Palladium schiff base complex immobilized on magnetic nanoparticles: An efficient and recyclable catalyst for Mizoroki and Matsuda-Heck coupling

Article abstract of DOI:10.1016/j.tetlet.2020.151801

The present work elucidates the catalytic efficiency of palladium Schiff base complex immobilized on amine functionalized magnetic nanoparticles for Heck coupling of structurally different aryl halide/arenediazonium tetrafluoroborate with styrene/acrylate/acrylonitrile. Matsuda-Heck coupling proceeds in aqueous media at room temperature whereas Mizoroki-Heck coupling was carried out at 80 °C. Both reactions were successfully furnished with low catalyst loading. The catalyst was easily separated from reaction mixture and reused up to six times without significant loss of catalytic activity.

Full text of DOI:10.1016/j.tetlet.2020.151801

Tetrahedron Letters xxx (xxxx) xxx
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Palladium schiff base complex immobilized on magnetic nanoparticles:
An efficient and recyclable catalyst for Mizoroki and Matsuda-Heck
coupling
Sandip P. Vibhute a, Pradeep M. Mhaldar a, Rajendra V. Shejwal b, Gajanan S. Rashinkar a,
Dattaprasad M. Pore a,
⇑
a Department of Chemistry, Shivaji University, Kolhapur 416004, India
b Lal Bahadur Shastri College of Arts, Science and Commerce, Satara, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The present work elucidates the catalytic efficiency of palladium Schiff base complex immobilized on
amine functionalized magnetic nanoparticles for Heck coupling of structurally different aryl halide/
arenediazonium tetrafluoroborate with styrene/acrylate/acrylonitrile. Matsuda-Heck coupling proceeds
in aqueous media at room temperature whereas Mizoroki-Heck coupling was carried out at 80 °C.
Both reactions were successfully furnished with low catalyst loading. The catalyst was easily separated
from reaction mixture and reused up to six times without significant loss of catalytic activity.
Ó 2020 Published by Elsevier Ltd.
Received 25 January 2020
Revised 24 February 2020
Accepted 2 March 2020
Available online xxxx
Keywords:
Coupling reaction
Nanocatalyst
Heck
Recyclable
Introduction
Over the decades, various homogeneous catalytic systems, with
special ligands have been used for Heck coupling [7]. However,
Palladium catalyzed Heck cross-coupling represent versatile
tool for the carbon–carbon bond formation [1–3]. Heck cross-cou-
pling has witnessed a widespread applications in organic synthesis
and pharmaceuticals over last two decades and recognized the
nobel prize to Heck, Suzuki and Nigeshi in 2010. Depending upon
the coupling partner of alkenes with aryl halides or arenediazo-
nium salts, two types of Heck coupling viz Mizoroki-Heck and Mat-
suda-Heck coupling exist. These are well established reactions
useful in modern organic synthesis. Heck coupling plays a pivotal
role in organic synthesis and has great industrial potential for
the syntheses of fine chemicals, natural products, bioactive com-
pounds, and advanced materials [4]. Heck coupling is catalyzed
by Pd, and ligand as co-catalyst in basic conditions. The nature of
ligand has an influence on the stability and efficiency of Pd cata-
lyst. If ligand is not coordinated to the Pd, the process becomes
costly, retains toxic ligand and its derivatives, thus causing the sep-
aration of products complicated [5]. In light of these facts scientists
are engaged in development of either ligand-free methods or
methods involving reusable co-ordinated ligand Pd complex for
Heck coupling [6].
most of them suffer from drawbacks such as high ligand sensitivity
towards air and moisture, tedious multistep synthesis, high cost of
the ligand and use of various additives and harmful organic sol-
vents. Because of the high cost of Pd, its recycling and recovery
has became more necessary. To circumvent these problems, a vari-
ety of inorganic and organic solid-supported catalytic systems
have been developed [8–10]. However, compared with their homo-
geneous counterparts, the solid-supported catalysts often suffer
from lower activity and selectivity [11,12]. Thus, it is highly desir-
able to develop new heterogeneous catalytic systems comparable
to homogeneous catalysts in catalytic performance. Recently, our
group has designed magnetically separable catalyst, Pd-AcAc-
Am-Fe3O4@SiO2 (Fig. 1) and explored its catalytic activity in
Suzuki-Miyaura cross coupling [13].
In continuation with our research interest in coupling reactions
[14–18] and Pd-AcAc-Am-Fe3O4@SiO2, herein we explored cat-
alytic efficiency of Pd-AcAc-Am-Fe3O4@SiO2 for the Mizoroki as
well as Matsuda-Heck coupling.
Result and discussion
⇑
Initially, we have focused our attention on standardization of
the procedure for Mizoroki-Heck coupling of bromobenzene and
Corresponding author.
E-mail address: p_dattaprasad@rediffmail.com (D.M. Pore).
https://doi.org/10.1016/j.tetlet.2020.151801
0040-4039/Ó 2020 Published by Elsevier Ltd.
Please cite this article as: S. P. Vibhute, P. M. Mhaldar, R. V. Shejwal et al., Palladium schiff base complex immobilized on magnetic nanoparticles: An effi-
cient and recyclable catalyst for Mizoroki and Matsuda-Heck coupling, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2020.151801

2
S.P. Vibhute et al. / Tetrahedron Letters xxx (xxxx) xxx
(Scheme 1). The trans-products were selectively obtained in all
cases. The results exhibited that the above catalytic system is
remarkably active and tolerates a range of functional groups. It
was observed that the reactions of aryl iodides with terminal ole-
fins, proceeds smoothly compared to aryl bromides and chlorides
due to the lower bond energy of C-I in comparison with C-Br and
C-Cl. The reaction of chlorobenzene with butyl acrylate, styrene
and acrylonitrile afforded the product in lower yield than the
iodobenzene (Table 2, entries 3e, 3j & 3p). The reaction of aryl
halides bearing electron withdrawing groups such as -NO2, -
COCH3, and -CN are faster than those with electron-donating
groups such as -CH3 and -OCH3. Also, the Heck coupling of steri-
cally hindered 1-iodonaphthalene afforded a good yield of the cor-
responding product (Table 2, entry 3k).
Changing the quantity from 1 equiv. to 1.5 equiv. of diazonium
salt has no remarkable change in the yield of cross coupling pro-
duct (Table 3, entry 8). Furthermore, amount of non-ionic surfac-
tant, Triton X-100 was varied from 1 mol % to 10 mol % and
observed that, 5 mol % of the surfactant gives better yield of the
product (Table 3, entry 8). Therefore, a solution of arenediazonium
salt in water was allowed to react with 1.2 equiv. of butyl acrylate,
5 mol % of surfactant, Triton X-100 in the presence of 20 mg
(0.2 mol % Pd) of catalyst at room temperature and obtained 98%
yield (Table 3, entry 10) of Matsuda-Heck coupling.
To evaluate the scope of the protocol, we applied these opti-
mum conditions to screen different olefins and arenediazonium
tetrafluoroborate salts (Scheme 2). The results are summarized in
Table 4. We have studied the coupling of styrene with arenediazo-
nium salts under the optimized reaction conditions. Due to the
poor reactivity of the styrene substrate, the moderate yields of
the products were obtained (Table 4, entries 6a–6e). In all cases,
the coupling between arenediazonium tetrafluoroborate salts
bearing electron donating as well as electron withdrawing groups
with acrylate substrates, proceeded smoothly to afford the corre-
sponding products in 92–98% yield (Table 4, entries 6f–6m). How-
ever, high yields were obtained for the arenediazonium salts,
bearing strong electron withdrawing groups with acrylonitrile
(Table 4, entry 6p).
Fig. 1. Catalyst: Pd-AcAc-Am-Fe3O4@SiO2.
styrene as model reaction to evaluate the influence of solvent, base
and amount of catalyst. The results are summarized in Table 1.
When the reaction was performed in the absence of the catalyst,
no product was detected. However, when the reaction was per-
formed with Pd-AcAc-Am-Fe3O4@SiO2 in DMF (Table 1, entry 3),
the product was obtained in 82% yield after 5 h, which indicates
that palladium plays a crucial role of catalyst in the Mizoroki-Heck
coupling.
It was also observed that the yield of product improved to 92%
in presence of DMF solvent and triethylamine (TEA) as a base
(Table 1, entry 6). The acid formed in the reaction gets neutralized
with triethyl amine forming a highly hydrophobic quaternary salt
and this step is essential for breaking the activated complex, lead-
ing to product formation which generates again the catalytic spe-
cies for fresh reactant. The amount of catalyst was also varied
and we observed that even though with increasing the amount of
catalyst to 0.5 mol %, no significant change in the yield or reaction
time was found (Table 1, entry 8), while decreasing the amount of
catalyst (0.2 mol %) reduced the yield of product to 88% (Table 1,
entry 10). The reaction was conducted with various bases such as
NaOH, K2CO3, and TEA. Among them, TEA exhibited the best result.
Moreover, with the aim of checking the influence of solvent and
temperature on the reaction yield, various organic solvents such
as CH3CN, EtOH, toluene, and DMSO were examined at wide range
of temperature 25–120 °C. Gratifyingly, it is found that the entry 9
of Table 1 is the best conditions for Pd-AcAc-Am-Fe3O4@SiO2 cat-
alyzed Mizoroki-Heck coupling.
A plausible mechanism for the Pd-AcAc-Am-Fe3O4@SiO2 cat-
alyzed Mizoroki–Heck and Matsuda-Heck cross-couplings is pro-
posed in Scheme 3. The mechanism begins with the reduction of
Pd(II) to the active Pd(0) species in the presence of alkene. Then,
oxidative addition of the CAX bond of an aryl halide (X = I, Br or
In order to check the catalytic activity of Pd-AcAc-Am-Fe3O4@-
SiO2 towards other reactants under optimized conditions, various
types of iodo-, bromo-, and chloroaryl derivatives with electron-
donating and electron-withdrawing groups were coupled with dif-
ferent vinylic substrates like acrylates, styrene and acrylonitrile
–N+2BF-4) to the palladium atom generates the
intermediate (A). In the next step, Pd (II) forms a
r
-arylpalladium
-complex
p
Table 1
Effect of solvents, base and amount of catalyst on Mizoroki-Heck coupling.a
Entry
Solvent
Base
Amount of Catalyst (Mol % Pd)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
10
Water
Water
DMF
DMF
DMF
DMF
DMF: Water
DMF
DMF
DMF
NaOH
K2CO3
NaOH
K2CO3
K2CO3
TEA
TEA
TEA
TEA
TEA
–
12
12
5
5
4
4
5
4
4
NR
Trace
82
86
86
92
72
92
92
0.4
0.4
0.4
0.4
0.4
0.4
0.5
0.3
0.2
4
88
a
Reaction conditions: Bromobenzene (1 mmol), styrene (1.1 mmol), base (2 mmol), temp. = 80 °C, solvent = DMF 5 mL; bIsolated yield.
Please cite this article as: S. P. Vibhute, P. M. Mhaldar, R. V. Shejwal et al., Palladium schiff base complex immobilized on magnetic nanoparticles: An effi-
cient and recyclable catalyst for Mizoroki and Matsuda-Heck coupling, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2020.151801

S.P. Vibhute et al. / Tetrahedron Letters xxx (xxxx) xxx
3
Scheme 1. Mizoroki-Heck coupling of different aryl halides with alkenes.
Table 2
Pd-AcAc-Am-Fe3O4@SiO2 catalyzed Mizoroki-Heck coupling.
Reaction conditions: Aryl halide (1 mmol), alkene (1.1 mmol), Pd-AcAc-Am-Fe3O4@SiO2 (0.3 mol % Pd), triethylamine (2 mmol), temp. = 80 °C solvent = DMF (5 mL). Yields are
isolated.
followed by the migratory insertion of acrylate, results in the for-
mation of palladium–carbon bond via a syn-addition, which gives
complex (B). In the last step, cycle completed with formation of
coupling product by b-hydride elimination and regeneration of
Pd (0) occurs via reductive elimination of Pd (II).
The reusability of the catalyst was investigated for both Mizor-
oki-Heck and Matsuda-Heck coupling. (Fig. 2) After the first cycle
of the reaction, nanocatalyst was recovered with help of an exter-
nal magnet and then washed thoroughly with ethyl acetate
(2 Â 10 mL) and ether. The recovered nanocatalyst was dried under
vacuum at 50 °C. Then, model reaction of Mizoroki-Heck and Mat-
suda-Heck was carried out under optimized reaction conditions.
The results indicated that, at the end of six successive runs, there
is no significant loss in the catalytic activity of the catalyst.
The high catalytic efficiency of the Pd-AcAc-Am-Fe3O4@SiO2 for
Mizoroki-Heck coupling elucidated by comparison study with dif-
ferent catalysts from the literature (Table 5). The heterogenized Pd/
MnBDC in DMF offered heck product at very high reaction time
(Table 5, entry 1). Some of the Pd catalytic systems were furnished
at very high temperature (120 °C) (Table 5, entries 2–6). Ferrite
supported Schiff base immobilized palladium (Fe3O4@Schiff-base-
Pd) catalyzed heck reaction at 100 °C resulted in 3 h with low yield
(Table 5, entry 7). Overall Pd-AcAc-Am-Fe3O4@SiO2 is found to be
catalyst of choice in terms of stability, non-toxicity, low loading
of Pd in DMF in 3 h with very high yield (Table 5, entry 9).
We examined the Matsuda-Heck Coupling in the presence of
several homogeneous and heterogeneous catalysts in comparison
with Pd-AcAc-Am-Fe3O4@SiO2 (Table 6). The catalytic system
Please cite this article as: S. P. Vibhute, P. M. Mhaldar, R. V. Shejwal et al., Palladium schiff base complex immobilized on magnetic nanoparticles: An effi-
cient and recyclable catalyst for Mizoroki and Matsuda-Heck coupling, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2020.151801

4
S.P. Vibhute et al. / Tetrahedron Letters xxx (xxxx) xxx
Table 3
Effect of solvents, amount of surfactant and catalyst on Matsuda-Heck coupling.a
Entry
Solvent
Equiv. of salt
Triton X-100 (mol %)
Amount of catalyst (Mol % Pd)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
DMF
Ethanol
H2O
THF
CH3CN
H2O
H2O
H2O
H2O
H2O
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.5
1.2
1.2
1.2
10
10
10
10
10
1
5
5
5
5
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.5
0.3
0.2
0.1
2
82
95
98
62
85
89
98
98c
98
98
91
12
0.5
5
4
4
0.5
1.0
0.5
0.5
2.0
9
10
11
H2O
5
a
b
c
Reaction conditions: Benzenediazodium salt (1.2 mmol), butyl acrylate (1 mmol), temp = r.t, solvent = 3 mL.
Isolated yield.
temp. 50 °C.
Scheme 2. Matsuda-Heck coupling of different arenediazonium salt with alkenes under the optimized conditions.
Please cite this article as: S. P. Vibhute, P. M. Mhaldar, R. V. Shejwal et al., Palladium schiff base complex immobilized on magnetic nanoparticles: An effi-
cient and recyclable catalyst for Mizoroki and Matsuda-Heck coupling, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2020.151801

S.P. Vibhute et al. / Tetrahedron Letters xxx (xxxx) xxx
5
Table 4
Pd-AcAc-Am-Fe3O4@SiO2 catalyzed Matsuda-Heck coupling.
Reaction conditions: arenediazonium salt (1 mmol), olefin/acrylate/acrylonitrile (1.2 mmol), Catalyst (0.2 mol % Pd), Triton X-100 (5.0 mol %), H2O (3 mL). Yields are isolated.
Scheme 3. Plausible mechanism for Heck cross coupling.
in organic solvent with 1 mol% of Pd loading (Table 6, entries 2
& 4). The Pd(OAc)2 homogeneously catalyzed heck coupling in
ionic liquid as solvent and water with Triton X-100 furnished
high yield but with high loading of Pd (Table 6, entries 3 & 5).
From this study it reveals that the catalyst, Pd-AcAc-Am-Fe3O4@-
SiO2 in comparison with reported catalyst is superior with marks
of eco-friendly reaction conditions and high yield in short reac-
tion time (Table 6, entry 6).
Conclusion
In summary, we have disclosed modified protocol for Heck cou-
pling. The experimental procedure is simple, avoided the use of
organic solvents for Matsuda-Heck coupling which is in agreement
with green chemistry principles, utilization of an inexpensive and
readily available catalyst, good reactivity to generate the corre-
sponding products in good to excellent yields for all reactions are
the advantages of the present method. In addition, the catalyst
was easily separable from the reaction mixture by external magnet
and can be reused for six runs without any significant loss of sta-
bility and activity.
Fig. 2. Reusability of Pd-AcAc-Am-Fe3O4@SiO2.
Agarose supported nano Pd comprised good yield at optimum
reaction conditions, but accompanied with more reaction time
(Table 6, entry 1). In some reports, the reaction was carried out
Please cite this article as: S. P. Vibhute, P. M. Mhaldar, R. V. Shejwal et al., Palladium schiff base complex immobilized on magnetic nanoparticles: An effi-
cient and recyclable catalyst for Mizoroki and Matsuda-Heck coupling, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2020.151801

6
S.P. Vibhute et al. / Tetrahedron Letters xxx (xxxx) xxx
Table 5
Comparison of the present methodology with other reported catalysts for the Mizoroki-Heck Coupling.
Entry [Ref.]
Catalyst
Reaction conditions
Time (h)
Yield (%)a
TONb
TOFc (hÀ1
)
1 [19]
2 [20]
3 [21]
4 [22]
5 [23]
6 [24]
7 [25]
8 [26]
Pd/MnBDC
PFG-Pd
Schiff-base-Pd@MNPs
Pd-Py- MCM-41
Palladium(II) + SBA-16
Fe3O4@MCM-41@Pd-SPATB
Fe3O4@Schiff-base-Pd
Fe3O4@SiO2–TCT–PVA–Pd(0)
Pd-AcAc-Am-Fe3O4@SiO2
Et3N, DMF, 90 °C, 0.12 mol% Pd
K2CO3, DMF, 120 °C, 1.7 mol% Pd
K2CO3, DMF, 120 °C, 2.62 mol% Pd
K2CO3, DMF, 120 °C, 3.12 mol% Pd
K2CO3, DMF, 80 °C, 1 mol% Pd
K2CO3, PEG, 120 °C 0.94 mol % Pd
Cs2CO3, H2O, 100 °C, 0.3 mol % Pd
Piperidine, reflux, 0.25 mol % Pd
TEA, DMF, 80 °C, 0.3 mol% Pd
9–12
3
6
4
1
0.5
3
6
4
88
90
97
94
98
92
76
94
96
880
53
37
30
98
73
18
6
7.5
98
196
84
63
40
98
253
376
320
9 [This Work]
aIsolated yield, bTON = mol product/mol cat, cTOF = TON/reaction time (hÀ1).
Table 6
Comparison of the present methodology with other reported catalysts for the Matsuda-Heck Coupling.
Entry [Ref.]
Catalyst
Reaction conditions
Time (h)
Yield (%)a
TONb
TOFc (hÀ1
)
1 [27]
2 [28]
3 [29]
4 [30]
5 [16]
6 [This work]
Agarose supported nano Pd
PS-NHC-Pd(II)
Pd(OAc)2
Pd/Al2O3
Pd(OAc)2
H2O, 40 °C, 0.26 mol % Pd
EtOH, r.t., 0.9 mol% Pd
BMIMBF6, 70–80 °C, 10–20 mol % Pd(OAc)2
MeOH, 25 °C, 1 mol% Pd
H2O, Triton x-100, r.t. 2 mol % Pd(OAc)2
3
1
6.5
0.5
1
83
94
88
95
100
98
319
104
–
–
–
106
104
–
–
–
Pd-AcAc-Am-Fe3O4@SiO2
H2O, Triton X-100, r.t., 0.2 mol% Pd
0.5
490
980
a
b
c
Isolated yield.
TON = mol product/mol cat.
TOF = TON/reaction time (hÀ1).
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2065–2076.
Acknowledgement
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One of the authors DMP grateful to acknowledge, Shivaji
University, Kolhapur for Financial Assistance through Research
Strengthening Scheme. [SU/C&U.D.Section/89/1386]. Author SPV
also grateful to acknowledge Atpadi Education Society’s Shrimant
Babasaheb Deshmukh Mahhavidyalaya, Atpadi for their co-opera-
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Appendix A. Supplementary data
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Supplementary data to this article can be found online at
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Please cite this article as: S. P. Vibhute, P. M. Mhaldar, R. V. Shejwal et al., Palladium schiff base complex immobilized on magnetic nanoparticles: An effi-
cient and recyclable catalyst for Mizoroki and Matsuda-Heck coupling, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2020.151801