Polymer (fiber)-supported palladium catalyst containing imidazolinyl rings and its application to the Heck reaction

Article abstract of DOI:10.1016/S0040-4039(03)00812-8

A polymer (fiber)-supported palladium catalyst was synthesized simply from commercially available polyacrylonitrile(PAN) fiber. Its high activity and selectivity for Heck reactions were measured; its activity remained unchanged after being recycled 20 times.

Full text of DOI:10.1016/S0040-4039(03)00812-8

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 3955–3957
Polymer (fiber)-supported palladium catalyst containing
imidazolinyl rings and its application to the Heck reaction
a
a,
b
a
a,
Kunhua Lin, Maoping Song, * Dongmei Cai, Xinqi Hao and Yangjie Wu *
a
Department of Chemistry, Zhengzhou University, Zhengzhou 450052, PR China
b
Department of Chemistry, University of Science and Technology of China, Hefei 230026, PR China
Received 17 January 2003; revised 10 March 2003; accepted 21 March 2003
Abstract—A polymer (fiber)-supported palladium catalyst was synthesized simply from commercially available polyacryloni-
trile(PAN) fiber. Its high activity and selectivity for Heck reactions were measured; its activity remained unchanged after being
recycled 20 times. © 2003 Elsevier Science Ltd. All rights reserved.
Polymer-supported palladium reagents have been used
extensively as important catalysts in organic synthesis
since Trost and Teranishi reported their application as
The following considerations prompted us to choose
PAN fiber as a polymer support for our experiments.
Firstly, this fiber has a larger surface area than a
common resin. Secondly, the nitrile group in PAN can
be easily converted to imidazoline, which facilitates
coordination with palladium. Moreover, the commer-
cially available PAN materials are somewhat cheaper
than most other resins.
catalysts for the formation of carbonꢀcarbon bonds in
1
1
978. Since then, polymer-supported palladium
reagents have been used in numerous kinds of synthetic
reactions with success and continue to attract much
2
attention. Although they have many advantages such
as being clean and recyclable, many based on resins are
2a,b,3
phosphine-containing.
Quite recently, Colacot
Scheme 1 shows the synthetic pathway to polymer-sup-
ported palladium catalyst A. This heterogeneous cata-
lyst can be easily prepared from the commercially
available PAN fiber. The grafting reaction with
triethylenetetramine (H N(CH CH NH) CH CH NH )
reported Suzuki reactions promoted successfully by
4
‘
Fibercats’ at room temperature. In this paper we
report a simple synthesis of a fiber supported palladium
catalyst and its application to Heck reactions.
2
2
2
2
2
2
2
Scheme 1.
Keywords: polymer-supported; fiber; palladium; imidazoline; Heck reaction.
*
Corresponding authors. Tel.: 86-371-7979408; fax: 86-371-7979408; e-mail: wyj@zzu.edu.cn
0
040-4039/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4039(03)00812-8

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956
K. Lin et al. / Tetrahedron Letters 44 (2003) 3955–3957
Scheme 2.
leads to the formation of imidazoline rings (Fiber I),
subsequent coordination with palladium dichloride pro-
ducing the palladium complex with imidazoline rings
attached to the PAN backbone (Scheme 1).
It is well known that the commercial PAN fiber is not
pure polyacrylonitrile. It contains copolymer and other
additives, which make it easy for the fiber to be dyed
and also enhance its stability. So, for our purposes, the
coordinating ability of PAN fiber with palladium
dichloride was measured. The results indicated that
nitrile groups do not coordinate with Pd even under
forcing conditions (refluxing in methanol for 2 days).
Such results are different from those mentioned in
The fabric palladium catalyst was characterized by
elemental analysis, IR, SEM and XPS. The strong
−
1
absorption at 2243 cm indicating the presence of the
nitrile group in the PAN was weak both in the fiber (I)
5
−
1
Sherrington’s reports.
and in the catalyst A. The absorption at 1645 cm ,
corresponding to the imine groups appeared strongly in
For the purpose of finding out which was the best catalyst
or the Heck reaction, the activities (Scheme 2) of three
types of palladium complex containing heterocyclic rings
were examined. The results are listed in Table 1.
−
1
fiber (I), and shifted to 1662 cm in catalyst A. From
analysis of the surface using Scanning Electron
Microscopy (SEM), we concluded that the surface of
catalyst A changed significantly from ditch shape to
nearly planar after reaction, and that the palladium
components had dispersed on the planar surface. The
XPS results show that the valencies of palladium on the
fiber were Pd(II) and Pd(0); their 3d5/2 and 3d3/2 bind-
ing energies were 338.10, 337.15 and 342.30, 340.95 eV,
respectively. The mechanical properties were measured
on a material test instrument (Instron 4465). The
Tenacity at Break of catalyst A was 2.7 CN/Dtex, 80%
compared to the original 3.4 CN/Dtex of PAN.
From Table 1, it can be seen that excellent conversions
could be achieved when catalysts A and C were used
(
entries 1 and 3), but the activity of B was very low
(entry 2). These results indicate that the reactive moiety
in both catalysts A and C was a palladium complex
involving imidazoline.
The results of Heck reactions promoted by catalyst A,
listed in Table 2, showed: (1) The reaction did not have
a
Table 1. The activities of different Pd-containing catalysts
Catalystb
Pd in catalyst (mmol/g)
Pd used in Heck reaction (mmol)
Isolated yield (%)
c
Entry
1
2
3
A
B
C
0.576
3.01
3.10
1%
2%
1%
98
8
100
a
ArI: 1.0 mmol, solvent: 1,4-dioxane, base: Et N, temperature: 100°C, time: 1 h, R=Me.
3
b
A-fiber containing palladium and imidazoline complex; B-complex obtained from the reaction of triethylenetetramine with PdCl2 (2:1, mole
ratio); C-complex obtained from the reaction of imidazoline with PdCl2 (2:1, mole ratio).
Isolated yields based on PhI.
c
Table 2. The results of Heck reactions catalyzed by catalyst A
Entry
PhI (mmol)
R
Cat. (mmol)
Base
Solvent
Time (h)
Yielda (%)
TONsc
1
2
3
4
5
6
7
8
9
1
1
1
1
1
Et
Et
Et
Et
Et
Et
Et
Me
Me
Bu
Bu
Bu
0.01
0.01
0.01
0.01
0.01
0.01
0.003
0.001
0.01
0.01
0.01
0.003
Et N
Dioxane
Dioxane
Dioxane
Dioxane
Toluene
Benzene
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
1
0.15
0.5
2
2
3
130
12
2
1
2
97
25
89
72
81
76
95
92
3
Et N
3
Et N
3
Na CO
2
3
Et N
3
1
Et N
3
100
10
10
1
1
100
Et N
31500
9240
990
3
Et N
3
b
Et N
99
3
10
11
12
Et N
94
100
94
3
Et N
3
Et N
92
31233
3
a
b
c
Isolated yields based on PhI.
The procedure was repeated 20 times, and the catalyst showed no loss of activity after recycling 20 times.
Turnover numbers.

K. Lin et al. / Tetrahedron Letters 44 (2003) 3955–3957
3957
an induction period (entries 2 and 3), because part of
Pd(II) had changed into Pd(0), which was confirmed by
XPS determination. (2) Addition of base was necessary
Commun. 2000, 1877–1878; (e) Schwarz, J.; Bohm, V. P.
W.; Gardiner, M. G.; Grosche, M.; Herrmann, W. A.;
Hievinger, W.; Raudschl-Sieber, G. Chem. Eur. J. 2000,
1773–1780; (f) Shuttleworth, S. J.; Allin, S. M.; Wilson, R.
D.; Nasturica, D. Synthesis 2000, 8, 1035–1077; (g) White-
wombe, N. J.; Hii, K. K.; Gibson, S. E. Tetrahedron 2001,
(
entries 1 and 4). The Heck reaction with no additional
base, but using the excess basic groups on the fiber (for
example, the imidazoline) was attempted, but the result
were unpredictable, probably because the catalyst
became coated with the salt formed. (3) The best
turnover numbers (TONs) were 31,500 for a single run
5
7, 7449–7476; (h) Bennur, T. H.; Ramani, A.; Bal, R.;
Chanda, B. M.; Sivasanker, S. Catal. Commun. 2002, 3,
93–496.
4
(
entry 7). The catalyst can be reused at least 20 times
3
4
5
. Andersson, C. M.; Karabelas, K.; Hallberg, A. J. Org.
Chem. 1985, 50, 3891–3895.
. Colacot, T. J.; Gore, E. S.; Kuber, A. Organometallics
without any loss of activity. The products obtained
were trans, as determined by H NMR spectroscopy,
1
which is different from that reported by Bhalchandra,
2
002, 21, 3301–3304.
. Tang, H. G.; Sherrington, D. C. Polymer 1993, 34, 2821–
829.
. Bhanage, B. M.; Arai, M. Catal. Rev. 2001, 43, 315–344.
. Typical synthetic procedure: Into solution of
6
Bhanage and Masahik Arai.
2
When chlorobenzene was used as a substrate, only a
trace of product was obtained, even under pressure.
Reaction of bromobenzene or p-nitrochlorobenzene
with methyl acrylate using catalyst A under the same
reaction conditions (Table 2, entry 9), gave yields of 47
and 8%, respectively.
6
7
a
triethylenetetramine (5 g) in glycol (50 mL), PAN fiber (1.0
g, 3.33 dtex, 65 mm, Kingshan Co. Ltd, Shanghai) was
immersed at 120°C for 2 h. After the mixture had cooled
to room temperature, the fiber was recovered by filtration,
then washed with H O, immersed in H O (100 mL) for at
2
2
In summary, we have described the synthesis of a
polymer (fiber)-supported palladium catalyst and its
catalytic activity in Heck reactions. The fiber catalyst
can be recycled more than 20 times without any loss of
least 30 min, and filtered. This procedure was repeated
until the pH value of the H O washing was 7, which
2
ensured complete removal of the amine and any soluble
materials from the fiber. The fiber was then dried at 60°C
in vacuo. It became yellow and contained 1.72 mmol/g
imidazoline. The fiber (0.1 g) was immersed in saturated
7
activity or selectivity.
PdCl /methanol solution (ca. 100 mL) at room tempera-
2
References
ture under argon and in the dark for 2 days. When the
reaction was complete, the color of the methanol solution
of palladium dichloride changed from red–brown to pale
brown as a result of palladium(II) loss to the fiber. After
the coordination reaction, the fiber was extracted with
methanol for at least 24 h at room temperature to remove
any palladium complex that was not chemically bonded to
the fiber. The fiber was deep-brown in color and contained
0.576 mmol/g palladium after drying in vacuo.
1
2
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