Green Conversion of CO2 and Propargylamines Triggered by Triply Synergistic Catalytic Effects in Metal–Organic Frameworks

Article abstract of DOI:10.1002/anie.202106773

Cyclization of propargylamines with CO₂ to obtain 2-oxazolidone heterocyclic compounds is an essential reaction in industry but it is usually catalyzed by noble-metal catalysts with organic bases as co-catalysts under harsh conditions. We have synthesized a unique Cu^I/Cu^II mixed valence copper-based framework {[(Cu^I₆I₅)Cu₃^IIL₆(DMA)₃](NO₃)?9DMA}_n (1) with good solvent and thermal stability, as well as a high density of uncoordinated amino groups evenly distributed in the large nanoscopic channels. Catalytic experiments show that 1 can effectively catalyze the reaction of propargylamines with CO₂, and the yield can reach 99 %. The turnover frequency (TOF) reaches a record value of 230 h^?1, which is much higher than that of reported noble-metal catalysts. Importantly, this is the first report of heterogeneously catalyzed green conversion of propargylamines with CO₂ without solvents and co-catalysts under low temperature and atmospheric pressure. A mechanistic study reveals that a triply synergistic catalytic effect between Cu^I/Cu^II and uncoordinated amino groups promotes highly efficient and green conversion of CO₂. Furthermore, 1 directly catalyzes this reaction with high efficiency when using simulated flue gas as a CO₂ source.

Full text of DOI:10.1002/anie.202106773

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How to cite:
International Edition: doi.org/10.1002/anie.202106773
German Edition: doi.org/10.1002/ange.202106773
MOF-Catalyzed Reactions
Green Conversion of CO and Propargylamines Triggered by Triply
2
Synergistic Catalytic Effects in Metal–Organic Frameworks
Xiao-Lei Jiang, Yue-E Jiao, Sheng-Li Hou,* Liang-Chen Geng, Hao-Zhe Wang, and Bin Zhao*
Dedicated to the 100th anniversary of Chemistry at Nankai University
Abstract: Cyclization of propargylamines with CO to obtain
required in CO chemical conversion, which can result in
2
the increase of energy consumption and reaction cost.
2
[3]
2
-oxazolidone heterocyclic compounds is an essential reaction
in industry but it is usually catalyzed by noble-metal catalysts
with organic bases as co-catalysts under harsh conditions. We
Therefore, it becomes an ideal goal for researchers to realize
the green conversion of CO and substrates, requiring that
2
I
II
have synthesized a unique Cu /Cu mixed valence copper-
such reactions were completed by noble-metal free catalyst
with low pressure, room temperature, solvent free, and co-
catalyst free. Up to now, cyclic organic carbonates can be
I
II
based framework {[(Cu I )Cu L (DMA) ](NO )·9DMA}
n
6
5
3
6
3
3
(1) with good solvent and thermal stability, as well as a high
density of uncoordinated amino groups evenly distributed in
the large nanoscopic channels. Catalytic experiments show that
effectively generated by such green conversion of CO and
epoxides. However, the investigations on the green con-
2
[4]
1
can effectively catalyze the reaction of propargylamines with
versions of CO with propargylamines or alkynyl alcohol have
2
CO , and the yield can reach 99%. The turnover frequency
been hardly reported based on heterogeneous catalysts so far.
Actually, the reaction of carboxylic cyclization of prop-
2
À1
(
TOF) reaches a record value of 230 h , which is much higher
than that of reported noble-metal catalysts. Importantly, this is
the first report of heterogeneously catalyzed green conversion
argylamines and CO is considered as one of the important
2
methods to prepare oxazolidinones, which are important
heterocyclic compounds in the field of organic synthesis and
of propargylamines with CO without solvents and co-catalysts
2
[
5]
under low temperature and atmospheric pressure. A mecha-
nistic study reveals that a triply synergistic catalytic effect
pharmaceutical chemistry. To date, many homogeneous and
heterogeneous catalysts have been developed and used in
I
II
[6]
between Cu /Cu and uncoordinated amino groups promotes
such reaction, and great progress has been made. For
[
7]
highly efficient and green conversion of CO . Furthermore,
example, Hong and co-workers developed a cyanuric acid-
based organocatalyst, which can directly capture and convert
2
1
directly catalyzes this reaction with high efficiency when
using simulated flue gas as a CO source.
CO in air into 2-oxazolidinone at 1008C in the presence of
DMSO. Islam et al. anchored Ag nanoparticles into the
porous COF, and the Ag@COF catalyst can effectively
2
2
[
8]
Introduction
catalyze the reaction of propargylamines with 1 atm CO in
2
Excessive emissions of industrial waste gas have caused
many environmental problems, and its main component CO2
is one of the culprits causing the greenhouse effect. Mean-
a solvent free condition at 408C. In these results, noble metal
and/or harsh reaction conditions become necessary to im-
prove catalytic efficiency. Therefore, it is extremely challeng-
ing but of great significance to develop high-efficiency noble-
metal free heterogeneous catalysts that can green catalyze
while, CO as an abundant, inexpensive, easily obtained, and
2
renewable C1 resource has been widely used as a feedstock
for various valuable chemical products, such as methanol,
cycloaddition of propargylamines with CO at low temper-
2
[
1]
formic acid, cyclic carbonates, and others. Among them, the
ature and low pressure in the absence of co-catalysts and
solvent.
formation of CÀN, CÀC, and CÀO bonds between CO and
2
substrates can obtain high value-added drug precursors and
To realize the goal mentioned above, we intend to design
[
2]
I
II
raw materials for fine chemicals. But CO has high chemical
a Cu /Cu mixed valence MOF catalyst to greenly catalyze the
2
4
inertness and thermodynamic stability due to its unique P3
cyclization of propargylamine and CO based on the following
2
delocalized electronic structure, and one or more of these
conditions like the noble metal catalyst, high pressure, high
temperature, co-catalyst and proper solvents are usually
considerations, 1) metal–organic frameworks as promising
heterogeneous catalysts have been widely used in catalytic
[
9]
[10]
[11]
[12]
hydrogenation, hydration, coupling, cyclization and
[13]
other reactions due to their highly dispersed catalytic active
sites, easily modified framework structure, adjustable pore
size, and so on. 2) Copper-based MOFs displayed high
[*] Dr. X.-L. Jiang, Y.-E. Jiao, Dr. S.-L. Hou, L.-C. Geng, H.-Z. Wang,
Prof. Dr. B. Zhao
Department of Chemistry, Key Laboratory of Advanced Energy
Material Chemistry, MOE, Renewable Energy Conversion and Storage
Center (RECAST), Nankai University
Tianjin 300071 (China)
E-mail: housl@nankai.edu.cn
catalytic activity in the reported chemical conversion of CO
2
I
I
and various substrates. For example, Cu I -Gd and In-Cu I
4 4
x
y
can activate the alkynyl, then catalyze the carboxylation of
phenylacetylene and cyclization of propargyl alcohols, re-
[
14]
II
spectively. [Cu 30] and MMPF-10 can effectively catalyze
the cyclization of aziridines with CO in a solvent-free
zhaobin@nankai.edu.cn
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
https://doi.org/10.1002/anie.202106773.
2
[15]
system. 3) Considering the highly effective catalytic activity
I
II
of copper-based MOFs, the design of Cu /Cu mixed valence
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MOF can achieve the goal of synergistic catalysis and improve Results and Discussion
catalytic activity. 4) As a cheap metal, Cu based catalyst can
replace the noble metals such as Ag, Pt and Au while ensuring
catalytic efficiency, thus reducing the cost of catalysis.
Along this idea, in this contribution, a unique three-
dimensional (3D) mixed valence copper-based cationic
Green block crystals of 1 were obtained through a solvo-
thermal reaction of CuI, Cu(NO ) and the ligand HL at
1208C for 3 days. Single crystal X-ray diffraction analysis
3
2
reveals that 1 crystallizes in the hexagonal system with P6 /m
3
I
II
framework {[(Cu I )Cu L (DMA) ](NO )·9DMA}
(1)
HL: 5-aminonicotinic) was synthesized and structurally
space group (CCDC number: 1975383; Supporting Informa-
tion, Table S1). The asymmetric unit includes a [Cu I ] cluster,
6
5
3
6
3
3
n
(
6
5
characterized. Compound 1 displays high stability in various
common solvents. 1 not only can greenly and efficiently
catalyze the cyclization of propargylamine into oxazolidi-
nones under solvent-free and co-catalyst free conditions, but
one and a half [Cu (COO) (DMA) ], and six HL. The [Cu I ]
2 4 2 6 5
I
cluster contains six Cu ions, three m -bridging and two
4
I
m -bridging iodide ions. The six Cu ions form a triangular
3
I
prism unit, and each Cu ion coordinates with three iodide
ions (Figure 1a; Supporting Information, Figure S1a). The
[Cu I ] cluster is further linked by six pyridyl N atoms from six
[
16]
also can directly utilize CO in flue gas as raw materials to
2
perform this reaction under green conditions. The turnover
6
5
À1
frequency (TOF) can reach 230 h , which is the highest value
ligands to form a 6-connected [Cu I N ] moiety (Figure 1c).
6 5 6
in all the reported such reactions. And the framework can
remain intact at least five catalytic cycles. This is the first case
that a noble-metal free heterogeneous catalyst can catalyze
the green conversion of propargylamine with CO2 in the
absence of solvents and co-catalyst.
Both Cu1A and Cu1B are linked by four carboxylate groups
from four L ligands to form 4-connected binuclear paddle-
À
wheel [Cu (COO) (DMA) ] moiety, and the terminal posi-
2
4
2
II
tions of two Cu ions are occupied by DMA molecules
(Figure 1b,c; Figure S1b). Considering the [Cu I ] and
6
5
[
Cu (COO) (DMA) ] as independent nodes for 6 and 4
2 4 2
connections, ligand as linker, the 3D framework (Figure 1e)
can be simplified as stp-type topology (Figure 1 f; Fig-
I
II
Figure 1. a) [Cu I ] cluster in compound 1. b) Coordination environment of Cu (COO) unit in 1. c) Coordination environment of HL and Cu /Cu
6
5
2
4
ions. d) The 1D channel along the c-axis, and the dimensions of the 1D channel, are determined by the distance between two opposing amino
groups. e) 3D framework of 1 along the c-axis. f) The stp topology of 1 from the c-axis.
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ure S1d). In addition, the oxidation state of Cu nodes was
determined by XPS spectra (Figure S2), and the peaks of
Table 1: Comparison with the TOF of other catalysts.
Catalyst
Additive/Solvent
T
t
[h]
TOF
I
II
À1
9
32.38 eV and 934.56 eV can be classified as Cu and Cu ,
[8C]
[h
]
respectively. The peak area ratio is about 2:1, which proves
1
–
30
100
50
60
40
30
30
30
30
0.17
8
6
4
15
0.17
0.17
0.17
0.17
230
I
that the trigonal-prismatic cluster [Cu I ] is formed by Cu ,
[19]
6
5
[
Ru]/PPh3
Toluene
DBU/DMSO
DBU/DMSO
10
1.7
and the paddle-wheel moiety [Cu (COO) (DMA) ] is made
[6d]
2
4
2
TMOF-3-Ag
NiBDP-AgS
AuCl(IPr)
CuI
II
[6e]
of Cu . The result implies that 1 is a cationic framework, and
the counterions NO3 were determined by FT-IR and XPS
spectra. The IR peak at 1360 cm (Figure S3) can be
49.5
À
[20]
CH
OH
3
3
À1
–
–
–
–
83
PdI -KI
64
189
57
2
attributed to the characteristic peak of the counterions
AgOAc
Pd(OAc)2
À
NO3 . The peak at 406.5 eV in the XPS spectra can be
À
[17]
identified as the peak of N1s in NO3
.
Along the c-axis, six
Turnover frequency was evaluated at optimal conditions and calculated
by the mole number of products per mole number of catalytically active
Cu per hour. A complete table is provided in Table S3.
[
Cu I ] clusters and six [Cu (COO) (DMA) ] are connected
6
5
2
4
2
by ligand to form a large channel with a diameter of 1.45 nm
-NH to -NH , Figure 1d). The [Cu I ] clusters and high
(
2
2
6 5
density of uncoordinated amino groups are evenly distributed
in the large nanoscopic channels, which provides an available
[
a]
Table 2: Carboxylic cyclization of propargylamine with CO2.
[
2f]
platform to promote the catalytic reaction of CO2. After
squeezing all of the guest solvent molecules, the total
available space can reach 34.7%, calculated by the PLATON
[18]
program.
The PXRD patterns (Figure S4) exhibit that the exper-
imental peaks of 1 are consistent with the simulated one,
which demonstrates the high phase purity of 1. Then the
stability of 1 was systematically explored. Firstly, TGA
analysis (Figure S5) shows that the framework of 1 can keep
stable until 2208C, which proves that it has good thermal
stability. Subsequently, 1 was soaked in H O, CH OH, DMF,
2
3
acetone, CH Cl and other common organic solvents for 12 h,
2
2
and the corresponding PXRD patterns are consistent with the
original one, indicating that 1 possesses high solvent stability
(
Figure S6). Inspired by the remarkable stability, mixed
valence copper active centers, and densely exposed uncoor-
dinated amino groups in 1D channels, we explored its ability
to catalyze the cyclization of propargylamine and CO . To
2
optimize the catalytic conditions, 2-methyl-3-butyn-2-amine
was selected as the model substrate. The results in Table S2
showed the catalytic activities under different conditions.
Encouragingly, the yield of 2-oxazolidinone can reach 99%
under optimal reaction conditions (308C, 1 atm CO and 1 h)
2
without any co-catalyst and solvent. The TOF for this system
À1
[a] Reaction conditions: substrate (1.3 mmol), 1 catalyst (20 mg,
0.057 mmol based on Cu), CO (1 bar). a: 1 h, solvent free. b–e: 3 h,
solvent free. f: 3 h, solvent free, triethylamine (50 mL). g: 10 h, DMSO
can reach 230 h , which is even much higher than noble-
À1
2
metal based catalysts, such as PdI -KI (64 h ) and AgOAc
(
2
À1
189 h ; Table 1; Tables S3). All these results suggest that 1 is
1
1
1
mL, triethylamine (50 mL). The yields were determined by H NMR with
,3,5-trimethoxybenzene as the internal standard.
a highly efficient catalyst for the green conversion of
propargylamine and CO2.
Subsequently, based on the optimal reaction conditions,
several typical propargylamines with different substituents
were further investigated, and the yields of the target
catalysts were firstly explored under the same optimal
conditions, but there are almost no products obtained from
HL (< 1%, Entry 2). When CuI is used as catalyst (Entry 4),
and the yield can reach 58%, which is higher than that of
Cu(NO ) as catalyst (34%, Entry 3), indicating the active
2
-oxazolidinones are summarized in Table 2. Various prop-
argylamines with methyl, propyl, butyl, and cyclohexyl groups
were employed, and the corresponding 2-oxazolidinones
products were obtained with high yields from 86% to 99%
3
2
I
II
center of Cu is more efficient than Cu . In order to further
(
Entries 2a to 2f). However, due to the high steric resistance
explore the high efficiency catalytic effect of 1, two reported
[21]
[14b]
of the molecule, it is hard for 1 to catalyze the conversion of
MOFs HKUST-1 (Figure S8) and In-Cu4I4
(Figure S9)
biological macromolecule rasagiline and CO (1 g).
were synthesized as control groups to explore the catalytic
properties. The reaction efficiency of HKUST-1 (44%, En-
2
I
II
Then, the roles of Cu , Cu and amino group in this
reaction were systematically explored by a series of control
experiments (Table 3). The HL, CuI, and Cu(NO3)2 as
II
try 5) based on Cu node is lower than that of In-Cu I (66%,
4
4
I
Entry 6) based on Cu node. But the catalytic yields of both
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Table 3: Control experiments for carboxylic cyclization of propargyl-
[
a]
amine with CO2.
[
b]
Entry
Catalyst
Yield
1
2
3
4
5
6
7
8
9
1
HL
Cu(NO3)2
CuI
HKUST-1
In-Cu4I4
2
2 + TEA
L-Cu4I4
99
<1
34
58
44
66
67
73
62
69
65
83
89
10
11
12
13
HL+CuI+Cu(NO3)2
CuI + TEA
1-Zn
1-Co
[a] Reaction conditions: substrate (1.3 mmol), catalyst (0.057 mmol),
CO (1 bar), 1 h, and solvent free. [b] The yields were determined by
2
1
H NMR with 1,3,5-trimethoxybenzene as the internal standard.
MOFs are higher than that of their corresponding copper salts
(
Cu(NO ) : 34% and CuI: 58%), indicating that the porous
3 2
framework structure can enhance catalytic activity. Further-
more, to explore the role of amino groups in the framework
for this reaction, 5-hydroxynicotinic acid (HL ) was used to
1
replace HL, and the isomorphic 2 with 1 (Figure S10) was
successfully synthesized, and many uncoordinated -OH rather
than -NH groups exist in the 1D channels of 2. Under the
2
same reaction conditions, 2 displayed considerable catalytic
efficiency with a yield of 67% (Entry 7), but the value is
significantly lower than that of 1, which suggests that amino
groups in the MOFs can further improve the catalytic activity.
Based on the experiment of Entry 7, organic base TEA as co-
catalyst was introduced into the reaction, and the correspond-
ing yield can further increase to 73% (Entry 8), indicating
that the amino groups in catalyst 1 can act as a base to activate
the substrate. These results are also consistent with those of
other control experiments, in which CuI and CuI/TEA as
catalysts were also explored (Entries 4 and 11). Furthermore,
the mixture of raw materials HL, CuI and Cu(NO3)2 as
catalyst was directly used to catalyze this reaction, and the
product yield was only 69% (Entry 10). At the same time,
a discrete L-Cu I cluster (Figure S11) was also synthesized
Figure 2. a) SEM image of 1-Zn and e) 1-Co. b) Energy-dispersed X-ray
mapping image of Cu obtained from 1-Zn and f) 1-Co. c) Energy-
dispersed X-ray mapping image of Zn obtained from 1-Zn and g) Co
2+
obtained from 1-Co. d) XPS spectra of 1 after exchange by Zn (1-Zn)
4
4
2+
and h) Co (1-Co).
[
14b]
accordingly, and the product yield is 62% (Entry 9).
catalytic activities in Entries 9 and 10 are lower than that of
under the same conditions, indicating that the 3D frame-
The
1
conditions, the product yields of 1-Zn (83%, Entry 12) and
1-Co (89%, Entry 13) as catalysts are lower than that of
work with a large channel is conducive to the enrichment of
substrates and thus can promote the reaction efficiency.
2
+
1 (99%), which proving that the Cu as the catalytic active
II
To explore the effect of Cu , we rationally replace a part
site plays an important role in promoting this reaction. Based
2
+
2+
2+
I
of Cu in 1 with Zn and Co , marked as 1-Zn and 1-Co,
on the above data, it is easy to find that the amino group, Cu
II
respectively (Figure S12). The EDS-mapping of SEM proved
and Cu exist a positive synergistic effect, and the reaction
2
+
2+
that Zn and Co replaced part of Cu in 1 (Figure 2). And
can be carried out efficiently under green conditions. These
results mentioned above reveal that 1 is an efficient catalyst
without other solvents or co-catalyst for the cyclization of
propargylamine with CO2 under mild conditions, whose
catalytic activity is even higher than that of noble metal
based catalysts. The outstanding catalytic activity of 1 can be
the XPS peaks at 1044.9 eV, 1021.8 eV, 796.8 eVand 781.1 eV
II
II
II
II
can be attributed to Zn 2p , Zn 2p , Co 2p and Co 2p
3/
2,
1
/2
[
3/2
1/2
22]
respectively (Figure 2d,h), revealing Zn and Co replaced
part of Cu in 1, and the ICP results also confirm this
conclusion (Table S4). Based on the synthesized 1-Zn/Co,
their catalytic activities in the cycloaddition of propargyl-
I
II
attributed to the following aspects: 1) The Cu /Cu active sites
are evenly anchored in the 1D channel, which can effectively
amines with CO were explored. Under the same catalytic
2
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[
a]
catalyze this reaction; 2) The large pore structure of 1 can
Table 4: Carboxylic cyclization of propargylamine with CO in flue gas.
2
enrich substrates, shorten the distance between substrates and
catalytic active centers, which will greatly improve the
catalytic efficiency; 3) The high-density of uncoordinated
amino groups in the large channels of 1 can provide alkalinity
for the catalytic system and further promote the ring closure
to the oxazolidinones. Therefore, there is no need to add
additional bases as co-catalysts; 4) The ternary active sites of
I
II
Cu /Cu and amino groups in the metal–organic framework
play a synergistic catalytic effect and can improve the catalytic
efficiency in the green catalytic system without solvent and
co-catalyst.
[23]
The concentration of CO in flue gas is about 20–30%.
2
If CO in flue gas can be directly used as C1 source for
2
catalytic reaction, not only can the emission of CO2 be
decreased, but also the industrial cost for CO enrichment and
2
transport can be reduced. Thus, the raw materials cost of CO2
fixation can be reduced and the industrial output value can be
improved effectively. However, chemical fixation of CO in
flue gas is extremely challenging. The low concentration of
2
[
0
a] Reaction conditions: substrate (2.6 mmol), 1 catalyst (40 mg,
.114 mmol based on Cu, about 4.4 mol%), mixed gas (1 bar, CO2
[
24]
CO in the substrate will dramatically reduce the conversion
2
concentration 25%). a–e: 20 h, solvent free. f: 20 h, triethylamine
(50 mL). The yields were determined by H NMR with 1,3,5-trimeth-
1
efficiency. Therefore, developing a catalyst with high activity
in the green conversion of CO from flue gas is significant and
meaningful. Inspired by the high efficiency of 1 in catalyzing
oxybenzene as the internal standard, which were consistent with GC-MS
yields.
2
cycloaddition of CO and propargylamine, we further ex-
2
plored the catalytic efficiency of 1 under simulated flue gas
conditions. As shown in Table S5, the yield with mixed gases
(
initial CO concentration: 25%) can reach 96% (Table S5,
2
Entry 6) under mild reaction conditions (at 308C, 20 h and
without any solvent or co-catalyst), which indicates that 1 has
potential applications for direct synthesize the target products
from flue gas. Based on this, several typical propargylamine
compounds with methyl, propyl, butyl, and cyclohexyl
substituents were further investigated. As summarized in
Table 4, the corresponding 2-oxazolidinones products were
obtained with good yields (84–96%, 2a–2f). All these results
suggest that 1 as a highly efficient catalyst can effectively
catalyze the reaction of propargylamine with simulated flue
gas, which shows a new prospect for the direct utilization of
waste gas in industry.
Figure 3. Catalyst recycling study for compound 1.
As a heterogeneous catalyst, recyclable performance is
also an important indicator in practical application. There-
fore, the recycle performance of 1 was further explored, and
the detailed experimental procedures are given in the
Supporting Information. The results in Figure 3 exhibited
that the catalyst can be recycled at least five times without
significant reduction in catalytic activity. Furthermore, the
PXRD pattern (Figure S15) after five catalytic cycles is in line
with the original one, proving that the framework of 1 can
remain intact at least five catalytic cycles. Catalyst filtration
tests reveal that 1 is a heterogeneous catalyst (Figure S14).
ICP-MS test shows that the leakage of copper ions was 0.13%
after catalysis, and the low leaching value indicates that 1 is
stable during the catalysis process. Then the stability of reused
2
À1
a slight decrease from 1823 to 1688 m g after the catalytic
reaction, indicating that the pore characteristics of compound
1 can be well retained after the catalytic reaction.
To explore the reaction mechanism, NMR and IR
methods were used (Figure 4; Figure S20).
interactions between propargylamine and catalyst were
monitored by C NMR. When 1 was added to the substrate,
the cleavage of two types of carbon signal peaks (“c” in
Figure 4b (d = 44.87 ppm) and “d” in Figure 4b (d =
32.27 ppm)) is caused by the activation of the amino group
in substrate. As a control, the carbon signals “c” and “d”
display obvious cleavage after adding CuI, while the two
peaks appear no change when adding Cu(NO ) , only the
[
25]
Firstly, the
1
3
3
2
I
1
was further proved by TGA, XPS and FT-IR analysis
peak “a” becomes weak. Proving that Cu nodes are the main
catalytic center for this reaction. The role of Cu in the
reaction has also been confirmed in the reported literature.
And the catalytic effect of 1 was significantly better than that
I
(
Figures S16–S18), and all these results show that 1 is stable in
[26]
the catalytic cycles and can be used as a recyclable hetero-
geneous catalyst. As shown in Figure S19, the Brunauer–
Emmett–Teller (BET) surface area of compound 1 reveals
I
of Cu , it proved that the amino group of 1 could synergisti-
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and the product oxazolidinone was continuously obtained.
Based on above results, the possible mechanism for this
reaction was proposed in Scheme S1. Firstly, the amino group
anchored in 1 could work as a Lewis-base to assist dehydro-
genation in the propargylamine (2), and form the intermedi-
ate state (3). Secondly, the activated nitrogen atom of the
amino group reacts with carbon dioxide to form a carbamate
I
anion (4). Subsequently, the Cu in the [Cu I ] cluster of
6
5
1
attacks the CꢀC bond of propargylamine, and the carba-
mate ion transition state (5) is formed. Then, catalyzed by the
[
II
Cu I ] cluster and Cu paddle wheel nodes, a five-membered
6 5
ring (6) is formed. Finally, (a1) re-participates in the reaction,
and returns the hydrogen atom to the target product (8)
through a transition state (7), and the catalyst 1 was
regenerated at the same time.
Conclusion
In conclusion, a mixed valence copper-based cationic
framework 1 was synthesized and structurally characterized,
and the unique structure of 1 displays good stability in various
organic solvents. Benefitting from the ternary active sites of
I
II
Cu /Cu and amino groups in the large 1D nanoscopic
channels, 1 can effectively and rapidly catalyze the green
cyclization of propargylamine with CO under solvent-free
2
and co-catalyst free conditions. The TOF reaches a record
À1
value of 230 h , which is the highest in the reported
literature. Control experiments and tests have illustrated that
I
II
there is a triply synergistic effect between [Cu I ] nodes, Cu
6
5
paddle wheel nodes, and uncoordinated amino groups that is
responsible for highly efficient catalysis. Importantly, 1 also
can directly utilize CO in simulated flue gas to react with
2
propargylamines. To our knowledge, this is the first report of
a heterogeneous catalyst that can directly catalyze green
Figure 4. a) The cyclization reaction of substrate and CO monitored
2
1
3
by C NMR (D -DMSO). Reaction conditions: 2-methyl-3-butyn-2-
6
cyclization of propargylamine with CO without any solvent
amine (150 mL), 1 (20 mg), and CO (1 bar) were stirred at 308C. The
2
2
peaks at 40 ppm are attributed to D -DMSO. b) Activation of the
propargylamine by different systems (D -DMSO).
or co-catalyst under low temperature and atmospheric
pressure.
6
6
cally promote the reaction rate, which has also been Acknowledgements
[
23]
II
demonstrated in previous work. In addition, Cu as Lewis
I
acid is more acidic than that of Cu . Lewis catalyst with strong
This work was supported by NSFC (Grant No. 21625103 and
21971125), the China Postdoctoral Science Foundation
(2020T130319, 2019M660978), and the Fundamental Re-
search Funds for the Central Universities, Nankai University
(63201017), SFC of Tianjin (20JCYBJC01200) and 111
project (B12015).
acidity can active the O from carbonate intermediate
(
Supporting Information, (5) in Scheme S1) and promote
the cyclization of propargylamines with CO , which is
2
[15,27]
II
observed in reported results.
Cu nodes can promote
the formation of carbonate intermediates and further facili-
tating intramolecular ring closure reactions. And the cycliza-
tion reaction of substrate and CO was monitored by
2
1
3
13
C NMR (Figures 4a). The C peaks at d = 70.7 and Conflict of Interest
3.1 ppm are attributed to CꢀC groups and its strength
9
weakened and disappeared with the extension of reaction
time. Meanwhile, the peaks of C=C (d = 83.4 and 154.3 ppm)
and C=O (d = 162.8 ppm) appeared and gradually strength-
ened. These results indicated that the CꢀC group is activated
The authors declare no conflict of interest.
Keywords: CO · flue gas · green catalysis · MOFs · synergism
2
by
1 and the substrate is gradually converted into
2
-oxazolidone. Then, the FT-IR spectra (Figure S20) further
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Manuscript received: May 20, 2021
Accepted manuscript online: June 30, 2021
5
Version of record online: && &&
,
&&&&
&
&&&
www.angewandte.org
ꢀ 2021 Wiley-VCH GmbH
Angew. Chem. Int. Ed. 2021, 60, 2 – 9
These are not the final page numbers!

Angewandte
Research Articles
Chemie
Research Articles
MOF-Catalyzed Reactions
A mixed valence copper-based cationic
I
II
framework {[(Cu I )Cu L (DMA) ]-
6
5
3
6
3
X.-L. Jiang, Y.-E. Jiao, S.-L. Hou,*
L.-C. Geng, H.-Z. Wang,
(NO )·9DMA} was synthesized. The
3 n
material realized the efficient and green
B. Zhao*
&&&& — &&&&
conversion of propargylamine with CO in
2
flue gas under solvent-free and co-cata-
lyst free conditions.
Green Conversion of CO and
2
Propargylamines Triggered by Triply
Synergistic Catalytic Effects in Metal–
Organic Frameworks
Angew. Chem. Int. Ed. 2021, 60, 2 – 9
ꢀ 2021 Wiley-VCH GmbH
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&&&&
These are not the final page numbers!