that after each run, the show that after removal of the solid catalyst, the reaction
catalyst easily and completely was separated by external mixture retained its activity and after 135 min, the reaction
magnet and there were no problems due to the reduction was split at a conversion of 30%. This may be related to
of magnetic properties.
the presence of active dissolved Pd.
The general methods for the leaching study is hot
It may be established that the results of the hot
filtration test or split test. Especially in the case of the filtration test were in accordance with those of the
Heck reaction, how the reaction starts with a solid catalyst recycling experiments (Table 1). The atomic absorption
has received a great deal of attention. In principle, the spectroscopy data for palladium amount in MMNP after
two discussed possibilities were that either the reaction the general Heck reaction (Table 6, entry 1) shows that
is catalyzed by a heterogeneous surface mechanism or the palladium leached is about 2.4% that is negligible. As
that dissolved palladium, which is generated by metal shown in Table 1, compare of the Pd loading on the fresh
leaching (Bucsi et al., 2017).
catalyst and reused catalyst after run 1 and also run 2,
To improve the understanding of the dynamic leaching show that there is not considerable leaching. This result
process under Heck reaction conditions, Köhler et al. and also result of hot filtration confirms that Palladium
(2002) reported that a large amount of Pd was dissolved in heterogeneous samples can dissolve and then redeposit
into the solvent during the Heck coupling of chloroarenes on the surface of the support material.
and then the Pd species were redeposited on the surface
We recommend that the MMNP catalyst is superior
of the support material. After further investigation, it was in terms of palladium consumption amount compared
demonstrated that palladium is dissolved simultaneously to some other catalysts that had been used in the Heck

ꢀ
M. Abdollahi-Alibeik et al.: Magnetically recoverable nanostructured Pd complex of dendrimeric type ligand
ꢀ195
reaction. A comparative study of the MMNP catalytic for various loading of ligand:PdCl2 and results showed less
activity with other reported heterogeneous palladium leaching for 100:10 ratio and also mild decrease in activity
base in Heck reaction is reported in Table 7. The results for this sample. High products yields, simple workup and
show that our work in terms of reaction time, yield and the easy recovery of the catalyst are some advantages of this
palladium consumption amount is superior to the other catalyst.
catalysts. Furthermore, other advantages of our method
are lack of usage of an inert atmosphere and moderate
reaction temperature, with respect to the others. However, Experimental
it should be emphasized that the results reported in Table 7
were obtained under very different reaction conditions
Material and methods
and therefore the results could not be compared
correctly.
All chemicals were commercial and used as revived.
Progress of the reactions were determined by thin layer
chromatography and all yields refer to isolated products.
1
3 Conclusion
NMR spectra for H and 13C were recorded on a Bruker
1
DRX-400 AVANCE (400 MHz for H and 100 MHz for 13C)
Finally, we have introduced a new magnetically recyclable spectrometer in CDCl3. The melting point of solid products
catalyst with magnetite core and dendrimeric palladium were determined by Buchi melting point model B-540.
complex on the MCM-41 (Fe3O4@MCM-41-NE2-EDA-Pd Infrared spectra of all products and the catalyst were
(MMNP),Si:Fe3O4=40:1,loadingmassratioofligand:PdCl2= recorded on a Bruker FT-IR Equinox 55 spectrophotometer
100:10). The catalyst is efficient in the Heck reaction at in KBr disks. Thermogravimetric analysis (TGA) was
130°C in DMF as solvent. The catalyst leaching was studied performed using
a
thermal gravimetric analysis
Table 6:ꢁRecovery and reuse of MMNP for the Heck reaction.
Entry
Catalyst
Fresh
Pd mol% before reaction
Pd mol% after reaction
Time (h)
2:15
Yield (%)a
1
2
3
0.42
0.41
0.39
0.41
0.39
0.38
95
95
91
Cycle 1
Cycle 2
3:00
3:40
a Isolated yield.
Table 7:ꢁThe comparative study of MMNP catalytic activity with other catalyst in Heck reaction.
Entry Catalyst
Pd mol% Temp (°C) Solvent
Time (h)
2:15
3
Yield (%)a
Reference
This work
1
2
3
4
5
MMNP
0.42
1
130
100
130
140
120
DMF
95
84
Pd-DABCO-γ-Fe2O3
HMMS-NH2-Pd
MNP@NHC-Pd
Si-PNHC-Pd
Solvent-free
NMP
(Sobhani and Pakdin-Parizi, 2014)
(Wang et al., 2014)
4
8
>99
72
0.56
0.5
DMF
22
5
(Wilczewska and Misztalewska, 2014)
(Tamami et al., 2013)
NMP
90
a Isolated yield.

ꢀ
196ꢀ
M. Abdollahi-Alibeik et al.: Magnetically recoverable nanostructured Pd complex of dendrimeric type ligand
instrument (STA 504 thermo-gravimetric analyzer) in the (5 mL, 22.6 mmol) was added dropwise to this suspension
temperature range of 50-800°C (10°C/min). Transmittance and then allowed to cool to ambient temperature. The
electron microscopy (TEM) analysis was performed on a micellar template was generated by hydrolysis of the
Zeiss-EM10C – 80 KV was used to obtain TEM images. XRD precursor compound using aqueous ammonia to adjust
patterns were recorded by a Bruker D8 ADVANCE X-ray the pH of the suspension up to 10 under vigorous stirring.
diffractometer using nickel filtered Cu Ka radiation (λ = The gel was transferred to a Teflon lined stainless steel
1.5406 Å). The magnetic measurement of samples was autoclave and heated for 18 h at 120°C for hydrothermal
carried out in a vibrating sample magnetometer VSM-4 treatment. The gel was collected by centrifugation and
inh, Daghigh Meghnatis Kashan Co at room temperature. washed with deionized water (2 × 100 mL) and ethanol
Pd loading and leaching tests were carried out with an (2 × 100 mL). After filtration and washing, the MNP@
Atomic Absorption Spectroscopy (AAS) Analyticjena MCM-41 was dried in an oven at 120°C for 2 h and the
spectrometer model novAA 300. The pore analysis and template was removed by calcination at 450°C for 6 h.
BET surface area were performed on a micromeritics
model ASAP2020 by N2 physical adsorption–desorption
at 77.4 K. Samples were degassed at 120°C under flowing Preparation of palladium complex of dendrimer type
nitrogen for 2 h. The pore size distribution was calculated ligand on magnetic MCM-41 (MMNP)
by the Barret-Joyner-Halenda (BJH) method. The specific Post-synthesis organic modification of magnetic
surface area (SBET) was calculated from the adsorption mesoporousmaterialswascarriedoutbystirringamixtureof
data using the BET equation.
MNPs@MCM-41 (1 g) and 3-aminopropyltrimethoxysillane
(APTMS) (1.075 g, 6 mmol) in CHCl3 (10 mL) under reflux
condition and inert gas for about 4 h. The resulting product
(MNPs@MCM-41-NH2, Scheme 3-II) was filtered, washed
with CHCl3 (3 × 3 mL) and dried at 70°C. The solid (1 g) was
stirred with ethyl acrylate (400 mg, 4 mmol) in methanol
Preparation of palladium complex catalyst
Preparation of Fe3O4 (MNPs)
The Fe3O4 magnetic nanoparticles (MNPs) was readily (10 mL) at 50°C for 4 days and then was detached with an
prepared by co-precipitation of ferrous and ferric ions in external magnet, washed with methanol (3 × 3 mL) and
a basic solution. Generally, FeCl2‧4H2O (1.52 g, 8 mmol) dried at 60°C for 1 h (MNPs@MCM-41-NE2, Scheme 3-III).
and FeCl3‧6H2O (4.24 g, 16 mmol) were dissolved in For lengthening the dendrimer chain, MNP@MCM-41-NE2
deionized water (100 mL) under vigorous stirring using (1 g) was reacted with ethylenediamine (300 mg, 5 mmol)
a mechanical stirrer at 60°C for about 30 min. Then the and p-toluenesulfonic acid (246 mg, 1.4 mmol) in ethanol
pH was changed to basic by slow addition of ammonia (10 mL) at 60°C for 2 days. The resulting material was
solution (30 mL, 25%) and the mixture became black detached with an external magnet, washed with ethanol
immediately. The stirring was continued for about 30 min (3 × 3 mL) and dried at 60°C for 1 h (MNPs@MCM-41-
and the black precipitate (MNPs) was collected using a NE2-EDA, Scheme 3-IV). Finally the Pd-complex was
permanent magnet at the bottom of the flask and washed synthesized by addition of MNPs@MCM-41-NE2-EDA (1 g)
with deionized water (3 × 30 mL). The synthesized MNPs to a solution of palladium chloride (100 mg, 0.57 mmol)
was dried at 80°C in an oven for 3 h.
in ethanol:aceton:HCl (5 mL:5 mL:1 drop) and stirring of
the mixture at ambient temperature for about 2 days. The
resulting solid was detached with an external magnet,
washed with ethanol (3 × 3 mL) and dried at 60°C for 1 h
Hydrothermal preparation of MNP@MCM-41
Synthesis of magnetic MCM-41 was carried out via the (MMNP, Scheme 3-V).
hydrothermal method using Fe3O4 (MNPs) as a magnetic
nanoparticle agent, cetyltrimethylammonium bromide
(CTAB) as the template, tetraethylorthosilicate (TEOS) as General procedure for the Heck reaction
the silica source and ammonia as the pH control agent A 5 mL round bottom flask was charged with MMNP
with the gel composition of Fe3O4:H2O:CTAB:SiO2:NH4OH = (10 mg), an appropriate amount of DMF (1 mL), aryl halide
0.025:480:0.127:1:1.26. At first, MNPs (0.132 g, 0.568 (1.0 mmol), olefin (2.5 mmol) and TEA (303 mg, 3.0 mmol)
mmol) was dispersed in deionized water (200 mL) using and a magnetic stir bar. The mixture was stirred for an
ultrasound, followed by the slow addition of CTAB (1.04 g, appropriate time under reflux condition. The reaction
2.67mmol)totheobtainedsuspensionwithstirringandthe progress was monitored by TLC (n-hexane:acetone, 80:20
temperature was adjusted to 70°C. Tetraethyl orthosilicate as eluent). After the reaction completion, the mixture

ꢀ
M. Abdollahi-Alibeik et al.: Magnetically recoverable nanostructured Pd complex of dendrimeric type ligand
ꢀ197
Abdollahi-Alibeik M., Moaddeli A., Masoomi K., BF3 bonded
nano Fe3O4 (BF3/MNPs): An efficient magnetically recyclable
catalyst for the synthesis of 1,4-dihydropyrano[2,3-c]pyrazole
derivatives. RSC Adv., 2015, 5, 74932-74939.
Abdollahi-Alibeik M., Pouriayevali M., 12-Tungstophosphoric acid
supported on nano sized MCM-41 as an efficient and reusable
solid acid catalyst for the three-component imino Diels–Alder
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new magnetically recoverable nanostructured catalyst for the
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was cooled to ambient temperature and the catalyst was
detached from the reaction mixture with an external
magnet. The resultant remaining mixture was diluted
with H2O (9 mL) followed by extraction with chloroform
(3 × 3 mL). The organic layer was dried over Na2SO4 and
the solvent was evaporated under reduced pressure to
obtain crude product. The corresponding pure products
were obtained by preparative thin layer chromatography
on silica gel using n-hexane:ethylacetate (95:5) as eluent
or by recrystallization (ethanol:water).
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Physical and spectroscopic data for selected
compounds
Ethyl (E)-3-(4-nitrophenyl)acrylate: Yield: 95%, cream
solid, mp: 134-136°C (Lit: (Movassagh and Rezaei, 2015)
135-138°C). FT-IR (KBr); ῡ (cm–1): 979 (C–H trans-alkene
bend.), 1030 (C–O), 1341 (NO2 symmetric), 1517 (NO2
asymmetric), 1450 and 1597 (C=C aromatic), 1645 (C=C
alkene), 1713 (C=O Ester), 2851, 2936, 2984 (C–H aliphatic),
3079 (C-H alkene stretch.), 3108 (C–H aromatic stretch.).
1H NMR (500 MHz, CDCl3): δ (ppm) = 1.39 (t, 3H, J = 7.0
Hz, CH3), 4.33 (q, 2H, J = 7.0 Hz, CH2), 6.59 (d, 1H, J =
16.5 Hz, CH), 7.72 (d, 2H, J = 8.5 Hz, Ar–H), 7.62 (d, 1H, J =
16.5 Hz, CH), 8.28 (d, 2H, J = 8.5 Hz, Ar–H). 13C NMR (125
MHz, DMSO-d6): δ (ppm) = 14.98, 61.27, 123.29, 124.74,
130.27, 141.32, 142.60, 148.89, 166.51.
Bahrami K., Khodaei M.M., Meibodi F.S., Suzuki and Heck cross-
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(E)-1-Nitro-4-styrylbenzene: Yield: 98%, Orang solid,
mp: 154-155°C, (Lit: (Farjadian et al., 2015) 155-157°C).
FT-IR (KBr); ῡ (cm–1): 970 (C–H trans-alkene bend.), 1344
(NO2 symmetric), 1509 (asymmetric), 1447, 1591 (C=C
aromatic), 1631 (C=C alkene), 3076 (C–H alkene stretch.),
1
3102 (C–H aromatic stretch.). H NMR (250 MHz, CDCl3):
Choudary B.M., Kantam M.L., Reddy N.M., Gupta N.M., Layered-
δ (ppm) = 8.6 (d, 2H, J = 7.5 Hz, p-Ar-H), 7.57 (d, 2H, J = 7.5
Hz, p-Ar–H), 7.49 (d, 2H, J = 7.5 Hz, Ar–H), 7.26-7.36 (m, 3H,
Ar–H), 7.21 (d, 1H, J = 15.0 Hz, CH), 7.07 (d, 1H, J = 15.0 Hz,
CH). 13C NMR (62.50 MHz, CDCl3): δ (ppm) = 143.8, 133.3,
128.9, 128.8, 128.7, 127.0, 126.9, 126.4, 124.1, 121.9.
double-hydroxide-supported
Pd(TPPTS)(2)Cl-2:
a
new
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Acknowledgement: We are thankful to the Yazd
University Research assembly for partial support of this
work.
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