Highly effective cellulose supported 2-aminopyridine palladium complex (Pd(II)-AMP-Cell?Al2O3) for Suzuki-Miyaura and Mizoroki–Heck cross-coupling

Article abstract of DOI:10.1016/j.reactfunctpolym.2020.104586

In the present work, a novel, highly efficient, retrievable organo–inorganic hybrid heterogeneous catalyst (Pd(II)-AMP-Cell?Al₂O₃) has been prepared by covalent grafting of 2-aminopyridine on chloropropyl modified cellulose-alumina composite followed by complexation with palladium acetate. The catalyst was characterized by techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), inductive coupled plasma-atomic emission spectroscopy (ICP-AES) and thermo gravimetric analysis (TGA). The catalyst has been successfully employed in Suzuki-Miyaura as well as Mizoroki–Heck cross-coupling reactions. The reactions proceed smoothly resulting in the high yields of cross-coupling products (81 to 95%) within short reaction times. The catalyst can be efficiently recovered by simple filtration and reused for multiple cycles without considerable loss in the catalytic activity. The key-features of the present protocol include mild reaction conditions, simple work-up procedure, high stability of the catalyst, high turnover number (TON) and frequency (TOF), ease recovery and reusability of the catalyst.

Full text of DOI:10.1016/j.reactfunctpolym.2020.104586

ReactiveandFunctionalPolymers152(2020)104586
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Reactive and Functional Polymers
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Perspective Article
Highly effective cellulose supported 2-aminopyridine palladium complex
(Pd(II)-AMP-Cell@Al2O3) for Suzuki-Miyaura and Mizoroki–Heck cross-
coupling
Pradeep Mhaldar, Sandip Vibhute, Gajanan Rashinkar, Dattaprasad Pore⁎
Department of Chemistry, Shivaji University, Kolhapur, Maharashtra 416 004, India
A B S T R A C T
In the present work, a novel, highly efficient, retrievable organo–inorganic hybrid heterogeneous catalyst (Pd(II)-AMP-Cell@Al2O3) has been prepared by covalent
grafting of 2-aminopyridine on chloropropyl modified cellulose-alumina composite followed by complexation with palladium acetate. The catalyst was characterized
by techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction
(XRD), inductive coupled plasma-atomic emission spectroscopy (ICP-AES) and thermo gravimetric analysis (TGA). The catalyst has been successfully employed in
Suzuki-Miyaura as well as Mizoroki–Heck cross-coupling reactions. The reactions proceed smoothly resulting in the high yields of cross-coupling products (81 to
95%) within short reaction times. The catalyst can be efficiently recovered by simple filtration and reused for multiple cycles without considerable loss in the
catalytic activity. The key-features of the present protocol include mild reaction conditions, simple work-up procedure, high stability of the catalyst, high turnover
number (TON) and frequency (TOF), ease recovery and reusability of the catalyst.
1. Introduction
renewable natural feedstocks on the earth. It is a linear polymer made
up of repeating units of β-D-glucose linked by 1,4-glycosidic bonds. It
has an unusual structure in which every other glucose monomer is
flipped over and packed tightly as extended long chains. This confers
rigidity and high tensile strength to cellulose. Furthermore, multiple H-
bonding between the individual chains makes cellulose insoluble in
aqueous as well as most of the other commonly employed solvents [12].
In addition, the hydroxyl groups in cellulose are potentially accessible
for grafting thereby allowing facile introduction of suitable functional
groups in its matrix. These unusual properties have made cellulose a
carbon neutral, non-petroleum based and biodegradable support in the
preparation of heterogenous catalysts. A plethora of reports concerning
successful applications of cellulose supported catalysts such as CELL-Pd
(0) [13], CELL-Cu(0) [14], CEL-Ru [15], HBimCl-M/HCMC [16]
mediated organic transformations are reported. Amongst various cel-
lulose supported catalysts, modified cellulose–aluminum oxide com-
posite [Cell/Al2O3] in which aluminum oxide is highly dispersed on the
cellulose surface represents versatile composite for the preparation of
cellulose supported catalysts [17]. In this composite, surface Al-OH
groups can be easily modified with linker groups that allow further
surface-modification with suitable organic functionalities [18]. The
modified cellulose‑aluminum oxide composite hybridized with palla-
dium has been employed as superior catalysts for heterocyclic synthesis
and coupling reactions [19,20]. Furthermore, in recent years, many
cellulose supported Pd based systems have been reported for diverse
Cross-coupling reactions constitute an indispensable toolkit for CeC
bond formation and are one of the most focused areas of organic
chemistry owing to their importance in the synthesis of complex mo-
lecules. Amongst various cross-coupling reactions, the palladium-cata-
lyzed Suzuki-Miyaura and Mizoroki-Heck cross-couplings have became
extremely powerful synthetic tools for the synthesis of biaryls and
olefination of aryl halides, respectively. The resulting coupling products
comprise a wide range of natural products, agrochemicals, organic
polymers, pharmaceuticals, and advanced materials [1–3]. Owing to
their ability of rapidly assembling molecular complexity, a large
number of transition metal nanoparticles and transition metal sup-
ported catalysts have been developed for Suzuki-Miyaura, Mizoroki-
Heck as well as other cross-coupling reactions [4–7]. A versatile class of
catalysts for cross-coupling reactions are palladium metal immobilized
on various traditional supports such as polymers [8], resins [9], acti-
vated carbon, ferrites, silicates [10], carbon nanotubes [11] and dif-
ferent inorganic materials. However, from the green chemistry per-
spectives, a heterogenous catalyst consisting of palladium supported on
renewable feedstock-based support would be valuable addendum in the
area of heterogenous catalysis.
Green chemistry necessitates a paradigm shift from traditional
supports to renewable feedstock-based supports in the preparation of
heterogenous catalysts. Cellulose represents one of the most abundant
⁎ Corresponding author.
E-mail address: p_dattaprasad@rediffmail.com (D. Pore).
https://doi.org/10.1016/j.reactfunctpolym.2020.104586
Received 3 February 2020; Received in revised form 30 March 2020; Accepted 3 April 2020
Availableonline07April2020
1381-5148/©2020PublishedbyElsevierB.V.

P. Mhaldar, et al.
ReactiveandFunctionalPolymers152(2020)104586
CeC bond formation reactions. The amine-functionalized cellulose
supported catalyst (CL-DETA-Pd) was prepared by Dong et al. and
employed in Suzuki-Miyaura cross coupling [21]. The same research
group performed Suzuki coupling using a multi-functional cellulose
supported Pd(II)-Schiff base complex acronymed as CNC-APTES-IS-Pd.
[22] Cellulose nanocrystals mounted Pd (II) Schiff base catalyst, CNC-
APTES-IS-Pd was developed by Seyednejhad et al. and employed for
CeC bond formation via Ullmann and Suzuki cross-couplings [23].
Kumbhar et al. reported a cellulose–aluminum oxide composite mod-
ified organofunctionalized Pd catalyst for Suzuki-Miyaura cross cou-
pling. The careful scrutiny of the majority of the reported cellulose
supported Pd based catalysts involve direct coordination of palladium
with cellulose which is relatively weak in nature thereby causing
leaching of metal leading to catalyst deactivation. In addition, many
reports are influenced by high reaction temperature, harmful solvents,
long reaction time, and comparatively low yields. To overcome these
shortcomings, it is highly necessary to develop a robust and efficient
cellulose supported Pd based catalyst for achieving cross-coupling re-
actions under truly heterogeneous conditions.
give Cell@Al2O3 composite as a white precipitate.
2.3.2. Preparation of chloropropyl-Cell@Al2O3
A mixture of Cell@Al2O3 composite (10 g) and 3- chloropropyl-
triethoxysilane (9.40 g, 40 mmol) in toluene (25 mL) was refluxed for
24 h. The resultant mixture was filtered, washed with toluene and fi-
nally dried in oven at 60 °C to afford chloropropyl-Cell@Al2O3.
2.3.3. Preparation of 2-aminopyridine immobilized on functionalized
Cell@Al2O3viz AMP-Cell@Al2O3
Chloropropyl-Cell@Al2O3 (0.5 g) was treated with 2-aminopyridine
(5 mmol) in dioxane (10 mL) under reflux conditions for 48 h. The
resultant mixture was filtered, washed with dioxane (3 × 5 mL),
chloroform (3 × 5 mL) and dried in oven at 65 °C for 8 h to afford 2-
aminopyridine immobilized on Cell@Al2O3 acronymed as AMP-
Cell@Al2O3.
2.3.4. Preparation of Pd-AMP- Cell@Al2O3
A mixture of AMP-Cell@Al2O3 (1 g) and palladium acetate (0.1 g) in
acetic acid (10 mL) was heated at 80 °C for 10 h to generate cellulose
supported 2-aminopyridine palladium complex acronymed as Pd(II)-
AMP-Cell@Al2O3.
In continuation with our efforts to develop heterogeneous catalysts
for CeC bond formation [24–27], herein we report an efficient method
for Suzuki-Miyaura as well as Mizoroki-Heck cross-coupling catalyzed
by the hybrid cellulose–aluminum oxide supported palladium compo-
site [Pd(II)-AMP-Cell@Al2O3].
2.4. General procedure for Suzuki–Miyaura cross-coupling
2. Experimental
A round bottom flask (50 mL) equipped with condenser was charged
with aryl halide (1.0 mmol), arylboronic acid (1.2 mmol), K2CO3
(2 mmol), Pd(II)-AMP-Cell@Al2O3 (40 mg) and dimethyl formamide
(DMF) (5 mL). The mixture was stirred in an oil bath at 80 °C. Upon
completion of the reaction as monitored by thin layer chromatography
(TLC) (petroleum ether:ethyl acetate, 95:0.5), the reaction mixture was
filtered. The filtrate was extracted with ethyl acetate (3 × 5 mL). The
combined organic layers were collected, dried over anhydrous Na2SO4,
and concentrated in vacuum to afford the crude products. These pro-
ducts were purified by silica gel column chromatography (Ether /
EtOAc = 9:1 v/v).
2.1. General
Melting points were determined in an open capillary and are un-
corrected. All reactions were carried out under aerobic conditions in
dried glassware's. Infrared spectra were measured with a Perkin-Elmer
Fourier-transform infrared spectrophotometer (FTIR). 1H and 13C NMR
spectra were recorded on a Brucker AV 400 (400 MHz for 1H and
100 MHz for 13C NMR) spectrometer using CDCl3 as solvent and tet-
ramethylsilane (TMS) as an internal standard. Chemical shifts (δ) are
expressed as parts per million (ppm) values and coupling constants are
expressed in hertz (Hz). The thermal gravimetric analysis (TGA) curve
was obtained on the instrument, TA SDT Q600 in the presence of static
air at a linear heating rate of 10 °C/min from 25 °C to 600 °C. XRD
pattern was taken by using Ultima IV, Rigaku Corporation. SEM was
done using HITACHI S-4800. EDX analysis was done on JSF-7600F.
TEM was analyzed on PHILIPS CM 200. Inductively coupled plasma
atomic emission spectroscopy (ICP-AES) was carried on ARCOS,
Simultaneous ICP Spectrometer. All chemicals were obtained from local
suppliers and used without further purification.
2.5. General procedure for Mizoroki-Heck cross-coupling
To a mixture of aryl halide (1 mmol), olefin (1.2 mmol) and trie-
thylamine (3 mmol) in DMF (5 mL), Pd(II)-AMP-Cell@Al2O3 (40 mg)
was added and reaction mixture was stirred at 100 °C. The reaction
progress was monitored by TLC (petroleum ether–ethyl acetate, 9:1).
Upon completion of reaction as monitoted by TLC, the reaction mixture
was filtered, catalyst was washed with water (3 × 5 mL) and filtrate
was extracted with ethyl acetate (3 × 5 mL). The combined organic
layers were collected, dried over anhydrous Na2SO4 and concentrated
to afford crude products. These products were purified by column
chromatography [petroleum ether/ethyl acetate (9:1) v/v].
2.2. Material
Microcrystalline cellulose (Thomas Baker, Degree of polymerization
≤350), Aluminum chloride hexahydrate (Al2Cl3.6H2O) (Thomas
Baker), 3-chloropropyl)triethoxysilane (Alfa Aesar), 2-aminopyridine
(Spectrochem), dioxane (Thomas Baker), palladium (II) acetate (Sigma
Aldrich), all other reagents and solvents were commercially obtained
and used without further purification.
2.6. Recycling and reusability of Pd(II)-AMP-Cell@Al2O3
After completion of the model reaction, insoluble catalyst was re-
covered by simple filtration and washed with water(3 × 5 mL) and
acetone (3 × 5 mL). The catalyst was dried in oven at 60 °C and reused
for the next cycle. The reusability of the Pd(II)-AMP-Cell@Al2O3 was
examined up to five cycles for both Suzuki-Miyaura and Mizoroki-Heck
couplings under optimal reaction conditions.
2.3. Preparation of of cellulose supported 2-aminopyridine palladium
complex (Pd(II)-AMP-Cell@Al2O3)
2.3.1. Preparation of cellulose aluminum oxide composite (Cell@Al2O3)
The Cell@Al2O3 composite was synthesized according to procedure
in literature [32,33]. About 15 g of Aluminium chloride hexahydrate
(Thomas Baker) and 15 g of microcrystalline cellulose (Thomas Baker)
were dissolved in 200 mL of water and the mixture was stirred for 24 h.
The mixture was filtered and the solid obtained was exposed to am-
monia gas, washed with distilled water and dried at 80 °C overnight to
3. Results and discussion
Our initial studies were focused on the preparation of cellulose
supported 2-aminopyridine palladium complex (Scheme 1). Initially,
Al2O3 was finely dispersed on the cellulose with the aid of AlCl3.6H2O
in aqueous solution to afford cellulose-alumina composite acronymed
as Cell@Al2O3. The Al-OH group of synthesized Cell@Al2O3 have
2

P. Mhaldar, et al.
ReactiveandFunctionalPolymers152(2020)104586
Scheme 1. Preparation of Pd(II)-AMP-Cell@Al2O3
inherent ability to form a stable Al-O-Si bonds with Si-OR groups of
diverse coupling reagents. Thus, we prepared chloropropyl-Cell@Al2O3
by treating Cell@Al2O3 and 3-chloropropyltriethoxysilane. Further,
reaction of chloropropyl-Cell@Al2O3 with 2-aminopyridine afforded
AMP-Cell@Al2O3 with good degree of organofunctionalization. Finally,
the complexation of AMP-Cell@Al2O3 with palladium (II) acetate af-
forded the desired cellulose supported 2-aminopyridine palladium
complex acronymed as Pd(II)-AMP-Cell@Al2O3.
However, the decrease in the intensity of the reflections of cellulosic
phase after loading of Al2O3 and Pd reveals the amorphous materials
which are present over the surface of cellulose interfering the diffrac-
tion phenomenon (Fig. 1).
The morphological characteristics of Pd(II)-AMP-Cell@Al2O3 have
been studied with various surface analysis techniques such as scanning
electron microscopy (SEM) and tunneling electron microscopy (TEM).
The SEM image of microcrystalline cellulose demonstrated rough and
irregular rock like morphology (Fig. 2a) whereas an appraisal of the
SEM images of Pd(II)-AMP-Cell@Al2O3 displayed smooth flakes for-
mation. The transition in morphology from rough and irregular rock to
smooth flakes demonstrated successful grafting of Al2O3 on cellulose
which provides surface area for Pd deposition (Fig. 2a-c). TEM micro-
graphs revealed the smooth flakes morphology, which is in good
agreement with SEM analysis. TEM images disclosed the uniform dis-
persion of Pd nanoparticles in the cellulose matrix. The spherical Pd
nanoparticles exhibit dimensions from 8 to 11 nm (Fig. 3d-e). (For in-
terpretation of the references to color in this figure, the reader is re-
ferred to the web version of this article.)
The catalyst, Pd(II)-AMP-Cell@Al2O3 was characterized by various
analytical techniques.
The XRD analysis of Pd(II)-AMP-Cell@Al2O3 was carried out. The
overlay of powder XRD patterns of cellulose (Cell), Cell@Al2O3, Pd(II)-
AMP-Cell@Al2O3 highlighted by black, red and blue color, respectively
in Fig. 1. The XRD patterns show the reflection only due to the cellu-
losic phase. The appearance of reflections in the XRD pattern due to Pd
and Al2O3 phases are not observed due to the lack of long-range peri-
odicity of Pd species and amorphous nature of Al2O3, respectively.
Since Suzuki and Heck couplings performed at high temperature,
the thermal stability of catalyst becomes an important property as it has
significant influence on activity and reusability. To evaluate thermal
stability of the Pd(II)-AMP-Cell@Al2O3 complex, thermo gravimetric
analysis (TGA) was performed (Fig. 4). The thermogram reveals initial
weight loss (8.71%) at temperature 25–103 °C due to evaporation of
loosely bonded water moelcules on surface of complex. Further en-
hancement in temperature from 263°C to 365°C results in gradual de-
composition of organic functionalities and polymeric carrier in complex
with abrupt weight loss (86.58%). Finally, the residual weight 4.7%
indicates the formation of Al2O3, SiO2 and oxides of Pd. The TGA re-
veals that the complex is thermally stable up to 263 °C.
The energy dispersive X-ray spectroscopy (EDX) of Pd(II)-AMP-
Cell@Al2O3 disclosed 4.80% loading of Pd. EDX image reveals the
presence of palladium in complex confirming the successful grafting of
2-aminopyridine and complexation with Pd on the Cell@Al2O3 (Fig. 5).
Next, we explored catalytic activity of Pd(II)-AMP-Cell@Al2O3 in
Suzuki–Miyaura cross-coupling.
A model reaction of iodobenzene (1.0 mmol) and phenylboronic
acid (1.2 mmol) was chosen for Suzuki coupling to investigate optimal
reaction conditions with respect to solvents and bases. We screened
Fig. 1. XRD patterns of cellulose (Cell), Cell@Al2O3 and Pd(II)-AMP-
Cell@Al2O3.
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P. Mhaldar, et al.
ReactiveandFunctionalPolymers152(2020)104586
Fig. 2. SEM image of microcrystalline cellulose (a) and Pd(II)-AMP-Cell@Al2O3 (b) & (c).
Fig. 3. TEM image of Pd(II)-AMP-Cell@Al2O3 showing cellulose matrix (a) and Pd Cell incorporation (b).
Fig. 4. TGA–DTA spectrum of Pd(II)-AMP-Cell@Al2O3.
different solvents viz. absolute ethanol, DMF, 95% EtOH, CH3CN, to-
luene and water for the model reaction. Only 72% of the desired pro-
duct was obtained within 3 h when the reaction was carried out in
absolute ethanol with Pd(II)-AMP-Cell@Al2O3 (40 mg) and K2CO3
(2.0 mmol) as a base at 80°C (Table 1,Entry 1). Amongst tested solvents,
DMF was found to be the choice of solvent in terms of yield (95%) and
time (1 h) (Table 1, Entry 6). Even though a mixed solvent system,
DMF:H2O (v/v: 5:5) was employed for the model reaction furnished
poor yield of product (Table 1,Entry 7). Then the effect of amount of a
catalyst was screened with DMF as solvent for the model reaction
4

P. Mhaldar, et al.
ReactiveandFunctionalPolymers152(2020)104586
Fig. 5. EDS spectrum of Pd(II)-AMP-Cell@Al2O3.
Table 1
Optimization of reaction conditions for Suzuki–Miyaura cross couplinga.
Pd-AMP-Cell@Al 2O3
B(OH)2
I
+
K2CO3
Solvent
80o C
Entry
Solvent
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
EtOH
3
2.5
2
4
5
1
2
2
1.5
1.5
72
76
82
80
62
95
88
78
92
90
95% EtOH
CH3CN
Toluene
H2O
DMF
DMF:H2O (5:5)
DMF (catalyst: 20 mg)
DMF (catalyst: 30 mg)
DMF (catalyst: 50 mg)
9
10
a
Reaction conditions: Iodobenzene (1.0 mmol), phenylboronic acid (1.2 mmol), K2CO3 (2.0 mmol), solvent (6 mL) and Pd(II)-AMP-Cell@Al2O3 (40 mg), temp.:
80 °C.
b
Isolated yields.
The effect of various organic/inorganic bases such as K3PO4, K2CO3,
Na2CO3, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,4-diazabicyclo
[2.2.2]octane (DABCO), triethylamine (TEA) and NaHCO3 in DMF for
the Suzuki–Miyaura cross-coupling was examined for reaction of io-
doanisole (1.0 mmol) with phenylboronic acid (1.2 mmol) in the pre-
sence of catalyst (40 mg). We found that, K2CO3 signify excellent result
in short reaction time (Table 2, Entry 7). To check the effect of tem-
perature, the model reaction, was performed at room temperature led
corresponding biphenyl in moderate yield (58%) (Table 2, Entry 8).
When the temperature was raised to 60 °C, no drastic improvement in
the yield of the product was observed (Table 2, Entry 9). However, best
yield of product was observed when the model reaction was carried out
at 80 °C.
The yields of Pd(II)-AMP-Cell@Al2O3 catalysed model reaction of
iodoanisol and phenyl boronic acid in DMF were tested with respect to
time at various temperature (Fig. 6). No product formation was ob-
served when reaction was performed at 30 °C. However, when the re-
action was carried out at 50 °C and 60 °C corresponding product was
formed in low yields. Gratifyingly, Suzuki product was obtained in high
yield (94%) at 80 °C in 60 min, further rise in the time exhibit no
change in the yield. At 100 °C reaction was preceded with nearly same
yield. Finally, we concluded that 80 °C is optimum temperature to
Table 2
Screening of various bases for Suzuki–Miyaura cross couplinga.
Entry
Base
Temperature (°C)
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
9
Na2CO3
K3PO4
TEA
80
80
80
80
80
80
80
RT
60
3.5
4
2.5
3
76
68
80
70
65
56
94
58
72
DBU
NaHCO3
DABCO
K2CO3
K2CO3
K2CO3
2
3.5
1.5
2
2
a
Reaction conditions: Iodoanisole (1.0 mmol), phenylboronic acid
(1.2 mmol), base (2.0 mmol), solvent (6 mL), Pd(II)-AMP-Cell@Al2O3 (40 mg),
temp.: 80 °C.
b
Isolated yield.
(Table 1, Entries 8-10). The best yield was obtained with 40 mg of
catalyst, Pd(II)-AMP-Cell@Al2O3. From the above observations it was
concluded that the DMF as a solvent and use of 40 mg of Pd(II)-AMP-
Cell@Al2O3 furnished high yield of Suzuki-Miyaura cross coupling
product.
5

P. Mhaldar, et al.
ReactiveandFunctionalPolymers152(2020)104586
Fig. 6. Effect of Temperature with reaction time on yield of Suzuki Miyaura coupling of iodoanisole (1.0 mmol), phenylboronic acid (1.2 mmol) in DMF (5 mL) by Pd
(II)-AMP-Cell@Al2O3.
[6 mL DMF, 40 mg of catalyst and K2CO3, 80 °C, 4 h]. However, re-
action didn't proceed to synthetically useful degree even though tem-
perature was increased to 100 °C as the corresponding product viz.
methyl-(2E)-3-(4-methoxyphenyl) prop-2-enoate was obtained in 78%
yield (Table 4, entry 1). Interestingly, when K2CO3 was replaced by TEA
for the same reaction, we observed significant increase in yield of
corresponding product (92%) in 2 h at 100 °C (Table 4, entry 4). As
compared to TEA, other bases like K2CO3, K3PO4 and NaHCO3 showed
poor yields (Table 4, entries 2–3). Thus, TEA was selected as a base for
Mizoroki-Heck cross-coupling. Next, an array of solvents viz 95% EtOH,
H2O, CH3CN, dichloromethane (DCM) and toluene were screened for
the model reaction by employing TEA as base which led inferior yield
[25–65%] (Table 4, entries 5–9).
After optimization of reaction condition for Mizoroki-Heck cross-
coupling, the scope of the Mizoroki-Heck cross-coupling was in-
vestigated for different aryl halides possessing electron-withdrawing
and electron-donating groups such as –OMe, −Me, -NH2, –COCH3,
-NO2 with methyl acrylate, styrene and acrylonitrile [Table 5, Entries
1–16]. All reactions were proceeded smoothly with high yield in ade-
quate reaction time.
The plausible mechanism for Suzuki-Miyaura and Mizoroki-Heck
cross coupling is depicted in Scheme 3, based on the literature [28,29].
Initially, active catalytic species Pd(0) is generated in situ from Pd(II) in
Pd(II)-AMP-Cell@Al2O3. Further, mechanism involves three steps viz
oxidative addition of the halide, transmetalation and reductive elim-
ination to give substituted biaryls. For Heck reaction, the mechanism
involves the oxidative addition of the halide, migratory insertion of the
olefin and β-hydride elimination to form the product. The regeneration
of palladium (0) catalyst takes place using a base in the reductive
elimination step.
Scheme 2. Pd(II)–AMP–Cell@Al2O3 catalyzed Suzuki–Miyaura cross coupling
furnish the reaction smoothly led high yield of product.
After the optimization of reaction conditions, the generality of the
protocol of Suzuki–Miyaura cross-coupling was verified by exploring
substrate scope under the optimized reaction conditions. A wide range
of aryl halides was treated with phenyl boronic acids in DMF (5 mL)
and Pd(II)-AMP-Cell@Al2O3 (40 mg) at 80 °C [Scheme 2]. Various
substituted aryl halides possessing electron donating and/or with-
drawing moieties were explored with simple phenyl boronic acid
furnished corresponding products with good to excellent yield (Table 3,
Entries 1–10). The catalytic system tolerates wide range of functional
groups vizeNH2, eOH, eNO2, eCN, eCF3, eCOMe, eMe and eOMe on
aryl halide indicating that the electronic nature of substituents have no
dramatic effects on the efficiency of the catalyst. Further, several sub-
stituted aryl boronic acids and heterocyclic boronic acids were reacted
with aryl halides to extend the generality of the method. The reactions
between electron withdrawing and/or donating substituent's on aryl
boronic acids with substituted aryl halides furnished better yields
(Table 3, Entries 12–15). The boronic acid containing heteroatom
treated with aryl halide under optimized reaction conditions afforded
significant yield (Table 3, Entries 16–18). The study of substrate scope
clearly demonstrated the superiority of Pd(II)-AMP-Cell@Al2O3 in the
Suzuki–Miyaura cross-coupling.
An admirable performance of Pd(II)-AMP-Cell@Al2O3 for Suzuki-
Miyaura cross coupling provoked us to extend its catalytic efficiency for
Mizoroki-Heck cross-coupling.
Initially, we employed reaction conditions of Suzuki Miyaura for
Mizoroki-Heck cross-coupling of 4-iodoanisole and methyl acrylate
The catalytic activity of Pd-AMP-Cell@Al2O3 was examined by
comparing it with several reported catalysts for Suzuki–Miyaura and
Mizoroki–Heck cross-coupling reactions [Tables 6 & 7]. The compar-
ison reveals that the most of reported Pd catalysts acquired high Pd
6

P. Mhaldar, et al.
ReactiveandFunctionalPolymers152(2020)104586
Table 3
Pd(II)–AMP–Cell@Al2O3 catalyzed Suzuki–Miyaura cross coupling of various aryl halides and arylboronic acidsa.
Entry
Aryl halide
Aryl boronic acid
Product
Time (h)
Yieldb (%)
TONc
TOFd
1
2
3
4
5
6
7
8
R = 4-H, X = -I
R' = H
R' = H
R' = H
R' = H
R' = H
R' = H
R' = H
R' = H
R = 4-H, R' = H
1
1
1.5
1.5
2
2
1
2.5
2
3
95
94
87
88
86
88
92
86
88
84
92
88
86
88
90
5000
4947
4578
4631
4523
4631
4842
4523
4631
4421
4842
4631
4523
4631
4736
5000
4947
3052
3087
2263
2315
4842
1809
2315
1473
3228
3087
1809
2315
2368
R = 4-OMe, X = -I
R = 4-CH3, X = -Br
R = 4-NH2, X = -Br
R = 4-COCH3, X = -Br
R = 4-CHO, X = -Br
R = 4-Ph, X = -Br
R = 4-CN, X = -I
R = 3-CHO, X = -Br
R = 4 -NO2, X = -Br
R = 4-OCH3, X = -I
R = 4-OMe, X = -I
R = 4-H, X = -I
R = 4-OMe, R' = H
R = 4-CH3, R' = H
R = 4-NH2, R' = H
R = 4-COCH3, R' = H
R = 4-CHO, R' = H
R = 4-Ph, R' = H
R = 4-CN, R' = H
9
R' = H
R' = H
R = 3-CHO, R' = H
R = 4-NO2, R' = H
R = R' = 4-OCH3,
R = 4-OMe, R' = 4-Br
R = 4-H, R' = 4-NO2
R = 4-CN, R' = 3-CH3
R = 4-COCH3,R' = 4-CH3
10
11
12
13
14
15
R' = 4-OCH3
R' = 4-Br
R' = 4-NO2
R' = 3-CH3
R' = 4-CH3
1.5
1.5
2.5
2
R = 4-CN, X = -I
R = 4-COCH3, X = -Br
2
I
B(OH)2
x
R
x
R
R = 4-H, X = S
R = 4-H, X = O
16
17
18
R = 4-H, X = -I
R = 4-H, X = -I
X = -S
X = O
1.5
1.5
1.5
91
90
88
4789
4736
4631
3192
3157
3087
CH
CH
3
3
O
O
Br
O
a
Reaction conditions: Aryl halide (1.0 mmol), aryl boronic acid (1.2 mmol), K2CO3 (2.0 mmol), Pd(II)–AMP–Cell@Al2O3 (40 mg) and DMF (6 mL), temp.: 80 °C.
Isolated yield.
TON = mol. Product/mol. of Pd.
TOF = TON/reaction time in h.
b
c
d
the reactions without significant change in the catalytic efficiency.
The loading of palladium in the reused Pd(II)-AMP-Cell@Al2O3 was
examined by ICP-AES analysis. The analysis revealed 4.68% of Pd in the
reused catalysts which is nearly equal to fresh catalyst (4.85% of Pd).
The minor loss of palladium (< 3%) indicates negligible leaching of the
Pd in spite of using highly polar DMF solvent. This confirms the strong
bonding between the Pd and 2-aminopyridine ligand anchored on
chloropropyl Cell@Al2O3 that affix good stability, reusability of catalyst
and prevents leaching of the palladium.
Table 4
Screening of various bases and solvents for Mizoroki–Heck Cross couplinga.
Entry
Base
Solvent
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
9
K2CO3
K3PO4
NaHCO3
TEA
TEA
TEA
TEA
TEA
TEA
DMF
DMF
DMF
DMF
95% EtOH
H2O
CH3CN
DCM
4
5
8
2
3
10
8
6
5
78
70
60
92
40
25
64
56
65
Toluene
4. Conclusion
a
Reaction conditions: 4-Iodoanisole (1 mmol), methyl acrylate (1.1 mmol),
Pd(II)-AMP-Cell@Al2O3 (40 mg), base (3 mmol), solvent (5 ml) at 100 °C.
We have successfully prepared a novel, highly efficient, stable and
recyclable cellulose supported Pd based complex for Suzuki-Miyaura
and Mizoroki–Heck cross coupling. The use of cellulose as an in-
expensive and eco-benign support, simple preparation method of
complex, effective loading of Pd, high TON & TOF are key features of
theprepared complex. Furthermore, the complex could be easily sepa-
rated by simple filtration, recovered and reused several times.
Considering environmental and economic concerns, prepared complex
could be considered as a feasible alternative for cross-coupling reac-
tions.
b
Isolated yield.
loading, harsh reaction conditions, lower yields of product, longer re-
action time for the reaction. Pd-AMP-Cell@Al2O3 is superior in terms of
non-toxicity, lower Pd content, better reaction condition and high
yields of product.
Recyclability and reusability are the most important features of
heterogeneous catalysts. The recyclability and reusability of Pd(II)-
AMP-Cell@Al2O3 for Suzuki–Miyaura cross-coupling and Mizoroki-
Heck cross-coupling were performed with the corresponding model
reactions under optimized reaction conditions. After completion of the
model reaction, insoluble catalyst was recovered by simple filtration
and extensively washed with water and acetone. The recovered catalyst
was dried in oven at 50 °C and employed in the next cycle under op-
timum reaction conditions. The results are depicted in Fig. 7. Pleas-
ingly, Pd(II)-AMP-Cell@Al2O3 could be reused for five cycles for both
Data availability statement
The raw/processed data required to reproduce these findings cannot
be shared at this time as the data also forms part of an ongoing study.
7

P. Mhaldar, et al.
ReactiveandFunctionalPolymers152(2020)104586
Table 5
Pd(II)–AMP–Cell@Al2O3 catalyzed Mizoroki-Heck cross-coupling of various aryl halides and olefinsa.
Entry
R
X
R'
Time (h)
Yieldb (%)
cTON
dTOF (h−1
)
1
2
3
4
5
6
7
8
H
OCH3
CH3
NH2
COCH3
NO2
I
I
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
COOtBu
COOtBu
COOtBu
COOtBu
COOtBu
Ph
2
2
2
2.5
3
3
2
2
2.5
3
2.5
3
2
2.5
2.5
3
92
92
88
86
82
80
90
88
84
81
86
84
88
86
82
81
4842
4842
4631
4526
4315
4210
4736
4631
4421
4263
4526
4421
4631
4526
4315
4263
2421
2421
2315
1810
1438
1403
2368
2315
1768
1421
1810
1473
2315
1810
1726
1421
Br
Br
Br
Br
Br
I
Br
Br
Br
I
H
OCH3
CHO
COCH3
CH3
9
10
11
12
13
14
15
16
CN
OCH3
COCH3
CHO
NO2
I
Br
Br
Br
Ph
CN
CN
a
Reaction conditions: aryl halide (1 mmol), olefin (1.1 mmol), Pd(II)–AMP–Cell@Al2O3 (40 mg), TEA (3 mmol), DMF (5 ml), at 100 °C.
Isolated yield.
TON = mol. product/mol. catalyst.
TOF = TON/reaction time in h.
b
c
d
Scheme 3. Plausible mechanism for Suzuki-Miyaura and Mizoroki-Heck cross couplings
8

P. Mhaldar, et al.
ReactiveandFunctionalPolymers152(2020)104586
Table 6
Comparison of Pd(II)-AMP-Cell@Al2O3 with other catalysts for Suzuki-Miyaura cross coupling.
Entry
Catalyst
Reaction conditions
Time (h)
Yield (%)
Ref.
1
2
3
4
5
6
7
SBA-15–EDTA–Pd
Pd@SBA-15/ILDABCO
NHC-Pd(II) complex
D-2PA-Pd(II)@SBA-15
SiO2-pA-Cyan-Cys-Pd
Pd–BOX
K2CO3, DMF,120 °C, 7 Wt% Pd
K2CO3, H2O, 80 °C, 0.5 mol% Pd
K3PO4, H2O, TBAB, 40 °C (0.2 mol%)
K2CO3, DMF,120 °C, 15 mg Cat.
K2CO3, H2O, 100 °C (0.5 mol%)
K2CO3, DMF, 70 °C, (2 mol%)
K2CO3, DMF, 70 °C, (40 mg)
8
12
6
5
5
83
95
94
85
95
100
98
[30]
[31]
[32]
[33]
[34]
[35]
[This work]
6
1
Pd(II)-AMP-Cell@Al2O3
Table 7
Comparison of Pd(II)-AMP-Cell@Al2O3 with other catalysts for Mizoroki-Heck cross coupling.
Entry
Catalyst
Reaction conditions
Time (h)
Yield (%)a
Ref.
1
2
3
4
5
6
7
8
Pd-TPA/ZrO2 (0.4 mol%)
Fe3O4@CS-SB-Pd (1.0 mol%)
Pd/ED-MIL-101
K2CO3, DMF, 120 °C
Et3N, DMF, 120 °C
Et3N, DMF, 120 °C
MeCO2Na/DMAc/120 °C
Et3N, DMF, 120 °C
Et3N, DMF, 100 °C
6
4
12
2
3
2.5
3
2
95
98
98
97
90
96
94
94
[36]
[37]
[38]
[39]
[40]
[41]
[42]
[This work]
PdNP@NG (0.1 mol%)
Pd-ZnFe2O4 MNPs (4.62 mol%)
Pd-imino-Py-γ-Fe2O3 (1 mol%)
Fe3O4@EDTA-PdCl2 (20 mg)
Pd(II)-AMP-Cell@Al2O3
K2CO3, TBAB, H2O, 80 °C
K2CO3, DMF, 100 °C, (40 mg)
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Fig. 7. Reusability study of Pd(II)-AMP-Cell@Al2O3.
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Declaration of Competing Interest
[24] S.P. Vibhute, P.M. Mhaldar, S.N. Korade, D.S. Gaikwad, R.V. Shejawal, D.M. Pore,
Tetrahedron Lett. 41 (2018) 3643.
[25] D.S. Gaikwad, K.A. Undale, D.B. Patil, D.M. Pore, J. Iran. Chem. Soc. 16 (2019) 253.
[26] S.P. Vibhute, P.M. Mhaldar, R.V. Shejawal, D.M. Pore, Tetrahedron Lett. 11 (2020)
151594.
The authors declare that they have no known competing financial
interestsor personal relationships that could have appeared to influence
the work reported in this paper.
[27] S.P. Vibhute, P.M. Mhaldar, D.S. Gaikwad, R.V. Shejwal, D.M. Pore, Monatsh. Chem. 151
(2020) 87.
Acknowledgement
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One of the authors, Pradeep Mhaldar, is grateful to the Council of
Scientific and Industrial Research (CSIR), New Delhi, Government of
India, for the award of the Junior Research Fellowship (File no. 09/
816(0040)/2017-EMR-I).
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9