A chiral salen-based MOF catalytic material with high thermal, aqueous and chemical stabilities

Article abstract of DOI:10.1039/c7dt01116d

A highly stable chiral salen-based metal-organic framework [(Cu₄I₄)₂L₄]·20DMF·3CH₃CN (1) [L = (R,R)-N,N′-bis(3-tert-butyl-5-(4-pyridyl)salicylidene)-1,2-diphenylethylenediamine nickel(ii)] has been sy

Full text of DOI:10.1039/c7dt01116d

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ISSN 1477-9226
PAPER
Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
framework
a Zr-metal–organic
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A Chiral Salen-based MOF Catalytic Material with highly thermal,
aqueous and chemical stabilities
Received 00th January 20xx,
Accepted 00th January 20xx
Jiawei Li, Yanwei Ren,* Chaorong Qi and Huanfeng Jiang*
DOI: 10.1039/x0xx00000x
A highly stable chiral salen-based metal-organic framework [(Cu4I4)2L4]·20DMF·3CH3CN (1) [L is (R, R)-N,N’-bis(3-tert-butyl-
5-(4-pyridyl)salicylidene)-1,2-diphenylethylenediamine nickel(II)] has been synthesized and characterized by single crystal
X-ray diffraction and other physicochemical methods. 1 exhibits a rare 8-fold interpenetrated 3D framework constructed
by 4-connecting Cu4I4 cluster and 2-coordinating L ligand. Remarkably, in spite of 8-fold interpenetration, 1 still possesses
two types of 1D chiral hydrophobic channels with pore window sizes of 6.77 × 8.64 Å2 and 6.09 × 10.96 Å2 along
crystallographic a axis. All Ni(salen) moieties of L lie inside of 1D channels and the empty coordination sites of Ni2+ orient
to the cavities. PXRD and N2 adsorption measurements confirmed 1 is extremely stable under high temperature (> 400 oC),
in water vapor (90% relative humidity), in acid/base aqueous solution (pH 0-14), and in saturated NaOH solution at 100 oC,
as well as in 30 wt% H2O2 and 70 wt% tert-butyl hydroperoxide solution. 1 was proved to be an excellent recycled
heterogeneous catalyst for the conversion of simulated industrial CO2 (that is, involving tiny amounts of water vapor and
other acidic gas) with epoxides into cyclic carbonates under mild conditions for the first time. The synthesis of β-hydroxy-
1,2,3-triazoles from the same epoxides, alkyne and sodium azide was also catalyzed by 1 in aqueous solution with high
yield. Interestingly, the cycloaddition reaction of CO2 to bulky epoxides show a decrease in the activity with an increase in
the alkyl chain length of the substrate because of confinement of the channel size of 1, showing size-dependent selectivity.
The plausible catalytic mechanisms for these two reactions have also been proposed.
www.rsc.org/
catalysts, the use of heterogeneous MOFs catalysts simplifies
the work-up procedure by allowing simple filtration to recover
the solid, facilitating product separation and catalyst reuse.
Introduction
Moreover, MOFs can prolong catalyst lifetimes owing to the
elimination of multimolecular deactivation pathways.
Metal-organic frameworks (MOFs), constructed from the
linkages of metal nodes and organic ligands, are emerging as
compelling porous materials for various applications such as
gas adsorption,1 photoluminescence,2 sensors,3 heterogeneous
catalysis4 and so on. Unlike inorganic zeolites, MOFs can be
rationally designed through judicious selection of numerous
metal centers and organic ligands, providing tailor-made
topology structures and desired chemical behaviors. MOFs
also tend to take the highly ordered crystal structures that can
be easily characterized by single crystal X-ray crystallography,
which is conducive to their structure-property relations
elucidation and function adjustments. Therefore, the
combination of organic ligands and crystal engineering in
MOFs synthesis provides a unique platform for rational design
and development of multifunctional inorganic-organic hybrid
materials. Currently, through ligand design, various well-
defined molecular catalysts, especially metalloporphyrin5 or
metallosalen,6 have been incorporated into MOFs which show
superior performances in various heterogeneous catalytic
processes. Compared to corresponding homogeneous
On the other hand, the chemical (more specifically,
hydrolytic) and thermal stabilities of MOFs catalytic materials
are important, because many catalytic processes often need
high temperature, varying pH value and being carried out in
aqueous phase for environment friendly synthesis.
Unfortunately, most of reported MOFs represent weak water-
stability, except for some examples of MILs,7 UiOs8 and ZIFs9
series MOFs. In general, the framework stability is determined
by the metal-ligand bond strength and the number of ligands
linked to each metal center. Up to now, there are three main
strategies to enhance the coordination bond strength so as to
improve the water-stability of MOFs: 1) choosing high
oxidation state metals (such as Cr3+, Al3+, Fe3+, and Zr4+) to
construct strong coordination bond with organic carboxylate
ligands, like MILs and UiOs; 2) using azolate-containing ligands
(such as pyrazole, triazolate and tetrazolate) to form strong
anionic, nitrogen-metal bonds, like ZIFs; and 3) incorporating
hydrophobic groups near coordination sites or onto ligands
through direct synthesis or postsynthetic modification to
increase MOFs hydrophobicity, thus protecting coordination
bond from hydrolysis.10 In addition, framework catenation is
also an effective approach to improve the heat and water
endurance of MOFs because of space-filling effect.11 For
examples, with the first strategy above, many
Key Laboratory of Functional Molecular Engineering of Guangdong Province, School
of Chemistry and Chemical Engineering, South China University of Technology,
Guangzhou, 610641, P. R. China. E-mail: renyw@scut.edu.cn, jianghf@scut.edu.cn;
Fax: +86-20-87112906.
†Electronic Supplementary Information (ESI) available: IR, UV-vis and MS spectra,
NMR data of ligand L. IR spectrum, crystallographic data, space-filling model and metalloporphyrin-based MOFs, such as PCN-22x (X =2, 3, 4,
TG curve of 1. NMR data of β-hydroxy-1,2,3-triazoles, GC-MS analyses of cyclic
carbonates (PDF).
and 5), PCN-600 and Al-PMOF possessing high stability in
acidic, neutral or basic aqueous solutions have been
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prepared.5f, 12 Very recently, using the second strategy, Li and moieties. Furthermore, the catalytic performance of this MOF
Zhou reported
novel MOF, PCN-601, constructed by material was also investigated for a Cu+-catalyzed three-
a
pyrazolated-based porphyrin ligand.13 This MOF exhibits component azide-alkyne cycloaddition reaction with water as
excellent stability and retains its crystallinity and porosity in solvent. The catalytic results revealed that this MOF is an
saturated sodium hydroxide solution. These results greatly excellent recycled heterogeneous catalyst in aqueous phase,
extend the application range of metalloporphyrin-based MOFs water vapor, and at high temperature.
in heterogeneous catalysis fields. However, as for
metallosalen-based MOFs in which chiral sources can be
introduced easily, no study has yet investigated the chemical
and thermal stability, although the immobilization of
metallosalen moieties into MOFs skeletons have successfully
Experimental
Materials and Methods
been realized by our and other groups for their crucial roles in
asymmetric catalysis.6d,
All of the reagents were commercially available and were used
6e, 14
Generally, metallosalen ligands
without further purification. Powder X-ray diffraction (PXRD)
patterns were collected on a Bruker D8 powder diffractometer at
40kV, 40mA with Cu Kα radiation (λ=1.5406 Å), with a scan speed of
possess bulky size and incline to construct MOFs with extra
large cavities, thereby the frameworks are highly vulnerable
and unstable toward water, heat and other stimulus.6g
Therefore, engineering robust chiral metallolsalen-based MOFs 17.7 s/step and a step size of 0.01995o (2θ). Thermogravimetric
that can tolerate various harsh chemical environments is very
important for expanding their application ranges.
(TG) analyses (were performed on a Q600 SDT instrument under a
flow of N2 at a heating rate of 10oC/min. 1H NMR and 13C NMR were
Recently, the conversion of carbon dioxide (CO2) to cyclic
carbonates catalyzed by MOFs has attracted increasing
attention,5a, 6d, 6e, 15 mainly based on the following reasons: 1)
CO2 is a nontoxic, non-flammable and renewable C1 building
block, and 2) cyclic carbonates are widely used as electrolytes
for lithium-ion batteries, precursors for polymeric materials,
and intermediates for fine chemicals. However, all reports
utilized pure CO2 to explore this transformation. Note that the
pure CO2 is usually obtained by purifying flue gases from
power plants and industrial furnaces which contain large
amounts of CO2, together with other gases such as acidic
oxides (SO3, SO2 and NO2) and water vapor, depending on the
fuel being used. The purification process is time-consuming
and needs additional energy cost. Therefore, the development
of highly efficient and stable heterogeneous catalysts for the
conversion of industrial CO2 at atmospheric pressure and room
temperature remains a challenge.
done on
a Bruker Model AM-400 (400MHz) spectrometer.
Elemental analyses (EA) for C, H and N were carried out using a
Vario EL III Elemental Analyzer. Infrared (IR) spectra were measured
from a KBr pellets on a Nicolet Model Nexus 470 FT-IR spectrometer
in the range of 4000-400 cm-1. Gas chromatography-mass
spectroscopy (GC-MS) spectrometry was recorded on Shimadzu
Model GCMS-QP5050A system that was equipped with
a
0.25mm×30m DB-WAX capillary column. The content of metal ions
was determined by Atomic Absorption Spectrometer (AAS) (Z-2000,
HITACHI). The gas adsorption measurements were performed on a
MicroActive ASAP 2460 systems under N2 (77 K), N2 (273 K) and CO2
(273 K and 298 K). Water vapor adsorption Isotherms were
conducted on an Intelligent Gravimetric Analyzer (IGA-3series,
Hiden Isochema) at 298 K and 1 bar.
Herein, based on a multi-strategies integration that involves
incorporating hydrophobic groups onto metallosalen ligand,
framework catenation and selection of topology structure, the
first highly stable chiral metallosalen-based MOFs material,
Synthesis of Ligand
The synthetic route of metallosalen L is shown in Scheme 1.
N
N
O
{[(Cu4I4)2L4]·20DMF·3CH3CN} (1) was successfully synthesized
N
OH
through CuI and predesigned metallosalen L (Ni(salen) in
Scheme 1). The framework structure exhibits a rare [4+4] 8-
fold interpenetrated structure with 2-connected Ni(salen)
linkers and 4-connected cubic Cu4I4 clusters nodes.
Remarkably, in spite of 8-fold interpenetration, the structure
possesses two types of 1D channels with pore window sizes of
6.77 × 8.64 Å2 (I) and 6.09 × 10.96 Å2 (II) along the
crystallographic a axis, and the inner two face-to-face Ni2+
atoms distances are in the dimensions of 14.1 × 13.3 Å2 (I) and
14.3 × 13.2 Å2 (II), respectively. As expected, this MOFs shows
good thermal stability (> 400 oC), water stability [involving 1 M
of HCl solution, saturated NaOH solution, 30 wt% H2O2
aqueous solution and 70 wt% tert-butyl hydroperoxide (TBHP)
aqueous solution], and water vapor stability. To the best of our
knowledge, this MOF material is also the first example with
high stability constructed by neutral pyridine linker and zero-
valent metal clusters. With the superior thermal and chemical
stabilities in hand, we investigated the catalytic activity of this
MOF for the synthesis of cyclic carbonates by the cycloaddition
of epoxides with CO2 (or in the presence of acidic gas SO2 and
water vapor) utilizing the embedded Lewis acidic Ni(salen)
tBu
tBu
tBu
tBu
tBu
N
N
OH
OH
N
N
O
O
Ni(OAc)2
MeOH
+
Ni
L
EtOH, reflux
8 h
H2
N
NH2
N
N
Scheme 1. Synthesis of the metallosalen L
(R,R)-N,N’-bis(3-tert-butyl-5-(4-pyridyl)salicylidene)-1,2-
diphenylethylenediame: A mixture of compound 3-tert-butyl-5-(4-
pyridyl)salicylaldehyde (510.8 mg, mmol), (R,R)-1,2-
2
diphenylethylenediamine (212 mg, 1 mmol, 0.5 equiv), in EtOH (15
mL) was heated to reflux for 8 h before being allowed to cool to
room temperature. The solvent was evaporated under reduced
pressure. The crude product was purified by flash chromatography
on silica gel with EtOAc to get a yellow solid. Yield: 629 mg (91 %).
Melt Point: 132.5-133.2 oC. IR (ν/cm-1): 3399.7, 3028.7, 2955.7,
2911.2, 2871.2, 1625.9, 1594.7, 1445.7, 1391.6, 1265.9, 1170.4,
1056.2, 990.5, 890.4, 821.3, 773.2, 703.6, 623.7, 545.6, 511.3. EA,
2 | J. Name., 2012, 00, 1-3
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o
calcd. for C46H46N4O2: C, 80.43; H, 6.75; N, 8.16; found: C, 80.39; H, MeOH for three times, the catalyst was dried under 100 C for 2 h.
6.78; N, 8.13. 1H NMR (CDCl3): δ 14.08 (s, 2H), 8.57(s,4H), 8.42(s, Then it was ready for another run.
2H), 7.51(s, 2H), 7.33(s, 4H), 7.24(s, 12H), 4.79(s,2H), 1.44(s, 18H).
Crystal Structure Determination and Refinements
13C NMR (400 MHz, CDCl3): δ 166.84, 161.34, 150.03, 147.95,
Single-crystal XRD analyses of 1 was performed on an Xcalibur Onyx
Nova four-circle diffractometer using CuKα radiation (λ =1.54184 Å)
at 100 K. The empirical absorption correction was performed using
the CrystalClear program. The structure was solved by direct
methods and refined on F2 by full-matrix least-squares technique
using the SHELXL-2016/6 program package.16 The Cu, Ni and I atoms
in the asymmetric unit were located firstly from the difference
Fourier map and refined anisotropically. The other atoms (O, C and
N) in the salen framework were then located from the difference
Fourier map and refined isotropically, as a result of the relatively
weak diffraction, (which is not uncommon for this kind of
framework with large solvent accessible void space). Restraints
(DELU and SIMU) on displacement parameters, and DFIX for bond
lengths of salen framework were applied, and all phenyl rings of
1,2-diphenylethylenediimine on salen ligand were constrained to
ideal six-member rings. SQUEEZE subroutine of the PLATON
software suite17 was applied to remove the scattering from the
138.93, 138.39, 128.54, 128.46, 128.30, 127.98, 127.85, 127.58,
120.87, 118.82, 80.06, 35.05, 29.24.
(R,R)-N,N’-bis(3-tert-butyl-5-(4-pyridyl)salicylidene)-1,2-
diphenylethylenediamine nickel (II) (L): A solution of above metal-
free salen ligand (0.365 g, 0.5 mmol) in MeOH (30 mL) was added
dropwise to Ni(OAc)2·4H2O (0.125 g, 0.5 mmol) in MeOH (30 mL).
The reaction mixture was stirred at room temperature for 2 h, and
then reflux for 3 h. The resulted red powder was collected by
filtration, washed with MeOH and dried under reduced pressure.
Yield: 717 mg (96 %). Melt Point: 401.8-402.3 oC. IR (ν/cm-1):
3028.5, 2949.2, 2908.7, 1611.8, 1588.3, 1548.5, 1496.5, 1438.5,
1398.4, 1331.6, 1287.7, 1263.9, 1233.5, 1174.1, 1080.5, 991.6,
900.2, 860.9, 824.4, 788.2, 763.2, 698.7, 637.9, 619.6, 575.3, 520.5.
EA, calcd. for C46H44N4NiO2: C, 74.30; H, 5.96; N, 7.53; found: C,
74.26; H, 6.01; N, 7.47. HR-MS: m/z, 743.2914 (M+H+).
Synthesis of [(Cu4I4)2L4]·20DMF·3CH3CN (1)
Solvothermal reaction of CuI (40 mg, 0.2 mmol), KI (40 mg, 0.24 highly disordered guest molecules. The resulting new HKL file was
mmol) and L (15 mg, 0.02 mmol) was performed in a mixture used to further refine the structure. Hydrogen atoms attached to
solvent of N,N-dimethylformamide and acetonitrile (DMF/CH3CN, carbon were placed in geometrically idealized positions and refined
3mL/1mL) in a 10 mL vial and heated at 100 oC for three days, then using a riding model. The crystal data and refinement parameters
the reaction was cooled to room temperature at a rate of 5 oC/h. are listed in Table 1. Note that the contributions of guest molecules
The product was isolated by decanting the mother liquor and have been included in the overall formula, formula weight, density,
washing with DMF and CH3CN. Yield: 31 mg (34 %). IR: 3026.1, F(000) calculations reported in Table 1 and in the CIF. CCDC
2947.4, 2907.0, 1670.9, 1593.6, 1544.6, 1501.5, 1430.3, 1403.8, 1522765 contains the supplementary crystallographic data for this
1387.4, 1331.3, 1286.7, 1262.8, 1221.1, 1172.5, 1082.3, 1015.2, paper.
956.9, 899.7, 824.4, 787.9, 765.9, 699.7, 633.7, 602.1, 575.8, 516.5.
EA, calcd. for C250H325Cu8I8N39Ni4O28: C, 49.36; H, 5.39; N, 8.98;
Table 1. Crystal data and structure refinements for 1
found: C, 49.81; H, 5.65; N, 9.38.
Compound
1
Empirical formula
Formula weight
Crystal system
Space group
C250H325Cu8I8N39Ni4O28
6082.88
Cycloaddition reactions from Epoxides and CO2
Epoxides (2 mmol), 1 (23 mg, 0.5 mol%), and tetrabutyl ammonium
bromide (TBAB) (3 mg, 0.5 mol %) were heated at 100 oC for 12 h
with a CO2 balloon. Solvent was not needed in all these reactions.
The mixture was filtered to remove the solid phrase and the filtrate
was analyzed with GC-MS.
orthorhombic
P 221 21
Cell parameters
a = 18.4248(2) Å α = 90o
b = 35.8993(7) Å β = 90o
c = 36.7318(4) Å γ =90o
24295.8(6)
Volume (Å3)
Z
4
Cycloaddition Reactions from Epoxides with Azides and Alkynes
Density (calcd. g/cm3)
Absorption coeff. (mm-1)
F(000)
1.663
NaN3 (72 mg, 1.1 mmol), epoxide (1 mmol), and alkyne (1 mmol)
were added to 3 mL of H2O with 1 (23 mg, 1 mol%). The reaction
mixture was warmed to 60 oC under N2 atmosphere for 24 h. The
mixture was filtered to remove the solid phrase and the filtrate was
extracted with ethyl acetate (10 mL × 3). The solvent was removed
in vacuum and then column chromatography was performed to
obtain the pure products.
9.383
12357
Crystal color & shape
θ range data collection
Limiting indices
Reflections collected
unique
Brown and block
1.72 to 66.21
-20<=h<=21, -42<=k<=42, -41<=l<=43
35689
30079
Refinement method
Goodness-of-fit on F2
Final R indices [I>2σ(I)]
R indices (all data)
Full-matrix least-squares on F2
Recycle Experiments
1.063
R1 = 0.1242, wR2 = 0.3141
R1 = 0.1346, wR2 = 0.3234
The recyclability of 1 was tested with three consecutive runs. The
solid phrase was filtered and collected. By washing with DMF and
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Results and discussion
(b)
(a)
Synthesis
The new ligand L was obtained in two steps from Schiff base
condensation between (R, R)-1,2-diphenylethylenediamine and 3-
tert-butyl-5-(4-pyridyl)salicylaldehyde, followed by metalation with
Ni(OAc)2·4H2O. The IR spectrum (Fig. S1 in Supporting information,
SI) of L shows that the C=N stretching vibration shift to about 1588
cm-1 expected for the nickel coordinated to salen ligand. The UV-vis
spectrum (Fig. S3 in SI) of L presents one broad peak in the visible
region at 400-500 nm, attributed to the d-d transition of the square-
+
(d)
(c)
planar four-coordinated Ni2+ 6e
This result indicates that the
.
pyridine of L is not involved in the coordination to the Ni2+ ion, and
can be used as a metalloligand to construct MOFs. Meanwhile, we
selected (R, R)-1,2-diphenylethylenediamine to synthesize
metallosalen ligand based on the following considerations: 1) it can
provide potential chiral source into MOF for enantioselective
catalysis; 2) the introduction of diphenyl group can enhance the
MOFs hydrophobicity, and thereby improving the framework water-
resistance; 3) the diphenyls group may also facilitate the growth of
high-quality MOF crystals owing to their strong π-π stacking and
space-filling effect. On the other hand, we chose cubic Cu4I4 cluster
as node because it can construct MOFs with dia topology which
generally present high thermal stability.18 Moreover, MOFs formed
by Cu4I4 clusters with elongated liner bridging ligands can possess
high-fold interpenetrated configuration that also favor the
framework stability.
2 nm
(f)
(e)
Fig. 1 (a) Structures of L and the Cu4I4 cluster; (b) View of the coordination
environment of the Cu4I4 cluster; (c) View of the adamantine-like network; (d)
View of the cavities along crystallographic c axis in single non-interpenetrated
network; (e) View of the 3D dia network; (f) View of the [4+4] 8-fold
interpenetration mode.
Solvothermal reaction of L, CuI and KI in a mixed solvent of
o
DMF/CH3CN at 100 C led to brown single crystals of 1 suitable for
the single-crystal X-ray diffraction. 1 is stable in air and insoluble in
water and common organic solvents. The solvent contents were
1
established by a combination of EA, TG analysis (Fig. S10 in SI), H
NMR studies (Fig. S7 in SI), and in conjunction with the electron
count from SQUEEZE (see CIF). The phase purity of bulky sample
was evidenced by experimental PXRD, which matches well with the
theoretical pattern simulated from simulated data (see Fig. 6).
I
Crystal Structure
II
Crystal structure analysis reveals that
1 crystallizes in the
orthorhombic chiral space group P22121. There are two types of
independent asymmetric units crossed each other which consist of
one Cu4I4 cluster and two L ligands (Fig. S8 in SI). In Cu4I4 moiety
each Cu+ is coordinated by three μ3-I- and one pyridyl nitrogen atom
from L (Fig. 1a). The Cu-I distances range from 2.596 to 2.815 Å, and
the Cu-Cu distances vary from 2.566 to 2.640 Å, comparable to
those in the reported Cu4I4 clusters-based MOFs.18, 19 Each Ni2+ ion is
coordinated in a nearly square-planar geometry with two nitrogen
atoms and two oxygen atoms from L ((Ni-O)avg=1.8255 Å, (Ni-
N)avg=1.826 Å) (Fig. 1a). The L acts as linear bridge to connect two
Cu4I4 clusters, and each Cu4I4 cluster serves as 4-connecting node to
link four L ligands in tetrahedral configuration (Fig. 1b). This
connection mode leads to the formation of a basic adamantine-like
Fig. 2 Top left: view of the interpenetrated framework along crystallographic a
axis; Top right: view of the one type of hydrophobic pore in 1; Bottom left: view
of the other type of hydrophobic pore in 1; Bottom right: view of the hydrophobic
network (Fig. 1c), and further extension of the network to other groups around Cu4I4 cluster.
orientations forms the 3D frameworks with dia topology (Fig. 1e).
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Note that a single non-interpenetrated network possesses an extra
large cavity sizes up to 20 Å along crystallographic c axis (Fig. 1d),
Pristine
(a)
250
200
150
100
50
and such an extremely large cavity induces
a rare 8-fold
RT-24h (1M HCl)
100oC-24h (s NaOH)
After water vapor test
interpenetrated framework (Fig. 1f). The 8-fold interpenetration
framework in 1 is unusual and can be best described as [4+4]
interpenetration mode, in which a single network is interpenetrated
by other three identical networks to form a 4-fold interpenetrated
network that then cross each other. A literature survey shows [4+4]
8-fold interpenetration mode is rare.20 Remarkably, in spite of 8-
fold interpenetration, the structure still possesses two types of 1D
channel with pore window sizes of 6.77 × 8.64 Å2 (I) and 6.09 ×
10.96 Å2 (II) along crystallographic a axis, and the inner two face-to-
face Ni2+ atoms distances are in the dimensions of 14.1 × 13.3 Å2 (I)
and 14.3 × 13.2 Å2 (II), respectively (Fig. 2). Moreover, the chiral
source, diphenyl groups of L stretch into the pores, building a chiral
hydrophobic channels environment, which has the potential for
chiral recognition and enantioselectivity. PLATON calculation
reveals that 1 has 41.5% of the total volume available for guest
inclusion. It is worth noting that all Ni(salen) moieties lie inside of
1D channels and the empty coordination sites of Ni2+ orient to the
cavities. Therefore, the trapped substrate molecules are available
for Lewis acidic activation in the 1D channels whose surfaces are
uniformly arranged with chiral Ni(salen) moieties with
coordinatively unsaturated Ni2+ ions. A deeper structure analysis
reveals that each Cu4I4 cluster is toughly shielded by two tert-butyls,
three phenyls and four pyridine groups from other interpenetrated
nets (Fig. 2). These weak π-π stacking interactions may stabilize the
compound and facilitate the growth of single crystals, since the
substitution of (R, R)-1,2-diphenylethylenediamine by (R, R) -1,2-
cyclohexanediamine in L failed to obtain the ideal single crystal. We
envision that this structural character might exhibit the combined
effects of ligands hydrophobicity and structural interpenetration to
protect Cu4I4 clusters and Cu-N bonds from exposure to water.
5
10 15 20 25 30 35 40 45 50
Pore Width (A)
0
0.0
0.2
0.4
0.6
0.8
1.0
P/Po
60
50
40
30
20
10
0
(b)
273K CO2 ads.
298K CO2 ads.
273K N2 ads.
0.0
0.2
0.4
0.6
0.8
1.0
P/Po
Fig. 3 (a) N2 adsorption/desorption isotherms of 1, and acid- and base- and water-
treated samples of 1 at 77 K; (b) Adsorption/desorption isotherms of 1 for CO2 at
273K and 298K, and N2 at 273 K (closed circles represent adsorption and open
circles represent desorption).
Stability
The thermal stability of 1 was firstly investigated by TG analysis
under N2 atmosphere. The TG curve of 1 shows a total weight loss
of 26% from 40 oC to 160 oC, corresponding to the loss of
disordered solvent molecules (20 DMF and 3 CH3CN) in the
channels. The sharp weight loss after 410 °C indicates the collapse
of the framework (Fig. S10 in SI). In order to further confirm the
thermal endurance of 1, in situ variable-temperature PXRD was
then measured (Fig. 4). The PXRD patterns show that the
crystallinity of 1 keeps intact until 400 oC, and higher temperature
(450 oC) results in the loss of crystallinity because of the
disappearance of the PXRD peaks around 4.8o and 9.5o, which is in
well accordance with TG curve. It is reported that the metallosalen-
based MOFs usually possess extra large cavity, thereby the formed
frameworks are generally unstable toward heat.6g In view of the
relatively weak neutral pyridine-metal bond, we speculate that the
high thermal stability may be attributed to the strong framework-
framework interaction of the 8-fold interpenetration in 1, because
interpenetration has been proved to be an effective way to improve
MOFs thermal stability.21
Gas Adsorption
Before gas adsorption measurement, the sample of
1 was
o
immersed in CH3CN solution for 12 h and then activated at 150 C
under high vacuum for 12 h. As can be seen from Fig. 3a, the N2
adsorption isotherm of 1 reveals Type I behavior, indicative of
microporous material. The N2 uptake at 77 K is 199 cm3/g and the
apparent surface area is calculated using the BET method to be 527
m2/g. The CO2 adsorption of
1 was also measured because
unsaturated Ni2+ ions might have high affinity to CO2 molecules. The
result shows that the maximal adsorbed amounts at 1 atm are
36.98 cm3/g at 273K and 21.79 cm3/g at 298K (Fig. 3b), respectively.
The calculated value of the isosteric heat of adsorption (Qst) of 1 for
CO2 at low coverage is 37.86 KJ/mol using Clausius-Clapeyron
equation. In comparison, adsorption test of 1 for N2 at 273 K
revealed negligible uptake, and this behavior shows a selective
uptake of CO2 over N2, which mainly result from the stronger
interaction of CO2 with open metal sites owing to the significant
quadrupole moment and polarizability of CO2 over N2.15i The results
here indicate that 1 has potential to be utilized in the industrial gas
separation and purification process.
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pH = 0 to 14 for 24 h, and the crystallinity of the sample remains
intact, as supported by the PXRD analysis (Fig. 5c). Furthermore, N2
adsorption/desorption isotherms of
1 after acid- and base-
treatments were conducted, and the results confirmed the
maintenance of porosity of 1 under these harsh conditions (Fig. 3a).
Note that the N2 uptakes after above treatments are slight higher
than that of the pristine one. We suggest that this might attribute
to the thorough evacuation of the residual solvent molecules in the
framework through above treatments. This phenomenon was also
be observed in other reported MOFs.13 Additionally, AAS analysis of
the filtrate revealed that no Ni2+ or Cu+ ions were detected. More
impressively, immersing the sample in saturated NaOH solution
(about 20 mol/L) at 100 oC for 24 h have no any influence to the
framework integrity. However, when immersing the sample in
concentrate HCl for 1 h, the framework of 1 collapsed (from PXRD
pattern, data not shown) and AAS showed detectable Ni2+ in liquid
phase. Although recently there is one pyrazolate-based porphyrinic
MOF that can retain crystallinity and porosity in saturated NaOH
solution at 100 oC,13 to the best of our knowledge, 1 is the first MOF
material that shows extreme stability in both moderate acid and
strong base solutions, which makes it possible to act as potential
candidate for industrial applications involved acid or alkali
conditions.
450oC
400oC
350oC
300oC
250oC
As-synthesized
Simulated
10
20
30
40
2 theta/degree
Fig. 4 In situ variable-temperature PXRD of 1 under N2 atmosphere.
The improvement of MOFs chemical and hydrothermal stability is
largely related to the resistance towards liquid water and water
vapor, respectively. Thus, 1 was firstly immersed in aqueous
solution for 24 h, and its PXRD pattern indicates no any change
compared to the as-synthesized one (Fig. 5a). To further evaluate its
water endurance, 1 was immersed in aqueous solution for 1 month
or in boiling water for 24 h. The same PXRD patterns were
witnessed, implying maintenance of the framework. Generally, two
hydrophobicity mechanisms are possible for the high water stability
in MOFs.22 In one path, water molecules are completely blocked
from entering into the pores of the framework due to external
hydrophobic groups. In the other path, water molecules are actually
adsorbing into the framework, but the internal hydrophobicity
inhibits the water from clustering and attacking the metal-ligand
bonds. Considering the hydrophobicity both inner the channel
surfaces and around metal clusters of 1 (Fig. 2), we seek to figure
out which mechanism may be responsible for the high water
resistance. Thus, water vapor adsorption isotherm was conducted
(Fig. 5b), as water vapor, consisting mainly of single molecule, can
permeate into the framework while liquid water inclines to cohere
into cluster molecules that may be blocked by the framework
lacking of cluster-size pores. As shown in Fig. 5b, the adsorbed
amount of water vapor increases with relative humidity (RH), and
the maximum water vapor capacity at 90 % RH is 7.12 mmol/g. This
result manifests that a small amount of water molecules can
actually enter into the channels of 1. The desorption curve shows
the water vapor can be totally excluded from the network when the
steam was transferred to dry air, which indicates no change of the
framework after exposure into water vapor. Furthermore, PXRD
measurement and BET analysis for the sample after water vapor
treatment confirm its framework integrity (Fig. 3a and Fig. 5a).
From above results, as well as the crystal structure of 1, it can be
concluded that the hydrophobic channel surfaces as the first shield,
block the large-sized water clusters, and the adsorbed single water
molecules are prevented from clustering and cohering by other
hydrophobic groups around the Cu4I4 clusters, as the second shield.
The excellent water stability of 1 drives us to evaluate its acid-
base resistance. 1 was treated under aqueous solution ranging from
The extraordinary stability of 1 in basic or acid aqueous solution
could be explained from thermodynamic perspective. In basic
condition, the decomposition procedure of 1 could be regarded as a
competition between pyridine groups of L and OH- for Cu4I4
clusters. Intuitively, the Lewis acid metal clusters Cu4I4 should form
stronger bonds with more basic (higher pka) ligands, that is, Cu4I4-
(OH)4 moiety should has been more base-stable than 1, because
pyridine is lesser basicity (pka = 4.60) than OH- (pka = 14). However,
1 actually appears to be more stable partly because it possesses 8-
fold interpenetration. Interpenetration crystal structures are more
thermodynamically stable23 and also lead to lower water adsorption
loadings. In addition, there is another competition between salen2-
and OH- for Ni2+. Compared to OH-, salen2- is a tetradentate
chelating ligand and has higher crystal filed stabilization energy, and
thereby the coordination between salen2- and Ni2+ is stronger than
that between OH- and Ni2+. This coordination thermodynamically
not only ensures the rigidity of L and then enhances the framework
stability, but also endows intact catalytic centres even in extremely
basic aqueous solution. On the other hand, in moderate acidic
solution (pH =1), the main driving force of framework disassociation
becomes the competition between Cu4I4 clusters and H+ for the
pyridine groups of L. Due to the low pka value of pyridine, the
equilibrium is more inclined to the MOF formation state and the
Ni(salen) moieties in L also maintain because of lower pka (9.96) of
phenol. However, in concentrate HCl solution, high concentration of
H+ not only results in the formation of H2salen moieties and then
lower rigidity of L, but also makes L become pyridinium and thereby
leads to the decomposition of 1. With respect to the kinetic
decomposition of MOFs in solution, Zhou13 recently reported a "3D
chelating effect" that when the connectivities of the ligand and
metal node in MOFs are high, partial ligand dissociation can scarcely
6 | J. Name., 2012, 00, 1-3
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cause collapse of the whole framework owing to the high rate of
Finally, since a large number of catalysis involved the use of
defect reparation. However, in our MOF, despite low connectivities oxidants, and Cu+ ion in solution is usually susceptible to be
for L and metal node Cu4I4, the rare 8-fold interpenetration oxidized, we investigated the framework stability of 1 towards
configuration equally generates
a
very high "effective different oxidants. Firstly, 1 was placed at ambient conditions for 3
concentration" of coordination moiety around the defect site. We months, and the crystallinity remained unchanged (Fig. 5d),
call this a "high-interpenetrated chelating effect".
indicating molecular oxygen in atmosphere cannot oxidize Cu+ in
Cu4I4 clusters. Next, stronger oxidants H2O2 (30 wt% in H2O) and
30
(a)
(b)
25
Adsorption
Desorption
20
15
10
5
after water vapor test
100oC water for 24h
water for 1 month
water for 24h
Simulated
0
10
20
30
40
0
20
40
60
80
100
2 theta/degree
Relative humidity (%)
(c)
(d)
s NaOH at 100 o
C
s NaOH
10M NaOH
PH=14
PH=0
PH=1
PH=2
70 wt%TBHP for 24h
30 wt%H2O2 for 24h
PH=3
air for 3 month
Simulated
PH=4
synthesized
10
20
30
40
50
10
20
30
40
2 theta/degree
2 theta/degree
Fig. 5 (a) PXRD patterns for water treated samples of 1; (b) Water vapor sorption-desorption isotherm of 1; (c) PXRD patterns of sample of 1 after acid or base treated
for 24 h; (d) PXRD patterns of samples of 1 after oxidants treated for 24 h or in air for 3 months.
TBHP (70 wt% in H2O) have negligible influence to the framework (SO3, SO2, NO2, etc) and water vapour, these MOFs might collapse
integrity (Fig. 5d). These results reveal that the Cu4I4 clusters in 1 and lost their activities when exposed to these mixed gases. As
are stable to common oxidants and 1 has potential applications in discussed above, 1 possesses 1D open chiral channels, with the
heterogeneous oxidation reactions, because Ni(salen) units inner walls decorated with unsaturated Ni2+ ions with the empty
represented certain activity for alkene epoxidation.24 Therefore, the coordination sites orienting to the cavities, which could be
as-synthesized 1 possesses high thermal stability, water stability, as considered as an ideal “nanoreactor”. The extreme stability of 1
well as chemical stability for acid, base, and common oxidants.
towards heat, water, water vapor, and acid or base aqueous
solution, as well as its selective CO2 uptake property motivated us
to investigate its catalytic property for heterogeneous cycloaddition
of epoxides with simulated industrial CO2 involving water vapor and
acid gases.
Cycloaddition of CO2 with Epoxides catalyzed by 1.
Ni2+ ion has been proved to be an effectively catalytic site for the
cycloaddition reaction of CO2 with epoxides.6d, 6e, 15d, 25 We have
reported two Ni(salen)-based MOFs that could be used as efficient
and recyclable heterogeneous catalysts for the synthesis of cyclic
Firstly, styrene oxide was selected as the benchmark substrate,
and several kinds of reaction variables were investigated as
summarized in Table 2. The optimized reaction condition involved 2
mmol epoxide, 1 atm of CO2 in the presence of 0.5 mol % of 1 and
0.5 mol % of TBAB at 100 °C for 12 h, with 84% conversion and 99%
selection for cyclic carbonate. It can be seen that both 1 and TBAB
play critical roles and are indispensible to this reaction (entries 1-2,
Table 2), which is in accordance with other reported binary
carbonates by the cycloaddition of CO2 with epoxides utilizing
6e
Ni(salen) moieties as Lewis acidic site.6d,
On the other hand,
although a large number of MOFs have been utilized in the
conversion of CO2 into cyclic carbonates,16 most of these catalytic
processes involved the use of high purity CO2. However, as
industrial CO2 usually contains various gases such as acidic oxides
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catalysts.16 The catalytic performance of 1 was higher than that of (entry 8, Table 2). A mixed gas of CO2, H2O and SO2 was also applied
the control homogenous catalyst L (entry 6, Table 2, the molar in this catalytic system, and the result shows that 1 can be used
amount of L was the same as in 1) or the combination of L and CuI under acidic condition with a conversion of 80% (entry 9, Table 2).
(entry 7, Table 2, the molar ratio = 1:1), clearly indicating that an Furthermore, the results of the recycling experiments showed no
additive or synergistic Lewis acidic activation of Ni(salen) units in 1 obvious loss of activity for this MOF catalyst after being used three
works during the catalytic process. As water could immediately times under mixed gas of CO2, H2O and SO2 (entries 10-11, Table 2).
turned into vapor in this reaction system (100 oC), we added 0.1 mL The catalysts recovered from the catalytic reactions under pure
of water to this reaction to serve as a mixed gas of CO2 and H2O. CO2,
Impressively, water vapor had negligible influence to this reaction
Table 2. Optimization of reaction parameters for cycloaddition of CO2 with styrene oxide catalyzed by 1.a
Entry
1
Catalyst
Additive
TBAB
-
Temperature
100
Atmosphere
CO2
Conversion (%)b
Selectivity (%)b
-
16
5
99
99
99
99
99
99
99
99
99
99
99
2
1
100
CO2
3
1
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
25
CO2
4
4
1
50
CO2
21
84
63
70
81
80
79
77
5
1
100
CO2
6
L
100
CO2
7
L+CuI
100
CO2
8c
9d
10e
11f
1
1
1
1
100
CO2+H2O
CO2+H2O+SO2
CO2+ H2O + SO2
CO2+ H2O + SO2
100
100
100
aReaction conditions: epoxide (2 mmol),
bConversion and selectivity were determined by GC-MS. c0.1 mL water was added. d0.1 mL water was added and V(CO2):V(SO2)=10:1. eSecond cycle. fThird cycle.
1
(0.5 mol%) and TBAB (0.5 mol%) under CO2 (1 atm pressure), reaction time 12 h.
mixed gas of CO2 and H2O, mixed gas of CO2, H2O and SO2, all
Generally, since different reaction conditions such as catalytic
exhibited the almost same PXRD patterns as the simulated one, centres character, catalysts loading, CO2 pressure, reaction time
unambiguously confirming the stability of 1 (Fig. 6), which is and temperature were used, it is hard to critically evaluate and
thankful for its high thermal and chemical stability. AAS analysis of compare the efficacy of reported MOFs catalysts. Thus, we take a
the supernatant revealed no metal leaching into the reaction 3D Ni(II)-based MOFs that possesses coordinatively unsaturated
mixture, indicating the heterogeneous nature of this reaction. Ni(II) sites in its 1D channels as an approaching comparison.15i For
Unfortunately, no any enantiomeric excess (ee) value was observed styrene oxide, this Ni(II)-based MOFs (0.5 mol% loading) gave 80%
in this reaction despite a chiral catalyst was used. When the conversion at 80 °C and 0.8 Mpa CO2 pressure for 12 h, while 1
reaction temperature decreased to 50 oC, a sharply reduced exhibits almost the same conversion (84%) under relatively mild
conversion was obtained but yet without significantly ee value conditions (entry 5, in Table 2). In addition, the catalytic capability
(entry 4, Table 2). Further lowering the temperature to 25 oC only of 1 is higher than that of our previously reported Ni(salen)-based
produced a negligible conversion. These results imply that 1 may MOFs.6d, 6e A rational explanation for the higher activity of 1 is that
not fit the enantioselectivity catalysis for the synthesis of cyclic it is a microporous material, which benefits CO2 capture and
carbonates from CO2 and racemic epoxides. Nevertheless, we accordingly increases the reaction concentration of CO2, as well as
envision that this highly stable chiral MOF catalytic material might the synergistic Lewis acidic activation of high density Ni(salen) units
have potential value in other asymmetric catalytic reactions.
in 1D channels. Therefore, 1 represents a rare example of highly
Based on above optimum conditions, the catalytic system was stable MOF for efficient conversion of CO2 (or involving tiny
then investigated for other epoxides such as epichlorohydrin, 1,2- amounts of water vapor and/or SO2) under relatively mild
epoxyhexane and 1,2-epoxyoctane (Table 3). The excellent conditions.
conversion of epichlorohydrin can be ascribed to the electron-
According to the above experimental results and previous
withdrawing Cl group which facilities the nucleophilic attack of Br- reports,15 we proposed the reaction was initialized by the activation
during the ring opening of the epoxides (entry 1, Table 3). 1,2- of epoxides through the coordination to unsaturated Ni2+ ions inner
epoxyhexane and 1,2-epoxyoctane give the corresponding cyclic the channels. The adjacent unsaturated Ni2+ ions were responsible
carbonates with a conversion of 65% and 42%, respectively (entries for the capture and polarization of CO2. Then, the activated
3 and 4, Table 3). The gradually reduced activity could mostly be epoxides were attacked by Br- generated from TBAB at the less
attributed to the confinement of the channel size of 1, which hindered carbon atom to provide intermediate alkoxide species.
restricts the diffusion rate of larger substrate and product through The polarized CO2 interact with oxygen anion of the intermediate
the channel. The size-dependent selectivity observed here suggests alkoxide to generate metal carbonates, which undergoes
that the catalysis reaction took place in the channels not on the intramolecular ring-closure to give the corresponding cyclic
catalyst surface.
carbonates (Fig. S13 in SI).
8 | J. Name., 2012, 00, 1-3
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the high efficiency of 1 for this reaction. 1,2-epoxyhexane and 1,2-
epoxyoctane were found to have similar yields of 77% and 73%,
respectively (entries 3-4, Table 4). In view of the large sizes of the
corresponding products, we proposed these catalysis might be
occurred on the surface of MOF. It was observed that bis-triazole
could be obtained when epichlorohydrin was used as the substrate
(entry 1, Table 4). This can be explained by the presence of Cl- as
good leaving group to allow for a second addition.26, 27 The catalyst
could be reused for three consecutive cycles without apparent loss
of activity and the PXRD pattern of the recovered catalyst remain
unchanged after catalytic reaction (Fig. 6). AAS analysis of the
filtrate also indicates no metal leaching into the filtrate. Control
experiment revealed that ligand L was far less effective in catalyzing
the conversion of styrene oxide into corresponding product (with
only 8% isolated yield) and inorganic salt CuI (1 mol%) gave product
with 82% conversion, which indicated the reaction is catalyzed by
Cu+ ion. The proposed mechanism for this reaction involves two
paths: 1) Cu+ firstly activate the epoxide which was then attacked
by N3- at the less hindered carbon atom to provide a 2-azido-1-
phenylethanol intermediate; and 2) phenylacetylene then interacts
with Cu+ to give Cu-acetylide intermediate, which was followed by
the addition to 2-azido-1-phenylethanol to generate the final
product.26 These results further evidence the applicability of 1 as an
effective heterogeneous catalyst in aqueous solution.
f
e
d
c
b
a
10
20
30
40
2 theta/degree
Fig. 6 (a) Simulated PXRD pattern from CIF file; (b) PXRD pattern of as-synthesized
1; (c) PXRD pattern of 1 after cycloaddition of epoxide with pure CO2; (d) PXRD
pattern of 1 after cycloaddition of epoxide with CO2 and H2O; (e) PXRD pattern of
1 after cycloaddition of epoxide with CO2, H2O and SO2; (f) PXRD pattern of 1
after cycloaddition of epoxide with alkyne and azide.
Table 3. The sysnthesis of various cyclic carbonates catalyzed by 1.a
Entry
Substrate
Product
Yield( %)b
TONc
200
O
O
O
O
1
99(99)
Cl
Cl
O
O
O
O
O
84(99)
168
2
3
4
O
Conclusions
O
65(99)
42(99)
130
84
O
O
O
O
In summary, we successfully construct a highly stable chiral
Ni(salen)-based MOF possessing 1D open channel using the
multi-strategies integration involving ligands hydrophobicity,
framework interpenetration and topologic structure. PXRD and
N2 adsorption confirmed its crystallinity and porosity
maintained under high temperature (> 400 oC), in water vapor,
in acid/base aqueous solution (pH 0-14), and in saturated
NaOH solution at 100 oC, as well as in common oxidants
aqueous solution (30 wt% H2O2 and 70 wt% tert-butyl
hydroperoxide). As a heterogeneous catalyst, this MOF can
efficiently catalyze the cycloaddition of simulated industrial
CO2 with epoxides, as well as cycloaddition of epoxides with
azides and alkynes under mild conditions. Furthermore, the
catalyst can be easily separated and reused for successive
three cycles without significant loss of the activity and
structure integrity. These results not only promote the
synthetic strategy of MOFs with high acid-base resistance, but
also greatly extend the scope of applications for salen-based
MOF, especially in aqueous media. The exploration of this
highly stable chiral MOFs enantioselective activities in
asymmetric catalysis is ongoing in our laboratory.
O
aReaction conditions: substrate (2 mmol), catalyst (0.5 mol%), TBAB (0.5mol%),
CO2 (1 atm), 100 oC, 12 h. bDetermined by GC-MS. cTON: moles of cyclic
carbonate per mole of catalyst used.
Cycloaddition of epoxides with azides and alkynes catalyzed by 1
Of special interests are β-hydroxy-1,2,3-triazoles that are often
used in industrial applications, such as anti-HIV, anti-bacterial and
anti-allergy. Cu+ ion is highly efficient for the multi-component
synthesis of β-hydroxy-1,2,3-triazoles via in situ azidolysis of
epoxides in the presence of alkynes with water as solvent. So far,
various solid materials such as SiO2,26 zeolites27 and activated
carbon28 have been modified by Cu+ and act as effective catalysts
for the formation of β-hydroxy-1,2,3-triazoles. As most MOFs
suffered from weak water stability, this reaction with water as
solvent is still not realized by MOFs catalysts. Owing to the
extremely superior water endurance and potential Cu+ catalytic
sites of 1, we investigated the synthesis of value-added triazoles
from the same epoxides above used. Identically, styrene oxide was
used as the model substrate and the optimized reaction conditions
involved 1 mmol epoxides, 1.1 mmol sodium azide, 1.1 mmol
phenylacetylene in the presence of 1 mol % of 1 and 3 mL of H2O at
Acknowledgements
The authors thank the National Key Research and
Development Program of China (2016YFA0602900) and the
National Natural Science Foundation of China (21372087 and
21420102003) for the financial support.
o
60 C for 24 h (entry 2, Table 4). The catalytic results revealed that
all substrates showed moderate to excellent conversions, indicating
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Table 4. The synthesis of various β-hydroxy-1,2,3-triazoles catalyzed by 1.a
Cui, Chem. Commun. 2016, 52, 13167-13170; (c) A. Bhunia, S.
Dey, J. M. Moreno, U. Diaz, P. Concepcion, K. Van Hecke, C.
Entry
Substrate
Product
Yield (%)b
TONc
N
N
Janiak and P. Van Der Voort, Chem. Commun. 2016, 52
1401-1404; (d) Y. W. Ren, Y. C. Shi, J. X. Chen, S. R. Yang, C. R.
Qi and H. F. Jiang, RSC. Adv. 2013, , 2167-2170; (e) Y. W.
,
N
N
O
N
N
OH
1d
81
81
Cl
3
HO
Ren, X. F. Cheng, S. R. Yang, C. R. Qi, H. F. Jiang and Q. P.
Mao, Dalton Trans. 2013, 42, 9930-9937; (f) J. M. Falkowski,
O
N
2
3
N
N
C. Wang, S. Liu and W. B. Lin, Angew. Chem. Int. Ed. 2011, 50
,
89
77
73
89
77
73
8674-8678; (g) F. J. Song, C. Wang, J. M. Falkowski, L. Q. Ma
and W. B. Lin, J. Am. Chem. Soc. 2010, 132, 15390-15398.
G. Ferey, C. Mellot-Draznieks, C. Serre, F. Millange, J. Dutour,
S. Surble and I. Margiolaki, Science. 2005, 309, 2040-2042.
J. H. Cavka, S. Jakobsen, U. Olsbye, N. Guillou, C. Lamberti, S.
HO
7
8
N
N
O
N
Bordiga and K. P. Lillerud, J. Am. Chem. Soc. 2008, 130
13850-13851..
,
HO
N
N
N
9
K. S. Park, Z. Ni, A. P. Cote, J. Y. Choi, R. Huang, F. J. Uribe-
Romo, H. K. Chae, M. O'Keeffe and O. M. Yaghi, P. Natl.
Acad. Sci. 2006, 103, 10186-10191.
O
4
aReaction conditions: substrate (1 mmol), NaN3 (1.1 mmol), alkyne (1.1 mmol),
catalyst (1 mol%), H2O (3 mL), 60 oC, 24 h. bDetermined by isolated yields. TON:
moles of cyclic carbonate per mole of catalyst used. dNaN3 (2.2 mmol) and alkyne
10 (a) F. Drache, V. Bon, I. Senkovska, C. Marschelke, A.
Synytska and S. Kaskel, Inorg. Chem. 2016, 55, 7206-7213; (b)
S. Øien-Ødegaard, B. Bouchevreau, K. Hylland, L. Wu, R.
Blom, C. Grande, U. Olsbye, M. Tilset and K. P. Lillerud, Inorg.
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