Self-assembly of tetranuclear 3d-4f helicates as highly efficient catalysts for CO2cycloaddition reactions under mild conditions

Article abstract of DOI:10.1039/d0dt01743d

A series of novel asymmetry 3d-4f helicates Zn3LnL4 (H2L = N-(2-((3,5-di-tert-butyl-2-hydroxybenzylidene)amino)ethyl)-2-hydroxybenzamide, Ln = Dy(1), Gd(2), Er(3)) were successfully constructed via selective incorporation of groups with different coordination capabilities. These helicates with the well-defined conformation demonstrate high catalytic efficiency in converting CO2 to cyclic carbonates under mild conditions. Particularly, Zn3ErL4 showed superior catalytic performance with high catalytic activity (TOF up to 38?000 h-1) and extraordinary selectivity (up to 99%) across the wide substrate scope. Meanwhile, these 3d-4f helicates showed stable catalytic performance without being influenced by the moisture and air. The results presented herein highlight an important consideration for constructing heterometallic and asymmetric complexes for catalyzing CO2 conversion.

Full text of DOI:10.1039/d0dt01743d

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ISSN 0306-0012
COMMUNICATION
Douglas W. Stephen et al.
N-Heterocyclic carbene stabilized parent sulfenyl, selenenyl,
and tellurenyl cations (XH , X = S, Se, Te)
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DOI: 10.1039/D0DT01743D
ARTICLE
Self-assembly of tetranuclear 3d-4f helicates as highly efficient
catalysts for CO cycloaddition reactions under mild conditions
2
a
a
a
b
a
Huan Yang , Guoshu Gao , Wanmin Chen , Li Wang* , and Weisheng Liu*
3 4 2
A series of novel asymmetry 3d-4f helicates Zn LnL (H L = N-(2-((3,5-di-tert-butyl-2-hydroxybenzylidene)amino)ethyl)-2-
hydroxybenzamide, Ln = Dy(1), Gd(2), Er(3)) were successfully constructed via selective incorporation of groups with
Received 00th January 20xx,
Accepted 00th January 20xx
different coordination capabilities. These helicates with the well-defined conformation demonstrate high catalytic efficiency
2 3 4
in converting CO to cyclic carbonates under mild conditions. Particularly, Zn ErL showed superior catalytic performance
-1
with high catalytic activity (TOF up to 38000 h ) and extraordinary selectivity (up to 99%) across the wide substrate scope.
Meanwhile, these 3d-4f helicates showed stable catalytic performance without being influenced by the moisture and air.
The results presented herein highlight an important consideration for constructing heterometallic and asymmetric
DOI: 10.1039/x0xx00000x
2
complexes for catalyzing CO conversion.
Introduction
In recent years, the conversion of CO into valuable chemicals
2
has received a significant amount of attention in both industry
and academia, largely on account of its economic and
environmental impact. Particularly, the cycloaddition of CO
over the ligand structures provided an unheralded interest in
increasing the catalytic activity and selectivity of these CO
cycloaddition reactions.
2
Helices, as the essential assemble formation in the majority
of natural compounds and biology molecules, playing a critical
role in endowing selective recognition and expressing behaviors
that closely related to the central biology process. Similarly, the
spatial coordination between the ligands and metal ions in
complexes could also lead to the assembly of the highly
organized helix architectures. Most recently, different types of
the helical metal complexes (helicates) have been extensively
investigated, from double-stranded to multiple stranded, linear
to circular, two centers to multiple centers and singular metal
1
-10
2
with epoxides to cyclic carbonates, as one of the most effective
and important routes for carbon capture and use (CCU), has
been widely studied experimentally and theoretically owing
in particular to their green chemistry for 100% atom
efficiency.1
1-16
Meanwhile, the cyclic carbonates are industrially
very significant and have been extended to versatile
applications from fabricating the polycarbonate materials to the
pharmaceutical and fine chemical industries.
several types of catalyst systems have been extensively studied
for these cycloaddition reactions.
examples is symmetric metallosalen-complexes, which the
metal ions such as Al, Zn, Cr, Co, Mn and Ru et al was
coordinated within the N2O2 donor pocket structure provided
by the salen ligand.2
interaction with the catalyst, the selective incorporation of the
1
7-23
To date,
4
2-50
ion to multi-ones.
The versatile structures of the helical
2
4-28
metal complexes provide an ideal platform for mimicking the
biology behavior like enzyme catalyzing, gene and protein-
expressing.
In terms of catalyzing applications, the heterometallic
helicates, bearing different metal ions (transition-metal ions or
f-block elements) in one complex, is one of the most attractive
one as the multiple metal centers offer divers metal-binding
domains for the higher order of the complex construction and
are able to provides various interactions with catalytic substrate
One of the most common
9-36
2
In order to ensure the CO sufficiently
catalytically Lewis base sites for CO
2
fixation and activation is
paramount.1
3, 32, 37-41
Reducing the distance between amide
group (Lewis basic center) and metal ions (Lewis acid center)
can effectively enhance the contact between two reactants and
further accelerate the reactions. Therefore, the precise control
5
1-54
in the single molecules.
helicates with different assembly architectures were reported
by our group, which showed the catalyzing ability in the CO
Several 3d-4f heterometallic
2
cycloaddition reactions under the ambient environment with
a. Key Laboratory of Nonferrous Metals Chemistry and Resources Utilization of Gansu
Province and State Key Laboratory of Applied Organic Chemistry, College of
Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P. R.
China. E-mail: liuws@lzu.edu.cn
55-58
wide scope of epoxides.
However, the search for new
hetero-multinuclear cooperative structures is still pivotal in this
area, where structures with well-defined reactivity and
enhanced catalysis profiles are needed.
b.
College of Chemistry and Chemical Engineering, Xi’an Shiyou University, Xi’an
7
10065, P.R. China.
†
Electronic Supplementary Information (ESI) available: Figure S1–S6 containing
Herein,
cooperative structures Zn
designed and synthesized in this work (Scheme 1). The
a
series of novel 3d-4f hetero-multinuclear
characterization details for ligand and complexes. Table S1–S4 containing additional
structural data. CCDC 1942931-1942933. For ESI and crystallographic data in CIF see
DOI: 10.1039/x0xx00000x
3
LnL (Ln = Dy (1), Gd (2), Er (3)) were
4
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ARTICLE
Journal Name
decomposition of the complex structures. The TGA proved
View Article Online
DOI: 10.1039/D0DT01743D
excellent thermal stability without any obvious decomposition
from room temperature up to 344 °C which further provided a
steady platform for catalytic applications.
Structure Characterization
The crystals of the three complexes were prepared in a clear
mixed solution of acetonitrile and methanol containing
deprotonated ligand, Ln(NO ) ·6H O and Zn(NO ) ·H O by slow
3 3 2 3 2 2
Scheme 1. Assembly strategy for the 3d-4f heterometallic
helicates as the efficient catalysts for CO conversion reactions.
2
evaporation of the solvent. Due to the isomorphic crystal
structures in complexes 1-3, complex 3 was taken as an example
for further crystal structure discussions. The unit cell is formed
by an equal amount of the M enantiomer and P enantiomer,
thus the crystal system is achiral (Figure S7). The asymmetric
helical structure consists of four deprotonated ligands, three
bifunctional ligand, containing both C=N and C=O groups with
different binding preferences for selectively coordinated with
Zn and Ln ions, contributes to the construction of 3d-4f
2
+
3+
5
9-61
heterometallic helix structures.
revealed the asymmetric conformation with the potential
catalytically active sites for CO cycloaddition reactions. The
The crystal structure further
2+
3+
2
Zn ions, one Er ion, one monodentate nitrate and two
acetonitrile as one unit in the lattice. In the complex, four
presence of lanthanide ions in these 3d-4f hetero-multinuclear
structures leads to the additional Lewis-acid sites which
enhanced catalytic reactivity. The catalytical properties of
2+
3+
ligands and three Zn are wrapped around the lanthanide Er
center. Among them, Zn3 and Er1 are entangled in a head-to-
head manner by two deprotonated ligands forming a double
2
different complexes in CO cycloaddition reactions have been
systematically valued across the wide substrates scope while
the stability of the acquired catalysts was compared in the
presence of water and air. The mechanism of the catalyzing
process in relation to the metal ions as well as the special
conformation of the complexes was further discussed.
3+
helix. As a consequence of the large coordination number of Er ,
two ligands are insufficient to meet the coordinating
requirements of lanthanide ions, and further coordination with
the other two deprotonated ligands which the carbonyl group
and phenolic hydroxyl are inevitable to meet the saturated
eight-coordinated environment. The Schiff base imine group at
Results and discussion
Design and synthesis
A tetradentate ligand bearing C=N and C=O groups as metal
binding sites was synthesized via two-step reactions (amidation
and condensation) from the commercially available
reactants.6
2-64
The formation of the ligand was confirmed by
mass spectrometry, NMR, and FT-IR spectroscopy (Detailed in
the experimental section and Figure S1-S5). As shown in
Scheme 1, the ligand was designed with different binding
2
+
3+
groups for selectively coordination of Zn and Ln ions
respectively. Meanwhile, the flexible and asymmetric backbone
was formed, contributing to the spiral structure. As expected,
three asymmetry and novel tetranuclear helicates Zn
assembled by adding the Zn(NO ·6H O and Ln(NO
a mixed acetonitrile-methanol (4:1) solution of H L in presence
3
LnL
4
were
)
3 2
2
3 3
) ·6H
2
O to
2
of equivalent triethylamine. Single crystal X-ray structural
analysis revealed that 1-3 are isostructural and crystallized in
the monoclinic P-1 space group, which is only differed in the
number of solvent molecules in the lattice. In parallel, FT-IR
(Figure S5) and elemental analysis indicated that complexes 1-3
are isostructural. In order to estimate the stability of the
complexes, thermal gravimetric analysis (TGA) was performed
(Figure S6). The TGA demonstrated that the complexes 1-3 have
high thermal stability and the thermal performances between
the different catalysts are similar due to isomorphism. Taking
complex 3 as an example, 3.6% of the weight loss in the range
of 30 to 195°C, owing to the presence of solvent molecules in
the crystal lattice. The weight decreased rapidly with the loss of
Figure 1. (a) Coordination model of the ligand. (b) Coordination
model of the ligand. (c) Molecular structure of the tetranuclear
helicate. (d) Coordination polyhedrons of the Er and Zn ions in
complex 3. For clarity, half of the structure is transparent.
Hydrogen atoms and solvent molecules are omitted.
4
8.4% in 344 to 535 °C interval which is attributed to the
2
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to
the other end of the two ligands coordinated with Zn1 and Zn2 Table 1. Synthesis of cyclic carbonate via insertion of CO
ions could further stabilize the lanthanide ions and zinc ions. In styrene oxide catalyzed by complexes 1-3 .
the complex, the Er3+ ion is eight-coordinated in the central
2
View Article Online
D
a
OI: 10.1039/D0DT01743D
O
O
O
O
3
+
position. The coordination polyhedron of Er ion is a
dodecahedron. Both Zn1 and Zn2 are bridged on two sides of
cat., co-cat.
T, P
+
CO2
3
+
the Er ion via the phenolic hydroxyl from two ligands. Zn1 and
Zn2 are all four-coordinated with one N atoms of the imine from
the deprotonated ligands and three O atoms of the phenolic
hydroxyl from three ligands. The coordination polyhedron
shows a tetrahedral configuration. The Zn3 ion is coordinated
with two N atoms of the imine and two O atoms of the phenolic
hydroxyl from the deprotonated ligands and monodentate
coordinated nitrate. The coordination polyhedron is a square
pyramid configuration. In the crystal, the distance between Er1
and Zn1, Zn2, Zn3 is 3.307, 3.305 and 6.686 Å, respectively.
These ions are centered on lanthanide ions, extend in different
directions and are linearly arranged in a 3:1 pattern to form a
unique 3d-4f asymmetric unsaturated double helix structure,
which as the novel structure is reported for the first time.
T
P
(bar)
10
10
10
10
10
10
10
10
10
10
1 0
10
10
10
Time
Yield
(%)b
93
TOF
Entry
Cat.
-1 c
(
°C
)
(h)
2
(h )
1
2
1
2
3
3
-
120
120
120
120
120
120
120
120
80
4650
4600
4750
50
2
92
3
2
95
4d
5
2
1
2
33
47
69
-
6
2
H L
2
2350
13800
3300
1700
38000
4650
4800
4850
-
7
3
3
3
3
3
3
3
-
0.5
3
8
99
9
2
34
1
0e
1 f
120
120
120
120
120
2
76
1
2
93
96
97
34
Catalytic performance
1
2g
3h
4i
2
2
CO conversion reactions receive a significant amount of
1
2
attention across a range of fields of science and energy area,
largely on account of their low cost, environmentally friendly
and easily accessible precursor. Previous research has shown
1
2
a
Reaction conditions: 10 mmol styrene oxide, 0.01mol%
Yield was
H NMR analysis. Selectivity of cyclic carbonates
to epoxides. A series of multiple nuclear 3d-4f complexes which were all > 99%.
TOF = conversion·ncat-1·h-1
Without co-
contain the similar structure of classical salen complexes have catalyst.
Catalyst reduced to 0.001 mol%. Not excluding the
been synthesized. In the structure, monodentate coordinated air inside the reaction system.
0.02mL of H O was added to the
that salen zinc-containing compounds have preferable catalyst, 0.8 mol% co-catalyst TBAB, 10 bar.
performance in the catalytic reaction of the cycloaddition of CO
determined by
b
1
2
c
d
.
e
f
g
2
-
2+
3+
h
NO
3
with Zn can be displaced by suitable substrates, La and reaction system. 0.2mL of H O was added to the reaction
2
Zn2+ ions act as Lewis acidic sites to enhance the catalytic system. Without catalyst, 0.02mL of H O was added to the
i
2
activity, and amides coordinated with lanthanide can be reaction system.
considered as basic sites. The above inferred that complexes
have great prospects in CO
Styrene oxide (SO) was taken as a model substrate to achieve satisfactory catalytic yield (1%, 33%, respectively) in the
investigate the cycloaddition reaction in which the CO reacts cycloaddition reaction, but the yield was increased to 95% in the
2
conversion reactions.
entry 4) nor TBAB (0.8 mol%, Table 1, entry 5) alone could
2
with epoxides to form cyclic carbonates. Firstly, the effect of the binary catalytic system composed of complex 3 and TBAB.
lanthanide metal ions on the catalytic reaction was investigated. Besides, considering Lewis base site (N atom) may also
0
.01 mol% of helicates 1-3 as the catalyst and 0.8 mol% of contribute to the cycloaddition reaction in which H L combined
2
tetrabutylammonium bromide (TBAB) as cocatalyst was used to with TBAB was utilized as a catalyst for the model reaction
catalyze the cycloaddition reaction under 120 °C, 1 MPa without (Table 1, entry 6). The yield of the cycloaddition reaction was
solvent for 2 h. As shown in Table 1 (entry 1-3), catalysts 1-3 increased to 47% compared with the system only contained
have obtained excellent yields (93%, 92% and 95%, respectively) TBAB as the control, which further confirmed our assumption.
-
1
-1
-1
with high TOF values (4650 h , 4600 h and 4750 h ,
Because there are multiple factors that affect the
3
+
respectively). The results indicated that different Ln have little cycloaddition reaction, variable control studies are performed
effect on the activity of the catalyst while the catalytic activity to optimize the reaction conditions. The reaction yield remains
3
+
increased as the decrease of Ln radius. We chose complex 3 above 90% when pressure was reduced from 10 bar to 2 bar,
as a model catalyst in the further optimization process and the related TOF changed slightly which suggests the
regarding to its catalytic activity. Owning to the vital role of the pressure had no obvious effect on this system (Figure 2b). The
co-catalysts in the epoxides ring-opening process and the yield progressively increased with time and the growth rate
reaction intermedia formation process, the effect of various co- gradually decreased (Figure 2c). The yield can reach 69% after
catalysts on catalytic performance, such as TBAC, TBAB, TBAI, half hour with a high TOF 13800 h-1 (Table 1, entry 7),
PPN-Cl, under the same conditions has been studied (Figure 2a). meanwhile, when the reaction time was extended to 3 h, the
The results demonstrate that TBAB is the finest selection of co- yield was more than 99% with a TOF of 3300 h-1 (Table 1, entry
catalyst in this system. Neither catalyst 3 (0.01 mol%, Table 1, 8). We further investigated the effect of the temperature on
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1
20 °C under 8 bar for 2 hours. Water and air have a large
View Article Online
DOI: 10.1039/D0DT01743D
2
impact on the most catalytic system in CO cycloaddition
reactions, therefore it is necessary to explore the stability of our
catalytic system. As the control experiment, the conversion rate
can still reach 93% without gas exchange (Table 1, entry 11). In
comparison, the presence of moisture even a large amount
Table 2. Various carbonates from different epoxides catalyzed
by various catalysts under different conditions.
Yield
Yield
(%)
Entry Substrate
Product
TOF c
TOF c
a
b
(%)
O
O
O
O
1
93 9300 97 1213
95 9500 91 1138
O
O
O
O
2
O
O
O
O
3
4
Br
95 9500 99 1238
78 7800 83 1038
Br
O
O
O
O
O
O
O
O
5
6
7
98 9800 99 1238
95 9500 99 1238
93 9300 98 1225
O
O
O
O
Figure 2. The yields of cycloaddition reaction of epoxy styrene
and carbon dioxide under different reaction conditions: (a) 10
mmol styrene oxide, 0.01 mol% catalyst, 0.8 mol% co-catalyst,
O
O
O
O
O
O
O
O
O
1
20 °C, CO
2
at 10 bar, 1 h. (b) 10 mmol styrene oxide, 0.01 mol%
at 10 bar. (c)
0 mmol styrene oxide, catalyst (0–0.01mol%), 0.8 mol% TBAB
O
catalyst, co-catalyst (0.2–1 mol%), 120 °C, 2 h, CO
1
2
O
O
O
O
2
as the co-catalyst, 120 °C, 2 h, CO at 10 bar. (d) 10 mmol
O
8
9
1
86 8600 89 1113
97 9700 99 1238
97 9700 99 1238
O
styrene oxide, 0.01 mol% catalyst, 0.8 mol% TBAB as the co-
catalyst, temperature (40-120 °C), 2 h, CO at 10 bar. (e) 10
mmol styrene oxide, 0.01 mol% catalyst, 0.8mol% TBAB as the
co-catalyst, 120 °C, time (0.5-3 h), CO at 10 bar. (f) 10 mmol
styrene oxide, 0.01 mol% catalyst, 0.8 mol% TBAB as the co-
catalyst, 120 °C, time 2 h, CO at (2–10 bar).
2
O
O
O
O
O
O
O
O
2
O
O
O
2
O
O
0
1
O
O
the reaction. The conversion rate was increased slowly between
0 °C and 60 °C, while remarkable increase happened at
temperature 80 °C, 100 °C, 120 °C with linear correlation (Figure
O
O
O
4
O
O
1
1
O
98 9800 99 1238
93 9300 98 1225
2
8
d). It should be noted that when the temperature drops to
0 °C, the value of TOF can still reach 1700 h (Table 1, entry 9).
-1
O
O
O
With different loading of co-catalyst TBAB (0.4 mol%, 0.6 mol%,
.8 mol%, 1.0 mol%, respectively), high yield was attained with
2
0
-1
-1
-1
-1
considerable TOF as 4050 h , 4650 h , 4750 h , 4850 h ,
respectively (Figure 2e). TOF changed little when the amount of
co-catalyst is more than 0.6 mol%. The concentration of the
catalyst reduced from 0.01 mol% to 0.001 mol%, the
corresponding yield was decreased by only 19% (Figure 2f). TOF
O
O
O
O
1
1
3
4
36 3600 33 413
67 6700 61 763
O
O
O
O
-1
of the catalyst was reached to the highest as 38000 h when
catalyst 3 was 0.001mol% and co-catalyst TBAB was 0.8 mol%
a
Reaction conditions: 10 mmol epoxide, 0.005 mmol% catalyst,
0
(Table 1, entry 10), indicating such catalyst achieve the excellent
b
.6 mmol% TBAB, 120 °C, 2 h, 8 bar. 10 mmol epoxide, 0.01
catalytic performance with a high TOF. Therefore, the optimal
reaction conditions for the cycloaddition reaction were 0.005
mmol% of the catalyst with 0.6 mmol% of co-catalyst TBAB, at
mmol% catalyst, 1 mmol% TBAB, 80 °C, 8 h, 8 bar. TOF =
-1
-1
c
1
conversion·ncat ·h . Yields were determined by H NMR.
Selectivity of cyclic carbonates were all > 99%.
4
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of water (volume ratio = 18%) was explored which the which weakens the C-O bond strength in epoxides.VTiehweAnrt,ictlehOenBlinre−
conversion rate is slightly improved (Table 1, entries 12-13). from TBAB attacked the less steric resisDtaOnI:c1e0.c10a3r9b/oDn0DaTt0o1m743oDf
One possible reason is that the presence of water accelerates the epoxide which was coordinated with metal center,
the co-catalyst hydrolyzing, makes the co-catalyst better meanwhile, the epoxide ring was opened due to the strong
participate in the catalytic reaction, and has excellent resistance electronegativity and lower steric resistance of Br atoms.
to water. (Table 1, entry 14). To evaluate the catalytic Subsequently, CO
2
is inserted into the Zn3-O bond and
performance of our catalytic system, we compared it with the cyclization takes place by the internal attack of carbon dioxide
Zn-containing complexes and lanthanide catalysts, such as on the C-Br bond while the co-catalyst recovered. In addition,
2
5
65
66
67
Zn(OPO)
2
,
Zn-CMP, ZnBr
2
,
Ni(PPh
3
)Cl
2
/PPh
3
/Zn, Yb- the catalyst can synergistically functionalize by introducing
affinity to multiple Lewis acid sites,
6
8
69
mesocate, and Helicate-1(Zn-Tb). The results show that our amide groups to increase CO
2
catalytic system has higher catalytic activity than most used which lead to higher catalyst efficacy.
catalyst system.
To further explore our catalytic system into the universal
scope, a series of epoxy compounds with different substituents
Experimental
were subjected to the cycloaddition reaction under different
conditions. The reactions for terminal epoxides achieve
impressive conversion rates (> 90%) and high selectivity (99%)
under 8 bar and 120 °C for 2 hours (Table 2, entries 1-12), except
for 2-decyloxirane (86%) and 2-(tert-butoxymethyl) oxirane
General information
Chemicals were purchased from commercial sources and used
without further purification. The infrared spectra were
recorded on a Bruker VERTEX 70 FT-IR spectrometer using KBr
pellets in the 400-4000 cm region. H and C NMR spectra
were recorded using a JNM-ECS 400M spectrometer using CDCl
-1
1
13
(78%), due to the large steric hindrance. However, compared
3
with terminal epoxides, the catalyst shows lower activity on
internal epoxides such as cyclohexene oxide and cyclopentene
oxide (Table 2, entries 13 and 14), being ascribed to the steric
effect. At the same time, the substrates expansion experiment
was carried out under the conditions of 80 °C and 8 bar for 8
hours. The results showed that under relatively mild conditions,
the catalyst still exhibits high catalytic activity for epoxides with
a wide substrate scope.
as a solvent and tetramethylsilane (TMS) as an internal standard.
The C, H, and N microanalyses were performed by using a Vario
EL cube elemental analyzer. TGA/NETZSCH STA449C instrument
for thermogravimetric analysis experiments was carried out
under nitrogen atmosphere, the test temperature is from 35 °C
-1
to 800 °C with the heating rate of 10 °C min . Single-crystal
X-ray diffraction data were collected on a Bruker FRAMBO
diffractometer (Mo radiation, λ = 0.71073 Å) at 293 K. Data
reduction was accomplished by the Bruker SAINT program.
Empirical absorption corrections were carried out on the
SADABS program. All the structures were solved by direct
methods and refined by a full-matrix least-squares technique
Catalytic mechanism
Based on the current experimental results and the reported
5
2, 54, 70-73
studies of catalyst systems,
a tentative mechanism was
. In
2
based on F of the SHELXL 2018 through Olex2 program. All the
proposed for the catalytic system in the conversion of CO
2
non-hydrogen atoms were refined anisotropically. The organic
the catalyst system, two kinds of metals were involved, in which
the eight-coordinated rare-earth ion is surrounded by four
ligands, and three zinc ions are divided in contrast. Since Zn ions
are relatively far from each other, it could act as independent
catalytic centers to activate the epoxide (Figure 3). The reaction
was initiated by the activation of epoxides. The coordination of
oxygen atoms of the epoxide with the Lewis acid metal sites
leads to electron transfer from oxygen to the metal center,
74
hydrogen atoms were generated geometrically. The specific
data of X-ray crystallography and experiment for the crystal are
listed in Table S1-S4. For details, see the CIF date in the support
part. The CCDC reference numbers of complexes 1-3 are
1
942931, 1942932 and 1942933.
Synthetic procedures
2
Synthesis of ligand H L: N-(2-aminoethyl)-2-hydroxybenzamide
75
was prepared according to the reported literature method.
3
,5-di-tert-butyl-2-hydroxybenzaldehyde (2.34 g, 10 mmol) was
added to a solution of N-(2-aminoethyl)-2-hydroxybenzamide
1.8 g, 10 mmol) in 100 mL methanol. The reaction mixture was
(
refluxed for 5 h and then cooled to the room temperature. The
crude product was separated by filtration and further
recrystallized in ethanol to afford H
2
L as a yellow solid (3.56 g,
, ppm): δ 12.26 (s, 1H), 8.41
1
Yield: 90%). H NMR (400 MHz, CDCl
3
(s, 1H), 7.39 (m, 2H), 7.32 (dd, 1H), 7.09 (d, 1H), 6.99 (dd, 1H),
6
.83 (m, 1H), 6.58 (s, 1H), 3.85 (s, 4H), 1.45 (s, 9H), 1.30 (s, 9H).
C NMR (100 MHz, CDCl , ppm): 170.3, 168.2, 161.6, 158.0,
3
1
3
1
1
40.5, 140.1, 136.9, 136.7, 134.5, 127.5, 126.3, 117.7, 114.2,
00.0, 58.7, 40.5, 35.1, 35.1, 34.3, 34.2, 31.6, 31.5, 29.5, 29.5.
–1
IR (KBr, υ, cm ): 3400 (s), 2962 (s), 1631 (s), 1591 (s), 1541 (s),
1
1
467 (s), 1442 (s), 1361 (s), 1334 (s), 1296 (s), 1272 (s), 1253 (s),
174 (s), 1147 (m), 1041 (m), 974 (w), 829 (w), 750 (s). Melting
Figure 3. A possible mechanism for the cycloaddition reaction.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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Plea sDe a dl too nn oT tr aa nd sj au cs tt i om n as rgins
Page 6 of 7
ARTICLE
Journal Name
+
point 138-140 ℃. ESI-MS m/z [(M+H) ]: 397.24.
The synthetic procedure of complex Zn LnL : In a 50 mL round
bottom flask, 27 μL (0.2 mmol) triethylamine was added to a
solution of H L (0.1 mmol) in 15 mL acetonitrile. Then the
Zn(NO ·H O (0.1 mmol) was added in the mixture solution and
stirred for 15 min to obtain a suspension solution. To this
solution, Ln(NO ·6H O (Ln = Dy, Gd, Er) (0.075 mmol) dissolved
in 5 mL methanol was added and then stirred at room
temperature for 1 hour. The product was filtered from the
reaction mixture and further crystallized at room temperature.
There are no conflicts to declare.
View Article Online
DOI: 10.1039/D0DT01743D
3
4
Acknowledgements
2
)
3 2
2
This work was supported by the National Natural Science
Foundation of China (Grant No. 21871122, 21431002), the
Fundamental Research Funds for the Central Universities (Grant
No. lzujbky-2018-kb12).
)
3 3
2
Zn
3
DyL
4
(1): Elemental analysis (%) found (calculated): C 56.48 Notes and references
(57.71), H 5.98 (6.08), N 6.37 (6.87), Zn 9.46 (9.62). IR (KBr, υ,
1
.
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535 (s), 1478 (m), 1436 (s), 1410 (m), 1384 (s), 1359 (m), 1316 2. M. Liu, J. Wu, X. Zhu, H. He, W. Jia and W. Xiang, Atmos. Environ.,
–1
cm ): 2958 (s), 2905 (s), 2866 (s), 1615 (s), 1591 (s), 1550(s),
2
1
(
(
Zn
(
m), 1258 (s), 1199 (w), 1164 (s), 1112 (w), 829 (m), 791 (w), 755
m), 699(w), 588 (w), 540 (w).
GdL (2): Elemental analysis (%) found (calculated): C 57.04
57.57), H 6.05 (6.06), N 6.33 (6.85), Zn 9.44 (9.64). IR (KBr, υ,
2015, 114, 75-82.
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.
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3
4
2
–
1
cm ): 2959 (s), 2908 (s), 2867 (s), 1614 (s), 1590 (s), 1550 (s),
534 (s), 1477 (m), 1439 (s), 1413 (m), 1383 (s), 1362 (m), 1317
2
1
6
7
8
.
.
.
(
(
m), 1257 (s), 1198 (w), 1166 (s), 1111 (w), 832 (m), 788 (w), 753
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J. Yang and P. Zhang, Renewable and Sustainable Energy
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Zn
3 4
ErL (3): Elemental analysis (%) found (calculated): C 56.32
(57.86), H 5.93 (6.09), N 6.50 (6.88), Zn 9.35 (9.59). IR (KBr, υ,
–1
cm ): 2958 (s), 2908 (s), 2868 (s), 1618 (s), 1592 (s), 1549 (s),
1
536 (s), 1476 (m), 1439 (s), 1415 (m), 1382 (s), 1359 (m), 1319 9. J. W. Maina, C. Pozo-Gonzalo, L. Kong, J. Schütz, M. Hill and L. F.
(
(
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1
1
1
1
1
2
General procedures for the cycloaddition of CO
carbonates
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to cyclic
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The reactions were carried out in 50 mL autoclave reactors with
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1
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cooled to room temperature, and a small amount of reaction
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mixture was taken to be analyzed by H NMR to calculate the
conversions of the reaction.
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2 3 4
catalytic activity and selectivity with a wide substrate scope
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Conflicts of interest
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| J. Name., 2012, 00, 1-3
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