A novel copper framework with amino tridentate N-donor ligand as heterogeneous catalyst for ring opening of epoxides

Article abstract of DOI:10.1002/aoc.6262

A novel metal–organic framework (MOF) [Cu₃L(2,6-NDC)₂]·0.5DMF (MOF-Cu-1) was synthesized by solvothermal reaction of copper nitrate trihydrate with 2,6-naphthalenedicarboxylic acid (2,6-H₂NDC) and amino tridentate N-donor

Full text of DOI:10.1002/aoc.6262

Received: 4 February 2021
DOI: 10.1002/aoc.6262
Revised: 26 March 2021
Accepted: 28 March 2021
F U L L P A P E R
A novel copper framework with amino tridentate N-donor
ligand as heterogeneous catalyst for ring opening of
epoxides
1
1
1
1
Zi-Qing Huang
| Zou-Hong Xu
| Xiao-Hui Liu
| Yue Zhao
|
1
1,2
1
Peng Wang
| Zhi-Qiang Liu
| Wei-Yin Sun
1
Coordination Chemistry Institute, State
Key Laboratory of Coordination
Chemistry, School of Chemistry and
Chemical Engineering, Nanjing National
Laboratory of Microstructures,
A
novel metal–organic framework (MOF) [Cu L(2,6-NDC) ]ꢀ0.5DMF
3
2
(MOF-Cu-1) was synthesized by solvothermal reaction of copper nitrate
trihydrate with 2,6-naphthalenedicarboxylic acid (2,6-H NDC) and amino
2
1
1
Collaborative Innovation Center of
Advanced Microstructures, Nanjing
University, Nanjing, China
tridentate N-donor containing ligand of N -(4-(1H-imidazol-1-yl)benzyl)-N -
(
(
2-aminoethyl)ethane-1,2-diamine (L). MOF-Cu-1 is a three-dimensional
3D) framework with one-dimensional (1D) channels. Because of the high
2
School of Chemistry and Chemical
stability of the framework and the existence of amino functional groups,
MOF-Cu-1 presents excellent heterogeneous catalytic activity for ring-opening
reaction of epoxides by amines and reusability for four cycles with negligible
loss of efficiency.
Engineering, Anhui Key Laboratory of
Functional Coordination Compounds,
Anqing Normal University, Anqing,
China
Correspondence
Zhi-Qiang Liu and Wei-Yin Sun,
Coordination Chemistry Institute, State
Key Laboratory of Coordination
Chemistry, School of Chemistry and
Chemical Engineering, Nanjing National
Laboratory of Microstructures,
Collaborative Innovation Center of
Advanced Microstructures, Nanjing
University, Nanjing 210023, China.
Email: dg1424045@smail.nju.edu.cn;
sunwy@nju.edu.cn
K E Y W O R D S
amino tridentate N-donor ligand, epoxides, heterogeneous catalyst, metal–organic framework,
ring-opening reaction
Funding information
Priority Academic Program Development
of Jiangsu Higher Education Institutions;
National Basic Research Program of
China, Grant/Award Number:
2017YFA0303504
1
| INTRODUCTION
and works less well with poor nucleophilic amines,
indicating that it is necessary to develop efficient catalysts
for the ring opening reaction of epoxides. Some homo-
[
2]
Epoxides are common organic molecules with wide range
of synthetic applications as intermediates in pharmaceu-
tical and agrochemical industries. The classical ring
opening approach of epoxides involves heating of epox-
ides with large excess of amines at elevated temperature
geneous catalysts, including metal salts and acid, have
[1]
[3–5]
already been applied.
However, with the rise of
environmental awareness, heterogeneous catalysis has
attracted extensive attention owing to the effective
Appl Organomet Chem. 2021;e6262.
wileyonlinelibrary.com/journal/aoc
© 2021 John Wiley & Sons, Ltd.
1 of 10
https://doi.org/10.1002/aoc.6262

2
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HUANG ET AL.
combination of the precise active sites of organometallic
complexes and feasible recycling utilization.
2.2 | Synthesis of [Cu L(2,6-NDC) ]ꢀ
3
2
[6–10]
0.5DMF (MOF-Cu-1)
Metal–organic frameworks (MOFs) have been
reported to present excellent performance in numerous
cases of heterogeneous catalytic organic reactions
resulting from their unique porous framework struc-
A mixture of 2,6-H NDC (17.4 mg, 0.08 mmol), L
2
(20.76 mg, 0.08 mmol) and Cu(NO ) ꢀ3H O (48.6 mg,
3
2
2
0.2 mmol) in N,N-dimethylformamide (DMF)/methanol
[11–17]
tures.
Among them, the instances of utilizing che-
mixed solvent (8 ml, v/v = 3/1) was sealed in a 15-ml
ꢁ
lating effect to design and synthesize novel stable
heterogeneous MOFs catalysts are particularly inter-
ested. It has been successfully verified that MOFs
equipped with amino tridentate N-donors are able to
withstand harsh heating and pressure conditions in
Teflon-lined reactor and heated for 72 h at 110 C under
autogenous pressure. After cooling down to room
ꢁ
temperature at a rate of 0.05 C per minute, blue
block crystals were isolated in 52% yield. FTIR-ATR
(Figure S1): 3175 (w), 1668 (w), 1610 (s), 1558 (vs), 1497
(m), 1391 (vs), 1346 (vs), 1192 (m), 1133 (w), 1056 (m),
920 (m), 885 (m), 779 (vs), 650 (m), 560 (m),
[18–20]
our previously reported works.
In this work, to
further explore the universality of this conception, we
designed, solvothermally synthesized and characterized
a novel crystalline MOF catalyst MOF-Cu-1, by utiliz-
ing Cu(NO ) ꢀ3H O, 2,6-naphthalenedicarboxylic acid
−1
522 (s), 470 (vs) cm . Elemental analysis calcd. for
C39.5H36.5Cu N O : C, 51.86; H, 4.02; N, 8.42%;
3
5.5 8.5
found C, 51.81; H, 4.25; N, 7.63%. EPR (Figure S2):
g ≈ 2.05642 at 90 K.
3
2
2
(
2,6-H NDC) and an amino tridentate N-donor con-
2
1
taining ligand, namely N -(4-(1H-imidazol-1-yl)benzyl)-
N -(2-aminoethyl)ethane-1,2-diamine (L) (Scheme 1).
1
The combination of ligand L with copper salt possesses
strong chelating effect comparing with the previously
2.3 | Catalytic reaction procedure
[18–21]
applied metal ions of Zn(II) and Cd(II).
Moreover,
As a typical reaction, styrene oxide (0.1 mmol) and
benzylamine (0.1 mmol) were placed in a reaction vessel
containing MOF-Cu-1 (1.5 mg, 1.7 mol%). Then, this
mixture was magnetically stirred under solvent-free con-
MOF-Cu-1 shows preeminent chemical stability in
varied solvent, and the heterogeneous catalytic activity
was further examined for the ring-opening reactions of
epoxides by different amines.
ꢁ
ditions at 25 C for 4 h. Next, dichloromethane was added
as a diluent solvent to separate the products from the
solid catalyst by centrifugation. The final target products
were isolated from the supernatant by column chroma-
tography with silica gel (CH Cl /n-hexane = 2:1). Identi-
2
2
| EXPERIMENTAL
2
2
1
13
.1 | Materials and characterization
fication of the products was implemented by H and
C
NMR techniques. After the end of the reaction, the
catalyst was refreshed by washing with dichloromethane
(3 × 5 ml) and dried in air. The recovered catalyst was
consecutively reused in the next cycle with fresh
substrates. Each cycle followed the same procedure for
catalyst recycling.
All commercially available chemicals and solvents are of
reagent grade and were used as received without further
purification. Ligand L was prepared according to the
[19]
previously reported procedures.
Powder X-ray diffrac-
tion (PXRD) data were collected on a Bruker D8 Advance
X-ray diffractometer with Cu Kα (λ = 1.5418 Å) radiation.
Thermogravimetric analysis (TGA) was carried out on a
Mettler-Toledo (TGA/DSC1) thermal analyser with a
2.4 | X-ray crystallography
ꢁ
−1
heating rate of 10 C min under a nitrogen atmosphere
ꢁ
from room temperature to 800 C. Fourier Transform
Crystallographic data for MOF-Cu-1 were collected on a
Bruker Smart Apex II CCD single-crystal X-ray diffrac-
tometer with graphite-monochromated Mo Kα radiation
(λ = 0.71073 Å) at 193 (2) K using the ω-scan technique.
The integration of the diffraction data and intensity
corrections for Lorentz and polarization effects were
Infrared-Attenuated Total internal Reflectance (FTIR-ATR)
spectra was measured on an infrared spectrophotometer
(
Bruker Tensor II) equipped with a diamond ATR module
−1
1
13
in the range of 400–4000 cm . H and C NMR spectra
were recorded on Bruker-DRX (500 and 125 MHz, respec-
[
22]
tively) instruments internally referenced to TMS (SiMe ) or
carried out using the SAINT program.
Semi-empirical
4
chloroform signals. Elemental analyses for C, H and N
were performed using an Elementar Vario MICRO. EPR
spectrum was obtained on a Bruker EMX plus-6/1 variable
temperature X-band apparatus in the solid state at 90 K.
absorption corrections were applied using SADABS
[
23]
program.
The structure was solved by direct methods
with SHELXT-2014, expanded by subsequent Fourier-
difference synthesis, and all the nonhydrogen atoms were

HUANG ET AL.
3 of 10
SCHEME 1 Schematic diagram of the formation of MOF-Cu-1, crystal structure and its application in heterogeneous catalysis
2
refined anisotropically on F using the full-matrix least-
TABLE 1 The crystallographic data of MOF-Cu-1
squares technique and the SHELXL-2018 crystallographic
[24,25]
MOF-Cu-1
software package.
The free solvent molecules in the
unit cell have been taken into account with the
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
39.50 3 5.50 8.50
C H36.50Cu N O
[26]
SQUEEZE option of the PLATON program.
Hydrogen
914.86
193 (2)
atoms were introduced at the calculated positions. The
SHELX was interfaced with SHELXLE GUI for most of
Triclinic
P-1
[27]
the refinement steps.
The final chemical formula of
MOF-Cu-1 was calculated based on volume/count elec-
tron analysis and the TG data of as-synthesized crystal
11.844 (2)
12.748 (2)
14.126 (2)
97.571 (2)
92.395 (3)
112.918 (3)
1937.1 (6)
2
(Figure S3). The reported refinement is of the guest-free
b (Å)
structure obtained by the SQUEEZE routine, and the
result was attached to the CIF file. The details of crystal
parameters, data collection and refinements are listed in
Table 1, and the selected bond lengths and angles are
given in Table S1.
c (Å)
ꢁ
α ( )
ꢁ
β ( )
ꢁ
γ ( )
3
V (Å )
Z
3
3
3
| RESULTS AND DISCUSSION
.1 | Crystal structure description
D
c
(g cm−
)
1.568
F (000)
934
ꢁ
θ range ( )
1.462–27.497
17,423
Reflections collected
Unique data
Single crystal X-ray diffraction (XRD) analysis reveals
that MOF-Cu-1 crystallizes in triclinic P-1 space group
8701
Goodness-of-fit
1.035
(Table 1). As shown in Figure S1, the FTIR shows that
a
there are no vibration bands between 1680 and
R
1
(I > 2σ(I))
0.0493
−
1
b
1
760 cm , implying the complete deprotonation of
wR2 (I > 2σ(I))
0.1411
2
−
2
,6-H NDC to give NDC
in MOF-Cu-1. The
2
a
R
1
= ΣjjF
o
j − jF
c
2
jj/ΣjF
o
j.
2
asymmetric unit of MOF-Cu-1 contains three copper
atoms, one L and two NDC ligands (Figure 1a). Cu is
b
2 1/2
2
2
2
wR
2
= jΣw(jF
o
2
j − jF
c
j )j/Σjw(F
o
) j , where w = 1/[σ (F
o
) + (aP) + bP].
2
−
2
P = (F
o
+ 2F
c
)/3.
1

4
of 10
HUANG ET AL.
five-coordinated by three nitrogen atoms (N1, N2 and
N3) from the amino tridentate N-donor of L and two oxy-
channels with size of 3.73 × 21.79 Å from the view along
a axis (Figure 1b). Two 3D nets mutually interpenetrate
each other to result in formation of a twofold inter-
penetrated structure (Figure 1b), which could be well
recognized as a kind of self-complementation to stabilize
2
−
gen ones from two different NDC . Cu is three-
3
coordinated by one nitrogen from imidazole group of L
2
−
and two oxygen atoms from two different NDC with T-
[
19]
shaped coordination geometry, whereas Cu has linear
the framework.
After the free solvent molecules were
2
3
[
CuO ] coordination environment. The T-shaped and lin-
removed, the void volume is approximately 387 Å per
2
3
ear coordination geometries together with consideration
1937.1 Å unit cell (20.0% of the total crystal volume). To
of charge balance of the framework imply that Cu and
better understand the nature of this intricate architec-
2
[
33]
Cu are monovalent Cu(I) rather than Cu(II). It means
ture, topological analysis was performed.
Cu can be
1
3
that Cu(II) was partially reduced to Cu(I) during the for-
considered as a three-connected node, WHEREAS Cu2
mation of MOF-Cu-1, which is speculated to arise from
and Cu are combined together as a four-connected node.
3
[28,29]
the reducing ability of DMF.
The presence of one
Accordingly, a three-nodal 3D net with a rare reported
2
3
2
6
16
5
Cu(II) was ensured by EPR spectral measurements. As
shown in Figure S2, the typical spectral shape and posi-
Schläfli symbol of {4 ꢀ6 ꢀ8}{4 ꢀ6} {4 ꢀ6 ꢀ8 ꢀ10} is gener-
2
ated (Figure 1c).
9
tion (g ≈ 2.05642) at 90 K confirmed the d configuration
[30–32]
2−
of Cu(II).
In turn, each L and NDC ligand links
two Cu atoms. Such arrangement produces a three-
dimensional (3D) framework with different channels
3.2 | PXRD and thermal analysis
(Figure S4), which is beneficial for mass transferring
PXRD pattern of as-synthesized MOF-Cu-1 was obtained
during the catalytic reactions. For example, there are
at room temperature. The positions of characteristic
FIGURE 1 (a) The coordination environment of Cu(II) and Cu(I) in MOF-Cu-1 with ellipsoids drawn at the 30% probability level.
Hydrogen atoms and solvent molecules are omitted for clarity. (b) The interpenetrating framework and channels of MOF-Cu-1 in the view
along a axis. (c) Topology of MOF-Cu-1

HUANG ET AL.
5 of 10
peaks are matched well with the simulated ones created
by single crystal data (Figure S5), manifesting the phase
purity of the synthesized sample. The simulated PXRD of
MOF-Cu-1 in Figure S5 has a low-angle peak that
appears of lower intensity in the experimental pattern,
which may result from the different crystal orientation
between the abundant crystal powders and a single crys-
PXRD patterns were tested for the dried samples. To our
delight, MOF-Cu-1 shows outstanding stability in these
solvents without variation of XRD patterns (Figure 2).
The results point out that the chemical stability of MOF-
Cu-1 offers great potential for gratifying heterogeneous
catalysis. Besides, the interpenetrating structure formed
by solvothermal reaction may also strengthen the stabil-
[34]
[37]
tal.
Thermogravimetric analysis (TGA) was performed
ity of MOF-Cu-1.
under N atmosphere to test the thermal stability of the
2
framework. As illustrated in Figure S3, the TG data of
MOF-Cu-1 exhibited gradual weight loss of 3.5 w%
before 225 C, which corresponds to the loss of free
3.4 | Catalytic properties
ꢁ
solvent DMF molecules (calcd. 3.9%). The following
weight loss was found to start from 225 C representing
the collapse of the framework, which was verified by the
phenomenon of turning to brown lump after heating to
The catalytic performance of MOF-Cu-1 was examined
by conducting amination of epoxides. For finding out
the optimal experimental conditions, styrene oxide
and benzylamine were selected as representative sub-
strates, as their product 2-(benzylamino)-2-phenylethanol
(abbreviated as BAPE) is a significant intermediate for
the synthesis of imines and oxazolidine derivatives, which
are critical to produce biological organic compounds
ꢁ
ꢁ
2
40 C. In order to prove the solvent molecules in the
ꢁ
pores, MOF-Cu-1 was heated to 225 C and kept for 5 h
in a nitrogen atmosphere for the solvent removal. The
TG data of the obtained sample indicates that the solvent
molecules has been cleaned up and the existence of DMF
in as-synthesized MOF-Cu-1 is verified by the disappear-
ance of the characteristic peak of 1493 cm in the FTIR-
ATR spectrum after heating (Figure S6).
the residue at 800 C for the sample after solvent removal
is approximately 26% corresponding to the CuO (calcd.
[38–40]
containing hetero-nitrogen atom (Scheme 2).
The
1
analysis of the resulted products was carried out by H
NMR using CH Br as an internal standard. Furthermore,
−1
2
2
[35,36]
In addition,
these experiments clearly suggest that MOF-Cu-1 can
effectively promote the reaction and afford BAPE as the
major product.
ꢁ
2
7%).
3.4.1 | Reaction solvent
3.3 | Chemical stability
Various solvents with different polarity such as acetoni-
trile, ethyl acetate (EA), tetrahydrofuran (THF),
dichloromethane (DCM), hexane and DMF were chosen
The chemical stability of MOF-Cu-1 was ascertained by
treating it in air with varied common solvent for 48 h.
FIGURE 2 Powder X-ray diffraction (PXRD) patterns of MOF-Cu-1 after preserving for 48 h under different conditions: air, acetone,
2
dichloromethane (DCM), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethyl acetate (EA), ethanol (EtOH), water (H O),
toluene, tetrahydrofuran (THF) and acetonitrile

6
of 10
HUANG ET AL.
and the ring-opening reactions between styrene oxide
and benzylamine exhibited not detectable to moderate
yield of 56% after stirring for 5 h at 25 C (Table 2, entries
TABLE 2 Optimization of reaction solvent for the ring opening
of styrene oxide by benzyl- amine employing MOF-Cu-1 as
heterogeneous catalyst
ꢁ
1
–6). Particularly, under solvent-free conditions, the ring-
opening reaction gratifyingly afforded a good yield up to
8% (Table 2, entry 7) under the identical conditions.
a
Entry
Solvent
Acetonitrile
EA
Yield of product (%)
1
2
3
4
5
6
7
16
9
45
With the comprehensive consideration of high efficiency
and eco-friendly and environmentally friendly chemistry,
the following experiments were all performed under
solvent-free conditions.
THF
41
DCM
Hexane
DMF
56
1
Not detectable
98
/
3
.4.2 | Reaction time and heterogeneous
Note: Reaction conditions unless specified otherwise: styrene oxide
catalysis
(
(
0.1 mmol), benzylamine (0.1 mmol), solvent (1 ml), catalyst MOF-Cu-1
ꢁ
1.5 mg), 25 C, 5 h.
a
1
For further study, the next logical action was to investi-
gate the influence of reaction time under the same
conditions. The time-dependent yield profile for the ring-
opening reaction of styrene oxide and benzylamine was
provided in Figure 3 by observing in the yield of desired
product BAPE as a function of reaction time. It was
found that 4 h was the optimal selection as acting as the
minimum time to complete the reaction (Figure 3a).
The yield was determined by H NMR analysis of crude product using
CH Br as an internal standard.
2
2
3.4.3 | Recycling performance
The high stability of MOF-Cu-1 in varied organic solvent
has already mentioned above and then the stability in the
optimal reaction conditions is further tested by stirring
For facilitating comparison,
without addition catalyst of MOF-Cu-1 was performed
Figure 3c) and displayed negligible yield, which stresses
a control experiment
ꢁ
for 4 h at 25 C without the use of solvent. After comple-
(
tion of the first-time reaction, the catalyst was recovered
by centrifuging, washing with dichloromethane and then
drying in air. The recovered catalyst was used for the next
round of reaction with fresh substrates under the identi-
cal conditions and showed almost consistent activity with
a slight decrease in the yield of BAPE (Figure 4). The
conversion decrease may be attributed to the loss of a
small amount of catalyst in the recovering experi-
the necessity of catalytic agent in the reaction between
styrene oxide and benzylamine. In order to further
validate whether the present catalytic method is inher-
ently heterogeneous or not, the catalyst MOF-Cu-1 was
filtered out from the mixture after reacting for 2 h with
the yield of 41%. Next, the reaction in the absence of cata-
lyst was carried out for the remaining time (Figure 3b).
The observed results suggested that the yield was almost
a constant after eliminating MOF-Cu-1 from the reaction
vessel, which excluded the possibility of catalysing by
species etched from the catalyst.
[
9,41]
ment.
In addition, the crystalline pattern of the cata-
lyst after being used for four cycles was tested by PXRD
analysis and revealed the identical XRD pattern with that
of the original MOF-Cu-1 (Figure 5), which indicated the
SCHEME 2 The reaction scheme for producing BAPE and the reported derivatives

HUANG ET AL.
7 of 10
FIGURE 3 Time-yield plot for ring opening of styrene oxide by
benzylamine using MOF-Cu-1 as a heterogeneous catalyst: (a) with
catalyst; (b) with filtering of the catalyst after reaction for 2 h;
FIGURE 5 Comparison of the Powder X-ray diffraction
PXRD) patterns of fresh sample of MOF-Cu-1 (a) with that of the
(
(
c) without catalyst. Reaction conditions: styrene oxide (0.1 mmol),
sample recovered after the first (b) and fourth (c) cycles of catalysis
ꢁ
benzylamine (0.1 mmol), MOF-Cu-1 (1.5 mg), 25 C, without
solvent. The yield was determined by 1H NMR analysis of crude
product using CH2Br2 as an internal standard
aniline, aromatic epoxide with alkylamine and alkyl
epoxide with aniline, were subjected to react under the
optimal conditions. As demonstrated in Table 3, great
reaction yields were achieved ranging from 85% to 98%
(
Table 3, entries 1–7, Figures S7–S13), and especially,
cyclohexene oxide provided a satisfactory yield of 85%
with benzylamine (Table 3, entry 7). In addition to the
excellent reactivity catalysed by MOF-Cu-1, the
regioselectivity is apparently controlled by the substrate
effect that the electronic property and steric hindrance of
the oxirane ring play a major role in the regioisomer of
[
42]
reaction products.
The reaction between styrene oxide
and aniline as well as 4-chlorostyreneoxide, respectively,
obtained 97% and 98% yields (Table 3, entries 1 and 2)
and the yields of the reactions between styrene oxides
and benzylamine, isopropylamine are 98% and 86%,
respectively (Table 3, entries 3 and 4). In the above situa-
tions, isomer A (Scheme 3) was detected as the main reg-
ioisomer that was dominated by the electronic
FIGURE 4 Circulation yields for the ring opening of styrene
oxide by benzylamine using MOF-Cu-1 as a catalyst
[
43,44]
effect.
It is supposed that the coordination between
MOF-Cu-1 and epoxide is conducive to form the carbo-
cation at aromatic methyl position, which could be stabi-
lized by p–π conjugation for reducing the transition state
structural integrity during the reaction process. To sum
up, these results indicate the excellent recyclable catalytic
performance of MOF-Cu-1 in this reaction.
[
45]
energy during the amino attack.
Isopropylamine is
apparently less reactive, which may arise from the higher
basicity of aliphatic amines resulting in the occupation of
the uncoordinated catalytic site and the catalyst poison-
[
46–48]
3.4.4 | Scope of substrates
ing.
Furthermore, when aniline individually reacted
with alkyl oxirane tert-butyl glycidyl ether and 1-bromo-
2,3-epoxypropane (Table 3, entries 5 and 6), the yields
were manifested as 96% and 90% and isomer B turned
into the major product. It is probably because of the prior
In order to further explore the applicable scope of this
catalytic reaction, multiple substrate combinations with
different features including the aromatic epoxide with

8
of 10
HUANG ET AL.
TABLE 3 Ring opening of varied epoxide by aryl and alkyl amine substrates employing MOF-Cu-1 as a heterogeneous catalyst
a
b
Entry
Epoxide
Amine
Major product
Major isomer
Yield (%) (A: B)
1
A
97 (97: trace)
2
3
A
A
98 (98: trace)
98 (98: trace)
4
5
A
B
86 (86: 3)
96 (trace: 96)
6
7
B
90 (5: 90)
-
85
ꢁ
Note: Reaction conditions unless specified otherwise: epoxide (0.5 mmol), amine (0.5 mmol), MOF-Cu-1 (7.5 mg, 0.026 mmol), 25 C, solvent free, stirred for
h.
4
a
The yields were calculated by using the isolated product.
b
1
The selectivity was determined by H NMR analysis of crude product using the major product as an internal standard.
steric effect, since the carbon atom with less substituted
functional groups becomes much more vulnerable to be
attacked by the nucleophilic amine owing to the disap-
yield, MOF-Cu-1 ranks among the top and also performs
well in reaction rate, generally manifesting excellent cata-
lytic efficiency.
[49]
pearance of the arylmethyl carbocation.
The catalytic
A possible mechanism is proposed for the aminolysis
of epoxide with MOF-Cu-1 as heterogeneous catalyst
based on the structure of MOF-Cu-1 and previous litera-
activity of our present MOF-Cu-1 is compared with other
previously reported works on the reaction of styrene
oxide and benzylamine (Table S2). In terms of product
[
50]
ture reports.
Besides the classical mechanism that the

HUANG ET AL.
9 of 10
SCHEME 3 Reaction scheme for the ring opening of epoxides by primary amine under neat conditions using MOF-Cu-1 as a
heterogeneous catalyst
coordinatively unsaturated metal centers serve as active
sites (Scheme S1), the structure of MOF-Cu-1 may also
plays a significant role in promoting catalytic efficiency.
As a matter of fact, the MOF is a porous framework
without end capping, and the walls of the macro-
intergranular pores are distributed with abundant
uncoordinated copper site, carboxylate and amino
groups. Compared with the majority of narrow internal
pores, a unique channel effect is allowed to display for
facilitating the diffusion and concentration of organic
substrates, intermediate formation and approach to the
Investigation; methodology. Wei-Yin Sun: Conceptuali-
zation; funding acquisition; project administration;
supervision.
CONFLICT OF INTEREST
All authors certify that they have no conflict of interest to
declare.
SUPPORTING INFORMATION DATA
CCDC—2045503 contains the supplementary crystallo-
graphic data for this contribution. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html (or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223–336-033; or deposit@ccdc.ca.
ac.uk).
[51]
active sites.
Furthermore, the interpenetrating struc-
ture of MOF-Cu-1 itself may play a significant role in
[52]
mass transferring.
As it is mentioned above, the inte-
gral bulky MOF-Cu-1 heterogeneous solid catalyst is a
functional porous structure that is beneficial to boost cat-
alytic efficiency.
DATA AVAILABILITY STATEMENT
The data that supports the findings of this study are
available in the supporting information of this article.
4
| CONCLUSIONS
In summary, a novel stable 3D MOF with coordinatively
unsaturated metal sites and amino tridentate N-donor
containing ligand L was successfully synthesized as a
heterogeneous catalyst for epoxide ring-opening reactions
by varied amines. The catalyst can be separated and
reused for multicycles without significant yield loss or
structural damage.
ORCID
Zi-Qing Huang https://orcid.org/0000-0003-0204-6689
Zou-Hong Xu https://orcid.org/0000-0002-4307-3280
Xiao-Hui Liu https://orcid.org/0000-0002-9460-7924
Yue Zhao https://orcid.org/0000-0001-6094-4087
Peng Wang https://orcid.org/0000-0002-8114-0202
Zhi-Qiang Liu https://orcid.org/0000-0002-1618-6095
Wei-Yin Sun https://orcid.org/0000-0001-8966-9728
ACKNOWLEDGEMENTS
We gratefully acknowledge the National Basic Research
Program of China (grant no. 2017YFA0303504) for the
financial support. This work was also supported by
a project funded by the Priority Academic Program
Development of Jiangsu Higher Education Institutions.
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