Metal β-diketonate complexes as highly efficient catalysts for chemical fixation of CO2 into cyclic carbonates under mild conditions

Article abstract of DOI:10.1039/c9dt03584b

The potential of metal β-diketonate complexes for the catalysis of the chemical fixation of CO₂ into cyclic carbonates at 1 atm CO₂ and near room temperature was demonstrated. Their potential for the capture and simultaneous conversi

Full text of DOI:10.1039/c9dt03584b

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PAPER
Metal β-diketonate complexes as highly efficient
catalysts for chemical fixation of CO into cyclic
carbonates under mild conditions†
2
Cite this: Dalton Trans., 2019, 48,
15970
Hongmei Wang, Zulei Zhang, Hailong Wang, Liping Guo * and Lei Li*
The potential of metal β-diketonate complexes for the catalysis of the chemical fixation of CO
carbonates at 1 atm CO2 and near room temperature was demonstrated. Their potential for the capture
and simultaneous conversion of CO in a dilute CO stream was also determined. The catalysts were
easily synthesized and commercially available. Therefore, this CO transformation was less energy- and
material-consuming, which made this reaction closer to true “green” chemistry.
2
into cyclic
Received 5th September 2019,
Accepted 24th September 2019
2
2
DOI: 10.1039/c9dt03584b
2
rsc.li/dalton
ation of CO is debatable. The entire process should be con-
sidered, including the following: costs for capture, storage,
2
Introduction
Carbon dioxide is an abundant, economical, nontoxic, and and transportation of purified CO
2
; the material and energy
renewable C1 feedstock in organic synthesis. The coupling consumption for catalyst preparation; and the energy con-
1
4
reaction of CO with epoxides to afford cyclic carbonates is one sumption in the course of CO2 transformation. The harsh
2
of the most promising reactions for the utilization of CO
2
,
temperatures and pressures required for the reactions are
because this transformation is 100% atom economical, and highly energy consuming. Therefore, as traditional catalyst
the products can be widely used. A wide range of catalytic research is relatively mature, less energy-consuming processes
1
systems have been developed for these reactions over the past should be explored. Fortunately, a number of catalysts have
decades. The early catalytic systems used simple quaternary been developed for CO2 conversion under mild conditions
2
ammonium/phosphonium salts (including ionic liquids),
(low temperature and pressure, even at atmospheric
3
3a,4
15
organic bases, inorganic or organic metal halides,
and pressure ) in recent years. Hydrogen-bond donor ammonium
transition metal complexes alone or in a physical mix. Then, salts, which were functionalized with –OH,
the structures of catalysts became more and more exquisite, both, and metal-based catalysts, including functionalized
the materials became more and more advanced, and the cata- metal
5
16
17
–NH2,
or
1
8
19
2
0
complexes
and
metal–organic
frameworks
6
a,c,21
lytic activity became more and more efficient. To date, catalysts (MOFs),
were studied for their use in the transformation
with multiple functionality in one molecule and a variety of new of CO2 into cyclic carbonates at 1 atm CO2 (Table S1†).
materials have been explored, including various metal–organic Nevertheless, most of the catalysts were not sufficiently
6
7
frameworks (MOFs), porous materials, multifunctional or effective, because most of the turnover frequencies (TOFs)
8
−1
polymerized ammonium/phosphonium salts, functional tran- were lower than 8 h . Although the TOFs of some catalysts
9
−1
sition metal complexes, and some other special catalysts such were higher than 8 h (Table S1,† entries 18, 21, and 26), the
as metal- and halide-free catalysts, N-doped carbons, and costs for catalyst preparation were relatively high. Thus, there
metal–organic nanotubes. However, given that CO is a highly is still plenty of room for improvement, such as reducing cata-
1
0
11
12
2
oxidized and stable molecule, in addition to the participation of lyst loading or lowering the cost for catalyst preparation.
catalysts and solvents, its conversion usually requires high
temperatures (>100 °C) and pressures (>1 MPa).
In the area of metal complex-catalyzed chemical fixation of
CO , metal(salen) complexes have attracted attention since
2
Moreover, CO
2 2 2
utilization is so attractive, because CO is their first use in the transformation of CO into cyclic carbon-
2
2
recognized as a primary greenhouse gas, and CO conversion ates. Over the past two decades, modifications and function-
may contribute to mitigating climate change.
2
1
3
However, alizations have been made in metal centers, the diamine
whether more CO
2
is emitted than converted in the transform- framework of ligands, and substituents on phenyl rings of sali-
cylaldehydes to improve their performance in the chemical fix-
ation of CO into cyclic carbonates or polycarbonates (the pro-
2
College of Biological, Chemical Science and Engineering, Jiaxing 314001, China.
E-mail: guolp@mail.zjxu.edu.cn, lei.li@mail.zjxu.edu.cn
ducts of the copolymerization of CO
2
with epoxides, which is
1
b,23
another route for the reaction of CO with epoxides).
Metal
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
2
C9DT03584B
β-diketonate complexes, which have similar coordination struc-
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tures to metal(salen) complexes and the possibility of to moderate catalytic activity (Table 1, entries 6–9), and the
2
4
functionalization in three positions of the ligand, were rest of the M(acac)n showed low catalytic activity at 40 °C
widely used in catalytic chemistry. However, in spite of their (Table 1, entries 10–16). The solubility of the complexes in the
facile preparation and chemical stability, their application in monomer was investigated to confirm whether there was a
the chemical fixation of CO did not attract much attention. relationship between the catalytic activity and the solubility of
2
M(acac) , the simplest metal β-diketonate complexes, are easily the complexes. Among the catalysts used above, no or very
n
2
5
synthesized or commercially available. In the present study, small amounts of precipitates were observed in the reaction
we tap into their potential for catalyzing reactions under mixture during the reaction at 40 °C, except for CoCl ·4H O,
2
2
extremely mild conditions.
2 2 2 3
CoAc ·4H O, Cd(acac) , and La(acac) . Since the catalytic activi-
ties of these four catalysts were relatively low, it might be con-
cluded that some catalysts with poor solubility exhibited poor
catalytic activity. But it could not be proved that the reason for
the poor catalytic activity was poor solubility, because it was
observed during the experiments that the solubility of Al(acac)3
was very good, but its catalytic activity was very low.
Results and discussion
We first examined the catalytic performances of several com-
n
mercially available M(acac) with 0.5 mol% catalyst loading
combined with tetrabutylammonium bromide (Bu NBr) for
4
The catalytic activity can be greatly influenced by minor
the cycloaddition of CO
pheric pressure and 40 °C (Table 1). When Bu
2
to 1,2-butene oxide (BO) at atmos-
NBr was used
27
alterations in ligands. Several similar Co(β-diketonato) com-
2
4
plexes with the –C(CH
CH in ligands were applied for the reaction (Table 2). The
performance of bis(dipivaloylmethanato)cobalt(II) (Co(dpm)2)
was equal to that of Co(acac) (Table 2, entries 1 and 2). The
catalytic activities of bis(benzoylacetonato)cobalt(II) (Co(bac)
and bis(dibenzoylmethanato)cobalt(II) (Co(dbm) ) were slightly
3 3 3
) , –CF , or –Ph group substituted for
alone, just 13% yield of 1,2-butylene carbonate (BC) was
obtained after 24 h (Table 1, entry 1), whereas the addition of
–
3
Co(acac)
valence state of cobalt had a pronounced effect on catalytic
activity, as Co(acac) showed extremely low catalytic activity
Table 1, entry 3). It was reported that metal halide/n-Bu NOAc
systems were effective for the conversion of epoxides into
2
enhanced the yield to 95% (Table 1, entry 2). The
2
2
)
3
2
(
4
lower than that of Co(acac)
one or two –CH groups in acetylacetonate were replaced by
CF , the catalytic activity was cut down so sharply that bis
2
(Table 2, entries 3 and 4). When
3
2
6
cyclic carbonates at 10–15 bar CO
CoAc ·4H O were combined with Bu
activity was found to be almost the same as that of Bu NBr
2
.
Herein, CoCl
2 2
·4H O and
NBr and their catalytic
–
3
2
2
4
(
6 2
hexafluoroacetonato)cobalt(II) (Co(F -acac) ) did not contrib-
4
ute to the catalytic activity anymore (Table 2, entries 5 and 6).
These results might be attributed to the electronic effect of
substituents. The addition of an electron-withdrawing group
alone (Table 1, entries 4 and 5). Some other M(acac)
n
such as
V(acac) , VO(acac) , Ni(acac) , and Zn(acac) exhibited excellent
3
2
2
2
3
such as –CF reduced the electron density of the oxygen atoms
in the ligand, which would result in the loss of the coordi-
nation bond of the ligand to the metal center, thereby redu-
cing the stability of the metal complex and leading to lower
catalytic activity.
Table 1 Screening of catalysts for the synthesis of cyclic carbonate
from CO and BO at atmospheric pressure
2
a
Reaction temperature had a significant effect on the reac-
tion activity (Table 3, entries 1–5). The reaction of CO
2
with BO
b
Entry
M(acac)
n
Yield (%)
a
Table 2 Catalytic activities of Co(β-diketonato)
2
c
1
2
3
4
5
6
7
8
9
—
13
95
21
14
20
95
88
76
43
18
22
16
21
24
13
25
Co(acac)
Co(acac)
CoCl
CoAc
V(acac)
VO(acac)
Ni(acac)
Zn(acac)
Fe(acac)
Fe(acac)
Al(acac)
Zr(acac)
MoO
Cd(acac)
La(acac)
2
3
2
·4H
·4H
2
O
2
O
2
3
2
2
b
2
Entry
Co(acac′)
R
R′
Yield (%)
2
1
1
1
1
1
1
1
0
1
2
3
4
5
6
2
3
1
2
3
4
5
6
Co(acac)
Co(dpm)
2
CH
C(CH
3
CH
C(CH
Ph
Ph
3
95
95
87
90
19
12
3
2
)
3 3
3 3
)
4
Co(bac)
Co(dbm)
2
CH
Ph
3
2
(acac)
2
2
2
Co(F
Co(F
3
-acac)
-acac)
2
CH
3
CF
CF
3
3
6
2
CF
3
3
a
a
Reaction conditions: BO (40 mmol), M(acac)
n
(0.2 mmol), Bu
4
NBr
2 4
Reaction conditions: BO (40 mmol), Co(acac′) (0.2 mmol), Bu NBr
b
b
(
0.2 mmol), 40 °C, 1 atm CO
the selectivities are >99%. Bu
2
(balloon), 24 h. Determined by GC and (0.2 mmol), 40 °C, 1 atm CO
4
NBr alone for the reaction. the selectivities are all >99%.
2
(balloon), 24 h. Determined by GC and
c
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Table 3 Effects of reaction parameters in the synthesis of cyclic car-
a
2 2
bonate from CO and BO catalyzed by Co(acac)
b
Equiv.
of cocat.
Temp.
(°C)
Time
(h)
Yield
(%)
Entry
Cocat.
1
2
3
4
5
6
7
8
9
Bu
Bu
Bu
Bu
Bu
4
4
4
4
4
NBr
NBr
NBr
NBr
NBr
1
1
1
1
1
0
0.1
0.2
1
2.5
5
7.5
10
2.5
5
7.5
10
5
5
5
5
5
20
30
40
50
50
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
24
24
24
24
12
12
12
12
12
12
12
12
12
4
4
4
4
12
12
8
12
12
12
37
70
95
>99
99
0
14
20
71
85
97
98
98
51
64
63
47
20
>99
None
Scheme 1 The proposed pathway for epoxide ring opening by
Co(acac) /Bu NBr.
2 4
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
4
4
4
4
4
4
4
4
4
4
4
4
4
4
NBr
NBr
NBr
NBr
NBr
NBr
NBr
NBr
NBr
NBr
NBr
NCl
NI
10
11
12
13
14
15
16
17
18
19
20
21
22
23
2
8
(Scheme 1). In addition to being a nucleophile in the ring
−
opening of the epoxide, Br could also coordinate with the
metal center. Therefore, Br− competed with the epoxide in
−
bonding to the metal center. When excess Br was loaded, co-
ordinated epoxides would be displaced from the metal center,
and the last two coordination sites of Co(acac) might be occu-
2
−
pied by Br , thereby leading to the reduction of reaction
c
NI
97(41 )
60
43
activity. This reason explains why the reaction activity with 10
equiv. of the cocatalyst was lower than that with 5 or 7.5 equiv.
of the cocatalyst. Nevertheless, in the absence of metal com-
BuMIMBr
BuPh PBr
BuPyBr
3
5
55
a
plexes, Br− alone can also promote the ring-opening reaction
2
Reaction conditions: BO (40 mmol), Co(acac) (0.2 mmol, 0.5 mol%),
b
−
1
>
0
atm CO
2
(balloon). Determined by GC and the selectivities are of epoxides. Considering this aspect, excess Br had a positive
c
99%. Co(acac)
2 4
(0.04 mmol, 0.1 mol%) and Bu NI (0.2 mmol,
effect on the reaction activity. Therefore, the addition of excess
catalysts did not reduce the catalytic activity significantly.
The process described above, which especially took place in
solution, had no prior direct evidence. As the reaction took
place in a transparent glass container, the color of the reaction
mixture noticeably changed from red to purple gradually when
.5 mol%).
can still be carried out at 20 °C at a reasonable rate. When the
temperature was raised to 50 °C, the substrate could be almost
completely converted to a cyclic carbonate after 12 h.
The boiling point of BO is 63 °C at atmospheric pressure.
Thus, 40 °C was chosen for the sake of convenience and safety
as the main operating temperature for further study.
4
the equiv. of Bu NBr was increased (Fig. 1). According to the
relationship between the absorption of visible light and the
observed color, red, fuchsia, and purple colors can be observed
when the light at wavelengths of 490–500, 500–560, and
Increasing the ratio of Bu NBr to Co(acac) from 0 to 5 had
4
2
560–580 nm was absorbed, respectively. Thus, the mixtures of
a pronounced positive effect on the catalytic activity (Table 2,
entries 6–11). Unsurprisingly, the reaction did not occur when
Bu NBr was not present in the catalytic system. Comparison of
4
the catalytic activity of Bu
4
NBr alone and that of Co(acac)
2
–
Bu NBr showed that Co(acac)
4
2
and Bu NBr catalyzed the reac-
4
tion synergistically. When the ratio was increased to 5, 97%
yield of BC was obtained after 12 h. When the ratios were 5,
7
.5, and 10, the conversion of BO was all nearly complete, and
the difference between these ratios was unremarkable (Table 2,
entries 11–13). As seen from Table 1, entry 1, Bu NBr could cat-
4
alyze the reaction alone, and a long reaction time might level
out the difference. Therefore, the reaction time was shortened
to 4 h (Table 2, entries 14–17) to highlight the difference. The
yield of BC with 10 equiv. of Bu
4
NBr was lower than that with
5
or 7.5 equiv. of Bu NBr, which meant that the addition of
4
excess cocatalyst was not conducive to the reaction, and this
2
2,23a
phenomenon was consistent with some relevant reports.
In the process of the reaction of CO2 with epoxides cata-
lyzed by metal complexes, a coordination bond was formed
between the metal center and the oxygen atom of the epoxide,
Fig. 1 The UV-vis absorption spectrum of the reaction mixtures. The
amount of each material in the mixtures was in accordance with Table 2
entries 6–13: BO (40 mmol), Co(acac)
2 4
(0.2 mmol), the ratio of Bu NBr/
thereby activating the epoxide and prompting its ring opening Co(acac)
2
: (1) 0, (2) 0.1, (3) 0.2, (4) 1, (5) 2.5, (6) 5, (7) 7.5, and (8) 10.
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Co(acac)
2
and Bu
4
NBr in BO, the compositions of which were Table 4 The conversion of CO
consistent with those of reaction mixtures, were characterized
by ultraviolet-visible (UV-Vis) spectroscopy. As shown in Fig. 1,
2
(or CO
2
in flue gas) with various epox-
a
ides at atmospheric pressure
solution 1 (with no Bu
peak near 495 nm and no obvious absorption near 548 nm.
With the increasing dosage of Bu NBr, the absorbance at
4
NBr) exhibits a significant absorption
4
around 495 nm decreased gradually and the absorbance at
around 548 nm increased accordingly. This indicates that the
peaks at around 495 nm and 548 nm might be caused by the
Co–BO and Co–Br coordination bonds, respectively. With the
b
Entry
R
Temp. (°C)
Time (h)
Yield (%)
c
1
2
3
4
5
6
7
Me
Et
40
40
40
40
40
70
70
70
8
8
8
8
8
2
4
4
97
97
58
67
82
85
>99
increasing dosage of Bu NBr, the BO bonded to the Co center
4
−
Ph
CH
Bu
Bu
Bu
Bu
was replaced by Br . The increase of the absorbance at around
2
Cl
5
48 nm was pronounced in the ratio range of 0 to 2.5, and
then gradually slowed down. When the ratio of Bu NBr to
4
Co(acac)
2
increased to 7.5, adding more Bu
4
NBr did not lead
d
e
8
49
to a pronounced increase in the absorbance at around 548 nm.
In addition, an absorption peak appeared at 450–490 nm,
a
Reaction conditions: Epoxides (40 mmol), Co(acac)
.5 mol%), Bu NI (1 mmol, 2.5 mol%), atm CO
Determined by GC. Operating pressure: 2 atm. Since the boiling
2
(0.2 mmol,
0
4
1
2
(balloon).
which decreased in intensity when the equiv. of Bu
4
NBr was
b
c
more than 2.5. Consequently, a new absorption peak appeared point of 1,2-propylene oxide (PO) is 34 °C, the pressure caused by the
at 650–700 nm, whose intensity continuously enhanced with
substrate gas is about 1 atm at 40 °C. Therefore, 2 atm pressure is
gets into the reaction system and the
partial pressure of CO is about 1 atm. HO (20 mmol), Co(acac)
required to make sure that CO
2
the increasing dose of Bu
4
NBr. These two absorption peaks
d
2
2
might correspond to the second Co–BO and Co–Br coordi- (0.1 mmol), Bu NI (0.5 mmol), and a dilute CO stream (a gas mixture
4
2
containing 10% v/v CO
2
and 90% v/v N
2
) with a total flow of 10 sccm.
Conversion of CO was 92%. Conversion of CO calculated as the
2 2
ratio between the moles of cyclic carbonate formed and the moles of
CO2 that flowed through the reaction (1 sccm = 7.43 × 10 mol s
0.7 mmol of CO flowed for 4 h).
nation bonds, respectively, and when the equiv. of Bu NBr was
4
e
more than 2.5, the second BO bonded to the Co center began
−
−7
−1
to be replaced by Br .
;
1
2
The effect of anions and cations of the cocatalyst was
further studied with 5 equiv. of the cocatalyst. As to the anions
4
of Bu NX (Table 3, entries 11, 18–20), the order of activity was
−
> Br− > Cl , which was consistent with the order of their
−
gas mixture containing 10% v/v CO2 and 90% v/v N ) was
I
2
2
9
studied briefly. The boiling point of BO is low, and the raw
materials could be easily carried away by the excess gas. Thus,
non-volatile 1,2-hexene oxide (HO) was chosen as the sub-
strate. The reaction was operated at 70 °C to shorten the time
and thus reduce the loss of raw materials. The result showed
nucleophilicity. When Bu
4
NCl was used, BC yield was only
NI was used, a BC yield of 97%
2
0% after 12 h, but when Bu
4
−
1
was obtained after 8 h (TOF = 24.2 h ). Co(acac) still showed
2
good catalytic activity and led to 41% yield of BC after 8 h even
when the amount was reduced to 0.1 mol% (Table 3, entry 20).
−
1
that 92% of CO in a dilute CO stream could be captured and
The TOF value of Co(acac) was 51.2 h , which exceeded the
2
2
2
simultaneously converted into cyclic carbonate when the total
flow of the dilute CO stream was 10 sccm (Table 4, entry 8),
which meant that the catalyst was also effective for the capture
TOF values of most of the catalytic systems reported previously
under similar reaction conditions (Table S1†). The order of
2
cocatalysts with different cations was Bu NBr > BuMIMBr >
4
2
and simultaneous conversion of CO in flue gas.
3
BuPyBr > BuPh PBr (Table 3, entries 11, 21–23). The solubility
and the electrostatic interactions between anions and cations
of cocatalysts in BO (BO itself acted as solvent in the reaction),
−
which influenced the concentration of Br disassociated from
the bromide salt, might affect the performance of the cata-
Conclusions
3
0
lytic system. As observed in the experiment, a certain amount In conclusion, the catalytic potential of M(acac) -based cata-
n
of BuPh
exceeded the TOF values of most of the catalytic systems from CO
reported previously. Considering the low cost and easy prepa- transformation could be achieved under the conditions of
ration of metal β-diketonate complexes, this method has the 1 atm CO , near room temperature, and without additional sol-
potential for CO utilization. vents. With 0.5 mol% Co(acac) , 97% yield of 1,2-butylene car-
The catalytic system was effective for the coupling reaction bonate was obtained after 8 h (TOF = 24.2 h− ) at 1 atm CO2
of CO with a variety of terminal epoxides, including aliphatic and 40 °C. When the loading of the catalyst was reduced to
3
PBr was not soluble in BO. As seen, this value of TOF lytic systems was tapped for the synthesis of cyclic carbonates
2
and epoxides under extremely mild conditions. The
2
2
2
1
2
and aromatic epoxides (Table 4, entries 1–5). The transform- 0.1 mol%, the yield of 1,2-butylene carbonate was 41% (TOF =
ation of CO commonly uses purified CO , thereby resulting in 51.2 h− ). Furthermore, this system with 1,2-hexene oxide as
1
2
2
high energy and capital costs for its capture, storage, and the substrate could capture and simultaneously convert 92%
transportation. Thus, the activity of this system for the capture of CO in a dilute CO stream (a gas mixture containing 10%
2
2
and simultaneous conversion of CO in a dilute CO stream (a v/v CO and 90% v/v N ). In addition to being less energy con-
2
2
2
2
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suming, the preparation of the catalyst was facile and less
2 3 2 6 2
The synthesis of Co(dbm) , Co(F -acac) and Co(F -acac)
material consuming, which made this transformation of CO2 was similar to that of Co(bac)2.
closer to true “green” chemistry. Tetrabutylammonium halide
was used as a cocatalyst, and its excess dosage had a negative
effect on the reaction activity. The UV-Vis spectrum of the reac-
tion mixture was used to investigate the mechanism, and to 506.0928).
Co(dbm)
2
. Yellow solid, yield 91%.
−
1
IR (KBr): ν/cm 1594, 1547, 1524, 1480, 1454 and 1395.
+
+
MS (ESI ): m/z 506.0893 (calcd for [Co(C H O ) + H ]
1
5
11 2 2
the best of our knowledge, this evidence has not been provided
11 2 2 2
Anal. calcd for Co(C15H O ) ·2H O: C, 66.55; H, 4.84; Co,
in other studies. Three positions in the ligand of M(acac) can 10.88. Found: C, 66.80; H, 4.52; Co, 10.32. The ratio of C/Co
n
be modified or functionalized to highlight the great value of calcd for Co(C15
H
11
O
2
)
2
·nH
2
O: 6.12. Found: 6.47.
this catalyst system in further studies.
Co(F -acac) . Dark purple powder, yield 87%.
3 2
−
1
IR (KBr): ν/cm 1625, 1531, 1465 and 1401.
−
MS (ESI ): m/z 395.9830 (calcd for [Co(C
5
H
4
F
3
O
2
)
2
·
−
CH
3
OH-H] 395.9843).
Experimental
General information
Anal. calcd for Co(C H F O ) : C, 32.90; H, 2.21; Co, 16.14.
5
4 3 2 2
Found: C, 33.20; H, 2.42; Co, 15.85. The ratio of C/Co calcd for
Co(C ·nH O: 2.04. Found: 2.09.
Co(F -acac) . Reddish brown powder, yield 81%.
NMR spectra were recorded with a 500 MHz Bruker spectro-
meter and calibrated with tetramethylsilane (TMS) as the
internal reference. Infrared spectra measurements were per-
formed on a Thermo 470 FT-IR spectrometer. UV-Vis spectra
measurements were performed on an Agilent Cary 5000
spectrometer. GC/MS analysis was performed on an Agilent
5
H
4
F
3
O
2
)
2
2
6
2
−
1
IR (KBr): ν/cm 1645, 1534, 1483 and 1400.
MS (ESI ): m/z 503.9269 (calcd for [Co(C
CH OH-H] 503.9277).
−
5
HF
6
O
2
)
2
·
−
3
5 6 2 2
Anal. calcd for Co(C HF O ) : C, 25.39; H, 0.43; Co, 12.46.
7
890A gas chromatograph with an Agilent 5975C mass-selec-
tive detector. GC analysis was performed on an Agilent
890 gas chromatograph with an HP-5 column and an FID
Found: C, 26.65; H, 0.54; Co, 12.09. The ratio of C/Co calcd for
Co(C HF O ) ·nH O: 2.04. Found: 2.20.
5
6
2 2
2
6
detector. ESI-MS analyses were performed on a Waters LCT
premier XE mass spectrometer. The catalysts were dissolved in
CH OH for ESI-MS analyses. The carbon and the hydrogen
3
contents of Co(β-diketonato)2 were analysed on a Thermo
Fisher Flash 2000 elemental analyser (EA) and the cobalt con-
tents were analysed on an Agilent 720 inductively coupled
plasma atomic emission spectrometer (ICP-AES). Both the EA
and the ICP-AES were performed at Shanghai Huiming Testing
Equipment Co., Ltd. Reagents and starting materials were all
used as received unless otherwise stated.
Synthesis of [BuMIM]Br and [BuPy]Br
-Butyl-3-methylimidazolium bromide (BuMIMBr) and 1-butyl-
pyridin-1-ium bromide ([BuPy]Br) were synthesized as
1
3
1
described.
BuMIM]Br. The synthesis of [C MIM]Br was carried out in
[
4
a 100 mL round-bottomed flask, which was immersed in a
recirculating heated water bath and fitted with a reflux conden-
ser. 1-Bromobutane (41.1 g, 0.3 mol) was dropped into
n-methylimidazole (20.5 g, 0.25 mol) at 80 °C for 1 h. After the
addition, the reaction mixture was stirred for another period of
4
h at 80 °C. The remaining 1-bromobutane was removed by
Synthesis of cobalt(II) β-diketonate complexes
heating the residue at 80 °C under high vacuum until the weight
of the residue remained constant. H NMR (CDCl ): δ (ppm)
Bis(benzoylacetonato)cobalt(II) (Co(bac)
nato)cobalt(II) (Co(dbm)2), bis(trifluoroacetonato)cobalt(II)
Co(F -acac) ), and bis(hexafluoroacetonato)cobalt(II) (Co(F
acac) ) were synthesized as described. Bis(dipivaloylmethanato)
cobalt(II) (Co(dpm) ) was purchased from Alfa Aesar Co., Ltd.
2
), bis(dibenzoylmetha-
1
3
1
3
0.20 (s, 1H), 7.77 (s, 1H), 7.66 (s, 1H), 4.35–4.39 (t, 2H), 4.15 (s,
H), 1.98–1.86 (m, 2H), 1.45–1.32 (m, 2H), 0.95–0.98 (t, 3H).
(
3
2
6
-
25
2
[
BuPy]Br. The synthesis of [BuPy]Br was similar to that of
2
1
[C MIM]Br. H NMR (CDCl ): δ (ppm) 9.26 (t, 2H), 8.37–8.34 (t,
4
3
Co(bac)
2
. Cobalt(II) acetate tetrahydrate (1.49 g, 6 mmol) in
1
1
H), 7.95–7.93 (d, 2H), 4.73–4.67 (m, 2H), 1.78–1.73 (m, 2H),
.12–1.09 (m, 2H), 0.68–0.62 (m, 3H).
6
1
mL of water was added into benzoylacetone (1.62 g,
0 mmol) in 6 mL of ethanol. 3 mol L aqueous ammonia
−
1
was added dropwise until the solution was slightly basic. A
large amount of yellow-brown product precipitated immedi-
The coupling reaction of CO with epoxide
2
ately. Then the reaction mixture was stirred for 2 hours at A typical procedure for the reaction of CO with epoxide was
2
5
0 °C. The product was filtered off, washed alternately with carried out in a 25 mL Schlenk tube with a magnetic stir bar.
water and ethanol, and then dried under vacuum overnight to For a typical run, the epoxide (40 mmol) and the catalyst
yield 1.30 g (68%) of pinkish brown powder. (appropriate amount) were introduced into the tube and the
tube was vacuum-sealed and then purged with CO 3 times.
The tube which was connected to a balloon filled with CO was
then placed in a preheated water bath and allowed to stir (at
O: C, 60.16; H, 5.05; Co, 400 rpm) for a designated time frame. The product yields and
4.76. Found: C, 60.85; H, 4.67; Co, 14.21. The ratio of C/Co selectivity were determined by GC analysis. Some typical pro-
ducts were analyzed by GC/MS.
−
1
IR (KBr): ν/cm 1592, 1559, 1515, 1486, 1453 and 1405.
2
+
+
MS (ESI ): m/z 382.0661 (calcd for [Co(C10
H
9
O
2
)
2
+ H]
2
3
1
82.0615).
9 2 2 2
Anal. calcd for Co(C10H O ) ·H
calcd for Co(C H O ) ·nH O: 4.08. Found: 4.28.
1
0
9
2 2
2
15974 | Dalton Trans., 2019, 48, 15970–15976
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Paper
The reaction of CO
out in a 25 mL stainless steel autoclave. The operating pressure
was maintained at 0.2 MPa during the reaction.
2
with 1,2-propylene oxide was carried
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Co(acac)
into the flask. The flask was vacuum-sealed and then purged
with the dilute CO stream (a gas mixture containing 10% v/v
CO and 90% v/v N ) 3 times. Then the dilute CO stream was
bubbled through the reaction solution and the flask was
placed in a preheated water bath and allowed to stir (at 400
2
(0.1 mmol), and Bu
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NI (0.5 mmol) were introduced
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2
2
2
2
rpm) for 4 h. The flow of the dilute CO stream was 10 sccm.
6
7
8
(a) B. Aguila, Q. Sun, X. Wang, E. O’Rourke, A. M. Al-Enizi,
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Conflicts of interest
10107; (b) X. Y. Li, Y. Z. Li, Y. Yang, L. Hou, Y. Y. Wang and
There are no conflicts to declare.
Z. Zhu, Chem. Commun., 2017, 53, 12970; (c) H. He,
J. A. Perman, G. Zhu and S. Ma, Small, 2016, 12, 6309;
(
d) B. Parmar, P. Patel, R. S. Pillai, R. K. Tak, R. I. Kureshy,
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(a) H. H. Wang, L. Hou, Y. Z. Li, C. Y. Jiang, Y. Y. Wang and
Z. Zhu, ACS Appl. Mater. Interfaces, 2017, 9, 17969;
This work was supported by the Program for Public
Technology of Zhejiang Province (LGF18B060003) and the
Program for Science and Technology of Zhejiang Province
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15976 | Dalton Trans., 2019, 48, 15970–15976
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