Cobalt-based catalytic system for the chemical fixation of CO2 under solvent-free conditions

Article abstract of DOI:10.1002/aoc.5427

We have described a novel and efficient method for synthesizing cyclic carbonates with ‘Co (NO₃)₂ ^.6H₂O/L6’-catalyzed coupling of epoxides and CO₂ under solvent-free conditions. We proposed a possible reaction mechanism based on some control experiments. Phenylpropiolic acid could be provided by using the same method.

Full text of DOI:10.1002/aoc.5427

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Received: 5 October 2019
DOI: 10.1002/aoc.5427
Revised: 24 November 2019
Accepted: 25 November 2019
F U L L P A P E R
Cobalt-based catalytic system for the chemical fixation of
CO2 under solvent-free conditions
Fengtian Wu1
| Yu Lin2
1Jiangxi Province Key Laboratory of
Polymer Micro/Nano Manufacturing and
Devices, East China University of
Abstract
We have described a novel and efficient method for synthesizing cyclic carbon-
.
Technology, Nanchang, 330013, China
ates with ‘Co (NO3)2 6H2O/L6’-catalyzed coupling of epoxides and CO2 under
2College of Chemistry and Chemical
Engineering, Xinyang Normal University,
Xinyang, 464000, China
solvent-free conditions. We proposed a possible reaction mechanism based on
some control experiments. Phenylpropiolic acid could be provided by using the
same method.
Correspondence
Fengtian Wu, Jiangxi Province Key
Laboratory of Polymer Micro/Nano
Manufacturing and Devices, East China
University of Technology, Nanchang
330013, China.
K E Y W O R D S
carbon dioxide, chemical fixation, cobalt, cyclic carbonates, epoxide
Email: wufengtian123@126.com
Funding information
The Doctoral Research Project of East
China University of Technology, Grant/
Award Number: 1410000387; Doctoral
Research Project, Grant/Award Number:
1410000387
1 | INTRODUCTION
indispensable in the process. These conditions require
energy consumption, and may thus cause serious envi-
The chemical conversion of CO2 into value-added bulk
and fine chemicals has attracted considerable attention
in recent years,[1] because CO2 is an abundant inexpen-
sive, nonflammable, and renewable C1 synthon.[2] This
C1 feedstock could be utilized for the synthesis of carba-
mate derivatives, cyclic urethanes, N,N0-disubstituted
urea compounds, formic acid, poly (carbonates), carbox-
ylic acids, carbon monoxide and others.[3] Among them,
cyclic carbonates are an important compound, due to its
high atom efficiency and the widespread application of
products such as degrease in medicine, electrolytes in
lithium ion batteries, and eco-friendly non-protic
solvents.[4]
ronmental problems.[6] In hence, great efforts have been
made for the development of effective catalytic systems
such as, imidazolium salts,[7] quaternary ammonium
salt,[8] quaternary phosphonium salt,[9] dipyridine salt,[10]
phenolic resin,[11] organic polymer based on
organosilicone and urea,[12] MOFs,[13] Zn@Salen-typle
porous material,[14] hypercrosslinked porous polymer
materials,[15] ionic liquid,[16] metal complex,[17] and pro-
ton donor,[18] for the coupling of epoxides and CO2.
Although numerous catalysts promote the reaction to
form the corresponding cyclic carbonates in excellent
yields, in many case, harsh reaction conditions, the large
loading amount of catalyst, metal halide or halide salt as
co-catalyst are required. To circumvent these disadvan-
tages, new types of active and efficient catalysts are desir-
able to be developed.
One of the most successful method for preparing five-
membered cyclic carbonates is the cycloaddition of CO2
and epoxides (Scheme 1).[5] Cyclic carbonates have been
synthesized in industries, but high pressure, high temper-
ature, and large catalyst loading amount are
As a continuation of our study on using ligands for
enhancing the coupling reaction,[19] and encouraged by
Appl Organometal Chem. 2020;e5427.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5427

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WU AND LIN
Table 1, only 17% 2a yield was obtained in the absence of
ligand (entry 1). Then, O,O-type ligands L2, L3, and L4
were investigated, the yields were slightly increased
(entries 2, 3, and 4). When N,O-type ligand L5 was used,
48% yield was provided (entry 5). When quadridentate
O,N-ligand L6 was employed, 63% 2a yield was obtained,
may due to its strong coordination ability to cobalt (entry
6).
SCHEME 1 The reaction of epoxides and CO2
To further increase the reaction efficiency, we
examined other reaction conditions (Table 2). More
starting material was recovered without metal and co-
the Werner group's work,[20] which depicted that catalyst
system ‘CaI2/L1’ (or ‘CaI2/18-crown-6’) could be used for
the synthesis of cyclic carbonates from epoxides and CO2
(Scheme 2, a and b), we tried the reaction in the presence
of different ligands, and found that the combination of
.
catalyst (entry 1). Co (NO3)2 6H2O was crucial for the
successful reaction, and KI also played important role
in this transformation (entries 2 and 3). Next, other
metal catalysts were investigated, the results indicated
.
.
‘CoNO3 6H2O/L2’ could efficiently promote the coupling
that Co (NO3)2 6H2O was the superior choice over
reaction of CO2 and epoxides in solvent-free reactions
(Scheme 2, c).
others (entries 4, 5, and 6). Moreover, evaluation of
co-catalysts such as KBr, KCl, NaI, and NaCl were
underwent, KBr was better in promoting the transfor-
mation (entries 7, 8, 9, and 10). Switching the CO2
pressure to 0.3 and 0.6 MPa, the yields of 2a were
obtained in 71% and 82%, respectively (entries 11 and
12). In addition, the effects of reaction time were scru-
tinized, the results showed that 5 hr was optimal
2 | RESULT AND DISCUSSION
Our attempt was commenced with the transformation of
ꢀ
styrene oxide 1a and CO2 at 100 C in 5 hr. As shown in
SCHEME 2 The ligand-promoted cobalt-
catalyzed reaction of epoxides and CO2

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CHEMICAL FIXATION OF CO2
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TABLE 1 Screening ligands for the reactiona
Entry
Ligand
-
Yield (%)b
1
2
3
4
5
6
22
26
32
39
48
63
L2
L3
L4
L5
L6
.
aReaction conditions: 1a (5 mmol), CO2 atmospheric pressure, Co (NO3)2 6H2O (0.1 mmol), L2-L5 (0.2 mmol), L6 (0.1 mmol), KI (0.1 mmol), 100 ꢀC, 5 hr;
bYields were determined by 1H NMR spectroscopy using 1,1,2,2-tetrachloroethane as the internal standard.
(entries 13 and 14). From the above, the best reaction
(2 m and 2n). The reaction of glycidol (or cyclohexene
oxide) and CO2 offered the corresponding products in
poor yield (2o and 2p).
conditions were 1a (5 mmol), CO2 pressure (0.6 MPa),
.
Co (NO3)2 6H2O (0.1 mmol), L6 (0.1 mmol), KBr
ꢀ
(0.1 mmol), 100 C, 5 hr.
To elucidate the reaction mechanism, we performed
some control experiments shown in Scheme 4. In the
Having optimized the reaction conditions, we
started to expand the substrate scope of the reaction.
As summarized in Scheme 3, epoxides containing phe-
.
presence of Co (NO3)2 6H2O, the model reaction was
hardly occurred (Scheme 4, a). We treated the reaction
under the KBr, 12% 2a yield was observed (Scheme 4,
b). In combination of and KBr, the yield was increased
to 25% (Scheme 4, c). These experiments suggested
that KBr addition may affect 2a to become more active
intermediate to complete the reaction, and Co
nyl
group
were
successfully
converted
into
corresponding products in good yields (2a-2f). Epoxide
with weak electron-withdrawing group in phenyl was
superior to the one with electron-donating group (2a-
2c vs 2d). Ester group was tolerant under the optimal
reaction conditions (2e-2 g and 2i). The length of
alkyl group had a little negative effect on the reaction
(2j-2 l). The carbon–carbon double bond was compati-
ble under these reaction conditions, producing the tar-
get compounds 2 g and 2 h in 85% and 89% 1H
NMR yields. Epibromohydrin and epichlorohydrin was
tested and found to be tolerant in the transformation
.
(NO3)2 6H2O could promote the reaction in the pres-
ence of KBr. Then we attempted to carry out the reac-
tion between 3a and CO2, which 73% 2a yield was
obtained (Scheme 4, d). This result demonstrated that
3a may be transformed into an active bromine inter-
mediate. When we carried the reaction under different
amount of L6 (0.1 mol, 0.2 mol, 0.3 mol), the product

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WU AND LIN
TABLE 2 The other optimization of reaction conditionsa
Entry
[M]
Co-catalyst
Yield (%)b
1
-
-
-
17
15
2
KI
.
3
Co (NO3)2 6H2O
Zn (NO3)2
-
14
4
KI
51
5
Fe (NO3)3
KI
48
.
6
Cu (NO3)2 6H2O
KI
42
.
7
Co (NO3)2 6H2O
KBr
KCl
NaI
NaCl
KBr
KBr
KBr
KBr
65
.
8
Co (NO3)2 6H2O
54
.
9
Co (NO3)2 6H2O
57
.
10
11c
12d
13f
14g
Co (NO3)2 6H2O
46
.
Co (NO3)2 6H2O
71
82, 77e
.
Co (NO3)2 6H2O
.
Co (NO3)2 6H2O
52
.
Co (NO3)2 6H2O
85
.
aReaction conditions: 1a (5 mmol), CO2 atmospheric pressure, Co (NO3)2 6H2O (0.1 mmol), L6 (0.1 mmol), co-catalyst (0.1 mmol), 100 ꢀC, 5 hr;
bYields were determined by 1H NMR spectroscopy using 1,1,2,2-tetrachloroethane as the internal standard;
cCO2 (0.3 MPa);
dCO2 (0.6 MPa);
eIsolated yield;
f3 hr;
g8 hr;
yields were 18%, 28%, and 31%, suggesting that L6
could promote the reaction in some extend (Scheme 4,
e), which may be attributed to the hydrogen bond
donor catalysis.[21] However, with the aid of Co
(Scheme 4, f????????). Under the standard reaction con-
ditions, the yield was 82% (Scheme 4, g), may due to
that the complex compound from Co (NO3)2 6H2O and
L6 could obviously expedite the reaction with the
assistance of KBr, and hydrogen bond donor catalysis.
.
.
(NO3)2 6H2O and L6, no increasing yield was provided