Use of CuO encapsulated in mesoporous silica SBA-15 as a recycled catalyst for allylic C-H bond oxidation of cyclic olefins at room temperature

Article abstract of DOI:10.1039/c7ra02995k

CuO nanoparticles were deposited on SBA-15 in three routes. These were metal loading on SBA-15 and calcination at 550 °C (Cu-SBA-15), metal loading on 3-aminopropyl-trimethoxysilane grafted SBA-15 and calcination at 550 °C (Cu-N-SBA-15), and metal loading

Full text of DOI:10.1039/c7ra02995k

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Use of CuO encapsulated in mesoporous silica SBA-
15 as a recycled catalyst for allylic C–H bond
Cite this: RSC Adv., 2017, 7, 19330
oxidation of cyclic olefins at room temperature†
Saadi Samadi,*ab Akram Ashouri and Mehdi Ghambarianc
a
CuO nanoparticles were deposited on SBA-15 in three routes. These were metal loading on SBA-15 and
ꢀ
calcination at 550 C (Cu–SBA-15), metal loading on 3-aminopropyl-trimethoxysilane grafted SBA-15
ꢀ
and calcination at 550 C (Cu–N–SBA-15), and metal loading on 3-aminopropyl-trimethoxysilane grafted
ꢀ
SBA-15 and reduction by NaBH
4
then calcination at 550 C (Cu–B–N–SBA-15). These catalysts were
characterized through powder X-ray diffraction (XRD), BET nitrogen adsorption–desorption methods,
energy dispersive X-ray (EDX), atomic absorption spectroscopy (AAS), elemental mapping, scanning
electron microscopy (SEM), and Fourier transform infrared (FT-IR) spectroscopy. The result of the
3
heterogeneous catalysts being applied in the monometallic direct catalytic esterification of sp C–H
Received 13th March 2017
Accepted 17th March 2017
bonds in cyclic olefins for the first time is reported, using tert-butyl 4-nitrobenzoperoxoate at room
temperature. Allylic esters were obtained as the product of the C–H bond oxidation reaction in
moderate to good yields (up to 99%) within reasonable reaction times. Also, the recovered catalyst (Cu–
B–N–SBA-15) is applicable in the oxidation reaction for four times with little loss in reactivity and yield.
DOI: 10.1039/c7ra02995k
rsc.li/rsc-advances
4
0,41
42–44
41,45,46
41
47
48
Co(III),
Rh(I),
Co(II),
Cu
Mn(III),
Ce(IV),
Fe(II),
Rh(II),
1
. Introduction
4
9,50
5–13
and a variety of ligands. However, copper-
3
The direct functionalization of sp C–H bonds is one of the most catalysis – due to its low cost – is the most popular in this
1–4
important reactions in organic synthesis. Oxidation reaction eld, although their large industrial scale usage is limited.
of these bonds at the allylic position of cycloolens (Kharash–
On the other side, supported nanometals are one of the most
Sosnovsky reaction) can be used as one of the most straight- important categories of heterogeneous catalysts with broad
forward synthetic routes for the preparation of highly func- applications in the industry. Some materials, such as SBA-15,
tionalized olens such as allylic esters and allylic alcohols that MCM-41 and zeolite were applied for the preparation of metal
are important intermediates in the synthesis of leukotriene B
4
nanoparticles.
6
7
8
(ref. 5) chrysanthemic acid, brevetoxin and amyrin. The
Among them, SBA-15 has some advantages such as hexago-
nature of the metal salt, perester oxidant, and reaction condi- nally arrayed channels and narrow pore size distribution so that
5
1–53
tions including solvent and temperature are affected this reac- it has attracted great attention.
Immobilization of metal NPs
9–17
tion remarkably.
within a silica scaffold prevents agglomeration and surface
Allylic C–H bond oxidation have been studied by homoge- fouling, and aids in NP recovery and recycling.
54–57
1
8–24
18–21,23
neous catalysts such as selenium,
selenium dioxide,
In our previous work, we reported the effect of some addi-
with tives such activated silica gel, mesoporous MCM-41, SBA-15
24
18–24
diselenides and pentauorobenzeneselenic acid
25–30
31–37
25
25,38,39
different metals such as Hg(II),
Pd(II),
Pb(IV), Cr(VI),
silica, nanocrystalline MgO, CuO and TiO
and SBA-15 was shown better results than others.
2
on this reaction
58–61
The strong
effect of these additives encouraged us to prepare and charac-
terize CuO encapsulated in mesoporous silica SBA-15 with
various Cu loadings in the range of 1–12 wt% by an impregna-
tion method in three routes, which was applied in allylic C–H
a
Laboratory of Asymmetric Synthesis, Department of Chemistry, Faculty of Science,
University of Kurdistan, Zip Code 66177-15175, Sanandaj, Iran. E-mail: s.samadi@
uok.ac.ir
b
Research Centre of Nanotechnology, University of Kurdistan, P.O. Box 416, Sanandaj,
1
–13
bond oxidation of cyclic olens.
Iran
c
Gas Conversion Department, Faculty of Petrochemicals, Iran Polymer and
Petrochemical Institute, P.O. Box 14975-112, Tehran, Iran
2
. Experimental
†
Electronic supplementary information (ESI) available: Supplementary data
1
13
(
included IR, H and C spectra of compounds 1–5 and the procedure of
2.1. General remarks
synthesis 1, IR, SEM, EDX, X-ray scattering and elemental mapping for prepared
All reagents and starting materials were purchased from
Aldrich, Merck, Fluka and Sigma. Cycloolens were distilled
catalysts and the typical procedure for the synthesis of SBA-15, NH
See DOI: 10.1039/c7ra02995k
2
–SBA-15).
19330 | RSC Adv., 2017, 7, 19330–19337
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from calcium hydride before use. All solvents for the reactions
2.2.2. Typical procedure for Cu–N–SBA-15 (ref. 51). The
were also dried and distilled immediately before use. Melting procedure for preparation of this catalyst was same as 2.2.1. but
points were measured on an Electrothermal 9100 apparatus NH –SBA-15 (ref. 63) was used instead of SBA-15 (S5–S7, S10–
2
and are uncorrected. Fourier transform infrared (FT-IR) spec- S13 in ESI† and Fig. 1–3).
trum was recorded on a Bruker Vector 22 spectrometer using
2.2.3. Typical procedure for Cu–B–N–SBA-15. To produce
pressed KBr pellets. X-ray diffraction patterns were obtained this catalyst, the same procedure was used as 2.2.2. with this
on a Simens D500 diffractometer with Cu Ka radiation. The difference that before calcination step, the modied meso-
SEM image and EDX patterns were taken using VEGA\\- porous stirred with 10 mL of 0.1 M NaBH ethanol solution at
4
51
TESCAN. The surface area was calculated by the BET method room temperature for 2 hours. (Fig. 1–3).
in Quantachrome Instruments.
2
.3. Allylic C–H bond oxidation of cyclic olens
Allylic oxidation of cycloolens was drown in Scheme 2.
.3.1. General procedure for allylic C–H bond oxidation of
2.2. The preparation of heterogeneous catalysts
2
The preparation of Cu–B–N–SBA-15 was drown in Scheme 1.
cycloolens by using tert-butyl 4-nitrobenzoperoxoate. The
ꢀ
2.2.1. Typical procedure for Cu–SBA-15. A round-bottomed heterogonous catalyst was preheated under vacuum at 80 C for

ask (50 mL) equipped with a stirrer bar was charged with 2 g of 2 h. To a round bottom ask (25 mL), 40 mg of dried heter-
SBA-15 (ref. 62) and ethanol (20 mL). Then Cu(NO was added ogonous catalyst, cycloolen (5 mmol) and acetonitrile (4 mL)
to the reaction mixture and stirred for 10 h at room tempera- were added and stirred for 30 minute at room temperature then
3 2
)
58
ture. The resultant material was collected by ltration and tert-butyl p-nitrobenzoperoxoate 1 (0.203 g, 0.85 mmol) was
ꢀ
washed thoroughly with C
2
H
5
OH, dried at 100 C and calcined added slowly. The mixture was stirred until TLC showed the
ꢀ
51–53
at 550 C for 5 h (S2–S4, S8 and S9 in ESI† and Fig. 1–3).
complete consumption of the perester.
Scheme 1 Synthesis of Cu–B–N–SBA-15.
2
Fig. 1 FT-IR spectra of SBA-15 (a), NH –SBA-15 (b), Cu–SBA-15 (c), Cu–N–SBA-15 (d), Cu–B–N–SBA-15 (e).
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When the reaction was completed, the heterogonous catalyst Table 1 BET surface area of SBA-15, NH
was isolated by ltration, and then thoroughly washed three
2
–SBA-15, Cu–SBA-15, Cu–
N–SBA-15, Cu–B–N–SBA-15
times with methylene chloride and air-dried. Aer ltration, the
methylene chloride phase was washed with saturated aqueous
BET surface area
2
ꢁ1
Entry
Sample
(m g
)
NH
and dried over MgSO
vacuum, and the product puried with column chromatography
4
Cl (10 mL) aer that saturated aqueous NaHCO
3
(10 mL)
. The solvent was evaporated under
1
2
3
4
5
SBA-15
Cu–SBA-15
NH –SBA-15
2
Cu–N–SBA-15
912
438
544
305
293
4
(
ethyl acetate/n-hexane 2–10%) to afford white solid up to 99%
58–61
yield (S14–24 in the ESI†).
Cu–B–N–SBA-15
ꢀ
Cyclopent-2-en-1-yl 4-nitrobenzoate (2). Mp: 76–79 C (lit. 77–
ꢀ
1
7
(
(
2
9 C (ref. 58)); R ¼ 0.57 (90 : 10, n-hexane : EtOAc); H NMR
f
ꢀ
300 MHz, CDCl ): d (ppm) ¼ 1.94–2.00 (1H, m), 2.41–2.50
3
H
Cyclooct-2-en-1-yl 4-nitrobenzoate (4). Mp: 72–73 C (lit. 71–
ꢀ
1
2H, m), 2.59–2.67 (1H, m), 6.05 (2H, m), 6.33 (1H, m), 8.25 (d,
7
4 C (ref. 58)); R
f
¼ 0.67 (n-hexane : EtOAc; 90 : 10); H NMR
1
3
H, J ¼ 8.7 Hz), 8.29 (d, 2H, J ¼ 8.7 Hz); C NMR (75 MHz,
): d
(ppm) ¼ 29.2, 31.3, 81.7, 123.5, 128.4, 131.1, 136.6,
39.1, 150.6, 165.2.
Cyclohex-2-en-1-yl 4-nitrobenzoate (3). Mp: 68–70 C (lit. 68–
(300 MHz, CDCl ): d
3
H
(ppm) ¼ 1.51–1.76 (7H, m), 2.11–2.40 (3H,
CDCl
1
3
C
m), 5.56–5.59 (1H, m), 5.77–5.85 (1H, m), 5.90–5.94 (1H, m),
8
2
1
3
.28–8.36 (4H, m); C NMR (75 MHz, CDCl
3
): d
C
(ppm) ¼ 22.8,
ꢀ
4.9, 25.2, 30.8, 35.7, 73.8, 124.1, 130.4, 131.1, 133.0, 149.7,
ꢀ
1
7
1 C (ref. 58)); R ¼ 0.64 (n-hexane : EtOAc; 90 : 10), H NMR
f
165.8.
ꢀ
(
5
300 MHz, CDCl ): d (ppm) ¼ 1.77–2.14 (6H, m), 5.61 (1H, m),
3
H
Cycloocta-2,6-dien-1-yl 4-nitrobenzoate (5). Mp: 72–75 C (lit.
ꢀ
1
.87 (1H, d, J ¼ 10.1 Hz), 6.10 (1H, d, J ¼ 10.1 Hz), 8.18–8.28 (4H,
7
4–76 C (ref. 58)); R
f
¼ 0.62 (n-hexane : EtOAc; 90 : 10); H NMR
13
m); C NMR (75 MHz, CDCl
3
): d
C
(ppm) ¼ 18.8, 25.0, 28.2, 69.8,
(300 MHz, CDCl ): d
3
H
(ppm) ¼ 2.21–2.41 (2H, m), 2.54–2.68 (2H,
123.4, 125.0, 130.7, 133.6, 136.2, 150.4, 164.3.
m), 2.85–2.95 (2H, m), 5.57–5.84 (4H, m), 6.17–6.26 (1H, m),
Scheme 2 Allylic C–H bond oxidation of cyclic olefins in the presence of heterogeneous catalyst.
Fig. 2 (A) Wide angle X-ray diffraction patterns of SBA-15, Cu–N–SBA-15, Cu–B–N–SBA-15. (B) Low angle X-ray diffraction patterns of SBA-15,
NH –SBA-15.
2
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.23 (2H, d, J ¼ 8.5 Hz), 8.30 (2H, d, J ¼ 8.4 Hz); C NMR (75
RSC Advances
1
3
8
The NH
2
–SBA-15 (b spectrum) was considered by peaks at
ꢁ
1
MHz, CDCl ): d (ppm) ¼ 27.6, 28.1, 28.5, 74.6, 124.3, 125.2, 1392 and 1553 cm which conrmed successfully immobili-
3
C
128.3, 129.4, 131.3, 132.5, 133.4, 150.2, 167.5.
zation of the amine functional group onto SBA-15. Character-
ꢁ
1
ized bands in Cu–N–SBA-15 at 805, 1079, 1631 and 1703 cm
ꢁ
1
and regarded bonds 806, 1083 and 1631 cm for Cu–B–N–SBA-
5 clearly demonstrated that the mesoporous structure of SBA-
3. Results and discussions
1
3.1. Characterization of heterogeneous catalyst
15 preserved aer modication (Fig. 1).
Low angle X-ray diffraction patterns of SBA-15 showed a peak
The catalyst was characterized by XRD, EDX, BET, SEM, AAS and
FT-IR.
ꢀ
at 2q ¼ 0.94 , corresponding to the (100) reection, and two
ꢀ
weak reections at about 1.47 and 1.8 . Comparison the X-ray
3
.1.1. Spectroscopic characterization. SBA-15, NH –SBA-
2
patterns of NH –SBA-15 with SBA-15 shows that the hexagonal
1
5, Cu–SBA-15, Cu–N–SBA-15, and Cu–B–N–SBA-15 were
2
ꢁ
1
pore structures of SBA-15 has been retained aer the immobi-
lization of (3-aminopropyl)trimethoxysilane in SBA-15 (Fig. 2B).
To prove the existence of copper on the surface of calcined
catalysts, the wide angle X-ray diffraction pattern of SBA-15 and
Cu-containing samples (SBA-15–N–Cu and SBA-15–N–B–Cu)
analyzed by FT-IR in the 400–4000 cm region (Fig. 1). The
wide bands at 1079–1250 cm were remarked as Si–O–Si
bands of the condensed silica network. The peak 803–806
ꢁ
1
ꢁ
1
cm can be assigned to the symmetric stretching vibration
of Si–O. In the case of Cu–SBA-15, the characteristic bands
51
ꢁ
1
were investigated.
were appeared at 804 and 1087 cm
.
Fig. 3 Scanning electron micrographs of Cu–B–N–SBA-15.
Fig. 4 Elemental mapping of the Cu–B–N–SBA-15 catalysts.
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a,b
Table 3 Effect of solvent on reaction at different temperatures
Entry
Catalyst
Solvent
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
Cu–SBA-15
CH
CH
CH
Acetone
Acetone
Acetone
CH
CH
CH
DMF
DMF
DMF
3
3
3
CN
CN
CN
37
34
25
25
40
20
86
62
70
70
50
52
80
87
99
75
77
82
25
28
22
35
40
45
Cu–N–SBA-15
Cu–B–N–SBA-15
Cu–SBA-15
Cu–N–SBA-15
Cu–B–N–SBA-15
Cu–SBA-15
Cu–N–SBA-15
Cu–B–N–SBA-15
Cu–SBA-15
Cu–N–SBA-15
Cu–B–N–SBA-15
Fig. 5 EDX spectrum of the Cu–B–N–SBA-15 catalysts.
Table 2 Effect of homogeneous and heterogeneous catalyst on
2
2
2
Cl
2
Cl
2
Cl
2
a,b
reaction at different temperatures in acetonitrile
1
1
1
0
1
2
a
Reaction conditions:
1
(0.2 mmol), cyclohexene (5 mmol),
heterogeneous catalyst (40 mg), in 3 mL solvents stirred at r.t.
b
Isolated yield.
Temperature
ꢀ
Entry
Catalyst
CuOAc
( C)
Time (h)
Yield (%)
ꢀ
As Fig. 2A shows, the reection of Cu–N–SBA-15 at 2q ¼ 23.5
ꢀ
1
2
3
4
5
6
7
8
9
25
25
25
25
25
25
25
25
40
40
40
Reux
Reux
Reux
120
110
>200
>200
<100
37
34
25
30
28
62
65
55
45
54
80
87
99
84
90
95
85
93
95
and for Cu–B–N–SBA-15 at 2q ¼ 23.7 with decreased intensity was
Cu(NO
3
)
2
ꢀ
ꢀ
ꢀ
remained aer impregnation in compare with SBA-15 at 2q ¼ 24.2 .
CuSO
CuO
4
The reexes assigned for CuO in Cu–N–SBA-15 at 2q ¼ 35.4 ,
ꢀ
ꢀ
ꢀ
3
8.3 and 47.4 , for Cu–B–N–SBA-15, CuO at 2q ¼ 35.4 , 38.6
2
Cu O
ꢀ
51
Cu–SBA-15
and Cu O at 2q ¼ 37.3 . Also wide angle X-ray diffraction
2
Cu–N–SBA-15
Cu–B–N–SBA-15
Cu–SBA-15
Cu–N–SBA-15
Cu–B–N–SBA-15
Cu–SBA-15
patterns powder X-ray diffraction data demonstrated that the
hexagonal structure of SBA-15 has been preserved during the
process of catalyst preparation.
10
11
12
13
14
30
32
27
27
Cu–N–SBA-15
Cu–B–N–SBA-15
Table 4 Effects of copper loading in Cu–B–N–SBA-15 on oxidation
a,b
reaction
a
Reaction conditions: 1 (0.2 mmol), cyclohexene (5 mmol), catalyst (40
b
3
mg), in 3 mL CH CN stirred. Isolated yield.
Entry
Cu
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%
11%
12%
150
120
90
60
48
40
36
30
25
46
59
75
35
40
46
57
64
70
80
87
99
67
55
40
1
1
1
0
1
2
Fig. 6 Correlation between recyclability of Cu–B–N–SBA-15 with
time and yield%.
a
Reaction conditions: 1 (0.2 mmol), cyclohexene (5 mmol), Cu–B–N–
b
3
SBA-15 (40 mg), in 3 mL CH CN stirred at r.t. Isolated yield.
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2
BET surface area of SBA-15, NH –SBA-15, Cu–N–SBA-15 and 3.2. Catalytic effects in allylic C–H bond oxidation of cyclic
Cu–B–N–SBA-15 are presented in Table 1. A signicant decrease olens
in the amount of nitrogen adsorption was observed with incor-
poration of copper in SBA-15, which means that the specic
3
.2.1. Optimization of the model reaction. The catalytic
activity of these catalysts was investigated in the copper-
catalyzed direct esterication of inert C–H bonds in cycloole-
ns. The optimization of the reaction conditions were carried
out by using cyclohexene as the substrate and tert-butyl p-nitro
perbenzoate 1 as an oxidant (S17–19 in the ESI†) in the pres-
ence of various homogeneous and heterogeneous catalyst in
acetonitrile at different temperature (Table 2).
When the reaction was catalyzed by different Cu salts as
homogenous catalyst, a low yielding reaction was observed
entries 1–5). Whereas by using heterogeneous catalysts which
surface area of Cu–SBA-15 decreases in compared with pure
2
ꢁ1
siliceous SBA-15. These amounts of 912 m g for SBA-15 were

2
ꢁ1
2
ꢁ1
decreased to 305 m g for Cu–N–SBA-15 and 293 m g for Cu–
B–N–SBA-15.
61
Morphological changes were investigated by SEM for SBA-15,
NH –SBA-15, Cu–SBA-15, Cu–N–SBA-15 (S4, S7, S10 and S13 in
2
the ESI†) and Cu–B–N–SBA-15 (Fig. 3).
Elemental composition of heterogeneous catalysts and the
dispersity of metal-oxide nanoparticles in the SBA-15 are further
claried by elemental mapping. This technique illustrated the
homogeneous dispersion of metallic CuO over the mesoporous
support (Fig. 4, S14 and S15 in the ESI†).
EDX was used to qualitatively distinguish the present
elements (Fig. 5, S5, S8 and S11 in the ESI†). The amounts of
copper in Cu–SBA-15, Cu–N–SBA-15, and Cu–B–N–SBA-15 were
determined by using atomic absorption spectroscopy 6.54, 8.83
and 8.86 wt% respectively.
(
Cu is encapsulated in SBA-15, reaction yields and rates were
considerably increased (entries 6–14 in Table 2).
The best result was achieved with 40 mg of Cu–B–N–SBA-15,
which afforded 2-cyclohexenyl-p-nitrobenzoate 3 (S14 and S15
in the ESI†) as product with 99% yield in 25 h at room
temperature (entry 9, Table 2). These results support the high
activity of Cu catalysts in the cyclohexene oxidation.
According to spectroscopic results, Cu–B–N–SBA-15 catalyst
has CuO and Cu
increased by this catalyst due to the existence of Cu
mentioning that, the active copper species involving in allylic
2
O. However, the rate of this reaction is
2
O. It worth
Table 5 Effects of catalyst loading of Cu–B–N–SBA-15 (Cu content
a,b
9
%) on reaction
51,58–61
oxidation reactions is copper(I).
The elemental mapping of
this catalyst proves the existence of boron element which is able
act as Lewis acid in allylic C–H bond oxidation of cyclic olens
(Fig. 5 and 6).
The effect of various solvents were investigated. The yield
was increased gradually with increasing polarity of solvents. It
was observed that acetonitrile is the best solvent for this reac-
Entry
Catalyst (mg)
Time (h)
Yield (%) tion (Table 3, entry 3).
The effects of copper and catalyst loading were also evalu-
ated. The results which described in Tables 4 and 5 showed that
the time and yield of reaction were affected by the amount of
copper doping and the amount of catalyst. The best results were
achieved when approximately 9 wt% loading of copper and
40 mg of catalyst per 5 mmol of substrate (cyclohexene) were
1
2
3
3
40
20
60
10
25
55
43
90
99
70
80
50
a
Reaction conditions: 1 (0.2 mmol), cyclohexene (5 mmol), Cu–B–N–
b
3
SBA-15 (mg), in 3 mL CH CN stirred at r.t. Isolated yield.
a,b
Table 6 Synthesis of allylic esters 2, 4, 5 by allylic oxidation of various cycloolefins over heterogeneous catalyst
2
4
5
Entry
Catalyst
Time (h)
Yield (%)
Time (h)
Yield (%)
Time (h)
Yield (%)
1
2
3
4
CuO
>250
80
64
22
54
65
80
>200
100
75
15
60
80
90
>150
42
35
28
75
80
85
Cu–SBA-15
Cu–N–SBA-15
Cu–B–N–SBA-15
50
50
22
a
b
Reaction conditions: 1 (0.2 mmol), cycloolens (5 mmol), catalyst (40 mg), in 3 mL MeCN stirred at r.t. Isolated yield.
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used (Table 4, entry 9 and Table 5, entry 1). Lowering the copper
loading to less than 4 wt% and increasing of this amount to 9
wt% led to sharp decrease in the desired results. The copper
content was analyzed by AAS.
7 E. Alvarez, M. T. Diaz, R. Perez, J. L. Ravelo, A. Regueiro,
J. A. Vera, D. Zurita and J. D. Martin, J. Org. Chem., 1994,
59, 2848–2876.
8 E. J. Corey and J. Lee, J. Am. Chem. Soc., 1993, 115, 8873–8874.
9 D. J. Rawlinson and G. Sosnovsky, Synthesis, 1972, 1–28.
Various allylic esters from different cycloolens (S20–28 in
the ESI†) were prepared under the optimized conditions, and 10 J. C. Frison, J. Legros and C. Bolm, Copper and Palladium
the results are shown in Table 6. The achieved results in the
presence of Cu–B–N–SBA-15 were better than others.
Catalyzed Allylic Acyloxylations, in Handbook of CH
Transformations, ed. G. Dyker, Wiley-VCH, Weinheim,
2005.
3.2.2. Recycling of the catalyst. The recovery and recyclability
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hexene was evaluated. As shown in Fig. 6, the catalyst was reused
for subsequent runs, up to four times with little loss in activity.
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ꢀ
ethanol and distilled water, dried at 70 C for 4 h under vacuum
and reused in the subsequent run.
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1
1
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2
4
. Conclusions
4
In conclusion, CuO encapsulated in mesoporous silica SBA-15
as monometallic catalysts has been synthesized through the
reaction of SBA-15 or aminopropyl modied SBA-15 with
Cu(NO ) under different conditions. The catalytic potential of
3 2
these heterogeneous catalysts was applied for the copper-
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3
21 W. Woggon, F. Ruther and H. Egli, J. Chem. Soc., Chem.
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catalyzed allylic oxidation of cycloolens via sp C–H bond
activation. Allylic esters were prepared in good yields, reason-
ably short period of time and high selectivity in acetonitrile in
the presence of 40 mg of Cu–B–N–SBA-15 with 9 wt% loading of
copper. For cyclohexene in comparison with other cycloolens,
the best result in term of yield (99%) and rate of reaction (25 h)
was obtained.
Mild conditions of this reaction in combination with recy-
clability of the catalyst, make the presented work a desire
approach to produce functionalized olens in compared to the
most of reports.
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We are grateful to the University of Kurdistan Research Coun-
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