Copper(I) and palladium nanoparticles supported on ethylenediamine- functionalized cellulose as an efficient catalyst for the 1,3-dipolar cycloaddition/direct arylation sequence

Article abstract of DOI:10.1002/aoc.3091

Cu(I) and nanoparticles of Pd supported on ethylenediamine-functionalized cellulose as a novel bio-supported catalyst was synthesized and characterized. The synthesized catalyst was found to be a highly efficient heterogeneous catalyst for the synthesis o

Full text of DOI:10.1002/aoc.3091

Full Paper
Received: 25 August 2013
Revised: 9 October 2013
Accepted: 12 October 2013
Published online in Wiley Online Library: 15 January 2014
(wileyonlinelibrary.com) DOI 10.1002/aoc.3091
Copper(I) and palladium nanoparticles supported
on ethylenediamine-functionalized cellulose as
an efficient catalyst for the 1,3-dipolar
cycloaddition/direct arylation sequence
Sajjad Keshipour and Ahmad Shaabani*
Cu(I) and nanoparticles of Pd supported on ethylenediamine-functionalized cellulose as a novel bio-supported catalyst was
synthesized and characterized. The synthesized catalyst was found to be a highly efficient heterogeneous catalyst for the
synthesis of 1,4,5-trisubstituted 1,2,3-triazoles through a sustainable 1,3-dipolar cycloaddition/direct arylation sequence.
The catalyst could be easily recovered by simple filtration and reused for at least five cycles without losing its activity.
Copyright © 2014 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: 1,3-dipolar cycloaddition; arylation; cellulose; heterogeneous catalyst
1,3-Dipolar cycloaddition and direct arylation tandem reaction
is a good strategy for the synthesis of 1,4,5-trisubstituted 1,2,3-
Introduction
Catalytic processes induced by heterogeneous catalysts are
interesting because of ease of handling, simple work-up and
regenerability. Recently, metal nanoparticles have attracted
much attention in view of their potential tunability in terms of
size, shape and activity.[1] However, control of nanoparticle prop-
erties, with particular respect to size and dispersity, is imperative
as this will determine activity in the desired applications. The
selection of the support in the design of heterogeneous catalysts
can help control their properties and enhance activity. Many
different materials have been employed to support nanoparticles
and various homogeneous catalysts, including mesoporous
silica,[2] activated carbon,[3] (bio) polymers[4] and biomass.[5]
As the most important structural material in plants, cellulose is
triazoles from simple starting materials. Cu(I)-catalyzed 1,3-dipolar
cycloaddition reaction has been used as a convenient route for
the synthesis of 1,2,3-triazoles in recent years.[18] Among proce-
dures for transition-metal-catalyzed direct arylations, strategies
relying on a Pd(0)/Pd(II) manifold arguably proved to be the most
versatile.[17] We wish to synthesize the Cu(I)/Pd(0) bifunctionalized
catalyst, which is catalytically applicable to both 1,3-dipolar cyclo-
addition and direct arylation reactions. Hence ethylenediamine–
cellulose (EDAC) modified with Cu(I) and Pd(0) (Cu(I)/PdNPs@EDAC)
was synthesized and used for the 1,3-dipolar cycloaddition/direct
arylation sequence in a one-pot strategy.
an almost inexhaustible polymeric raw material with fascinating Experimental
structure and properties. This polysaccharide is a highly function-
Preparation of Cu(I)/PdNPs@EDAC
alized and linear stiff-chain homopolymer, formed by the repeated
connection of d-glucose building blocks. Cellulose is characterized
by its hydrophilicity, chirality, biodegradability, broad chemical
modifying capacity and its formation of versatile semi-crystalline
fiber morphologies.[6] These abilities of the cellulose derivatives
make them interesting biodegradable metal supports.[7,8]
1,2,3-Triazoles are the most important heterocycles, owing to
their unique chemical and structural properties, and various syn-
thetic methods have been developed for their construction.[9] Re-
cently, the applications of this building block have been
extended into various research fields, such as biological sci-
ence,[10] material chemistry[11] and medicinal chemistry.[12]
1,4,5-Trisubstituted 1,2,3-triazoles are an important class of
triazoles that are difficult to synthesize from simple starting mate-
rials (Scheme 1).[13–17] Two-step reactions and tedious work-up
are drawbacks of the reports. Therefore, development of new
routes initiated from simple starting materials with least work-
up are of interest.
PdNPs@EDAC was synthesized according our previous report.[19]
For preparation of Cu(I)/PdNPs@EDAC, PdNPs@EDAC (2.00 g) was
added to a 5 ml solution of CuCl (0.60 mol lÀ1). The mixture was
stirred at room temperature for 24 h. Finally, Cu(I)/PdNPs@EDAC
was obtained as a dark solid from the mixture via filtration and
washed with acetone (3× 5 ml).
Typical Procedure for Synthesis of Product 6a
Benzyl bromide (1) (1.00 mmol), sodium azide (2) (1.20 mmol),
phenylacetylene (3) (1.00 mmol) and Et3N (0.50 mmol) were
*
Correspondence to: Ahmad Shaabani, Faculty of Chemistry, Shahid Beheshti
University, GC, PO Box 19396–4716, Tehran, Iran. E-mail: a-shaabani@sbu.ac.ir
Faculty of Chemistry, Shahid Beheshti University, Tehran, Iran
Appl. Organometal. Chem. 2014, 28, 116–119
Copyright © 2014 John Wiley & Sons, Ltd.

1,3-Dipolar cycloaddition/arylation sequence
of Cu(I) with PdNPs@EDAC. The results showed that reduction
of Pd(II) to Pd(0), after coordination to ethylenediamine, gave
the homogeneous smaller PdNPs distributed on the surface. After
deposition of Pd(0) on the cellulose backbone, Cu(I) was
complexed with ethylenediamine. Ethylenediamine was afforded
homogeneous distribution of Pd(0) and Cu(I) on the support,
enabling us to make a successful conversion with low loading
of Pd and Cu. Thus a very active, homogeneous and stable
heterogeneous catalytic system was obtained containing PdNPs
and Cu(I) on the surface of EDACs.
Characterization of Cu(I)/PdNPs@EDAC
Vacuum-dried Cu(I)/PdNPs@EDAC was employed for TGA, trans-
mission electron microscopy (TEM) and flame atomic absorption
spectroscopy (FAAS). TEM images of Cu(I)/PdNPs@EDAC revealed
that a large number of PdNPs with particles size between 4.8 and
9.1 nm were formed and uniformly distributed on to the surface
of EDAC after deposition (Fig. 1).
Pd and Cu(I) loading in the Cu(I)/PdNPs@EDAC catalyst was
determined to be 6.43 wt% and 0.81 wt%, respectively, based
on FAAS analysis. Also, our attempts to increase Cu(I) loading
even at high concentrations of Cu(I) failed (Table 1).
TGA evidenced that EDAC is decomposed at above 304 °C in air,
which is comparable and even better than cellulose (decomposi-
tion temperature > 290 °C).[8] Decomposition of PdNPs@EDAC
and Cu(I)/PdNPs@EDAC at about 240 °C indicated good thermal
stability for both compounds (Fig. 2). While the decomposition
temperature of PdNPs@EDACs decreased drastically when com-
pared with EDACs, the complexation of Cu(I) with PdNPs@EDAC
had no effect on the thermal properties of PdNPs@EDAC. This
may be attributed to the catalytic activity of Pd on the oxidative
degradation of cellulose.[20]
Scheme 1. Reported approaches for the synthesis of 1,4,5-trisubstituted
1,2,3-triazoles.
added to a round-bottomed flask containing a colloidal mixture
of Cu(I)/PdNPs@EDAC (0.04 g) in DMF (5 mL) and the mixture
was stirred at 100 °C for 2 h. Then, 2-iodotoluene (4a) (1.00 mmol)
was added to the reaction mixture and stirring was continued for
6 h. Upon completion, the reaction mixture was cooled to room
temperature, and Cu(I)/PdNPs@EDAC was separated by filtration
and washed with acetone (2 × 3 mL). The filtrate solvent was
evaporated under vacuum and the product 6a was purified by
column chromatography with n-hexane/ethyl acetate (4:1) in
91% yield as a yellow solid.
Recycling of Cu(I)/PdNPs@EDAC
After carrying out the reaction of benzyl bromide (1), sodium
azide (2), phenylacetylene (3) and 2-iodotoluene (4a), the reac-
tion mixture was filtered off and Cu(I)/PdNPs@EDAC separated
as a gray solid, washed with acetone (2 × 5 mL) and reused.
Table 1. Optimization of CuCl loading on the catalyst
[CuCl] (mol LÀ1
)
CuCl (wt%)
Entry
Results and Discussion
1
2
3
4
0.20
0.40
0.60
0.80
0.32
0.43
0.81
0.81
Synthesis of Cu(I)/PdNPs@EDAC
We functionalized cellulose with ethylenediamine as a ligand
with the capability of chemical coordination to Pd(II) and Cu(I).
Preparation of Cu(I)/PdNPs@EDAC was achieved in three steps,
including (i) complexation of Pd(II) with EDAC, (ii) reduction of
Pd(II) to Pd(0) to produce PdNPs@EDAC and (iii) complexation
Optimization conditions: PdNPs@EDAC (2.00 g), CuCl solution (5 mL),
room temperature, 24 h.
Figure 1. TEM images of (A) EDAC and (B) Cu(I)/PdNPs@EDAC.
Appl. Organometal. Chem. 2014, 28, 116–119
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S. Keshipour and A. Shaabani
20
-20
B: 239 C
C: 241 C
A: 304
C
-60
-100
0
100
200
300
400
500
Temperature [ºC]
Figure 2. TGA spectra of (A) EDAC, (B) PdNPs@EDAC and (C) Cu(I)/
PdNPs@EDAC in air.
Scheme 2. Cu(I)/PdNPs@EDAC-catalyzed one-pot synthesis of tiazoles.
triazole. These results are very promising, and good yields were
obtained in a relatively simple approach (Table 3).
Synthesis of 1-Benzyl-4,5-diphenyl-1H-1,2,3-triazoles
For elucidation of the catalytic activity of Cu(I), Pd and EDAC, the
reaction of benzyl bromide (1), sodium azide (2), phenylacetylene
(3) and 2-iodotoluene (4a) was investigated in the presence of
EDAC, PdNPs@EDAC and Cu(I)@EDAC. The reaction did not pro-
ceed using EDAC and PdNPs@EDAC as the catalysts, even after a
long duration of time. Also, 1-benzyl-4-phenyl-1H-1,2,3-triazole (5)
was obtained as the product in the presence of Cu(I)@EDAC in
84% yield.
The catalytic activity of the newly synthesized Cu(I)/PdNPs@EDAC
was evaluated through the 1,3-dipolar cycloaddition/direct
arylation sequence with benzyl bromide (1), sodium azide (2),
phenylacetylene (3) and 2-iodotoluene (4a) as a model reaction.
At low catalyst loading, the reaction required a long time to com-
plete. As the catalyst amount was increased to 1.50 mol% Cu and
3.66 mol% Pd the reaction proceeded more rapidly at 100 °C
(Table 2, entries 1–4). After screening a variety of solvents, DMF
was determined to be the best one (Table 2, entries 5–8). Since
the amounts of catalyst and solvent were optimized, the influ-
ence of base on the reaction was also studied (Table 2, entries
9–11). It was found that the best base was Et3N, with a molar ratio
phenylacetylene/Pd of 100/3.66 in DMF at 100 °C.
Table 3. Cu(I)/PdNPs@EDAC-catalyzed one-pot synthesis of 1-benzyl-
4,5-diphenyl-1H-1,2,3-triazoles
To evaluate the scope and limitations of the catalyst, we ex-
tended using Cu(I)/PdNPs@EDAC in a one-pot 1,3-dipolar cyclo-
addition/direct arylation sequence using various aryl bromides
and aryl iodides (4a–m) (Scheme 2).
Cu(I)/PdNPs@EDAC was recognized as a highly active catalyst
for thermal intermolecular copper-catalyzed 1,3-dipolar cycload-
dition reaction and palladium-catalyzed direct arylation of 1,2,3-
Table 2. Optimization of the reaction conditions for the 1,3-dipolar
Entry
ArX (4)
Product 6 Isolated yield (%)
cycloaddition/direct arylation sequencea
1
2
3
4
5
6
2-Iodotoluene (4a)
6a
6a
6b
6b
6c
91
90
85
81
83
82
Amount of catalyst Solvent
(Cu/Pd mol%)
Base
Isolated yield (%)
Entry
2-Bromotoluene (4b)
3-Iodotoluene (4c)
1
1.00/2.44
1.25/3.05
1.50/3.66
2.15/4.27
1.50/3.66
1.50/3.66
1.50/3.66
1.50/3.66
1.50/3.66
1.50/3.66
1.50/3.66
DMF
DMF
DMF
DMF
NMPb
H2O
Et3N
48
81
91
92
80
76
53
85
70
69
84
3-Bromotoluene (4d)
4-Bromoanisole (4e)
2
Et3N
3
Et3N
1-Bromo-4-(trifluoromethyl)
benzene (4f)
6d
4
Et3N
5
Et3N
7
4-Chlorobromobenzene (4g)
4-Fluorobromobenzene (4h)
4-Bromoacetophenone (4i)
Ethyl4-bromobenzoate (4j)
2-Bromopyridine (4k)
3-Bromopyridine (4l)
1-Bromonaphthalene (4m)
6e
6f
85
82
83
81
80
87
81
6
Et3N
8
7
CH3CN
PhCH3
DMF
DMF
DMF
Et3N
9
6g
6h
6i
8
Et3N
10
11
12
13
9
K2CO3
NaOAc
pyridine
10
11
6j
6k
aReaction conditions: benzyl bromide (1) (1.00 mmol), sodium azide
(2) (1.20 mmol), phenylacetylene (3) (1.00 mmol), 2-iodotoluene
(4a) (1.00 mmol), base (0.50 mmol), solvent (5 mL), 100 °C, 8 h.
bN-Methyl pyrolidone.
General reaction conditions: benzyl bromide (1) (1.00 mmol),
sodium azide (2) (1.20 mmol), phenylacetylene (3) (1.00 mmol),
aryl halide (4) (1.00 mmol), Et3N (0.50 mmol), DMF (5 mL),
100 °C, 8 h.
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Appl. Organometal. Chem. 2014, 28, 116–119

1,3-Dipolar cycloaddition/arylation sequence
Scheme 3. Proposed mechanism.
promising bio-support for catalysis, with good chemical stability
as indicated by recyclability of the catalyst.
Acknowledgment
We gratefully acknowledge financial support from the Research
Council of Shahid Beheshti University.
References
Figure 3. Successive trials using recoverable Cu(I)/PdNPs@EDAC for the
1,3-dipolar cycloaddition/direct arylation sequence. General reaction con-
ditions: benzyl bromide (1) (1.00 mmol), sodium azide (2) (1.20 mmol),
phenylacetylene (3) (1.00 mmol), 2-iodotoluene (4a) (1.00 mmol), DMF
(5 mL), Et3N (1.00 mmol), 100 °C, 8 h.
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The recyclability of Cu(I)/PdNPs@EDAC was surveyed. Only minor
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Conclusion
A
novel bio-supported Cu(I) and nanoparticles of Pd(0),
PdNPs@EDAC were synthesized by uniform distribution of PdNPs
on to ethylenediamine-functionalized cellulose and its com-
plexation with Cu(I). The catalyst successfully promoted the
1,3-dipolar cycloaddition/direct arylation sequence with fairly
good yields. This is an efficient one-pot strategy for the synthe-
sis of 1,4,5-trisubstituted 1,2,3-triazoles in good yields and short
reaction times starting from simple materials. The introduction
of ethylenediamine into the cellulose structure has advantages
such as contributing to a complexation of Cu(I) on the catalyst
Supporting Information
Additional supporting information may be found in the online
version of this article at the publisher’s web site.
surface. Also, ethylenediamine–cellulose proved to be
a
Appl. Organometal. Chem. 2014, 28, 116–119
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