Two Stable Heterometal-MOFs as Highly Efficient and Recyclable Catalysts in the CO2 Coupling Reaction with Aziridines

Article abstract of DOI:10.1002/asia.201900712

Two stable heterometal-organic frameworks, {Na[LnCo(DATP)₂(Ac)(H₂O)](NO₃)?DMA?11 H₂O}_n (Ln=Er(1) and Yb(2)), have been prepared with H₂DATP (4′-(3,5-dicarboxyphenyl)-2,2′:6′,2′′′-terpyridin

Full text of DOI:10.1002/asia.201900712

CHEMISTRY
AN ASIAN JOURNAL
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Accepted Article
Title: Two Stable Heterometal-MOFs as High-efficiency and Recyclable
Catalysts in the CO2 Coupling Reaction with Aziridines
Authors: Bin Zhao, Xiao-Min Kang, Lin-Hong Yao, and Zhuo-Hao Jiao
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Two Stable Heterometal-MOFs as High-efficiency and Recyclable
Catalysts in the CO2 Coupling Reaction with Aziridines
Xiao-Min Kang, Lin-Hong Yao, Zhuo-Hao Jiao and Bin Zhao*
Abstract:
Two
stable
heterometal-organic
frameworks
and
α-amino
acids,
and
so
forth.[9]
However,
{Na[LnCo(DATP)2(Ac)(H2O)](NO3)·DMA·11H2O}n (Ln = Er(1) and
Yb(2)) have been harvested with H2DATP (4'-(3,5-dicarboxyphenyl)-
2,2':6',2'''-terpyridine) as organic building block. These two
the only fly in the ointment is that the homogenous catalysts are
hard to be separated and recovered, limiting their practical
application
to
some
extent
and
being
contrary
isostructural
compounds
featuring
two-dimensional
layer
to the sustainable development. Comparably, heterogeneous
catalyst with excellent catalytic activity and recyclability plays a
crucial part in industrial production.
architectures possess outstanding thermal stabilities and excellent
chemical stabilities in common organic solvents and different
acid/base solutions with pH range changing from 1 to 13. Moreover,
compounds 1 and 2 serving as heterogeneous catalysts can
efficiently catalyse the CO2 fixation reaction with various aziridines to
result in corresponding oxazolidinones at 70°C. Importantly, the
good recyclable performance of 1 is observed in experimental
results at least ten times, which are further confirmed by PXRD, TGA
and ICP analyses.
Metal-organic frameworks (MOFs) composed by metal nodes
and organic blockings are sought after by scientific workers on
account of their charming architectures,[10] diverting properties
and potential applications.[11] Importantly, MOFs can be
exploited for the CO2 coupling reactions with terminal alkynes,
propargylic alcohols, propargylamines, aziridines and epoxides
as high-efficiency and recyclable heterogeneous catalysts.[12] To
the best of our knowledge, no heterometal-MOF as catalyst for
CO2 fixation with aziridines has been reported up to now.
In this contribution, two novel heterometal-MOFs have been
Introduction
harvested
characterized,
by
solvothermal reaction
formulated
and
structurally
as
In recent years, a series of energy and environmental problems
have gained utmost attention along with the acceleration of
industrialization.[1] On account of excessive consumption of
fossil fuels, a mass of pollutants have been produced, in which
waste gas as one of the main contaminants will cause air
pollution to threaten the safety of human and nature. Carbon
oxide (CO2), an important greenhouse gas derived from human
and industrial actions will be answerable for the climate change,
global warming and acid rain.[2] Meanwhile, CO2 serving as an
attractive C1 source can be extensively used in the synthetic
chemistry with many advantages, including nontoxic, abundant,
cheap and renewable features.[3] Hence, meeting the
requirements of CO2 capture and utilization simultaneously is
urgent and meaningful. For this purpose, a lot of efforts have
been put into the CO2 coupling reaction with heterocyclic
compounds to form multifarious high-valued chemicals, covering
oxazolidinones, cyclic carbonates, dimethyl carbonate, formic
acid and alkynyl carboxylic acid products, which are acquired
from fossil fuel resources currently.[4] It is worth mentioned that
the CO2 conversion with aziridines into oxazolidinones
stimulated tremendous interest on the basis of their efficient
reaction capacity, satisfactory atom utilization and ideal reaction
products. Oxazolidinones are of the particular importance not
only because they can be regarded as the chiral auxiliaries and
intermediates in organic synthesis,[5] but also they can be
applied to the pharmaceutical chemistry as antimicrobial
pharmaceuticals, like radezolid,[6] tedizolid[7] and linezolid.[8]
Previously, different kinds of homogenous catalysts perform
good catalytic activities in CO2 cycloaddition reaction with
aziridines, such as alkali metal halide, tetraalkylammonium salt
{Na[LnCo(DATP)2(Ac)(H2O)](NO3)·DMA·11H2O}n (Ln = Er (1)
and Yb (2), H2DATP 4'-(3,5-dicarboxyphenyl)-2,2':6',2'''-
=
terpyridine). Compound 1 possesses superior resistance to
various organic solvents and acid/alkali solutions with pH range
changing from 1 to 13. Particularly, with compounds 1 and 2 as
catalysts, efficient catalytic performances and ideal targets
(oxazolidinones) have been observed in the cycloaddition
reactions of CO2 and aziridines with various substituents under
different conditions. Moreover, 1 can be recycled at least ten
times with negligible change in catalytic activity, which is
confirmed by PXRD, TGA and ICP analyses.
Results and Discussion
Description for the Crystal Structure of
{Na[ErCo(DATP)2(Ac)(H2O)](NO3)·DMA·11H2O}n (1)
Compounds 1 and 2 were harvested by the reaction of mixed
solvents DMA/H2O (3:3), H2DATP ligand and Ln(NO3)3·5H2O
(Ln = Er (1) and Yb (2)) under solvothermal conditions. Single-
crystal diffraction analyses demonstrate that compounds 1 and 2
all crystallize in the monoclinic P21/c space group. In view of
these two structures are isomorphous, compound 1 as the
representative example was introduced in detail for the structural
analysis. As described in Figures. 1a and 1b, the asymmetric
unit of compound 1 contains one crystallographically distinct Er3+,
one independent Co2+ and two DATP2- as well as one
coordinated Ac-, one coordinated water molecule and one free
-
Na+, one NO3 , one DMA and eleven water molecules. The
-
presence of NO3 was confirmed by IR spectrum. Each seven-
[a]
Dr. X. Kang, Prof. B. Zhao
coordinated center Er3+ is completed by four carbonyl oxygen
atoms (O2, O6, O7, O10) from four different DATP2-, one water
molecule and two oxygen atoms from one Ac-, presenting an
irregular decanedron coordination configuration. By contrast, the
Co2+ occupying the center of octahedron adopts six-coordinated
College of Chemistry and Key Laboratory of Advanced Energy
Material Chemistry
Nankai University
Tianjin, 300071 (China)
E-mail: zhaobin@nankai.edu.cn
1
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geometry configuration and is chelated by six nitrogen atoms
(N1, N2, N3, N4, N5 and N6) from two H2DATP ligands. The Er-
O and Co-N bond lengths fall into the range of 2.201(4)-2.382(5)
Å (average 2.287 Å) and 1.851(5)-1.945(5) Å (average 1.913 Å),
respectively. The O-Er-O and N-Co-N bond angles change from
54.48(15)° to 178.15(17)° and 82.4(2)° to 178.5(2)°, respectively
(Table S1 in the Supporting Information). These data mentioned
above agree well with the reported those previously.[13] In
compound 1, the framework consists of two diverse building
blocks [Er(COO)4(Ac)(H2O)] and [Co(DATP)2], which are
connected by each other through H2DATP ligands to form a 2D
layer architecture (Figure 1c). A distinct structural feature in
compound 1 is that it possesses strong π-π stacking interactions
between two paralleled benzene rings in neighboring H2DATP
ligands (the distance between ring centroids is about 3.5749 Å,
and the dihedral angles range from 0 to 5.547°). The large
PXRD Analyses
The powder X-ray diffraction (PXRD) measurements have been
carried out for compounds 1 and 2. As presented in Figure S2 in
the supporting information, good agreement between the
experimental patterns and simulated one indicates high purity of
1 and 2. To further evaluate the solvents stability and pH stability
of compound 1, the crystal samples were soaked in common
organic solvents (1,4-dioxane, MeOH, n-BuOH, i-PrOH, CHY,
DMF, CH3CN, CH2Cl2, CCl4 and EtOH) and acid/base solutions
with different pH values falling into the range of 1 to 13 for 12 h,
respectively. The peaks of treated samples are in consistence
with the simulated ones, implying the structural integrity of
framework 1 (Figures S3 and S4 in the Supporting Information).
Consequently, the experimental results demonstrate that 1 owns
outstanding solvent stability and excellent acid/base stability
ranging from pH1 to pH13.
conjugated
π
electron system possibly makes
a great
contribution to the architectural stabilization of framework 1.[14]
TGA Investigations
The thermogravimetric analyses (TGA) were tested in the
temperature range from 30 to 700°C under N2 atmosphere to
explore the thermal stability of compounds 1 and 2, as shown in
Figure S5 in the Supporting Information. The TGA curves reveal
a weight loss of about 20.44% from 25°C to 355°C (calculated
20.72% and 20.63% for compounds 1 and 2, respectively),
which is ascribed to the removal of eleven free water molecules,
one free DMA molecule and one coordinated water molecule.
Then, a continuous weight loss can be observed beyond about
355°C , indicating the collapse of these frameworks. Therefore,
both compounds 1 and 2 perform high thermal stabilities above
355°C .
Catalytic Characterization
Given the unsaturated Ln3+ Lewis-acid sites in compounds 1 and
2, the catalytic abilities of them have been evaluated in the CO2
fixation reaction with aziridines. Then, the CO2 adsorption of
compounds 1 and 2 at 298 K have been be tested, as indicated
in Figure S6. Taking compound 1 as example, firstly, the
cycloaddition reaction of CO2 and probe substrate 1-ethyl-2-
phenylaziridine (a) into oxazolidinone has been carried out
under 2 MPa for 10 h with 0.1 mmol tetrabutylammonium
bromide (TBAB) and 20 mg compound 1 (0.68 mol% based on
center metal) serving as additive and catalyst, respectively. As
shown in Table 1 (entries 1–4), the catalytic performances for
the transformation from 1-ethyl-2-phenylaziridine (a) to 3-ethyl-5-
phenyloxazolidin-2-one (b) and 3-ethyl-4-phenyloxazolidin-2-one
(c) rise first and then fall from 30°C to 90°C. The experimental
results demonstrate that both lower and higher temperatures will
take the edge off the catalytic efficiency, and quantitative yield
(96%) and high selectivity have been observed at 70°C (Table 1,
entry 3). Secondly, the influence of other key parameters on
catalytic activity of the reaction have been investigated at 70°C ,
including CO2 pressure, reaction time as well as the amounts of
TBAB and sample 1. Entries 5 and 6 in Table 1 present different
catalytic results that the desired products have been gained with
yields of 94% and 25% at 1 MPa and 0.1 MPa, respectively.
Comparably, 1 MPa was selected as the first-rank CO2 pressure.
Then, shortening the reaction time from 10 h to 5 h, the yield of
corresponding product decreases by ten percent (Table 1, entry
Figure 1. a) The asymmetric unit of compound 1. b) The coordination
environments of Er3+, Co2+ and DATP2-. c) View of 2D-layer structure of 1. d)
Topological representation of 1. Color codes for atoms: green sphere, Er; pink,
Co; red, O; gray, C; blue, N. H atoms and solvent molecules are omitted for
clarity.
In order to get a better insight into the complicated framework
of 1, the freely available TOPOS software package was
employed.[15] Then, each [Er(COO)4(Ac)(H2O)] unit considered
as a 4-connected node links four DATP2-, and each Co2+ serving
as a 2-connected spacer connects two DATP2-, and each
DATP2- belongs to
a 3-connected node coordinates two
[Er(COO)4(Ac)(H2O)] units and one Co2+. In result, the 2D layer
structure of 1 can be simplified into a 3,4-connected double-
nodal topological network with the Schläfli symbol of
{4;6^2}2{4^2;6^2;8^2} (Figure 1d).
IR Studies
IR spectra of compounds 1 and 2 were performed at room
temperature and exhibited characteristic bands (Figure S1 in the
Supporting Information). The bands centered at v = 1366 and
1370 cm-1 for compounds 1 and 2 respectively are assigned to
-
the presence of NO3 .
2
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7). Then, the catalytic activity shows obvious reduction when
0.05 mmol (16.11 mg) co-catalyst TBAB was used (Table 1,
entry 8). With regard to catalyst amount, the yield change of
reaction products can be ignored although the sample 1 reaches
to 40 mg (Table 1, entry 9). Nevertheless, when 0.1 mmol TBAB
was applied alone to the CO2 transformation at 70°C , only 45%
yield for 3-ethyl-5-phenyloxazolidin-2-one has been harvested
(Table 1, entry 13), indicating the synergistic effect between co-
catalyst TBAB and Er3+ Lewis-acid active sites. Consequently,
the best reaction conditions should be 70°C under 1 MPa with
0.1 mmol TBAB and 20 mg catalyst for 10 h in solvent-free
system. What is particularly noteworthy is that compound 1
features the first heterometal-MOF based catalyst for the CO2
coupling with aziridines to result in corresponding
oxazolidinones.
Previously, some transition metal-based MOFs as catalysts for
this catalytic reaction have been reported, like [Cu30], [M2] (Co,
Mn and Ni), [Zn24] and MMPF-10 (M = Zr). For [Cu30], it performs
optimal yield of 99% for target product at 100°C under 2 MPa
CO2 pressure with 80 mg catalyst for 12 h.[16] Adopting the same
temperature and CO2 pressure with [Cu30], MMPF-10 has
obtained similar yield in 10 h.[17] Additionally, [M2] (Co, Mn and
Ni) can catalyze the CO2 conversion to form oxazolidinones
under mild conditions with quantitative yield (86% - 89%): 30°C ,
1 MPa, 10 h, 0.1 mmol TBAB and 20 mg catalyst.[18] Moreover,
with 20 mg [Zn24] as catalyst, good activity and excellent yield
(99%) have been observed under 2 MPa at 70°C for 12 h.[19]
Therefore, on the basis of previous work, the result of high-
efficiency catalysis will be met at the expense of higher
temperature, higher CO2 pressure, longer time or more catalyst
amount. In comparison, compound 1 can catalyze the reaction
more easily than [Cu30], [Zn24] and MMPF-10, and possesses
more outstanding catalytic capacity than [M2] (Co, Mn and Ni).
Then, the catalytic performance of compound 2 has been
assessed by the same strategy, and supreme conditions are
identified as 70°C , 2 MPa CO2, 20 mg catalyst 2 and 0.1 mmol
TBAB for 10 h. More rigorous CO2 pressure for compound 2
than 1 may be attributed to more superior Lewis-acid activity for
Er3+ than Yb3+ (Tables S3 in the Supporting Information).
Table 1. Cycloaddition reaction of CO2 with 1-ethyl-2-phenylaziridine under
various conditions. a)
Sequentially, we further study the catalytic potential of these
two compounds in CO2 cycloaddition reaction with some typical
aziridines substituted by different groups under optimized
conditions (the synthetic process of aziridines in Scheme S1 in
the Supporting Information). Then, the experimental results
listed in Table 2 (entries 1-5) reveal that the yields of
corresponding oxazolidinones change with the size and types of
substituent groups in substrates. For entries 1-3 in Table 2,
three aziridines with different substituent groups of ethyl, propyl
or butyl at the nitrogen atoms respectively have been utilized to
participate in the catalytic reaction. The results indicate that 1-
ethyl-2-phenylaziridine (Table 2, entry 1) owns better catalytic
property than 1-propyl-2-phenylaziridine and 1-butyl-2-
phenylaziridine (Table 2, entries 2 and 3), giving rise to different
yields from 94% to 91% in descending order for them. The
higher catalytic efficiency for 1-ethyl-2-phenylaziridine is possibly
ascribed to smaller steric hindrance for the ethyl than the propyl
and butyl group. Moreover, using 1-ethyl-2-(4-chlorophenyl)-
aziridine and ethyl-2-p-tolylaziridine as substrates, 3-ethyl-5-(4-
Entry
1
Catalyst 1 [mg]
T [°C]
30
50
70
90
70
70
70
70
70
70
70
70
70
Yieldb) [%]
37
Conversionc)
Regio-seld)
91:9
98:2
99:1
99:1
99:1
91:9
96:4
98:2
99:1
93:7
93:7
94:6
98:2
20
20
20
20
20
20
20
20
40
0
41
87
97
95
95
27
87
86
93
33
36
38
46
2
85
3
96
4
94
5e)
6f)
7g)
94
25
84
)
8h
84
9
92
chlorophenyl)oxazolidin-2-one
(86%)
and
ethyl-5-p-
10i)
11j)
31
tolyloxazolidin-2-one (70%) have been achieved by the CO2
fixation reactions (Table 2, entries 4 and 5). Hence, catalyst 1
can effectively catalyze the coupling reaction of CO2 and
multifarious aziridines in solvent-free system under 1 MPa
pressure at 70°C. The corresponding by-products of these CO2
cycloaddition reactions are detected and notified by 1H NMR
analyses (Figure S7).
0
34
)
12k
0
36
13
0
45
Next, we also have evaluated the reaction activity of
compound 2 in CO2 cycloaddition with various substituted
aziridines under similar conditions to compound 1 except for the
reaction pressure (2 MPa). As displayed in Table S4 in the
Supporting Information, final yields of corresponding
[a] Reaction conditions: 1-ethyl-2-phenylaziridine (294.4 mg, 2.0 mmol),
solvent-free, catalyst 1, TBAB (32.2 mg, 0.1 mmol), CO2 (2.0 MPa), 10 h, 20
mg catalyst 1 loading (based on metal center, about 0.68 mol%); [b] Total
yields of b and c determined by 1H NMR using 1,3,5-trimethoxybenzene (42.1
mg, 0.025 mmol) as an internal standard; [c] The conversion of products; [d]
Molar ratio of b to c; [e] CO2 (1.0 MPa); [f] CO2 (0.1 MPa); [g] t (5 h); [h] TBAB
(16.1 mg, 0.05 mmol); [i] TBAB (32.2 mg, 0.1 mmol) and Er(Ac)3·4H2O (5.69
mg, 0.014 mmol); [j] TBAB (32.2 mg, 0.1 mmol) and Er(NO3)3·5H2O (6.06 mg,
0.014 mmol); [k] TBAB (32.2 mg, 0.1 mmol) and ErCl3·6H2O (5.22 mg, 0.014
mmol).
oxazolidinones catalyzed by crystal
2
present the
same varying tendency in comparison with those catalyzed by 1:
3-ethyl-5-phenyloxazolidin-2-one with highest yield of 98%
(Table S4 in the Supporting Information, entry 4) and ethyl-5-p-
tolyloxazolidin-2-one (Table S4 in the Supporting Information,
entry 5) with the lowest yield of 70%. Considering the same
3
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structures of compounds 1 and 2, we speculate that the
otherness of Lewis-acid activity for Er3+ and Yb3+ may take the
responsibility for diverse catalytic abilities of compounds 1 and 2
and different reaction conditions.
Moreover, the stability of recovered 1 have been further
confirmed by PXRD, IR, TGA and ICP analyses. As indicated in
Figure S8 in the supporting information, the PXRD experiments
after ten catalytic recycling have been carried out. All PXRD
peak positions and intensity of recycled 1 agree well with those
of as-synthesized 1, proving the structural integrity and chemical
stability of the sample 1. Simultaneously, the consistency of the
IR spectra between sample 1 and the one after ten catalytic
recycles indicates its excellent stability (Figure S9). From the
TGA cure of recycled 1, it can be seen that the framework tends
to decompose over 350°C, which provides a fundamental
guarantee for catalyst 1 in high temperature environment (Figure
S10). Additionally, trace leakage of Er3+ ion (0.056%) for the
mixture filtrate after ten recycles was detected through ICP test,
indicative of the high stability of structure (Table S5).
Table 2. Synthesis of various oxazolidinones from CO2 and aziridines with
catalyst 1.a)
Entry
1
Substrate
Conv.b) [%]
Yieldb) [%]
Regio-selc)
99
94
99:1
2
3
99
99
92
91
96:4
94:6
Figure 2. Recycle experiments for the coupling reaction of CO2 with 1-ethyl-2-
phenylaziridine have been conducted for 10 h at 70°C under 1 MPa with 0.1
mmol TBAB and 20 mg catalyst in solvent-free system.
4
5
97
95
86
70
98:2
97:3
Finally, in order to better make the catalytic mechanism clear,
a variety of Erbium sources have been employed to catalyze the
CO2 fixation with aziridines, including Er(Ac)3, Er(NO3)3 and
ErCl3 (0.014 mmol). The low yields of corresponding
oxazolidinones were 31%, 34% and 36% respectively, revealing
that both free Er3+ and these three inorganic anions have no
obvious catalytic effects on the CO2 cycloaddition reaction
(Table 1, entries 10-12). In comparison, the yields of
oxazolidinones with Er-salts serving as catalyst and TBAB as
co-catalyst are inferior to that catalyzed solely by TBAB (45%),
which could be due to the interaction between free metal ions
with Br- ions to hinder the nucleophilic attack. However, when
the same amount of catalyst 1 takes the place of Er-salt to
catalyze the reaction, the optimum yield (94%) of target product
and excellent selectivity have been obtained in terms of other
conditions unchanged. Actually, the remarkable enhancement in
catalytic efficiency may be attributed to next two factors: (a) The
unsaturated seven-coordinated Ln3+ featuring more Lewis-acid
sites can effectively activate the substrates and CO2, which
benefits the acceleration of catalytic reaction; (b) The excellent
chemical stabilities and high thermostability ensure the structural
integrity during catalysis, providing more opportunities for the
nucleophilic attack of Br− towards aziridines without the
coordination interaction between free Ln3+ and Br- ions.
[a] Reaction conditions: aziridine (2.0 mmol), solvent-free, 20 mg catalyst 1
loading (based on metal center, about 0.68 mol%), TBAB (32.2 mg, 0.1 mmol),
CO2 (1.0 MPa), 10h; [b] Determined by 1H NMR using 1,3,5-
trimethoxybenzene (42.1 mg, 0.025 mmol) as an internal standard; [c] Molar
ratio of N2 to N3.
In fact, we all know that the recyclability of heterogeneous
catalyst plays an essential part in practical applications. Then,
the recycle performance of compound 1 has been explored in
the CO2 cycloaddition reaction. Through centrifugation and
filtration strategies, the compound 1 was separated from the
residue after reaction. The recycle experiments were repeated
ten times, and no significant change in catalytic activity could be
observed. The yields of oxazolidinones range from 94% (the first
run) to 89% (the tenth run) for compound 1 (Figure 2). As
described above, compound 1 features excellent chemical
stability in various organic solvents and acid/base solutions with
pH range from 1 to 13. After the catalytic cycloaddition reaction
of CO2 with aziridines, compound 1 still remains crystalline state
and no significant change in crystal color has been observed.
4
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In consideration of previous reports,[16-19] the possible
mechanism has been presumed for 1/TBAB-catalyzed CO2
fixation with aziridines into oxazolidinones (Figure S11 in the
Supporting Information). For the catalyst 1 as example, firstly,
the 2D framework of 1 enriched CO2 and substrate, and the
substrate was activated by unsaturated Erbium Lewis-acid sites
binding the N atom from aziridine. Then, the nucleophilic attack
of Br- on the aziridine gives rise to ring-opening process with two
different routes a and b. Subsequently, carbamate salt has
come into being by the reaction of CO2 and N atom from ring-
opened intermediate. Intramolecular ring-closing reaction
produces the corresponding oxazolidinone finally. With respect
of regioselectivity, N2 has been gained as the primary product
through path a with more stable carbamate salt intermediates.
NaC52H62CoErN8O26: C, 42.65; N, 7.65; H, 4.24. Found: C,
42.49; N, 7.51; H, 4.31 (Table S6 in the Supporting
Information).
Synthesis of compound 2
The synthesis of compound 2 is similar to that of 1, except that
Er(NO3)3·5H2O takes the place of Yb(NO3)3·5H2O (0.0112g,
0.025 mmol). Coupling the H2DATP ligand and Yb(NO3)3·5H2O
in mixed solvents (DMA/H2O) in 7 mL capped vial under same
hydrothermal conditions afforded orange block single crystals
(88% yield based on Yb(NO3)3·5H2O). Elemental analysis (%)
for 2 (NaC52H62CoN8O26Yb), Calcd: C 42.48, H 4.22, N 7.62.
Found: C 42.35, H 4.33, N 7.48 (Table S6 in the Supporting
Information).
Conclusions
General Methods and Characterization
In conclusion, two stable 2D heterometal-MOFs, named as
{Na[LnCo(DATP)2(Ac)(H2O)](NO3)·DMA·11H2O}n (Ln = Er(1) and
Yb(2)), have been prepared through solvothermal synthesis
technique and further structurally characterized. TGA and PXRD
investigations reveal that they own high thermostability and
strong resistance against various organic solvents and acid/base
The Fourier transform infrared (FT-IR) spectra were measured
by a Bruker Tensor 27 spectrophotometer as KBr pellets in the
range at 400 - 4000 cm−1. The element analyses (EA) data for C,
N and H were collected on Perkin-Elmer elemental analyzer.
Powder X-ray diffraction (PXRD) data were recorded on a
Rigaku D/Max-2500 diffractometer by using Cu Kα radiation (λ =
1.54056 Å) with a scan speed of 5° min−1 and 2θ region from 3°
to 60°. The thermogravimetric analyses (TGA) were performed
by a Netzsch TG 209 TG-DTA analyzer with test temperature
from 25°C to 700°C under nitrogen atmosphere. The 1H NMR
spectra of the catalytic products were monitored through a
Bruker 300 spectrometer and 1,3,5-trimethoxybenzene was
served as internal reference with chemical shifts in ppm. The
leakage contents of metal ions (Eu3+ and Yb3+) after catalytic
recycling in filter liquor were characterized by ICP-9000(N+M)
spectrometric analyses.
solutions with wide pH range (1
-
13). Importantly,
heterogeneous catalysts 1 and 2 can be applied for the CO2
cycloaddition with ten substituted aziridines to form high-value
products,
showing
excellent
catalytic
activity
and
environmentally friendly merit. Particularly, the catalytic activity
of recovered 1 can remain uncharged in comparison with
original one after ten recycling. To the best of our knowledge,
compound 1 belongs to the first heterometal-MOFs based
catalyst for the cycloaddition of aziridines and CO2.
General procedure for the CO2 coupling with aziridines to form
oxazolidinones was described as following: taking compound 1
as example, first step, 2 mmol the corresponding aziridines, 0.1
mmol tetrabutylammonium bromide (TBAB) (32.2 mg), and 20
mg 1 (0.014 mmol) (corresponding to 0.68 mol% metal center)
were slowly introduced into stainless-stale reaction vessel (25
mL). Then CO2 (2 MPa) was introduced into the vessel by using
carbon dioxide gas-holder and the resulting reaction mixture was
stirred at different temperatures, respectively. After 10 h, when
the reaction was cooled down to room temperature, 0.025 mmol
1,3,5-trimethoxybenzene (42.1 mg) as an internal standard and
5 mL CH2Cl2 were added into the reaction products. The mixture
was stirred 5 min and the desired product was applied to 1H
NMR after distillation under reduced pressure.
Experimental Section
Materials
All the chemicals including metal salts, organic ligand and
solvents utilized in this work for crystals preparation were
purchased without further purification. Erbium nitrate
pentahydrate (Er(NO3)3·5H2O, 99 wt%) and Ytterbium nitrate
pentahydrate (Yb(NO3)3·5H2O, 99 wt%) were provided by
Energy Chemical (China). H2DATP ligand (97 wt%) and DMA
solvent were achieved from Jinan heng chemical and Concord
(China), respectively.
Synthesis of Compound 1
Single-Crystal Structure Determination
Er(NO3)3·5H2O (0.0090 g, 0.02 mmol) and 4'-(3,5-
dicarboxyphenyl)-2,2':6',2'''-terpyridine (0.0099 g, 0.025
mmol) were dissolved in a DMA/H2O mixture with solvent
ratio of 1:1 (3 mL : 3mL). Addition of 100 µL HNO3 was
employed to regulate the pH value of the solution. Then the
resulting mixture was sealed in a 7 mL capped vial, and
was heated at 100 °C for 3 days under autogenous
pressure. The solvothermal reaction was cooled slowly
down to room temperature at 2 °C /h. Orange block crystals
Suitable crystals 1 and 2 were picked for single-crystal X-ray
diffraction analyses under
a cooled N2 atmosphere. All
crystallographic measurements were carried out by a Super
Nova Single Crystal Diffractometer configured with a graphite-
monochromatic Mo-Kα radiation (λ = 0.71073 Å). The - scan
technique was employed, and the crystal data was corrected for
Lorentz-polarization effects. Then, the structures of compound 1
and 2 were solved by directed methods and refined by using full-
matrix least squares on F2 with SHELXS and SHELXL
programs.[20] In terms of non-hydrogen atoms, they were refined
of compound
1 were prepared (89% yield based on
Er(NO3)3·5H2O). Element analysis (%) calcd for
5
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10.1002/asia.201900712
Chemistry - An Asian Journal
FULL PAPER
The authors declare no conflict of interest.
by utilizing anisotropic parameters while all the hydrogen atoms
were placed in calculated positions and refined employing a
riding model. In consideration of seriously disordered solvent
molecules in compounds 1 and 2, the PLATON/SQUEEZE have
been used to remove them.[21] The final formulas and structures
of 1 and 2 have been confirmed by the element analysis and
TGA analysis (Table S6 and Figure S5 in the Supporting
Information). Detailed crystal data and structure refinement for
compounds 1 and 2 are given in Table 3. Selected bond
distances and angles are listed in Table S1 in the Supporting
Information. The CCDC numbers of 1 and 2 are 1907482 and
1907484, respectively, and the files contain the supplementary
crystallographic data for this paper.
Keywords: heterometal-organic frameworks • heterogeneous
catalysis • CO2 fixation • oxazolidinones • cyclicity
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1
2
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formula
Fw
NaC52H62CoErN8O26
1463.08
120.00(10)
monoclinic
P21/c
NaC52H62CoN8O26Yb
1469.04
120.00(10)
monoclinic
P21/c
T/K
Cryst. Syst.
Space group
a/Å
10.0421(2)
29.0407(7)
19.0694(8)
90
10.0081(3)
29.0640(9)
19.0006(11)
90
b/Å
c/Å
[5]
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2023.
α/°
β/°
94.100(2)
90
93.713(4)
90
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γ/°
Volume/Å3
Z
5547.0(3)
4
5515.2(4)
4
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ρcalcg/cm3
μ/mm-1
F(000)
1.406
1.399
1.868
2.051
2976.0
2984.0
[8]
[9]
2θ range for data
6.006 to 50.02
5.858 to 50.016
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25544
0.0597
1.036
24445
0.0488
1.147
Rint
Goodness-of-fit
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Final R indexes
R1 = 0.0515,
wR2 = 0.1115
R1 = 0.0650,
wR2 = 0.1399
[I>=2σ (I)]
Final R indxes
R1 = 0.0729,
wR2 = 0.1193
R1 = 0.0735,
wR2 = 0.1437
[all data]
Δρmax/min
1.586/-1.076
2.108/-1.906
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21421001), and 111 Project (Grant B12015).
Conflict of interest
6
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7
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Text for Table of Contents
Xiao-Min Kang, Lin-Hong Yao,
Zhuo-Hao Jiao and Bin Zhao*[a]
Two
stable
heterometal-MOFs
{Na[LnCo(DATP)2(Ac)(H2O)](NO3)·DMA·11H2O}n
(Ln = Er(1) and Yb(2)) have been harvested and
structurally characterized, presenting excellent
catalytic performances and cyclicity in the CO2
fixation with aziridines into high-valued
oxazolidinones
Page No. – Page No.
Title Two Stable Heterometal-
MOFs as High-efficiency and
Recyclable Catalysts in the CO2
Coupling Reaction with Aziridines
8
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