Cu-MOF: An efficient heterogeneous catalyst for the synthesis of symmetric anhydrides: Via the C-H bond activation of aldehydes

Article abstract of DOI:10.1039/c8ra03870h

In this paper, an efficient and straightforward synthetic approach for the preparation of a number of symmetric carboxylic anhydrides was reported using Cu₂(BDC)₂(DABCO) as an efficient heterogeneous catalyst via the C-H bond activation of aldehydes with excellent yields and simple work up. This C-H bond activation reaction appears simple and convenient, has a wide substrate scope and makes use of cheap, abundant, and easily available reagents. The Cu-MOF catalyst was recycled and reused four times without any loss of catalytic activity.

Full text of DOI:10.1039/c8ra03870h

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Cu-MOF: an efficient heterogeneous catalyst for
the synthesis of symmetric anhydrides via the C–H
bond activation of aldehydes†
Cite this: RSC Adv., 2018, 8, 24203
Zahra Ahmadzadeh, Javad Mokhtari * and Morteza Rouhani
In this paper, an efficient and straightforward synthetic approach for the preparation of a number of
2 2
symmetric carboxylic anhydrides was reported using Cu (BDC) (DABCO) as an efficient heterogeneous
Received 6th May 2018
Accepted 14th June 2018
catalyst via the C–H bond activation of aldehydes with excellent yields and simple work up. This C–H
bond activation reaction appears simple and convenient, has a wide substrate scope and makes use of
cheap, abundant, and easily available reagents. The Cu-MOF catalyst was recycled and reused four times
without any loss of catalytic activity.
DOI: 10.1039/c8ra03870h
rsc.li/rsc-advances
23
and drugs. Symmetric anhydrides are well known as advanta-
geous acylating agents because they prevent by-product genera-
Metal–organic frameworks (MOFs), which are also called coor- tion due to their symmetric nature. The main classical synthetic
dination polymers, are synthesized from organic linkers and procedures for anhydride synthesis involve utilizing dehydrating
metal ions or clusters. Recently, MOFs have attracted much agents such as phosgene, acid chloride, thionyl chloride, benze-
Introduction
24
1
2
more attention due to their structural and chemical diversities nesulfonyl chloride, and phosphorous pentoxide in equivalent
and have become very popular in diverse research areas such as amounts which generally need harsh reaction conditions, are
3–5
6,7
8,9
10,11
catalysis,
chemical sensing, conversion etc.
In spite of their low thermal and chemical stabilities which
drug delivery,
gas storage,
adsorption,
usually expensive, have inaccessible reagents and catalysts, have
a time-consuming work-up etc. (Scheme 1).
12
13
25,26
For these reasons, researchers are always looking for novel
have limited their applications to only those under mild synthetic pathways which provide straightforward access to the
conditions, MOFs have achieved more attention in chemical desired anhydrides within a minimum reaction time with inex-
14
catalysis. Their efficient catalytic activities are caused by pensive starting materials and catalysts as well as mild reaction
27–29
several parameters such as the existence of suitable functional conditions.
A new approach involves the self-coupling of
groups on the organic linkages, the exibility of the framework aldehydes in the presence of transition metal catalysts such as
which facilities the acceptance of the guest molecule(s), the
15–17
internal channel surface area etc.
The active metal sites in
MOFs are fully exposed and thus provide a high degree of metal
dispersion. In addition, MOFs provide a highly versatile alter-
native to well-established porous materials by constructing
various transition metal nodes and a wide variety of organic
18
bridging ligands for specic catalytic applications. Among
MOFs, Cu-MOFs have attracted more interest because of their
outstanding catalytic activities, regular structural conguration
18
and some dominant electrical properties.
Anhydrides belong to the carboxylic acid derivatives and are
19
very useful reagents in organic synthesis and various other
20
reactions including the lactonization of silyl esters, asymmetric
21
esterications, the condensation reaction of free carboxylic
22
acids and alcohols and specially in the preparation of peptides
Department of Chemistry, Science and Research Branch, Islamic Azad University, P.O.
Box 14515/775, Tehran, Iran. E-mail: j.mokhtari@srbiau.ac.ir
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c8ra03870h
1
Scheme 1 Different methods for the synthesis of anhydrides.
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ꢀ
the reaction temperature was increased to 80 C and was
allowed to be stirred for 2 h. The reaction progress was moni-
tored by TLC. Aer completion of the reaction, the solvent was
evaporated under reduced pressure, and the residue was puri-

ed using silica gel column chromatography (hexane/ethyl
acetate (10 : 4)).
2 2
Scheme 2 The Cu (BDC) (DABCO) catalyzed synthesis of anhydrides
via C–H aldehyde bond activation.
Selected spectra data
1
Benzoic anhydride (2a). Yield ¼ 82%; liquid, H-NMR (500
3
0–32
copper.
A major drawback related to earlier methodologies is
MHz, CDCl ): d 7.46–7.51 (m, 4H, CH of Ar), 7.60–7.65 (m, 2H,
3
3
homogeneous systems and as a result, the isolation of catalysts
and work-up are difficult and time consuming. Therefore, the
development of new heterogeneous systems for the formation of
C–O bonds through C–H bond activation remains a great goal. A
few examples were reported for C–O bond formation via C–H
aldehyde bond activation. Corma recently published an
example for C–O bond formation via C–H aldehyde bond activa-
tion with Cu-MOF as the heterogeneous catalyst.
CH of Ar), 8.13 (d, 4H, J ¼ 7.86 Hz). Anal. calcd for C14
10 3
H O
(
226.23): C, 74.33; H, 4.46. Found: C, 74.35; H, 4.47.
ꢀ
4
-Nitrobenzoic anhydride (2i). Yield ¼ 68%; mp: 188–190 C,
1
3
H-NMR (500 MHz, CDCl
3
): d 8.14 (d, 4H, J ¼ 8.9 Hz, CH of Ar),
.26 (d, 4H, J ¼ 8.9 Hz, CH of Ar). Anal. calcd for C14
316.23): C, 53.18; H, 2.55; N, 8.86%. Found: C, 53.21; H, 2.58; N,
3
8
(
8
8 2 7
H N O
33
34
.87%.
-Hydroxy-3-methoxybenzoic anhydride (2m). Yield ¼ 73%;
H-NMR (500 MHz, CDCl ): d 3.98 (s, 6H, MeO), 6.17 (bs, 2H,
4
1
So, according to what is mentioned above and in continuation
of our interest in exploring the role of MOFs as efficient hetero-
geneous catalysts in organic synthesis and oxidative coupling
3
3
OH), 7.05 (d, 2H, J ¼ 8.4 Hz, CH of Ar), 7.43–7.45 (m, 4H, CH of
Ar). Anal. calcd for C16
C, 60.4; H, 4.46.
H
14
O
7
(318.28): C, 60.38; H, 4.43. Found:
35–37
reactions,
herein, we report the rst application of Cu-MOFs as
1
efficient heterogeneous catalysts for the synthesis of symmetric
carboxylic anhydrides 2 via the C–H activation of aldehydes 1
using TBHP as an oxidizing agent (Scheme 2). Good to excellent
yields, easy work-up of the catalyst, reusability, and minimal
reaction time are some of the benecial features of this reaction.
4
-Hydroxybenzoic anhydride (2l). Yield ¼ 70%; H-NMR (500
3
MHz, CDCl ): d 5.6 (bs, 2H, OH), 6.95 (d, 4H, J ¼ 8.6 Hz, CH of
3
3
Ar), 7.82 (d, 4H, J ¼ 8.6 Hz, CH of Ar). Anal. calcd for C H O
1
4
10 5
(
258.23): C, 65.12; H, 3.90. Found: C, 65.15; H, 3.94.
Results and discussion
Experimental section
Materials and methods
In this work, Cu
2 2
(BDC) (DABCO) was synthesized and charac-
terized by various techniques and according to our previously
All of the chemicals were purchased from commercial sources reported procedure. The XRD powder patterns of the resulting
and used without further purication. Cu (BDC) (DABCO) was solid were compared to the previously reported ones and sharp
synthesized according to a previously reported procedure. All peaks were present at 8q and 9q, which conrmed the formation
2
2
37
37
of the reactions were monitored by thin layer chromatography of Cu (BDC) (DABCO) (Fig. 2). The FT-IR spectra of Cu2(-
2
2
(
TLC) using plates coated with Merck 60 HF254 silica under UV BDC) (DABCO) exhibited the formation of Cu (BDC) (DABCO)
2
2
2
37
light. The BET (Brunauer–Emmett–Teller) surface area of the compared to our previous reports (Fig. S5a†). The nitrogen
samples was determined from N2 adsorption–desorption adsorption isotherm of Cu (BDC) (DABCO) presented a typical
2
2
isotherms using a micromeritics ASAP 2020 analyzer. The type-I prole with a relatively high Langmuir surface area of
2
ꢁ1
sample was characterized using a ZEISS scanning electron 1496 m g (Fig. S1†) and a median pore diameter of 3.9 nm
microscope (SEM) at 30 kV with a gold coating. Transmission (Fig. S1†). TGA results indicated that the material was stable up
ꢀ
electron microscopy (TEM) was carried out using an EM10C-100 to over 250 C (Fig. S6†). A SEM micrograph (Fig. S3†), consis-
kV series microscope from the Zeiss Company, Germany. A tent with the TEM observation (Fig. S4†), conrmed that
TGA/DSC (thermogravimetric analysis & differential scanning a highly crystalline material was achieved.
calorimetry) by METTLER TOLEDO, Switzerland, was used for
2 2
The synthetic Cu (BDC) DABCO was employed as a catalyst
thermogravimetric analysis (TGA) with a heating rate of in the C–H activation of aldehydes and the synthesis of anhy-
ꢀ
ꢁ1
1
0 C min under a nitrogen atmosphere. FT-IR spectra were drides. Firstly, to achieve the optimum reaction conditions,
1
recorded using a Shimadzu 8400s FT-IR spectrometer. H-NMR various parameters such as the solvent, the oxidant, the amount
spectra were recorded with a BRUKER DRX 500-AVANCE FT- of catalyst and the reaction time were examined.
3
NMR instrument (CDCl solution) at 500 MHz.
Selection of the best solvent
Synthesis of carboxylic anhydrides via the C–H activation of
aldehydes catalyzed by Cu (BDC) (DABCO)
The effect of various solvents such as dichloromethane
2
2
(
CH Cl ), chloroform (THF), dimethylformamide (DMF),
2 2
To a solution of aldehyde 1 (1 mmol) and Cu (BDC) (DABCO) ethanol (C H OH), water (H O) and acetonitrile (CH CN) was
2
2
2
5
2
3
(10% mol) in CH
3
CN (2 ml), 1.5 eq. from a 6 M solution of TBHP investigated for the C–H activation of benzaldehyde in the
in CH CN was added slowly over 5 minutes while stirring. Then, presence of the catalyst and TBHP as a model reaction. The
3
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a
Table 1 Solvent type optimization for the model reaction
Table 3 Effect of the type of oxidant in the synthesis of benzoic
anhydride
a
Entry
Solvent
Yield (%)
a
Entry
Oxidant
Yield (%)
1
2
3
4
5
6
CH
THF
DMF
2
Cl
2
Trace
10
20
15
25
1
2
3
4
Air
Oxone
H O
2 2
TBHP
—
—
—
82
C
2
H
5
OH
H
2
O
CH
3
CN
82
a
Reaction conditions: benzaldehyde (1 mmol), oxidant (1.5 mmol) and
CN (2 ml).
a
Reaction conditions: benzaldehyde (1 mmol), TBHP (1 mmol), catalyst CH
10 mol%) and solvent (2 ml).
3
(
groups such as vaniline, 4-methoxy benzaldehyde and 4-
hydroxy benzaldehyde were converted to anhydrides with good
to excellent yields.
In line with the results reported earlier by Saberi et al., and
Khatun et al. the reaction of benzaldehyde in the presence of
results are summarized in Table 1. It is obvious that the C–H
activation of benzaldehyde is solvent-dependent. It can be seen
that the maximum yield was obtained with the CH
3
CN solvent.
So, CH CN was chosen as an ideal solvent for this reaction.
3
The effect of the amount of catalyst. For the investigation of
the effect of the amount of catalyst on the C–H activation of
aldehydes, as mentioned above the reaction of benzaldehyde in
CuCl and CuCl
sponding anhydrides, 2a, aer 3 h, respectively (Table 5, entry 3
and 4). However, when CuCl and CuCl were replaced by Cu
BDC) DABCO, the reaction was considerably faster and affor-
2
and TBHP yielded 68 and 75% of the corre-
2
2
-
CH CN as the solvent in the presence of TBHP was chosen as
3
(
2
the model reaction. As shown in Table 2, 10 mol% of Cu-MOF
was the best amount of catalyst for the synthesis of benzoic
anhydride. The higher amounts of catalyst did not affect the
reaction distinctly (Table 2, entries 5 and 6).
Selection of the best oxidant. For the optimization and
2 2
selection of the best oxidant, air, TBHP, H O and oxone were
chosen and as shown in Table 3, entry 4, the best oxidant for
this reaction was TBHP. It is noteworthy that when hydrogen
peroxide was used as an oxidant a large part of aldehyde was
converted to carboxylic acid and no product was observed.
ded practically full conversion and full selectivity to 2a aer 2 h
Table 5, entry 7). In addition, aer the completion of the
(
reaction, the catalyst was easily separated by ltration or by
centrifuge and reused several times. As shown in Table 5, also,
there are many other reports on the synthesis of anhydrides
using aldehydes, but most of them have used an equivalent
amount of reagents and some of them are expensive and
Table 4 Generality investigation of the reaction through the synthesis
Aer optimization of the model reaction, the reaction of a vast number of asymmetric carboxylic anhydrides
generality was evaluated using a vast number of aromatic
aldehydes. The results are summarized in Table 4. The reaction
presented good to excellent results using functionalized
aromatic aldehydes with both electron-rich and electron-poor
substituents. The results showed a high catalyst prociency in
C–H bond activation and the synthesis of anhydrides. Patel
32
et al. have reported that aldehydes with electron-withdrawing
groups such as NO in para or ortho positions in the presence of
CuO nanoparticles resulted in no product being formed, while
in the present work aldehydes with electron-withdrawing 1a
2
a
ꢀ
Entry
R
Anhydride Yield (%) mp C (ref.)
H
2a
2b
2c
2d
2e
2f
2g
3h
2i
2j
2k
2l
2m
2n
2o
2p
82
78
81
75
79
78
80
81
68
67
76
70
73
78
80
78
76
Liquid [ref. 32]
83–86 [ref. 32]
95–97 [ref. 32]
180–182 [ref. 26]
218–220 [ref. 38]
86–88 [ref. 41]
76–78 [ref. 39]
84–87 [ref. 41]
188–190 [ref. 40]
136–137 [ref. 41]
Liquid [ref. 32]
Oil
1
1
1
1
1
1
1
b
4-Me
4-MeO
4-Cl
4-Br
2-Br
2-Cl
3-Cl
4-NO
2-NO
2-Me
4-OH
4-OH, 3-MeO
3-Me
3-Meo
4-F
2-Naphthaldehyde 2q
groups led to the corresponding anhydrides in relatively good
yields. On the other hand, aldehydes with electron-donating
c
d
e
f
g
h
Table 2 Optimization of the amount of Cu
2 2
(BDC) (DABCO) catalyst in
the synthesis of benzoic anhydride
a
1i
2
Entry
Amount of catalyst (mol%)
Yield (%)
1
1
1
1
1
1
1
1
j
k
l
m
n
o
p
q
2
1
2
3
4
5
6
1
2.5
5
10
20
30
41
52
60
82
81
83
Oil
Liquid [ref. 32]
Liquid [ref. 32]
112–114 [ref. 26b]
114–116 [ref. 32]
a
Reaction conditions: benzaldehyde (1 mmol), TBHP (1 mmol) and
CN (2 ml).
a
Reaction conditions: aromatic aldehydes (1 mmol), TBHP (1.5 mmol)
CH
3
and time: 2 h.
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Table 5 Comparison of the activity for different systems in the synthesis of benzoic anhydride
Entry
Catalyst
Reaction conditions
Time
Yield
Ref. no.
1
2
3
4
5
6
7
—
CH
2
Cl
2
, TCCA, Et
3
N
1 h
5 h
3 h
1 h
0.5 h
3
98
61
68
75
87
85
82
26
32
30
31
28
29
ꢀ
CuO nanoparticle
DCE, TBHP 120 C
ꢀ
CuCl
CuCl
—
—
Cu
2
CH
3
CN, TBHP, 80 C
DMSO, TBHP, rt
TBHP, TBAI, CH
TBHP, TBAI, PhClO, 80 C
ꢀ
3
CN, 70 C
ꢀ
ꢀ
2
(BDC)
2
DABCO-MOF
TBHP, CH
3
CN, 80 C
2 h
Present work
environmentally destructive (Table 5, entry 1, 5 and 6). On the
One of the important issues for heterogeneous catalysts is
other hand, CuO particles displayed the worst catalytic perfor- reusability. To investigate this issue for our catalyst, Cu-MOF was
mance (61% conversion), which indicates the crucial role of the recovered by simple ltration and washed with methanol and
microporous structure of Cu-MOF, which provides a higher dried in an oven. The recovered catalyst was reused for the C–H
availability of copper sites compared to the very low porosity activation of benzaldehyde and the formation of benzoic anhy-
32
2 2
structure of CuO (Table 5, entry 2). As a result, Cu-MOF is dride four times. The results indicate that Cu (BDC) DABCO can
expected to have exible and unsaturated coordination for be used for several cycles successfully with minimal loss of
aldehydes, which allows for the continuation of the reaction activity. As it is clear from the FESEM images, the morphology of
process and the avoidance of the reaction being blocked by very the structure is not changed aer 4 runs (Fig. 1).
42,43
rigid coordination.
The TEM image of recycled Cu (BDC) DABCO shows that the
2 2
The proposed reaction mechanism is shown in Scheme 3.
crystalline structure of Cu (BDC) DABCO is maintained aer 5
2 2
In this reaction, rstly, electron transfer from an exposed runs (Fig. 2).
t
Cu(II) at Cu-MOF to TBHP generates Cu(III) and BuOc. Then,
2 2
Recycled Cu (BDC) DABCO aer 5 runs maintained its
Cu(III) eliminates an electron from the other TBHP molecule and crystallinity based on PXRD (Fig. 3), but a slight degradation of
t
44,45
gives Cu(II) and BuOOc species. The activation of the hydrogen the structure and hydrolysis reaction
could possibly justify
t
ꢀ
atom from aldehyde by BuOc led to the formation of a benzoyl the presence of the peaks at higher values of 2q (30–40 ), which
radical which coupled with BuOOc, subsequently. Then the probably indicates the presence of Cu(OH)
cleavage of the O–O bond in the RCOOO Bu intermediate and it direct products of this reaction. In fact, under TBHP (70%)
t
46
2
or CuO, which are
t
coupling with another benzoyl radical resulted in the corre-
t
sponding anhydride and Buoc species, which could be used in
26
attracting the C–H bond of aryl-aldehyde.
Fig. 1 The FE-SEM image of fresh Cu
2 2
(BDC) DABCO (left) and the FE-
SEM image of recycled Cu (BDC) DABCO (right).
2
2
2 2
Scheme 3 The proposed mechanism for the synthesis of symmetric Fig. 2 The TEM image of fresh Cu (BDC) (DABCO) (left) and the TEM
carboxylic anhydrides via C–H activation. image of recycled Cu (BDC) (DABCO) (right).
2
2
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In conclusion, we have studied a simple and effective method
for the preparation of symmetric carboxylic anhydrides via C–H
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in the methods reported in the literature were produced with
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2
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Conflicts of interest
There are no conicts to declare.
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