Chiral metal-containing ionic liquid: Synthesis and applications in the enantioselective cycloaddition of carbon dioxide to epoxides

Article abstract of DOI:10.1007/s11426-011-4274-2

A series of novel chiral metal-containing ionic liquids (CMILs) consisting of the cation of crown ether-chelated potassium/sodium and the anion of chiral amino acids were designed and synthesized. These new CMILs were used to catalyze the enantioselective cycloaddition of epoxides and carbon dioxide incorporating with the salenCo(OOCCCl₃) to generate corresponding chiral cyclic carbonates under mild conditions. These new catalysts can be recycled at least five times without significant loss of activity and enantioselectivity.

Full text of DOI:10.1007/s11426-011-4274-2

SCIENCE CHINA
Chemistry
July 2011 Vol.54 No.7: 1044–1050
doi: 10.1007/s11426-011-4274-2
• ARTICLES •
Chiral metal-containing ionic liquid: Synthesis and applications in
the enantioselective cycloaddition of carbon dioxide to epoxides
SONG YingYing, JIN QianRu, ZHANG SuLing,
JING HuanWang* & ZHU QianQian
State Key Laboratory of Applied Organic Chemistry; College of Chemistry and Chemical Engineering, Lanzhou University,
Lanzhou 730000, China
Received January 11, 2011; accepted January 22, 2011
A series of novel chiral metal-containing ionic liquids (CMILs) consisting of the cation of crown ether-chelated potassium/
sodium and the anion of chiral amino acids were designed and synthesized. These new CMILs were used to catalyze the enan-
tioselective cycloaddition of epoxides and carbon dioxide incorporating with the salenCo(OOCCCl3) to generate corresponding
chiral cyclic carbonates under mild conditions. These new catalysts can be recycled at least five times without significant loss
of activity and enantioselectivity.
chiral metal-containing ionic liquids, epoxides, carbon dioxide, enantioselective cycloaddition, chiral cyclic carbonates
novel chiral salts consisting of natural amino acid anions
1 Introduction
and crown ether-chelated alkali metal cations. Because the
metal-containing ionic liquids (MILs) are different from the
classical ionic liquids, we defined MILs as the type of salts
with melting points lower than 200 °C. As continuation of
our efforts for the synthesis of chiral cyclic carbonates, we
report, herein, a new efficient catalyst system of (salen)
Co(OOCCCl3) and chiral metal-containing ionic liquid
(CMIL) for the enantioselective cycloaddition reaction of
CO2 to terminal epoxides (Scheme 1).
Ionic liquids have attracted increasing interests in both
academy and industry in view of their particular properties
such as excellent thermal and chemical stability, lower va-
por pressure and good tunable solubility [1–10]. Their ap-
plications have significantly increased in the last decade
exemplifying in material synthesis, separation sciences, and
reaction media, etc. [5]. Especially, they can be used as cata-
lysts in organic synthesis [11–16]. Even though some ionic
liquids have been used as catalysts in the coupling of CO2
and epoxides [17–21], chiral ionic liquids (CIL) used in
enantioselective cycloaddition reactions was only reported
once by our group [22]. Due to the fact that few literatures
reported enantiomerically pure cyclic carbonates [22–31],
new methodologies for the enantioselective cycloaddition of
CO2 to epoxides are still desired in terms of the atom economy
and environmentally benign characteristics of this reaction.
Recently, we have designed and synthesized a series of
*Corresponding author (email: hwjing@lzu.edu.cn)
Scheme 1 Enantioselective cycloaddition of CO2 to terminal epoxides.
© Science China Press and Springer-Verlag Berlin Heidelberg 2011
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Song YY, et al. Sci China Chem July (2011) Vol.54 No.7
1045
48H, 6 ×(CH2CH2O)), 3.88 (dd, 1H, J=4.2, 3.6 Hz, NH2CH)
ppm. 13C NMR (100 MHz, D2O)  36.9, 52.5, 69.9, 174.3,
177.5 ppm. Elemental Anal. calcd (%): C 42.26, H 7.51, N
1.73; found: C 42.34, H 7.24, N 2.03.
2 Experimental
2.1 Materials
Propylene oxide (PO) was distilled from CaH2. Other epox-
ides were purchased from Aldrich and used without further
purification. Enantiomeric excess of the resulting cyclic
carbonates was determined by chiral GC analysis (Supeclo-
DEX series (225) chiral column; injection temperature =
250 °C; detection temperature = 250 °C; 180 °C isothermal)
using a Varian CP-3800 gas chromatograph with N2 as the
carry gas. Elemental analyses were carried out on Carioel
elemental analyzer.
[15-C-5Na]2[L-Asp]·H2O
1H NMR (300 MHz, D2O)  2.60 (dd, 1H, J = 9.0, 9.3 Hz,
COOCH(H)), 2.82 (dd, 1H, J=3.6 Hz, COOCH(H)), 3.73 (s,
40H, 5 × (CH2CH2O)), 3.85 (dd, 1H, J = 3.9 Hz, NH2CH)
ppm. 13C NMR (75 MHz, D2O)  35.3, 51.3 69.5, 173.3,
177.0 ppm. Elemental Anal. calcd (%): C 45.35, H 7.45, N
2.20; found: C 45.24, H 7.18, N 2.03.
[18-C-6K][L-Val]·0.5H2O
1H NMR (300 MHz, D2O)  0.82 (d, 3H, J = 8.4 Hz, CH3),
0.92 (d, 3H, J = 6.9 Hz, CH3), 1.94 (m, 1H, CH(CH3)2), 3.09
(d, 1H, J = 5.1 Hz, NH2CH), 3.65 (s, 24H, 6 × (CH2CH2O))
ppm. 13C NMR (100 MHz, D2O)  17.1, 19.2, 31.6, 61.9,
70.0, 182.1 ppm. Elemental Anal. calcd (%): C 47.64, H
8.23, N 3.27; found: C 47.49, H 7.93, N 3.25.
2.2 Preparation of chiral metal-containing ionic liquids
The preparation of CMILs is a simple reaction. [18-C-6K]
[L-Thr] was chosen as model to illustrate the preparation
procedure. The synthesis of [18-C-6K][L-Thr] was carried
out by mixing the 1.1:1:1 molar ratio of L-Threonine, KOH
and 18-C-6 in water. The reaction mixture was stirred at
room temperature for 24 h and then concentrated under re-
duced pressure to afford a mixture of ionic liquid and su-
perabundant L-threonine. The mixture was then dispensed
into ethanol to precipitate out the unreacted L-threonine. The
filtrate was concentrated and dried under vacuum at 80 °C
to obtain the desired chiral MIL [18-C-6K][L-Thr] as a
white solid. All remaining CMILs were performed employing
a procedure analogous to that used to synthesize [18-C-6K]
[L-Thr].
[15-C-5Na][L-Val]·0.8H2O
1H NMR (300 MHz, D2O)  0.89 (m, 3H, CH3), 0.97 (m,
3H, CH3), 1.96 (m, 1H, CH(CH3)2), 3.10 (d, 1H, J =8.1 Hz,
NH2CH), 3.75 (s, 20H, 5 × (CH2CH2O)) ppm. 13C NMR (75
MHz, D2O)  16.8, 19.0, 31.3, 61.6, 69.1, 181.4 ppm.
Elemental Anal. calcd (%): C 48.20, H 8.52, N 3.75; found:
C 47.95, H 8.43, N 3.61.
[18-C-6K]2[L-Cys]·4H2O
1H NMR (300 MHz, D2O)  2.94 (dd, 1H, J = 7.8, 7.5 Hz,
SCH(H)), 3.17 (dd, 1H, J = 4.8 Hz, SCH(H)), 3.62 (dd, 1H,
J = 4.5 Hz, NHCH), 3.72 (s, 24H, 6 ×(CH2CH2O)) ppm. 13C
NMR (100 MHz, D2O)  43.6, 55.0, 69.9, 180.6 ppm.
Elemental Anal. calcd (%): C 39.29, H 7.25, N 3.05; found:
C 39.39, H 7.43, N 3.28.
Characterization of CMILs
[18-C-6K][L-amino acid anion] HRMS (ESI): m/z: calcd for
[18-C-6K] 303.1204; found: 303.1209. [15-C-5Na][L-amino
acid anion] HRMS (ESI): m/z: calcd for [15-C-5Na]
243.1203; found: 243.1200.
[18-C-6K][L-Thr]·2.5H2O
1H NMR (300 MHz, D2O)  1.25 (d, 3H, J = 6.6 Hz, CH3),
3.17 (d, 1H, J = 6.0 Hz, NH2CH), 3.72 (s, 24H, 6 × (CH2-
CH2O)), 4.00 (m, 1H, CHOH) ppm. 13C NMR (100 MHz,
D2O)  19.3, 61.9, 69.4, 69.9, 180.1 ppm. Elemental Anal.
calcd (%): C 41.19, H 7.99, N 3.00; found: C 41.19, H 7.57,
N 2.99.
[15-C-5Na]2[L-Cys]·2.5H2O
1H NMR (300 MHz, D2O)  2.93 (dd, 1H, J = 7.5, 7.8 Hz,
SCH(H)), 3.15 (dd, 1H, J = 4.5, 4.2 Hz, SCH(H)), 3.62 (dd,
1H, J = 4.8, 4.5 Hz, NHCH), 3.73 (s, 20H, 6 × (CH2CH2O))
ppm. 13C NMR (75 MHz, D2O)  42.1, 54.6, 69.2, 178.9
ppm. Elemental Anal. calcd (%): C 36.49, H 6.70, N 5.32;
found: C 36.55, H 6.81, N 5.42.
[15-C-5Na][L-Thr]
1H NMR (300 MHz, D2O)  1.17 (d, 3H, J = 6.3 Hz, CH3),
3.08 (d, 1H, J = 5.1 Hz, NH2CH), 3.64 (s, 20H, 5 × (CH2-
CH2O)), 3.92 (m, 1H, CHOH) ppm. 13C NMR (75 MHz,
D2O)  19.4, 61.8, 69.0, 179.4 ppm. Elemental Anal. calcd
(%): C 46.53, H 7.81, N 3.88; found: C 46.65, H 7.94, N 3.80.
[18-C-6K][L-Ala]·H2O
1H NMR (300 MHz, D2O)  1.25 (d, 3H, J = 6.9 Hz, CH3),
3.62 (m, 1H, CH), 3.67 (s, 24H, 6 × (CH2CH2O)) ppm. 13C
NMR (100 MHz, D2O)  17.1, 51.6, 70.0, 183.7 ppm.
Elemental Anal. calcd (%): C 43.99, H 7.88, N 3.42; found:
43.99, H 7.51, N 3.22.
[18-C-6K]2[L-Asp]·4H2O
1H NMR (300 MHz, D2O)  2.65 (dd, 1H, J = 8.7 Hz,
COOCH(H)), 2.83 (dd, 1H, J=3.3 Hz, COOCH(H)), 3.68 (s,
[15-C-5Na][L-Ala]
1H NMR (300 MHz, D2O)  1.27 (d, 3H, J = 6.9 Hz, CH3),

1046
Song YY, et al. Sci China Chem July (2011) Vol.54 No.7
3.37 (dd, 1H, J = 7.2, 5.7 Hz, CH), 3.72 (s, 20H, 5 × (CH2-
CH2O)) ppm. 13C NMR (75 MHz, D2O)  16.7, 50.6, 69.3,
176.8 ppm. Elemental Anal. calcd (%): C 47.12, H 7.91, N
4.23; found: C 47.09, H 7.79, N 4.33.
[18-C-6K][L-Trp]
1H NMR (300 MHz, D2O)  3.01 (dd, 1H, J = 7.8, 7.5 Hz,
CH(NH2)CH(H)), 3.23 (dd, 1H, J = 4.8 Hz, CH(NH2)CH
(H)), 3.56 (s, 24H, 6 × (CH2CH2O)), 3.64 (1H, NH2CH),
7.59 (m, 3H, ArH, -H), 7.45 (d, 1H, J =8.1 Hz, ArH), 7.68
(d, 1H, J = 9.0 Hz, ArH) ppm. 13C NMR (100 MHz, D2O) 
29.6, 56.3, 69.7, 110.0, 111.8, 118.8, 119.2, 121.8, 124.4,
127.3, 136.3, 180.8 ppm. Elemental Anal. calcd (%): C
54.53, H 6.96, N 5.53; found: C 54.49, H 6.74, N 5.57.
[18-C-6K][L-Lys]·0.6H2O
1H NMR (300 MHz, D2O)  1.40 (m, 2H, CH(NH2)CH2-
CH2), 1.64 (m, 4H, CH(NH2)CH2CH2CH2), 2.89 (t, 2H, J=
7.2, 7.5 Hz, CH2-NH2), 3.30 (t, 1H, J = 6.9 Hz, NH2CH),
3.71 (s, 24H, 6 × (CH2CH2O)) ppm. 13C NMR (100 MHz,
D2O)  22.2, 28.6, 33.9, 39.78, 55.8, 69.9, 182.8 ppm.
Elemental Anal. calcd (%): C 47.06, H 8.38, N 6.10; found:
C 46.98, H 8.35, N 6.17.
[15-C-5Na][L-Trp]
1H NMR (300 MHz, D2O)  3.07 (dd, 1H, J = 7.5 Hz,
CH(NH2)CH(H)), 3.25 (dd, 1H, J = 4.8 Hz, CH(NH2)-
CH(H)), 3.69 (s, 20H, 5 × (CH2CH2O)), 3.71 (1H, NH2CH),
7.21 (m, 3H, ArH, -H), 7.51 (d, 1H, J =8.4 Hz, ArH), 7.73
(d, 1H, J = 8.1 Hz, ArH) ppm. 13C NMR (100 MHz, D2O) 
29.6, 56.2, 69.4, 110.0, 111.8, 118.7, 119.2, 121.9, 124.4,
127.3, 136.3, 180.8 ppm. Elemental Anal. calcd (%): C
56.49, H 7.00, N 6.27; found: C 56.12, H 6.87, N 6.43.
[15-C-5Na][L-Lys]·0.5H2O
1H NMR (300 MHz, D2O)  1.39 (m, 2H, CH(NH2)CH2-
CH2), 1.62 (m, 4H, CH(NH2)CH2CH2CH2), 2.88 (t, 2H, J=
6.9, 7.2 Hz, NH2CH2), 3.30 (t, 1H, J = 6.3 Hz, NH2CH),
3.72 (s, 20H, 5 ×(CH2CH2O) ppm. 13C NMR (75 MHz, D2O)
 22.0, 27.3, 33.07, 39.4, 55.5, 69.4, 181.3 ppm. Elemental
Anal. calcd (%): C 48.35, H 8.62, N 7.05; found: C 48.07, H
8.77, N 6.89.
[18-C-6K][L-Leu]·1.5H2O
1H NMR (300 MHz, D2O)  0.92 (m, 6H, CH(CH3)CH3),
1.46 (m, 2H, CH(NH2)CH2), 1.68 (m, 1H, CH(CH3)CH3),
3.29 (dd, 1H, J = 6.0, 5.7 Hz, NH2CH), 3.71 (s, 24H, 6 ×
(CH2CH2O)) ppm. 13C NMR (100 MHz, D2O)  21.6, 22.7,
24.6, 44.1, 54.7, 69.9, 183.8 ppm. Elemental Anal. calcd
(%): C 46.94, H 8.53, N 3.04; found: C 46.94, H 8.41, N
2.66.
[18-C-6K]2[L-Glu]·0.5H2O
1H NMR (300 MHz, D2O)  2.05 (m, 2H, CH(NH2)CH2),
2.33 (t, 2H, J = 7.5 Hz, COO-CH2), 3.67 (m, 1H, NH2CH),
3.74 (s, 48H, 6 × (CH2CH2O)) ppm. 13C NMR (100 MHz,
D2O)  27.2, 33.6, 54.8, 69.8, 174.7, 181.2 ppm. Elemental
Anal. calcd (%): C 45.77, H 7.42, N 1.84; found: C 45.94, H
7.44, N 2.00.
[15-C-5Na][L-Leu]·1.2H2O
1H NMR (300 MHz, D2O)  0.95 (m, 6H, CH(CH3)CH3),
1.45 (m, 2H, CH(NH2)CH2), 1.69 (m, 1H, CH(CH3)CH3),
3.32 (dd, 1H, J = 5.7, 6.0 Hz, NH2CH), 3.74 (s, 20H, 5 ×
(CH2CH2O)) ppm. 13C NMR (100 MHz, D2O)  21.4, 22.5,
24.5, 43.8, 54.5, 69.1, 183.5 ppm. Elemental Anal. calcd
(%): C 48.65, H 8.78, N 3.55; found: C 48.47, H 8.56, N
3.40.
[15-C-5Na]2[L-Glu]·0.5H2O
1H NMR (300 MHz, D2O)  2.08 (m, 2H, CH(NH2)CH2),
2.33 (t, 2H, J = 7.5, 7.2 Hz, COOCH2), 3.62 (m, 1H,
NH2CH), 3.70 (s, 40H, 5 × (CH2CH2O)) ppm. 13C NMR (75
MHz, D2O)  27.4, 33.6, 54.8, 69.0, 175.3, 181.5 ppm.
Elemental Anal. calcd (%): C 46.87, H 7.55, N 2.19; found:
C 46.76, H 7.47, N 2.39.
[18-C-6K][L-Phe]·0.8H2O
1H NMR (300 MHz, D2O)  2.90 (dd, 1H, J = 7.2, 7.5 Hz,
CH(NH2)CH(H)), 3.07 (dd, 1H, J = 5.1, 5.4 Hz, CH(NH2)-
CH(H)), 3.58 (t, 1H, J = 5.7, 5.4 Hz, NH2CH), 3.69 (s, 24H,
6 × (CH2CH2O)), 7.36 (m, 5H, ArH) ppm. 13C NMR (100
MHz, D2O)  40.5, 57.5, 69.9, 126.9, 128.8, 129.6, 138.2,
181.4 ppm. Elemental Anal. calcd (%): C 52.33, H 7.44, N
2.91; found: C 52.12, H 7.21, N 3.05.
[18-C-6K][L-Met]·1.8H2O
1H NMR (300 MHz, D2O)  1.89 (m, 2H, CH(NH2)CH2),
2.14 (s, 3H, CH3), 2.58 (t, 2H, J = 7.5, 8.1 Hz, SCH2), 3.36
(dd, 1H, J = 6.0, 5.1 Hz, NH2CH), 3.70 (s, 24H, 6 × (CH2-
CH2O)) ppm. 13C NMR (100 MHz, D2O)  14.2, 29.8, 33.9,
55.3, 69.8, 182.1 ppm. Elemental Anal. calcd (%): C 42.18,
H 7.83, N 2.89; found: C 42.20, H 7.64, N 2.74.
[15-C-5Na][L-Met]·H2O
[15-C-5Na][L-Phe]·H2O
1H NMR (300 MHz, D2O)  1.89 (m, 2H, CH(NH2)CH2),
2.14 (s, 3H, CH3), 2.86 (t, 2H, J = 7.5, 8.1 Hz, SCH2), 3.37
(dd, 1H, J = 5.7, 5.4 Hz, NH2CH), 3.72 (s, 20H, 5 ×
(CH2CH2O)) ppm. 13C NMR (75 MHz, D2O)  14.1, 29.6,
33.2, 55.0, 69.2, 181.2 ppm. Elemental Anal. calcd (%): C
44.00, H 7.88, N 3.42; found: C 43.69, H 7.67, N 3.65.
1H NMR (300 MHz, D2O)  2.84 (dd, 1H, J = 7.2 Hz,
CH(NH2)CH(H)), 2.98 (dd, 1H, CH(NH2)CH(H)), 3.52 (t,
1H, J = 5.7, 6.6 Hz, NH2CH), 3.66 (s, 20H, 5 ×(CH2CH2O)),
7.28 (m, 5H, ArH) ppm. 13C NMR (100 MHz, D2O)  40.0,
57.3, 69.2, 126.9, 128.9, 129.5, 138.1, 181.1 ppm. Elemental
Anal. calcd (%): C 53.64, H 7.58, N 3.29; found: C 53.99, H

Song YY, et al. Sci China Chem July (2011) Vol.54 No.7
1047
7.29, N 3.58.
autoclave equipped with a magnetic stir bar and pressurized
with CO2 to 0.6 MPa. The autoclave was charged with pro-
pylene oxide (100 mmol), salenCo(OOCCCl3) catalyst (0.1
mmol) and CMIL (0.1 mmol). After a proper reaction time,
CO2 was released to terminate the reaction. The remaining
mixture was fractionally distilled under reduced pressure or
recrystallized in ethanol to obtain a pure chiral cyclic car-
bonate.
[18-C-6K][L-His]
1H NMR (300 MHz, D2O)  2.79 (dd, 1H, J = 8.4 Hz,
CH(NH2)CH(H)), 2.94 (dd, 1H, J = 5.1, 5.4 Hz, CH(NH2)-
CH(H)), 3.48 (dd, 1H, J = 5.1, 5.4 Hz Hz, NH2CH), 3.64 (s,
24H, 6 × (CH2CH2O)), 6.89 (s, 1H, 5-H), 7.64 (s, 1H, 2-H)
ppm. 13C NMR (100 MHz, D2O)  31.9, 56.1, 69.8, 118.1,
133.4, 135.9, 181.7 ppm. Elemental Anal. calcd (%): C
47.25, H 7.05, N 9.18; found: C 47.10, H 7.20, N 9.40.
3 Results and discussion
[15-C-5Na][L-His]
3.1 Properties of chiral metal-containing ionic liquids
1H NMR (300 MHz, D2O)  2.90 (dd, 1H, J = 7.5, 7.8 Hz,
CH(NH2)CH(H)), 3.04 (dd, 1H, J = 5.4 Hz, CH(NH2)-
CH(H)), 3.60 (dd, 1H, J = 5.1, 5.4 Hz, NH2CH), 3.75 (s,
20H, 5 × (CH2CH2O)), 6.98 (s, 1H, 5-H), 7.72 (s, 1H, 2-H)
ppm. 13C NMR (100 MHz, D2O)  31.0, 55.8, 69.1, 117.7,
133.2, 136.0, 179.9 ppm. Elemental Anal. calcd (%): C
46.26, H 7.28, N 10.12; found: C 46.39, H 7.57, N 10.25.
The obtained CMILs have high purity and give sharp melt-
ing points (Table 1). They have demonstrated good thermal
stabilities as measured by TG-DTA. Their colors range
from white to orange. Two of them are ILs at room tem-
perature (entries 4, 25). The rest are solids, in which
Table 1 The properties of chiral metal-containing ionic liquids (CMILs)
[18-C-6K][L-Ser]
[a]D20 d)
Entry
Ionic liquid a)
Color mp b) °C Td c) °C
1H NMR (300 MHz, D2O)  3.46 (t, 1H, J=4.8 Hz NH2CH),
3.69 (s, 24H, 6 × (CH2CH2O)), 3.77 (m, 2H, CH2OH) ppm.
13C NMR (100 MHz, D2O)  57.2, 62.9, 69.9, 177.1 ppm.
Elemental Anal. calcd (%): C 44.21, H 7.42, N 3.44; found:
C 44.61, H 7.26, N 3.57.
1
2
3
4
5
6
7
8
9
[18-C-6K][L-Thr]·2.5H2O
[15-C-5Na][L-Thr]
white
white
138
125
100
-48
130
133
127
152
85
174
172
173
138
188
142
160
152
189
157
183
162
192
183
189
148
194
172
197
222
182
154
179
157
194
143
196
177
5°
5°
4°
1°
+4°
+3°
43°
44°
1°
+1°
+3°
+2°
+1°
+1°
15°
14°
5°
5°
3°
4°
37°
36°
6°
7°
1°
2°
1°
2°
[18-C-6K]2[L-Asp]·4H2O
[15-C-5Na]2[L-Asp]·H2O
[18-C-6K][L-Val]·0.5H2O
[15-C-5Na][L-Val]·0.8H2O
[18-C-6K]2[L-Cys]·4H2O
orange
yellow
yellow
white
[15-C-5Na][L-Ser]
1H NMR (300 MHz, D2O)  3.45 (t, 1H, J = 4.5, 5.4 Hz,
NH2CH), 3.64 (m, 1H, CH(H)OH), 3.70 (s, 20H, 5 × (CH2-
CH2O)), 3.76 (m, 1H, CH(H)OH) ppm. 13C NMR (100
MHz, D2O)  56.6, 60.2, 69.2, 173.4 ppm. Elemental Anal.
calcd (%): C 43.82, H 7.64, N 3.93; found: C 43.70, H 7.32,
N 3.77.
orange
[15-C-5Na]2[L-Cys]·2.5H2O orange
[18-C-6K]2[L-Glu]·0.5H2O yellow
10 [15-C-5Na]2[L-Glu]·0.5H2O yellow
157
76
11 [18-C-6K][L-Lys]·0.6H2O
12 [15-C-5Na][L-Lys]·0.5H2O
13 [18-C-6K][L-Leu]·1.5H2O
14 [15-C-5Na][L-Leu]·1.2H2O
15 [18-C-6K][L-Trp]
orange
orange
yellow
white
56
94
[18-C-6K][L-Pro]
150
95
1H NMR (300 MHz, D2O)  1.89 (m, 3H, 3-H, 4-H), 2.22
(m, 1H, 3-H), 3.05 (m, 1H, 5-H), 3.23 (m, 1H, 5-H), 3.68 (s,
24H, 6 × (CH2CH2O)), 3.81 (m, 1H, 2-H) ppm. 13C NMR
(100 MHz, D2O)  24.5, 29.9, 46.1, 61.4, 69.5, 178.4 ppm.
Elemental Anal. calcd (%): C 48.90, H 7.72, N 3.35; found:
C 48.97, H 7.79, N 3.63.
brown
brown
yellow
yellow
yellow
yellow
yelow
yellow
orange
orange
yellow
orange
yellow
yellow
16 [15-C-5Na][L-Trp]
115
66
17 [18-C-6K][L-His]
18 [15-C-5Na][L-His]
113
55
19 [18-C-6K][L-Ser]
20 [15-C-5Na][L-Ser]
80
21 [18-C-6K][L-Pro]
95
[15-C-5Na][L-Pro]·H2O
22 [15-C-5Na][L-Pro]·H2O
23 [18-C-6K][L-Phe]·0.8H2O
24 [15-C-5Na][L-Phe]·H2O
25 [18-C-6K][L-Met]·1.8H2O
26 [15-C-5Na][L-Met]·H2O
27 [18-C-6K][L-Ala]·H2O
28 [15-C-5Na][L-Ala]
69
1H NMR (300 MHz, D2O)  1.87 (m, 3H, 3-H, 4-H), 2.22
(m, 1H, 3-H), 3.04 ((m, 1H, 5-H), 3.24 (m, 1H, 5-H), 3.70 (s,
20H, 5 × (CH2CH2O)), 3.80 (m, 1H, 2-H) ppm. 13C NMR
(100 MHz, D2O)  24.7, 30.2, 46.1, 61.5, 69.1, 179.7 ppm.
Elemental Anal. calcd (%): C 47.99, H 8.06, N 3.73; found:
C 47.75, H 8.05, N 3.88.
68
37
26
38
130
115
a) The chemical compositions were confirmed by elemental analysis. b)
Melting points were determined on an XT-4 melting point apparatus without
calibration. c) Decomposition temperature (Td) was determined by TG-DTA
heating at 10 °C min1 under nitrogen. d) Solution in H2O and c = 1.0.
2.3 Enantioselective cycloaddition of CO2 to epoxides
All coupling reactions were performed in a 100 mL stainless

1048
Song YY, et al. Sci China Chem July (2011) Vol.54 No.7
Table 2 The effect of [18-C-6K][L-amino acid anion] in the coupling
almost half of them have melting point lower than 100 °C
and the rest have melting points higher than 100 °C but
lower than 160 °C. The CMILs obtained are thermally sta-
ble up to 135 to 225 °C. Their specific rotations were also
determined.
reaction of CO2 and propylene oxide a)
Time Yield PC ee
b)
Entry
1
Co-catalyst
Krel
(h)
5.5
7.0
8.0
(%)
(%)
[18-C-6K][L-Val]·0.5H2O
43.6 53.8(S) 4.9
49.0 48.2(S) 4.4
50.5 46.8(S) 4.3
2 c)
3 d)
4 e)
5
[18-C-6K][L-Val]·0.5H2O
[18-C-6K][L-Val]·0.5H2O
[18-C-6K][L-Val]·0.5H2O
[18-C-6K]2[L-Glu]·0.5H2O
[18-C-6K]2[L-Glu]·0.5H2O
9.5
21
72
6.5
12
14
40.3 48.2(R) 3.9
27.2 64.0(S) 5.7
3.2 The effect of CMIL on the coupling of CO2 and PO
Our initial investigation showed that salenCo(OOCCCl3)
can successfully catalyze the coupling reaction of CO2 and
racemic PO in the presence of the CMILs such as [18-C-6K]
[L-amino acid anion] or [15-C-5Na][L-amino acid anion] to
form the pure chiral propylene carbonate without any by-
products. That is to say the conversion of PO equals to the
yield of propylene carbonate (PC). According to our previ-
ous study [32], the salts that consist of two parts: cation
(Lewis acid, electrophile) and anion (Lewis base, nucleo-
phile), have catalytic activity under a generally harsh condi-
tion. The metal-containing ionic liquid (MIL) is a good
catalyst since its cation can act as a Lewis acid center and
its amino acid anion can acts as a Lewis base center In the
catalyst systems, salenCo(OOCCCl3), which gives the
chiral Lewis acid center and works as the main catalyst, acti-
vates the epoxides, while the chiral anion of CMILs which
supplies the chiral Lewis base center for the coupling reac-
tion and functions as the co-catalyst, attacks the activated
epoxides to produce intermediates for the insertion of CO2
to lead to cyclic carbonates
3.1
5.4(S)
1.1
42.4 51.1(S) 4.4
41.3 48.0(R) 3.9
37.8 50.7(S) 4.1
6 c)
7
8
[18-C-6K][L-His]
[18-C-6K][L-Lys]·0.6H2O
11
12
48.1 46.2(S) 4.1
50.1 45.0(S) 4.4
9
[18-C-6K][L-Trp]
[18-C-6K][L-Ser]
11
32.4 53.4(S) 4.2
10
10
12
46.4 48.1(S) 4.2
52.5 46.1(S) 4.3
11
12
[18-C-6K][L-Thr]·2.5H2O
[18-C-6K][L-Phe]·0.8H2O
14
35.3 54.9(S) 4.6
11
32.5 52.5(S) 4.1
51.0 45.1(S) 4.1
5.5 f)
13
14
[18-C-6K][L-Leu]·1.5H2O
[18-C-6K][L-Ala]·H2O
5.5
35.8 51.1(S) 4.0
11
12
11
12
44.1 49.1(S) 4.2
48.6 47.7(S) 4.3
46.8 49.2(S) 4.4
49.0 47.9(S) 4.3
15
[18-C-6K][L-Pro]
16
[18-C-6K][L-Met]·1.8H2O
13
14
35.9 53.3(S) 4.4
34.5 52.5(S) 4.2
17
18
[18-C-6K]2[L-Cys]·4H2O
[18-C-6K]2[L-Asp]·4H2O
10
12
48.1 51.0(S) 4.8
50.9 48.8(S) 4.7
19
TBAB
1.3
40.8 33.7(S) 2.5
The results revealed that the ee values of chiral PC were
significantly enhanced compared to the ee values produced
by chiral catalyst (R, R)-1 combined with TBAB as the co-
catalyst (Table 2, entries 1, 5, 7–18 vs. 19). According to
Table 2, the most efficient catalytic system was salenCo
(OOCCCl3)/[18-C-6K][L-Val]·0.5H2O, which gave the highest
ee value of (S)-PC (53.8%) (entry 1). When the reaction was
carried out at 0 °C, the ee value of (S)-PC augmented to
64.0% (entry 3). Other catalyst systems of salenCo
(OOCCCl3)/[18-C-6K][L-amino acid anion] were also ef-
fective (Table 2, entries 5, 7–18). When the catalyst system
was switched from (R,R)-1 to (S,S)-1, the enantioselectvity
was decreased (entries 1, 2, 5, 6). The significant synergistic
effects between chiral catalysts and cocatalysts were re-
vealed: the cocatalyst with R,R chirality increased the ee
values of (S)-PC catalyzed by (R,R)-1 and it decreased the
ee values of (R)-PC catalyzed by (S,S)-1, which are consis-
tent with our previous report [22]. Higher yields could be
obtained when the reaction times were increased (entries 1,
8, 10, 14, 15, 18). It is worth noting that when chiral MIL of
[18-C-6K][L-Val]·0.5H2O was used alone as catalyst, the
reaction could also induce the chiral PC with 5.4% ee (entry
4) which is higher than that of 1% ee obtained by chiral IL
[22].
a) Reaction conditions: PO 100 mmol; catalyst: (R,R)-1 0.1 mmol; co-
catalyst 0.1 mmol; CO2: 0.6 MPa, T = 25 °C. b) Krel = ln[1c(1 +ee)/ln[1 
c(1  ee)], where c is the yield and ee% is the enantiomeric excess of the
resulting propylene carbonate. c) Catalyst: (S, S)-1. d) T = 0 °C. e) Catalyst:
[18-C-6K][L-Val]·0.5H2O 1.0 g. f] PO 50 mmol.
of (S)-PC (58.5%) was achieved with [15-C-5Na][L-Pro]·
H2O as the chiral cocatalyst (entry 10). In contrast to [18-C-
6K][L-amino acid anion], the coupling reaction catalyzed by
[15-C-5Na][L-amino acid anion] needs a longer period of
reaction time (Table 3 vs. Table 2). For the enantioselective
cycloaddition of CO2 to PO catalyzed by [18-C-6K]
[L-amino acid anion] or [15-C-5Na][L-amino acid anion],
higher yields and shorter reaction times were presented
when the amount of catalyst and cocatalyst was doubled
(Table 2, entry 12; Table 3, entries 1, 2, 11, 14).
3.3 Cycloaddition of CO2 to epoxides catalyzed by
salenCo(OOCCCl3)/[18-C-6K][L-Val]·0.5H2O
To further extend the reaction scope, various epoxides were
utilized as substrates in this coupling reaction using [18-C-
6K][L-Val]·0.5H2O as a chiral cocatalyst (Table 4). As can
be seen, the catalyst was effective for the cycloaddition of
1,2-epoxybutane to yield the corresponding chiral cyclic
carbonate (CC) with a good enantioselectivity (entry 1).
When the cocatalyst was switched from [18-C-6K]
[L-amino acid anion] to [15-C-5Na][L-amino acid anion],
similar results were obtained (Table 3). The highest ee value

Song YY, et al. Sci China Chem July (2011) Vol.54 No.7
1049
Table 3 The effect of [15-C-5Na][L-amino acid anion] in the coupling
Table 5 Recycling of catalyst salenCo(OOCCCl3)/[18-C-6K][L-Val]·
reaction of CO2 and propylene oxide a)
0.5H2O a)
Time Yield PC ee
Recycle time
Time (h)
5.5
Conv (%)
43.6
PC ee (%)
53.8(S)
54.2(S)
54.0(S)
53.5(S)
53.0(S)
Krel
4.9
4.9
4.8
4.6
4.5
Entry
Co-catalyst
[15-C-5Na][L-His]
Krel
(h)
(%)
(%)
Fresh
72
37.1 49.8(S) 3.9
48.2 41.2(S) 3.4
30.7 55.3(S) 4.4
50.2 46.3(S) 4.2
1
2
28 b)
72
1
2
3
4
5.5
42.3
[15-C-5Na][L-Val]·0.8H2O
24 b)
5.5
41.2
3
[15-C-5Na][L-Lys]·0.5H2O
[15-C-5Na][L-Trp]
80
86
100
72
67
85
91
72
35.3 50.0(S) 3.9
32.8 51.7(S) 4.0
34.2 52.7(S) 4.2
37.0 50.4(S) 4.8
33.4 50.9(S) 3.9
33.4 54.9(S) 4.5
35.3 53.1(S) 4.3
29.4 58.5(S) 4.8
5.5
40.0
4
5.5
39.1
5
[15-C-5Na][L-Ser]
a) Reaction conditions: PO 100 mmol; catalyst: (R,R)-1, 0.1 mmol;
[18-C-6K][L-Val]·0.5H2O 0.1 mmol; CO2: 0.6 MPa, T = 25 °C
6
[15-C-5Na][L-Thr]
7
[15-C-5Na][L-Phe]·H2O
[15-C-5Na][L-Leu]·1.2H2O
[15-C-5Na][L-Ala]
8
4 Conclusions
9
10
[15-C-5Na][L-Pro]·H2O
In summary, we have firstly designed and synthesized a
series of novel chiral metal-containing ionic liquids (CMILs)
that were used as chiral cocatalysts in the enantioselective
cycloaddition of CO2 to epoxides catalyzed by salenCo
(OOCCCl3). The new catalyst systems of salenCo(OOCCCl3)/
CMIL exhibit high activity under mild reaction conditions
and demonstrate the synergistic effect between the chiral
catalyst and cocatalyst.
62
41.3 44.5(S) 3.5
48.9 41.6(S) 3.4
11
[15-C-5Na][L-Met]·H2O
22 b)
12
13
[15-C-5Na]2[L-Glu]·0.5H2O
[15-C-5Na]2[L-Cys]·2.5H2O
88
95
35.9 53.2(S) 4.3
35.3 50.5(S) 3.9
46
36.6 49.5(S) 3.9
49.9 43.1(S) 3.7
14
[15-C-5Na]2[L-Asp]·H2O
19 b)
a) Reaction conditions: PO 100 mmol; catalyst: (R,R)-1, 0.1 mmol;
cocatalyst 0.1 mmol; CO2: 0.6 MPa, T = 25 °C. b) PO 50 mmol.
Table 4 Coupling of CO2 and various epoxides catalyzed by salenCo-
(OOCCCl3)/[18-C-6K][L-Val]·0.5H2O a)
This work was financially supported by the National Natural Science
Foundation of China (20973086).
Entry
Epoxide
1,2-epoxybutane
Time (h) Yield (%) CC ee (%)
1
2
3
4
21
31
28
48
35.1
21.8
38.5 b)
13.5 b)
50.8(S)
4.0(R)
3(S)
1
2
3
4
5
6
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The recycle of salenCo(OOCCCl3)/[18-C-6K]
[L-Val]·0.5H2O
Futhermore, the recycle and reuse of the catalysts were also
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(OOCCCl3)/[18-C-6K][L-Val]·0.5H2O was chosen as the
model catalyst and the results are listed in Table 5. The
recovery of catalysts was straightforward: the product of
PC was completely distilled under vacuum and the residue
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