W.-L. Wong et al. / Applied Catalysis A: General 472 (2014) 160–166
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N,N-diisopropylethylamine (8.0 mL) was heated to 130 ◦C for
10 h. The reaction mixture was then allowed to cool down to
room temperature, followed by the addition of 20 mL acetone.
The organic solvent was decanted to obtain an oily mixture. The
mixture was then washed with chloroform for several times to
remove unreacted starting materials. A pale yellow hygroscopic
solid of ionic liquid, 1·(Br)3, was obtained with 90% yield (6.2 g)
after dried under vacuum. 1H NMR (400 MHz D2O): ı 2.25 (s, 8H),
2.40-2.62 (m, 4H), 3.09 (s, 6H), 3.43-3.80 (m, 12H), 4.58 (t, 4H,
J = 8 Hz), 7.02 (t, 2H, J = 8 Hz), 7.46 (d, 2H, J= 8 Hz), 7.911 (t, 2H,
J = 8 Hz), 8.14 (d, 2H, J = 8 Hz); 13C NMR (400 MHz, D2O): ı 21.25,
23.42, 48.13, 50.53, 61.03, 64.64, 114.48, 116.49, 140.98, 143.22,
156.31; ESI-MS m/z: [M -3Br−]3+ = 141.5, [M -2Br−]2+ = 251.6,
252.6; Elemental analysis: Calcd. for C26H42N5Br3·H2O: C, 47.00;
H, 6.37; N, 10.54. Found: C, 47.05; H, 6.40; N, 10.56.
Scheme 1. Transformation of epoxides into cyclic carbonates with the addition of
CO2.
CO2 addition to aliphatic epoxides. This ionic liquid system over-
comes the shortcomings of using 1·(Br)3 alone in catalyzing the
non-polar substrates under mild conditions. We also present the
results of mechanistic study and density functional theory (DFT)
calculations which help to understand the reaction mechanism and
high reactivity of the catalyst.
2. Experimental
2.1. Chemicals and instruments
2.5. Preparation of ionic liquid 2·(Br)3
mixed solution of 2,2ꢀ-dipyridylamine (10.3 mmol,
Chemicals and solvents used are of analytical reagent grade and
used without further purification. Epoxides were purchased from
Aldrich or Acros Organic and used as received unless otherwise
noted. Hewlett–Packard 8900 equipped with an EC-1 or EC-WAX
A
1.8 g) in dichloromethane (4.0 mL), 1-(6-bromohexyl)-1-
methylpyrrolidinium bromide salt (22 mmol, 7.4 g), and
N,N-diisopropylethylamine (4.0 mL) was heated to 130 ◦C for
10 h. The reaction mixture was then allowed to cool down to
room temperature. After 20 mL of THF was added, the organic
solvent was decanted to obtain an oily mixture. The mixture
was then washed with acetonitrile for several times to remove
unreacted starting materials. A pale yellow hygroscopic solid of
ionic liquid, 2·(Br)3, was obtained with 80% yield (6.2 g) after dried
under vacuum. 1H NMR (400 MHz D2O): ı 1.39–1.53 (m, 8H),
1.74–1.85 (m, 4H), 1.85–1.94 (m, 4H), 2.15–2.30 (m, 8H), 3.01 (s,
6H), 3.41–3.59 (m, 12H), 4.34–4.38 (t, 4H, J = 7 Hz), 6.88-6.92 (t, 2H,
J = 7 Hz), 7.30 (d, 2H, J = 9 Hz), 7.78–7.83 (t, 2H, J = 7 Hz), 8.02 (d, 2H,
J = 9 Hz); 13C NMR (400 MHz, D2O): ı 21.21, 22.93, 25.10, 25.29,
28.22, 48.02, 53.35, 63.96, 64.20, 113.53, 115.91, 140.98, 142.19,
155.94; ESI-MS m/z: [M -3Br−]3+ = 169, [M -2Br−]2+ = 293.5, 294.5;
Elemental analysis: Calcd. for C32H54N5Br3·H2O: C, 50.14; H, 7.36;
N, 9.14. Found: C, 50.22; H, 7.41; N, 9.19.
column (Alltech Associates, Inc.) was used for GC–MS analysis. 1
H
and 13C NMR spectra were collected with Bruker DPX-400 MHz
spectrometer. ESI-MS analysis was carried out by using a VG Micro-
mass7070FMassSpectrometer. TheX-raycrystalstructureanaylsis
was performed on Bruker CCD area detector diffractometer using
MoKa radiation from a generator operating at 50 kV with 30 mA
condition. The intensity data were collected and corrected for SAD-
ABS (Sheldrick, 1996) program. The structure was solved by direct
methods, expended by difference Fourier syntheses, and refined by
full matrix least squares on F2 using the Bruker Smart and Bruker
SHELXT1 program packages. All non-hydrogen atoms were refined
anisotropically. The catalytic reactions were carried out in a 45 mL
autoclave reactor.
bromide salt
2.6. Preparation of ionic liquid 3·(Ntf)2
The intermediate was prepared according to the reported
method [72] and obtained in quantitative yields. 1H NMR (400 MHz
D2O): ı 2.14–2.25 (m, 4H), 2.30–2.41 (m, 2H), 3.08 (s, 3H), 3.51–3.62
(m, 8H). ESI-MS m/z: [M+] = 206, 208.
To 100 mL THF were added 1-methylpyrrolidine (135 mmol,
15 mL) and 1,6-dibromohexane (54 mmol, 13.2 g). The solution was
heated to reflux for 24 h. After the reaction, 50 mL of diethyl ether
was added to the solution and the resulting white precipitates were
collected by filtration. After washing with diethyl ether and drying
under vacuum, the product of bromide salt, 3·(Br)2, was isolated
with 98% yield (22.4 g) as a white hygroscopic powder. The com-
pound of 3·(Ntf)2 was obtained quantitatively via ion-exchange
with lithium bis(trifluromethane)sulfonimide salt (LiNtf) in water.
Characterization for 3·(Br)2: 1H NMR (400 MHz D2O): ı 1.43–1.57
(m, 4H), 1.84–1.98 (m, 4H), 2.25 (s, 8H), 3.09 (s, 6H), 3.34–3.47 (m,
4H), 3.48–3.66 (m, 8H); ESI-MS m/z: [M2+] = 127, [M -Br−]+ = 333,
335.
2.3. Preparation of 1-(6-bromohexyl)-1-methylpyrrolidinium
bromide salt
The intermediate of 1-(6-bromohexyl)-1-methylpyrrolidinium
bromide was prepared by the slow addition of 1-methylpyrrolidine
(20 mmol, 2.1 mL in 10 mL CH3CN) to 100 mL acetonitrile solution
with an excess amount of 1,6-dibromohexane (200 mmol, 30 mL)
at refluxing temperature for 24 h. After the reaction, acetonitrile
was removed and 50 mL of diethyl ether was added to form white
precipitates. The solid was collected by filtration and washed with
diethyl ether. After dried under vacuum, the product was obtained
as a white hygroscopic powder with 95% yields (6.4 g). 1H NMR
(400 MHz D2O): ı 1.38–1.48 (m, 2H), 1.48–1.58 (m, 2H), 1.79–1.95
(m, 4H), 2.23 (s, 4H), 3.06 (s, 3H), 3.32–3.40 (m, 2H), 3.45–3.59 (m,
6); 13C NMR (400 MHz D2O): ı 21.27, 22.90, 24.77, 26.76, 31.66,
34.84, 48.03, 64.12, 64.23; ESI-MS m/z: [M+] = 248, 250.
2.7. Preparation of single crystals of 1·(Br)3 for X-ray analysis
The ionic liquid 1·(Br)3 (250 mg) was completely dissolved in
hot acetonitrile. After cooling down the mixture to room tem-
perature, ethylacetate was added dropwise until the solution just
started to get cloudy. The single crystal suitable for X-ray crystal
structure analysis was obtained by the slow diffusion of diethyl
ether to the solution at room temperature. CCDC-709110 con-
tains the supplementary crystallographic data for this paper. The
detailed parameters are also available in the supporting informa-
tion.
2.4. Preparation of ionic liquid 1·(Br)3
A
mixed solution of 2,2ꢀ-dipyridylamine (10 mmol,
1.71 g) in dichloromethane (4.0 mL), 1-(3-bromopropyl)-
1-methylpyrrolidinium bromide salt (25 mmol, 7.2 g), and