A reusable CuSO4 · 5H2O/cationic 2,2′-bipyridyl system catalyzed homocoupling of terminal alkynes in water

Article abstract of DOI:10.1002/aoc.1780

A reusable CuSO₄ · 5H₂O/cationic 2,2′-bipyridyl system catalyzed the homocoupling reaction of terminal alkynes in water using I₂ as the additive in the presence or absence of tetrabutylammonium bromide, giving the 1,3-diynes in good to high yields. After reaction, the residual aqueous solution could be reused several times.

Full text of DOI:10.1002/aoc.1780

Full Paper
Received: 19 November 2010
Revised: 21 December 2010
Accepted: 17 January 2011
Published online in Wiley Online Library: 25 March 2011
(wileyonlinelibrary.com) DOI 10.1002/aoc.1780
ꢀ
A reusable CuSO · 5H O/cationic 2,2 -bipyridyl
4
2
system catalyzed homocoupling of terminal
alkynes in water
∗
Tzu-Min Wu, Shao-Hsien Huang and Fu-Yu Tsai
ꢀ
A reusable CuSO4 · 5H2O/cationic 2,2 -bipyridyl system catalyzed the homocoupling reaction of terminal alkynes in water using
I2 as the additive in the presence or absence of tetrabutylammonium bromide, giving the 1,3-diynes in good to high yields.
After reaction, the residual aqueous solution could be reused several times. Copyright ꢀc 2011 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
ꢁ
Keywords: copper(II) sulfate; cationic 2,2 -bipyridyl; water; reusable; terminal alkyne; homocoupling; 1,3-diyne
Introduction
Br Me N
NMe3 Br
3
The homocoupling of terminal alkynes is a straightforward
[
1]
method for the preparation of 1,3-diynes, which are impor-
N
N
[
2–7]
[8–12]
tant building blocks of natural products,
polymers,
1
pharmaceuticals[
13,14]
and organic/inorganic composites.
[15–18]
CuSO ·5H O/1 (5 mol%)
Subsequent to Glaser’s discovery of the homocoupling of cop-
per(I) phenylacetylide for the formation of 1,4-diphenyl-1,3-
butadiyne,[ Hay successfully improved the acetylenic coupling
4
2
R
R
R
KOAc, I , H O, 120 °C, 24 h
2
2
19]
with or without TBAB
[
20,21]
reaction by using a catalytic amount of Cu(I) salt.
Cur-
Scheme 1. Cu/1-catalyzed homocoupling of terminal alkynes in water.
rent methods for the transition-metal-catalyzed homocoupling
of terminal alkynes for 1,3-diyne synthesis include Pd/Cu co-
catalyst[
22–36]
and copper salt systems.
[37–46]
Although Pd/Cu
performed in neat water using CuSO4 · 5H2O/1 as a catalytic
system, and moreover, that this catalytic system can be reused
several times after simple extraction with hexane or EtOAc
catalytic systems are highly efficient and can be applied
under mild reaction conditions, Pd catalysts are more ex-
pensive than the cheaper and more readily available Cu
salts, and it would therefore be valuable to develop a new
copper catalytic system for the homocoupling of terminal
alkynes.
(
Scheme 1).
Results and Discussion
Copper-catalyzed homocoupling of terminal alkynes is usually
conducted in harmful organic solvents, such as CH3CN, DMF
As shown in Table 1, phenylacetylene 2a was chosen as the
reactant for the optimization of the homocoupling reaction
conditions. It was found that a 28% GC yield of 3a was obtained
[
40]
and toluene, although reactions in ionic liquids,
supercritical
CO2[
37,41]
and solvent-free conditions
[47]
have been reported. In
◦
recent years, with the development of environmentally benign
synthesis methods and sustainable technologies, there has been
an increasing number of attempts by chemists to perform
transition-metal-catalyzed organic reactions using water as the
reaction medium. Although the reaction rates of organic reactions
in water may be slower than those in organic solvents, the
advantages of the use of water as a solvent include not
only its low-cost, lack of toxicity and high safety, but also
the fact that it provides an opportunity for the recovery and
when the reaction vessel was sealed under air at 120 C for 24 h
in the presence of 5 mol% CuSO4 · 5H2O/1 and 1 equiv. KOAc
(entry 1). The addition of I2 as an oxidant was considered to elicit
superior results, 0.25 equiv. being sufficient for completion of
the homocoupling reaction (entries 2–4). We have previously
reported that 2-iodoethynylbenzene can be synthesized in a
68% yield using 1 equiv. 2a and 2 equiv. I2 in water under a
catalytic amount of CuI at room temperature.[ Thus, not only
the oxidative homocoupling of phenylethynylcopper(I) species to
56]
[
48–55]
recycling of the transition-metal catalysts.
We recently
ꢁ
developed a water-soluble cationic 2,2 -bipyridyl ligand 1 that
can be used in combination with Pd(NH3)2Cl2 to catalyze
terminal alkyne homocoupling reactions in the presence of
CuI as the co-catalyst in water under aerobic conditions, and
demonstrated the excellent reusability of this catalyst. Herein,
we report that the homocoupling of terminal alkynes can be
∗
Correspondence to: Fu-Yu Tsai, Institute of Organic and Polymeric Materials,
National Taipei University of Technology, 1, Sec. 3, Chung-Hsiao E. Rd., Taipei
06, Taiwan. E-mail: fuyutsai@ntut.edu.tw
1
[
36]
Institute of Organic and Polymeric Materials, National Taipei University of
Technology, 1, Sec. 3, Chung-Hsiao E. Rd., Taipei 106, Taiwan
Appl. Organometal. Chem. 2011, 25, 395–399
Copyright ꢀc 2011 John Wiley & Sons, Ltd.

T.-M. Wu, S.-H. Huang and F.-Y. Tsai
Table 1. Cu-catalyzed homocoupling of phenylacetylene 2a in
water
Table 2. Reuse studies of Cu/1-catalyzed homocoupling of pheny-
lacetylene 2a.a
a
Yield (%)b
·
CuSO4 5H O/1 (5 mol%)
2
Entry Initial run Reuse 1 Reuse 2 Reuse 3 Reuse 4 Reuse 5
Base, I , H O, 120
°C, 24 h
2
2
2a
1
2c
99 (95)
99 (95)
99 (93)
99 (94)
66 (60)
99 (92)
43 (33)
82 (76)
13
0
71 (62)
61 (53)
a
Reaction conditions: phenylacetylene (1 mmol), CuSO4 · 5H2O/1
◦
(
5 mol%), KOAc (1 mmol), I2 (0.25 mmol), H2O (3 ml) at 120 C for
3a
b
c
2
4 h. GC yields. Isolated yields are given in parentheses. 0.5 mmol of
Base (equiv.) Additive (equiv.) Yield (%)b
TBAB was added at the initial run.
Entry
[Cu] source
1
2
3
CuSO4 · 5H2O
CuSO4 · 5H2O
CuSO4 · 5H2O
CuSO4 · 5H2O
CuSO4 · 5H2O
CuSO4 · 5H2O
CuSO4 · 5H2O
CuSO4 · 5H2O
CuSO4 · 5H2O
CuSO4 · 5H2O
CuSO4 · 5H2O
CuSO4 · 5H2O
KOAc (1)
KOAc (1)
KOAc (1)
KOAc (1)
KOAc (1)
KOH (1)
–
28
50
I2 (0.1)
residual aqueous solution was subsequently charged with 2a,
KOAc and I2 for the next run. It was found that the residual
aqueous solution could be reused several times; however, catalyst
deactivation occurred during each run. Significant deactivation
of the catalytic system was observed after the first reuse run,
and the catalytic activity was completely lost at the fifth reuse
run (entry 1). We then experimented with the addition of
tetrabutylammonium bromide (TBAB) to the initial run, making
the reaction more homogeneous. As illustrated in entry 2, the
product yields were greatly improved: at the second reuse
run, a near-quantitative yield was still obtained, and even at
the fifth reuse run a 61% yield was obtained, indicating that
the use of this catalytic system may meet the goals of green
chemistry.
To explore the scope of this aqueous catalytic system, the
reactions of a variety of terminal alkynes with various functional
groups were evaluated (Table 3). The homocoupling of 4-
substituted aryl terminal alkynes under optimized conditions gave
good to high yields, and even alkali-sensitive carbonyl groups
were tolerated in this reaction (entries 1–4). 3-Substituted aryl
terminal alkynes 2f and 2g were also homocoupled efficiently
to afford the corresponding products, 3f and 3g, in 80 and
I2 (0.25)
I2 (0.5)
99 (95)
95 (90)
34
4
5c
I2 (0.25)
I2 (0.25)
I2 (0.25)
I2 (0.25)
I2 (0.25)
I2 (0.25)
I2 (0.25)
I2 (0.25)
I2 (0.25)
I2 (0.25)
I2 (0.25)
I2 (0.25)
I2 (0.25)
I2 (0.25)
I2 (0.25)
I2 (0.25)
I2 (0.25)
I2 (0.25)
6
7
8
9
11
NaOH (1)
K2CO3 (1)
Na2CO3 (1)
Cs2CO3 (1)
NaOAc (1)
Et3N (1)
14
5
7
1
1
1
1
1
1
1
1
1
1
2
2
2
0
1
2
3
4
5
6
7
8
9
0
8
13
41
Cu(NO3)2 · 3H2O KOAc (1)
CuCl2 · 2H2O KOAc (1)
54
42
Cu(ClO4)2 · 6H2O KOAc (1)
47
Cu(OAc)2·H2O
CuI
KOAc (1)
KOAc (1)
KOAc (1)
KOAc (1)
KOAc (1)
KOAc (1)
KOAc (1)
53 (45)
81 (70)
69 (61)
72 (64)
69 (62)
51 (42)
13
CuBr
CuCl
Cu2O
1
2d
CuO
CuSO4 · 5H2O
a
Reaction conditions: phenylacetylene (1 mmol), [Cu]/1 (5 mol%), base
◦
b
(
1 mmol), and H2O (3 ml) at 120 C for 24 h. GC yields. Isolated yields
83% yields, respectively (entries 5 and 6). The observation of
c
d
aregiveninparentheses. 2 mol%ofcatalystwasused. Intheabsence
slightly lower yields for the homocoupling of 2-substituted aryl
terminal alkynes 2h–2j was probably due to the steric congestion
of the substituent located at the ortho-position (entries 7–9).
Terminal alkynes 2k and 2l were also homocoupled, delivering the
corresponding products in 74 and 68% yields, respectively (entries
of 1.
form 3a, but also, to a certain extent, the cross-coupling of 2-
iodoethynylbenzene and phenylethynylcopper(I) species leading
to the formation of 3a, may be parallel routes in the terminal
1
0 and 11).
3
As for Csp -connected terminal alkynes, the employment of
[
45,57]
alkyne homocoupling reaction.
Our attempt to reduce the
hydroxyl-group-containing terminalalkynes2m–2oledtothefor-
mation of 3m–3o in yields between 67 and 90% (entries 12–14).
However, the homocoupling of alkyl terminal alkynes 2p–2r un-
der the optimized conditions afforded low isolated yields (entries
catalyst loading to 2 mol% resulted in the formation of 3a
in only a 34% yield (entry 5). Other inorganic and organic
bases were also employed in this reaction, but this resulted
in product yields of only 5–41% (entries 6–12). Among the
copper catalysts, although the use of copper halides afforded
yields between 69 and 81% (entries 17–19), the employment
of CuSO4 · 5H2O as the catalyst in entry 3 gave the best
results. For comparison, the reaction was also conducted in
the absence of ligand 1: this revealed the importance of the
ligand, 3a being obtained in only a 13% yield in this case
1
5, 17 and 19). The low reactivity of the alkyl terminal alkynes
was presumably due to their weak acidity as compared with aro-
matic terminal alkynes; similar results have been obtained in the
[44,58]
homocoupling of such alkynes in organic solvents.
Addition
of TBAB into the aqueous solution greatly improved the reac-
tion, giving 3p–3r in yields between 50 and 73% (entries 16, 18
and 20).
(
entry 22).
Under the optimized reaction conditions (Table 1, entry 3), we
studied the reusability of the residual aqueous solution, which
is important from the viewpoints of practical and industrial
applications. As shown in Table 2, after the completion of the
initial run of the homocoupling reaction of 2a, the reaction
mixture was extracted with hexane three times, and the
Conclusion
In conclusion, we have successfully combined CuSO4 · 5H2O
ꢁ
and a water-soluble cationic 2,2 -bipyridyl ligand to catalyze the
homocoupling of terminal alkynes for the formation of 1,3-diynes
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Copyright ꢀc 2011 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2011, 25, 395–399

ꢁ
A reusable CuSO4 · 5H2O/cationic 2,2 -bipyridyl system
a
Table 3. CuSO4 · 5H2O/1-catalyzed homocoupling of terminal alkynes in water.
CuSO4 5H O/1 (5 mol%)
·
2
R
R
R
KOAc, I2, H O, 120 °C, 24 h
2
2
3
Entry
1
Alkyne
Product
Yield (%)b
93
2b
3b
3c
3d
2
3
2c
81
63
MeO
O
MeO
OMe
O
2d
O
4
5
O
2e
2f
EtO
O
O
3e
3f
64
80
EtO
OEt
6
2g
OMe
3g
83
MeO
MeO
7
8
2h
2i
3h
3i
68
72
MeO
Cl
OMe
OMe
9
2j
3j
63
74
Cl
Cl
10
2k
3k
11
2l
3l
68
1
2
3
CH (CH ) OH
2m
2n
HO(H C) H C
CH (CH ) OH
3m
3n
67
72
2
2
3
2
3
2
2
2 3
1
HO
OH
OH
1
4
2o
2p
3o
3p
90
OH
HO
OH
1
1
1
1
1
2
a
5
(CH ) CH
H C(H C)
(CH ) CH
3
27
66
2
3
3
3
2
3
2
3
6c
7
(CH ) CH
2q
2r
H C(H C)
(CH ) CH
3
3q
3r
31
2
5
3
3
3
2
5
9
2
5
8c
9
73
(CH ) CH
H C(H C)
(CH ) CH
3
11
2
9
3
2
2
9
0c
50
◦
b
Reaction conditions: terminal alkyne (1 mmol), CuSO4 · 5H2O/1 (5 mol%), KOAc (1 mmol), I2 (0.25 mmol), H2O (3 ml) at 120 C for 24 h. Isolated
yields. c 0.5 mmol of TBAB was used.
Appl. Organometal. Chem. 2011, 25, 395–399
Copyright ꢀc 2011 John Wiley & Sons, Ltd.
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T.-M. Wu, S.-H. Huang and F.-Y. Tsai
ingoodtohighyields. ThisgreenprocedureemploysCuSO4 ·5H2O References
as a cost-effective catalyst and neat water as the solvent, which
enables the reuse of the catalytic system, and has potential for use
in industrial applications.
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