Catalytic Performance Studies of New Pd and Pt Schiff Base Complexes Covalently Immobilized on Magnetite Nanoparticles as the Environmentally Friendly and Magnetically Recoverable Nanocatalyst in C–C Cross Coupling Reactions

Article abstract of DOI:10.1007/s10562-017-2270-7

Abstract: Synthesis and characterization of new magnetically recoverable and high-performance nanocatalysts of Pd and Pt Schiff base complexes on magnetite nanoparticles were considered. Catalytic activity of these nanocatalysts was explored in Suzuki and Heck cross coupling reactions. The catalysts can be easily reused fourth consecutive runs without significant loss of catalytic efficiency.

Full text of DOI:10.1007/s10562-017-2270-7

Catalysis Letters
https://doi.org/10.1007/s10562-017-2270-7
Catalytic Performance Studies of New Pd and Pt Schiff Base
Complexes Covalently Immobilized on Magnetite Nanoparticles
as the Environmentally Friendly and Magnetically Recoverable
Nanocatalyst in C–C Cross Coupling Reactions
G. Rezaei1 · A. Naghipour1 · A. Fakhri1
Received: 22 September 2017 / Accepted: 4 December 2017
© Springer Science+Business Media, LLC, part of Springer Nature 2017
Abstract
Synthesis and characterization of new magnetically recoverable and high-performance nanocatalysts of Pd and Pt Schiff base
complexes on magnetite nanoparticles were considered. Catalytic activity of these nanocatalysts was explored in Suzuki
and Heck cross coupling reactions. The catalysts can be easily reused fourth consecutive runs without significant loss of
catalytic efficiency.
Graphical Abstract
Keywords Magnetically-recoverable nanocatalyst · Pd complex nanocatalyst · Pt complex nanocatalyst · Environmentally
based catalyst · Suzuki–Miyaura coupling · Mizoroki–Heck coupling
Extended author information available on the last page of the article
Vol.:(0123456789)
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G. Rezaei et al.
Scheme 1 Proposed structure
and preparation method for Pd
and Pt-Schiff base complexes on
Fe3O4 nanoparticles
nanocatalysts that can be consider as a bridge between het-
erogeneous and homogeneous catalysts. In addition, para-
magnetic nature of these catalysts facilitates easy and effi-
cient separation of catalysts from the reaction mixture with
an external magnet. These unique features make magnetic
nanocatalysts to be in accordance with green chemistry
standards. Up to now a large number of studies have been
reported that exhibit different kind of reactions catalyzed
efficiently using magnetic nanocatalysts [23–29].
1 Introduction
Schiff-bases as chelating multidentate ligands to stabilize
many different metals in various oxidation states have
played an influential role in the coordination chemistry.
Schiff-bases complexes have emerged widely in various
areas, including biological [1, 2], clinical [3, 4], analyti-
cal [5–7], and catalysis [8–11]. As yet, there has been a
noteworthy growth in the number of studies of these com-
pounds in different chemical processes such as, reduction,
oxidation, hydrogenation, carbon–carbon cross coupling
reactions, degradation, synthesis of organic compounds
and so on.
Herein, we report a Schiff base-functionalized magnetite
nanoparticle-supported stable Pd and Pt catalysts for appli-
cation in Suzuki and Heck coupling reaction.
C–C coupling reactions, mainly Suzuki and Heck reac-
tions have gained tremendous scientific and technologi-
cal interest in modern organic chemistry. These reactions
play key role in the synthesis of a large number of natural
products, pharmaceuticals [12–15], biologically active
compounds, agrochemicals and many advanced organic
building blocks. According to this background, several
catalytic systems such as homogenous Pd complex with a
diversity of ligands like phosphines [16], imidazole-phe-
nolates [17–19], Schiff bases [20, 21] and N-heterocyclic
carbenes [22] and also heterogeneous catalysts have been
employed to accelerate these coupling reactions. However,
factors including not being environmentally friendly cata-
lyst, low catalytic activity and selectivity, catalyst sepa-
ration, catalyst recycling and product contamination, not
easily available of catalysts, air-sensitive and quite expen-
sive catalysts limit the wide application of such catalysts
set in practical synthetic processes. Therefore, research-
ers search for further development of the catalytic sys-
tems that as homogenous catalysts can catalyze chemical
reactions with high selectively and reactivity and also as
heterogeneous catalysts can be recycled through simple
separation.
2 Results and Discussion
2.1 Catalyst Characterization
Considering clean and green catalyst recovery is one of the
principles of the chemical industry, Schiff base complexes
were prepared through immobilization over Fe3O4 nanopar-
ticles to allow easy catalysts separation and recovery. At
first, magnetite nanoparticles were synthesized based on co-
precipitation solution of Fe(II) and Fe(III) in alkaline pH.
Then, surfaces of Fe3O4 nanoparticles were functionalized
with amine groups. Reaction between these amine groups
and picolinaldehyde provide Schiff base ligands on the sur-
faces of Fe3O4 nanoparticles that are coordinated to Pd and
Pt (scheme 1).
FT-IR technique was applied in order to verify each syn-
thetic step in the preparation of the nanocatalysts has been
successfully accomplished (Fig. 1).
As can be seen in Fig. 1, the bands in the same region
around 570–590 cm−1 in FT-IR spectra of all samples cor-
responding to the characteristic Fe–O vibrations confirm the
existence of Fe3O4 nanoparticles in the synthesized com-
ponents. The broad bands around 3000–3500 cm−1 are due
to the hydroxyl groups stretching vibration. Introduction of
APTMS to the surface of Fe3O4 nanoparticles is designated
With the advent of nanoscience and the progresses have
been made in this field, it is possible to design magnetic
1 3

Catalytic Performance Studies of New Pd and Pt Schiff Base Complexes Covalently Immobilized…
Fig. 2 SEM images of a Pd and b Pt complex-functionalized Fe3O4
nanoparticles
catalysts are shown in Fig. 4. Based on magnetization curve,
saturation magnetization values of Pd and Pt complex-func-
tionalized Fe3O4 nanoparticles are 52.91 and 48.15 emu g−1
respectively that reveal they possess superparamagnetic
behavior and can be separated easily by an external mag-
netic field. Reduction of saturation magnetization values of
Pd and Pt relative to Fe3O4 nanoparticles, somehow can also
confirm functionalization of Fe3O4 nanoparticles with Pd
and Pt complex.
Fig. 1 FT-IR spectra of a Fe3O4 nanoparticles, b amine-functional-
ized Fe3O4 nanoparticle Fe3O4, c Schiff base-functionalized Fe3O4
nanoparticles and d Pd and e Pt complex-functionalized Fe3O4 nano-
particles
by the bands at 1006 and 2918 cm−1 that are associated to
the Fe–O–Si stretching vibration and C–H aliphatic vibra-
tion respectively. Reaction of the amine-functionalized
Fe3O4 nanoparticle with picolinaldehyde lead to prepara-
tion of Schiff base component on Fe3O4 nanoparticle that
is evidenced by the strong band at 1634 cm−1 due to C=N
stretching vibration. On metallation of Schiff base-function-
alized Fe3O4 nanoparticles with Pd and Pt prominent C=N
stretching frequency was just shifted to lower wave number
about 1627 and 1614 cm−1 respectively.
XRD studies were conducted in order to investigate
phase, purity and crystalline nature of Pd and Pt nano-
catalysts (Fig. 5). The position and relative intensities of
all peaks in the XRD pattern of all samples at 2θ of 30.1°,
35.4°, 41.5°, 51.5°, 57.1°, and 62.7° correspond to the dif-
fraction of (220), (311), (400), (422), (511), and (440) are
indexed with the XRD pattern of standard magnetite and
indicate retention of the crystalline cubic spinel structure
during surface modification. Appearance of the new peaks
apart from the original peaks at XRD pattern of Pd, and Pt
nanocatalysts was attributed to the Pd and Pt species.
TGA technique was used to determine thermal stability
and the percent of organic content chemisorbed onto the
surface of Fe3O4 nanoparticle (Fig. 6).
SEM images of Pd and Pt based nanocatalysts are shown
in Fig. 2a, b respectively. SEM images of the nanocatalysts
noticeably exhibit the formation of approximately spherical
nanoparticles with size ranging of 20–35 nm.
The elemental composition of the Pd and Pt complex-
functionalized Fe3O4 nanoparticles was assessed by EDX
analysis. The results presented in Fig. 3 reveal the presence
of the expected elements in the structure of the as-prepared
catalysts.
The weight loss for Fe3O4 nanoparticles, Pd and Pt nano-
catalysts occurring at T<220 °C, is attributed to the loss of
physisorbed solvent or trapped water. A mass loss of approx-
imately 14 and 10% between 220 and 820 °C temperature
The magnetic properties of Pd and Pt complex-function-
alized Fe3O4 nanoparticles were analyzed by VSM. The
room temperature magnetization curves of the magnetic
1 3

G. Rezaei et al.
range in the TGA curves of Pd and Pt nanocatalysts can
be related to the decomposition of Pd and Pt Schiff base
complex. Therefore, successful functionalization of Fe3O4
nanoparticle can also be inferred from TGA curve.
ICP-AES technique was used in order to indicate Pd and
Pt content in the nanocatalysts. Based on ICP results the
loading amount of Pd and Pt was estimated about 0.872 and
0.760 mmol g−1 respectively.
2.2 Catalytic Investigation
Following favored preparation and characterization of the
nanocatalysts, efficacy of them were initially experienced
in Suzuki coupling. In order to assess the best reaction con-
ditions, reaction of 4-iodotoluene and phenylboronic acid
was chosen as the model reaction. Tables 1 and 2 depict
results of different reaction parameters investigation such as
type of base, solvent, temperature and amount of catalysts.
As it clear in the absence of the base, no desired product
was formed. This indicate key role of base in C–C coupling
reactions. Examination organic and inorganic bases demon-
strated in the presence of K2CO3 the reaction reached com-
pletion. It has been proposed that K2CO3 facilitate replace-
ment of the halide in the coordination sphere of Pd and Pt
complex and facilitates an intramolecular transmetallation.
Testing different kind of kind of solvents in model reac-
tion reveal PEG was the best for both catalytic systems. In
order to show efficiency of the catalysts, the model reac-
tion was explored using different amount of the catalysts.
As it is reported, about Pd-catalyst the reaction proceeded
in excellent yield with 6 mg of catalyst while Pt-catalyst
gave desired product in excellent yield with 24 mg catalyst.
Then, the influence of the temperature on the reaction was
surveyed and the best result was obtained at 80 °C for both
catalysts with respect to reaction time and yield.
Fig. 3 EDX analysis of Pd and Pt complex-functionalized Fe3O4 nan-
oparticles
Fig. 4 VSM curves of Pd and Pt
complex-functionalized Fe3O4
nanoparticles
1 3

Catalytic Performance Studies of New Pd and Pt Schiff Base Complexes Covalently Immobilized…
Efficiency of Pt-catalyst was investigated in the model
reaction of 4-iodoanisol and n-butyl acrylate. It was
observed that the best yield was achieved when the reac-
tion was conducted with Et3N in the presence 20 mg of Pt-
catalyst at at 120 °C in PEG (Table 5).
With the optimized reaction conditions in hand, the versa-
tility of Pd and Pt-catalyst was extended by employing vari-
ous substituted aryl halides to react with n-butyl acrylate.
Coupling reaction of aryl iodides and bromides with n-butyl
acrylate Pd-catalyst led desired products in moderate to
excellent yields while about Pt-catalyst more difficult condi-
tion are needed and just in aryl iodides, products were gained
in moderate yields (Table 6).
Fig. 5 XRD patterns of Pd and Pt complex-functionalized Fe3O4 nan-
As reusability of the heterogeneous catalysts plays an
important role in industrial applications as well as in green
chemistry, scientists focus their attention on the synthesis of
catalysts that can be easy separate from the media. Simply
separation of the magnetic catalysts cause we turned our
attention to investigate recovery and reuse of the developed
Pd and Pt-catalysts in the model reaction of Suzuki coupling
reaction under determined optimized reaction conditions.
As seen in Fig. 7, the catalysts could be recycled for fourth
consecutive runs without noticeable loss in catalytic activity.
As Tables 7 and 8 clearly show the Pd and Pt complexes
supported on Fe3O4 nanoparticles are highly efficient in cata-
lyzing Suzuki and Heck coupling reaction and gave product
in comparison with the best of the well-known data from
the literature.
oparticles
Fig. 6 TGA curves of Pd and Pt complex-functionalized Fe3O4 nano-
particles
3 Experimental
After identifying optimal reaction conditions, general-
ity of the catalysts was developed by employing several
substituted aryl halides to react with phenylboronic acid.
The results are summarized in Table 3. Coupling reaction
of iodo, bromo, chlorobenzene and all substituted aryl hal-
ides (including electron-withdrawing and electron-donating
groups in ortho, para and meta position) with phenylboronic
acid in the presence of Pd-catalyst afforded satisfactory
yields. However, Pt-catalyst proceeded coupling reaction of
iodobenzene with phenylboronic acid in excellent yield. For
electron-donating substituted iodobenzene and withdrawing
substituted bromobenzene, the products in moderate yield
were achieved even though the reaction time was prolonged.
Encouraged by the accomplishments in Suzuki reaction,
catalytic activities of Pd- and Pt-catalyst were further evalu-
ated in Heck coupling reaction of aryl halides and n-butyl
acrylate. For Pd-catalyst reaction of iodobenzen and n-butyl
acrylate was chosen as the model reaction. As it is presented
in Table 4, the best optimized reaction condition was identi-
fied as follow: 6 mg of Pd-catalyst, K2CO3 as base, at 100 °C
in PEG.
All starting materials in high purity were purchased from
Merck and Aldrich. Fourier transform infrared (FT-IR) spec-
tra were recorded on a Perkin Elmer Spectrum 100 FT-IR
spectrophotometer in the range of 400–4000 cm−1 using KBr
pellets. Thermogravimetric analysis (TGA) was carried out
under air atmosphere on Shimadzu DTG-60 instrument.
X-ray diffraction (XRD) data were collected on a X’ Pert
Pro Panalytical with Cu Kα radiation (λ=1.54406 Å). The
morphology of the catalyst was obtained using a SIGMA
VP-500 ZEISS (scanning electron microscopy) SEM. Metal
content of the catalyst was measured by inductively cou-
pled plasma atomic emission analysis (ICP-AES) Optima
7300DV Perkin Elmer. The known products were charac-
terized by comparison of their spectral (1H-NMR, Bruker
NMR-Spectrometer FX 400Q) and physical data with those
of authentic samples.
3.1 Preparation of the Nanocatalyst
At first, magnetic Fe3O4 nanoparticles were synthesized
according to the chemical coprecipitation method [56].
1 3

G. Rezaei et al.
Table 1 Optimization of
reaction parameters for Suzuki
reaction of 4-iodotoluene with
phenylboronic acid catalyzed by
Fe3O4@Pd-based complex
Entry
Base
Solvent
T (°C)
Catalyst (mg)
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
–
Et3N
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
DMSO
DMF
100
100
100
100
100
100
100
100
60
80
120
80
80
80
6
6
6
6
6
6
6
6
6
6
6
4
10
6
6
10 h
60
60
60
90
90
15
90
30
15
15
15
15
90
90
–
62
98
98
96
91
94
98
86
98
94
95
98
25
38
Na2CO3
NaOH
NaHCO3
CH3COONa
K2CO3
KOH
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
9
10
11
12
13
14
15
80
Reaction condition: 4-iodotoluene (1 mmol), phenylboronic acid (1.2 mmol), base (2 mmol) and solvent
(2 ml)
aYields refer to those of pure isolated products
Table 2 Optimization of
reaction parameters for Suzuki
reaction of 4-iodotoluene with
phenyl boronic acid catalyzed
by Fe3O4@Pt-based complex
Entry
Base
Solvent
T (°C)
Catalyst (mg)
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
–
Et3N
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
DMSO
DMF
H2O
80
80
80
80
80
80
80
80
100
100
100
60
100
80
80
80
80
6
6
6
6
6
6
6
6
4
8
10
6
6
6
6
6
6
10 h
180
180
180
180
180
180
180
240
120
120
120
120
120
120
120
120
–
15
70
64
38
26
75
60
75
86
92
66
80
45
40
64
70
Na2CO3
NaOH
NaHCO3
CH3COONa
K2CO3
KOH
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
9
10
11
12
13
14
15
16
17
EtOH
Reaction condition: 4-iodotoluene (1 mmol), phenylboronic acid (1.2 mmol), base (2 mmol) and solvent
(2 ml)
aYields refer to those of pure isolated products
1 3

Catalytic Performance Studies of New Pd and Pt Schiff Base Complexes Covalently Immobilized…
Table 3 Suzuki coupling of aryl halides with phenyl boronic acid catalyzed by Fe3O4@Schiff base complex
Pd-catalysta
Time (min)
Pt-catalystb
Time (min)
Entry
Aryl halide
Mp (°C) [Ref]
Yield (%)c
98
Yield (%)c
1
2
3
4
25
10
15
25
100
180
120
60
94
68–70 [30]
98
98
98
80
92
67
49–51 [31]
45–48 [32]
Light yellow liquid [33]
5
6
60
60
95
62
30
60
60
39
88–90 [34]
Colorless oil [35]
7
45
30
70
40
30
91
98
90
94
96
180
160
170
140
100
84
55
58
70
60
68–70 [30]
8
45–47 [32]
9
86–89 [34]
10
11
56–59 [36]
viscous liquid [37]
12
13
40
30
98
57
130
–
82
–
112–114 [32]
96–98 [38]
1 3

G. Rezaei et al.
Table 3 (continued)
Pd-catalysta
Time (min)
Pt-catalystb
Time (min)
Entry
14
Aryl halide
Mp (°C) [Ref]
Yield (%)c
96
Yield (%)c
60
–
–
Colorless liquid [39]
15
16
30
55
52
95
–
–
–
–
49–51 [31]
68–70 [30]
aReaction condition: aryl halides (1 mmol), phenyl boronic acid (1.2 mmol), K2CO3 (2 mmol), Pd-catalyst (6 mg) and PEG (2 ml), 80 °C.
bReaction condition: aryl halides (1 mmol), phenyl boronic acid (1.2 mmol), K2CO3 (2 mmol), Pt-catalyst (10 mg) and PEG (2 ml), 100 °C.
cYields refer to those of pure isolated products
Table 4 Optimization of
reaction parameters for Heck
reaction of iodobenzene with
n-butyl acrylate catalyzed by
Fe3O4@Pd-Schiff base complex
Entry
Base
Solvent
T (°C)
Base (mmol)
Catalyst (mg)
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
Et3N
Na2CO3
NaOH
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
100
100
100
100
100
100
100
80
120
100
100
100
100
2
2
2
2
2
2
2
2
2
2
2
2
2
6
6
6
6
6
6
6
6
6
4
10
16
20
30
30
30
30
30
30
30
30
30
30
30
30
30
91
96
40
90
90
98
40
90
98
92
98
98
98
NaHCO3
CH3COONa
K2CO3
KOH
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
9
10
11
12
13
Reaction condition: iodobenzene (1 mmol), n-butyl acrylate (1.2 mmol), K2CO3 (2 mmol) and solvent
(2 ml)
aYields refer to those of pure isolated products
FeCl3·6H2O (2 mmol) and FeCl2·4H2O (1 mmol) were
concentrated ammonia solution was added quickly to the
mixture in one portion. Stirring was continued for another
30 min. The magnetite precipitates were magnetically
dissolved in 100 ml of deionized water and then the solu-
tion was degassed for 30 min at 70 °C, with vigorous stir-
ring. After being vigorously stirred for 30 min, 10 mL of
1 3

Catalytic Performance Studies of New Pd and Pt Schiff Base Complexes Covalently Immobilized…
Table 5 Optimization of
reaction parameters for Heck
reaction of iodobenzene with
n-butyl acrylate catalyzed by
Fe3O4@Pt-Schiff base complex
Entry
Base
Solvent
T (°C)
Base (mmol)
Catalyst (mg)
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
Et3N
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
DMSO
DMF
120
120
120
120
120
120
120
120
120
120
80
3
3
3
3
3
3
3
2
3
3
3
3
3
2
2
20
20
20
20
20
20
20
20
16
24
20
20
20
20
20
75
75
75
75
75
75
75
75
75
75
75
75
75
75
75
50
25
10
30
10
30
10
10
10
50
45
45
50
22
13
Na2CO3
NaOH
NaHCO3
CH3COONa
K2CO3
KOH
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
9
10
11
12
13
14
15
100
120
120
120
Reaction condition:4-iodoanisole (1 mmol), n-butyl acrylate (1.2 mmol), Et3N (3 mmol) and solvent
(2 ml), 120 °C.
aYields refer to those of pure isolated products
collected, washed several times with deionized water and
3.2 General Procedure for Suzuki Reaction
dried overnight to obtain Fe3O4 nanoparticles.
In order to introduce the amine groups to the surface
of Fe3O4 nanoparticles, 1 g of precipitated magnetite was
dispersed in ethanol (100 ml). Then, 1 mL of 3-aminopro-
pyl (triethoxy) silane (APTES) was added and the result-
ing mixture stirred at 60 °C for 24 h. The precipitate was
magnetically separated, washed several times with etha-
nol and dried under vacuum.
In a typical reaction, an overpressure screw-capped vial
was charged with arylhalides (1 mmol), phenylboronic
acid (1.2 mmol), base, and catalyst and PEG (4 mL). The
reaction mixture was stirred at appropriate temperature.
After completion of the reaction as monitored by thin layer
chromatography (TLC), the reaction mixture was cooled
to room temperature; the catalyst was separated by a per-
manent magnet, washed with water and EtOH, and stored
for the next run. The residual mixture was diluted with
H2O and the organic phase was extracted with dietyl ether
(4 × 15 mL). The extracted organic layers were dried over
Na2SO4, filtered and concentrated under reduced pressure
to get the desired product. These crude products were puri-
fied by recrystallization.
In continuous, for covalent grafting of Schiff base on
Fe3O4 nanoparticles, 1 g of freshly amine functionalized
Fe3O4 nanoparticles were dispersed in 40 mL ethanol
by sonication over 30 min. The resultant mixture was
charged with picolinaldehyde (5 mmol) and refluxed for
24 h. The mixture was cooled and the resulting nanopar-
ticles were magnetically separated, washed with ethanol
and then dried.
1
1,1′-biphenyl: H NMR (400 MHz, CDCl3) δ 7.52 (d,
Finally, 5 mmol of metal salt of K2PdCl4 or K2PtCl4
was added to the solution of dispersed Fe3O4@Schiff base
nanoparticles (1.0 g) in 60 mL ethanol. The resulting mix-
ture was refluxed for 24 h. The magnetic nanocatalyst
was collected by an external magnet, washed with ethanol
and dried.
J = 8.0 Hz, 4H), 7.41 (t, J = 8.0 Hz, 4H), 7.32–7.28 (m,
2H)). 13C NMR (100 MHz, CDCl3) δ 141.5, 128.6, 127.2,
127.3.
2-methyl-1,1′-biphenyl: 1H NMR (400 MHz, CDCl3) δ
7.71–7.60 (m, 1H), 7.55–7.45 (m, 3H), 7.43–7.40 (m, 1H),
7.38–7.36 (m, 1H), 7.34–7.26 (m, 3H), 2.35 (s, 3H). 13C
1 3

G. Rezaei et al.
Table 6 Heck coupling of aryl iodides/bromides with n-butyl acrylate catalyzed by Fe3O4@Schiff base complex
Pd-Catalysta
Time (min)
Pt-Catalystb
Time (min)
Entry
1
Aryl halide
Mp(°C) [Ref]
Yield (%)c
98
Yield (%)c
65
30
60
30
90
45
200
200
200
240
180
Pale yellow liquid [40]
Pale yellow liquid [40]
Pale yellow liquid [40]
Pale yellow liquid
2
3
4
5
98
98
95
95
53
69
62
45
Pale yellow liquid [40]
6
60
70
180
30
Pale yellow liquid [40]
7
180
160
120
120
96
80
47
93
–
–
–
–
–
–
–
–
Pale yellow liquid [40]
Pale yellow liquid [40]
Pale yellow liquid [40]
colorless oil [37]
8
9
10
11
12
70
98
30
–
–
–
–
60–63 [41]
120
yellow oil [42]
1 3

Catalytic Performance Studies of New Pd and Pt Schiff Base Complexes Covalently Immobilized…
Table 6 (continued)
Pd-Catalysta
Time (min)
Pt-Catalystb
Time (min)
Entry
13
Aryl halide
Mp(°C) [Ref]
34–36 [43]
Yield (%)c
51
Yield (%)c
–
40
–
14
90
32
–
–
60–62 [44]
aReaction condition: aryl halides (1 mmol), n-butyl acrylate (1.2 mmol), K2CO3 (2 mmol), Pd-Catalyst (6 mg) and PEG (2 ml), 100 °C.
bReaction condition: aryl halides (1 mmol), n-butyl acrylate (1.2 mmol), Et3N (3 mmol), Pt-Catalyst (20 mg) and PEG (2 ml), 120 °C.
cYields refer to those of pure isolated products
4-methyl-1,1′-biphenyl: 1H NMR (400 MHz, CDCl3) δ
7.81 (d, J = 7.6 Hz, 2H), 7.72 (d, J = 8.0 Hz, 2H), 7.60 (t,
J=7.6 Hz, 2H), 7.54 (t, J=7.20 Hz, 1H), 7.45 (d, J=8.0 Hz,
2H), 2.64 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 141.3,
138.5, 136.2, 128.9, 128.8, 127.3, 126.1, 21.3.
1
4-methoxy-1,1′-biphenyl: H NMR (400 MHz, CDCl3)
δ 7.58–7.51 (m, 4H), 7.43 (t, J = 8.0 Hz, 2H), 7.35–7.28
(m, 1H), 6.99 (d, J = 8.8 Hz, 2H), 3.86 (s, 3H). 13C NMR
(100 MHz, CDCl3) δ 159.2, 140.7, 133.8, 128.7, 128.1,
Fig. 7 Recyclability of Pd and Pt-catalysts in Suzuki model reaction
126.7, 126.6, 114.2, 55.3.
1
4-nitro-1,1′-biphenyl: H NMR (400 MHz, CDCl3) δ
8.3 (d, J = 8.8 Hz, 2H), 7.76 (d, J = 8.4 Hz, 2H), 7.63 (d,
J=8.0 Hz, 2H), 7.50–7.14 (m, 3H). 13C NMR (100 MHz,
CDCl3) δ 147.7, 146.1, 138.8, 129.2, 129.1, 128.0, 127.6,
124.2.
NMR (100 MHz, CDCl3) δ 141.2, 135.1, 130.3, 130.1,
129.3, 129.1, 128.0, 126.8, 126.7, 125.0, 20.3.
2-methoxy-1,1′-biphenyl: 1H NMR (400 MHz, CDCl3) δ
7.49 (d, J=7.2 Hz, 2H), 7.40 (t, J=7.2 Hz, 2H), 7.34–7.27
(m, 3H), 7.07 (d, J=8 Hz, 2H), 7.03 (t, J=7.6 Hz, 2H), 3.78
(s, 3H). 13C NMR (100 MHz, CDCl3) δ 157.3, 139.7, 131.4,
131.2, 130.3, 129.8, 128.9, 127.8, 121.7, 118.2, 112.4, 56.0.
2-phenylnaphthalene: 1H NMR (400 MHz, CDCl3) δ 8.12
(s, 1H), 7.96–7.82 (m, 3H), 7.77–7.72 (m, 3H), 7.50–7.46
(m, 4H), 7.39 (t, J = 7.6 Hz, 1H). 13C NMR (100 MHz,
Table 7 Comparison of the activity of various catalysts in coupling reaction of iodobenzene and phenylboronic acid
Entry
Catalytic system
Solvent/base
T (°C)
Time (min)
Yield (%)
References
1
2
3
4
5
6
7
8
Biopolymer–metal complex wool–Pd
PdNPs@Xylan-type hemicellulose
Ru-MPTAT-1
Fe3O4@PUVS-Pd
γ-Fe2O3-acetamidine-Pd
Fe3O4@PUNP-Pd
H2O/K2CO3
MeOH/ K2CO3
DMF/K2CO3
H2O/K2CO3
DMF/Et3N
D-H2O/K2CO3
PEG/K2CO3
PEG/K2CO3
75
50
80
90
100
90
80
16 h
120
300
60
60
60
90
97
88
97
84
97
98
82
[45]
[46]
[47]
[48]
[49]
[50]
This work
This work
Fe3O4@Pd complex
Fe3O4@Pt complex
40
130
100
1 3

G. Rezaei et al.
Table 8 Comparison of the
activity of various catalysts in
coupling reaction of aryl halide
and n-butyl acrylate
Entry Catalytic system
Solvent/base
T (°C) Time (min) Yield (%) References
1
2
3
4
5
6
7
8
SBA-16 supported Pd-complex DMA:H2O/Na2CO3 125
γ-Fe2O3-acetamidine-Pd
Si–PNHC–Pd
Pd–Fe3O4@Alg
Pd@MIL-101
Bio-Pd(0)
240
60
95
94
95
90
97
97
98
65
[51]
[49]
[52]
DMF/Et3N
NMP/ K2CO3
H2O/Et3N
100
120
85
120
180
120
12 h
30
[53]
[54]
[55]
This work
This work
DMF/Et3N: TBAB 120
DMF/Na2CO3
PEG/K2CO3
PEG/Et3N
80
100
120
Fe3O4@Pd complex
Fe3O4@Pt complex
200
CDCl3) δ 141.2, 138.5, 133.6, 132.6, 128.8, 128.4, 128.2,
127.6, 127.4, 127.3, 126.3, 125.9, 125.8, 125.
131.7, 129.6, 128.0, 117.2, 114.3, 64.3, 30.8, 21.4, 19.2,
13.7.
1
[1,1′-biphenyl]-4-amine: H NMR (400 MHz, CDCl3)
(E)-n-Butyl 3-(4-nitrophenyl)acrylate: 1HNMR
(400 MHz, CDCl3) δ (ppm): 8.20 (d, J = 8.55 Hz, 2H),
7.76–7.64 (m, 3H), 6.55 (d, J = 16.0 Hz, 1H), 4.24 (t,
J=6.3 Hz, 2H), 1.71–1.64 (m, 2H), 1.49–1.42 (m, 2H), 0.95
(t, J=7.7 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 166.1,
148.5, 141.6, 140.6, 128.6, 124.1, 122.6, 64.9, 30.7, 19.1,
13.7.
δ 7.52 (d, J = 8.4 Hz, 2H), 7.47–7.40 (m, 4H), 7.32 (t,
J = 7.6 Hz, 1H), 6.73 (d, J = 8.4 Hz, 2H), 3.71 (br s, 2H).
13C NMR (100 MHz, CDCl3,) δ 145.8, 141.2, 131.5, 128.7,
127.9, 126.4, 126.2, 115.3.
1
[1,1′-biphenyl]-4-carbaldehyde: H NMR (400 MHz,
CDCl3) δ 9.95 (s, 1H), 7.86 (d, J = 8.0 Hz, 2H), 7.64 (d,
J=8.0 Hz, 2H), 7.55 (d, J=8.4 Hz, 2H), 7.38 (t, J=7.2 Hz,
2H), 7.34 (t, J=7.2 Hz, 1H). 13C NMR (100 MHz, CDCl3)
δ 191.4, 147.2, 139.7, 135.2, 126.8, 130.2, 128.9, 128.6,
127.6, 127.3.
4 Conclusions
Considering attention that magnetic noncatalysts have been
received in term of green chemistry as well as industry, new
magnetically recoverable nanocatalysts of Pd and Pt were
synthesized. Fully characterization of the as-prepared mag-
netic nanocatalysts with FT-IR, SEM, XRD, TGA, VSM
and ICP-AES techniques, accurately confirms synthesis,
morphology, thermal stability, nano-size and magnetic
property of them. Pd-based nanocatalysts precede both
Heck and Suzuki C–C coupling reactions with satisfactory
results. While Pt-based nanocatalyst displays catalytic abil-
ity to effect Suzuki reaction. Superiority of being effort-
lessly recoverable by applying an external magnetic force,
the nanocatalysts reused forth runs without any noticeable
deterioration in catalytic activities.
3.3 General Procedure for Heck Reaction
A mixture of arylhalides (1 mmol), n-butyl acrylate
(1.5 mmol), base, the catalyst and PEG (4 mL) was placed
in an overpressure screw-capped vial and stirred at appropri-
ate temperature. After completion of the reaction, which was
checked by TLC, the reaction mixture was cooled to room
temperature. The catalyst was separated by magnetic decan-
tation, washed with water and EtOH to recover the catalyst
for the next run. The residual mixture was diluted with H2O,
followed by extraction with ethyl acetate (4×15 mL). The
combined organic layers were dried over anhydrous Na2SO4,
filtered and concentrated to get the desired product. These
crude products were purified by recrystallization.
1
(E)-n-Butyl cinnamate: H NMR (400 MHz, CDCl3) δ
Acknowledgements The authors appreciatively acknowledge the fund-
7.70 (d, J=16.0 Hz, 1H), 7.53–7.51 (m, 2H), 7.40–7.36 (m,
3H), 6.47 (d, J = 16.05 Hz, 1H), 4.21 (t, J = 6.9 Hz, 2H),
1.72–1.67 (m, 2H), 1.47–1.40 (sextet, J=7.45 Hz, 2H), 0.96
(t, J=7.45 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 167.0,
144.5, 134.5, 130.2, 128.8, 128.02, 118.3, 64.3, 30.8, 19.17,
13.72.
ing support received from the Ilam University, Ilam, Iran, on this work.
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Affiliations
G. Rezaei1 · A. Naghipour1 · A. Fakhri1
1
* A. Naghipour
Department of Chemistry, Faculty of Science, Ilam
Naghipour2002@yahoo.com
University, Ilam, Iran
G. Rezaei
gisarezaie@gmail.com
A. Fakhri
akram_fakhri2007@yahoo.com
1 3