Cu (I) immobilized on functionalized SBA-15: A recyclable catalyst for the synthesis of 1,3-diynes using terminal alkynes without base

Article abstract of DOI:10.1016/j.catcom.2013.04.012

A new functionalized SBA-15 catalyst immobilized CuI was successfully prepared, and the catalytic activity was tested in the oxidative homocoupling of terminal alkynes at the absence of base, and good to excellent yields was obtained to get 1,3-diynes without any side product formation in the solution of DMSO. Moreover, the system also allowed the synthesis of unsymmetric 1,3-diynes by cross-coupling of two different terminal alkynes. Finally, the catalyst could be reused for several times without a significant loss of activity.

Full text of DOI:10.1016/j.catcom.2013.04.012

Cu (I) immobilized on functionalized SBA-15: A recyclable catalyst for the
synthesis of 1,3-diynes using terminal alkynes without base
Zongyan Ma, Xiaoyu Wang, Shuoyun Wei, Honglei Yang, Fengwei
Zhang, Peng Wang, Miao Xie, Jiantai Ma
PII:
DOI:
Reference:
S1566-7367(13)00143-X
doi: 10.1016/j.catcom.2013.04.012
CATCOM 3477
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
21 December 2012
16 April 2013
17 April 2013
Please cite this article as: Zongyan Ma, Xiaoyu Wang, Shuoyun Wei, Honglei Yang,
Fengwei Zhang, Peng Wang, Miao Xie, Jiantai Ma, Cu (I) immobilized on functionalized
SBA-15: A recyclable catalyst for the synthesis of 1,3-diynes using terminal alkynes
without base, Catalysis Communications (2013), doi: 10.1016/j.catcom.2013.04.012
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ACCEPTED MANUSCRIPT
Cu (Ⅰ) immobilized on functionalized SBA-15: A recyclable
catalyst for the synthesis of 1,3-diynes using terminal alkynes
without base
Zongyan Ma a, Xiaoyu Wang b, Shuoyun Wei a, Honglei Yang a, Fengwei Zhang
a
a, Peng Wang a, Miao Xie a and Jiantai Ma
a
The Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu
Province, College of Chemistry and Chemical Engineering, Lanzhou University,
Lanzhou, 730000, P. R. China
b School of Earth Sciences, Lanzhou University, Lanzhou, 730000, P. R. China
Abstract
A new functionalized SBA-15 catalyst immobilized CuI was successfully
prepared, and the catalytic activity was tested in the oxidative homocoupling of
terminal alkynes at the absence of base, and good to excellent yields was obtained to
get 1,3-diynes without any side product formation in the solution of DMSO.
Moreover, the system also allowed the synthesis of unsymmetric 1,3-diynes by
cross-coupling of two different terminal alkynes. Finally, the catalyst could be reused
for several times without a significant loss of activity.
Keywords: SBA-15, immobilized Cu (Ⅰ), terminal alkynes, 1,3-diynes
Corresponding author: Tel.: +86–0931–891–2311; fax: +86–0931–891–2311.
E-mail address: majiantai@lzu.edu.cn (J.T. Ma)
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1. Introduction:
Conjugate 1,3-diynes are very important materials in numerous natural products in
the fields of pharmaceuticals and bioactive compounds, because they can be
converted into various structural entities, especially in the construction of
macrocyclic annulenes [1], substituted heterocyclic compounds [2], supramolecular
swiches [3] and carbon-rich materials [4]. Homocoupling of terminal alkynes was
pioneered by Glaser in 1869 [5,6], and nowadays, much attention has been devoted
to the development of new and efficient procedures for the synthesis of 1,3-diyne
derivatives. Traditionally, the homocoupling reaction of terminal alkyne was carried
out in catalytic systems mediated by a combination of palladium (Pd) and copper
salts [7]. Pd catalysts play a crucial role because of their mildness, efficiency and
high selectivity; however, they are expensive and often require air-sensitive and
expensive phosphine as well as foul-smelling amine reagents [8,9]. In addition, in
some of the Pd-catalyzed systems the formation of the desired homocoupling
products is accompanied by the generation of side products such as enynes. For these
reasons, it would be significant to develop an effective procedure for the
homocoupling of alkynes. Recently, it has been shown that the copper-mediated
oxidative homocoupling of terminal alkynes is an alternative and promising strategy
[10,11]. The further development of the Cu (Ⅰ) salt catalyzed reactions using O2 as an
environmentally benign oxidant appeared to be the most attractive approach in order
to meet the demand for high yields and high selectivities, simple experimental
procedures under mild reaction conditions, absence of expensive and harmful
reagents [12]. These Pd-free catalytic systems are efficient and economic, but their
imperfections include the employments of stoichiometric amounts of amine reagents,
high temperature, as well as a co-catalyst [13,14]. In the last few years, Cu
( )-catalyzed homocoupling reactions has been reported [15-17], however, ligands
and bases were required. For these reasons, the development of an economic and
effective method for the homocoupling of alkynes is necessary and significant.
In recent years, many methods have been developed to immobilize metal active
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sites on a large variety of solid supports, such as microporous polymers [18],
mesoporous materials [19-23], amorphous silica [24], carbon nanofibers [25] and
clay [26], making it easy and simple to separate the catalyst from the mixture.
SBA-15 has generated a great deal of interest in the area of catalysis due to its high
specific surface areas and large ordered pores raging from 2 to 50 nm with narrow
size distributions [27,28]. Moreover, the straight channel of SBA-15 is beneficial for
facilitating the entrance and diffusion of target metal sites. Its ordered structure can
be maintained during successive procedures, which resulted from the thicker SiO2
wall that aids in the maintenance of structural integrity. Besides, its matrix is
optically transparent in the visible region and favorably biocompatible [29].
Considering these attractive properties, new organic-inorganic nanocomposites based
on SBA-15 have been extensively investigated in the development of functional
materials in various fields [30,31].
To the best of our knowledge, a few studies have so far been carried out to
evaluate whether or not immobilized Cu(Ⅰ)-catalyzed alkyne homocoupling reaction
can be performed in the absence of any other additives [15]. Herein, we report an
economic and efficient system that allows the coupling reactions of terminal alkynes
based on Cu ( ) immobilized on mesoporous silica under an atmosphere of oxygen
without base. And it provided good to excellent yields with various alkynes as
substrates for the coupling reactions.
2. Experimental
2.1 Instuments
Infrared spectra (FT-IR) were obtained by the KBr disc technique and were
performed on NEXUS670. The elemental analysis (C, H and N) was acquired on
VarioEL. Thermal gravimetric analysis (TGA) was carried out under N2 atmosphere
on Netzsch STA 449C equipment. Low angle X-ray diffraction (XRD) analyses were
performed on a Rigaku D/max-2400 diffractometer, using Cu Κ radiation in the 2θ
α
range of 0.5-4°. The morphology of the samples was observed on a Tecnai G2 F30
transmission electron microscopy, and samples were obtained by placing a drop of a
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colloidal solution onto a copper grid and evaporating the solvent in air at room
temperature. The nitrogen adsorption/desorption experiments were performed at 77
K in a Micromeritics ASAP 2010 (USA). The samples were degassed at 373 K
overnight before the measurement. Inductively coupled plasma (ICP) on IRIS
Advantage analyzer was used for measuring the Cu content of the catalyst. The 29Si
CP MAS spectra were recorded on a Bruker AVANCE III 400 WB spectrometer
equipped with a 4 mm standard bore CP MAS probehead whose X channel was
tuned to 79.50 MHz
2.2 Synthesis of catalyst
3-Chloropropyltriethyoxysilane
(CPTES)
(0.2
mL,
0.83
mmol),
N,N,N',N'-tetraethylenetriamine (TEDETA) (0.2 mL, 0.78 mmol) and Triethylamine
(0.13 mL, 1 mmol) were dissolved in 30 mL distilled CH2Cl2. The resulting mixture
was then allowed to reflux for 24 h, and followed by evaporating under reduced
pressure. Then the resulted mixture and 0.5 g dried SBA-15 were added to 60 mL
toluene. The suspension was stirred for 24 h at 115 ℃. The modified SBA-15
(TEDETA/SBA-15) were collected by filtration and repeatedly washed with
anhydrous toluene, dichloromethane, and then ethanol under ultrasonic condition.
After dry under vacuum, TEDETA/SBA-15 was obtained. To 200 mL toluene, 0.5 g
TEDETA/SBA-15 and 0.076 g CuI was added. The mixture was bubbled with
nitrogen for 5 min and stirred at room temperature for 24 h. The solid was filtrated
and washed with toluene and ethanol respectively. The obtained solid was dried
under vacuum and was named as CuI-TEDETA/SBA-15. All the procedure was
carried out under an atmosphere of nitrogen. The structure of the functional molecule
and the synthesis process were shown in Scheme 1.
2.3 Typical experimental procedure for the coupling reaction
Catalyst (3 mol %) and phenylacetylene (0.5 mmol) were added to 2 mL DMSO
solution. The mixture was stirred at 50 ℃ under 1 atm pressure O2 for 6 h. The
progress of the reaction was monitored by TLC. After completion of the reaction, 10
mL of ethyl acetate was added. The mixture was filtered through a pad of diatomite
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under reduced pressure, and the filtration residue was washed with ethyl acetate.
Ethyl acetate was removed under reduced pressure. The residue was then purified by
column chromatography on silica gel using petroleum ether as eluent to afford the
correspongding 1,3-diynes.
3. Results and discussion
3.1. Catalyst characterization
The FT-IR spectra of SBA-15 and CuI-TEDETA/SBA-15 were showed in Fig. 1
respectively. Of the two curves, the bands at 3455 and 1637 cm-1 were attributed to
the stretching (3455 cm-1) and bending (1637 cm-1) vibrations of the surface silanol
groups and the adsorbed H2O. The typical Si-O-Si bands around 1086, 803 and 461
cm-1 associated with the formation of a condensed silica network were present in the
two spectra. The presence of broad bands at around 3000-2800cm-1 implied the
aliphatic C-H stretching vibration attributed to alkyl chains. The presence of
TEDETA in the modified SBA-15 was further corroborated by a broad band at 1471
cm-1, attributed to the C-N stretching vibration.
The XRD patterns of SBA-15 and CuI-TEDETA/SBA-15 were given in Fig. 2.
The fresh SBA-15 was highly ordered, showing three strong diffraction peaks for the
100, 110 and 200 planes. The reduction in the intensity of the (100), (110), and (200)
reflections for CuI-TEDETA/SBA-15 was attributed to the change in the
homogeneity and space correlation of pores caused by the functionalized monolayer
of silanes.
Complementary to the XRD data, the TEM images of the CuI-TEDETA/SBA-15
exhibited 2-D hexagonal arrays of silica pores channels with uniform diameter and
wall thickness (Fig. 3. b) compared with SBA-15 (Fig. 3. a). Furthermore, it can be
seen in Fig. 3. c that the catalyst still kept the hexagonal structure of SBA-15 even
after 5 runs.
The quantity of TEDETA molecules attached to the mesoporous silica surface was
estimated from the result of the TGA measurement, which was presented in Fig. 4.
For the two samples, a slight weight loss was observed below 200 ℃ due to the
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residual water in samples. According to curve (a), there was a continuous weight loss
of the SBA-15, and the amount of the weight loss was about 8.27 %, which was
typical for raw SBA-15. From the TGA weight loss curve (b) in Fig. 4., it can be
seen a considerable weight loss in the temperature range of 200-300 ℃, which
should be caused by the decomposition of organic components. And the content of
the TEDETA grafted onto the SBA-15 was about 10.3 wt% comparing with curve (a),
which was in agreement with the calculation result of the elemental microanalysis, in
which N content was 2.1 %. In addition, SBA-15 showed another weight loss in the
temperature range of 200-800 ℃ owing to the further condensation between Si-OH
groups.
The nitrogen adsorption isotherms (Fig. 5. (Ⅰ)) of CuI-TEDETA/SBA-15 and
SBA-15 showed type I-V plots with type H1 hysteresis loops for a typical
mesoporous material. A considerable decrease in surface area, pore volume, and pore
diameter was observed after chemical modification. The results indicated that the
BET surface area of CuI-TEDETA/SBA-15 decreases to 277.24 m2 g-1 compared
with 670.31 m2 g-1 of the original SBA-15. The pore volume of SBA-15 and
TEDETA/SBA-15 were 1.04 cm3 g-1 and 0.55 cm3 g-1 respectively, which were
calculated from the adsorption branch by using the BJH model. Pore size diameter
distributions presented as BJH plots in Fig. 5. (Ⅱ).
The 29Si NMR MAS spectrum and peak assignments for CuI-TEDETA/SBA-15
were depicted in Fig. 6. The three peaks at -110.9, -102.3 and -92.8 ppm were
attributed to silicon in the siloxane binding environment without hydroxyl groups
[Q4=(SiO)4Si], isolated silanol groups [Q3=(SiO)3Si-OH] and to geminal silanol
groups [Q2=(SiO)2-Si-OH] of the silica support. T3 [C-Si(OSi)3] attributed to Si
atoms bonded to C atoms of the propyl bridge of 3-Chloropropyltriethyoxysilane
was observed at δ=-67.8 ppm, which indicated that the ligand was bonded to the
silica surface. Finally, a shoulder at -58.5ppm was assigned to T2 units [RSiO2OH].
3.2. Catalytic activity for terminal alkynes coupling reaction.
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In our initial study, we chose the homocoupling reaction of phenylacetylene as a
model. We conducted blank tests to confirm the formation of CuI-TEDETA/SBA-15
as an active species. As shown in Table 1, when no catalyst or only
TEDETA/SBA-15 was added to the system, no product was formed (Table 1, entries
1, 2). At existence of 20 mg CuI, 6 hours later the yield was up to 99% (Table 1,
entry 3); However, it was difficult for the separation of CuI from the target product.
Moreover, it was uneasy for the reusability of CuI. When CuI-TEDETA/SiO2 and
CuI-TEDETA/SBA-15 were used as catalysts, the yields were 82% and 99%
respectively (Table 1, entries 4, 5). The results made it clear that
CuI-TEDETA/SBA-15 was the best catalyst for the system.
As shown in Table 2, a series of experiments were performed to identify the
ability of various bases and solvents for the reaction process, and the preliminary
studies revealed that the best result was obtained when the coupling was run in
DMSO without bases. When phenylacetylene was reacted 6 h in DMF solution
(Table 2, entry 2), we found that the yield was too low. So we prolonged the reaction
time to get high yields. And for all of the reactions, the selectivity was 100%, the
yields meant the conversion. Additionally, these results made it clear that high
polarity solvents, such as N, N-dimethyl formamide (DMF), dimethyl sulfoxide
(DMSO) and N-methyl pyrrolidone (NMP) (Table 2, entries 1-8), exhibited
significant superiorities over low polarity solvents (Table 2, entries 9-15). For DMF,
the addition of bases, whether organic or inorganic, made no significant difference in
the yields (Table 2, entries 2-6). Then we examined the influence of the temperature
and time on the yields (Table 2, entries 16-18) in the solution of DMSO. As can be
seen in the table, the product conversion was susceptible to temperature changes.
The decrease of reaction temperature led to longer reaction time and low yield (Table
2, entry 16).
Encouraged by the efficiency of the reaction described above, we set out to study
the effect of substituents on the homocoupling reactions of terminal alkynes under
optimized conditions (Table 3). The results showed that both the electron-rich (Table
3, entries 2-3) and electron-deficient (Table 3, entry 4) substrates provided the
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corresponding 1,4-disubstituted-1,3-diynes in good to excellent yields. For the
heterocyclic substituted terminal alkynes, the homocoupling reactions also
proceeded efficiently. The oxidation of 2-ethynylthiophene (Table 3, entry 6)
conducted more quickly than that of 2-ethynylpyridine (Table3, entry 5), which
could be attributed to the electron-donating nature of the thiophene group and the
electron-withdrawing nature of the pyridine group. When aliphatic acetylenes were
used, the yields were somewhat lower (entries 7-9). It is known that aliphatic
terminal alkynes are less reactive in undergoing Glaser coupling reaction, probably
due to the weaker acidity of the acetylenic proton.[32]
The cross-coupling of two different terminal alkynes was also investigated in the
catalytic system. As shown in Table 4, unsymmetrical 1,4-disubstituted-1,3-dimes
were produced in low yields. Obviously, the alkyne substrates were more inclined to
crosscoupling.
Finally, we examined the recovery and reuse of the catalyst (Table 5). After
completion of the reaction, the catalyst can be recovered by simple filtration and
drying under vacuum, and then can be reused for the next run. This reused catalyst
was re-employed in the successive cycles under identical conditions. According to
the ICP analyses, it was clear that a significant amount of Cu (Ⅰ) that immobilized
onto the silica surfaces were leached out after each completion of the coupling
reaction (shown in Fig.7 a). After five runs, over 40 wt% of copper was leached out.
As a result, the yields were lower and lower after each run (shown in Fig. 7 b). In
order to evaluate whether this reaction was actually catalyzed by Cu (I) when it was
still chelating to TEDETA or by the free Cu (I) catalyst released from the
dissociation from the solid support under the reaction conditions, we used 1 mg CuI
(more than the quantity of released Cu), and found only trace product was get. These
results clearly indicated that TEDETA was capable of capturing Cu (Ⅰ), however, the
molecular bond between DMSO and Cu (Ⅰ) also responsible for the copper leach.
3.3 Plausible mechanism for the homocoupling reaction
Scheme 2 illustrated the proposed mechanism for the homocoupling reaction of
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terminal alkynes, which was based on the reported mechanism for CuI catalyzed
Glaser type-coupling reaction [33,34]. The alkynylcopper intermediate was formed
from the reaction of a terminal alkyne and CuI-TEDETA/SBA-15, and then it
involved the oxidative reaction with O2 to the 1,3-diynes.
4. Conclusion
In conclusion, we have demonstrated an efficient method for the generation of
1,4-disubstituted-1,3-diynes in DMSO solution without base. The reaction proved to
be tolerant to a variety of substrates, and various of conjugated symmetrical or
unsymmetrical 1,3-diynes can be produced conveniently with good yields. The
catalyst can also be recycled five times without significant reduction in activity.
Additionally, the current protocol lies in simple experimental procedure as well as
avoidance of expensive palladium. These features make this methodology attractive
for use in combinatorial chemistry and industrial preparation.
Acknowledgements
This work was supported financially by the Key Laboratory of Nonferrous Metals
Chemistry and Resources Utilization, Gansu Province
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Figure captions
Scheme 1 The synthesis procedure of catalyst.
Scheme 2 A plausible mechanisms for the supported Cu ( )-mediated coupling
reaction of terminal alkyne
Fig. 1. FT-IR spectras of (a) SBA-15 and (b) TEDETA/SBA-15.
Fig. 2. X-ray diffraction patterns of (a) SBA-15 prior to and (b) TEDETA/SBA-15
Fig. 3. TEM images of (a) SBA-15, (b) TEDETA/SBA-15 and (c) catalyst recovered
after five runs
Fig. 4. TGA Thermogram of (a) SBA-15 and (b) TEDETA/SBA-15
Fig. 5. (Ⅰ) Nitrogen adsorption-desorption isotherms and (Ⅱ) pore size distribution of
(a) SBA-15 and (b) TEDETA/SBA-15.
Fig. 6. 29Si MAS spectrum of CuI-TEDETA/SBA-15
Fig. 7 Recovery and reuse of catalyst (a) catalyst loading after each run and (b) yield
after each run
Table 1 Effect of catalysts on the oxidative coupling of phenylacetylene[a]
Table 2 Preliminary survey of solvents and bases for the homocoupling reaction of
phenylacetylene [a].
Table 3 The homocoupling of terminal alkyne.
Table 4 The cross-coupling of the terminal alkyne.
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Scheme 1
13

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Scheme 2
14

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Fig. 1
15

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Fig. 2
16

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Fig. 3
17

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Fig. 4
18

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Fig. 5
19

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Q3
Q4
Q2
T3
T2
0
-40
-120
29Si / ppm
-160
-200
-80
δ
Fig.6
20

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Fig. 7
21

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cat (20 mg)
DMSO (2 mL)
Entry
catalyst
Time (h)
Temp
Selectivity (%) Yield(%)[b]
(℃)
1
2
3
4
5
none
24
24
6
90
90
90
90
90
0
none
none
>99
91
TEDETA/SBA-15
CuI
0
100
100
100
CuI-TEDETA/SiO2
CuI-TEDETA/SBA-15
12
6
>99
[a] The reaction was performed with phenylacetylene (0.5 mmol), catalyst 20 mg in
DMSO (2 mL) under 1 atm pressure of O2.
[b] Isolated yield.
Table 1
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cat (3 mol%)
solvent (2 mL)
Entry
Solvent
Base
Time (h)
Yield (%)[b]
Temp(℃)
1
2
DMSO
DMF
None
None
None
Et3N
90
90
90
90
90
90
90
90
80
90
65
40
90
78
64
25
50
70
6
>99
21
80
90
82
81
78
87
65
76
73
52
8.3
9.8
12
52
95
>99
6
3
DMF
24
24
24
24
24
24
24
24
24
24
24
24
24
24
6
4
DMF
5
DMF
K2CO3
Na2CO3
None
Et3N
6
DMF
7
NMP
8
NMP
9
CH3CN
1,4-dioxane
THF
None
None
None
None
None
None
None
None
None
None
10
11
12
13
14
15
16
17
18
CH2Cl2
Toluene
C2H5OH
CH3OH
DMSO
DMSO
DMSO
6
[a] The reaction was performed with phenylacetylene (0.5 mmol), catalyst 20 mg (3
mol%) and bases (1.5 mmol) in solvents (2 mL) under 1 atm pressure of O2.
[b] Isolated yield.
Table 2
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cat (3 mol%)
R1
R1
R1
DMSO (2 mL), 50 oC, O2
Entry
Substrate
Product
Time (h)
Yield (%)
1
6
>99[b]
2
3
4
5
6
5
5
>99[b]
>99[b]
90[b]
H3C
H C
CH
3
3
H3CO
F
H CO
3
OCH
F
3
6
F
24
12
82[b]
N
N
S
N
93[b]
S
S
46[c]
82[c]
HO
HO
OH
7
8
12
12
5
5
5
Br
65[c]
Br
Br
9
12
[a] The reaction was performed with alkynes (0.5 mmol) and 20 mg catalyst (3 mol%)
in DMSO (2 mL) under 1 atm pressure of O2.
[b] Isolated yield.
[c] yield determined by GC-MS
Table 3
24

ACCEPTED MANUSCRIPT
R1
R1
R2
b
Cu ( ) (3 mol%)
R1
R1
R2
R2
DMSO 2 mL, 50 , 1 atm O2
a
c
R2
Entry
Substrate
Cross coupling product
Time Yield (%)[b]
(h)
for a (b/c)
R1
R2
1
2
3
4
5
6
50 (25/20)
H C
3
CH3
6
48 (27/21)
S
S
12
6
53 (30/19)
52 (22/20)
N
N
F
F
6
45 (28/27)
H3C
H3CO
H C
OCH
3
3
6
6
54 (21/21)
H3C
F
F
H C
F
3
7
6
7
6
6
6
56 (20/20)
45 (27/24)
47 (23/27)
H3CO
H CO
3
F
F
F
S
S
S
H3C
H3C
S
[a] The reaction was performed with two alkynes (0.5 mmol, respectively) and 20 mg
catalyst (3 mol%) in DMSO (2 mL) under 1 atm pressure of O2.
[b] yield determined by GC-MS.
Table 4
25

ACCEPTED MANUSCRIPT
Graphical Abstract
26

ACCEPTED MANUSCRIPT
Highlights
► A copper-based catalyst was prepared facilely by the covalent immobilization
method.
► It showed high activity for the one-pot coupling reaction of terminal alkynes.
► It was heterogeneous in nature and can be reused without any reactivation
treatment.
► It was easily recovered by simple filtration.
► It was reused for 5 cycles without evident loss in activity.
27