Copolymerization of carbon dioxide and propylene oxide by several metallosalen-based bifunctional catalysts

Article abstract of DOI:10.1002/jccs.201800051

A series of new metallosalen-based bifunctional catalysts with Co(III), Cr(III), Fe(III), Mn(III), and Ni(III) were synthesized for the first time, and a detailed study on the mechanism of the copolymerization of CO₂ and propylene oxide (PO) was performed. Meanwhile, the impact factors of the reaction conditions (metal cations, temperature, CO₂ pressure, and reaction time) on catalytic activity and selectivity were investigated. The results indicated that, with the increase of temperature, both the catalyst efficiency and the molecular weight of the copolymer decrease for all the five complexes. The salen-Co(III) complex demonstrated higher activity under mild conditions: reaction temperature at 30 °C, copolymerization time of 24 hr, and 2 MPa of CO₂ pressure. The DSC curve indicated that the PPC by the salen-Co(III) complex has the highest T_g of 46.19 °C. DTGA curves demonstrated that there were two thermal degradation peaks: the first is for the ester bond, and the second is for the C?C bond.

Full text of DOI:10.1002/jccs.201800051

Received: 6 February 2018
Revised: 19 March 2018
Accepted: 20 March 2018
DOI: 10.1002/jccs.201800051
A R T I C L E
Copolymerization of carbon dioxide and propylene oxide
by several metallosalen-based bifunctional catalysts
Wenkai Zhu | Longchao Du | Siyu Qian | Qingsong Yang | Wanjie Song
School of Chemistry and Chemical Engineering
A series of new metallosalen-based bifunctional catalysts with Co(III), Cr(III),
and Key Laboratory of Environment-friendly
Polymer Materials of Anhui Province, Anhui
Fe(III), Mn(III), and Ni(III) were synthesized for the first time, and a detailed
study on the mechanism of the copolymerization of CO2 and propylene oxide
(PO) was performed. Meanwhile, the impact factors of the reaction conditions
(metal cations, temperature, CO2 pressure, and reaction time) on catalytic activity
University, Hefei, PR China
Correspondence
Longchao Du, School of Chemistry and Chemical
Engineering and Key Laboratory of Environment-
friendly Polymer Materials of Anhui Province,
Anhui University, Hefei, PR China.
Email: dulongchao@sina.com
and selectivity were investigated. The results indicated that, with the increase of
temperature, both the catalyst efficiency and the molecular weight of the copoly-
mer decrease for all the five complexes. The salen-Co(III) complex demonstrated
Funding information
ꢀ
higher activity under mild conditions: reaction temperature at 30 C, copolymeri-
211 Project of Anhui University, Grant/Award
Number: J04100301; Anhui Province Key
Laboratory of Environment-friendly Polymer
Materials
zation time of 24 hr, and 2 MPa of CO2 pressure. The DSC curve indicated that
ꢀ
the PPC by the salen-Co(III) complex has the highest Tg of 46.19 C. DTGA
curves demonstrated that there were two thermal degradation peaks: the first is for
the ester bond, and the second is for the C C bond.
KEYWORDS
bifunctional catalysts, carbon dioxide, copolymerization, salen-M(III) complexes
Many heterogeneous catalytic systems have attracted
much attention and achieved good development.[7] Never-
1
| INTRODUCTION
Climate change is one of the main current societal chal-
lenges that we face, and CO2 is currently regarded as the
culprit. At the same time, the efficient transformation of
CO2 into high value-added chemical products has attracted
widespread attention from both academic research and
industrial production as CO2 is considered to be an inexpen-
sive and nontoxic C1 building block, and its conversion can
reduce the Greenhouse effect.[1] Polycarbonate was prepared
from CO2 and epoxides for the first time by Inoue and
coworkers in 1969.[2] Over the past decade, the many pro-
cesses have reported the alternating copolymerization of
CO2 with epoxides to provide polycarbonates[3] and five-
membered cyclic carbonates[4] (Scheme 1). Both polycarbo-
nates and cyclic carbonates have significant industrial appli-
cations. Polycarbonates have been used as potential
commodity applications, such as engineering materials,
packaging materials and reins, etc.[5] On the other hand,
cyclic carbonates are capable as nonpolar solvents and are
also vital intermediates for chemicals and pharmaceuticals.[6]
theless, these catalysts suffered some deficiencies, including
poor activity, inefficiency, and low selectivity. During the
past few years, the salen-type complexes with Schiff base as
ligand have gradually evolved. This kind of ligand system
is extensively noted as its structure can easily be modified
by introducing various substituents in aromatic nucleus as
well as different metals accessing the N2O2 coordination
pocket of these Schiff ligands, which act as the catalytic
center in CO2/epoxides copolymerizations.[4a] Furthermore,
much research demonstrated that salen–metal complexes
show higher catalytic activity and selectivity.[8] The special
features of these complexes are that the molecular weight of
the polymers can be controlled and polymers can be sepa-
rated on the basis of the distribution of molecular weight.[9]
In the present paper, we have designed and synthesized
a new salen ligand bearing quaternary ammonium salts
(Scheme 2). Based on the previous results, the research
focused on 2,4-dinitrophenoxy as both the axial anion X
and the counter anion Y in this ligand. In order to
© 2018 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J. Chin. Chem. Soc. 2018;1–9.
http://www.jccs.wiley-vch.de
1

2
ZHU ET AL.
some different metal cations on copolymerization. Here,
salen-Co(III), Cr(III), Fe(III), Mn(III), and Ni(III) com-
plexes were investigated as catalysts for the copolymeriza-
tion of CO2 and PO under various reaction conditions, and
the results were summarized in Table 1. The copolymeriza-
tion results indicated that the Co(III) cation is more compe-
tent for operation as an axial ligand, and the salen-Co(III)
complex displays more activity and selectivity than other
salen–metal cations complexes do. When the reaction was
O
C
O
catalyst
O
O
O
O
C
*
O
O
O
*
m
n
SCHEME 1 Copolymerization and cycloaddition of CO2 and epoxide
investigate the influence of different metals on catalytic effi-
ciency, some transition metals (Co(III), Cr(III), iron(III),
Mn(III), and Ni(III)) were selected for the copolymerization
of CO2 with propylene oxide (PO). Full details of the cou-
pling reaction of these transition metals with the salen
ligand and the catalytic copolymerization will be explicated.
ꢀ
conducted at 30 C under 2 MPa of CO2 pressure, the TON
of the salen-Co(III) complex was 1,125 with 24 hr, and the
selectivity of PPC was 58.13%. While using the salen-Cr
(III) complex as a catalyst, decreased activity was observed,
whose TON was 840. When the center cation was replaced
by Fe(III), Mn(III), or Ni(III), these complexes show much
lower activity (285–570). At the same time, it can be seen
that, as the temperature rises, the TON of the salen-Co(III)
complex decreases gradually. When the temperature
2
| RESULTS AND DISCUSSION
2.1 | Synthesis and characterization
As mentioned earlier, we have observed that salen–metal
catalyst systems demonstrated good activity and efficiency
for the copolymerization of CO2 with epoxides under mild
conditions. Accordingly, our primary goal was to synthesize
a new ligand and explore the influence of transition metals
on copolymerization.
ꢀ
increased to 40 C, the TON decreased to 915. As the tem-
perature further increased, the TON was remarkably reduced
ꢀ
to 375 at 80 C. The other four salen-M(III) complexes also
show the same trend. Simultaneously, it can be seen that the
same phenomenon occurs in the molecular weight of copol-
ymers (Figure 1). The copolymers by the salen-Co(III) com-
Firstly, 2-(4-hydroxyphenyl)ethanol was used as the raw
material, where all the hydrogens of hydroxyl were
substituted by reacting with NaOH and CH3I using Tetrahy-
drofuran (THF) as the solvent under stirring and refluxing
conditions to obtain compound 1. Subsequently, under the
catalysis of AlCl3, the acylation reaction of compound
1 and acetyl chloride occurred in CH2Cl2 under N2 atmo-
sphere, and then, compound 2 was produced. In the next
step, compound 2 and HBr reacted at elevated temperatures;
with the breaking of the ether bond, compound 3 was grad-
ually formed. In the fourth step, the bromine group of com-
pound 3 was substituted by I¯ in a refluxing solvent of
CH3CN to obtain compound 4. The vital step was the con-
densation of compound 4 with ethylenediamine to synthe-
tize the desired salen ligand (compound 5). The salen ligand
tethering quaternary ammonium salt (compound 6) was
obtained by the reaction of the ligand with triethylamine,
and then I¯was exchanged by BF4−. The salen–metal com-
plexes were formed via reaction of the ligand (compound 6)
with different metal salts, and then, O2 was introduced into
the solution to oxidize M2+ to M3+ (M Co, Cr, Fe, Mn and
Ni); at the same time, 2,4-dinitrophenoxy was introduced as
ꢀ
plex demonstrate the highest Mn of 101,435 at 30 C. With
increasing temperatures, the Mn decreased to 73,086 at
ꢀ
ꢀ
40 C. On further warming of up to 80 C, the Mn reduced
to 26,719. The gradually decreases of TON and Mn may be
attributed to the gradual depolymerization and degradation
of polycarbonate at high temperature. Previous literature has
confirmed this result.[11] Under the same conditions, the Mn
decreased in the following order: Co(III) > Cr(III) > Fe
(III) > Ni(III) > Mn(III), which is similar to that of TON.
OH
O
OH
O
OH
OCH3
OCH3 O
HBr
CH3I
Acetyl chloride
AlCl3
NaI
I
Br
OH
OCH3
OCH3
1
3
2
4
C
N
N
C
Anhydrous triethylamine
AgBF4
Ethylenediamine anhydrous
OH
HO
I
I
5
1
2,4-dinitrophenol
sodium 2,4-dinitrophenolate
both the axial anion X and the counter anion Y. H-NMR
(Nuclear Magnetic Resonance) spectra of the catalysts 7–11
were shown in Figure 5 and Figure S7–S10.
C
N
N
C
C
N
N
C
M
X
OH
HO
O
O
NEt3BF4
NEt3
Y
F4BEt3
N
YEt3N
6
X=Y= 2,4-dinitrophenoxy
2.2 | Polymerization studies
7
8
9
M=Co
M=Cr
M=Fe
According to the literature,[10] it is universally known that
different metal cations impart different activities and selec-
tivities to PO. Consequently, we first explored the effects of
10 M=Mn
11 M=Ni
SCHEME 2 Synthesis of salen ligand precursor and catalysts 7–11

ZHU ET AL.
3
TABLE 1 Comparison of the reactivities of catalysts 7–11 in the copolymerization of CO2/PO at Pco2 = 2 MPa, t = 24 hra
e
Selectivityc
Tg (ꢀC)
d
Entry
1
Cat
7
T (ꢀC)
30
40
60
80
30
40
60
80
30
40
60
80
30
40
60
80
30
40
60
80
TOF (hr−1 b
)
TON
1,125
915
630
375
840
555
345
240
570
390
270
210
285
660
270
165
405
270
180
105
PPC%
58.13
45.48
8.93
1.41
11.82
2.58
1.13
<1
PPO%
41.04
53.83
90.45
97.93
87.35
92.74
98.24
>99
CPC%
<1
Mn
Mw/Mn
1.15
1.25
1.29
1.23
1.29
1.23
1.26
1.40
1.33
1.31
1.51
1.41
1.09
1.13
1.23
1.27
1.46
1.26
1.35
1.22
Tg1
Tg2
46.9
38.2
26.3
15.6
35.3
23.1
14.4
10.3
23.8
16.3
11.5
8.8
101,435
73,086
38,127
26,719
63,688
46,052
23,800
14,156
61,730
39,962
24,320
13,434
33,319
28,257
9,238
46.19
46.07
44.73
43.78
45.09
44.07
43.37
–
−72.29
−72.85
−73.76
−75.86
−72.71
−75.06
−75.89
−76.13
−74.54
−75.48
−76.04
−76.67
−75.27
−75.74
−76.06
−75.96
−74.03
−74.89
−75.46
−75.93
2
7
<1
3
7
<1
4
7
<1
5
8
<1
6
8
4.68
<1
7
8
8
8
<1
9
9
3.58
1.76
<1
95.08
97.34
>99
1.34
<1
44.36
43.86
–
10
11
12
13
14
15
16
17
18
19
20
9
9
<1
9
<1
>99
<1
–
10
10
10
10
11
11
11
11
11.9
27.5
11.3
6.9
2.23
1.58
1.18
<1
97.12
97.85
98.23
>99
<1
43.84
43.67
43.48
–
<1
<1
<1
5,739
16.9
11.3
7.5
7.86
4.41
1.92
1.18
91.74
94.91
97.24
98.03
<1
56,643
32,316
17,984
8,273
44.62
43.83
43.91
43.67
<1
<1
4.4
<1
TOF refers to turn-overfrequency. TON refers to turn-over number.
a
Polymerizations run in neat PO (PO 10 g, cat: PO = 1:15,000 molar ratio).
Turnover frequency: mole of PO consumed by per mole of catalyst per hour.
Selectivity of copolymerization determined by 1H-NMR spectroscopy (CDCl3, 400 MHz).
Determined using Gel Permeation Chromatography (GPC) by a polystyrene standard.
Tg of PPC (Tg1) and PPO (Tg2) were determined by DSC.
b
c
d
e
According to the above results, it can be concluded that
was the highest, which indicated that the product has the
highest content of polycarbonates (PPC) at 30 C (the ratio
ꢀ
the salen-Co(III) complex has higher activity and catalytic
1
efficiency. The H-NMR of copolymers by the salen-Co(III)
of polycarbonate, polyether, and cyclic carbonate were
shown in Table 1). The peak at the 3.58 ppm is for the
polypropylene ether (PPO). When the temperature is greater
ꢀ
complex from 30 to 80 C is shown in Figure 2. The peak
ꢀ
value of the 5.00 ppm for the synthesized product at 30 C
ꢀ
than 40 C, the peaks at 5.00 ppm are almost absent,
80ºC
60ºC
40ºC
30ºC
6
5
4
3
2
1
ppm
FIGURE 1 Mn of polymers synthesized by catalysts 7–11 at different
temperatures. In all case, Pco2 = 2 MPa, t = 24 hr
FIGURE 2 1H-NMR spectrum of polymers synthesized at different
temperatures using catalyst 7 in CDCl3

4
ZHU ET AL.
It can be seen in Table 3 that the CO2 pressure also has
a marked effect on the catalytic activity of the salen-Co(III)
complex. The pressure trend for copolymerization are simi-
lar to that of time. When the pressure increased from 1 to
2 MPa, TON increased from 225 to 1,125, and the selectiv-
ity of PPC increased from 2.43% to 58.13%. At the same
time, the Mn increased from 9,091 to 101,435. When the
pressure increased further, the value of TON and the selec-
tivity of PPC and Mn obviously decreased. With the pres-
sure increasing to 4 MPa, TON has a drop-off to 285, the
selectivity of PPC decreased to 4.43%, and Mn decreased to
26,453. In the polymerization process, the catalyst first acti-
vated propylene oxide and then reacted with CO2. When the
pressure of carbon dioxide is too high, it will hinder the
reaction of the catalyst and propylene oxide and result in
low catalyst efficiency. The same phenomenon has been
reported by Meng et al.[12] This result demonstrated that the
first-rank pressure for the formations of copolymer
was 2 MPa.
f
g
e
O
b
*
d
a
O
O
O
*
c n
m
c
HT
f
d
b
g
a
e
TT
HH
155.0
154.5 154.0
153.5 153.0
ppm
152.5
152.0
151.5
151.0
160
140
120
100
80
60
40
20
0
ppm
FIGURE 3 13C-NMR spectrum of copolymer (entry 1 in Table 1)
indicating that PPO is the main content of the synthesized
products after the temperature rises above than 40 C.
Meanwhile, the peaks of hydroxyl groups, around
ꢀ
2.3 | Thermal properties
δ = 1.9 ppm, were strengthened, which confirmed the
above finding. For entry 1, the C-NMR of copolymer is
The Differential Scanning Calorimeter (DSC) curves of the
copolymers (Table 1, entries 1, 5, 9, 13, and 17) by the cat-
alysts 7–11 are shown in Figure 4, which adopted the data
from the second heating–cooling cycle. It can be seen that
some differences appear in curves, which may be caused by
different contents of PPC in copolymers. The Tg of PPC
1
shown in Figure 3, and the characteristic peaks for PPC at
δ(ppm) 20.9, 71.1, 73.9, and 153.1 ppm are ascribed to the
carbon atoms of CH3, CH, CH2, and OCOO groups, respec-
tively. The peaks for polypropylene ether (PPO) are at 19.7
(CH3), 66.5 (CH2), and 75.2 (CH).
ꢀ
ranges from 42 to 47 C; among them, entry 1 by the salen-
ꢀ
Because the salen-Co(III) complex has the highest cata-
lytic efficiency, the effects of time and pressure on copoly-
merization were also studied. It is noted in Table 2 that,
when the reaction time increased from 12 to 24 hr, the
selectivity of PPC increased from 8.67% to 58.13%, TON
increased from 195 to 1,125, and Mn increased from 45,796
to 101,435. Nevertheless, when time is lengthened further,
both TON and Mn dramatically decreased. At 48 hr of copo-
lymerization time, the selectivity of PPC decreased to
7.68%, TON decreased to 420, and Mn decreased 55,232. It
may be that at the very start, improving time is beneficial to
copolymerization, and further prolonging the reaction time
results in the degradation of copolymers.
Co(III) complex has the highest Tg of 46.19 C. This may
be that due to the highly isotactic PPC prepared by the
salen-Co(III) complex, which was distinctly verified by
Figure 3, and the Tg of the highly isotactic copolymer is
obviously higher than those of atactic copolymers.[13] For
this reason, entry 1 has the highest Tg of PPC.
The typical TG/DTG curves of the copolymers (Table 1,
entries 1, 5, 9, 13, and 17) can be observed in Figure 5.
These copolymers showed several welꢀl-defined steps of
weight loss when heated from 30 to 600 C under N2 atmo-
sphere. The copolymers were found to be stable below
ꢀ
100 C. Heated further, the DTG curves revealed two steps
of thermal degradation. For entry 1, the first thermal
TABLE 2 Effect of reaction time: complex 7 catalyzed copolymerization of CO2/PO at T = 30 ꢀC, p = 2 MPaa
Selectivityc
d
Entry
T (hr)
12
TOF (hr−1 b
)
TON
195
PPC%
8.67
PPO%
90.63
41.04
72.07
91.54
CPC%
<1
Mn
Mw/Mn
1.30
1
2
3
4
8.1
46.9
29.4
17.5
45,796
101,435
69,725
55,232
24
1,125
705
58.13
27.14
7.68
<1
1.15
36
<1
1.27
48
420
<1
1.38
a
b
c
d
Polymerizations run in neat PO (PO 10 g, cat: PO = 1:15,000 molar ratio).
Turnover frequency: mole of PO consumed by per mole of catalyst per hour.
Selectivity of copolymerization determined by 1H-NMR spectroscopy (CDCl3, 400 MHz).
Determined using GPC by a polystyrene standard.

ZHU ET AL.
5
TABLE 3 Effect of CO2 pressure: complex 7 catalyzed copolymerization of CO2/PO at T = 30 ꢀC, t = 24 hra
Selectivityc
d
Entry
P (MPa)
TOF (hr−1 b
)
TON
225
PPC%
2.43
PPO%
96.78
41.04
66.02
94.74
CPC%
<1
Mn
Mw/Mn
1.31
1
2
3
4
1
2
3
4
9.4
46.9
24.4
11.9
9,091
1,125
585
58.13
33.27
4.43
<1
101,435
62,781
26,453
1.15
<1
1.21
285
<1
1.43
a
b
c
d
Polymerizations run in neat PO (PO 10 g, cat: PO = 1:15,000 molar ratio).
Turnover frequency: mole of PO consumed by per mole of catalyst per hour.
Selectivity of copolymerization determined by 1H-NMR spectroscopy (CDCl3, 400 MHz).
Determined using GPC by a polystyrene standard.
ꢀ
degradation peak appeared at 209 C, and the reason may
be due to the break of ester bond of PPC and the volatiliza-
tion of more CPC (five membered cyclic carbonates), which
resulted in a low degradation temperature compared to the
other four entries. This result is also consistent with the
selectivity of the PPC value in Table 1. The next weight
nitrogen with the standard Schlenk techniques. PO was pur-
chased from Shanghai Macklin Biochemical Co., Ltd and
distilled under refluxed over CaH2. Except methanol, which
was distilled using sodium, all reagents (THF, CH2Cl2,
CH3CN, cyclohexane) were dried by distillation over CaH2.
Hydrogen bromide was purchased from Shanghai Richjoint
Chemical Reagents Co., Ltd. and used as received without
ꢀ
loss in 359 C may be caused by the breaking of the C C
bond. For entry 5, the first weight loss is centered at
241 C, and the second appears at 384.1 ꢀC. For entry
9, the first weight loss occurs at 221 C, and the other one
is at 378 C. For entry 13, the maximum weight loss tem-
peratures are 234 and 368 C, respectively. For entry
17, the copolymer has two weight loss steps at 234 and
1
any further purification. H-NMR (400 MHz) spectra were
ꢀ
recorded on a Varian Mercury Plus 400 using CDCl3 or
DMSO-d6 as solvent. The Fourier transform infrared (FTIR)
spectra were collected on a Nicolet MAGNA-IR750 with
samples prepared as KBr pellet. The TGA data were
obtained under a nitrogen flow rate of 6 × 10−5 m3/min and
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
a scan rate of 20 C/min using a Shimadzu TGA-50H ther-
368 C. At the same time, the DTG curves indicated the
moanalyzer. The glass transition temperatures were investi-
gated with a Perkin-Elmer 7 DSCꢀ instrument, and the
samples were heated at the rate of 20 C/min under nitrogen
flow. The molecular weights (Mn and Mw) were determined
by a Waters Millennium instrument with polystyrene stan-
dards. For experimental details, see Supporting Information.
50 wt% weight loss temperature (Td) appeared at
247–328 C for these five samples. The results from DSC
and Thermogravimetric Analysis (TGA)/ Differential Ther-
mal Gravity Analysis (DTGA) indicate that the synthesized
copolymers are suitable as sealants.
ꢀ
3
| EXPERIMENTAL
3.2 | Synthesis of compound 1–11
3.2.1
| Synthesis of compound 1
3.1 | Materials and instrumentation
2-(4-Hydroxyphenyl)ethanol (11.68 g 0.08 mol) and NaOH
(15 g 0.375 mol) were added to a flask and combined with
Unless otherwise explained, all manipulations were carried
out in a standard glove box under an atmosphere of dry
5
100
1
0
4
catalyst 10
80
60
40
20
0
-1
-2
-3
3
catalyst 11
catalyst 9
2
-4
catalyst 10
catalyst 11
catalyst 9
catalyst 8
catalyst 7
-5
-6
1
catalyst 8
-7
-8
0
catalyst 7
-9
-10
-1
0
100
200
300
400
500
600
-100
-50
0
50
100
150
Temperature(ºC)
Temperature(ºC)
FIGURE 4 DSC curves of the copolymers synthesized by catalysts 7–11.
In all cases, T = 30 ꢀC, Pco2 = 2 MPa, t = 24 hr
FIGURE 5 TGA and DTGA curves of the copolymers synthesized by
catalysts 7–11. In all cases, T = 30 ꢀC, Pco2 = 2 MPa, t = 24 hr

6
ZHU ET AL.
THF (350 mL). After the mixture was stirred at room tem-
perature for 1 hr, CH3I (30 g 0.211 mol) was subsequenꢀtly
added into the flask. Then, the solution was heated to 66 C
and refluxed for 2 days. After cooling to room temperature,
the solution was extracted using CH2Cl2, and the organic
phase was collected and dried with anhydrous MgSO4.
Thereafter, the solvent was removed under vacuum to
obtain a pure product (12.21 g, 92%). IR(KBr): 1,213
The reaction mixture was refluxed for 2 days, and on cool-
ing to room temperature, the solid was removed by filtration
and washed thrice with CH2Cl2. The solution was concen-
trated under reduced pressure; after that, the resulting prod-
uct was eluted with petroleum ether and ethyl acetate (v/v,
10:1) through column chromatography with silica gel. The
pure product was 6.96 g (82.7%). IR(KBr): 3,462(OH)
1
cm−1. H-NMR(CDCl3): δ = 2.64(s, 3H, CH C O), 3.12
(Ar O C),
1,030(C O C)cm−1
.
1H-NMR(CDCl3):
(t, J = 7.51 Hz, 2H, C CH2), 3.33(t, J = 7.51 Hz, 2H,
Ar CH2), 6.93(d, J = 8.52 Hz, 1H, Ar H), 7.33(dd,
J = 2.10 Hz, 1H, Ar H), 7.55(d, J = 1.30 Hz, 1H, Ar H),
and 12.19(s, 1H, Ar OH).
δ = 2.80(t, J = 7.51 Hz, 2H, C CH2), 3.32(s, 3H,
O CH3), 3.53(t, J = 7.5 Hz, 2H, Ar CH2), 3.73(s, 3H,
Ar O CH3), 6.81(d, J = 9.61 Hz, 1H, Ar H), and 7.11(d,
J = 8.49 Hz, 1H, Ar H).
3.2.5
| Synthesis of compound 5
3.2.2
| Synthesis of compound 2
Compound 4 (6.38 g 0.022 mol) was placed in a three-neck
flask under an N2 atmosphere in a glove box, and then,
anhydrous ethylenediamine (0.66 g 0.011 mol) and cyclo-
hexane (150 mL) were added. The reaction mixture was
Compound 1 (10 g 0.06 mol) was dissolved in anhydrous
dichloromethane (350 mL), and then, the solution was
poured into a four-neck flask. Meanwhile, AlCl3 and acetyl
chloride were weighed into the flask under an N2 atmo-
ꢀ
ꢀ
stirred for 24 hr at 80 C. After the solution cooled to room
sphere. The reaction mixture was stirred for 24 hr at 0 C.
temperature, it was filtered through Celite, and the filtrate
was distilled by a rotary evaporator. The resulting yellow
solid was adequately pure of the desired product without
further purification (3.87 g 58.2%). IR(KBr): 3,481(OH),
Then, the solution was treated with glacial hydrochloric
acid, and the organic phase was extracted by CH2Cl2; the
resulting solution was dried with anhydrous MgSO4 for
2 hr. After removal of the solvent under reduced pressure,
the crude product was purified by column chromatography
using silica gel. The yield was 71.4% (8.96 g). IR(KBr):
1,615(C N)cm−1
.
1H-NMR(CDCl3): δ = 2.40(s, 3H,
CH3 C O), 3.10(t, J = 7.72 Hz, 2H, C CH2), 3.30(t,
J = 7.72 Hz, 2H, Ar CH2), 3.92(t, J = 7.56 Hz, 2H,
N CH2), 6.87(d, J = 8.44 Hz, 1H, Ar H), 7.11(dd,
J = 2.00 Hz, 1H, Ar H), 7.32(s, 1H, Ar H), and 12.19(s,
1H, Ar OH).
1
1,710(C O)cm−1. H-NMR(CDCl3): δ = 2.60(s, 3H, CH3
C O), 2.84(t, J = 6.88 Hz, 2H, C CH2), 3.34(s, 3H,
O CH3), 3.57(t, J = 6.91 Hz, 2H, Ar CH2), 3,89(s, 3H,
Ar O CH3), 6.90(d, J = 8.45 Hz, 1H, Ar H), 7.33(d,
J = 8.49 Hz, 1H, Ar H), and 7.59(s, 1H, Ar H).
3.2.6
| Synthesis of compound 6
3.2.3
| Synthesis of compound 3
Compound 5 (0.5 g 0.828 mmol) was dissolved in CH3CN
(50 mL) at the temperature of 65 C, and anhydrous triethy-
lamine (0.419 g 4.14 mmol) was added under N2 atmo-
sphere. The reaction mixture was heated to 81 C and
Compound 2 (8 g 0.038 mol) was weighed into a one-neck
round bottom flask (100 mL) in a glove box, and then,
hydrogen bromide (6.76 g 0.0836 mol) was slowly added.
The reaction mixture was refluxed for 2 days. After the
resulting solution cooled to room temperature, the organic
phase was extracted by CH2Cl2. Afterward, the solution
was dried over anhydrous MgSO4, and it was filtered
through Celite. The solvent was removed by a rotary evapo-
rator to obtain the crude product, and it was then refined by
eluting column chromatography. The yield was 82.5%
ꢀ
ꢀ
stirred for 48 hr. After the solution cooled to the room tem-
perature, CH3CN was removed with a rotary evaporator to
obtain residue. Subsequently, the residue was triturated in
diethyl ether. The obtained yellow powder was dissolved in
CH3CN (50 mL), and then, AgBF4 (0.326 g 1.66 mmol)
was added to the solution under an N2 atmosphere.[14] After
the solution was stirred at room temperature for 24 hr, it
was filtered through Celite. The solvent was removed under
vacuum to obtain the desired ligand. The yield was 73.6%
(7.62 g). IR(KBr): 3,343(OH), 641(C Br) cm−1. H-NMR
1
(CDCl3): δ = 2.64(s, 3H, CH3 C O), 3.13 (t,
J = 7.30 Hz, 2H, C CH2), 3.55(t, J = 7.31 Hz, 2H,
Ar CH2), 6.94(d, J = 8.45 Hz, 1H, Ar H), 7.30(dd,
J = 2.17 Hz, 1H, Ar H), 7.57(d, J = 2.14 Hz, 1H, Ar H),
and 12.19(s, 1H, Ar OH).
(0.443 g). IR(KBr): 3,464(OH), 1,645(C N) cm−1 1H-
.
NMR(DMSO-d6): δ = 1.17(t, J = 7.27 Hz, 18H, C CH3),
2.42(s, 6H, CH3 C O), 3.10(q, J = 7.27 Hz, 12H,
N CH2), 3.21(t, J = 7.72 Hz, 4H, C CH2), 3.54(t,
J = 7.53 Hz, 4H, Ar CH2), 4.06(t, J = 7.35 Hz, 4H,
N CH2), 6.97(d, J = 2.25 Hz, 2H, Ar H), 7.50(dd,
J = 2.10 Hz, 2H, Ar H), 7.83(s, 2H, Ar H), and 11.78(s,
2H, Ar OH).
3.2.4
| Synthesis of compound 4
To a three-neck flask containing compound 3 (7 g
0.029 mol) in 200 mL of CH3CN, NaI (4.34 g 0.029 mol)
was added under an N2 atmosphere in standard glove box.

ZHU ET AL.
7
g
processes as those of compound 7 using this yellowish-
k
C
N
N
C
green
precipitate.
1H-NMR(DMSO-d6):
δ = 1.21(t,
c
Co
h
J = 7.28 Hz, 18H, C CH3), 2.32(s, 6H, CH3 C O), 3.11
(q, J = 7.46 Hz, 12H, N CH2), 3.22(t, J = 7.27 Hz, 4H,
C CH2), 3.56(t, J = 7.47 Hz, 4H, Ar CH2), 4.46(t,
J = 6.98 Hz, 4H, N CH2), 7.24(d, J = 2.31 Hz, 3H,
Ar H), 7.65(d, J = 2.14 Hz, 2H, Ar H), 8.07(dd,
J = 2.34 Hz, 2H, Ar H), 8.34(s, 2H, Ar H), 8.64(d,
J = 2.26 Hz, 3H, Ar H), and 9.11(s, 3H, Ar H). Anal.
Calc.(C52H63CrN10O17): C, 54.21; H, 5.51; N, 12.6.
Found: C, 53. 98; H, 5.48; N, 12.34.
O
O
X
i
Y e d
a b f
NEt3
YEt3N
j l
X=Y= 2,4-dinitrophenoxy
l
k
a
b c
g h
d
j
e
i
f
3.2.9
| Synthesis of compound 9
The compound 6 (0.2 g 0.28 mmol) and 1.0 equiv of anhy-
drous iron(II) acetate (0.048 g 0.28 mmol) were dissolved
in 50 mL of MeOH. The solution was heated to reflux for
2 hr under an N2 atmosphere.[16] After cooling to room tem-
perature, the resulting solution was filtered via Celite, and
then, the solvent was removed to acquire the red precipitate.
Thereafter, the precipitate was washed and triturated in
diethyl ether. Fe2+ were oxidized to Fe3+ by introducing
oxygen into the solution. This specific step was similar to
the procedure of compound 7. 1H-NMR(DMSO-d6):
δ = 1.22(t, J = 7.34 Hz, 18H, C CH3) 2.41(s, 6H,
CH3 C O), 3.13(q, J = 7.12 Hz, 12H, N CH2), 3.19(t,
J = 7.07 Hz, 4H, C CH2), 3.53(t, J = 7.56 Hz, 4H,
Ar CH2), 4.31(t, J = 6.98 Hz, 4H, N CH2), 7.07(d,
J = 2.31 Hz, 3H, Ar H), 7.58(d, J = 2.14 Hz, 2H, Ar H),
7.93(d, J = 2.17 Hz, 2H, Ar H), 8.24(t, 2H, Ar H), 8.84
(d, J = 2.15 Hz, 3H, Ar H), and 9.27(s, 3H, Ar H). Anal.
Calc.(C52H63FeN10O17): C, 54.03; H, 5.49; N, 12.12.
Found: C, 53.88; H, 5. 53; N, 12.24.
12
10
8
6
4
2
0
ppm
FIGURE 6 1H-NMR spectrum of the catalysts 7 in DMSO-d6
3.2.7
| Synthesis of compound 7
The compound 6 (0.2 g 0.28 mmol) and anhydrous
cobalt(II) acetate (0.049 g 0.28 mmol) were dissolved in
MeOH (50 mL) under N2 atmosphere. To produce a
brownish-red solution, the reaction mixture was stirred for
6 hr at room temperature. Then, the product was isolated
through Celite, the solvent was removed, and the precipitate
was triturated in diethyl ether. To a flask containing the pre-
cipitate
with CH2Cl2, 2,4-dinitrophenol (0.051 g
0.28 mmol) was added under an O2 atmosphere. After the
solution was stirred for 12 hr at room temperature, sodium
2,4-dinitrophenolate (0.17 g 0.83 mmol) was added and
stirred for an additional 24 hr. The solution was filtered,
and then, the filtrate was removed under reduced pressure
1
to form the brown product (0.26 g 82.2%). The H-NMR
spectrum of compound 7 is shown in Figure 6. H-NMR
3.2.10
| Synthesis of compound 10
1
A solution of anhydrous manganese(II) acetate (0.048 g
0.28 mmol) in MeOH (10 mL) was added to a solution of
compound 6 (0.2 g 0.28 mmol) in MeOH (40 mL) under
N2 atmosphere. The mixture was stirred under refluxing for
3 hr.[17] Later, the solution was cooled to ambient tempera-
ture and then was filtered by Celite. The solution was then
removed by reduced pressure, and the brown precipitate
was triturated in diethyl ether and further dried in vacuum.
Mn2+ were oxidized to Mn3+ by introducing oxygen into
the solution. The same processes of compound 7 were
applied to the next step of compound 10 using this precipi-
tate. 1H-NMR(DMSO-d6): δ = 1.19(t, J = 7.34 Hz, 18H,
C CH3), 2.42(s, 6H, CH3 C O), 3.13(q, J = 7.46 Hz,
12H, N CH2), 3.19(t, J = 7.18 Hz, 4H, C CH2), 3.52(t,
J = 7.09 Hz, 4H, Ar CH2), 4.84(t, J = 7.73 Hz, 4H,
N CH2), 6.91(d, J = 2.25 Hz, 3H, Ar H), 8.06(d,
J = 2.26 Hz, 2H, Ar H), 8.49(dd, J = 2.44 Hz, 2H,
Ar H), 8.89(s, 2H, Ar H), 9.33(d, J = 2.45 Hz, 3H,
Ar H), and 9.79(s, 3H, Ar H). Anal. Calc.
(DMSO-d6): δ = 1.19(t, J = 7.45 Hz, 18H, C CH3), 2.43
(s, 6H, CH3 C O), 3.13(q, J = 7.27 Hz, 12H, N CH2),
3.20(t, J = 7.72 Hz, 4H, C CH2), 3.56(t, J = 7.47 Hz, 4H,
Ar CH2), 4.12(t, J = 7.24 Hz, 4H, N CH2), 6.76(d,
J = 2.12 Hz, 3H, Ar H), 6.97(d, J = 2.25 Hz, 2H, Ar H),
7.52(dd, J = 2.10 Hz, 2H, Ar H), 7.86(s, 2H, Ar H), 8.38
(d, J = 2.18 Hz, 3H, Ar H), and 8.84(s, 3H, Ar H). Anal.
Calc.(C52H63CoN10O17): C, 53.89; H, 5.48; N, 12.08.
Found: C, 53.44; H, 5.32; N, 12.24.
3.2.8
| Synthesis of compound 8
To a solution of compound 6 (0.2 g 0.28 mmol) in MeOH
(50 mL), anhydrous chromium(II) chloride (0.034 g
0.28 mmol) was added. The mixture was stirred under an
N2 atmosphere at ambient temperature for 24 hr.[15] The
yellowish-green solid was obtained through Celite, and the
solvent was removed and then washed by diethyl ether. Cr2
+
were oxidized to Cr3+ by introducing oxygen into the
solution. This compound was prepared by the same

8
ZHU ET AL.
(C52H63MnN10O17): C, 54.07; H, 5.50; N, 12.13. Found: C,
53.94; H, 5.42; N, 12.28.
complexes. Under identical reaction conditions, we have
confirmed through experiments that the influence of metal
cations on catalytic efficiency followed the order
Co3+ > Cr3+ > Fe3+ > Ni3+ > Mn3+. For copolymeriza-
3.2.11
| Synthesis of compound 11
ꢀ
The compound 6 (0.2 g 0.28 mmol) was dissolved in
MeOH (50 mL), and Ni(OAc)2Á4H2O (0.06 g 0.28 mmol)
was added under the protection of N2. The solution was
warmed to reflux for 24 hr and then cooled to room temper-
ature.[18] Subsequently, the solution was filtered through
Celite, and the solvent was removed by rotary evaporation.
A yellow product was formed, which was triturated in
diethyl ether and further dried in vacuum. Ni2+ were oxi-
dized to Ni3+ by introducing oxygen into the solution. The
specific approach was the same as those procedures of com-
pound 7. 1H-NMR(DMSO-d6): δ = 1.22(t, J = 6.98 Hz,
18H, C CH3), 2.38(s, 6H, CH3 C O), 3.11(q,
J = 7.18 Hz, 12H, N CH2), 3.19(t, J = 7.18 Hz, 4H,
C CH2), 3.54(t, J = 7.53 Hz, 4H, Ar CH2), 5.14(t,
J = 7.09 Hz, 4H, N CH2), 7.95(d, J = 2.09 Hz, 3H,
Ar H), 8.27(d, J = 2.26 Hz, 2H, Ar H), 8.49(dd,
J = 2.18 Hz, 2H, Ar H), 8.90(s, 2H, Ar H), 9.15(d,
J = 2.18 Hz, 3H, Ar H), and 9.60(s, 3H, Ar H). Anal.
Calc.(C52H63NiN10O17): C, 53.90; H, 5.48; N, 12.09.
Found: C, 53.78; H, 5.22; N, 12.18.
tion of CO2/PO at 30 C and 2 MPa CO2 pressure by utiliz-
ing salen-Co(III) complex, 58.13% of PPC selectivity was
obtained within 24 hr, with the highest Mn value of
101,435.
DSC curves indicated that the Tg of the obtained PPC
ꢀ
ranged from 42 to 47 C for the five complexes. Among
them, the PPC by the salen-Co(III) complex has the high-
ꢀ
est Tg of 46.19 C. DTGA curves showed that there were
two thermal degradation peaks. The first peak might be
due to the thermal degradation of ester bond of PPC and
the second peak to the breaking of the C C bond.
The results from DSC and TGA/DTGA indicate that
the synthesized copolymers are fit for application as
sealants.
ACKNOWLEDGMENTS
The authors are grateful for financial support from the
211 Project of Anhui University (J04100301) and Anhui
Province Key Laboratory of Environment-friendly Polymer
Materials.
3.3 | Copolymerization of CO2 and PO
ORCID
The stainless steel autoclave equipped with a motor stirrer
was first dried at 60 C for 24 hr under vacuum. Later, after
Longchao Du
http://orcid.org/0000-0002-2414-2076
ꢀ
cooling to room temperature, the sole catalyst (compound
7–11) was placed in the aꢀutoclave and was then succes-
sively dried in vacuo at 60 C. After the prescribed time of
24 hr, the autoclave was cooled, and the neat PO was added
by injection port into the autoclave. The reactor was pres-
surized to appropriate pressure (1, 2, 3, 4 MPa) with CO2;
after that, the reactor was stirꢀred and heated to the anticipant
temperature (30, 40, 60, 80 C) for the setup reaction time
(12, 24, 36, 48 hr). The reaction system was then cooled,
CO2 gas was slowly exhausted, and the autoclave was
opened. The reaction mixture was filtered through a pad of
silica gel with methylene chloride to remove only the cata-
lyst residue, but copolymer has without any further purifica-
tion. The isolated copolymer was collected via drying in
vacuum to obtain constant weight. The copolymer was ana-
lyzed by 1H-NMR.
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How to cite this article: Zhu W, Du L, Qian S,
Yang Q, Song W. Copolymerization of carbon diox-
ide and propylene oxide by several metallosalen-
based bifunctional catalysts. J. Chin. Chem. Soc.
2018;1–9. https://doi.org/10.1002/jccs.201800051