Co6(μ3-OH)6 cluster based coordination polymer as an effective heterogeneous catalyst for aerobic epoxidation of alkenes

Article abstract of DOI:10.1039/c3dt52562g

A new hexaprismane Co(ii)₆(μ₃-OH)₆ cluster-based three-dimensional coordination polymer ({Co(μ₃-OH) (HCOO)_0.72(CH₃COO)_0.28}_n, Co6-CP) was successfully synthesized and characterized with single-crystal XRD, IR spectra, TGA spectra and elemental analysis. Co6-CP was used as an effective heterogeneous catalyst for the aerobic epoxidation of various alkenes. For the catalytic epoxidation of trans-stilbene, the conversion and selectivity towards the epoxide reached 98.6 and 98.0%, respectively. Also, an average TOF of 22 h^-1 was obtained for the reaction. The results indicated that Co6-CP displayed excellent aerobic epoxidation activity among the reported coordination polymer materials, even rivaling the traditional heterogeneous cobalt catalysts. The influence of the reaction parameters such as temperature and oxygen flow rate for the epoxidation of the trans-stilbene were also studied in detail.

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Co (μ -OH) cluster based coordination polymer as an effective
6
3
6
heterogeneous catalyst for aerobic epoxidation of alkenes
a‡
b‡
b
c
c
b
b
Junkuo Gao, Linlu Bai, Qian Zhang, Yongxin Li, Ganguly Rakesh, Jong-Min Lee, Yanhui Yang,* and
a
Qichun Zhang*
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
A new hexaprismane Co(II) (μ -OH) cluster-based three-dimensional coordination polymer ({Co(μ3-
6
3
6
OH)(HCOO)0.72(CH COO)0.28}n, Co6-CP) was successfully synthesized and characterized with single-
3
crystal XRD, IR spectra, TGA spectra and elemental analysis. Co6-CP was used as effective
heterogeneous catalyst for the aerobic epoxidation of various alkenes. For the catalytic epoxidation of the
trans-stilbene, the conversion and the selectivity towards the epoxide reached 98.6% and 98.0%,
1
0
-
1
respectively. Also, the average TOF of 22 h was obtained for the reaction. The results indicated that
Co6-CP displayed excellent aerobic epoxidation activity among the reported coordination polymer
materials, even rivaling the traditional heterogeneous cobalt catalysts. The influence of reaction
parameters such as temperature and oxygen flow rate for the epoxidation of the trans-stilbene were also
studied in detail.
1
5
.
45
catalysts in the alkene epoxidation give good activity and even
Introduction
1
1
asymmetric selectivity. However, the very high turn-over
frequencies (TOFs) and numbers (TONs) that required for
industrial oxidation or oxygenation reactions are still not
achieved. In addition, the CP catalyzed alkene epoxidation using
molecular oxygen as the only oxidant without the assistance of
Catalytic epoxidation of alkenes takes a vital position in both
organic synthesis and industrial processes for producing the
highly reactive epoxides as one type of the most useful synthetic
intermediates. Traditional epoxidations normally involve
2
2
3
0
5
0
50
peroxide-oxidants such as H O , PHIO, ethylbenzene
2
2
12
any sacrificial reductant or additive is rarely reported.
hydroperoxide, and tert-butyl hydroperoxide (TBHP), which are
Here, we report a newly synthesized hexaprismane Co(II) (μ -
strongly oxidative, corrosive, toxic, and environmentally
6
3
1
unfriendly. As the increasing concerns on the development of
OH)
cluster-based three-dimensional CP, noted as Co6-CP
6
green catalytic technology, directly employing free oxygen/air in
(Figure 1) as an effective recyclable heterogeneous catalyst for
the epoxidation (aerobic epoxidation) process is suggested to be 55 the epoxidation of alkenes with oxygen as the only oxidant.
the ideal oxidant choice and this process can contain the
2
maximum content of active oxygen. Nevertheless, without
additional radical initiators and reducing reagents, maintaining
high conversion and high selectivity at the same time for the
application of oxygen in the alkene epoxidation is a big
3
challenge.
3
5
Although the heterogeneous gold catalyst is reported to show
promising behavior in the aerobic epoxidations, its limited
activity for several alkenes drives further investigation of other
4
types of catalysts. Coordination polymers (CPs) or metal-organic
frameworks (MOFs) are rapidly emerging class of
multifunctional hybrid materials that have potential applications
4
0
5
6
7
8
in gas storage, separation, chemical sensors, nonlinear optics,
9
magnets and biology. CPs are also considered to be useful for
diverse heterogeneous catalytic applications as either catalysts or
6 3 6
Figure 1. a). The 3D structure of Co6-CP. b). The Co (μ -OH) cluster
subunit in Co6-CP. Color code: red ball, Oxygen; gray ball, Carbon; blue
ball, Cobalt; white ball, hydrogen.
1
0
catalyst supports. Several works have already shown that CPs as
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Results and Discussion
the epoxide selectivity surpass all the ones reported with CP
materials as heterogeneous catalyst for converting trans-stilbene
Synthesis and characterization of Co6-CP.
1
1a, 11h, 12a, 14
to corresponding epoxide,
and rival those of the
1
5
The Co6 cluster based CP (Co6-CP) was synthesized using the 60 traditional heterogeneous catalysts. Moreover, most of these
solvothermal method from the reaction of Co(NO ) and NaOAc
works involving CP catalysts are required to employ either
peroxides or co-catalysts due to the limited catalytic activity of
CPs. From the aspect of catalytic ability, the Co6-CP catalyst
takes the lead among the CP materials to have achieved good
3
2
5
0
5
0
5
0
5
0
5
in 1:2 ratio in DMF and methanol and in the presence of pyridine.
o
The reaction at 110 C for 5 days afforded cubic purple crystals
which were characterized via the single crystal XRD method. The
detailed crystal analysis showed that Co6-CP crystallized in the 65 activity which does not fade next to the traditional heterogonous
trigonal space group R-3. The structure of the Co6-CP is shown
in Figure 1. Each Co(II) octahedrally coordinates with three OH
groups and three oxygen atoms from the carboxylate groups. The
oxygen atom in each OH group bridges with three different Co
atoms to form a hexaprismane Co (OH) cluster. Each Co cluster
catalysts of good activity.
1
1
2
2
3
3
4
4
6
6
6
is further connected with six neighboring Co clusters by edge
6
sharing via the bidentate carboxylate groups to form a three-
dimensional network. The carboxylate groups are coordinated
2
+
1
2
with three Co atoms in two different clusters with µ -η :η
3
mode (Figure S5). There are two different organic ligands in the
crystal, the acetate group and formate group. The acetate group
comes from the sodium acetate starting materials while the
formate is resulted from the decomposition of DMF. Formate and
acetate groups share the same coordination site with a ratio of
about 2.57:1 which was further confirmed from elemental
analysis and TGA curve. The molecular formula of Co6-CP
could be regarded as {Co(μ -OH)(HCOO) (CH COO) } .
Since the formate and the acetate occupied the same position in
coordination, it is impossible to indicate their exact places in
structure analysis. The experimental powder XRD pattern for
Co6-CP matches very well with the simulated one generated on
the basis of single crystal structure analysis, which confirms the
phase purity of the bulk materials of Co6-CP (Figure S1 in
Supplementary Information).
3
0.72
3
0.28 n
Figure 2. The epoxidation of trans-stilbene catalyzed by Co6-CP. The
reaction conditions refer to the foot note of Table 1.
7
0
As the next step, the effects of temperature, oxygen flow rate,
catalyst amount and the initial substrate concentration were
studied in detail for the aerobic epoxidation of trans-stilbene. As
shown in Figure 3a, higher temperatures improved the reaction
7
8
8
9
9
5
0
5
0
5
The IR spectra of Co6-CP are shown in Figure S2
o
rate. The conversion was very low at 90 C (40.9 %) while at 110
-
1
(
Supplementary Information). The strong peak at 3512 cm could
o
C the reaction reaches a higher conversion (larger than 95%).
be assigned to the v(O-H),. The v(C-H) of the methyl group is
The selectivity increased from 97.0% to 99.1% when the reaction
-
1
-1
-1
located at 2924 cm and 2855 cm . The peak at 747 cm and
6
o
o
temperature increased from 90 C to 100 C; then, a slight
decrease of selectivity was displayed with the further increase of
reaction temperature. The oxygen flow rate also has obvious
influence on the reaction rate. As shown in Figure 3b, only a
conversion of 60.8% was achieved when the oxygen flow rate is
-
1
81 cm could be assigned to the Co-O stretching vibration for
Co(μ -OH) group, confirming the existence of Co-hydroxide
3
1
3
cluster in the crystal.
The thermal stability of Co6-CP was investigated by
Thermogravimetric (TG) (Figure S3 in Supplementary
1
0 ml/min while the epoxidation conversion was efficiently
Information). The decomposition temperature of Co6-CP is about
improved to 92.7% at a flow rate of 60 ml/min. Note that the
selectivity (above 97.0% all the time) showed a small change.
This phenomenon is quite consistent with the results obtained by
W. Kleist et al., indicating that high oxygen availability is critical
o
2
80 C and almost no weight loss happened when heating to 262
o
C, which indicates the quite good thermal stability of the crystal.
A sharp weight loss (40%) occurred in the temperature range of
o
2
80-330 C due the decomposition of the organic ligand. Then,
12a
to the aerobic epoxidation. The reaction rate increases with the
o
there was no further weight loss till 800 C.
amount of catalyst (Figure 3c) till which reaches 2 mg since the
conversion of the reactant has reached its limitation. This
indicates that the mass transfer effect might not majorly limit the
reaction rate. Furthermore, the initial substrate concentration
effect is examined keeping the constant cobalt/substrate ratio by
adjusting the volume of the solvent. It’s found that within limits a
higher initial concentration gave a higher conversion as shown in
Figure 3d. The solvent plays vital role for the epoxidation
reaction. The use of dimethyl sulfoxide (DMSO) and 1,2-
Dichlorobenzene did not yield any epoxidation products. On the
Aerobic epoxidation activity of Co6-CP.
The activity of Co6-CP was studied with the epoxidation of
trans-stilbene as the test reaction with molecular oxygen as the
oxidant and N,N-Dimethylformamide (DMF) as solvent. Figure 2
shows the time course of the epoxidation of the trans-stilbene.
After reaction for 6 hours, the conversion and the selectivity
towards the epoxide reached 98.6% and 98.0%, respectively. The
5
0
-
1
5
5
average TOF of 22 h was obtained for the reaction lasting for 6
hours. The high TOF value and excellent conversion along with
1
00 other hand cyclohexanone and N,N-Dimethylacetamide (DMA)
2
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a
proved to be suitable solvents, affording rather high reaction rate,
Table 2. Epoxidation of various alkenes over Co6-CP.
as shown in Table 1.
b
Entry
Substrate
Conversion
%)
Selectivity
Turnover
(
(%)
c
number
1
2
3
4
trans-Stilbene
cis-Stilbene
Styrene
98.6
66.2
94.2
16.5
98.0
84.3
76.8
97.5
133.1
89.4
127.2
22.3
cis-
Cyclooctene
5
6
7
1-Decene
14.0
0.2
83.4
100.0
76.7
18.9
0.3
Figure 3. (a) The reaction temperature effect on the epoxidation of trans-
stilbene over Co6-CP. (b) The oxygen flow rate effect on the epoxidation
of trans-stilbene over Co6-CP. The reaction time is 3 h and other
conditions refer to the footnote of Table 1. (c) The catalyst amount effect
on the epoxidation of trans-stilbene. (d) The initial concentration effect
on the epoxidation of trans-stilbene over Co6-CP. All reaction conditions
refer to the foot note of Table 1.
5
0
d
trans-Stilbene
trans-Stilbene
e
22.6
30.5
1
a. Reaction conditions: substrate, 2 mmol; Co6-CP, 2 mg; solvent, DMF
a
20 mL; oxygen flow rate 30 mL/min, reaction time 6 h, reaction
temperature 120 C.
Table 1. Solvent effect on the epoxidation over Co6-CP.
o
30
Entry
Substrate
Conversion (%) Selectivity (%)
b. The selectivity is towards corresponding epoxide for each substrate: for
trans-stilbene the by-product is benzaldehyde; for cis-stilbene the by-
products are trans-stilbene and benzaldehyde; for styrene the by-products
are benzaldehyde and benzoic acid; for cis-cyclooctene the by-products
are 2-cyclooctene-1-one.and 4-cyclooctene-1-one; for 1-decene the by-
product is 3-decanone.
3
5
1
2
3
4
5
DMF
DMSO
98.6
-
98.0
-
c. TON is calculated by mmol of substrate converted to corresponding
epoxide/mmol of cobalt in the Co6-CP.
d. Radical scavenger 0.02 mmol butyl hydroxy toluene (BHT) is added.
1,2-Dichlorobenzene
DMA
-
-
40
e. The epoxidation of trans-stilbene was performed in a closed reaction
system with the oxygen pressure of 20 bar instead of the oxygen flow.
97.1
98.0
73.4
90.8
Cyclohexanone
An important issue of coordination polymer materials as solid
1
0c, 16
catalyst is if the catalysis proceeds mainly heterogeneously.
a. Reaction conditions: trans-stilbene, 2mmol; Co6-CP, 2mg; solvent,
0ml; oxygen flow rate 30ml/min, reaction time 6h, reaction temperature
120 C.
45 In our research, the catalyst was removed by hot filtration to
examine the nature of the catalysis. As shown in Figure 4, the
reaction proceeds after the removal, but with an obvious reduce
of reaction rate. Indeed after the whole reaction duration for 6h,
the residue liquid solution was obtained by removing the catalyst
2
o
1
5
Except for trans-stilbene, the Co6-CP was found to be capable
50
and characterized by ICP-MS. The cobalt amount in the liquid is
only 1.00 ppm, amounting to approximately 1% of the employed
Co, indicating limited amount of cobalt of Co6-CP leached out.
To exclude the possibility that the catalytic activity were
attributed to the leached-out homogeneous cobalt species, the
of catalyzing the epoxidation of other various alkenes and the
results were summarized in Table 2. As shown in Table 2, no
matter for the cyclo-alkene (cis-cyclooctene) of rigid structure
and weak nucleophilicity (entry 4) or the aliphatic alkene (1-
decene) (entry 5) Co6-CP shows quite good catalytic activity
2
0
during the conversion to corresponding epoxide. The excellent 55 Co6-CP was pretreated in DMF at the reaction temperature for
catalytic behavior for the aerobic epoxidation reaction raises the
prospect of using the CP material for the green industrial
epoxidation process.
6h before reaction, and then, the catalytic result was examined
with the reactant added as shown in Figure 5. Comparing with the
reaction without the pretreated process, however, a higher
reaction rate was not observed. Basing all above, it’s reasonable
2
5
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to attribute the excellent catalytic activity mainly to the
heterogeneous route with Co6-CP.
Figure 6. The recycle of Co6-CP for the epoxidation of trans-stilbene.
To uncover the epoxidation with Co6-CP as a primary catalyst,
the reaction was performed with the addition of a very small
amount of free radical scavenger butylhydroxytoluene (BHT)
while keeping all other reaction conditions same. As shown in
entry 6 of Table 2, the conversion of trans-stilbene decreased
almost to zero. This observation indicates the radical nature of the
active oxygen species. As shown in Figure 2, an obvious
induction period appeared in the beginning of the epoxidation. In
addition, trans-stilbene oxide has been observed as the main
product in the epoxidation of cis-stilbene. Furthermore, we have
confirmed that the isomerization of cis-stilbene to trans-stilbene
and that of cis-stilbene oxide to trans-stilbene oxide do not take
Figure 4. The comparison of the epoxidation of trans-stilbene with and
without catalyst removal after 1h. The reaction conditions refer to the
footnote a of Table 1.
5
3
3
4
4
5
5
6
0
5
0
5
0
5
0
place in the absence of O under the same reaction conditions.
2
Thus radical intermediate formed after the attack of the active
oxygen may have a long enough lifetime to rotate around the
single carbon–carbon bond to undergo isomerization, which is
also due to the larger thermodynamical stability of trans-isomer
than that of cis-isomer. Considering that the induction period is a
typical feature of the radical reactions along with the retarded
epoxidation when radical scavenger exists and the isomerization
of the cis-stilbene to trans-stilbene during the epoxidation as
described above, it can be obviously concluded that the Co6-CP
catalyzed epoxidation of alkene to be the radical chain reaction
Figure 5. The comparison of the epoxidation of trans-stilbene with Co6-
CP and pretreated Co6-CP in DMF. The reaction conditions refer to the
footnote a of Table 1.
1
0
After confirming the heterogeneity of the Co6-CP, the stability
as an essential property to assess a heterogeneous catalyst was
carefully examined. The recycle usage of the Co6-CP was shown
in Figure 6. In the second-run and third-run test, the selectivity
showed almost no change while the conversion was slight
reduced, which indicated the good stability of the catalyst except
for the excellent catalytic activity. The stability of Co6-CP was
further examined by powder XRD and IR spectra. The XRD
pattern of the Co6-CP after reaction (Figure S1 in Supplementary
Information) didn’t show obvious changes. In addition, IR spectra
of both pristine and spent Co6-CP have been studied (Figure S2)
and no obvious peak-shifts were observed. This result together
with the XRD result could furthermore support the recycle usage
result and indicate the excellent stability of the Co6-CP.
1
2a, 16b
chain reaction.
It is well known that many Co(II) complexes can bind O and
2
1
7
activate it to form complexes (e.g. Co(III)-(O -)). Therefore, we
2
proposed that a similar binding of O to the Co(II) sites may also
2
1
5
occur in the initial step. The intermediate Co(III)-(O -) species
2
might undergo further reactions to generate an active oxygen
species with a radical nature responsible for the epoxidation. To
confirm if the oxidation state change of cobalt appears during the
reaction, the pristine Co6-CP and spent one were carefully
characterized by UV-vis (Figure S4). The UV/Vis spectrum of
the pristine Co6-CP is in complete agreement with the
coordination environment revealed by X-ray single-crystal
structure analysis: each Co(II) is octahedrally coordinated by
three OH groups and three oxygen atoms from the carboxylate
2
0
2
5
65 groups. The broad band at 450 nm is assigned to the transition
4
4
18
T (P)→ T (F). The bands at 475 and 510 nm characteristic of
1
g
1g
4
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Dalton Transactions
2
+
high-spin Co ions in octahedral coordination, which can be 55 out on a TA Instrument Q500 Thermogravimetric Analyzer at a
4
2
4
19
o
o
assigned to the transitions T1g → T and A respectively.
heating rate of 10 C/min up to 800 C.
a
1g
2g
The band at 486 nm arises from the d→d transition according to
2
0
Synthesis
of
compound
{Co(μ3-
3 2
Hitchman. For contrast, in the spectra of the spent Co6-CP, the
bands at 450 and 475 nm disappeared while the bands at 486 nm
and 510 nm shift slightly to 487 nm and 515 nm, respectively,
OH)(HCOO)0.72(CH COO)0.28}n (Co6-CP). Co(NO ) .6H O
(86 mg, 0.5 mmol), NaOAc (82 mg, 1 mmol) and pyridine (0.5
5
0
5
0
5
3
2
indicating a slight change of the coordination between the ligands 60 mL) were added to a solution of DMF (3 mL) methanol (3 mL)
and cobalt. This small change cannot be detected by the XRD
spectrum of the spent Co6-CP. The adsorption of the Co(III) was
negligible, however this isn’t sufficient to exclude the possibility
and H O (0.5 mL). The mixture solution was sealed in a teflon-
2
o
lined steel autoclave and heating at 110 C for 5 days. Dark
purple cubic crystals were isolated after filtration in 62% yield
with respect to Co. Anal. Calcd (%) for Co(μ3-
1
1
2
2
of the formation of active Co(III)-(O -) specie because of the
2
possible reduction by the reaction mixture. On the other hand, in 65 OH)(HCOO)0.72(CH COO)0.28: C, 12.34; H, 2.07. Found: C,
3
the transition-metal-catalyzed aerobic epoxidation of alkenes, the
concomitant by-product aldehydes are often considered to act as
12.28; H, 2.09.
Crystallographic measurements. Data collection of crystals was
carried out on Bruker APEX II CCD diffractometer equipped
sacrificial reductants to interact with the Co(III)-(O -) specie and
2
result in the formation of peroxide oxygen species. However, it’s
noteworthy that the Co6-CP catalyzed epoxidation of trans-
stilbene gives very high epoxide selectivity with only trace
amount of benzylalhyde as the by-product. Since several works
reported the successful heterogeneous cobalt-catalyzed alkene
epoxidation involving the amide solvent, the epoxidation process
has been proposed that the olefin transformation is accompanied
by significant DMF oxidation to N-formyl-N-methylformamide
with
a
graphite-monohromatized MoKα radiation source
7
0
(λ=0.71073 Å). Empirical absorption was performed, and the
structure was solved by direct methods and refined with the aid of
a SHELXTL program package. All hydrogen atoms were
calculated and refined using a riding model. CCDC number for
Co6-CP is 915825.
2
1
75 Catalytic reaction. The epoxidation of various alkenes using
molecular O2 was carried out in a bath-type reactor operated
under atmospheric conditions: a three-necked glass flask (50 mL)
precharged with 2 mmol of alkenes, 2 mg of Co6-CP, 20 ml of
DMF as well as a stirring bar, was heated by a silicon oil bath,
where a thermocouple was applied to control the temperature and
a reflux condenser to condense the vapor of products. In each
reaction run, the mixture was heated to the desired reaction
temperature under vigorous stirring (stirring rate: 1000 rpm).
Oxygen flow was bubbled at 30 ml/min controlled by a mass
(
FMF). Thus, we believe that the epoxidation mechanism
involving the solvent (DMF) as co-oxidation may account for the
negligible UV-vis spectral change of the spent catalyst. The
mechanism was further confirmed by that FMF was detected in
after-reaction mixture through GC-MS.
80
Conclusion
3
3
4
0
5
0
In conclusion, we have demonstrated that the new hexaprismane
Co (µ -OH) cluster based three-dimensional CP can efficiently
6
3
6
catalyze the epoxidation of alkenes with molecular oxygen as the 85 flow controller into the mixture to initiate the reaction.
oxidant, which is a green route to obtain epoxides. In the catalytic
epoxidation of the trans-stilbene, the conversion and the
selectivity towards the epoxide reached 98.6% and 98.0%,
To investigate the oxygen pressure effect, the reaction was
alternatively carried out in a stainless steel reactor with Teflon
liner (Parr 4950, controller 4843). The residual air inside the
-
1
respectively. The average TOF of 22 h was obtained for the
reactor was expelled by pressurizing and releasing O several
2
reaction lasting for 6 hours. The high TOF value and excellent 90 times. The reaction was performed under the oxygen pressure of
conversion and selectivity are among the most efficient catalytic
activities in all reported CP materials. The excellent catalytic
behavior for the aerobic epoxidation reaction raises the prospect
of using the CP material as green epoxidation catalysts for
industrial process.
20 bar, with the other reaction conditions unchanged.
The liquid mixture after reaction with Co6-CP filtered was
analyzed by Agilent gas chromatograph 6890 equipped with a
HP-5 capillary column ( 30 m long and 0.32 mm in diameter,
95 packed with silica-based supelcosil) and flame ionization detector
(FID). Dodecane was the internal standard. The by-products were
Experimental Section
identified by a gas chromatography-mass spectrometry (GCMS,
Agilent, GC 6890N, MS 5973 inert).
For reaction time effect examination, the reaction in the first 1h
00 was performed from 15 min to 1 h with 15 min interval, next
from 2 h to 6 h with 1 h interval.
Materials. All chemicals were purchased from Alfa Aesar, TCI
chemical and Aldrich and used without further purification.
1
4
4
5
1
Characterization. Powder X-ray diffraction data were recorded
on a Bruker D8 Advance diffractometer with a graphite-
monochromatized Cu Ka radiation. FTIR spectra were recorded
from KBr pellets by using a Perkin Elmer FTIR SpectrumGX
Recycle of Co6-CP.After each reaction cycle, the filtered
catalysts were recovered by washing with plenty of acetone
(>99%, Sigma–Aldrich) and dried in vacuum at 373 K. Then the
5
0
spectrometer. Elemental analyses were obtained from a
1
05 recycled catalysts were reused under the same reaction condition
as described above.
EuroVector Euro EA elemental analyzer. ICP-MS analyses were
performed on a ICP-MS Agilent 7700 spectrometer, before which
the samples were digested assisted by the CEM MDS-5
microwave oven. Thermogravimetric analysis (TGA) was carried
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Characterization of Co6-CP.The spent Co6-CP was obtained
filtered were recovered by washing with plenty of acetone (>99%,
Sigma–Aldrich) after each reaction cycle and dried in vacuum at
50
Chem. Int. Ed., 2008, 47, 6638; (e) K. Guillois, L. Burel, A. Tuel and V.
Caps, Appl. Catal. A, 2012, 415, 1; (f) P. A. Shringarpure and A. Patel,
Ind. Eng. Chem. Res., 2011, 50, 9069.
3
73 K. Then the spent Co6-CP was characterized by XRD and
4
5
(a) M. Kotobuki, R. Leppelt, D. A. Hansgen, D. Widmann and R. J.
Behm, J. Catal., 2009, 264, 67; (b) M. Ojeda and E. Iglesia, Chem.
Commun., 2009, 352; (c) M. Ojeda, B. Z. Zhan and E. Iglesia, J. Catal.,
5
FT-IR for comparison with the pristine CP.
5
6
6
7
7
8
8
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0
5
0
5
0
5
Cobalt leaching examination by ICP-MS. A hot solution
obtained after 8 h reaction time was filtered and 5.00 mL of this
solution was used for further analysis. After evaporating the
organic solvent in vacuum over night the residual was dissolved
in concentrated HNO and diluted with double distilled water to
1
2
012, 285, 92; (d) J. H. Huang, T. Akita, J. Faye, T. Fujitani, T. Takei
and M. Haruta, Angew. Chem. Int. Ed., 2009, 48, 7862.
(a) M. P. Suh, H. J. Park, T. K. Prasad and D. W. Lim, Chem. Rev.,
2
012, 112, 782; (b) K. Sumida, D. L. Rogow, J. A. Mason, T. M.
1
0
3
McDonald, E. D. Bloch, Z. R. Herm, T. H. Bae and J. R. Long, Chem.
Rev., 2012, 112, 724; (c) H. X. Deng, S. Grunder, K. E. Cordova, C.
Valente, H. Furukawa, M. Hmadeh, F. Gandara, A. C. Whalley, Z. Liu,
S. Asahina, H. Kazumori, M. O'Keeffe, O. Terasaki, J. F. Stoddart and
O. M. Yaghi, Science, 2012, 336, 1018; (d) X. J. Wang, P. Z. Li, Y. F.
Chen, Q. Zhang, H. C. Zhang, X. X. Chan, R. Ganguly, Y. X. Li, J. W.
Jiang and Y. L. Zhao, Sci. Rep., 2013, 3, 921, Doi 10.1038/Srep01149.
(a) E. D. Bloch, W. L. Queen, R. Krishna, J. M. Zadrozny, C. M. Brown
and J. R. Long, Science, 2012, 335, 1606; (b) J. R. Li, J. Sculley and H.
C. Zhou, Chem. Rev., 2012, 112, 869; (c) M. C. Das, S. C. Xiang, Z. J.
Zhang and B. L. Chen, Angew. Chem. Int. Ed., 2011, 50, 10510; (d) S.
C. Xiang, Z. J. Zhang, C. G. Zhao, K. L. Hong, X. B. Zhao, D. R. Ding,
M. H. Xie, C. D. Wu, M. C. Das, R. Gill, K. M. Thomas and B. L. Chen,
Nat. Commun., 2011, 2, 204; (e) J. K. Sun, M. Ji, C. Chen, W. G. Wang,
P. Wang, R. P. Chen and J. Zhang, Chem. Commun., 2013, 49, 1624.
0.0 mL. The measurements were performed with an ICP-MS
Agilent 7700 spectrometer before which the samples were
digested assisted by the CEM MDS-5 microwave oven.
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ACKNOWLEDGMENT
6
Q.Z. acknowledges the financial support from AcRF Tier 1 (RG 16/12) and Tier 2
(
ARC 20/12 and ARC 2/13) from MOE, CREATE program (Nanomaterials for
Energy and Water Management) from NRF, and New Initiative Fund from NTU,
Singapore.
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Notes and references
a
School of Materials Science and Engineering, Nanyang Technological
University, Singapore 639798, Singapore; E-mail: qczhang@ntu.edu.sgc
7 (a) H. Xu, F. Liu, Y. J. Cui, B. L. Chen and G. D. Qian, Chem.
Commun., 2011, 47, 3153; (b) X. Rao, T. Song, J. Gao, Y. Cui, Y.
Yang, C. Wu, B. Chen and G. Qian, J. Am. Chem. Soc., 2013, 135,
b
School of Chemical and Biomedical Engineering, Nanyang
Technological University, Singapore 639798 (Singapore). E-mail:
yhyang@ntu.edu.sg
2
5
1
5559; (c) L. E. Kreno, K. Leong, O. K. Farha, M. Allendorf, R. P. Van
c
School of Physical and Mathematical Sciences, Nanyang Technological
Duyne and J. T. Hupp, Chem. Rev., 2012, 112, 1105; (d) Y. J. Cui, Y. F.
Yue, G. D. Qian and B. L. Chen, Chem. Rev., 2012, 112, 1126; (e) Y. J.
Cui, H. Xu, Y. F. Yue, Z. Y. Guo, J. C. Yu, Z. X. Chen, J. K. Gao, Y.
Yang, G. D. Qian and B. L. Chen, J. Am. Chem. Soc., 2012, 134, 3979;
University, Singapore 637371, Singapore
†
Electronic Supplementary Information (ESI) available: P-XRD pattern,
IR spectra, TGA spectra and the UV-Vis spectra of Co6-CP. See
DOI: 10.1039/b000000x/
3
0
(f) Y. Kang, F. Wang, J. Zhang and X. H. Bu, J. Am. Chem. Soc., 2012,
1
34, 17881.
‡
1
Both authors have equal contribution to this paper.
8 (a) J. C. Yu, Y. J. Cui, C. D. Wu, Y. Yang, Z. Y. Wang, M. O'Keeffe, B.
L. Chen and G. D. Qian, Angew. Chem. Int. Ed., 2012, 51, 10542; (b) Z.
Guo, R. Cao, X. Wang, H. Li, W. Yuan, G. Wang, H. Wu and J. Li, J.
Am. Chem. Soc., 2009, 131, 6894; (c) Q. Huang, J. F. Cai, H. Wu, Y. B.
He, B. L. Chen and G. D. Qian, J. Mater. Chem., 2012, 22, 10352; (d)
Q. A. Huang, J. C. Yu, J. K. Gao, X. T. Rao, X. L. Yang, Y. J. Cui, C.
D. Wu, Z. J. Zhang, S. C. Xiang, B. L. Chen and G. D. Qian, Cryst.
Growth Des., 2010, 10, 5291; (e) O. R. Evans and W. B. Lin, Chem.
Mater., 2001, 13, 3009; (f) C. Wang, T. Zhang and W. B. Lin, Chem.
Rev., 2012, 112, 1084.
(a) H. M. Neu, M. S. Yusubov, V. V. Zhdankin and V. N. Nemykin,
Adv. Synth. Catal., 2009, 351, 3168; (b) J. T. Groves and R. Quinn, J.
Am. Chem. Soc., 1985, 107, 5790; (c) S. T. Oyama, Mechanisms in
homogeneous and heterogeneous expxidation catalysis, Elsevier B. V.,
Amsterdam, 2008.
3
4
4
5
0
5
90
2
3
(a) G. J. ten Brink, I. W. C. E. Arends and R. A. Sheldon, Science, 2000,
2
87, 1636; (b) R. A. Sheldon, Chem. Soc. Rev., 2012, 41, 1437; (c) M.
Shibuya, Y. Osada, Y. Sasano, M. Tomizawa and Y. Iwabuchi, J. Am. 95 9 (a) H. Xu, X. T. Rao, J. K. Gao, J. C. Yu, Z. Q. Wang, Z. S. Dou, Y. J.
Chem. Soc., 2011, 133, 6497; (d) A. F. Lee, C. V. Ellis, J. N. Naughton,
M. A. Newton, C. M. A. Parlett and K. Wilson, J. Am. Chem. Soc.,
Cui, Y. Yang, B. L. Chen and G. D. Qian, Chem. Commun., 2012, 48,
7377; (b) J. Gao, K. Ye, M. He, W.-W. Xiong, W. Cao, Z. Y. Lee, Y.
Wang, T. Wu, F. Huo, X. liu and Q. Zhang, J. Solid State Chem., 2013,
206, 27; (c) P. Horcajada, R. Gref, T. Baati, P. K. Allan, G. Maurin, P.
2
011, 133, 5724.
(a) H. Tanaka, H. Nishikawa, T. Uchida and T. Katsuki, J. Am. Chem.
Soc., 2010, 132, 12034; (b) D. Gajan, K. Guillois, P. Delichere, J. M. 100 Couvreur, G. Ferey, R. E. Morris and C. Serre, Chem. Rev., 2012, 112,
Basset, J. P. Candy, V. Caps, C. Coperet, A. Lesage and L. Emsley, J.
Am. Chem. Soc., 2009, 131, 14667; (c) C. Aprile, A. Corma, M. E.
Domine, H. Garcia and C. Mitchell, J. Catal., 2009, 264, 44; (d) G.
Jiang, J. Chen, H. Y. Thu, J. S. Huang, N. Zhu and C. M. Che, Angew.
1232; (d) A. C. McKinlay, R. E. Morris, P. Horcajada, G. Ferey, R.
Gref, P. Couvreur and C. Serre, Angew. Chem. Int. Ed., 2010, 49, 6260;
(e) J. Gao, M. He, Z. Y. Lee, W. Cao, W.-W. Xiong, Y. Li, R. Ganguly,
T. Wu and Q. Zhang, Dalton Trans., 2013, 42, 11367; (f) P. Horcajada,
6
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

View Article Online
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Page 7 of 8
Dalton Transactions
T. Chalati, C. Serre, B. Gillet, C. Sebrie, T. Baati, J. F. Eubank, D.
289, 259; (b) X. Y. Quek, Q. H. Tang, S. Q. Hu and Y. H. Yang, Appl.
Heurtaux, P. Clayette, C. Kreuz, J. S. Chang, Y. K. Hwang, V. Marsaud, 40 Catal. A, 2009, 361, 130; (c) A. Dhakshinamoorthy, M. Alvaro and H.
P. N. Bories, L. Cynober, S. Gil, G. Ferey, P. Couvreur and R. Gref,
Garcia, Acs Catal., 2011, 1, 48.
Nat. Mater., 2010, 9, 172.
15 (a) D. Farrusseng, S. Aguado and C. Pinel, Angew. Chem. Int. Ed.,
2009, 48, 7502; (b) J. Jiang, R. Li, H. Wang, Y. Zheng, H. Chen and J.
Ma, Catal. Lett., 2008, 120, 221; (c) D. Jiang, A. Urakawa, M. Yulikov,
T. Mallat, G. Jeschke and A. Baiker, Chem. Eur. J., 2009, 15, 12255; (d)
F. Gandara, A. de Andres, B. Gomez-Lor, E. Gutierrez-Puebla, M.
Iglesias, M. A. Monge, D. M. Proserpio and N. Snejko, Cryst. Growth
Des., 2008, 8, 378; (e) D. Jiang, T. Mallat, D. M. Meier, A. Urakawa
and A. Baiker, J. Catal., 2010, 270, 26; (f) H. Furutachi, S. Fujinami, M.
Suzuki and H. Okawa, J. Chem. Soc. Dalton Trans., 1999, 2197; (g) M.
D. Hughes, Y. J. Xu, P. Jenkins, P. McMorn, P. Landon, D. I. Enache,
A. F. Carley, G. A. Attard, G. J. Hutchings, F. King, E. H. Stitt, P.
Johnston, K. Griffin and C. J. Kiely, Nature, 2005, 437, 1132.
16 (a) J. Q. Li, B. Marler, H. Kessler, M. Soulard and S. Kallus, Inorg.
Chem., 1997, 36, 4697; (b) H. K. Lee, C. H. Lam, S. L. Li, Z. Y. Zhang
and T. C. W. Mak, Inorg. Chem., 2001, 40, 4691; (c) D. M. Jiang, A.
Urakawa, M. Yulikov, T. Mallat, G. Jeschke and A. Baiker, Chem. Eur.
J., 2009, 15, 12255.
5
0
5
0
5
0
5
10 (a) H. L. Jiang and Q. Xu, Chem. Commun., 2011, 47, 3351; (b) M.
Yoon, R. Srirambalaji and K. Kim, Chem. Rev., 2012, 112, 1196; (c) J.
Lee, O. K. Farha, J. Roberts, K. A. Scheidt, S. T. Nguyen and J. T.
Hupp, Chem. Soc. Rev., 2009, 38, 1450; (d) P. Kaur, J. T. Hupp and S.
T. Nguyen, Acs Catal., 2011, 1, 819; (e) Y. B. Huang, Z. J. Lin and R.
Cao, Chem. Eur. J., 2011, 17, 12706; (f) M.-H. Xie, X.-L. Yang, Y. He,
J. Zhang, B. Chen and C.-D. Wu, Chem. Eur. J., 2013, DOI:
45
50
55
60
65
1
1
2
2
3
3
1
0.1002/chem.201302025; (g) T. Yang, H. Cui, C. Zhang, L. Zhang
and C.-Y. Su, Inorg. Chem., 2013, 52, 9053.
1
1 (a) A. Dhakshinamoorthy, M. Alvaro and H. Garcia, Catal. Sci.
Technol., 2011, 1, 856; (b) S. H. Cho, B. Q. Ma, S. T. Nguyen, J. T.
Hupp and T. E. Albrecht-Schmitt, Chem. Commun., 2006, 2563; (c) O.
K. Farha, A. M. Shultz, A. A. Sarjeant, S. T. Nguyen and J. T. Hupp, J.
Am. Chem. Soc., 2011, 133, 5652; (d) A. M. Shultz, O. K. Farha, J. T.
Hupp and S. T. Nguyen, Chem. Sci., 2011, 2, 686; (e) Y. B. Huang, T.
F. Liu, J. X. Lin, J. A. Lu, Z. J. Lin and R. Cao, Inorg. Chem., 2011, 50,
2
191; (f) X.-L. Yang, M.-H. Xie, C. Zou, Y. He, B. Chen, M. O’Keeffe
17 (a) E. Giamello, Z. Sojka, M. Che and A. Zecchina, J. Phys. Chem.,
1986, 90, 6084; (b) C. Comuzzi, A. Melchior, P. Polese, R. Portanova
and M. Tolazzi, Inorg. Chem., 2003, 42, 8214.
and C.-D. Wu, J. Am. Chem. Soc., 2012, 134, 10638; (g) A. M. Shultz,
A. A. Sarjeant, O. K. Farha, J. T. Hupp and S. T. Nguyen, J. Am. Chem.
Soc., 2011, 133, 13252; (h) F. J. Song, C. Wang, J. M. Falkowski, L. Q.
Ma and W. B. Lin, J. Am. Chem. Soc., 2010, 132, 15390; (i) M. Zheng,
Y. Liu, C. Wang, S. B. Liu and W. B. Lin, Chem. Sci., 2012, 3, 2623; (j)
M. Tonigold, Y. Lu, B. Bredenkotter, B. Rieger, S. Bahnmuller, J.
Hitzbleck, G. Langstein and D. Volkmer, Angew. Chem. Int. Ed., 2009,
18 L. Poul, N. Jouini and F. Fievet, Chem. Mater., 2000, 12, 3123.
19 (a) A. A. Verberckmoes, B. M. Weckhuysen and R. A. Schoonheydt,
Micropor. Mesopor. Mat., 1998, 22, 165; (b) Y. Okamoto, K. Nagata, T.
Adachi, T. Imanaka, K. Inamura and T. Takyu, J. Phys. Chem., 1991,
95, 310; (c) M. G. F. da Silva, Mater. Res. Bull., 1999, 34, 2061.
20 M. A. Hitchman, Inorg. Chem., 1977, 16, 1985.
4
8, 7546.
12 (a) M. J. Beier, W. Kleist, M. T. Wharmby, R. Kissner, B. Kimmerle,
21 Z. Opre, T. Mallat and A. Baiker, J. Catal., 2007, 245, 482.
P. A. Wright, J. D. Grunwaldt and A. Baiker, Chem. Eur. J., 2012, 18,
8
2
87; (b) S. Bhattacharjee, D. A. Yang and W. S. Ahn, Chem. Commun.,
011, 47, 3637; (c) Y. Nishiyama, Y. Nakagawa and N. Mizuno, Angew.
70
Chem. Int. Ed., 2001, 40, 3639.
13 (a) R. Chakrabarty, P. Sarmah, B. Saha, S. Chakravorty and B. K. Das,
Inorg. Chem., 2009, 48, 6371; (b) R. Chakrabarty, S. J. Bora and B. K.
Das, Inorg. Chem., 2007, 46, 9450.
1
4 (a) A. Dhakshinamoorthy, M. Alvaro and H. Garcia, J. Catal., 2012,
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A new hexaprismane Co(II) (μ -OH) cluster-based coordination polymer showed excellent activity and selectivity in the
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