Betti base-modified magnetic nanoparticles as a novel basic nanocatalyst in Knoevenagel condensation and its related palladium nanocatalyst in Suzuki coupling reactions

Article abstract of DOI:10.1002/aoc.3532

Betti base-modified Fe₃O₄ nanoparticles have been successfully designed and synthesized for the first time through the condensation of Fe₃O₄ magnetic nanoparticles coated by (3-aminopropyl)triethoxysilane with β

Full text of DOI:10.1002/aoc.3532

Full paper
Received: 14 April 2016
Revised: 5 May 2016
Accepted: 7 May 2016
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.3532
Betti base-modified magnetic nanoparticles as a
novel basic nanocatalyst in Knoevenagel
condensation and its related palladium
nanocatalyst in Suzuki coupling reactions
a
a
b
Payam Heidari , Ramin Cheraghali and Hojat Veisi *
3 4
Betti base-modified Fe O nanoparticles have been successfully designed and synthesized for the first time through the conden-
sation of Fe magnetic nanoparticles coated by (3-aminopropyl)triethoxysilane with β-naphthol and benzaldehyde. Their appli-
3 4
O
cation as a novel magnetic nanocatalyst in the Knoevenagel condensation and also application to immobilization of palladium
nanoparticles for Suzuki coupling reactions have been investigated which opens a new field for application of Betti base deriva-
tives in organic transformations. The synthesized inorganic–organic hybrid nanocatalyst has been fully been characterized using
Fourier transform infrared, X-ray diffraction, vibrating sample magnetometry, transmission and scanning electron microscopies,
energy-dispersive X-ray, wavelength-dispersive X-ray and X-ray photoelectron spectroscopies and inductively coupled plasma
techniques. The catalyst was easily separated with the assistance of an external magnet from the reaction mixture and reused
for several consecutive runs with no significant loss of its catalytic efficiency. Copyright © 2016 John Wiley & Sons, Ltd.
Keywords: betti base; organocatalyst; magnetic; palladium; nanoparticles; Knoevenagel; Suzuki
the surface immobilization strategy is the covalent attachment of
an organic compound or ligand to the solid surface.
Introduction
[11]
Nanoscale palladium particles make them attractive in catalysis due
to their large surface area. Several palladium nanoparticles (NPs) as
catalysts for carbon–carbon coupling reactions such as the Suzuki–
Betti base (1-α-aminobenzyl-2-naphthol), easily prepared via
modified Mannich reaction from 2-naphthol, benzaldehyde and
ammonia, contains two potentially reactive functional groups
(amino and hydroxyl) and two rigid rings (phenyl and naphthyl),
which might manifest good activity in chemical transformation af-
ter functionalization with other groups. Betti base and its deriva-
tives have been known since the beginning of the twentieth
century ; however, further research into their applications has
remained unreported for some time. Only in recent decades has
there been an increasing focus on the application of Betti base in
asymmetric reactions due to the functional groups and chiral cen-
tre. Many authors have already reported the use of Betti base deriv-
[
1–3]
Miyaura reaction have been reported.
Palladium-catalysed
cross-coupling reactions of organo-halides with olefins (Heck) and
organo-boronic acids (Suzuki) for carbon–carbon bond formation
are extremely useful to the chemical industry and in research. Since
their discovery they have evolved into a general technique in pre-
paring biologically active functionalized biphenyls which are impor-
tant intermediates or products in drug discovery, pharmaceuticals
[12]
[
4,5]
and agricultural compounds.
such as [Pd(OAc) ] and [Pd(PPh
Historically, palladium complexes
Cl ] have been widely used as ho-
2
3
)
2
2
[4]
mogeneous catalyst systems in cross-coupling reactions. Among
various palladium catalysts for the Suzuki–Miyaura coupling reac-
tion, homogeneous catalysts have been widely investigated, while
less expensive heterogeneous catalysts have received scanter at-
tention. Homogeneous palladium catalysts are not used in indus-
trial application due to the difficulty in separating and recycling,
low catalytic efficiency and the high leaching of metal species. In or-
atives as chiral catalysts in asymmetric addition of Et Zn to
2
[13]
[14]
aldehydes and the asymmetric allylic alkylation reaction. Nev-
ertheless, upon searching the literature, no example dealing with
Betti base supported on magnetic NPs was found, which encour-
aged us to design and support Betti base on the surface of Fe O4
3
NPs and to investigate their application as a novel magnetic base
nanocatalyst and also their ability to immobilize palladium NPs as
a magnetic palladium nanocatalyst in Suzuki coupling reactions.
[
6–9]
der to solve the problem, new strategies should be developed.
In recent decades, as an important family of separation materials,
magnetic Fe NPs have attracted considerable attention in chem-
istry and material sciences, due to their potential applications in ca-
3 4
O
*
Correspondence to: Hojat Veisi, Department of Chemistry, Payame Noor
University, Tehran, Iran. E-mail: hojatveisi@yahoo.com
[
10]
talysis and biomedicine.
The immobilization of homogeneous
catalysts on solid supports opens up new avenues for design and
engineering of new and stimulating catalysts. These structures are
easily separable from a reaction mixture, allowing the recovery of
the solid and eventually its reuse. The highest level of evolution in
a Department of Chemistry, College of Science, Saveh Branch,Islamic Azad
University, Saveh, Iran
b Department of Chemistry, Payame Noor University, 19395-4697, Tehran, Iran
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.

P. Heidari et al.
Experimental
Preparation of Magnetic Fe O NPs
3
4
Naked Fe O NPs were prepared by chemical co-precipitation of
3
4
2+
3+
Fe and Fe ions with a molar ratio of 2:1. Typically, FeCl ꢀ6H O
3
2
(
5.838 g, 0.0216 mol) and FeCl ꢀ4H O (2.147 g, 0.0108 mol) were dis-
2
2
solved in 100 ml of deionized water at 85 °C under nitrogen atmo-
sphere and vigorous mechanical stirring (500 rpm). Then, 10 ml of
2
5% NH OH was quickly injected into the reaction mixture in one
4
2+
3+
portion. The addition of the base to the Fe /Fe salt solution re-
sulted in the immediate formation of a black precipitate of mag-
netic NPs. The reaction continued for another 25 min and the
mixture was cooled to room temperature. Subsequently, the resul-
tant ultrafine magnetic particles were treated by magnetic separa-
tion and washed several times with deionized water.
Preparation of Fe O /Pr-NH
2
3
4
The obtained magnetic NP powder (500 mg) was dispersed in 50 ml
of toluene solution by sonication for 20 min, and then
3
-aminopropyltriethoxysilane (APTES; 5 mmol) was added to the
mixture. The mixture was refluxed under argon atmosphere at
00 °C for 48 h. The product was separated by filtration, washed
1
3 4 3 4
Scheme 1. Preparation of catalysts: Fe O /Betti base and Fe O /Betti base/Pd.
with ethanol and dried under vacuum for 24 h at 50 °C. The precip-
itated product (Fe O /Pr-NH ) was dried at room temperature un-
3
4
2
der vacuum.
ethanol. Then, the solvent was evaporated. The products were iden-
tified using H NMR, C NMR and Fourier transform infrared (FT-IR)
spectroscopies.
1
13
Preparation of Fe O /Betti Base/Pd(0)
3
4
The obtained Fe O /Pr-NH nanoparticles (500 mg) were dispersed
3
4
2
Suzuki–Miyaura Coupling Reaction
in 70 ml of ethanol by sonication for 20 min, and then β-naphthol
1 mmol) and benzaldehyde (1 mmol) were added to the reaction
(
In a typical reaction, 7 mg of Fe O /Betti base/Pd (0.002 mmol Pd)
3
4
mixture. The reaction mixture was stirred under nitrogen atmo-
sphere at 80 °C for 24 h. Then, the reaction mixture was cooled to
room temperature, and the resulting NPs were washed with etha-
nol several times and separated using magnetic decantation and
dried at room temperature.
was placed in a 25 ml Schlenk tube, and 1 mmol of aryl halide in
3 ml of water–ethanol (1:1), 0.134 g (1.1 mmol) of phenylboronic
acid and 0.276 mg of K CO (2 mmol) were added. The mixture
2
3
was then stirred for the desired time at 40 °C. The reaction was
monitored by TLC. After completion of the reaction, 5 ml of ethanol
was added, and the catalyst was removed using an external
magnet. Further purification was achieved by column chromatog-
raphy (n-hexane–acetone; 4:1). The products were identified using
Then, the Fe O /Betti base (500 mg) was dispersed in CH CN
3
4
3
(30 ml) in an ultrasonic bath for 30 min. Subsequently, a yellow so-
lution of PdCl (30 mg) in 30 ml of acetonitrile was added to the dis-
2
1
13
persion of Fe O /Betti base and the mixture was stirred for 10 h at
H NMR and C NMR spectroscopies.
3
4
2
5 °C. Then, the Fe
decantation and washed with CH
the unattached substrates.
The reduction of Fe /Betti base/Pd(II) by NaBH
as follows: 500 mg of Fe /Betti base/Pd(II) was dispersed in 20 ml
of water, and then 1 mmol of NaBH in 1 ml of water was added and
the reaction was carried out at room temperature for 5 h. The final
product, Fe /Betti base/Pd(0), was washed with water and dried
in vacuum at 40 °C. Scheme 1 depicts the synthetic procedure for
Fe /Betti base/Pd.
3
O
4
/Betti base/Pd(II) was separated by magnetic
3
CN, water and acetone to remove
Results and Discussion
3
O
4
4
was performed
3 4
O
Fe
works,
3
O
4
particles were synthesized according to our previously
[
15]
and subsequently were coated with APTES to achieve
4
aminopropyl-functionalized magnetic NPs. Ultimately, the reaction
of amino groups with β-naphthol and benzaldehyde gave the cor-
3
O
4
responding Betti base. Finally, the Betti base immobilized on Fe
O
3 4
(Fe /Betti) was coordinated with PdCl and subsequently its re-
3
O
4
3
O
4
2
duction by NaBH led to the corresponding palladium NPs sup-
4
ported on magnetic NPs. Finally, the mixture was collected using
an external magnet, followed by drying in vacuum. The routes
employed for the fabrication of the catalysts are shown in Scheme 1.
Knoevenagel Condensation Catalysed by Fe
3 4
O /Betti Base
In a typical reaction, a mixture of Fe /Betti base composite
3 4
O
(
0.05 g), benzaldehyde (1 mmol) and ethanol (5 ml) was placed in
The content of linked Betti base on Fe
elemental analysis which revealed a loading of ca 0.28 mmol of
Betti base per gram of Fe . In addition, the palladium content
of the catalyst as estimated using atomic absorption spectroscopy
was 0.25 ± 0.001 mmol g . This indicated that all of the anchored
organic ligand moieties have approximately and efficiently coordi-
nated with palladium ions providing catalytic active sites. The
3 4
O was measured through
a round-bottom flask. The reaction vessel was sonicated for 5 min
at room temperature to disperse the magnetic NPs in the solution.
Then, malononitrile (1.1 mmol) was added to the mixture and
stirred at room temperature for 60 min. The progress of the reaction
was monitored by TLC. After completion of the reaction, the cata-
lyst was separated with a magnet and was washed with hot
3 4
O
ꢁ
1
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Appl. Organometal. Chem. (2016)

Betti base-modified magnetic nano particles
characterization of the catalyst was carried out using FT-IR spectros-
copy, X-ray diffraction (XRD), CHN elemental analysis, field emission
scanning electron microscopy (SEM), energy-dispersive X-ray spec-
troscopy (EDX), wavelength-dispersive X-ray spectroscopy (WDX),
transmission electron microscopy (TEM), X-ray photoelectron spec-
troscopy, inductively coupled plasma (ICP) analysis and vibrating
sample magnetometry (VSM). The as-synthesized catalyst can be
well dispersed in various polar or nonpolar solvents, such as water,
ethanol, acetone, dimethylformamide (DMF), ethyl acetate, cyclo-
hexane, etc.
Figure 1 shows FT-IR spectra of Fe O and Fe O /Betti base. The
3
4
3 4
FT-IR spectrum of the magnetic NPs alone shows a stretching vibra-
ꢁ
1
tion at 3381 cm which incorporates the contributions from both
symmetric and asymmetric modes of the O–H bonds which are at-
[
16]
tached to the surface iron atoms.
The bands at low
ꢁ
1
wavenumbers (≤700 cm ) come from vibrations of Fe–O bonds
of iron oxide, which for bulk Fe O samples appear at 570 and
75 cm but for Fe O NPs at 624 and 572 cm as a blue shift,
3
4
ꢁ
1
ꢁ1
3
3 4
[
17–19]
due to the size reduction.
The presence of an adsorbed water
layer is confirmed by a stretch for the vibrational mode of water
ꢁ
1
found at 1622 cm . The FT-IR spectra of Fe O /Betti base and
3 4
Figure 2. SEM image of Fe O /Betti base/Pd.
3
4
Fe O show Fe–O vibrations in the same vicinity. The introduction
3
4
3 4
of Betti base groups to the surface of Fe O is confirmed by the
ꢁ
1
bands at 1022, 1642, 2927, 3028 and 1384 cm assigned to the
Fe–O–Si, C¼C, alkyl C–H, aryl C–H stretches and amine C–N
stretching, respectively. All of those bands reveal that the surface
3 4
of Fe O NPs is successfully modified with Betti base groups for
the metal–ligand coordination.
The morphology and size of the catalyst were evaluated using
SEM and TEM analysis (Figs 2 and 3). The SEM image of the final cat-
alyst shows the formation of uniform and monodispersed NPs
(
Fig. 2).
TEM images of the Fe
palladium NPs with nearly spherical morphology are grafted on
amidoxime-functionalized Fe NPs (Fig. 3). In the TEM images,
3 4
O /Betti base/Pd catalyst reveal that the
3 4
Figure 3. TEM images of Fe O /Betti base/Pd.
3 4
O
iron oxide NPs of 15–20 nm in diameter and palladium nanoparti-
cles of ca 3 nm entrapped in iron oxide are observed.
The elemental composition was determined using EDX analysis
and the results, shown in Fig. 4, indicate Si, O, C, N, Fe and Pd signals
3 4
that are provided by Fe O /Betti base/Pd. For further characteriza-
tion of the sample, WDX-coupled quantified SEM mapping of the
sample was also investigated (Fig. 5). WDX can provide qualitative
information about the distribution of different chemical elements
in the catalyst matrix. Looking at the compositional maps of Fe, Si,
3 4
Figure 4. EDX spectrum of Fe O /Betti base/Pd.
C, N and Pd, and mainly the combined composition image, the
presence of palladium NPs with good dispersion is clearly distin-
guished in the composite.
The XRD pattern of Fe O /Betti base/Pd is presented in Fig. 6. The
3 4
characteristic diffraction peaks at 2θ of 30.3°, 35.6°, 43.2°, 53.8°, 57.3°
Figure 1. FT-IR spectra of (a) Fe
O
3 4
3 4
and (b) Fe O /Betti base.
and 62.8° correspond to the diffraction of (220), (311), (400), (422),
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.
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P. Heidari et al.
3 4
redispersion process of the Fe O /Betti base/Pd catalyst. Therefore,
the above mentioned results indicate an easy and efficient way to
separate and recycle the prepared catalyst from the reaction solu-
tion using an external magnetic force.
3 4
Then, in order to evaluate the basic activity of Fe O /Betti base
and metal-containing Fe /Betti base/Pd as heterogeneous cata-
3 4
O
lysts, the Knoevenagel condensation and Suzuki–Miyaura coupling
reactions were chosen as probe reactions, respectively. The addi-
tion of malononitrile to various benzaldehydes using Fe O /Betti
3
4
was performed under air (balloon). To optimize the reaction
conditions, 4-chlorobenzaldehyde (1 mmol) and malononitrile
(1.1 mmol) were used as model substrates. Conditions such as cat-
alyst amount, solvent and time were investigated. The best result is
obtained by carrying out the reaction with a 1:1 molar ratio of
4
-chlorobenzaldehyde and malononitrile at 40 °C in 2 ml of EtOH
3 4
Figure 5. SEM image of Fe O /Betti base/Pd and elemental maps of Fe, Si,
C, N and Pd atoms.
for 1 h. The results are summarized in Table 1.
To study the effect of amount of catalyst, the Knoevenagel con-
densation was carried out with various amounts of catalyst
(Table 1). When the amount of catalyst increases from 0.04 to
0.05 g, the product yield increases significantly from 82 to 96%,
which is due to the availability of more basic sites. After that, the
yield remains almost stable between 0.05 g and 0.06 g. Therefore,
0.05 g was chosen as the optimized amount of catalyst for further
experiments.
It should be noted that the non-functionalized magnetic NPs
3 4
(Fe O ) are not active in the Knoevenagel condensation, with less
Figure 6. XRD pattern of Fe
3
O
4
/Betti base/Pd.
than 10% conversion observed after 4 h (Table 1, entry 4). This indi-
cates the need for the Betti base coating on the surface of the mag-
netic NPs to create basic sites.
3 4
(511) and (440) of Fe O . The entire diffraction pattern matches
[
20]
With a reliable set of conditions in hand (Table 1, entry 6), we also
probed the scope and generality of the developed protocol with a
variety of aromatic, aliphatic and heteroaromatic aldehydes using
magnetic Betti base and the results are summarized in Table 2. All
the reactions are able to undergo the corresponding Knoevenagel
condensation well. In addition, it is found that substituent groups
of aromatic aldehydes have an effect on the Knoevenagel reaction:
aldehyde with electron-withdrawing group is observed to be more
reactive than that with electron-donating group (Table 2, entries 3
and 4). Moreover, heteroaromatic and aliphatic aldehydes are
with the magnetic cubic structure of Fe
3 4
O (JCPDS 65–3107).
Typical diffraction peaks of Pd(0) corresponding to (111), (200)
and (220) are observed at 40.2°, 46.7° and 68.2° (JCPDS 87–0638)
in the pattern. The results from XRD imply that the palladium NPs
have been successfully immobilized onto the surface of the mag-
netic particles.
VSM measurements were carried out at room temperature. The
magnetization curves measured for Fe
base/Pd are presented in Fig. 7. The magnetic saturation values of
3 4 3 4
O and Fe O /Betti
ꢁ
1
Fe
tively. The decrease in the saturation magnetization is due to the
presence of the Betti base and palladium NPs on the Fe surface.
Moreover, the inset image in Fig. 7 shows the separation–
3 4 3 4
O and Fe O /Betti base/Pd are 61.8 and 55.2 emu g , respec-
3 4
O
a
Table 1. Optimization of Knoevenagel reaction conditions
b
Entry
Catalyst (mg)
T (°C)
Solvent
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
—
—
—
40
40
40
40
40
40
40
30
25
40
40
—
10
10
10
4
0
0
MeCN
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
—
0
Fe
3
O
4
(40)
10
82
96
96
90
70
75
85
Fe
Fe
Fe
Fe
Fe
Fe
Fe
3
O
4
O
4
O
4
O
4
O
4
O
4
O
4
/Betti (40)
/Betti (50)
/Betti (60)
/Betti (50)
/Betti (50)
/Betti (50)
/Betti (50)
2
3
1
3
1
3
2
3
3
10
1
3
2
1
3
MeCN
2
a
Reaction conditions: 4-chlorobenzaldehyde (1 mmol), malononitrile
/Betti base, solvent (5 ml).
(
1.1 mmol), Fe
O
3 4
b
Isolated yield.
3 4 3 4
Figure 7. VSM curves of Fe O and Fe O /Betti base/Pd.
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Appl. Organometal. Chem. (2016)

Betti base-modified magnetic nano particles
Table 2. Knoevenagel condensation with various substrates catalysed
a
3 4
by Fe O /Betti base
b
Entry
RCHO
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
C
6
H
5
1.2
1.5
1
95
90
96
96
90
92
96
70
90
4-CH
4-ClC
4-NO
4-OHC
3
C
6
H
4
6 4
H
2
C
6
H
4
0.5
2
6 4
H
4-Pyridyl
2-Furyl
Cinamyl
Propyl
1.5
1.5
4
1
a
Figure 9. Heterogeneity test for Knoevenagel condensation of
-chlorobenzaldehyde and malononitrile.
Reactions were carried out under aerobic conditions in 5 ml of EtOH,
.0 mmol of aldehyde and 1.1 mmol of malononitrile in the presence
4
1
of catalyst (50 mg) at 25 °C.
b
Isolated yield.
found to be more reactive (Table 2, entries 6, 7 and 9).
Cinnamaldehyde is found to be much less reactive than other alde-
hydes in the Knoevenagel condensation with only approximately
70% conversions being observed (Table 2, entry 8).
Considering that one key feature of our catalyst was magnetic
response, we investigated the reusability and the recycling of
the catalyst, and found that the catalyst can be completely re-
covered using an external permanent magnet, giving GC yield
still higher than 90% after five recycles during Knoevenagel con-
densation (Fig. 8).
In general, when using a supported catalyst, a crucial issue is the
possibility that some active sites are lost from the solid support to
the liquid phase, and these leached species are responsible for a
significant loss of the catalytic activity. Therefore, in order to prove
the heterogeneous nature of the catalyst, a heterogeneity test was
performed, in which the catalyst was separated from the reaction
mixture using a magnet at approximately 50% conversion of the
starting material. The reaction progress in the filtrate was moni-
tored (Fig. 9). No further reaction conversion is observed even at ex-
tended time, indicating that the nature of reaction process is
heterogeneous and there is no reaction in the homogeneous
phase.
Scheme 2. Possible mechanism for the Knoevenagel condensation
catalysed by Fe /Betti base.
3 4
O
iminium ion compared to the carbonyl species facilitates
Knoevenagel reaction between aryl aldehyde and malononitrile.
Continuing the work, the catalytic activity of Fe O /Betti base/Pd
3 4
was evaluated in the Suzuki–Miyaura reaction. Initially, we opti-
mized the conditions for the coupling reaction between
bromoacetophenone and phenylboronic acid as a model reaction.
The influence of reaction parameters such as the base (Et
and K CO ), the solvent (nonpolar, protic and aprotic) and the
amount of catalyst were investigated (Table 3). Among the bases
evaluated, K CO is found to be the most effective. Water–EtOH
3
N, NaOAc
2
3
A possible mechanism for the reaction using magnetic Fe O /
3
4
Betti base as clean catalyst is shown in Scheme 2. According to
the mechanism, magnetic Fe O /Betti base readily catalyses the for-
2
3
(1:1) is the best choice as solvent.
3
4
mation of Knoevenagel product. The higher reactivity of the
To investigate the generality of this cross-coupling, we studied
the reaction of phenylboronic acid with a range of aryl halides un-
der the optimized conditions (Table 4). Phenyl iodide, bromide and
chloride all react efficiently with phenylboronic acid (Table 4, en-
tries 1–14). Aryl halides with electron-withdrawing or electron-
releasing groups react with phenylboronic acid to afford the corre-
sponding products in high yields. It is found that the yield when
using an ortho-substituted aryl iodide is lower (Table 4, entry 4) than
when using a para- or meta-substituted aryl iodide (Table 4, entries
5
and 6). The coupling reaction of aryl chlorides with phenylboronic
acid requires extended reaction time compared to aryl iodides and
bromides, producing the desired products in moderate yield
(Table 4, entries 13 and 14).
One of the main advantages of magnetite NP-supported cata-
lysts is the easy separation and recycling of the catalyst. To study
the recycling properties of this catalyst, the reaction of
bromoacetophenone with phenylboronic acid under the optimized
reaction conditions was selected. The results show that the catalyst
3 4
Figure 8. Separation and reuse of the magnetic Fe O /Betti base catalyst.
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.
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P. Heidari et al.
Table 3. Optimization of conditions for Suzuki–Miyaura reaction of
a
bromoacetophenone with phenylboronic acid
b
Entry
Solvent
Pd (mol%)
Base
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
DMF
Toluene
EtOH
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.01
K
K
K
K
K
2
2
2
2
2
CO
CO
CO
CO
CO
3
1
88
65
75
60
96
65
80
70
3
1
3
1
2
H O
3
1
c
c
c
c
EtOH–H
EtOH–H
EtOH–H
EtOH–H
2
O
2
O
2
O
2
O
3
0.5
1
NaOAc
Et
CO
Figure 10. Recycling of Fe
under similar conditions.
3 4
O /Betti base/Pd for Suzuki coupling reaction
3
N
1
K
2
3
1
a
Reaction conditions: bromoacetophenone (1 mmol), PhB(OH)
/Betti base/Pd, solvent (3 ml).
2
(
1.1 mmol), Fe
O
3 4
b
Isolated yield.
O = 1:1.
indicates the stability of the catalyst during the reaction. In addition,
SEM and TEM images (Fig. 11) of the catalyst after the five run show
that the nanostructure of the catalyst is preserved. In addition the
TEM image of the catalyst after being reused five times shows that
the palladium NPs are still well dispersed and no obvious aggrega-
tion is observed. To investigate the heterogeneity of the catalyst,
we conducted a hot filtration test for the Suzuki reaction between
c
EtOH–H
2
Table 4. Suzuki cross-coupling of aryl halides with phenylboronic acid
catalysed by Fe O /Betti base/Pd
3 4
a
3 4
bromoacetophenone and phenylboronic acid using Fe O /Betti
base/Pd under the same conditions. The reaction was allowed to
proceed for 20 min (yield of 75%), and then the catalyst was sepa-
rated. However, there is no increase in yield of the desired product
when the reaction is continued for a further 1 h after the catalyst
was magnetically separated, confirming the heterogeneous charac-
ter of the catalyst.
b
Entry
RC
6
H
4
X
X
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
H
I
0.25
0.50
0.30
0.50
0.50
0.75
1
98
96
98
85
96
95
96
96
92
90
96
92
70
65
4-CH
4-COCH
3
I
We also performed solid-phase poisoning tests using 3-
3
I
mercaptopropyl-functionalized silica (SH-SiO ) as an effective palla-
2
2-CH
4-CH
3
O
O
I
dium scavenger which selectively coordinates and deactivates the
[
21]
3
I
leached out palladium. Thereby, cessation of the reaction is ex-
pected if the coupling reaction is catalysed by palladium species
leached from the solid support. The kinetic profiles of typical Suzuki
3-NO
H
2
I
Br
Br
Br
Br
Br
Br
Cl
Cl
4-COCH
3
0.50
2
reactions in the presence and absence of SH-SiO are shown in
2
4-CH
4-CH
4-Cl
3
O
Fig. 12. The results clearly indicate that the catalytic activity of
Fe O /Betti base/Pd is not affected even in the presence of the poi-
10
11
12
13
14
3
1.5
1
3
4
soning agent.
3-NO
H
2
2
(Reactions conditions: 2 ml of mixture of EtOH and H O (1:1),
2
10
1.0 mmol of bromoacetophenone, 1.1 mmol of phenylboronic acid
and 2 mmol K CO in the presence of catalyst (0.007 g, 0.02 mol%
4-CH
3
12
2
3
a
Pd) and 0.1 mmol of SH-SiO at 40 °C. Conversion of reactant was
determined using GC.)
2
Reactions were carried out under aerobic conditions in 3 ml of EtOH–
H
2
2
O (1:1), 1.0 mmol of aryl halide,1.1 mmol of phenylboronic acid and
mmol of K CO in the presence of catalyst (7 mg, 0.02 mol% Pd) at
2
3
4
0 °C.
b
Isolated yield.
is recyclable in seven consecutive runs just by decantation with a
magnetic bar with no significant loss of catalytic activity (Fig. 10).
In addition, one of the attractive features of this catalytic system
is the rapid and efficient separation of the catalyst using an appro-
priate external magnet, which minimizes the loss of catalyst during
separation.
The leaching of palladium into the reaction solution after five
runs was determined using ICP analysis to be 1.35%, which
Figure 11. TEM and SEM images of reused catalyst after five runs.
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Copyright © 2016 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. (2016)

Betti base-modified magnetic nano particles
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Conclusions
In summary, the successful synthesis of two novel magnetically sepa-
rable catalysts in which magnetic Fe was modified by Betti base
3 4
O
groups as nanomagnetic base catalyst in the Knoevenagel condensa-
tion and also its application to immobilization of palladium NPs for
Suzuki coupling reactions has been investigated. Studies of the struc-
ture of these materials suggest that they have stable structures with
relevant organic components covalently attached to their surfaces.
Moreover, the synthesized hybrid materials were found to be environ-
mentally friendly catalysts with a high catalytic performance. The ben-
efits of these catalysts are the cheap and uncomplicated synthetic
pathways, and mild and efficient C–C coupling reactions in green me-
dia. Notably, the recyclability of the catalysts using an external magnet
and no palladium leaching from Fe O /Betti/Pd are good characteristics.
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3
4
Acknowledgements
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We are grateful to Payame Noor University (PNU) and Saveh Branch
of Islamic Azad University for partial support of this work.
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Appl. Organometal. Chem. (2016)
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