Copolymerization of carbon dioxide and propylene oxide catalyzed by two kinds of bifunctional salen-cobalt(III) complexes bearing four quaternary ammonium salts

Article abstract of DOI:10.1002/jccs.201900077

Two new bifunctional salen-cobalt(III) complexes were synthesized, which consist of salicylaldehyde bearing four quaternary ammonium salts and two different diamines. The copolymerization results indicated that decreasing temperature is advantageous for both the complexes. Of both the diamines, the complex 9 with o-diaminobenzene has a higher catalytic effect compared to complex 6 with 1,2-diaminocyclohexane. The catalytic effect of complex 9 is over 3.5 times than that of complex 6 at a temperature of 30°C. The research of P_CO2 on the copolymerization revealed that the first-rank pressure was at 2 MPa for the two complexes. The highest turnover number are under conditions of T = 30°C, P_CO2 = 2 MPa, and t = 24 hr. Differential scanning calorimeter curves indicated that poly(propylene carbonate) (PPC) by complex 9 has the highest Tg of 54.2°C. DTGA curves showed 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.201900077

Received: 1 March 2019
Revised: 26 April 2019
Accepted: 19 May 2019
DOI: 10.1002/jccs.201900077
A R T I C L E
Copolymerization of carbon dioxide and propylene oxide
catalyzed by two kinds of bifunctional salen-cobalt(III)
complexes bearing four quaternary ammonium salts
Longchao Du | Chengze Wang | Weiju Zhu | Jie Zhang
School of Chemistry and Chemical
Engineering & the Key Laboratory of
Abstract
Environment-friendly Polymer Materials of
Anhui Province, Anhui University, Hefei,
PR China
Two new bifunctional salen-cobalt(III) complexes were synthesized, which consist
of salicylaldehyde bearing four quaternary ammonium salts and two different
diamines. The copolymerization results indicated that decreasing temperature is
advantageous for both the complexes. Of both the diamines, the complex 9 with o-
diaminobenzene has a higher catalytic effect compared to complex 6 with
1,2-diaminocyclohexane. The catalytic effect of complex 9 is over 3.5 times than
that of complex 6 at a temperature of 30ꢀC. The research of PCO2 on the copolymer-
ization revealed that the first-rank pressure was at 2 MPa for the two complexes.
The highest turnover number are under conditions of T = 30ꢀC, PCO2 = 2 MPa, and
t = 24 hr. Differential scanning calorimeter curves indicated that poly(propylene car-
bonate) (PPC) by complex 9 has the highest Tg of 54.2ꢀC. DTGA curves showed
that there were two thermal degradation peaks, the first is for the ester bond, and the
second is for the C–C bond.
Correspondence
Longchao Du, School of Chemistry and
Chemical Engineering & the Key
Laboratory of Environment-friendly
Polymer Materials of Anhui Province,
Anhui University, Hefei, PR China.
Email: dulongchao@sina.com
Funding information
Anhui Province University Natural Science
Research Project, Grant/Award Number:
KJ2017A008; Natural Science Foundation of
Anhui Province, Grant/Award Number:
No.1808085ME55, No.1908085MB51;
Anhui Province Key Laboratory of
Environmentally friendly Polymer Materials
K E Y W O R D S
carbon dioxide, propylene oxide, quaternary ammonium salt, salen-cobalt complexes, synthesis
(Scheme 1). This latter event can be a major reaction pathway
when utilizing aliphatic epoxides such as ethylene oxide, pro-
1 | INTRODUCTION
Carbon dioxide is currently regarded as the major cause of
greenhouse effect, but at the same time CO2 is an abundant,
inexpensive, and renewable resource, which makes it an attrac-
tive C1 feedstock to be used in several important industrial pro-
cesses.[1] Since Inoue and coworkers first reported the
conversion of carbon dioxide and epoxide to polycarbonate in
1969,[2] increasing studies are being carried out worldwide.[3–7]
The copolymerization process is often accompanied by the for-
mation of varying amounts of ether linkages, which are the
result of consecutive epoxide ring opening. Thereinto, five-
membered cyclic carbonates are obvious by-products in these
reactions, which are formed by a backbiting mechanism, thus
shortening the polymer chain by one unit each occurrence[8,9]
pylene oxide (PO), and styrene oxide.
For the copolymerization reaction, various catalysts
including heterogeneous and homogeneous metal-based
complexes have been developed. Typical heterogeneous cat-
alysts include ZnEt2-active hydrogen containing compound
systems,[10,11] zinc dicarboxylates,[12–14] double metal cya-
nide complexes,[15–18] and rare-earth metal coordination ter-
nary catalysts.[19,20] Though the chemical structures or
crystal structures of heterogeneous catalysts are not clear,
they are convenient for synthesis and handling, showing
more potential for industrial applications.
Homogeneous catalysts are interesting for academic
research, and Inoue developed the first single-site homogeneous
© 2019 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J Chin Chem Soc. 2019;1–8.
http://www.jccs.wiley-vch.de
1

2
DU ET AL.
O
C
formylation of 4-hydroxyphenethyl alcohol using sodium
hydroxide and chloroform was successfully carried out with
good efficiency (71.3% yield). Because sulfoxide chloride
does not react with the aldehyde, alcohol hydroxyl was
transformed into the chlorine group in 40.3% yield. Because
chloroalkane is difficult to attack, the chloro-compound was
transformed into a more reactive iodo-compound 3 in 97.6%
yield. To study the electronic effect on the copolymerization
of CO2 and PO, 1,2-diaminocyclohexane and o-
diaminobenzene were used, respectively, for salen-type
ligands 4 and 7. After salen-type ligand was generated from
compound 3, triethylamine could attack the iodo-group
yielding a salen-type ligand containing four quaternary
ammonium salts. Because iodide anion intervenes in the
O
O
catalyst
O
O
O
O
C
*
O
O
O
*
m
n
SCHEME 1 Copolymerization of CO2 and epoxide
catalyst, metal tetraphenylporphyrin complex, for epoxide-CO2
copolymerization.[21] Later, homogeneous catalysts including
metal-porphyrin,[22,23] zinc phenolate,[24] and discrete b-
diiminate zinc[25] have been developed.
Among various discrete metal complex catalytic systems
explored so far, metal salen complexes[26] have attracted
considerable attention in the past decade due to their easy
synthesis, stability against moisture or air, and unprece-
dented opportunities for regioregularity and stereochemistry
control, etc. More recently, functional metal salen complex-
based catalysts received much attention, especially single-
component bifunctional metal salen complexes instead of
binary catalysts. Based on the previous results, in the present
article, we have synthesized two new single-component
bifunctional salen-cobalt(III) complexes containing quater-
nary ammonium salts, and hope to better understand the dif-
ferent amines on the copolymerization of CO2 and PO.
−
metallation reaction, it was replaced with an inert BF4
through treatment of AgBF4. Metallation was carried out
using a routine method involving the treatment of Co(OAc)2
in ethanol and oxidation using O2 in the presence of an
equivalent amount of 2,4-dinitrophenol. Finally, anion
exchange reaction was carried out by stirring the BF4− com-
plex over a slurry of three equivalents of sodium 2,4-dinitro-
phenolate in CH2Cl2.
2.2 | Polymerization studies
Two kinds of salen–Co(III) complexes 6 and 9 were used as
catalysts to investigate the electronic effect of different
diamines on the copolymerization of CO2 and PO. And the
copolymerization results are listed in Table 1. Figure 1
shows the typical 1H-NMR spectrum of the copolymers
using complexes 6 and 9 as catalysts in CDCl3. The charac-
teristic peaks for poly(propylene carbonate) (PPC) are as fol-
lows: 1H-NMR (CDCl3), δ(ppm) 1.34 (d, 3H, CH3,
J = 5.5 Hz), 4.17 (m, 2H, CH2CH), and 5.00 (m, 1H,
CH2CH). The peaks of polypropylene ether (PPO) are at
1.16 ppm (d, 3H;–CH3–), 3.58 ppm (2H; –CH2CH–), and
3.45 ppm (1H; –CH2CH–). The copolymerization was firstly
2 | RESULTS AND DISCUSSION
2.1 | Synthesis and characterization
As stated above, salen–cobalt(III) complexes were used as
catalysts for the copolymerization of CO2 and PO. Suitable
ligands should be beneficial for this purpose. This motivates
us to synthesize new ligands on the basis of previous studies.
Here, our group designed two new bifunctional Salen–Co
(III) catalysts containing quaternary salts, the structure can
be seen in the Scheme 2 as complexes 6 and 9. First,
SCHEME 2 Synthetic route of two
catalysts

DU ET AL.
3
TABLE 1 CO2/(propylene oxide)
Entry Cat T (ꢀC) P (MPa) TONb Conv.c(%) fco2
Mne×10−3 Mw/Mn
d
copolymerization resultsa
1
6
6
6
6
6
6
6
9
9
9
9
9
9
9
30
40
60
80
30
30
30
30
40
60
80
30
30
30
2
2
2
2
1
3
4
2
2
2
2
1
3
4
180.1
173.7
145.4
121.3
120.9
118.3
126.1
643.6
568.8
346.3
186.2
478.3
381.2
285.1
1.21
1.17
0.98
0.81
0.81
0.79
0.85
4.32
3.82
2.33
1.25
3.21
2.56
1.92
0.257 42.7
0.165 39.4
0.092 45.9
0.063 32.5
0.185 36.1
0.157 40.5
0.094 26.1
0.362 56.2
0.276 48.9
0.189 46.1
0.132 61.8
0.306 49.2
0.229 51.8
0.152 38.5
1.31
1.19
1.51
1.22
1.31
1.39
1.48
1.61
1.58
1.43
1.52
1.21
1.55
1.32
2
3
4
5
6
7
8
9
10
11
12
13
14
aPolymerization conditions: PO 10 g, cat: PO = 1:15,000 M ratio, and time 24 hr.
bTurnover number: mole of PO consumed by per mole of the catalyst.
cBased on the conversion of PO.
dCarbonate fraction determined using 1H NMR spectroscopy (CDCl3, 400 MHz).
eDetermined on GPC using a polystyrene standard.
9 has a higher catalytic effect on the copolymer produced.
The catalytic effect is over 3.5 times compared with that of
complex 6 at 30ꢀC. Even at the highest temperature of 80ꢀC,
the catalytic effect of complex 9 is 1.32 times than that of
complex 6. It can be possible due to the higher steric bulk of
1,2-diaminocyclohexane than 1,2-diaminobenzene, which
results in the copolymer produced by complex 9 having a
higher yield and a carbonate fraction.
entry 8
entry 1
It can be seen from Table 1 that the CO2 pressure has also a
marked effect on the catalytic activity of the complexes. For
complex 6, when the pressure was increased from 1 to 2 MPa,
c
TON increased from 120.9 to 180.1 and fco2 increased from
6
ppm
5
4
3
2
1
0.185 to 0.257. When the pressure was increased further, the
value of TON, carbonate fraction decreased obviously. With
the pressure increasing to 4 MPa, TON dropped off to 126.1,
FIGURE 1 1H-NMR spectrum of the copolymers with entries
1 and 8 using complexes 6 and 9 as catalysts in CDCl3
c
fco2 to 0.094. This phenomenon revealed that the first-rank
pressure for the formation of copolymer was at 2 MPa. At the
same time, it can be seen that the complex 9 has higher cata-
lytic activity than complex 6. For complex 9, when the pressure
was increased from 1 to 2 MPa, TON increased from 478.3 to
643.6, and fco2c increased from 0.306 to 0.362. Upon increasing
carried out at 2 MPa and 24 hr and at different temperatures
(30–80ꢀC). From entries 1–4 and 8–11, it can be seen that
the catalytic efficiency increases with decreasing tempera-
ture. The decrease of polymer yield at higher temperature
may be caused by the selectivity for PPO and the decompo-
sition of the polycarbonate. When the temperature is 30ꢀC,
the copolymerization has the highest turnover number
(TON) of 180.1 and 643.6 for complexes 6 and 9, respec-
tively. At the same time, it can be seen that entry 1 has the
highest carbonate fraction (fco2c) of 0.257 for complex 6, and
that of entry 8 is 0.362 for complex 9. Furthermore, complex
c
the pressure further, the values of TON and fco2 decreased
obviously. Upon increasing pressure to 4 MPa, TON dropped
off to 285.1, fco2c to 0.152.
2.3 | Thermal properties
The differential scanning calorimeter (DSC) curves of the
copolymers (entries 1 and 8) are shown in Figure 2. It can

4
DU ET AL.
temperature compared to the entry 8. This result is also con-
sistent with the fco2 value in Table 1. The next weight loss at
370.4ꢀC may be caused by the breaking of the C–C bond.
For entry 8, the first weight loss is centered at 256.2ꢀC and
the second appears at 378.1ꢀC. At the same time, the DTG
curves indicated the 50 wt% weight loss temperature (Td)
appeared at 303–339ꢀC for the two samples. The results
from DSC and TGA/DTGA indicate that the synthesized
copolymers are suitable as sealants.
5
0
entry 8
entry 1
-5
-10
-15
-20
-25
3 | EXPERIMENTAL
-50
0
50
100
3.1 | Materials and instrumentation
Temperature(°C)
All manipulations were performed under an inert atmosphere
using standard glove box and Schlenk techniques. Ethanol
was dried using sodium and diethyl phthalate. Tetrahydrofu-
ran (THF), PO, CH3CN, CH2Cl2, methylbenzene, and
CHCl3 were dried by stirring over CaH2, and were subse-
quently vacuum transferred to reservoirs. 1HNMR
(400 MHz) was recorded on a Varian Mercury Plus 400.
Fourier transform infrared (FTIR) studies were recorded on
a Nicolet MAGNA-IR750 apparatus using a thin film with
the ratio of sample to KBr of 1:100 by mass. The TGA pro-
files were performed on a Shimadzu TGA-50H the-
rmoanalyzer under a nitrogen flow rate of 6 × 10−5 m3/min
at a scan rate of 20ꢀC/min. The glass transition temperature
was determined on a Perkin-Elmer 7 DSC instrument at a
heating rate of 20ꢀC/min under nitrogen flow. Gel perme-
ation chromatograms (GPC) were obtained at room tempera-
ture in THF using Waters Millennium with polystyrene
standards.
FIGURE 2 DSC curve of the copolymers with entries 1 and
8 synthesized by complexes 6 and 9
be seen that some differences appear in curves, which may
be caused by different contents of PPC and PPO in copoly-
mers. These curves demonstrated that the glass transition tem-
perature (Tg) of PPO is −63.1ꢀC, and the Tg of PPC was
measured to be 50.1ꢀC for entry 1 and 54.2ꢀC for entry 8.
The Tg of highly isotactic copolymer is obviously higher than
those of atactic copolymers,[27] and due to the highly isotactic
PPC prepared by complex 9, entry 8 has higher Tg of PPC.
The typical TG/DTG curves of the copolymers (Table 1,
entries 1 and 8) can be observed in Figure 3. These copoly-
mers showed several well-defined steps of weight loss, when
heated from 30 to 600ꢀC under a N2 atmosphere. The copol-
ymers were found to be stable below 150ꢀC. Upon heating
further, the DTG curves revealed two-step thermal degrada-
tion. For entry 1, the first thermal degradation peak appeared
at 248ꢀC, the reason may be due to the breaking of the ester
bond of PPC, which resulted in a low degradation
3.2 | Synthesis and characterization of
compounds 1–9
3.2.1 | Synthesis of compound 1
100
4-Hydroxyphenethyl alcohol (5.150 g, 0.0373 mol), sodium
hydroxide (8.981 g, 0.224 mol), and 50 mL water were put
into a flask, then chloroform (13.595 g, 0.114 mol) was
added. The reaction was carried out at 100ꢀC for 24 hr. After
the reaction was quenched and the organic phase was col-
lected, the water phase was further extracted with additional
chloroform (3 × 25 mL). The combined chloroform was
dried over anhydrous MgSO4, and the solvent was removed
with a rotary evaporator. Yellowish oily product was
obtained (4.422 g, 71.3%). IR(KBr) cm−1:3,403(OH), 1,653
4
entry 8
80
entry 1
60
2
40
20
0
0
entry 8
300
entry 1
1
(C=O). H-NMR (CDCl3): δ 10.89(s, 1H, Ar-OH), 9.86(s,
100
200
400
500
600
1H, CHO)7.42(s, 1H, m-H), 7.39(d, J = 8.5 Hz, 1H, o-H),
6.94(d, J = 8.2 Hz, 1H, m-H), 3.87(t, J = 6.1 Hz, 2H, CH2),
2.86(t, J = 6.6 Hz, 2H, benzyl-CH2), and 1.69(s, 1H,
phenemyl-OH). Anal. Calc.(C9H10O3): C, 65.05; H, 6.07%.
Temperature(°C)
FIGURE 3 TGA and DTGA curves of the copolymers with
entries 1 and 8 synthesized by complexes 6 and 9

DU ET AL.
5
1
Found: C, 65.11; H, 6.02%. The HNMR spectrum of com-
pound 1 is shown in Figure S1.
white (R,R)-1,2-diaminocyclohexane-(+)tartrate solid was
obtained by filtering. The yield was 69.6%.
(R,R)-1,2-diaminocyclohexane-(+)tartrate (0.775 g, 0.00291
mol)was put into saturated potassium hydroxide, (R,R)-1,2-
diaminocyclohexane was extracted using CH2Cl2. Com-
pound 3 (1.601 g, 0.00581 mol) and above-mentioned
(R,R)-1,2-diaminocyclohexane were put into a flask, and
then ethanol (20 mL) was added. The reaction mixture was
stirred overnight at room temperature. The reaction depos-
ited a light-yellow solid with 95.4% yield. IR(KBr)
cm−1:3,424(OH), 2,137(C=N)1,632(C=O), and 479(C–I);
1H-NMR(CDCl3):δ 13.21(s, 2H, Ar-OH), 8.21(s, 2H,
N=CH), 7.05(d, J = 8.1 Hz, 2H, m-H), 6.96(d, J = 8.5 Hz,
2H, o-H), 6.84(d, J = 8.4 Hz, 2H, m-H), 3.36–3.31(m, 2H,
cyclohexyl-CH), 3.23(t, J = 7.6 Hz, 4H, CH2I), 3.03(t,
J = 7.7 Hz, 4H, benzyl-CH2), 1.97–1.87 (m, 4H,
cyclohexyl-CH2), and 1.52–1.45(m, 4H, cyclohexyl-CH2).
Anal. Calc.(C24H28O2N2I2): C, 45.73; H, 4.48; N, 4.44%.
3.3 | Synthesis of compound 2
Compound 1 (4.422 g, 0.0266 mol), sulfoxide chloride
(6.335 g, 0.0532 mol), and 30 mL dichloromethane were put
into a flask. The reaction was carried out for 24 hr. The reac-
tion was quenched by the addition of water (15 mL). The
organic phase was collected and the water phase was further
extracted with additional CH2Cl2 (3 × 25 mL). After the
combined dichloromethane was dried over anhydrous
MgSO4, the solvent was removed with a rotary evaporator.
The mixture was purified by column chromatography on sil-
ica gel and compound 2 was obtained (1.982 g, 40.3%).
IR(KBr) cm−1:3,427(OH), 1,653(C=O), and 653(C–Cl). 1H-
NMR (CDCl3):δ 10.62(s, 1H, Ar-OH), 10.24(s, 1H, CHO),
7.56(s, 1H, m-H), 7.44(d, J = 8.5 Hz, 1H, o-H), 6.96(d,
J = 8.4 Hz, 1H, m-H), 3.81(t, J = 6.9 Hz, 2H, CH2Cl),
and 2.98(t, J = 6.9 Hz, 2H, benzyl- CH2). Anal. Calc.
(C9H9O2Cl): C, 58.55; H, 4.91%. Found: C, 58.61; H,
1
Found: C, 45.68; H, 4.43; N,4.52%. The HNMR spectrum
of compound 4 is shown in Figure S4.
1
3.3.3 | Synthesis of compound 5
4.96%. The HNMR spectrum of compound 2 is shown in
Figure S2.
Compound 4 (1.211 g, 0.00192 mol) and triethylamine
(0.391 g, 0.00384 mol) were weighed into a one-neck flask,
and CH3CN (30 mL) was added. After the flask was con-
nected with a reflux condenser, the solution was refluxed for
2 days under a N2 atmosphere. After the solution was cooled
to room temperature, the solvent was removed under vacuum
to give a residue, which was subsequently triturated in diethyl
ether to give a light yellow powder in quantitative yield. To a
flask containing the powder, AgBF4 (0.752 g, 0.00384 mol)
and EtOH (30 mL) were added. The solution was stirred over-
night in the dark to generate AgI, which was filtered off inside
a glove box. The solvent was removed under vacuum to give
a yellow solid, which was purified by chromatography on a
short pad of silica gel, eluting with EtOH and CH2Cl2 (v/v,
1:5). The yield was 0.952 g (66%). IR(KBr) cm−1:3,449(OH),
3.3.1 | Synthesis of compound 3
Compound 2 (1.982 g, 0.0107 mol) was dissolved in CH3CN
(30 mL) and NaI (4.812 g, 0.0321 mol) was added. The
resulting mixture was stirred at 80ꢀC for 24 hr. After the reac-
tion mixture was cooled to room temperature, water (30 mL)
was added. The product was extracted using CH2Cl2
(3 × 10 mL). After the combined organic phase was dried
over anhydrous MgSO4, all volatiles were removed with a
rotary evaporator to yield a yellow solid product that was pure
enough to be used for the next reaction without further purifi-
cation. Yield was 2.883 g (97.6%). IR(KBr) cm−1:3,444(OH),
1,656(C=O), and 488(C–I)；1H-NMR (CDCl3):δ 10.62
(s, 1H, Ar-OH), 10.24(s, 1H, CHO), 7.53(s, 1H, m-H), 7.42
(d, J = 10.3 Hz, 1H, o-H), 6.94(d, J = 8.4 Hz, 1H, m-H),
3.44(t, J = 7.3 Hz, 2H, CH2I), and 3.07(t, J = 7.3 Hz, 2H,
benzyl- CH2). Anal. Calc.(C9H9O2I): C, 39.16; H, 3.29%.
1
1,630(C=N); H-NMR (CDCl3):δ 10.89(s, 2H, Ar-OH), 9.88
(s, 2H, N=CH), 7.41(d, J = 7.1 Hz, 2H, m-H), 7.36(d,
J = 7.5 Hz, 2H, o-H), 6.94(d, J = 7.8 Hz, 2H, m-H),
3.54–3.46(m, 2H, cyclohexyl-CH), 3.12–3.04(m, 16H,
CH2N), 2.86(t, J = 6.6 Hz, 4H, benzyl-CH2), 1.98–1.93
(m,4H, cyclohexyl-CH2), 1.68–1.62 (m,4H, cyclohexyl-CH2),
and 1.40 (t, J = 6.9 Hz, 18H, CH3). Anal. Calc.
(C36H58O2N4B2F8): C, 57.46; H, 7.77; N, 7.45%. Found: C,
1
Found: C, 39.21; H, 3.34%. The HNMR spectrum of com-
pound 3 is shown in Figure S3.
1
3.3.2 | Synthesis of compound 4
57.51; H, 7.81; N, 7.42%. The HNMR spectrum of com-
pound 5 is shown in Figure S5.
L(+)-Tartaric acid (30.0 g, 0.2 mol), water (100 mL), and
1,2-diaminocyclohexane (45.681 g, 0.4 mol) were put into a
flask. The reaction was carried out for 2 hr at 65ꢀC. Then,
acetic acid (25 mL) was added for another 2 hr. The reaction
was quenched by addition of ice water (15 mL) and then the
3.3.4 | Synthesis of compound 6
Cobalt(II) acetate (0.224 g, 0.00127 mol) and Compound
5 (0.952 g, 0.00127 mol) were dissolved in ethanol (30 mL)

6
DU ET AL.
inside a glovebox. Red solid precipitated immediately. After
stirring for 2 hr at room temperature, the solvent was
removed, and the residue was triturated in diethyl ether. The
solid was dissolved in CH2Cl2 containing 2,4-dinitrophenol
(0.234 g, 0.00127 mol), and the resulting solution was
stirred for 2 hr under an O2 atmosphere. After sodium
2,4-dinitrophenolate (0.785 g, 0.00381 mol) was added, the
reaction mixture was stirred overnight at room temperature.
The solution was filtered over Celite, and the solvent was
removed under vacuum to give a brown powder that was
pure enough to be used for polymerization without further
purification. Yields were quantitative. IR(KBr) cm−1:1,560
(C=N), 1,348(Ar-NO2); 1H-NMR (CDCl3):δ 8.61 (s, 3H,
[NO2]2C6H3O), 8.27 (d, J = 8.2 Hz, 3H, [NO2]2C6H3O),
7.79(s, 2H, N=CH), 7.72(d, J = 9.4 Hz, 2H, m-H), 7.49(d,
J = 7.0 Hz, 2H, o-H), 6.84(d, J = 8.2 Hz, 2H, m-H), 6.63
(m, 3H, [NO2]2C6H3O), 3.55–3.48(m, 16H, CH2N),
3.31–3.27(m, 2H, cyclohexyl-CH), 2.77(t, J = 8.3 Hz, 4H,
benzyl-CH2), 1.93–1.87 (m,4H, cyclohexyl-CH2), 1.57–1.49
(m,4H, cyclohexyl-CH2), and 1.23 (t, J = 8.1 Hz, 18H,
CH3). Anal. Calc.(C54H65CoN10O17): C, 54.72; H, 5.53;
and N, 11.82%. Found: C, 54.46; H, 5.54; and N, 11.84%.
The 1H NMR spectrum of compound 6 is shown in
Figure 4.
and 522(C–I)；1H-NMR (CDCl3):δ 10.88(s, 2H, Ar-OH),
9.82(s, 2H, N=CH), 8.56(d, J = 7.1 Hz, 2H, m-H), 7.31(d,
J = 6.1 Hz, 2H, o-H), 7.14(d, J = 8.1 Hz, 2H, m-H), 6.96(d,
J = 6.5 Hz, 2H, o-H), 6.88(d, J = 7.4 Hz, 2H, m-H), 3.47(t,
J = 6.6 Hz, 4H, CH2I), and 2.68(t, J = 7.4 Hz, 4H, benzyl-
CH2). Anal. Calc.(C24H22O2N2I2): C, 46.18; H, 3.55; and N,
4.49%. Found: C, 46.21; H, 3.59; and N, 4.52%. The
1HNMR spectrum of compound 7 is shown in Figure S6.
3.3.6 | Synthesis of compound 8
Compound 7 (1.200 g, 0.00191 mol) and triethylamine
(0.387 g, 0.00382 mol) were weighed into a one-neck flask,
and CH3CN (30 mL) was added. After the flask was con-
nected with a reflux condenser, the solution was refluxed for
2 days under a N2 atmosphere. After the solution was cooled
to room temperature, the solvent was removed under vac-
uum to give a residue, which was subsequently triturated in
diethyl ether to give a light yellow powder in quantitative
yield. To a flask containing the powder, AgBF4 (0.753 g,
0.00387 mol) and EtOH (30 mL) were added. The solution
was stirred overnight in the dark to generate AgI, which was
filtered off inside a glove box. The solvent was removed
under vacuum to give a yellow solid, which was purified by
chromatography on a short pad of silica gel, eluting with
EtOH and CH2Cl2 (v/v, 1:5). The yield was 86%. IR(KBr)
cm−1:3,280(OH), 1,590(C=N)；1H-NMR (CDCl3):δ 10.88
(s, 2H, Ar-OH), 9.87(s, 2H, N=CH), 8.04(d, J = 7.6 Hz, 2H,
m-H), 7.38(d, J = 6.6 Hz, 2H, o-H), 7.32(d, J = 7.5 Hz, 2H,
m-H), 6.97(d, J = 6.8 Hz, 2H, o-H), 6.74(d, J = 7.8 Hz, 2H,
m-H), 3.36(t, J = 8.3 Hz, 4H, benzyl-CH2), 3. 16–3.10(m,
16H, CH2N), and 1.52 (t, J = 7.2 Hz, 18H, CH3). Anal.
Calc.(C36H52O2N4B2F8): C, 57.93; H, 7.02; and N, 7.51%.
Found: C, 57.96; H, 7.07; and N, 7.49%. The 1HNMR spec-
trum of compound 8 is shown in Figure S7.
3.3.5 | Synthesis of compound 7
Compound 3 (4.401 g, 0.0159 mol) was put into a flask with
a condensation reflux device, o-diaminobenzene (0.859 g,
0.00795 mol) and methylbenzene 30 mL were added into
the flask. The reaction mixture was reflowed for 2 days and
then recrystallized by alcohol. The yield was 54.3%.
IR(KBr) cm−1:3,500(OH), 1,629(C=N), 1,247(aniline-N),
n
m
l
d
X
3.3.7 | Synthesis of compound 9
HC
N
N
CH
e
g
h
Co
j k
+
i
+
O
NEt
NEt
-
O
Cobalt(II) acetate (0.224 g, 0.00127 mol) and Compound
8 (0.941 g, 0.00127 mol) were dissolved in ethanol (30 mL)
inside a glovebox. Red solid precipitated immediately. After
stirring for 2 hr at room temperature, the solvent was
removed, and the residue was triturated in diethyl ether. The
solid was dissolved in CH2Cl2 containing 2,4-dinitrophenol
(0.234 g, 0.00127 mol), and the resulting solution was
stirred for 2 hr under an O2 atmosphere. After sodium
2,4-dinitrophenolate (0.785 g, 0.00381 mol) was added, the
reaction mixture was stirred overnight at room temperature.
The solution was filtered over Celite, and the solvent was
removed under vacuum to give a brown powder that was
pure enough to be used for polymerization without further
purification. Yields were quantitative. IR(KBr) cm−1:1,584
3
3
abc
-
X
X
X=2,4-dinitrophenoxide
f
k
i,j
h
n
m
c
a
f
d
b
g
l
e
12
10
8
6
4
2
ppm
FIGURE 4 1H NMR spectrum of complex 6 in DMSO-d6

DU ET AL.
7
by vacuum (10 mmHg) transfer into a cooled (−20ꢀC)
receiving flask. A small amount of the residue was removed
for 1H NMR and GPC analyses.
h
g
a
j
d
f
m
l
m
k
4 | CONCLUSIONS
b,c,i
e
Two new bifunctional salen-cobalt(III) complexes were
synthesized, which consist of salicylaldehyde bearing four
quaternary ammonium salts and two different diamines.
The copolymerization results indicated that with the
increase of temperature, both the catalyst efficiency and
carbonate fraction decrease for the two complexes. Of both
the diamines, the complex 9 with o-diaminobenzene has
higher catalytic effect compared to complex 6 with
1,2-diaminocyclohexane. The catalytic effect of complex
9 is over 3.5 times than that of complex 6 at a temperature
of 30ꢀC.The highest TON were obtained under conditions
of T = 30ꢀC, PCO2 = 2 MPa, and t = 24 hr for complex
6 and 9, respectively. The research of PCO2 on the copoly-
merization revealed that the first-rank pressure was at
2 MPa for the two complexes.
DSC curves indicated that the PPC by complex 9 has the
highest Tg of 54.2ꢀC. DTGA curves showed that there were
two thermal degradation peaks. The first peak might be due
to the thermal degradation of the ester bond of PPC, and the
second peak due to the breaking of the C–C bond. The
results obtained from DSC and TGA/DTGA indicate that the
synthesized copolymers are fit for application as sealants.
k,l
de
f
a
j
c
b
g
h
i
12
10
8
6
4
2
0
ppm
FIGURE 5 1H NMR spectrum of complex 9 in DMSO-d6
(C=N), 1,341(Ar-NO2)；1H-NMR (CDCl3):δ 9.87(s, 2H,
N=CH), 7.63 (s, 3H, [NO2]2C6H3O), 7.55 (d, J = 7.4 Hz,
3H, [NO2]2C6H3O), 7.39(d, J = 8.1 Hz, 2H, m-H), 7.25(d,
J = 7.3 Hz, 2H, o-H), 7.15(d, J = 8.4 Hz, 2H, m-H), 6.92(d,
J = 7.2 Hz, 2H, m-H), 6.76(d, J = 7.5 Hz, 2H, m-H), 6.55
(m, 3H, [NO2]2C6H3O), 3.61(t, J = 7.6 Hz, 4H, benzyl-
CH2), 3. 21–3.16(m, 16H, CH2N), and 1.51 (t, J = 7.9 Hz,
18H, CH3). Anal. Calc.(C54H59CoN10O17): C, 55.01; H,
5.04; and N, 11.88%. Found: C, 55.12; H, 5.09; and N,
11.84%. The 1H NMR spectrum of compound 9 is shown in
Figure 5.
ACKNOWLEDGMENTS
The authors are thankful for financial support from the
Anhui Province University Natural Science Research Project
(No. KJ2017A008), the Anhui Provincial Natural Science
Foundation (No. 1808085ME55, No. 1908085MB51), and
Anhui Province Key Laboratory of Environmentally friendly
Polymer Materials.
3.4 | Copolymerization of CO2 and PO
The copolymerization of CO2 and PO was carried out in a
100 mL autoclave, which was equipped with a magnetic stir-
rer. The clean autoclave was dried at 80ꢀC for 24 hr in a vac-
uum oven, and quickly transferred into a dry glove box. The
complex was dried at 80ꢀC for 24 hr prior to being used for
the polymerization process; dry complex was charged into
the autoclave. The autoclave was then capped with its head,
and the entire assembly was connected to the reaction sys-
tem equipped with a vacuum line. The autoclave, with the
complex in it, was further dried for 24 hr under vacuum at
80ꢀC in an oil bath. After drying, the autoclave was purged
with carbon dioxide and evacuated alternately three times,
followed by adding purified PO using a syringe. After run-
ning for the condition indicated in Table 1 below, the reactor
was cooled to room temperature. After the CO2 gas was
released, the reactor was opened. The catalyst was filtered
and the unreacted PO was isolated at ambient temperature
REFERENCES
[1] M. Aresta, A. Dibenedetto, Catal. Today 2004, 98, 455.
[2] S. Inoue, H. Koinuma, T. Tsuruta, J. Polym. Sci. Part B: Polym.
Phys. 1969, 7, 287.
[3] M. H. Chisholm, Z. Zhou, J. Mater. Chem. 2004, 14, 3081.
[4] C. T. Cohen, T. Chu, G. W. Coates, J. Am. Chem. Soc. 2005, 127,
10869.
[5] D. J. Darensbourg, Chem. Rev. 2007, 107, 2388.
[6] X. J. Qin, L. C. Du, C. Wang, Z. Yang, M. Zhang, J. Chin. Chem.
Soc. 2017, 64, 547.
[7] W. K. Zhu, L. C. Du, S. Y. Qian, Q. S. Yang, W. J. Song,
J. Chin. Chem. Soc. 2018, 65, 841.
[8] D. J. Darensbourg, S. B. Fitch, Inorg. Chem. 2008, 47, 11868.
[9] D. J. Darensbourg, A. I. Moncada, Macromolecules 2009, 42, 4063.

8
DU ET AL.
[10] M. Kobayashi, S. Inoue, T. Tsuruta, Macromolecules 1971, 4, 658.
[11] W. Kuran, S. Pasynkiewicz, J. Skupinska, A. Rokicki, Makromol.
Chem. 1976, 177, 11.
[12] M. Ree, J. Y. Bae, J. H. Jung, T. J. Shin, Y. T. Hwang, T. Chang,
Polym. Eng. Sci. 2000, 40, 1542.
[13] S. Klaus, M. W. Lehenmeier, E. Herdtweck, P. Deglmann,
A. K. Ott, B. Rieger, J. Am. Chem. Soc. 2011, 133, 13151.
[14] S. J. Wang, L. C. Du, X. S. Zhao, Y. Z. Meng, S. C. Tjong,
J. Appl. Polym. Sci. 2002, 85, 2327.
[23] Y. S. Qin, X. H. Wang, X. J. Zhao, F. S. Wang, Chin. J. Polym.
Sci. 2008, 26, 241.
[24] X. Zou, C. Wang, Y. Wang, K. Shi, Z. Wang, D. Li, X. Fu, Poly-
mers 2017, 1, 108.
[25] D. R. Moore, M. Cheng, E. B. Lobkovsky, G. W. Coates, J. Am.
Chem. Soc. 2003, 125, 11911.
[26] B. Y. Liu, Y. H. Gao, X. Zhao, W. D. Yan, X. H. Wang,
J. Polym. Sci. Part A: Polym. Chem. 2010, 48, 359.
[27] G. W. Coates, D. R. Moore, Angew. Chem. Int. Ed. 2004, 43, 6618.
[15] Y. Xu, L. Lin, C. T. He, J. Qin, Z. Li, S. Wang, M. Xiao,
Y. Meng, Polym. Chem.-UK 2017, 28, 363.
[16] X. K. Sun, S. Chen, X. H. Zhang, G. R. Qi, Prog. Chem. 2012,
24, 1776.
[17] X. H. Zhang, R. J. Wei, X. K. Sun, J. F. Zhang, B. Y. Du,
Z. Q. Fan, G. R. Qi, Polymer 2011, 52, 5494.
SUPPORTING INFORMATION
Additional supporting information may be found online in
the Supporting Information section at the end of this article.
[18] Z. F. Li, Y. S. Qin, X. J. Zhao, F. S. Wang, S. B. Zhang,
X. H. Wang, Eur. Polym. J. 2011, 47, 2152.
[19] A. S. Abu-Surrah, H. M. Abdel-Halim, H. A. N. Abu-Shehab,
E. Al-Ramah, Transit. Metal. Chem. 2016, 1, 42.
[20] Z. L. Quan, X. H. Wang, X. J. Zhao, F. S. Wang, Polymer 2003,
44, 5605.
[21] N. Takeda, S. Inoue, Bull. Chem. Soc. Jpn. 1978, 51, 3564.
[22] W. Wu, Y. S. Qin, X. H. Wang, F. S. Wang, J. Polym. Sci. Part
A: Polym. Chem. 2013, 51, 493.
How to cite this article: Du L, Wang C, Zhu W,
Zhang J. Copolymerization of carbon dioxide and
propylene oxide catalyzed by two kinds of
bifunctional salen-cobalt(III) complexes bearing four
quaternary ammonium salts. J Chin Chem Soc. 2019;
1–8. https://doi.org/10.1002/jccs.201900077