Application of an air-and-moisture-stable diphenylphosphinite cellulose-supported nanopalladium catalyst for a Heck reaction

Article abstract of DOI:10.1007/s11164-012-0504-2

A diphenylphosphinite cellulose-supported nanopalladium (Cell-OPPh ₂-Pd⁰) was conveniently prepared from cellulose and chlorodiphenylphosphine in pyridine, followed by treatment of an ethanol solution of palladium chloride. The prepared catalysis was found to be air- and moisture-stable and have significant catalytic activities in Heck coupling under mild operating conditions. Various phenyl halides were coupled with alkenes in DMF under air, to afford the corresponding products in good yields. Furthermore, the catalyst can be easily recovered by simple filtration and reused for up to six cycles without losing its activity. Springer Science+Business Media B.V. 2012.

Full text of DOI:10.1007/s11164-012-0504-2

Res Chem Intermed (2012) 38:1807–1817
DOI 10.1007/s11164-012-0504-2
Application of an air-and-moisture-stable
diphenylphosphinite cellulose-supported
nanopalladium catalyst for a Heck reaction
Qingwei Du Yiqun Li
•
Received: 21 September 2011 / Accepted: 1 February 2012 / Published online: 22 February 2012
Ó Springer Science+Business Media B.V. 2012
Abstract A diphenylphosphinite cellulose-supported nanopalladium (Cell–
OPPh -Pd ) was conveniently prepared from cellulose and chlorodiphenylphos-
0
2
phine in pyridine, followed by treatment of an ethanol solution of palladium
chloride. The prepared catalysis was found to be air- and moisture-stable and have
significant catalytic activities in Heck coupling under mild operating conditions.
Various phenyl halides were coupled with alkenes in DMF under air, to afford the
corresponding products in good yields. Furthermore, the catalyst can be easily
recovered by simple filtration and reused for up to six cycles without losing its
activity.
Keywords Diphenylphosphinite cellulose Á Polymer-supported catalyst Á
Heterogeneous catalyst Á Nanopalladium Á Heck reaction
Abbreviations
Cell–OPPh -Pd Diphenylphosphinite cellulose-supported nanopalladium
0
2
ICP-AES
FTIR
XRD
Inductively coupled plasma-atomic emission spectrometry
Fourier transform infrared spectroscopy
X-ray diffraction
TGA
SEM
Thermo gravimetric analyses
Scanning electron microscopy
TEM
MCC
Cell–OPPh2
Transmission electron microscopy
Microcrystalline cellulose
Diphenylphosphinite-functionalized cellulose
Q. Du Á Y. Li (&)
Department of Chemistry, Jinan University, Guangzhou 510632, China
e-mail: tlyq@jnu.edu.cn
123

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Q. Du, Y. Li
Introduction
The palladium-catalyzed carbon–carbon coupling reaction is a versatile and
important organic transformation process. In particular, the Heck reaction [1, 2],
which is a palladium-catalyzed coupling of aryl halides with alkenes, is one of the
most important methods for the formation of a carbon–carbon bond to yield a
variety of organic compounds. These coupling products find good applications as
intermediates in the preparation of materials, natural products, and bioactive
compounds [3–7]. The traditional procedure for a Heck reaction is generally
catalyzed by homogeneous Pd complexes [8–14]. Although homogeneous catalysts
often have greater activity in such transformations, most are expensive, not easily
available, require air-free handling to prevent oxidation, and have cumbersome
separation of the catalyst from the reaction mixture at the end of the reaction.
The heterogenization of these catalysts on polymeric supports therefore constitutes
a logical approach to combining their homogeneous catalytic properties with the
advantages of heterogeneous catalysts, for example, the high activity, convenient
work-up, easy separability and reusability, and low toxicity. Therefore, the
development of an insoluble heterogeneous palladium catalyst has attracted
much attention in organic synthesis. In recent years, a considerable number of
heterogeneous palladium catalysts have been reported being used under mild and/or
environmentally benign reaction conditions. These include palladium immobilized
on organic polymer matrix (polystyrene [15], polyvinyl chloride [16], polymethyl
methacrylate [17], polyether dendrons [18]), palladium immobilized on inorganic
carrier (carbon [19], palladium supported on metal oxides [20], carbon nanotubes
[
21], clays [22], zeolites [23], molecular sieves [24], and silica [25], etc.).
It is well known that cellulose is widely used, inexpensive, and easily modified
by functionalization, which makes it a suitable polymeric support for heterogeneous
catalysts. Palladium is well known to form stable complexes with a wide variety of
organic ligands containing P, N, O, etc., due to its pronounced coordination
properties. In a continuation of our work on the development of simple and reliable
procedures for immobilization of catalytically active palladium nanoparticles on
functionalized cellulose, herein, we report the preparation and characterization of
the diphenylphosphinite-functionalized cellulose-supported nanopalladium catalyst
0
Cell–OPPh -Pd ) and, further, to use it as a recyclable heterogeneous catalyst for
(
the Heck coupling reaction of aryl halides with alkenes in ambient atmosphere.
2
Experimental
General
Melting points were measured on an Electrothermal X6 microscopic digital melting
point apparatus. IR spectra were recorded on a Nicolet 6700 spectrometer using KBr
1
pellets. H NMR spectra were recorded on a 300-MHz BRUKER AVANCE
instrument using CDCl3 as solvent and TMS as internal standard. Elemental
analyses were performed on a PerkinElmer EA2400II elemental analyzer.
1
23

Application of an air and moisture catalyst
1809
The elemental palladium content of the polymeric catalysts was determined by
PerkinElmer Optima 2000DV inductively coupled plasma (ICP) spectroscopy.
Scanning electron microscopy (SEM) was performed on a Philips XL 30ESEM
instrument. Transmission electron microscopy (TEM) was performed on a JEM-
2
100F instrument operating at 200 kV. The microcrystalline cellulose (MCC) and
other chemicals were obtained from commercial sources and used directly as
received.
Preparation of diphenylphosphinite cellulose (Cell–OPPh2)
Cellulose (3.0 g) and dry pyridine (120 mL) was added into a round-bottomed flask
and the mixture was vigorous stirred at 80–90 °C for 30 min. After being cooled to
room temperature, chlorodiphenylphosphine (12.0 mL) was added to the mixture
and the reaction mixture was further stirred at room temperature for 5 days. The
reaction mixture was then filtered and the solid was washed thoroughly with a large
volume of ethanol to remove the trace amount of pyridine and dried under vacuum
at 60 °C to afford white diphenylchlorophosphine-functionalized cellulose
(
Cell–OPPh ).
2
0
Preparation of Cell–OPPh -Pd complex
2
To a solution of PdCl (0.16 g, 0.9 mmol) in 95% ethanol (30 ml) was added the
2
Cell–OPPh (2.0 g). The mixture was refluxed for 24 h. The mixture was allowed to
2
cool and then filtered. The resulting product was washed sequentially with ethanol
(
give the dark gray polymeric palladium complex (Cell–OPPh -Pd ).
3 9 25 mL) and Et O (3 9 25 mL), and was then dried under vacuum at 60 °C to
2
0
2
General procedure for arylation of styrene with aryl halides
A mixture of aryl halide (1.0 mmol), styrene (1.5 mmol), Bu N (2.0 mmol), DMF
3
0
5.0 mL) and the Cell–OPPh -Pd complex (0.007 mmol of Pd, 0.7 mol%) was
(
2
stirred in an oil bath at 110 °C. The process was monitored by TLC. The mixture
was cooled and quenched by Et O (15.0 mL) after the completion of the reaction.
2
0
The Cell–OPPh -Pd catalyst can be separated and reused in the next run by
2
filtration, sequential washing with distilled water, ethanol, and dried. The ethereal
solution was washed with 6 M HCl, brine, and dried over anhydrous MgSO4.
The product was obtained after removing the ethereal solution by a rotary evaporator.
These desired pure products were further purified by recrystallization with ethanol.
General procedure for arylation of aryl halides with acrylic acid
A mixture as given above using acrylic acid in place of styrene was stirred in an oil
bath at 110 °C. The end of the reaction was monitored by TLC. The mixture was
then poured into H O (10 mL) and Na CO (0.3 g) was added. After stirring for
2
2
3
0
10 min, the Cell–OPPh -Pd catalyst was separated from the mixture by filtration
2
and reused in the next run after washing with distilled water, ethanol, and drying.
123

1810
Q. Du, Y. Li
The aqueous phase was acidified with 6 M HCl to precipitate the crude solid
product. The pure product was obtained by recrystallization from ethanol.
Characterization of selected products
All the products (3a–3j) are known and data are found to be identical with those
reported in the literature elsewhere. The data of selected products are as follows:
1
3
a: mp 121–122 °C. H NMR (CDCl , 300 MHz) d: 7.19-7.56 (m, 9H, Ar–H),
3
7
.11 (s, 2H, CH=CH), 2.39 (s, 3H, CH ); IR (KBr) m: 3079, 3050, 3022, 1643, 1593,
3
-1.
1
509, 1447, 969, 808, 749, 690 cm
1
3
b: mp 198–199 °C. H NMR (CDCl , 300 MHz) d: 7.79 (d, 1H, COOH), 7.47
3
(
d, 2H, Ar–H), 7.24 (d, 2H, Ar–H), 7.22 (d, 1H, =CH) 6.40 (d, 1H, =CH) 2.39
s, 3H, CH ); m: 3028–2588, 1682, 1623, 1607, 1513, 1423, 1311, 1258, 1223, 988,
(
3
-
1.
9
44, 813, 688 cm
1
3
c: mp 136–138 °C. H NMR (CDCl , 300 MHz) d: 7.03–7.47 (m, 9H, Ar–H),
3
6
.93 (s, 2H, CH=CH), 3.85 (s, 3H, OCH ); IR (KBr) m: 3061, 3022, 3002, 2836,
3
-1.
1
655, 1601, 1511, 1446, 1245, 1030, 967, 812, 750, 689 cm
1
3
e: mp 126–127 °C. H NMR (CDCl , 300 MHz) d: 7.32–7.62 (m, 10H, Ar–H),
3
7
6
.21 (s, 2H, CH=CH); IR (KBr) m: 3058, 3019, 1647, 1597, 1494, 1451, 962, 775,
-1.
92 cm
g: mp 159–160 °C. H NMR (CDCl , 300 MHz) d: 8.23 (d, 2H, Ar–H), 7.31-
1
3
3
7
.65 (m, 7H, Ar–H), 7.17 (s, 2H, CH=CH); IR (KBr) m: 3077, 1633, 1595, 1454,
-1.
1
509, 1344, 971, 833, 767, 695 cm
Results and discussion
0
Preparation and characterization of Cell–OPPh -Pd catalysts
2
0
The Cell–OPPh -Pd catalyst was prepared with diphenylphosphinite cellulose and
2
0
palladium chloride in ethanol (Scheme 1). The prepared Cell–OPPh -Pd catalyst
was characterized by inductively coupled plasma-atomic emission spectrometry
2
(
(
ICP-AES), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction
XRD), thermo gravimetric analyses (TGA), scanning electron microscopy (SEM)
and transmission electron microscopy (TEM).
The resulting sample was studied by ICP-AES in order to determine the amount
of palladium dispersed in the solid. The metal palladium content of the catalyst was
0
2
Scheme 1 Preparation of the Cell–OPPh -Pd
1
23

Application of an air and moisture catalyst
1811
found to be 0.33 mmol/g. The IR spectra of the cellulose (curve A), diphenylpho-
sphinite-functionalized cellulose (Cell–PPh ) (curve B) and diphenylphosphinite-
2
0
functionalized cellulose (Cell–OPPh -Pd ) catalysts (curve C), were recorded,
respectively (Fig. 1). Compared with the curve A, the presence of absorption peak
2
-
1
of C–O–P bond (1,030.8, 731.2, 694.2 cm ) in the spectrum of Cell–OPPh (curve
2
B) indicates that diphenylphosphinite was introduced into the cellulose, but this
0
-
band is negatively shifted to 1,024.5, 732.3, 695.2 cm in the Cell–OPPh -Pd
1
2
(curve C) indicating coordination of the phosphine atom with the palladium and
further confirming the formation of a palladium complex on the surface of the
polymer.
0
The high-angle XRD patterns of the Cell–OPPh -Pd catalyst and the Cell–
2
OPPh matrix are shown in Fig. 2. Besides the broad diffraction ascribed to the
2
polymeric scaffold, the other three typical diffraction peaks at 2h of 40.0, 46.1, and
6
7.5 °, the diffraction of the (111), (200), and (220) lattice planes of palladium
crystalline structure are clearly observed. The pattern B only displays a broad
diffraction with 2h ranging from 5 to 35 °, which suggests the amorphous structure
of the polymeric scaffold.
Generally, the Heck reaction was conducted under the heated condition. The
0
thermal stability of Cell–OPPh -Pd catalyst has a great effect on the catalytic
activity and the reused performance. The TGA curves of the cellulose and Cell–
2
0
OPPh -Pd catalyst are shown in Fig. 3. An initial weight loss of around 3.5% was
2
observed up to 100 °C, which was likely due to the loss of the adsorptive water and
a weight loss near 240 °C (very strong) is attributed to the decomposition of
0
catalyst. These results indicate that the Cell–OPPh -Pd catalyst has a good thermal
2
stability from room temperature to 240 °C.
0
The morphology of Cell–OPPh -Pd and the Cell–OPPh was studied by SEM
2
2
and TEM. As shown in Fig. 4, a clear change in morphology is observed after
anchoring palladium on the polymer support. TEM images of fresh prepared
0
Cell–OPPh -Pd catalyst showed the presence of palladium nanoparticles of about
2
Fig. 1 IR spectra of the
cellulose (spectrum A),
1
00
80
7
32.3
Cell–OPPh
Cell–OPPh
2
(spectrum B) and
-Pd catalysts
0
2
(spectrum C)
695.2
C
B
6
4
2
0
0
0
0
731.2
1
024.5
6
94.2
1030.8
A
4
000 3500 3000 2500 2000 1500 1000 500
-
1
Wavenumber(cm )
123

1812
Q. Du, Y. Li
Fig. 2 XRD pattern of the
(111)
1
600
Cell–OPPh
Cell–OPPh
2
matrix (A) and
-Pd catalyst (B)
0
1400
2
B
1
200
000
(
200)
1
(
220)
800
600
400
200
0
A
-
200
10
20
30
40
50
60
70
80
2
θ (°)
Fig. 3 TG curve of the
cellulose (A) and Cell–OPPh
1
00
2
-
0
Pd (B) under nitrogen flow
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
A
B
1
00
200
300
400
500
600
Temperature (°c)
0
-Pd (b)
Fig. 4 SEM images of the Cell–OPPh
2
(a) and the fresh catalyst Cell–OPPh
2
3
–10 nm size distributed on the surface of the polymer matrix (Fig. 5a, b). The
TEM image also showed the slightly agglomeration of nanopalladium after the used
six times, which has not apparently lower the catalytic activity (Fig. 5c).
1
23

Application of an air and moisture catalyst
1813
0
2
Fig. 5 TEM image of the fresh Cell–OPPh -Pd catalyst at low (a) and high (b) magnification and the
recovered catalyst after being reused six runs (c) at low magnification
Heck cross-coupling reactions
In order to find a suitable condition for the reactions, the influences of base, solvent,
and amount of catalyst on Heck coupling were carefully examined by using the
reaction of 4-iodoanisole and styrene as the model reaction (Scheme 2). The results
are summarized in Tables 1, 2, and 3, respectively.
Initially, in order to find a suitable base for the reactions, various bases were
studied in the model reaction. As shown in Table 1, the rate of reaction and the
activity of the catalyst were significantly influenced by the base used. Among the
bases screened, Bu N was the best base for this reaction (Table 1, entry 3). Next,
3
the effect of solvent on the Heck reaction was also examined. The results are listed
in Table 2. Among the studied solvents, DMF was so chosen for the solvent in the
heck reaction with best results.
It is a key issue to note that the amount of palladium catalyst plays an important
role in the product yields. The Heck reaction was studied with the amount of
catalyst ranging from 0.15 to 0.9 mol% with model reaction (Table 3). It was found
that the Heck reaction could be carried out efficiently even with a low amount of
the catalyst (0.15 mol% Pd) with 67% product yield. Increasing the amount of
Scheme 2 Reaction of 4-iodoanisole with styrene
123

1814
Q. Du, Y. Li
Table 1 The results of the
reaction of 4-iodoanisole with
styrene in the presence of
different bases
a
Yield (%)
Entry
Base
0
Time (h)
1
2
3
4
5
6
24
2.5
2
0
73
89
48
67
47
Et
Bu
CO
3
N
Reaction conditions: base
3
N
0
2
(2.0 mmol), Cell–OPPh -Pd
K
2
3
7
(0.007 mmol of Pd), and 5.0 mL
DMF at 110 °C
Na CO3
2
10
9
a
Isolated yield based on
-iodoanisole
NaOH
4
Table 2 Effect of solvent on
the cross-coupling reaction
a
Yield (%)
Entry
Solvent
Time (h)
1
2
3
4
5
6
DMF
2
89
65
71
59
67
43
DMSO
6
3
Reaction conditions: Bu N
0
CH
95% EtOH
DMF:H O=1:1
Dioxane
3
CN
8
(
2.0 mmol), Cell–OPPh
2
-Pd
(0.007 mmol of Pd), and 5.0 mL
9
solvent at 110 °C
2
4.5
a
Isolated yield based on
-iodoanisole
13
4
Table 3 Effect of amount of
0
a
Yield (%)
Entry
Amount of catalyst
mmol Pd)
Time
2
Cell–OPPh -Pd catalyst on the
(
cross-coupling reaction
1
2
3
4
5
0.15%
0.3%
0.5%
0.7%
0.9%
5
4
2
2
2
67
83
88
91
90
Reaction conditions: Bu
3
N
0
2
(2.0 mmol), Cell–OPPh -Pd ,
and 5.0 mL DMF at 110 °C
a
Isolated yield based on
-iodoanisole
4
palladium catalyst gave higher yield until the amount of the catalyst increases to
0
.7 mol%.
On the basis of the optimized reaction conditions, the coupling reactions between
a variety of aryl halides and alkenes were carried out to explore the general
0
effectiveness of the Cell–OPPh -Pd nanoparticles catalyst (Scheme 3). The results
2
are listed in Table 4.
As shown in Table 4, due to the high reactivity of the aryl iodides, the reactions
of both electron-rich (Table 4, entries 1–4) and electron-deficient substrates
(
Table 4, entries 7–10) with styrene and acrylic acid proceeded well and gave
high yields for the corresponding products. However, the substituent effects in the
aryl bromides appeared to be more significant than in the aryl iodides and the
reactivity of aryl bromides with electron-withdrawing substituent (Table 4, entries
1
7–18) was higher than that of aryl bromides with electron-donating substituent
Table 4, entries 11–14).
(
For practical applications of heterogeneous systems, the lifetime of the catalyst
and its level of reusability are important factors. To clarify this issue, we performed
1
23

Application of an air and moisture catalyst
1815
Scheme 3 Heck reaction of aryl halides with alkenes
Table 4 The coupling reactions of aryl halides with olefins
a
Yields (%)
Entry
R
1
R
2
X
Time (h)
Product
1
2
3
4
5
6
7
8
9
CH
3
3
Ph
I
2
3
3a
3b
3c
3d
3e
3f
88
84
89
90
91
90
94
93
90
91
61
54
67
70
81
82
86
88
0
CH
COOH
Ph
I
OCH
OCH
H
3
I
2
3
COOH
Ph
I
2.5
2
I
H
COOH
Ph
I
3
NO
NO
Cl
2
I
1.5
2
3g
3h
3i
2
COOH
Ph
I
I
2
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
Cl
COOH
Ph
I
2
3j
CH
CH
3
Br
Br
Br
Br
Br
Br
Br
Br
13
15
9
3a
3b
3c
3d
3e
3f
3
COOH
Ph
OCH
OCH
H
3
3
COOH
Ph
10
7
H
COOH
Ph
7.5
5
NO
2
2
3g
3h
NO
COOH
5
Reaction conditions: aryl halides (1.0 mmol), olefins (1.5 mmol), Bu
3
2
N (2.0 mmol), Cell–OPPh -Pd
(
a
0.007 mmol of Pd), and 5.0 mL DMF at 110 °C
Isolated yield based on aryl halide
a
Fig. 6 Recycling of the Cell–
Yield (%)
0
100
OPPh
reaction. Reaction conditions:
-iodoanisole (1.0 mmol),
styrene (1.5 mmol), Bu
2
-Pd for the Heck
9
2
91
92
9
0
89
88
4
8
6
4
2
0
0
0
0
0
3
N
2
-Pd
0
(2.0 mmol), Cell–OPPh
(0.007 mmol of Pd), and 5.0 mL
DMF at 110 °C. Isolated yield
based on 4-iodoanisole
1
2
3
4
5
6
Cycles
123

1816
Q. Du, Y. Li
a set of experiments using the recycled catalyst. We found that the catalyst showed
excellent recyclability in the Heck coupling reaction of 4-iodoanisole with styrene
(
distilled water, ethanol, and dried in vacuum. The catalyst was then directly reused
Fig. 6). After the first run, the catalyst was recovered by filtration, washed with
0
under the same conditions mentioned above. The Cell–OPPh -Pd catalyst showed
2
unchanged catalytic activity in at least six reaction cycles. No catalyst deterioration
0
was observed, confirming the high stability of the heterogeneous Cell–OPPh -Pd
2
catalyst under the reaction conditions. The ICP analysis the Pd loading of the Cell–
OPPh -Pd catalyst after six cycles of reusability for Heck reactions is 0.31 mmol/g.
2
It showed that only a very small amount of the Pd metal is removed from the
Cell–OPPh substrate.
2
Conclusions
0
In summary, we have prepared a Cell–OPPh -Pd catalyst by a simple procedure
2
of applying the corresponding diphenylphosphinite-functionalized cellulose (Cell–
OPPh ) and PdCl in an ethanol solution. It was found that the novel heterogeneous
2
2
palladium nanoparticle is a highly efficient, air- and moisture-stable and recoverable
catalyst for the Heck reaction under the optimum conditions. This procedure offers
several advantages such as short reaction time, simple experimental and isolated
procedure, satisfactory yields of products, as well as excellent catalytic activity and
reusability. Further application of the catalyst system to other palladium-catalyzed
transformations is in progress.
Acknowledgments We are grateful to the National Natural Science Foundation of China (nos.
2
8
1072077 and 20672046), the Guangdong Natural Science Foundation (nos. 10151063201000051 and
151063201000016) and the Guangzhou Science and Technology Project (2010Y1-C511) for financial
support.
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