Coordinate-polymerized organic ligand towards an efficient catalyst for selective hydrocarbon oxidation

Article abstract of DOI:10.1039/c6ra12422d

Here we show catalyst design based on an isoxazole derivative via a coordinate-polymerized strategy. Three new coordination polymers, [Co(bpp)(mpca)₂] (1), [Zn(bpp)(mpca)₂] (2), and [Cd(bpp)(mpca)₂] (3) [bpp = 1,3-bis(4-pyridyl)propane, mpca = 5-methyl-3-phenylisoxazole-4-carboxylic acid], have been synthesized under hydrothermal conditions. Single crystal X-ray diffraction analysis reveals that, compounds 1-3 exhibit similar wave-like chains, with mpca functioning as pendant phenyl-isoxazole arms. Catalytic experiments show that all three compounds can be used as efficient heterogeneous catalysts for the selective oxidation of cyclooctene.

Full text of DOI:10.1039/c6ra12422d

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Coordinate-polymerized organic ligand towards an
efficient catalyst for selective hydrocarbon
oxidation†
Cite this: RSC Adv., 2016, 6, 63940
*
*
Kaixuan Li,‡ Hailiang Hu,‡ Beibei Liu, Xiaoling Lin, Hui Huang, Yang Liu
*
and Zhenhui Kang
Here we show catalyst design based on an isoxazole derivative via a coordinate-polymerized strategy. Three
new coordination polymers, [Co(bpp)(mpca)2] (1), [Zn(bpp)(mpca)2] (2), and [Cd(bpp)(mpca)2] (3) [bpp ¼ 1,3-
bis(4-pyridyl)propane, mpca ¼ 5-methyl-3-phenylisoxazole-4-carboxylic acid], have been synthesized
under hydrothermal conditions. Single crystal X-ray diffraction analysis reveals that, compounds 1–3
exhibit similar wave-like chains, with mpca functioning as pendant phenyl-isoxazole arms. Catalytic
experiments show that all three compounds can be used as efficient heterogeneous catalysts for the
selective oxidation of cyclooctene.
Received 13th May 2016
Accepted 27th June 2016
DOI: 10.1039/c6ra12422d
www.rsc.org/advances
a weak N–O bond that can be easily cleaved to form an active
diradical (Scheme S1†),17–20 which is favorable for the catalytic
Introduction
process. However, in organic reaction systems, mpca (as cata-
lyst) would suffer from stability and isolation difficulties. While,
the coordinate-polymerized design could offer the desired
advantages, such as additional thermal stability, and change
from homogeneous to heterogeneous catalysis.21–23 With regard
to the above aspects, the mpca as organic ligand was introduced
into the hybrid system with the purpose of coordinate-
polymerization. On the other hand, to extend the structure,
another exible ligand 1,3-bis(4-pyridyl)propane (bpp) with no
catalytic activity was employed (shown in Scheme 1b).24–27 In
this work, three new coordination polymers, [Co(bpp)(mpca)2]
(1), [Zn(bpp)(mpca)2] (2), [Cd(bpp)(mpca)2] (3) have been
successfully synthesized under hydrothermal conditions.
Compounds 1–3 exhibit similar one-dimensional (1D) struc-
tures with mpca functioning as pendant phenyl-isoxazole arms.
Catalytic experiments show that all of the three title compounds
exhibit excellent catalytic activity for selective oxidation of
cyclooctene with air as oxidant directly. Compared with homo-
geneous catalyst of mpca with low conversion (19.98%),
compounds 1–3 can be used as efficient heterogeneous cata-
lysts, which exhibits high conversion based on cyclooctene
owing to the enhanced catalytic activity (45.77, 37.78 and
39.08% for 1, 2, and 3, respectively).
The selective catalytic oxidation of hydrocarbons is a signicant
synthetic method for important chemical intermediates in the
manufacture of high-value ne chemicals, high-tonnage
commodities and pharmaceuticals.1–4 However, these reac-
tions still suffer from low conversion and unsatisfactory selec-
tivity.3,5,6 Crystal engineering allows the combination of
multiple well dened moieties and the integration of different
functional units in one system.7–11 Notably, coordination poly-
mers (CPs) with designable structural features provide a plat-
form for catalyst design at molecular and atomic levels.12–15
From the viewpoint of catalyst design,16 an isoxazole derivative
(5-methyl-3-phenylisoxazole-4-carboxylic acid, mpca; shown in
Scheme 1a) caught our attention. The isoxazole group has
Scheme 1 Representation of ligands mpca (a) and bpp (b).
Institute of Functional Nano & So Materials (FUNSOM), Jiangsu Key Laboratory for
Carbon-Based Functional Materials & Devices, Soochow University, Suzhou, Jiangsu
215123, China. E-mail: zhkang@suda.edu.cn
Experimental section
Materials and measurements
† Electronic supplementary information (ESI) available: Additional gures, TG
curves, XRPD patterns, IR spectra and analysis, detailed crystallographic data
and structural renement parameters, selected bond distances and selected
hydrogen bond parameters for compounds 1–3. CCDC 1478067–1478069. For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c6ra12422d
All reagents and solvents were used as received from commer-
cial sources without further purication. Elemental analyses
were performed on an EA-1110 elemental analyzer. The FT-IR
spectra were recorded on a HYPERION spectrometer with
‡ These authors contributed equally to this work.
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a pressed KBr pellet in the 4000–400 cmꢀ1 region. The X-ray
power diffraction (XRPD) data were collected by an X'Pert-
ProMPD (Holand) D/max-gA X-ray diffractometer in a at
Table 1 Crystal data and structure refinements for compounds 1–3
1
2
3
˚
plate geometry with Cu Ka radiation (l ¼ 1.5406 A). Thermog-
Formula
Fw
C
35H30CoN4O6
C35H30ZnN4O6
668.00
Monoclinic
P21/c
12.2829(7)
14.9256(8)
20.7045(9)
90.00
125.874(2)
90.00
3075.7(3)
4
1.443
0.852
1384.0
16 101
5410
C35H32CdN4O7
733.05
Triclinic
ꢀ
P1
ravimetric (TG) analysis was carried out with a Pyris-Diamond
661.56
Monoclinic
P21/c
12.4940(17)
15.187(2)
20.2212(19)
90.00
126.581(6)
90.00
3081.1(7)
4
1.426
0.611
1372.0
15 813
5433
ꢁ
Cryst. syst.
Space group
TG/DTA instrument in owing N2 with a heating rate of 10 C
minꢀ1. All samples of catalytic experiments were determined by
˚
a (A)
11.5100(11)
12.0412(12)
13.0266(12)
97.693(2)
107.578(2)
100.029(2)
1661.0(3)
2
1.466
0.711
748.0
8842
5754
424
0.0227
1.013
0.0260
0.0666
a
gas chromatography (Agilent GC 7890A) and a gas
˚
b (A)
chromatography-mass spectroscopy (Trace ISQ).
˚
c (A)
a (ꢁ)
b (ꢁ)
g (ꢁ)
Syntheses
3
˚
The title compounds 1–3 were synthesized under similar
hydrothermal conditions from a mixture of mpca, bpp, and
M(Ac)2 (1: M ¼ Co; 2: M ¼ Zn; 3: M ¼ Cd) in a molar ratio of
1 : 1 : 2. The suspension was sealed into a 15 mL Teon-lined
V (A )
Z
Dc (g cmꢀ3
)
m (mmꢀ1
F(000)
)
ꢁ
autoclave and kept under autogenous pressure at 120 C for 3
Collcd rens
Unique rens
Parameters
Rint
days. Aer cooling to room temperature slowly, purple block
crystals of 1, colorless block crystals of 2 and 3 suitable for X-ray
diffraction analysis were isolated. Yield: 35% for 1, 20% for 2,
and 40% for 3 with respect to M(Ac)2. Elemental analyses calc. for
1: C, 63.49; H, 4.53; N, 8.46. Found: C, 63.52; H, 4.56; N, 8.42. For
2: C, 62.8; H, 4.49; N, 10.18. Found: C, 62.81; H, 4.52; N, 10.14.
For 3: C, 57.29; H, 4.37; N, 9.28. Found: C, 57.33; H, 4.39; N, 9.25.
415
0.0433
1.009
0.0421
0.1228
415
0.0372
1.031
0.0486
0.1298
GOF on F2
a
R1 [I > 2s(I)]
b
wR2 (all data)
P
P
P
P
a
b
2
R1 ¼ ||F0| ꢀ |Fc||/ |F0|. wR2 ¼ [w(F0 ꢀ Fc2)2]/ [w(F02)2]1/2
.
Selective oxidation experiments
geometrically and rened isotropically with xed thermal
factors. A summary of the crystallographic data and structure
renement details is given in Table 1. Selected bond distances
The selective oxidation of cyclooctene was carried out in the
absence of solvents. The cyclooctene (5 mL, 95%) and different
catalysts (50 mg) were added to 20 mL round bottom ask with
water condenser and continuous magnetic stirring at 80 ꢁC
using tert-butyl hydroperoxide (TBHP, 200 mL, 70%) as initiator
and air as oxidant. Aer ltering off the catalyst, the oxidation
products were analyzed by gas chromatography (GC) and gas
chromatography-mass spectroscopy (GC-MS).
ꢁ
˚
(A) and angles ( ) are listed in Table S1.† Hydrogen-bonding
parameters are summarized in Table S2.† CCDC numbers are
1478067–1478069† for 1–3, respectively.
TG and PXRD analyses
Thermogravimetric (TG) analyses of 1–3 were performed on poly-
crystalline samples under a nitrogen atmosphere to check their
thermal stability (Fig. S12†). For 1, the weight loses 60.74% for the
decomposition of mpca in the temperature range of 215 to 335 ꢁC
(calcd 60.82%). In the temperature range of 335 to 800 ꢁC, the 1D
structure of 1 decomposes completely. The remaining weight of
8.92% is in accord with the mass of Co residue (8.92%). For 2, in
the temperature range of 220 to 315 ꢁC, the weight loss of 60.48%
corresponds to the loss of mpca ligands (60.24%). The bpp ligands
do not decompose completely at 800 ꢁC. For 3, the structure began
Recycle test
For the recycle test of the compounds, the catalyst (compound
1/2/3, 50 mg) was separated from the reaction solution aer the
rst catalytic cycle, washed several times with distilled water to
remove the physisorbed molecules, and dried. Then the catalyst
was reused in a new catalytic experiment. The repeated catalysis
experiments were carried out ve times using the recycled
catalyst. In contrast, the recycle test of the physical mixture
materials of compounds was not performed. Because some
components in the physical mixture materials system dissolve
in the cyclooctene, which means it can't be reused as hetero-
geneous catalysts in another catalytic system.
ꢁ
ꢁ
to decompose at about 180 C, and ended at about 500 C. For
mpca, it decomposes completely in the range of 165 to 272 ꢁC.
The PXRD patterns of compounds 1–3 were recorded at room
temperature. As shown in Fig. S13,† all of the major diffraction
peaks of experimental patterns match well with their theoretical
patterns, indicating the phase purities of these compounds.
X-ray crystallographic study
Crystal data for compounds 1–3 were collected by a Bruker APEX-
Results and discussion
Structure of compounds 1–3
˚
II CCD diffractometer with Mo Ka radiation (l ¼ 0.71073 A) at
296 K. The structures were solved by the direct methods and
rened on F2 by full-matrix least-squares using the SHELXTL Structure analysis reveals that compound 1 crystallizes in
crystallographic soware package.28,29 For all the compounds, all a monoclinic system with space group P21/c. The asymmetric
non-hydrogen atoms were rened anisotropically, and all the unit consists of one Co2+ ion, one bpp and two mpca molecules,
hydrogen atoms attached to carbon atoms were generated as shown in Fig. 1a. In 1, the Co atom is six-coordinated by two
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From the structural descriptions above, we can see that
different choice of the transition metals apparently induce
various coordination and conformation modes of ligands. For
bpp, different conformations with similar bridging mode have
been observed in 1–3 (Fig. S5†). For mpca, when Co2+ was
introduced to the system in 1, the mpca adopts the simple
chelate mode which acts as terminal ligand by its two carboxyl
oxygens. When Zn2+ was used in 2, mpca acted as a mono-
dentate ligand by one carboxyl oxygen, hanging on both sides of
the chain. In 3, mpca utilize a chelate mode, similar to that in 1.
Arrangements of mpca hanging up and down the chain are also
different. In 1 and 2, the mpca ligands arrange in a head-to-
head mode, while in 3, a shoulder-by-shoulder mode is
observed (Fig. S6†). Despite the slight difference, the main
structural feature of mpca relies on the terminal role that
functioning as pendant phenyl-isoxazole arms within all of the
three title compounds.
In present system, the coordinate-polymerized design also
offer some advantages. Compared with mpca ligand, which
ꢁ
suffers from a low thermal stability (decomposition at 165 C),
the mpca-based hybrid material of 1 exhibits a higher stability
(decomposition at 215 ꢁC), as illustrated in Fig. 2. Additional
stabilization arises from the geometrical constraints of
coordinate-polymerized structure, which contains a cascade of
coordinate and hydrogen bonds. Similar phenomenon has also
been observed for compounds 2 and 3. On the other hand, the
solution processes of mpca and 1 soaked in cyclooctene at
different time periods are shown in Fig. 3. The mpca is entirely
dissolved within 10 min, while compound 1 is indissoluble
within at least 10 days. The results implied that, when
coordinate-polymerized, the hybrid material of 1 could be used
as heterogeneous catalyst.
Fig. 1 (a) The coordination environment view of compound 1. All
hydrogen atoms are omitted for clarity. (b) The 1D wave-like chain in 1.
(c) The 2D supramolecular layer. Hydrogen bonds were replaced by
red dotted line.
Selective oxidation of cyclooctene
N atoms from two bpp ligands and four O atoms from two mpca
ligands, forming a [CoN2O4] octahedron (Fig. S1a†). In 1, all
adjacent [CoN2O4] octahedrons are linked by bpp ligands to
form a wave-like chain, with mpca functioning as pendant
phenyl-isoxazole arms (Fig. 1b). Furthermore, the adjacent
chains are parallel arranged via the hydrogen bonds between
the pendant arms of mpca, forming a two dimensional (2D)
supramolecular layer (Fig. 1c). Note that two adjacent supra-
molecular layers could join together via hydrogen-bonding
interactions to form a double layer structure (Fig. S2†).
As for compounds 2 and 3 (Fig. S3 and S4†), wave-like chain
structures, similar to that of 1, are also observed (Table 2). As is
known, different metal ions have preferential coordination
geometry due to their electronic congurations. In detail, each
Zn2+ ion in 2 is four-coordinated by two O atoms from two mpca
ligands and two N atoms from two bpp ligands in a [ZnO2N2]
tetrahedron (Fig. S1b†). In 3, each Cd2+ ion is seven-coordinated
by four chelating O atoms from two mpca ligands, two N atoms
from two bpp ligands and one O atom from a coordinated water
molecule, thus, the coordination polyhedron around Cd2+ ion is
a [CdN2O5] decahedron (Fig. S1c†). Bond lengths around metal
centres are normal (Table S1†), except weak Zn–O interactions
that are much longer according to the literature.30–32
The catalytic activities of mpca (31 mg), bpp (15 mg), metal ion
(Co2+, 19 mg Co(Ac)2) and compounds 1–3 were investigated
over the selective oxidation of cyclooctene in the molar ratio of
2 : 1 : 1 : 1 with absence of solvents, using TBHP as initiator and
air as oxidant at 80 ꢁC (Fig. S7†). Fig. 4a shows the relationship
between the conversion of cyclooctene and reaction time with
mpca, bpp and Co2+ ion as catalysts, respectively. Detailed
conversion of cyclooctene and selectivity of oxidation products
using mpca, bpp and Co2+ ion as catalysts are shown in Table
S3.† As is shown, the catalytic activities are obviously different.
For mpca and Co2+ ion, the conversion of cyclooctene reached
19.98 and 17.27%, respectively. While for bpp, it was just about
2.20%. Selectivity of epoxycyclooctane with mpca, bpp and Co2+
ions are shown in Fig. 4b. The selectivity was up to 86.26, 94.96
and 94.18%, respectively. The results indicate the comparative
catalytic activities of mpca and Co2+ ions, while bpp exhibits no
obvious catalytic activity.
In the following experiments, the catalytic activities of
compound 1 and physical mixture materials of 1 (mixture of
bpp, mpca and Co(Ac)2) were performed. Fig. 4c shows conver-
sion of cyclooctene achieved by compound 1 and physical
mixture materials of 1. Detailed data of the catalytic experiments
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Table 2 A summary of structural information of compounds 1–3
Compounds
1
2
3
Different TM ions
Coordination modes of TM
Coordination modes of mpca
Similar 2D supramolecular structure
are less than 100%, which may owe to the further oxidation of
some C8 products to other carbon oxides. With catalyst of the
physical mixture materials, the selectivity of epoxycyclooctane
was up to 96.72% aer 48 h, which is higher than that of
compound 1. However, the selectivity of 2-cyclooctenone was
about 3.05%, which is lower than that of compound 1. These
results demonstrate that, aer coordinate-polymerized, the
hybrid structure of compound 1 as catalyst exhibits higher
catalytic activities than that of the physical mixture materials of
1, and the catalytic activity can be remarkably enhanced.
In order to study the stability of compound 1 as catalyst in
Fig.
temperature.
2 TG spectra of 1 and mpca, showing the decomposition the catalytic system, the repeated experiments were designed
and performed. The catalyst (compound 1) was separated from
the reaction solution aer the rst catalytic cycle, washed
several times with distilled water to remove the physisorbed
molecules, and dried. Then the catalyst was reused in a new
catalytic experiment. The repeated catalysis experiments were
carried out ve times using the recycled catalyst. The relation-
ship between the conversion of cyclooctene/selectivity of
different products and recycling times is shown in Fig. 4e. The
catalytic cycle results show that the conversion of the cyclo-
octene decreases a little with increasing the cyclic number of
catalytic cycles. And the selectivity of epoxycyclooctane and 2-
cyclooctenone is similar to those of the rst catalytic run. Fig. 4f
shows the XRPD patterns of compound 1 as catalyst aer each
recycling time. And the position of peaks is almost no change
during 5 recycling times. The results conrm compound 1 still
retains its catalytic activities and is stable enough aer ve
catalytic cycles.
Next, the catalytic activities of 2 and 3 were also investigated
for oxidation of cyclooctene under the similar conditions. The
high conversion of cyclooctene achieved with catalysts 2
(37.78%) and 3 (39.08%) demonstrate their catalytic activities
(Fig. 5a). As is shown, the conversion of cyclooctene achieved by
2 is a little higher than that of 3 before 24 h, aer that, it is lower
than that of 3. For 2, the conversion increased gradually before
36 h and then grew quickly. For 3, the conversion increased
Fig. 3 (a) Photographs of ligand mpca soaked in cyclooctene at
different time periods. It shows the total dissolution of mpca in
cyclooctene within 10 min. (b) Photographs of compound 1 immersed
in cyclooctene for 10 days.
for 1 and physical mixture materials of 1 is shown in Table S4.† It
can be seen that the conversion increased with the increasing
reaction time. Aer 48 h, the conversion was up to 45.77% with
catalyst 1, while for physical mixture materials of 1, it was
30.15%. Fig. 4d exhibits the selectivity of different oxidation
products achieved by compound 1 and physical mixture mate-
rials of 1. We can see that, the selectivity of epoxycyclooctane
with catalyst 1 increased from 75.28 to 90.85% aer 48 h, while
the selectivity of 2-cyclooctenone decreased from 22.76 to 9.08%.
The total selectivities of epoxycyclooctane and 2-cyclooctenone
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ꢀ
Fig. 6 The ESR signals of the DMPO–cO2 adducts (compound 1 in
methanol solution). DMPO (dimethyl pyridine N-oxide) works as the
free radical trapping agent.
To demonstrate that compounds 2 and 3 are stable enough
for catalytic cycles, a series of catalytic experiments were per-
formed, and detailed results are shown in Fig. S8.† It's clearly
that, aer 5 times of catalytic experiments, the conversion and
selectivity are almost the same. From the XRPD patterns, we can
see that the position of peaks is almost no change during 5
recycling times. These results demonstrate that 2 and 3 as
catalysts are stable enough for catalytic cycles. Further blank
reactions (i.e., without catalysts) do not result in any epoxide
and/or other products. Moreover, the ltrate tests (additional 48
h reaction aer removing the catalysts from the reaction
system) show no catalytic activities (the conversion was 0),
indicating that the catalytic activities originated from the
addition of compounds 1–3 and is not caused by molecular
species in solution. All the catalytic experiments above
demonstrate that compounds 1–3 indeed act as heterogeneous
catalysts in the present catalytic systems.
Fig. 4 (a) The relationship between the conversion and reaction time
with mpca, bpp and metal ion (Co2+) as catalysts. (b) The relationship
between the selectivity and reaction time with mpca, bpp and metal
ion (Co2+) as catalysts. (c) The relationship between the conversion
and reaction time with compound 1 and physical mixture materials of 1
as catalysts. (d) The relationship between the selectivity and reaction
time with compound 1 and physical mixture materials of 1 as catalysts.
(e) The relationship between the conversion/selectivity and recycling
times with compound
1 as catalyst. (f) The XRPD patterns of
compound 1: after 1, 2, 3, 4 and 5 times recycling.
To conrm the air activation by the catalyst 1–3, the spin-
trapping electron spin resonance (ESR) characterization was
carried out. The radicals of superoxide radicals (cO2ꢀ) are
captured in methanol solution. In Fig. 6, the signal of six typical
quickly from 24 to 36 h, and then grew gradually. The selectivity
of epoxycyclooctane achieved by 2 and 3 is shown in Fig. 5b.
Note that the selectivity achieved by 3 is always higher than that
of 2. The detailed conversion/selectivity for 2 and 3 are shown in
Table S5 and S6.† As the control experiments, the physical
mixtures of each component for compounds 2 and 3 were used
as catalysts. As is shown, the catalytic activities of 2 and 3 are
much higher than that of corresponding physical mixtures.
ꢀ
characteristic peaks of DMPO–cO2 adducts are cleꢀarly exhibi-
ted. For 2 and 3, similar characteristic peaks of cO2 were also
observed (Fig. S9 and S10†).
Based on the ESR analysis and above catalytic results, it can
be inferred that the possible mechanism for the oxidation
reaction can be described as follows. Firstly, molecular chemi-
sorption of O2 occurred on the surface of 1-dimensional coor-
dination polymers, where O2 was formed active oxygen species
Fig. 5 (a) The relationship between the conversion of cyclooctene
and reaction time with catalyst 2 and 3 respectively. (b) The relation-
ship between the selectivity of epoxycyclooctane and reaction time Scheme
2
Possible selective oxidation mechanism based on
with catalyst 2 and 3, respectively.
compound 1.
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(cO2ꢀ) with the action of initiator and catalyst. Then, the active
oxygen species would be quickly consumed by the cyclooctene
to form a primary epoxide epoxycyclooctane, and then epox-
ycyclooctane was converted into 1,2-cyclooctanediol, but 1,2-
cyclooctanediol was unstable and further converted into 2-
cyclooctenone in the sequential oxidation process. The repeti-
tion of such reactions constituted the catalytic process, as
illustrated in Scheme 2.
6 F. E. Kuhn, E. Herdtweck, J. J. Haider, W. A. Herrmann,
¨
˜
I. S. Goncalves, A. D. Lopes and C. C. Romao, J. Organomet.
Chem., 1999, 583, 3.
7 J. P. Zhang, Y. B. Zhang, J. B. Lin and X. M. Chen, Chem. Rev.,
2012, 112, 1001.
8 R. Breslow, Science, 1982, 218, 532.
9 A. Stein, B. Melde and R. Schroden, Adv. Mater., 2000, 12,
1403.
10 Z. H. Peng, Angew. Chem., Int. Ed., 2004, 43, 930.
11 Y. F. Song, D. L. Long and L. Cronin, Angew. Chem., Int. Ed.,
2007, 46, 3900.
Conclusion
We demonstrated the catalyst design based on an isoxazole
derivative via a coordinate-polymerized strategy. Three new
coordination polymers have been synthesized under hydro-
thermal conditions. Compounds 1–3 exhibit similar wave-like
chains, with isoxazole-based ligand mpca functioning as
pendant arms. Catalytic experiments show that all of the three
title compounds can be used as efficient heterogeneous cata-
lysts for selective oxidation of cyclooctene. Compared with
homogeneous catalyst of mpca with low conversion, heteroge-
neous catalysts 1–3 exhibit high conversion owing to the
enhanced catalytic activity. The results presented here may
open a promising route for the design and fabrication of more
CPs with specic catalytic properties.
12 N. Mizuno, S. Hikichi, K. Yamaguchi, S. Uchida,
Y. Nakagawa, K. Uehara and K. Kamata, Catal. Today,
2006, 117, 32.
13 D. Hagrman, P. J. Hagrman and J. Zubieta, Angew. Chem., Int.
Ed., 1999, 38, 3165.
¨
14 C. Streb, C. Ritchie, D.-L. Long, P. Kogerler and L. Cronin,
Angew. Chem., Int. Ed., 2007, 46, 7579.
15 C. Inman, J. M. Knaust and S. W. Keller, Chem. Commun.,
2002, 156.
16 Y. Ding, J. X. Meng, W. L. Chen and E. B. Wang,
CrystEngComm, 2011, 13, 2687.
17 C. M. Nunes, I. Reva and R. Fausto, J. Org. Chem., 2013, 78,
10657.
18 S. A. Lang and Y. I. Lin, Comprehensive Heterocyclic
Chemistry, Oxford, Pergamon, U. K., 1984, vol. 6, Part 4B.
Acknowledgements
¨
19 P. Grunanger and P. Vita-Finzi, Chemistry of Heterocyclic
This work is supported by Collaborative Innovation Center of
Suzhou Nano Science and Technology, the National Basic
Research Program of China (973 Program) (2012CB825803,
2013CB932702), the National Natural Science Foundation of
China (51422207, 51132006, 51572179, 21471106, 21501126),
the Specialized Research Fund for the Doctoral Program of
Higher Education (20123201110018), the Natural Science
Foundation of Jiangsu Province of China (BK20140310), China
Postdoctoral Science Foundation (2014M560445, 2015T80581)
and a project funded by the Priority Academic Program Devel-
opment of Jiangsu Higher Education Institutions (PAPD).
Compounds, Wiley, New York, 1991, vol. 49, Part 1.
20 T. M. V. D. Pinhoe Melo, Curr. Org. Chem., 2005, 9, 925.
21 D. G. Sun, F. X. Sun, X. Y. Deng and Z. H. Li, Inorg. Chem.,
2015, 54, 8639.
22 D. B. Shi, Y. W. Ren, H. F. Jiang, B. W. Cai and J. X. Lu, Inorg.
Chem., 2012, 51, 6498.
23 L. Liu, C. Huang, L. Zhang, R. Ding, X. N. Xue, H. W. Hou
and Y. T. Fan, Cryst. Growth Des., 2015, 15, 2712.
24 X. S. Qu, L. Xu, G. G. Gao, F. Y. Li and Y. Y. Yang, Inorg.
Chem., 2007, 46, 4775.
25 X. L. Wang, Y. F. Bi, B. K. Chen, H. Y. Lin and G. C. Liu, Inorg.
Chem., 2008, 47, 2442.
26 H. H. Zou, Y. P. He, L. C. Gui and F. P. Liang, CrystEngComm,
2011, 13, 3325.
Notes and references
1 S. Caron, R. W. Dugger, S. G. Ruggeri, J. A. Ragan and
D. H. B. Ripin, Chem. Rev., 2006, 106, 2943.
2 A. K. Suresh, M. M. Sharma and T. Sridhar, Ind. Eng. Chem.
Res., 2000, 39, 3958.
¨
27 R. Sibile, T. Mazet, E. Elkaım, B. Malaman and M. François,
Inorg. Chem., 2013, 52, 608.
28 G. M. Sheldrick, SHELXS-97, Program for Crystal Structure
¨
Solution, University of Gottingen, Germany, 1997.
3 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.
29 G. M. Sheldrick, SHELXL-97, Program for Crystal Structure
¨
Renement, University of Gottingen, Germany, 1997.
30 A. Neels and H. Stoeckli-Evans, Inorg. Chem., 1999, 38, 6164.
31 Y. Z. Tang, X. F. Huang, Y. M. Song, H. Chan and R. G. Xiong,
Inorg. Chem., 2006, 45, 4868.
32 P. Chaudhuri, M. Hess, J. Muller, K. Hildenbrand, E. Bill,
T. Weyhermuller and K. Wieghardt, J. Am. Chem. Soc.,
1999, 121, 9599.
¨
4 F. E. Kuhn, E. Herdtweck, J. J. Haider, W. A. Herrmann,
˜
I. S. Goncalves, A. D. Lopes and C. C. Romao, J. Organomet.
Chem., 1999, 583, 3.
5 O. P. H. Vaughan, G. Kyriakou, N. Macleod, M. Tikhov and
R. M. Lambert, J. Catal., 2005, 236, 401.
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