Study of electronic effect in bifunctional catalysts for the copolymerization of CO2 and PO/CHO

Article abstract of DOI:10.1002/jccs.202000103

Carbon dioxide (CO₂) is an easily available renewable carbon source that can be used as a comonomer in the catalytic ring-opening polymerization of epoxides to form aliphatic polycarbonates. Herein, a series of new Salen-Co(III) bifunctional catalysts were synthesized for the first time, and they were studied to catalyze the copolymerization of CO₂ and propylene oxide (PO)/cyclohexene oxide (CHO). At the same time, the effects of reaction conditions (electronic effect, temperature, time) on catalytic activity and selectivity were investigated. The results show that the Salen-Co(III) complexes with electron-withdrawing groups have higher selectivity and activity for propylene carbonate (PPC)/cyclohexylene carbonate (PCHC). At the same time, the Salen-Co(III) complexes can better catalyze the copolymerization of CHO and CO₂ than that of PO and CO₂. The catalytic efficiency of the four complexes increased with increasing temperature, and the best reaction condition is 80°C, 30 min and 2 MPa of CO₂.

Full text of DOI:10.1002/jccs.202000103

Received: 24 March 2020
Revised: 11 April 2020
Accepted: 20 April 2020
DOI: 10.1002/jccs.202000103
A R T I C L E
Study of electronic effect in bifunctional catalysts for the
copolymerization of CO2 and PO/CHO
Yang Hu | Longchao Du
Chenxi Shao
| Cun Li | Jiale Shen | Weiju Zhu
|
School of Chemistry and Chemical
Engineering, Anhui University, Hefei, PR
China
Abstract
Carbon dioxide (CO2) is an easily available renewable carbon source that can
be used as a comonomer in the catalytic ring-opening polymerization of epox-
ides to form aliphatic polycarbonates. Herein, a series of new Salen-Co(III)
bifunctional catalysts were synthesized for the first time, and they were studied
to catalyze the copolymerization of CO2 and propylene oxide (PO)/cyclohexene
oxide (CHO). At the same time, the effects of reaction conditions (electronic
effect, temperature, time) on catalytic activity and selectivity were investigated.
The results show that the Salen-Co(III) complexes with electron-withdrawing
groups have higher selectivity and activity for propylene carbonate (PPC)/
cyclohexylene carbonate (PCHC). At the same time, the Salen-Co(III) com-
plexes can better catalyze the copolymerization of CHO and CO2 than that of
PO and CO2. The catalytic efficiency of the four complexes increased with
increasing temperature, and the best reaction condition is 80ꢀC, 30 min and 2
MPa of CO2.
Correspondence
Longchao Du, School of Chemistry and
Chemical Engineering, Anhui University,
Hefei 230601, PR China.
Email: dulongchao@sina.com
Funding information
the Anhui Province University Natural
Science Research Project, Grant/Award
Number: KJ2017A008; the Anhui
Provincial Natural Science Foundation,
Grant/Award Numbers: 1808085ME55,
1908085MB51; Anhui Province Key
Laboratory of Enviorment-friendly
Polymer Materials
K E Y W O R D S
bifunctional catalysts, copolymerization, salen-Co(III) complexes
1 | INTRODUCTION
polycarbonate can be used as a packaging material and
medical polymer material.[8] Cyclic carbonate is a solvent
Carbon dioxide (CO2) is a renewable and nontoxic C1
resource, and its fixation and utilization are basic eco-
nomic and ecological issues. Reversible coupling of CO2
and epoxides to form a degradable polycarbonate can
reduce dependence on petroleum products.[1–3] In this
case, converting CO2 to a functional, biodegradable poly-
mer material or cyclic carbonate is a new approach.[4–6]
This has become one of the main directions for the eco-
nomic and environmentally friendly polycarbonate and
cyclic carbonates industry.[7] Polycarbonates and cyclic
carbonates have broad application prospects in the indus-
try. As an engineering plastic with potential applications,
with high polarity and high boiling point, which can be
used as an electrolyte for lithium batteries. It is also an
important intermediate for chemicals and drugs.[9,10]
However, due to the thermodynamic stability of CO2, a
highly reactive catalyst for CO2 conversion is required.
In the past 40 years, considerable effort has been
devoted to developing efficient catalyst systems.[11–14]
Today, scientists in various countries have developed a
large number of catalytic systems that can promote the
alternating copolymerization of CO2 and epoxide to syn-
thesize polycarbonate and five-membered cyclic carbon-
ates (Scheme 1).[12,15–19] Among many catalytic systems,
© 2020 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J Chin Chem Soc. 2020;1–9.
http://www.jccs.wiley-vch.de
1

2
HU ET AL.
SCHEME 1 Copolymerization and cycloaddition of CO2 and epoxides
heterogeneous catalytic systems are widely used in the
reaction of CO2 and epoxy compounds.[14,20,21] In 1969,
Inoue et al. discovered that diethyl zinc/water can cata-
lyze the reaction of epoxides with CO2 to form an ali-
phatic carbonate (APC).[22] In 2012, Y.Z. Meng prepared
a new type of composite zinc catalyst, which catalyzed
the ternary copolymerization of CO2 with PO and CHO,
and the mechanical properties and thermal degradation
properties of the copolymer were improved.[23] Zinc-
based catalytic systems are highly active, relatively safe,
and easy to handle. However, the obtained polymer has a
low molecular weight and a long polymerization time,
which limits its industrial application and development.
G.R. Qi prepared the double metal cyanide Zn3[Fe
(CN)6]2, which is used to catalyze the copolymerization
of CO2/PO. When the central metal was changed from Fe
to Co, the electronic structure of Zn was changed, and
the catalytic activity was greatly improved.[24] At the
same time, the development of the Salen-type complex
with Schiff base as a ligand has attracted researcher's
attention. Salen is a general term for diimine tetradentate
Schiff base ligands. Their metal complexes are metal
high-resistance homogeneous catalysts, which were first
synthesized by Pfeiffer in 1933.[25] Schiff base itself can
be used as a catalyst for the cycloaddition reaction of car-
bon dioxide and epoxy compounds. The complexes of
some transition metals and main metals can greatly
improve the catalytic activity.[26] These metals mainly
include Cr, Co, and Mn, et al.27,28 In the study of Salen
metal complexes catalyzing the copolymerization of CO2
and epoxy compounds, bifunctional catalysts have caused
extensive research.[29,30] Le Borgne and colleagues pre-
pared the first aluminum salt complexes as early as 1989,
and they proved their effectiveness for living polymeriza-
tion of epoxides.[31–33] Lee and his colleagues discovered
a series of Salen-Co(III) complexes containing quaternary
ammonium salts. These complexes showed high activity
and excellent temperature tolerance in the copolymeriza-
tion of CO2 and epoxides, and obtained high-molecular
weight polycarbonate.[34]
In order to study the properties of multifunctional
Schiff base metal complexes in catalyzing the copoly-
merization of carbon dioxide, we synthesized a series
of novel salen ligand bearing quaternary ammonium
salts, which use 2,4-dinitrophenoxy as both the axial
anion X and the counter anion Y in this ligand
(Scheme 2). To further study the influence of the elec-
tron effect on the catalytic efficiency, the catalysts with
different functional groups were selected on the copo-
lymerization of PO/CHO and CO2. The details of these
specific reaction processes and catalytic copolymeriza-
tion will be clarified.
2 | RESULTS AND DISCUSSION
2.1 | Synthesis and characterization
Based on previous research results, we know that the
Salen metal catalyst system show excellent activity and
efficiency for the copolymerization of CO2 with epox-
ides. Therefore, our main goal is to synthesize new
ligands and explore the effects of electronic effects on
copolymerization.
First, using Al2O3 as a catalyst, N2 is introduced
under low-temperature conditions, and acylation of
o-cresol and 4-chlorobutyryl chloride occurs in CH2Cl2
to form compound 5. Subsequently, compound 5 and
triethylsilane react in trifluoroacetic acid at room tem-
perature. Si-H bond breaks, and H attacks C=O in

HU ET AL.
3
SCHEME 2 Synthesis of salen ligand precursor and catalysts 1–4
1
compound 5 to form compound 6. In the next step, com-
pound 6 is introduced into the aldehyde group by using
acetonitrile as a solvent and reacting with paraformalde-
hyde and triethylamine under a N2 atmosphere to
obtain compound 7. Since the electronegativity of I− is
weaker than that of Cl−, the compound linked to I is
unstable and easily displaced. In order to facilitate the
modification of the Schiff base, the chloro group of
compound 7 is substituted with I− in a refluxing sol-
vent of CH3CN to get compound 8. The condensation
reaction of compound 8 with amine compounds is a
crucial step to synthesize the desired salen ligand
(compound 9–12). So far, we have synthesized four
Schiff bases with different groups. In the next step, the
reaction is carried out with anhydrous tri-n-
butylamine and Schiff base to attach it to the methy-
lene group at the end of the Schiff base, and then
the axial anion X and the counter anion Y. The H-
NMR spectrum of Catalyst 1–4 is shown in Figure 1.
2.2 | Polymerization studies
It can be seen from the catalytic results (Table 1) that the
four Salen-Co(III) catalysts have low selectivity for
PPC/PCHC when catalyzing the copolymerization of
PO/CHO and CO2. The same phenomenon has been
reported by R. Duan et al.[35] This phenomenon may be
caused by the weak electronic communication between
o-phenylenediamine and the π system in Salen-Co(III),
which leads to a decrease in the selectivity of the catalysts
for PPC/PCHC. This article will mainly focus on the
influence of electronic effects on the copolymerization of
PO/CHO and CO2.
In order to address the relationship between the
structure and activity of the complex, the catalytic effects
on the copolymerization of PO/CHO and CO2 were stud-
ied using complexes containing different groups
(Table 1). The copolymerization results show that
replace the I− with BF4 to obtain the compound 13–
−
16. The Salen-metal complex is formed by reacting a
ligand with cobalt acetate, and then Co2+ is oxidized to
Co3+ by introducing O2 into the solution. Subse-
quently, the 2,4-dinitrophenoxy group was added as

4
HU ET AL.
complex 2 containing an electron-withdrawing group
exhibits higher selectivity and activity than Salen-Co(III)
complexes containing other groups. In the PO and CO2
copolymerization results, when the reaction was carried
out at 40ꢀC under a pressure of 2 MPa CO2, the turnover
number (TON) of the complex 2 containing a chlorine
atom was 168 at 6 hr, and the fPPC was 0.78%. When the
complex 1 was used as a catalyst, a decrease in activity
was observed, and its TON was 126. When the electron-
donating group is contained in the complex, the differ-
ence in activity and selectivity between the complex
2 and the complex 3,4 is more remarkable, and the com-
plex 3 has only about 55% of the activity and selectivity of
the complex 2. This indicates that when different
electron-withdrawing groups are introduced into the cat-
alyst, the selectivity and activity of the catalysts for PPC
can be changed, and as the electron-withdrawing ability
of the catalyst is enhanced, the selectivity and activity of
the catalyst for PPC are enhanced. The same results were
obtained in CHO and CO2 copolymerization. The above
conclusions may be related to the catalytic process of the
catalysts. The Salen-Co(III) complex has a quadrangular
pyramidal spatial configuration, so PO can coordinate to
the opposite side of the center metal to form a stable octa-
hedral spatial configuration. When PO contacts Salen-Co
(III) complex, the oxygen atom in propylene oxide is acti-
vated by the metal ion of the catalyst. Since the electron-
withdrawing group is introduced into the complex 2, the
Lewis acidity of the metal ion becomes stronger, so that
the metal ion absorbs electrons from the oxygen atom of
propylene oxide. This process weakens the C–O bond
FIGURE 1 1H-NMR spectrum of the catalysts in DMSO-d6
TABLE 1
CO2/(propylene oxide)/epoxy cyclohexane copolymerization resultsa
Entry
1
Cat
1
Monomer
PO
T (ꢀC)
40
Yield (g)
0.052
0.070
0.040
0.033
0.064
0.084
0.060
0.059
0.085
0.106
0.082
0.082
0.149
0.172
0.140
0.130
TOFb (hr−1
)
TON
126
168
96
fPPC PCHC
/
c (%)
fcPC/CCHC
c (%)
21
28
16
13
26
36
24
24
36
45
34
34
62
72
71
55
0.76
0.78
0.48
0.40
0.94
1.13
0.66
0.61
2.04
2.66
1.89
1.85
2.41
3.67
1.96
2.02
0.10
0.08
0.13
0.18
0.17
0.15
0.18
0.20
0.13
0.09
0.14
0.21
0.20
0.16
0.25
0.27
2
2
PO
40
3
3
PO
40
4
4
PO
40
78
5
1
PO
80
156
216
144
144
216
270
204
204
372
432
426
330
6
2
PO
80
7
3
PO
80
8
4
PO
80
9
1
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
40
10
11
12
13
14
15
16
2
40
3
40
4
40
1
80
2
80
3
80
4
80
aPolymerization condition: PO/CHO 10 g, 2 MPa, 6 hr cyclic cyclohexene carbonate (CCHC), cyclic propylene carbonate (cPC),
poly(cyclohexylene carbonate) (PCHC), poly(propylene carbonate) (PPC).
bTurnover frequency: mole of PO/CHO consumed by per mole of catalyst per hour.
cCarbonate fraction determined by 1H-NMR spectroscopy (CDCl3, 400 MHz).

HU ET AL.
5
polarity and makes the C–O bond easier to break. It is
more conducive to the insertion of CO2 into propylene
oxide. Therefore, the selectivity and activity of the cata-
lysts for PPC increased with the enhancement of the
electron-withdrawing ability in the catalysts. These con-
clusions can also be proved in the copolymerization of
CHO and CO2.
of four Salen-Co(III) complexes at 80ꢀC. When complex
2 catalyzed the copolymerization of CO2 and PO, the
peak of 5.00 ppm of the synthesized product was highest.
This shows that complex 2 has the highest selectivity for
PPC. When the complex 1, 3, and 4 was used to catalyze
the copolymerization of CO2 and PO, the 5.00 ppm peak
of the synthesized product decreased. This shows that the
At the same time, it can be seen that when the tem-
perature is raised to 80ꢀC, the copolymerization results of
PO/CHO and CO2 also showed the same trend as that at
40ꢀC. When the reaction was carried out at 80ꢀC, 2 MPa
CO2, the selectivity and TON value of the four Salen-Co
(III) complexes for PPC/PCHC generally increased. It is
shown that the Salen-Co(III) complex has higher selectiv-
ity and activity with increasing temperature.
When exploring the Salen-Co(III) complexes to cata-
lyze the copolymerization of different substrates with
CO2, we chose PO and CHO. The results show that
Salen-Co(III) complexes have higher activity and selectiv-
ity in catalyzing the copolymerization of CHO and CO2.
This phenomenon may be related to the different ring
tensions of epoxy compounds. In the catalytic process,
the ring tension of CHO is higher than PO, which makes
CHO ring opening easier. This facilitates the insertion of
CO2 into CHO. Therefore, Salen-Co(III) complex has
higher activity and selectivity in catalyzing the copoly-
merization of CHO and CO2.
In addition, we also studied the effect of time on the
copolymerization of PO and CO2. It can be seen from
Table 2 that when the reaction time is reduced from 6 to
0.5 hr under the reaction of 40ꢀC and 2 MPa CO2, the
selectivity of the four catalysts to PPC is enhanced. It is
worth noting that when the time is shortened to 0.5 hr,
the turnover frequency (TOF) value is increased by
100 times relative to 6 hr, but TON is slightly reduced. It
shows that the improvement of time is favorable for
copolymerization, but when the reaction time is further
delayed, the copolymer is degraded.
FIGURE 2 (a) 1H-NMR spectrum of the copolymerized
product of CO2 and PO at 80ꢀC, 6 hr, 2 MPa CO2 using different
catalysts in CDCl3, (b) 1H-NMR spectrum of the copolymerized
product of CO2 and CHO at 80ꢀC, 6 hr, 2 MPa CO2 using different
catalysts in CDCl3
Based on the above results, it can be concluded that
the Salen-Co(III) complex has higher selectivity and
1
activity at 80ꢀC. Figure 2 shows H-NMR of a copolymer
TABLE 2
CO2/propylene oxide
Entry Cat Monomer Yield (g) TOFb (hr−1
)
TON fPPCc (%) fcPCc (%)
copolymerization resultsa
1
2
3
4
1
2
3
4
PO
PO
PO
PO
0.043
0.057
0.041
0.034
207
279
198
164
103
139
99
0.87
1.01
0.69
0.55
0.15
0.10
0.26
0.28
82
aPolymerization condition: PO 10 g, 2 MPa, 40ꢀC, 0.5 hr cyclic propylene carbonate (cPC), poly(propylene
carbonate) (PPC).
bTurnover frequency: mole of PO consumed by permole of catalyst per hour.
cCarbonate fraction determined by 1H-NMR spectroscopy (CDCl3, 400 MHz).

6
HU ET AL.
selectivity of complexes 1, 3, and 4 to PPC decreases. The
above results indicate that when catalyzing the copoly-
merization of CO2 and PO, the Salen-Co(III) complex
containing an electron-withdrawing group has higher
selectivity for PPC. In the copolymerization of CO2 and
CHO catalyzed by four Salen-Co(III) complexes,
according to the integration results, the peak at 4.65 ppm
of the synthesized product also showed the above trend.
This indicates that the when catalyzing the copolymeriza-
tion of CO2 and CHO, the Salen-Co(III) complex con-
taining electron-withdrawing group has higher selectivity
to PCHC.
8.86 (s, 2H, N=CH), 7.48–7.37 (m, 4H, Ar-H), 7.29 (s,
2H, Ar-H), 7.17 (s, 2H, Ar-H), 3.29–3.25 (m, 4H,
CH2Cl), 2.58 (m, 4H, Ar-CH2), 2.17 (s, 6H, Ar-CH3),
1.85–1.57 (m, 8H, CH2CH2).
3.2.2 | Synthesis of 10
The compound synthesized using the same conditions
and procedure as those for 9, starting with 5. A light yel-
low oil was obtained in quantitative yield. IR(KBr): 3,386
1
cm−1 (Ar-OH), 1,619 cm−1 (C=N), 657 cm−1 (Ar-Cl). H-
NMR (400 MHz, DMSO): δ = 12.92 (s, 1H, Ar-OH), 12.81
(s, 1H, Ar-OH), 8.91 (s, 1H, N=CH), 8.86 (s, 1H, N=CH),
7.59 (s, 1H, Ar-H), 7.51–7.43 (m, 2H, Ar-H), 7.29 (s, 1H,
Ar-H), 7.28 (s, 1H, Ar-H), 7.20–7.17 (m, 2H, Ar-H),
3.35–3.25 (m, 4H, CH2Cl), 2.60–2.50 (m, 2H, Ar-CH2),
2.20–2.15 (m, 6H, Ar-CH3), 1.82–1.58 (m, 8H).
3 | EXPERIMENTAL
3.1 | Materials and synthetic protocols
Reactions were carried out under inert atmosphere in
Schlenk glassware or in a purified nitrogen-filled drybox.
Except methanol and ethanol was distilled using sodium,
Solvents (THF, CH2Cl2, CH3CN,) were dried using a puri-
fication system composed of calcium hydride. General
chemical reagent were purchased from Shanghai Macklin
Biochemical Co, Aladdin Industrial Co, or Shanghai
Richjoint Chemical Reagents Co., and used with as
received. The samples were made into KBr tablets, and
the Fourier transform infrared (FTIR) spectra were col-
lected on a Vertex80. Elemental analyses were performed
3.2.3 | Synthesis of 11
The compound synthesized using the same conditions and
procedure as those for 9, starting with 5. A light yellow oil
was obtained in quantitative yield. IR(KBr): 3,423 cm−1 (Ar-
1
OH), 1,616 cm−1 (C=N), 1,495 cm−1 (Ar-OCH3). H-NMR
(400 MHz, DMSO): δ = 13.23 (s, 1H, Ar-OH), 13.03 (s, 1H,
Ar-OH), 8.87 (s, 1H, N=CH), 8.84 (s, 1H, N=CH), 7.45 (d,
J = 8.8Hz, 1H, Ar-H), 7.29 (s, 1H, Ar-H), 7.24 (s, 1H, Ar-H),
7.17 (s, 1H, Ar-H), 7.13 (s, 1H, Ar-H), 7.04 (s, 1H, Ar-H),
6.97 (d, J = 8.7 Hz, 1H, Ar-H), 3.85 (s, 3H, OCH3), 3.35–3.27
(m, 4H, CH2Cl), 2.60–2.50 (m, 4H, Ar-CH2), 2.18 (s, 3H, Ar-
CH3), 2.16 (s, 3H, Ar-CH3), 1.82–1.58 (m, 8H).
1
on a Fisons (Model EA 1108 CHNSO). H-NMR spectra
were recorded on a nuclear magnetic resonance (NMR)
spectrometer (AVANCEII, 400 MHz). Samples were dis-
solved in CDCl3 or CD3SOCD3 with tetramethylsilane as
an internal standard.
3.2.4 | Synthesis of 12
3.2 | Synthetic protocols for Scheme 2
The compound synthesized using the same conditions and
procedure as those for 9, starting with 5. A light yellow oil
was obtained in quantitative yield. IR(KBr): 3,420 cm−1 (Ar-
The synthetic route to complex 1–4 is illustrated in
Scheme 2. Compound 5–8 were prepared according to lit-
eratures reported previously.[34] Detailed synthetic proce-
dures are described below.
1
OH), 1,619 cm−1 (C=N). H-NMR (400 MHz, DMSO): δ =
13.16 (s, 1H, Ar-OH), 13.08 (s, 1H, Ar-OH), 8.86 (m, 2H,
N=CH), 7.36 (d, J = 8.0 Hz, 1H, Ar-H), 7.27 (s, 1H, Ar-H),
7.26 (s, 1H, Ar-H), 7.22 (s, 1H, Ar-H), 7.20 (s, 1H, Ar-H),
7.18–7.13 (m, 2H, Ar-H), 3.35–3.27 (m, 4H, CH2Cl),
2.60–2.50 (m, 4H, Ar-CH2), 2.39 (s, 3H, Ar-CH3), 2.20–2.13
(m, 6H, Ar-CH3), 1.84–1.59 (m, 8H).
3.2.1 | Synthesis of 9
Compound 8 (1.04 g, 3.27 mmol) was dissolved in the etha-
nol in a three-neck round flask under a N2 atmosphere. The
reation mixture was stirred at 80ꢀC for 8 hr. After comple-
tion of reaction, the solution was placed in the ice bath
for 2 hr. The product is a yellow solid (0.43 g 43%).
IR(KBr): 3,378 cm−1 (Ar-OH), 1,618 cm−1 (C=N).
1H-NMR (400 MHz, DMSO): δ = 13.07 (s, 2H, Ar-OH),
3.2.5 | Synthesis of 13
Compound 9 (0.5 g 0.692 mmol) was dissolved in CH3CN
(50 ml) at the temperature of 61ꢀC, and anhydrous tri-n-

HU ET AL.
7
butylamine (0.513 g 2.77 mmol) was added under N2
atmosphere. The reaction mixture was stirred for 48 hr.
After being cooled, the solvent was then removed by
rotary evaporation. Subsequently, the obtained residue
was dissolved in CH3CN (50 ml), and AgBF4 (0.275 g
1.41 mmol) was added under a N2 atmosphere. The solu-
tion was stirred at room temperature for24 hr and then
filtered through Celite. The solvent was removed in
vacuo. The resulting solid was further treated with anhy-
drous ether to afford compound 11 as a yellow solid. The
yield was 73.6%. IR(KBr): 3,428 cm−1 (Ar-OH), 1,617 cm−1
(C=N). 1H-NMR (400 MHz, DMSO): δ = 13.11 (s, 2H, Ar-
OH), 8.88 (s, 2H, N=CH), 7.40–7.46 (m, 4H, Ar-H), 7.32 (s,
2H, Ar-H), 7.20 (s, 2H, Ar-H), 3.20–3.11 (m, 4H, CH2Cl),
3.10–2.94 (m, 12H, NCH2), 2.91–2.84 (m, 12H, CH2),
2.58–2.51 (m, 4H, Ar-CH2), 2.17 (s, 6H, Ar-CH3), 1.67–1.56
(m, 12H, CH2), 1.58–1.22 (m, 8H, CH2CH2), 0.90 (t, J =
7.3Hz, 9H, CH3).
3.2.8 | Synthesis of 16
The compound synthesized using the same conditions
and procedure as those for 13, starting with 12. A light
yellow oil was obtained in quantitative yield. IR(KBr):
3,421 cm−1 (Ar-OH), 1,616 cm−1 (C=N). H-NMR (400
1
MHz, DMSO): δ = 13.19 (s, 1H, Ar-OH), 13.11 (s, 1H, Ar-
OH), 8.86 (m, 2H, N=CH), 7.36 (d, J = 8.1 Hz, 1H, Ar-H),
7.32 (s, 1H, Ar-H), 7.30 (s, 1H, Ar-H), 7.25 (s, 1H, Ar-H),
7.19 (s, 1H, Ar-H), 7.18 (s, 1H, Ar-H), 7.17 (d, J = 8.6 Hz,
1H, Ar-H), 3.14–3.09 (m, 4H, CH2Cl), 3.10–2.90 (m, 12H,
NCH2), 2.91–2.82 (m, 12H, CH2), 2.76–2.64 (m, 4H, Ar-
CH2), 2.40 (s, 3H, Ar-CH3), 2.20–2.14 (m, 6H, Ar-CH3),
1.68–1.59 (m, 12H, CH2), 1.58–1.19 (m, 8H, CH2CH2),
0.95–0.80 (m, 9H, CH3).
3.2.9 | Synthesis of 1
Compound 13 (0.2 g 0.20 mmol) and anhydrous cobalt
(II) acetate (0.035 g 0.20 mmol) were dissolved in MeOH
(50 ml) under N2 atmosphere. The reaction mixture was
stirred at room temperature for 6 hr. Then, the product
was separated by celite, and the precipitate was triturated
in diethyl ether. Subsequently, the obtained residue was
dissolved in CH2Cl2 (50 ml), and 2,4-dinitrophenol
(0.036g, 0.20 mmol) was added under O2 atmosphere.
After the solution was stirred at room temperature for
approximately 12 hr, sodium 2,4-dinitrophenolate (0.12 g,
0.60 mmol) was added and stirred for further 24 hr, and
then filtered through Celite. The solvent was removed in
vacuo. The resulting solid was further treated with anhy-
drous ether to afford compound 1 as a brown solid (0.33
g, 86.2%).1H-NMR (400 MHz, DMSO) δ = 8.78 (s, 2H,
N=CH), 8.58 (d, J = 13.7 Hz, 3H, Ar-H), 7.82 (d, J = 8.3
Hz, 3H, Ar-H), 7.54–7.47 (m, 2H, Ar-H), 7.39 (s, 2H, Ar-
H), 7.27 (s, 2H, Ar-H), 6.98–6.88 (m, 2H, Ar-H), 6.38 (s,
3H, Ar-H), 2.94–2.88 (m, 4H, CH2Cl), 2.88–2.82 (m, 12H,
NCH2), 2.68 (s, 6H, Ar-CH3), 2.60–2.54 (m, 12H, CH2),
2.52–2.49 (m, 4H, Ar-CH2), 1.70–1.60 (m, 12H, CH2),
1.59–1.24 (m, 8H, CH2CH2), 0.95–0,78 (m, 9H, CH3).
Anal. Calc.(C72H95CoN10O17): C, 60.43; H, 6.63; N, 9.79.
Found: C, 60.35; H, 6.58; N, 9.84.
3.2.6 | Synthesis of 14
The compound synthesized using the same conditions
and procedure as that for 13, starting with 10. A light
yellow oil was obtained in quantitative yield. IR(KBr):
3,423 cm−1 (Ar-OH), 1,617 cm−1 (C=N), 688 cm−1 (Ar-
1
Cl). H-NMR (400 MHz, DMSO): δ = 12.94 (s, 1H, Ar-
OH), 12.83 (s, 1H, Ar-OH), 8.92 (s, 1H, N=CH), 8.88
(s, 1H, N=CH), 7.59 (s, 1H, Ar-H), 7.51–7.43 (m, 2H,
Ar-H), 7.35–7.29 (m, 2H, Ar-H), 7.24–7.18 (m, 2H,
Ar-H), 3.14–3.05 (m, 4H, CH2Cl), 3.04–2.92 (m, 12H,
NCH2), 2.91–2.80 (m, 12H, CH2), 2.62–2.54 (m, 4H,
Ar-CH2), 2.20–2.12 (m, 6H, Ar-CH3), 1.68–1.58
(m, 12H, CH2), 1.58–1.16 (m, 8H, CH2CH2), 0.90–0.73
(m, 9H, CH3).
3.2.7 | Synthesis of 15
The compound synthesized using the same conditions
and procedure as those for 13, starting with 11. A light
yellow oil was obtained in quantitative yield. IR(KBr):
3,419 cm−1 (Ar-OH), 1,617 cm−1 (C=N), 1,495 cm−1 (Ar-
OCH3). 1H-NMR (400 MHz, DMSO): δ = 13.26 (s, 1H, Ar-
OH), 13.03 (s, 1H, Ar-OH), 8.90 (s, 1H, N=CH), 8.86 (s,
1H, N=CH), 7.45 (d, J = 8.7 Hz, 1H, Ar-H), 7.34 (s, 1H,
Ar-H), 7.30 (s, 1H, Ar-H), 7.21 (s, 1H, Ar-H), 7.16 (s, 1H,
Ar-H), 7.12 (s, 1H, Ar-H), 7.02 (d, J = 8.7 Hz, 1H, Ar-H),
3.85 (s, 3H, OCH3), 3.17–3.12 (m, 4H, CH2Cl), 3.11–2.96
(m, 12H, NCH2), 2.94–2.82 (m, 12H, CH2), 2.62–2.54 (m,
2H, Ar-CH2), 2.28–2.07 (m, 6H, Ar-CH3), 1.68–1.59 (m,
12H, CH2), 1.59–1.15 (m, 8H, CH2CH2), 0.95–0.78 (m,
9H, CH3).
3.2.10 | Synthesis of 2
The compound synthesized using the same conditions
and procedure as those for 1, starting with 10. A brown
1
solid was obtained in quantitative yield. H-NMR (400
MHz, DMSO): δ = 8.84 (s, 1H, N=CH), 8.77 (s, 1H,
N=CH), 8.58 (d, J = 12.8 Hz, 3H, Ar-H), 7.81 (d, J = 7.7
Hz, 3H, Ar-H), 7.58 (d, J = 8.7 Hz, 1H, Ar-H), 7.43 (s, 1H,

8
HU ET AL.
Ar-H), 7.40–7.35 (m, 2H, Ar-H), 7.31–7.27 (m, 2H, Ar-H),
7.14 (s, 1H, Ar-H), 6.36 (s, 3H, Ar-H), 2.94–2.88 (m, 4H,
CH2Cl), 2.86–2.81 (m, 12H, NCH2), 2.67 (s, 3H, Ar-CH3),
2.60–2.53 (m, 12H, CH2), 2.51–2.48 (m, 4H, Ar-CH2),
1.68–1.60 (m, 12H, CH2), 1.56–1.26 (m, 8H, CH2CH2),
autoclave, and then heated to a predetermined tempera-
ture with stirring. When the reaction has reached a pre-
determined time, the reaction system is cooled to room
temperature. Before opening the autoclave, CO2 was
slowly discharged from the autoclave. The reaction mix-
ture was filtered through a pad of silica gel to remove cat-
alyst residues. The polymerized product was dried in a
vacuum oven to constant weight.
0.94–0.79
(m,
9H,
CH3).
Anal.
Calc.
(C72H94CoClN10O17): C, 59.01; H, 6.41; N, 9.56. Found: C,
58.64; H, 6.38; N, 9.63.
3.2.11 | Synthesis of 3
4 | CONCLUSIONS
The compound synthesized using the same conditions
In summary, we have successfully synthesized Salen-Co
(III) complexes with different groups, and prepared
copolymers of CO2 and PO/CHO. With increasing tem-
perature, the selectivity and activity of all four Salen-Co
(III) complexes for PPC/PCHC increased. Under the
same reaction conditions, experiments have confirmed
the effect of the different groups in the Salen-Co(III)
complex on the copolymerization of CO2 and PO/CHO.
The results show that the Salen-Co(III) complex with
electron-withdrawing group has the highest selectivity
and activity for PPC/PCHC in the copolymerization reac-
tion of CO2 and PO/CHO. At the same time, when Salen-
Co(III) complex catalyzes the copolymerization of differ-
ent substrates with CO2, the catalyst has higher activity
and selectivity for the formation of PCHC.
and procedure as those for 1, starting with 11. A brown
1
solid was obtained in quantitative yield. H-NMR (400
MHz, DMSO): δ = 8.75 (d, J = 11.5 Hz, 3H, Ar-H), 8.41 (s,
1H, N=CH), 8.38 (s, 1H, N=CH), 8.07 (d, J = 7.7 Hz, 3H,
Ar-H), 7.39 (s, 1H, Ar-H), 7.35 (s, 1H, Ar-H), 7.30–7.20
(m, 2H, Ar-H), 7.17–7.10 (m, 2H, Ar-H), 6.94 (s, 1H, Ar-
H), 6.66 (s, 3H, Ar-H), 3.97 (s, 3H, Ar-OCH3), 2.93–2.87
(m, 4H, CH2Cl), 2.86–2.77 (m, 12H, NCH2), 2.68 (s, 3H,
Ar-CH3), 2.62–2.54 (m, 12H, CH2), 1.70–1.60 (m, 12H,
CH2), 1.58–1.18 (m, 8H, CH2CH2), 0.93–0.75 (m, 9H,
CH3). Anal. Calc.(C73H97CoN10O18): C, 60.01; H, 6.64; N,
9.58. Found: C, 59.49; H, 6.57; N, 9.83.
3.2.12 | Synthesis of 4
ACKNOWLEDGEMENTS
The compound synthesized using the same conditions
and procedure as those for 1, starting with 12. A brown
solid was obtained in quantitative yield.1H-NMR (400
MHz, DMSO) δ = 8.75 (s, 1H, N=CH), 8.71 (s, 1H,
N=CH), 8.62 (d, J = 13.7 Hz, 3H, Ar-H), 7.86 (d, J = 8.3
Hz, 3H, Ar-H), 7.41–7.32 (m, 2H, Ar-H), 7.26 (s, 1H, Ar-
H), 7.20 (s, 1H, Ar-H), 7.15–7.10 (m, 2H, Ar-H), 7.08 (s,
1H, Ar-H), 6.17 (s, 3H, Ar-H), 2.95–2.90 (m, 4H, CH2Cl),
2.89–2.83 (m, 12H, NCH2), 2.67 (s, 3H, Ar-CH3),
2.60–2.55 (m, 12H, CH2), 2.51 (s, 3H, Ar-CH3), 2.51–2.49
(m, 4H, Ar-CH2) 1.69–1.61 (m, 12H, CH2), 1.58–1.26 (m,
8H, CH2CH2), 0.93–0.79 (m, 9H, CH3). Anal. Calc.
(C73H97CoN10O17): C, 60.68; H, 6.71; N, 9.69. Found: C,
60.37; H, 6.64; N, 9.71.
The authors are thankful for financial support from the
Anhui Province University Natural Science Research Pro-
ject (No. KJ2017A008), the Anhui Provincial Natural Sci-
ence Foundation (Nos. 1808085ME55, 1908085MB51),
and Anhui Province Key Laboratory of Enviorment-
friendly Polymer Materials.
ORCID
Longchao Du https://orcid.org/0000-0002-2414-2076
Weiju Zhu https://orcid.org/0000-0002-8743-1238
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How to cite this article: Hu Y, Du L, Li C,
Shen J, Zhu W, Shao C. Study of electronic effect
in bifunctional catalysts for the copolymerization
of CO2 and PO/CHO. J Chin Chem Soc. 2020;1–9.
https://doi.org/10.1002/jccs.202000103
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