Bifunctional organocatalyst for activation of carbon dioxide and epoxide to produce cyclic carbonate: Betaine as a new catalytic motif

Article abstract of DOI:10.1021/ol102539x

Bifunctional organocatalysts bearing an ammonium betaine framework have been developed as a new catalytic motif for the activation of carbon dioxide and epoxides to produce cyclic carbonates.

Full text of DOI:10.1021/ol102539x

ORGANIC
LETTERS
2010
Vol. 12, No. 24
5728-5731
Bifunctional Organocatalyst for
Activation of Carbon Dioxide and
Epoxide To Produce Cyclic Carbonate:
Betaine as a New Catalytic Motif
Yoshihiro Tsutsumi, Kyohei Yamakawa, Masahiko Yoshida, Tadashi Ema, and
Takashi Sakai*
DiVision of Chemistry and Biochemistry, Graduate School of Natural Science and
Technology, Okayama UniVersity, Tsushima, Okayama 700-8530, Japan
tsakai@cc.okayama-u.ac.jp
Received October 19, 2010
ABSTRACT
Bifunctional organocatalysts bearing an ammonium betaine framework have been developed as a new catalytic motif for the activation of
carbon dioxide and epoxides to produce cyclic carbonates.
Activation and fixation of carbon dioxide (CO2) has been a
challenging subject in organic synthesis because of the poor
Scheme 1
.
CO2 Activation by Ammonium Betaine
Organocatalyst
reactivity of CO2.1 The importance of this subject is growing
steadily because of the utility of CO2 as a renewable carbon
source. Among various methods, catalytic conversion of CO2
is extremely significant from the chemical and industrial
viewpoints.1,2 To address this subject, we focused on
organocatalysis, which has achieved a remarkable develop-
(1) Reviews: (a) Yin, X.; Moss, J. R. Coord. Chem. ReV. 1999, 181,
27–59. (b) Jessop, P. G.; Joo´, F.; Tai, C.-C. Coord. Chem. ReV. 2004, 248,
2425–2442. (c) Omae, I. Catal. Today 2006, 115, 33–52. (d) Sakakura, T.;
Choi, J.-C.; Yasuda, H. Chem. ReV. 2007, 107, 2365–2387. (e) Darensbourg,
D. J. Chem. ReV. 2007, 107, 2388–2410. (f) Sakakura, T.; Kohno, K. Chem.
Commun. 2009, 1312-1330. (g) North, M.; Pasquale, R.; Young, C. Green
Chem. 2010, 12, 1514–1539. (h) Riduan, S. N.; Zhang, Y. Dalton Trans.
2010, 39, 3347–3357.
ment in a decade by the ingenious designs of catalysts.3
Scheme 1 illustrates an ammonium betaine framework for
the cooperative activation of CO2 to give a reactive inter-
mediate that may be useful for various transformations. We
envisioned that the aryloxide anion would have both nu-
cleophilic and leaving abilities, both of which are essential
for catalysis, and that the quaternary ammonium cation might
stabilize the anion formed by the nucleophilic addition to
CO2.
(2) (a) Sugimoto, H.; Kimura, T.; Inoue, S. J. Am. Chem. Soc. 1999,
121, 2325–2326. (b) Choi, J.-C.; He, L.-N.; Yasuda, H.; Sakakura, T. Green
Chem. 2002, 4, 230–234. (c) Ihata, O.; Kayaki, Y.; Ikariya, T. Angew.
Chem., Int. Ed. 2004, 43, 717–719. (d) Nakano, K.; Kamada, T.; Nozaki,
K. Angew. Chem., Int. Ed. 2006, 45, 7274–7277. (e) Ukai, K.; Aoki, M.;
Takaya, J.; Iwasawa, N. J. Am. Chem. Soc. 2006, 128, 8706–8707. (f)
Goettmann, F.; Thomas, A.; Antonietti, M. Angew. Chem., Int. Ed. 2007,
46, 2717–2720. (g) Kayaki, Y.; Yamamoto, M.; Ikariya, T. J. Org. Chem.
2007, 72, 647–649. (h) Minakata, S.; Sasaki, I.; Ide, T. Angew. Chem., Int.
(3) (a) Berkessel, A.; Gro¨ger, H. Asymmetric Organocatalysis; Wiley-
VCH: Weinheim, Germany, 2005. (b) Seayad, J.; List, B. Org. Biomol.
Chem. 2005, 3, 719–724.
Ed. 2010, 49, 1309–1311
.
10.1021/ol102539x  2010 American Chemical Society
Published on Web 11/24/2010

Extensive studies have been done to achieve clean,
selective, and atom-economic coupling reactions of CO2 with
epoxides to give cyclic carbonates, which are useful as
synthetic intermediates, aprotic polar solvents, and feedstocks
for engineering plastics.4-9 To test our strategy for the direct
activation of CO2 (Scheme 1), we decided to employ this
coupling reaction. When we initiated this study, no betaines
had been reported as catalysts for this reaction. Although
betaine-acid salts have been reported to act as catalysts,8
ammonium halides bearing the carboxyl group are generated
in situ, and the proposed mechanism is different from our
strategy outlined in Scheme 1. During this study, Ooi and
co-workers have revealed the great potential of betaines as
catalysts for asymmetric Mannich-type reactions.10 Here we
report bifunctional organocatalysts functioning as metal-free,
halogen-free, and solvent-free catalysts for the coupling
reactions of CO2 with epoxides.
Figure 1. Bifunctional organocatalysts bearing an ammonium
betaine framework.
Betaines 1-8 (Figure 1) were synthesized as described in
the Supporting Information, and they were screened for
catalytic activity toward the conversion of 1,2-epoxyhexane
(9a) into 10a. A stainless autoclave was charged with epoxide
9a, catalyst, and then CO2 (initial pressure 1 MPa), and the
mixture was stirred at 120 °C for 24 h. The results are
summarized in Table 1. Among ortho-substituted betaines
1-3, 3 with the trimethylammonium group gave the best
result (entries 1-3). The bulky substituent, such as the allyl
and benzyl groups, is likely to hinder the access of CO2/
epoxide to the phenolate anion. Next, we tried to tune the
Table 1. Synthesis of Cyclic Carbonate 10a from CO2 and
1,2-Epoxyhexane (9a) with Organocatalystsa
entry
catalyst
loading (mol %) yield (%)b
1
2
3
4
5
6
7
8
1
2
3
4
4
4
5
5
5
6
7
8
3
3
3
3
2
1
3
2
1
3
3
3
1
3
3
3
3
61
60
76
>99
>99
88
>99
>99
88
84
93
99
77
(4) (a) Kruper, W. J.; Dellar, D. V. J. Org. Chem. 1995, 60, 725–727.
(b) Kim, H. S.; Kim, J. J.; Lee, S. D.; Lah, M. S.; Moon, D.; Jan, H. G.
Chem.sEur. J. 2003, 9, 678–686. (c) Paddock, R. L.; Nguyen, S. T. Chem.
Commun. 2004, 1622–1623. (d) Jiang, J.-L.; Gao, F.; Hua, R.; Qiu, X. J.
Org. Chem. 2005, 40, 381–383. (e) Mele´ndez, J.; North, M.; Pasquale, R.
Eur. J. Inorg. Chem. 2007, 3323–3326. (f) Zhang, X.; Jia, Y.-B.; Lu, X.-
B.; Li, B.; Wang, H.; Sun, L.-C. Tetrahedron Lett. 2008, 49, 6589–6592.
(g) Yin, S.-F.; Shimada, S. Chem. Commun. 2009, 1136–1138. (h) Mele´ndez,
J.; North, M.; Villuendas, P. Chem. Commun. 2009, 2577–2579
.
(5) (a) Kihara, N.; Hara, N.; Endo, T. J. Org. Chem. 1993, 58, 6198–
6202. (b) Yano, T.; Matsui, H.; Koike, T.; Ishiguro, H.; Fujihara, H.;
Yoshihara, M.; Maeshima, T. Chem. Commun. 1997, 1129–1130. (c)
Yamaguchi, K.; Ebitani, K.; Yoshida, T.; Yoshida, H.; Kaneda, K. J. Am.
Chem. Soc. 1999, 121, 4526–4527. (d) Song, J.; Zhang, Z.; Han, B.; Hu,
9
10
11
12
13
14
15
16
17
S.; Li, W.; Xie, Y. Green Chem. 2008, 10, 1337–1341
.
8
(6) (a) Calo´, V.; Nacci, A.; Monopoli, A.; Fanizzi, A. Org. Lett. 2002,
4, 2561–2563. (b) Kawanami, H.; Sasaki, A.; Matsui, K.; Ikushima, Y.
Chem. Commun. 2003, 896–897. (c) Takahashi, T.; Watahiki, T.; Kitazume,
S.; Yasuda, H.; Sakakura, T. Chem. Commun. 2006, 1664–1666. (d) Tian,
J.-S.; Miao, C.-X.; Wang, J.-Q.; Cai, F.; Du, Y.; Zhao, Y.; He, L.-N. Green
Chem. 2007, 9, 566–571. (e) Sakai, T.; Tsutsumi, Y.; Ema, T. Green Chem.
2008, 10, 337–341. (f) Sun, J.; Zhang, S.; Cheng, W.; Ren, J. Tetrahedron
L-Phe
11
4
61
15
o-dimethylaminophenol
p-MeOC6H4OH/DMAP7a,c
PhN+Me3·PhO-
a Conditions: 9a (1.2 mL, 10 mmol), catalyst (quantity indicated above),
1 MPa CO2, 120 °C, 24 h, in a 50-mL autoclave. b Determined by 1H NMR,
using 2-methoxynaphthalene as an internal standard.
Lett. 2008, 49, 3588–3591
.
(7) (a) Shen, Y.-M.; Duan, W.-L.; Shi, M. AdV. Synth. Catal. 2003, 345,
337–340. (b) Barbarini, A.; Maggi, R.; Mazzaacani, A.; Mori, G.; Sartori,
G.; Sartorio, R. Tetrahedron Lett. 2003, 44, 2931–2934. (c) Shen, Y.-M.;
Duan, W.-L.; Shi, M. Eur. J. Org. Chem. 2004, 3080–3089. (d) Qi, C.;
Jiang, H.; Wang, Z.; Zou, B.; Yang, S. Synlett 2007, 255–258. (e) Zhou,
H.; Zhang, W.-Z.; Liu, C.-H.; Qu, J.-P.; Lu, X.-B. J. Org. Chem. 2008, 73,
8039–8044. (f) Kayaki, Y.; Yamamoto, M.; Ikariya, T. Angew. Chem., Int.
distance between the two functional groups in the catalyst
in two ways: one is to employ meta- and para-isomers 4
and 5, and the other is to examine biaryl systems 6-8. To
our delight, biphenyl compound 6 gave a higher yield than
3 (entries 3 and 10). To suppress the rotational flexibility
determining the distance between the two functional groups,
we replaced the phenyl group by the naphthyl group. As
expected, catalytic activity increased in the following order:
6 < 7 < 8 (entries 10-12). In the case of 8, the catalyst
loading could be reduced to 1 mol % although the yield
decreased a little (entry 13). We anticipated that because of
Ed. 2009, 48, 4194–4197
(8) Zhou, Y.; Hu, S.; Ma, X.; Liang, S.; Jiang, T.; Han, B. J. Mol. Catal.
A: Chem. 2008, 284, 52–57
.
.
(9) (a) Du, Y.; Cai, F.; Kong, D.-L.; He, L.-N. Green Chem. 2005, 7,
518–523. (b) Xie, Y.; Zhang, Z.; Jiang, T.; He, J.; Han, B.; Wu, T.; Ding,
K. Angew. Chem., Int. Ed. 2007, 46, 7255–7258. (c) He, J.; Wu, T.; Zhang,
Z.; Ding, K.; Han, B.; Xie, Y.; Jiang, T.; Liu, Z. Chem.sEur. J. 2007, 13,
6992–6997
.
(10) (a) Uraguchi, D.; Koshimoto, K.; Ooi, T. J. Am. Chem. Soc. 2008,
130, 10878–10879. (b) Uraguchi, D.; Koshimoto, K.; Ooi, T. Chem.
Commun. 2010, 46, 300–302. (c) Uraguchi, D.; Koshimoto, K.; Miyake,
S.; Ooi, T. Angew. Chem., Int. Ed. 2010, 49, 5567–5569.
Org. Lett., Vol. 12, No. 24, 2010
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the long distance between the two functional groups in the
catalyst, meta- and para-isomers 4 and 5 would show lower
catalytic activity than ortho-isomer 3. Contrary to our
expectation, however, 4 and 5 even showed higher catalytic
activity (entries 4 and 7). We suppose that this is because
the oxyanion moiety in 4 and 5 is sterically less hindered
than that in 3. In both cases, when the catalyst loading was
reduced to 2 mol % and 1 mol %, respectively, the product
was obtained in >99% and 88%, the latter of which was
higher than that attained by 8 (entries 5, 6, 8, and 9).
Amino acids are zwitterions capable of showing high
catalytic activity yet under more harsh conditions.7d To
directly compare the catalytic powers, we used L-phenyla-
lanine under the same reaction conditions (entry 14). As a
result, the product 10a was obtained in a much lower yield
(11%), which suggests that the phenolate anion is a better
nucleophile than the carboxylate anion. Next, we examined
o-dimethylaminophenol, where the hydroxy group can be
activated by the dimethylamino group via the intramolecular
hydrogen bonding (entry 15). Despite structural similarity
to 3, o-dimethylaminophenol gave 10a in only 4% yield,
which indicates the importance of the naked phenolate anion.
A highly active cocatalyst system with p-methoxyphenol
(Lewis acid) and 4-(dimethylamino)pyridine (DMAP, Lewis
base) has been reported.7a,c We used this catalytic system
under the same conditions to obtain 10a in 61% yield (entry
16). Finally, phenyltrimethylammonium phenoxide
(PhN+Me3·PhO-) was examined. This ion-paired complex
was found to be much inferior to the betaine counterpart
such as 3-5 (entry 17). We suppose that ion-pair formation
occurs tightly in PhN+Me3·PhO-, hindering the insertion of
CO2/epoxide, while the betaine structure is more favorable
because the phenolate anion is remote from the quaternary
ammonium cation. On the basis of these observations, we
conclude that the nucleophilicity of the phenolate anion is
the most important factor and that electrostatic stabilization
of the anion generated by attacking CO2/epoxide is less
important.
Figure 2. The catalytic activity for the synthesis of 10a is compared
between 4 (red: 2 mol %; orange: 1 mol %) and 5 (blue: 2 mol %;
light blue: 1 mol %) by changing the reaction temperature. The
NMR yield was determined by using 2-methoxynaphthalene as an
internal standard.
Table 2. Synthesis of Various Cyclic Carbonates with Catalyst 4a
The difference in the catalytic activity of 4 and 5
became clear as the reaction temperature was decreased
(Figure 2); meta-isomer 4 was found to be more active
than para-isomer 5. This can be partially ascribed to the
higher nucleophilicity of the phenolate anion of 4 because
of the lack of the conjugation stabilization. Interestingly,
the yields dropped sharply around 70-90 °C for unknown
reasons. The catalyst might precipitate below the critical
temperature. The use of 2 mol % of 4 at 90 °C afforded
10a in 98% yield. Using the most active catalyst 4 (3 mol
%), the substrate scope was explored. The results are
summarized in Table 2. Various epoxides 9b-f were
converted into the corresponding cyclic carbonates 10b-f
in excellent yields (80-99%).
Next, we decided to isolate and characterize a key
intermediate, a betaine-CO2 adduct (Scheme 2). A stainless
autoclave was charged with catalyst 4 (151 mg, 1.00 mmol)
and CO2 (1 MPa), and the mixture was stirred at a constant
temperature (7-90 °C) for 24 h. Careful release of CO2 gave
a white powder. The product was characterized by an
a Conditions: 9 (10 mmol), catalyst 4 (3 mol %), 1 MPa CO2, 120 °C,
24 h, in a 50-mL autoclave. b Isolated yield.
absorption at 1655 cm-1 (CdO stretching vibration) in the
IR spectrum and an additional signal at 161.2 ppm (carbonyl
C) in the 13C NMR spectrum, which strongly support the
formation of a 4-CO2 adduct.11 To examine whether the
4-CO2 adduct is the reaction intermediate, we heated this
adduct with an excess amount of epoxide 9a (10.0 mmol)
under Ar in an autoclave at 120 °C for 24 h (Scheme 2). As
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Org. Lett., Vol. 12, No. 24, 2010

Scheme 2. Formation of Betaine-CO2 Adduct and
Scheme 3. Proposed Catalytic Cycle
Demonstration of Reaction Intermediate
a result, cyclic carbonate 10a was obtained. The yields are
shown in Figure 3, where the reaction temperature for the
In summary, we have proposed a new catalytic motif for
CO2 activation. Bifunctional organocatalysts bearing an
ammonium betaine framework have been developed for the
activation of carbon dioxide and epoxides to produce cyclic
carbonates. Among them, betaine 4 is one of the most active
catalysts that can function under the metal-free, halogen-
free, and solvent-free conditions. The betaine-CO2 adducts
will be used for various purposes. In particular, the fact that
the 4-CO2 adduct was formed even at 15 °C is promising
because this type of betaine may also be useful for carbon
capture and storage (CCS).12
Acknowledgment. We are grateful to the SC-NMR
Laboratory of Okayama University for the measurement of
NMR spectra.
Figure 3. The synthesis of 10a by the reaction of the 4-CO2 adduct
with an excess amount of epoxide 9a under Ar in a 30-mL autoclave
at 120 °C for 24 h. The reaction temperature for the formation of
the 4-CO2 adduct is shown in the horizontal axis.
Supporting Information Available: Synthetic procedures,
synthesis of CO2 adducts and subsequent reaction with
epoxide, optimization of the reaction conditions, and copies
of NMR spectra of all new compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
formation of the 4-CO2 adduct is shown in the horizontal
axis. Figure 3 clearly indicates that the 4-CO2 adduct was
formed most efficiently at 15 °C, which indicates that the
nucleophilicity of the aryloxide of betaine 4 is very high.11
At higher temperatures, the decarboxylation reaction seems
to proceed faster. We consider that the rate-determining step
is the epoxide ring-opening step because the catalytic reaction
proceeded well above 90 °C (Figure 2). On the basis of these
observations, we propose the catalytic cycle as shown in
Scheme 3.
OL102539X
(11) The weight of the powder was increased by 28 mg at 15 °C, and
the subsequent reaction with 9a gave 10a in 63%. Similar results were
obtained for catalyst 5 (weight increase: 29 mg; IR: 1631 cm-1; NMR:
161.2 ppm; formation of 10a: 41%) and catalyst 6 (weight increase: 30
mg; IR: 1655 cm-1; NMR: 161.3 ppm; formation of 10a: 65%).
(12) (a) D’Alessandro, D. M.; Smit, B.; Long, J. R. Angew. Chem., Int.
Ed. 2010, 49, 6058–6082. (b) Wang, C.; Mahurin, S. M.; Luo, H.; Baker,
G. A.; Li, H.; Dai, S. Green Chem. 2010, 12, 870–874.
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