A functionalized graphene oxide and nano-zeolitic imidazolate framework composite as a highly active and reusable catalyst for [3 + 3] formal cycloaddition reactions

Article abstract of DOI:10.1039/c5ta03008k

We report a facile coordination-induced growth approach to fabricate a SO₃H-functionalized graphene oxide and nanosized zeolitic imidazolate framework composite (ZIF-8@SO₃H-GO) under mild conditions. The interactions between the func

Full text of DOI:10.1039/c5ta03008k

Journal of
Materials Chemistry A
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A functionalized graphene oxide and nano-zeolitic
imidazolate framework composite as a highly
active and reusable catalyst for [3 + 3] formal
cycloaddition reactions†
Cite this: DOI: 10.1039/c5ta03008k
Yongyi Wei,‡ Zhongkai Hao,‡ Fang Zhang* and Hexing Li*
We report a facile coordination-induced growth approach to fabricate a SO
3
H-functionalized graphene
3
oxide and nanosized zeolitic imidazolate framework composite (ZIF-8@SO H-GO) under mild
conditions. The interactions between the functional groups on the sheets of GO with Zn(II) ions of the
ZIF-8 precursor initiated the nucleation and growth of ZIF-8 on the GO and meanwhile nanosized ZIF-8
particles were well dispersed on the sheets of GO. Owing to the co-existing basic imidazole moieties
3ꢀ
2ꢀ
2+
from ZIF-8 and the SO and CO -functional groups on the sheets and Zn ions from ZIF-8 in this
Lewis acid rich composite, it exhibited high catalytic reactivity and selectivity in [3 + 3] formal
cycloaddition reactions that consist of two-step Knoevenagel-type condensation and electrocyclic ring-
closure to give various synthetically valuable pyranyl heterocycles. Interestingly, it was especially
advantageous for the large sized reactants. The results indicated that it displayed 2 times higher reactivity
compared to ZIF-8 nanoparticles due to the newly formed mesopores in the junctions between GO
sheets and ZIF-8 nanoparticles. More importantly, it could be conveniently recovered and recycled 10
times without the loss of activity.
Received 25th April 2015
Accepted 8th June 2015
DOI: 10.1039/c5ta03008k
www.rsc.org/MaterialsA
To date, some MOFs have been developed for various multistep
reactions in different acid/base, oxidation/reduction, and
Introduction
1
0
Metal–organic frameworks (MOFs) are ordered porous crystal- metal–organic combination ways, including pristine MOFs,
11
line materials constituted by metal ion nodes and organic organic-functionalized MOFs and metal particle loaded
molecule linkers in a specic coordination number and geom- MOFs. However, the existence of diffusion limitation caused
12
1
etry. Because of their large surface area, high porosity, and by the relatively small pores in most of these reported MOFs
precisely controllable structure and functionality, MOFs have impedes their practical usefulness in multiple chemical trans-
attracted enormous interest in heterogeneous catalysis formations. Moreover, these above-mentioned MOFs have
2
recently. Until now, they have been extensively used in a wide rarely been adopted to construct synthetically useful and
13
range of chemical transformations, such as acid or base catal- complex molecules. Therefore, the design of the novel MOF-
3
,4
5
6
ysis, selective oxidation, asymmetric organic synthesis and based solid catalyst with high reactivity and stability for multi-
7
photocatalysis. In this context, one of the most promising step synthesis still remains a big challenge.
applications is the use of MOFs as solid catalysts for multistep
Recently, graphene oxide (GO) with a two-dimensional sheet-
synthesis because the versatilities in component and like structure and abundant functional groups has provided a
morphology of MOFs allow for an extensive tunability in the novel platform for the nucleation and subsequent growth of
composition, conguration and dispersion of varied active MOFs, resulting in the generation of a series of MOF@GO
8
14
species. Obviously, these systems offer signicant benets to hybrid nanocomposites. Interestingly, these functional mate-
chemical synthesis owing to the increased process intensica- rials exhibited remarkably enhanced properties compared to
9
tion and sustainability, and the reduction of costs and wastes.
the individual corresponding MOFs or GO in adsorption
applications such as CO2 capture and reactive adsorption of
toxic gas, due to the additional pores existing at the MOF@GO
The Education Ministry Key Lab of Resource Chemistry and Shanghai Key Laboratory
of Rare Earth Functional Materials, Shanghai Normal University, Shanghai 200234, P.
R. China. E-mail: zhangfang@shnu.edu.cn; HeXing-Li@shnu.edu.cn; Fax: +86 21 6432
15
interface and the increased dispersive interactions. In spite of
these recent advances, there has been relatively little explora-
tion in heterogeneous catalysis by using MOF@GO nano-
2
272; Tel: +86 21 6432 2272
16
†
Electronic supplementary information (ESI) available: Experimental section. See composites, especially for multistep reactions. Herein we
DOI: 10.1039/c5ta03008k
These authors contributed equally to this work.
report for the rst time the synthesis of a functionalized
‡
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ꢀ1
ꢁ
graphene oxide and nano-ZIF-8 composite (ZIF-8@SO H-GO) by solution (3.5 mol L ) at 30 C under magnetic stirring. Aer
3
a facile coordination-induced growth approach. Owing to the stirring for 12 h, the white powder was collected by centrifu-
co-existing basic imidazoles and abundant Lewis acidic species gation and washed with deionized water and ethanol three
ꢀ
ꢀ
ꢁ
including the SO and CO2 -functional groups on the sheets times, dried in a vacuum at 80 C for 6.0 h.
3
2
+
and Zn ions, it showed excellent catalytic reactivity and
selectivity in [3 + 3] formal cycloaddition reactions that
comprise two-step Knoevenagel-type condensation and elec-
trocyclic ring-closure to give a variety of synthetically valuable
pyranyl heterocycles. It is noteworthy that it was especially
advantageous for the large size molecules due to the newly
formed mesopores in the junctions between GO sheets and ZIF-
2
. Characterization
The nitrogen, carbon and sulfur contents were calculated with a
Vario EL III Elemental analysis analyzer. The surface electronic
states were analyzed by X-ray photoelectron spectroscopy (XPS,
Perkin-Elmer PHI 5000C ESCA). All the binding energy values
were calibrated by using C1S ¼ 284.6 eV as a reference. X-Ray
diffractions (XRD) were performed on a Rigaku D/MAX B
8
nanoparticles. Meanwhile, it was also easily isolated by simple

ltration and reused ten times without signicant degradation
diffraction system with Cu Ka radiation. N
2
adsorption–
in catalytic activity.
desorption isotherms were obtained on a Micromeritics
ASAP2020 analyzer. Transmission electron microscopy (TEM)
images were obtained on a JEOL JEM2011 electron microscope.
Experimental section
1.
Sample preparation
3. Activity test
1
.1 Synthesis of sulfonated graphene oxide (SO H-GO).
3
Graphene oxide (GO) was rst prepared by the conventional In a typical procedure of the [3 + 3] formal cycloaddition reac-
Hummers method. In a typical procedure, the mixture of 1.0 g tion, 1.0 mmol 1,3-cyclohexanedione, 1.0 mmol 3-methyl-2-
natural graphite powder and 1.0 g anhydrous NaNO was added butenal, 50 mg solid catalyst and 5.0 mL CH
2
Cl
2
were mixed and
3
ꢁ
slowly into 40 mL concentrated H SO (98%) in an ice bath. allowed to stir at 20 C for 24 h. The product was extracted with
2
4
Aer continuous stirring for 2.0 h, 5.0 g KMnO
4
was gradually ethyl acetate, followed by analysis on a high performance liquid
added into the mixture. Next, the mixture temperature was chromatography analyzer (HPLC, Agilent 6410 series Triple
ꢁ
increased to 35 C and allowed to stir for another 24 h. Then, Quad) equipped with an Agilent C18 column. The reaction
ꢁ
aer the temperature was adjusted to 60 C, 100 mL 0.50 mol conversion was calculated based on the consumption of 3-
ꢀ
1
L
H
2
SO
4
aqueous solution was added. Aer stirring for 2.0 h, methyl-2-butenal and the selectivity was determined by the yield
ꢁ
the temperature was increased to 95 C. Subsequently, 100 mL of the achieved pyranyl heterocycle product.
3
0% H O aqueous solution and 1000 mL H O were successively
In order to determine the catalyst recyclability, ZIF-8@SO
3
H-
2
2
2
added into the mixture. Aer stirring for 0.5 h, the solid sample GO-2 was centrifuged aer each run of the [3 + 3] formal
ꢀ
1
was thoroughly washed with 0.50 mol L HCl aqueous solution cycloaddition reaction with 1,3-cyclohexanedione and 3-methyl-
and water ve times. The obtained graphene oxide was collected 2-butenal as the reactants and the clear supernatant liquid was
ꢁ
by centrifugation and vacuum drying at 60 C for 12 h. Aer decanted slowly. The residual solid catalyst was washed thor-
that, 0.50 g GO was introduced into 10 mL chlorosulfonic acid oughly with toluene and dichloromethane, followed by vacuum
ꢁ
(
HSO
3
Cl) under a nitrogen atmosphere and then sonicated for drying at 80 C for 6.0 h. Then, the catalyst was re-used with a
0
.5 h. Aer stirring for 12 h, the mixture was added into 500 mL fresh charge of solvent and reactants for subsequent recycle
deionized water and allowed to stir for 1.0 h. The obtained runs under the same reaction conditions.
product was separated by centrifugation, washed with ethanol
ꢁ
and water, and dried in a vacuum at 80 C for 10 h.
Results and discussion
1.2 Fabrication of the graphene oxide-nano-zeolitic imi-
dazolate framework composite (ZIF-8@SO
3
H-GO). First, a The synthesis of the graphene oxide and nano-zeolitic imida-
H-GO) is illustrated in
idazole aqueous solution (3.5 mol L ) at 30 C and sonicated Scheme 1. Briey, GO was prepared according to the previously
certain amount of GO was dispersed into 10 mL 2-methylim- zolate framework composite (ZIF-8@SO
3
ꢀ1
ꢁ
17
for 0.5 h. Then, 1.0 mL Zn(NO
L
3
)
2
aqueous solution (0.50 mol reported Hummers method.
) was added dropwise into the mixture under magnetic (HSO Cl) was chosen to react with GO to afford SO H-func-
Then, chlorosulfuric acid
ꢀ
1
3
3
stirring and aerward continuously stirred for 12 h. Aer tionalized GO (SO H-GO). Next, SO H-GO was added into a
3
3
centrifugation, the solid sample was washed with imidazole mixture of 2-methylimidazole and Zn(NO
buffer solution and ethanol three times to thoroughly remove The coordination interactions of the SO and COO ions on
3
3ꢀ
)
2
aqueous solution.
ꢀ
the uncoordinated Zn ion and 2-methylimidazole. Finally, the the sheets of GO with Zn ions initiated the growth of ZIF-8
ꢁ
product was dried at 80 C in a vacuum for 12 h. The nal nanoparticles, leading to the formation of the ZIF-8@SO
3
H-GO
H- nanocomposite. In parallel, ZIF-8 nanoparticles were also
H-GO-3, corresponding to 50 mg, 100 mg synthesized in aqueous solution by using the same precursors.
and 200 mg GO used in the initial mixture, respectively. Elemental analysis revealed that the sulfur content in the GO
.3 Synthesis of nano-zeolitic imidazolate frameworks sample was only 0.105 wt% (Table S1†). Also, the S2p XPS
catalyst could be dened as ZIF-8@SO
GO-2 and ZIF-8@SO
3 3
H-GO-1, ZIF-8@SO
3
1
ꢀ1
(
3 2
ZIF-8). 1.0 mL Zn(NO ) aqueous solution (0.50 mol L ) was spectrum (Fig. S1†) revealed that no apparent signal of the
added dropwise into 10 mL 2-methylimidazole aqueous sulfur element could be detected, conrming the negligible
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Scheme 1 Schematic synthesis of ZIF-8@SO H-GO composites.
sulfur species in the GO sample due to the efficient washing
18
work-up treatment. For comparison, the amount of sulfur was
found to be 1.75 wt% in SO H-GO (Table S1†). FTIR spectra
H-GO exhibited an additional peak at
090 cm characteristic of the stretching vibration of the S]O
3
(
1
Fig. S2†) showed that SO
3
ꢀ1
19
bond in comparison with GO. In addition, the S2p XPS spec-
trum (Fig. 1a) of SO H-GO displayed an obvious peak at 168.6 eV
3
20a
associated with the S–O bond. These results indicated the
successful modication of SO H groups on the GO. Moreover,
the C1s spectrum of SO H-GO (Fig. 1b) revealed that the peak at
86.9 eV characteristic of C–OH and C–O–C moieties almost
Fig. 1 S2p XPS spectra (a) of SO
XPS spectra (b) of GO, SO H-GO and ZIF-8@SO
spectra (c) of ZIF-8 and ZIF-8@SO H-GO-2.
3
H-GO and ZIF-8@SO
3
H-GO-2, C1s
3
3
3
H-GO-2 and N1s XPS
3
3
2
completely disappeared while the peaks at 284.7 and 289.1 eV
2
corresponding to sp C–C bonding and the carboxylic acid
20b
group remained almost the same with GO, suggesting the different samples are shown in Fig. 2b. Only a very low amount
incorporation of SO H-groups on the GO via a possible esteri- of N2 molecules was adsorbed on the GO. Meanwhile, ZIF-8
3

cation reaction between the surface hydroxyl groups (OH–) displayed the type I adsorption–desorption isotherm, indicating
19a
25
and HSO
3
Cl. Furthermore, the FTIR spectrum of the repre- its microporous structure. The shape of the isotherms for all
H-GO-2 (Fig. S2†) exhibited the typical ZIF- the ZIF-8@SO H-GO composites was quite similar to ZIF-8.
sentative ZIF-8@SO
absorption peaks at 990, 1585 and 2960 cm corresponding However, the additional small hysteresis loops at a high relative
to C–N stretch, C]N stretch and aliphatic C–H stretch of pressure around p/p ¼ 0.47–1.0 can be seen in ZIF-8@SO H-
3
3
ꢀ1
8
0
3
21
imidazole groups, respectively. In addition, the N1s XPS GO-1 and ZIF-8@SO H-GO-2. It was probably assigned to the
3
spectrum of ZIF-8@SO
3
H-GO-2 (Fig. 1c) displayed almost the formation of mesopores that existed in the junctions between
26
same peak at 398.7 eV indicative of imidazole moieties with ZIF- ZIF-8 and GO surface for ZIF-8@SO H-GO composites. As
3
22
8
nanoparticles, demonstrating the effective nucleation and shown in Table 1, the average pore sizes of ZIF-8@SO H-GO-1
3
growth of ZIF-8 on the GO. Interestingly, the S2p XPS spectrum and ZIF-8@SO H-GO-2 calculated from their adsorption
3
(
Fig. 1a) revealed the complete disappearance of the S–O bond branches were 1.9 and 2.1 nm, further conrming the newly
signal for the ZIF-8@SO H-GO-2 composite. Also, the C1s XPS generated mesopores. Moreover, the specic surface areas and
spectrum of ZIF-8@SO H-GO-2 (Fig. 1b) showed that the peak at pore volumes of ZIF-8@SO H-GO samples were gradually
89.1 eV attributed to the carboxylic acid group also dis- decreased with the increasing GO percentages in these
3
3
3
2
ꢀ
appeared. This phenomenon suggested that both SO
COO ions initiated the growth of ZIF-8 on the sheets of GO, proportion of nonporous GO in the composites.
3
and composites (Table 1), which can be explained by the increasing
ꢀ
thereby these functional groups were covered by ZIF-8 aer the
formation of the ZIF-8@SO H-GO composite.
The morphologies of ZIF-8@SO H-GO composites were
indicated by transmission electron microscopy (TEM). In the
3
3
XRD spectra (Fig. 2a) showed that the major diffraction peak absence of GO, the as-made ZIF-8 nanoparticles displayed the
at 2q ¼ 10.2ꢁ assigned to the (001) plane in GO almost approximate rhombohedral shape with a particle size in the
3
completely disappeared and changed to a broad peak in SO H- range of 80 to 100 nm (Fig. 3a). In comparison, ZIF-8 particles
GO. In combination with its TEM image (Fig. S3†), these results with around 100 nm size were randomly distributed on the GO
revealed that the sheets of SO H-GO were efficiently exfoliated layers in ZIF-8@SO H-GO-1 (Fig. 3b). However, for ZIF-8@SO H-
with single or several layers, providing a suitable two-dimen- GO-2, most of ZIF-8 particles with about 80 nm size and some
3
3
3
2
3
sional support to attach the nanoparticles on its sheets.
Accordingly, XRD spectra of these ZIF-8@SO H-GO composites surface (Fig. 3c). However, ZIF-8 particles with ca. 80 nm size
exhibited similar well resolved diffraction peaks to those of ZIF- were sporadically dispersed in the stacked interlays of ZIF-
nanoparticles, evidently identifying the generation of ZIF-8 8@SO H-GO-3 (Fig. 3d). The drastic morphological differences
smaller particles with 20–30 nm size were densely laid on the
3
8
3
24
with a crystalline size on the nanoscale. The intensities of highlighted the critical role of GO as a novel support for
diffraction peaks were gradually decreased with the increase in mediating the growth of ZIF-8. It is also important to note that
amounts of GO in the initial solution, which was maybe the decreased amount of GO (50 mg) caused the bigger ZIF-8
attributed to the reduced ZIF-8 size and the increased amount size probably due to the less coordination sites while the
of low crystallinity GO. Additionally, N sorption isotherms of increased amount of GO (200 mg) induced the irregular
2
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Fig.
3
3 TEM images of ZIF-8 (a) and ZIF-8@SO H-GO (b–d)
composites.
3
SO H-GO also showed low conversion (40%). ZIF-8 nano-
particles obtained good conversion with 81%. It is worth
mentioning that all the ZIF-8@SO H-GO composites promoted
3
this reaction with the enhanced catalytic reactivity and ZIF-
8@SO
3
H-GO-2 gave the excellent result with 94% conversion.
This phenomenon suggested that the basic imidazole moieties
ꢀ
ꢀ
2+
and the SO
these Lewis acid rich composites cooperatively catalyzed this
3
and CO -functional groups and Zn ions in
2
13
3
reaction. The inferior reactivity of ZIF-8@SO H-GO-1 could be
attributed to the bigger ZIF-8 particle size and the lowest cata-
lytic efficiency of ZIF-8@SO H-GO-3 could be assigned to the
3
reduced accessible active sites. Interestingly, the physical
2
Fig. 2 XRD spectra (a) and N adsorption–desorption isotherm (b) of
different samples.
3
mixture of SO H-GO and ZIF-8 still achieved the unsatisfactory
yield (76%), probably due to the increased mass transfer resis-
tance between two different solid catalysts, especially in stirring
reaction conditions. Moreover, the commonly used homoge-
distribution maybe owing to the serious accumulation of GO
sheets.
28
14b,h
neous Lewis acid AlCl3 was chosen for comparison. It dis-
played the similar conversion (97%) with ZIF-8@SO H-GO-2,
The [3 + 3] formal cycloaddition reaction is the important
tool for constructing the piperidine ring, which is one of the
most common structural subunits in natural products and
biologically active compounds. It consists of a Knoevenagel-type
condensation followed by a reversible 6p-electron electrocyclic
3
further conrming the excellent catalytic performances of the
ZIF-8@SO H-GO composite.
3
3
To further explore the advantage of ZIF-8@SO H-GO, we
chose 3-(9-anthryl)acrylaldehyde with a very large molecular size
as the reactant (Table 2). ZIF-8 exhibited a signicantly
decreased conversion (37%), because of its small micropore it
was difficult to allow the effective diffusion for large molecules.
Meanwhile, the other byproduct was formed due to the self-
condensation of a,b-unsaturated aldehydes, leading to the
27
ring-closure. In this regard, we rst employed a [3 + 3] formal
cycloaddition reaction between 1,3-cyclohexanedione and 3-
methyl-2-butenal as a model reaction to evaluate the catalytic
3
efficiencies of ZIF-8@SO H-GO composites. As summarized in
Table 2, the blank experiment could not give any products and
29
reduced selectivity (90%). Note that ZIF-8@SO H-GO-2 dis-
3
played good conversion (71%) and excellent selectivity (98%). As
Table 1 Textural parameters of different samples
3
a result, the yield of ZIF-8@SO H-GO-2 was 2 times higher than
that of ZIF-8. This remarkable enhancement could be explained
by the fact that the newly formed mesopores in the junctions
between GO sheets and ZIF-8 nanoparticles were readily
accessible to the reactants with the decreased mass transfer
Pore volume
Pore size
(nm)
2
ꢀ1
3
ꢀ1
Sample
GO
BET (m g
)
(cm g
)
58 ꢂ 4
60 ꢂ 5
0.05
0.07
0.76
0.52
0.43
0.18
—
—
—
1.9
2.1
—
30
SO
3
H-GO
resistance.
Encouraged by these promising results, we next investigated
the capability of the ZIF-8@SO H-GO-2 catalyst for the other
ZIF-8
1315 ꢂ 39
842 ꢂ 26
643 ꢂ 21
242 ꢂ 8
ZIF-8@SO
ZIF-8@SO
ZIF-8@SO
3
H-GO-1
3
H-GO-2
3
H-GO-3
3
heterocycle synthesis (Table 3). For 4-pyran-3,6-dione partici-
pating [3 + 3] formal cycloaddition reactions, similar benets
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Table 2 Catalytic properties of different catalysts in [3 + 3] formal
cycloaddition reactions between 1,3-cyclohexanedione and a,b-
a
unsaturated aldehydes
Catalyst
Aldehyde
Product
Conv. (%)
Sel. (%)
ZIF-8@SO
ZIF-8@SO
ZIF-8@SO
3
3
3
H-GO-1
H-GO-2
H-GO-3
90
94
85
40
81
77
97
59
71
47
33
37
42
99
99
99
99
99
99
99
95
98
91
98
90
97
SO
ZIF-8
SO H-GO + ZIF-8
AlCl
3
H-GO
Scheme
2
A possible cooperative catalytic mechanism of ZIF-
8
@SO H-GO for the [3 + 3] formal cycloaddition reaction.
3
b
3
c
3
ZIF-8@SO
ZIF-8@SO
ZIF-8@SO
3
3
3
H-GO-1
H-GO-2
H-GO-3
These results clearly demonstrated the generality of the strategy
for the use of ZIF-8@SO H-GO nanocomposites for the multi-
3
SO
3
H-GO
step synthesis of structurally diverse and functionalized mole-
cules. On the basis of these results, a plausible cooperative
ZIF-8
SO H-GO + ZIF-8
3
b
mechanism for the ZIF-8@SO
3
H-GO catalyzed [3 + 3] formal
a
Reaction conditions: 50 mg ZIF-8@SO
3
H-GO, ZIF-8 or SO
3
H-GO, 1.0
ꢀ
cycloaddition reaction was proposed (Scheme 2). The SO
3
and
mmol 1,3-cyclohexanedione, 1.0 mmol aldehyde, 5.0 mL of CH
T ¼ 20 C and t ¼ 24 h. 30 mg GO + 20 mg ZIF-8. 13.3 mg AlCl
2
Cl ,
2
ꢁ
b
c
ꢀ
2+
3
.
CO -functional groups on the sheets and Zn ions from ZIF-8
2
in this Lewis acid rich composite activated a,b-unsaturated
aldehyde through hydrogen bonding to the carbonyl group,
while the neighbouring imidazole groups of ZIF-8 on the sheets
of GO attacked the dione. Then, both the Lewis acids and base
moieties stabilized the intermediate and generated the
condensation product aer eliminating one molecule of water.
were also achieved with superior reactivity for ZIF-8@SO
3
H-GO-
2. It displayed the higher catalytic efficiencies in all the a,b-
unsaturated aldehydes compared with ZIF-8. Note that it
showed the same trend for the large size molecules. For
example, for these aromatic aldehydes, it exhibited at least 2.0
times improved conversion compared to ZIF-8 nanoparticles.
3
Aer the electrocyclic ring closure process, the ZIF-8@SO H-GO
31
composite gave the nal pyranyl heterocycle product.
Furthermore, we examined the durability of ZIF-8@SO
3
H-
GO-2 in the [3 + 3] formal cycloaddition reaction with 1,3-
cyclohexanedione and 3-methyl-2-butenal as the reactants. No
signicant decrease could be found in the yield of 7,8-dihydro-
2,2-dimethyl-2H-chromen-5(6H)-one aer being used repeti-
tively ten times (Fig. 4). Elemental analysis (Table S1†) revealed
that aer being used ten times, the nitrogen content in the
Table 3 Catalytic properties of ZIF-8@SO
3
H-GO-2 and ZIF-8 in [3 +
3
] formal cycloaddition reactions between 4-pyran-3,6-dione and
a
a,b-unsaturated aldehydes
Catalyst
Aldehyde
Product
Conv. (%) Sel. (%)
ZIF-8@SO
ZIF-8
ZIF-8@SO
ZIF-8
3
H-GO-2
3
H-GO-2
3
H-GO-2
72
54
63
41
99
99
99
99
ZIF-8@SO
ZIF-8
51
26
99
99
ZIF-8@SO
ZIF-8
3
H-GO-2
H-GO-2
40
21
99
99
ZIF-8@SO
ZIF-8
3
31
15
93
91
a
Reaction conditions: 50 mg ZIF-8@SO
3
H-GO-2 or ZIF-8, 1.0 mmol 4-
ꢁ
Fig. 4 The recycling test of ZIF-8@SO H-GO-2 in the [3 + 3] formal
pyran-3,6-dione, 1.0 mmol aldehyde, 5.0 mL of CH
t ¼ 24 h.
2
Cl
2
, T ¼ 20 C and
3
cycloaddition reaction between 1,3-cyclohexanedione and 3-methyl-
2-butenal. Reaction conditions are given in Table 2.
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recycled ZIF-8@SO H-GO-2 remained almost the same (13.2
Paper
3
4 J. W. Liu, L. F. Chen, H. Cui, J. Y. Zhang, L. Zhang and
C. Y. Su, Chem. Soc. Rev., 2014, 43, 6011.
wt%). Meanwhile, the TEM image of the recycled ZIF-8@SO H-
3
GO-2 conrmed almost no remarkable change in the structure
before and aer reuse (Fig. S4†). These results were in good
agreement with an excellent retention of the activity of the ZIF-
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In summary, we have synthesized a functionalized graphene
oxide and nano-ZIF-8 composite via a facile coordination-
induced approach. With highly dispersed basic ZIF-8 nano-
particles and rich Lewis acids in this composite, it showed a
cooperative catalytic behavior in [3 + 3] formal cycloaddition
reactions and obtained high catalytic reactivity and selectivity
for a wide range of reactants. It is worth mentioning that it was
advantageous for the large size molecules due to the diminished
diffusion limitation derived from the added mesopores in the 10 S. Rostamnia, H. Xin and N. Nouruzi, Microporous
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loss of activity. The presented strategy could be further extended
to the development of more robust MOF@GO nanocomposites
for multistep synthesis of synthetically valuable and complex
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This work was supported by the Natural Science Foundation of 12 (a) M. T. Zhao, K. Deng, L. C. He, Y. Liu, G. D. Li, H. J. Zhao
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