Synthesis of cyclic carbonates from carbon dioxide and epoxides catalyzed by a keggin-type polyoxometalate-supported rhenium carbonyl derivate in ionic liquid

Article abstract of DOI:10.1002/cctc.201402575

A monovacant Keggin-type polyoxometalate-supported trirhenium carbonyl derivate [(CH₃)₄N]₅H₂₃[(PW₁₁O₃₉){Re(CO)₃}₃(μ₃-O)(μ₂-OH)]₄·24H₂O was synthesized. It was used as a catalyst for the synthesis of cyclic carbonates from carbon dioxide and epoxides under mild reaction conditions with co-catalyst pyrrolidinium bromide. The catalyst system was recycled 10 times with only a small decline in yield. The catalytic mechanism was hypothesized based on experimental results and the frontier orbitals computed by DFT calculations.

Full text of DOI:10.1002/cctc.201402575

CHEMCATCHEM
COMMUNICATIONS
DOI: 10.1002/cctc.201402575
Synthesis of Cyclic Carbonates from Carbon Dioxide and
Epoxides Catalyzed by a Keggin-Type Polyoxometalate-
Supported Rhenium Carbonyl Derivate in Ionic Liquid
Zhiyuan Huo, Juan Zhao, Zhanwei Bu, Pengtao Ma, Qisen Liu, Jingyang Niu,* and
Jingping Wang*[a]
A monovacant Keggin-type polyoxometalate-supported trirhe-
nium carbonyl derivate [(CH3)4N]5H23[(PW11O39){Re(CO)3}3(m3-
O)(m2-OH)]4·24H2O was synthesized. It was used as a catalyst
for the synthesis of cyclic carbonates from carbon dioxide and
epoxides under mild reaction conditions with co-catalyst
pyrrolidinium bromide. The catalyst system was recycled
10 times with only a small decline in yield. The catalytic mech-
anism was hypothesized based on experimental results and
the frontier orbitals computed by DFT calculations.
the synthesis of cyclic carbonate.[6] In particular, ReI complexes
have proven effective for the transformation of CO2. ReI com-
plexes have usually been used as photocatalysts for the reduc-
tion of CO2 to CO.[12] However, their applications in the cou-
pling of CO2 with epoxides remain very rare. Hua et al. first re-
ported that [Re(CO)5Br] could be used as an active catalyst in
the synthesis of cyclic carbonates under harsh conditions.[7] Re-
cently, a tricarbonyl rhenium(I) complex has been described by
Wong et al. that could catalyze the chemical fixation of CO2
with epoxides in the presence of ionic liquid.[8]
As reported recently, there are plenty of binary catalyst sys-
tems containing Lewis acid and base centers that provide
good yields under mild reaction conditions for the cycloaddi-
tion reaction.[13] Delightfully, Hill et al. demonstrate that the Re
atoms are Lewis acid centers if in excited states, as the POM
moiety acts as a strong electron-withdrawing group.[14] The po-
tential catalytic properties obtained by the combination of
both of these systems greatly arouses our curiosity. Hence, it
still remains to develop the design of POM-supported rhenium
carbonyl derivatives as catalysts with enhanced properties for
CO2 conversion. It is beneficial for the transformation of CO2 to
use room-temperature ionic liquids as co-catalysts because of
their high CO2 solubility, negligible vapor pressure, high ion
conductivity, and excellent selectivity.[15–17] Furthermore, the
halide ions in ionic liquids are usually regarded as ideal nucleo-
philes (Lewis base centers) that can strongly lower the activa-
tion energy barrier of the reaction. In this paper, we report
a monovacant Keggin-type POM-supported rhenium carbonyl
derivate (1) used as an efficient and recyclable catalyst for the
CO2 cycloaddition reaction under mild reaction conditions with
1-ethyl-1-methylpyrrolidinium bromide (2) as the co-catalyst.
This catalyst system could circumvent many of the disadvan-
tages described above.
Chemical fixation of CO2 into useful chemical compounds has
attracted great attention in recent years because CO2 is an at-
tractive and potentially renewable C1 building block in organic
synthesis.[1] The cycloaddition of CO2 to epoxides to produce
five-membered cyclic carbonates is one of the most promising
strategies because cyclic carbonates can be widely used as
precursors for producing polycarbonates, aprotic polar sol-
vents, electrolyte components in lithium batteries, and fine
chemical ingredients.[2] Numerous catalysts have been devel-
oped for this aim, such as phosphonium salts,[3] transition
metal complexes,[4–8] quaternary ammonium salts,[9] alkali metal
salts,[10] and functional polymers.[11] However, although the ad-
vances are significant, most of these catalysts suffer from low
catalyst stability or reactivity, needing high temperatures and/
or pressures, and difficulty in recycling. Among the above cata-
lysts, transition metal complexes have emerged as a significant
type of catalyst for the coupling of CO2 with epoxides.[4–8] Sur-
prisingly, transition-metal-substituted polyoxometalates (POMs)
were found to have application in catalyzing the synthesis of
cyclic carbonate.[5,6] A zinc-substituted polyoxometalate, Na12-
[WZn3(H2O)2(ZnW9O34)2]·46H2O, in conjunction with dimethyl
amino pyridine was found to be an efficient catalyst in the cy-
cloaddition reaction.[5] Tetraalkylammonium salts of transition-
metal-substituted polyoxometalates, such as [(n-C7H15)4N]6[a-
SiW11O39Co] and [(n-C7H15)4N]6[a-SiW11O39Mn], could catalyze
Catalyst 1 was synthesized by reaction of [Re(CO)5Cl], reac-
tion intermediate B in the CH3CNÀH2O mixed solvent (see Sec-
tion S1 in the Supporting Information). Each unit lattice of
1 consisted of 4 [(PW11O39){Re(CO)3}3(m3-O)(m2-OH)]7À (1a) units,
5 [(CH3)4N]+ cations, 27 protons and 54 crystalline water mole-
cules (Figure 1). The crystal structure of 1a revealed a “cap”
model of the trirhenium carbonyl cluster that was combined
with [PW11O39]8À (Figure 1a). The POM moiety can be consid-
ered as an extremely active tetradentate ligand providing ex-
cellent coordination to the Re centers of the trirhenium car-
bonyl cluster. The trirhenium carbonyl cluster fragment of 1a
is remarkably similar to that reported by Hill et al.[14] The three
ReI centers in [{Re(CO)3}3(m3-O)(m2-OH)] are divided into two cat-
[a] Z. Huo, J. Zhao, Prof. Z. Bu, P. Ma, Q. Liu, Prof. J. Niu, Prof. J. Wang
Key Laboratory of Polyoxometalate Chemistry of Henan Province
Institute of Molecular and Crystal Engineering
College of Chemistry and Chemical Engineering
Henan University
Kaifeng 475004 (P.R. China)
E-mail: jyniu@henu.edu.cn
jpwang@henu.edu.cn
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201402575.
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 0000, 00, 1 – 5
&
1
&
ÞÞ
These are not the final page numbers!

CHEMCATCHEM
COMMUNICATIONS
www.chemcatchem.org
as a nucleophile by accelerating the ring-opening re-
action of the epoxide (see Table S2 in the Supporting
Information). These results showed that the co-cata-
lyst 2 played a crucial catalytic role.
On testing the recyclability of the catalyst system,
the results (see Figure 2) showed that it could be re-
cycled 10 times with a small gradual decline in yield
to 80.3% at the 10th cycle (Table 1, entry 11). Excit-
ingly, the IR spectra of the recovered catalyst systems
were almost identical to that of the fresh catalyst
system (Figure S9 in the Supporting Information), in-
dicating that the catalyst system was stable.
We then studied further applications of the catalyst
system and found it to be applicable to a wide range
of epoxides. As shown in Table 2, the catalytic activity
of the system depended greatly on the structure of
various epoxides. Both epichlorohydrin (2b) and gly-
Figure 1. a) Ball-and-stick representation of polyanion 1a. b) Polyhedral and ball-and-
stick representation of 1 follows the c direction. *: Re, *: O, *: C, *: P, *: W, &: PO4,
&: WO6.
egories. Re2 and Re3 reside in similar coordination environ-
ment, each of which is covalently bonded to three carbonyl li-
gands and O40 and O41, which forms one ReÀOÀW bond to
[PW11O39]8À. In comparison, Re1 is bonded to O40, which forms
two ReÀOÀW bonds to the POM moiety. Notably, one proton
should be localized on m2-O41 according to the bond valence
sun calculations[18] of all the oxygen atoms on 1a. The shortest
distance between the protonated O41 and O6W is 2.767 ꢁ,
confirming the existence of a hydrogen bond between them
(Figure 1a).
Table 1. Effect of reaction parameters on the coupling of CO2 and 1,2-
epoxy-3-phenoxypropane catalyzed by catalyst 1 with ionic liquid 2 as
the co-catalyst.[a]
Entry
1
2
P[b]
T
Yield[c]
[%]
TOF[d]
[hÀ1
]
[mol%]
[mol%]
[MPa]
[8C]
The ability of catalyst 1 to catalyze cyclic carbonate synthesis
from CO2 and epoxides with co-catalyst ionic liquid 2 were
studied. Then the effects of various reaction parameters on the
catalytic performance were researched in detail by using the
coupling of glycidyl phenyl ether (2a) with CO2 to produce 3-
phenoxy-1,2-propylene carbonate (3a) as a model reaction. We
were delighted to discover that catalyst 1 catalyzed the cyclo-
addition of CO2 with 2a in conjunction with ionic liquid 2. In
a blank experiment (see Table 1, entry 1), ionic liquid 2 itself
could convert the epoxide into 3a through a Lewis acid–Lewis
base mechanism[19] with BrÀ as a nucleophile, though the yield
was much lower. The yield was increased to 84.3% by the ad-
dition of 0.1 mol% (relative to epoxide) of 1 (entry 2). The out-
standing turnover frequency (TOF) of 843 hÀ1 was superior to
that of tricarbonyl rhenium(I) complex reported by Wong et al.
(ꢀ122 hÀ1).[8] If addition of 1 was increased incrementally from
0.12 to 0.15 mol%, the yield increased from 91.2 to 96.7% (en-
tries 3 and 4). The yield of 3a slightly depended on CO2 pres-
sure in the low pressure range (entries 6 and 7). However, the
yield was strongly affected by the reaction temperature (en-
tries 8–10). The increase of reaction temperature from 60 to
658C resulted in a rapid increase in the yield from 27.8 to
72.4% (entries 8 and 9). On increasing the reaction tempera-
ture to 758C, 97.2% yield was achieved (entry 10). We then
speculated on the catalytic role of co-catalyst 2. However, no
yield was obtained without co-catalyst 2 at 708C over 1 h
(Table 1, entry 12). If co-catalyst 2 was added incrementally
from 4 to 6 mol%, the yield increased from 58.3 to 77.2% (en-
tries 13 and 14). The BrÀ of co-catalyst 2 facilitated the reaction
1
2
3
4
5[e]
6
7
8
–
0.1
8
8
8
8
8
8
8
8
8
8
8
–
4
6
1.0
1.0
1.0
1.0
1.0
0.5
1.5
1.0
1.0
1.0
1.0
1.0
1.0
1.0
70
70
70
70
70
70
70
60
65
75
70
70
70
70
34.9
84.3
91.2
96.7
46.4
82.9
95.5
27.8
72.4
97.2
80.3
–
–
843
760
645
773
691
796
232
603
810
669
–
0.12
0.15
0.12
0.12
0.12
0.12
0.12
0.12
0.12
0.1
9
10
11[f]
12[g]
13
14
0.12
0.12
58.3
77.2
486
643
[a] Reaction conditions: epoxide (5 mmol, 680 mL), t=1 h. [b] Initial pres-
sure at RT. [c] Determined by GC with dimethyl phthalate as the internal
standard; selectivities were over 99% in all cases. [d] in
[molpropylene carbonate molcatalystÀ1 hÀ1]. [e] t=0.5 h. [f] Yield of the 10th cycle in
the recycling studies. [g] Without ionic liquid 2 (Lewis base center).
cidyl methacrylate (2c) are highly polar. Epichlorohydrin (2b)
exhibited the highest activity among the epoxides surveyed.
The excellent yield of 94.6% and high TOF of 1051 hÀ1 were
given by using epichlorohydrin at 708C for 0.75 h (Table 2,
entry 1) and glycidyl methacrylate (2c) displayed a good yield
of 93.2% within 1 h (Table 2, entry 2). Styrene oxide (2d) was
confirmed to be a less-reactive epoxide, with only 65.3% yield
obtained in 2 h followed by an increase in yield to 90.1% over
a further 3 h (Table 2, entries 3 and 4). This probably owed to
the steric hindrance of the phenyl group. However, the aliphat-
ic terminal epoxide 1,2-epoxyhexane (2e), comparatively non-
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 0000, 00, 1 – 5
&
2
&
ÞÞ
These are not the final page numbers!

CHEMCATCHEM
COMMUNICATIONS
www.chemcatchem.org
hardly participated in the reaction; an analogous result analysis
has been described by Wong et al.[8]
Finally, we investigated the reaction mechanism for the cy-
cloaddition of CO2 to epoxides. The [Re(CO)5Br]-catalyzed
mechanism was first proposed by Hua et al.[7] However, the
[Re(CO)5Br]-catalyzed reaction occurred under relatively harsh
conditions without a halide nucleophile (Lewis base center).
Under the conditions described herein, compound 1 was used
without co-catalyst to catalyze the cycloaddition reaction and
the experimental phenomena were consistent with those de-
scribed by Hua et al.[7] (see Table S1 in the Supporting Informa-
tion). This indicated that the reaction mechanism probably fol-
lowed that proposed for [Re(CO)5Br] under relatively harsh con-
ditions.[7] By comparison, no yield was obtained if 1 was used
without co-catalyst at 708C for 1 h (Table 1, entry 12), indicat-
ing that the [Re(CO)5Br]-catalyzed mechanism was not applica-
ble for our catalyst system under mild reaction conditions. If
pyrrolidinium bromide 2 was used as the co-catalyst, we ob-
tained high yield. An analogous result has been described by
Kleij et al.[20] indicating that the ring-opening procedure initiat-
ed by direct insertion of CO2 was highly energetically demand-
ing, which suggested that the procedure could only occur
under relatively harsh reaction conditions. In contrast, the
binary catalyst system for the cycloaddition of CO2 to epoxides
usually combines a Lewis acid center and a halide nucleophile,
which can reduce the energy barrier and facilitate subsequent
CO2 insertion.
Figure 2. Reuse of the catalyst system. Reaction conditions: 5 mmol 2a,
0.12 mol% 1, CO2 pressure 1.0 MPa, T=708C, t=1 h.
Table 2. Catalytic cycloaddition of CO2 (1.0 MPa) and various epoxides at
708C with ionic liquid 2 as the co-catalyst.[a]
Entry Substrate
t
[h]
Product
Yield[b] TOF[c]
[%]
[hÀ1
]
1
2b 0.75
94.6
1051
776
In this paper, DFT calculations demonstrate that the HOMO
orbitals are entirely localized on the trirhenium carbonyl cluster
fragment of 1a, whereas the LUMO orbitals exist wholly in the
POM moiety and are principally WÀO antibonding orbitals
(Figure 3). If the Re centers are in their excited states, electrons
can transfer easily from the Re centers to the POM moiety,
which makes the Re centers more electropositive. Thus, the Re
atoms in excited states are proved to be Lewis acid centers be-
cause the POM moiety acts as a strong electron-withdrawing
group. An analogous result analysis of DFT calculations has
been described by Hill et al.[14]
2
2c
1
93.2
3
4
2
3
65.3
90.1
272
251
2d
5
6
3
8
49.5
92.6
137
96
2e
2 f
7
1
11.6
97
Excitingly, the formation of a hydrogen bond between the
protonated m2-O41 and the nearby dissociative crystalline
water may activate the corresponding ReÀC bond and simulta-
neously activate the ring-opening reaction of epoxides.[21] Co-
incidently, the bond distances (Re3ÀC7: 2.02; Re3ÀC8: 1.93 ꢁ;
Figure 1a) are longer than others (ꢀ1.86 ꢁ), indicating that
the Re3ÀC7 bond is highly activated and more prone to break-
[a] Reaction conditions: catalyst 1 (0.12 mol%), epoxide (5 mmol), ionic
liquid 2 (8 mol%, 80 mg). CO2 was charged into an autoclave under an in-
itial pressure of 1.0 MPa at RT. [b] Determined by GC with dimethyl phtha-
late as the internal standard; selectivities were over 99% in all cases.
[c] In [molpropylene carbonate molcatalystÀ1 hÀ1].
polar, showed sluggish reactivity
(Table 2, entries 5 and 6). The
propylene oxide (2 f), as a low
boiling epoxide, gave only
11.6% yield after 1 h, which
could be because the propylene
oxide turned into
a gas at
1.0 MPa and 708C, most of
which then stayed in the upper
Figure 3. Several highest occupied (H=HOMO) and lowest unoccupied (L=LUMO) orbitals of 1a and their orbital
apex of the reaction vessel and energies in [eV].
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 0000, 00, 1 – 5
&
3
&
ÞÞ
These are not the final page numbers!

CHEMCATCHEM
COMMUNICATIONS
www.chemcatchem.org
patterns, elemental analyses, UV/Vis and IR spectra, ther-
mogravimetric analysis, and computational methods are
given in the Supporting Information. CCDC 1007587 con-
tains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements
We thank the National Natural Science Foundation of
China, the Foundation of Education Department of
Henan Province, and the Natural Science Foundation of
Henan Province for their financial support and Dr. Fu-
Qiang Zhang (Shangqiu Normal College) for his dedica-
tion to DFT computations and constructive suggestions.
Keywords: carbon dioxide fixation
functional calculations epoxides
polyoxometalates · rhenium
·
density
·
·
[1] a) C. Song, Catal. Today 2006, 115, 2–32; b) T. Sakakura, J. C.
Choi, H. Yasuda, Chem. Rev. 2007, 107, 2365–2387.
[2] a) A. A. G. Shaikh, S. Sivaram, Chem. Rev. 1996, 96, 951–976;
b) J. H. Clements, Ind. Eng. Chem. Res. 2003, 42, 663–674;
c) M. Yoshida, M. Ihara, Chem. Eur. J. 2004, 10, 2886–2893.
[3] L. N. He, H. Yasuda, T. Sakakura, Green Chem. 2003, 5, 92–
94.
Scheme 1. Proposed reaction mechanism for the cycloaddition of CO2 to epoxides.
age, which gives us crystallographic evidence to further specu-
late the mechanism of the catalytic reaction. Both of these fac-
tors lead to the Re3 center becoming a strong Lewis acid me-
diator for activating the epoxide. Considering the various kinds
of factors mentioned above and the universally recognized
mechanisms of the cycloaddition of CO2 to epoxides,[22,23] a pro-
posed reaction mechanism is illustrated in Scheme 1. It is sug-
gested that the epoxide is first activated by coordination to
the Re3 center, followed by epoxide ring-opening through the
nucleophilic attack of BrÀ, and the subsequent interaction of
the nucleophilic alkoxide intermediate with the electrophilic
CO2 to form the cyclic carbonate. Both the Lewis acidic center
(Re3) and the nucleophile (BrÀ) have the same importance in
this mechanism and the excellent synergistic effects greatly
promote the reactions.
[4] a) D. Jairton, F. D. S. Roberto, A. Z. S. Paulo, Chem. Rev. 2002, 102, 3667–
3692; b) F. W. Chen, T. Dong, Y. N. Chi, Y. Q. Xu, C. W. Hu, Catal. Lett.
2010, 139, 38–41.
[5] M. Sankar, N. H. Tarte, P. Manikandan, Appl. Catal. A 2004, 276, 217–
222.
[6] H. Yasuda, L. N. He, T. Sakakura, C. W. Hu, J. Catal. 2005, 233, 119–122.
[7] J. L. Jiang, F. X. Gao, R. M. Hua, X. Q. Qiu, J. Org. Chem. 2005, 70, 381–
383.
[8] W. L. Wong, K. C. Cheung, P. H. Chan, Z. Y. Zhou, K. H. Lee, K. Y. Wong,
Chem. Commun. 2007, 2175–2177.
[9] Y. Du, J. Q. Wang, J. Y. Chen, F. Cai, J. S. Tian, D. L. Kong, L. N. He, Tetra-
hedron Lett. 2006, 47, 1271–1275.
[10] J. W. Huang, M. Shi, J. Org. Chem. 2003, 68, 6705–6709.
[11] J. He, T. Wu, Z. Zhang, K. Ding, B. Han, Y. Xie, T. Jiang, Z. Liu, Chem. Eur.
J. 2007, 13, 6992–6997.
[12] a) J. Hawecker, J. M. Lehn, R. Ziessel, J. Chem. Soc. Chem. Commun.
1983, 536–538; b) A. J. Morris, G. J. Meyer, E. Fujita, Acc. Chem. Res.
2009, 42, 1983–1994; c) J. Ettedgui, Y. D. Posner, L. Weiner, R. Neumann,
J. Am. Chem. Soc. 2011, 133, 188–190.
In summary, we have reported a Keggin-type polyoxometa-
late-supported trirhenium carbonyl derivate. Notably, this work
features the combination of compound 1 and pyrrolidinium
bromide 2 for the formation of cyclic carbonates. The synergis-
tic effects greatly promote the reactions under mild conditions.
Significantly, the polyoxometalate moiety plays a particularly
positive role in the catalytic reactions. The mechanism pro-
posed is supported by both theoretical and experimental re-
sults and provides new insights into the design of more pow-
erful catalyst systems for the cycloaddition reaction.
[13] a) D. R. Moore, M. Cheng, E. B. Lobkovsky, G. W. Coates, Angew. Chem.
Int. Ed. 2002, 41, 2599–2602; Angew. Chem. 2002, 114, 2711–2714;
b) M. North, R. Pasquale, C. Young, Green Chem. 2010, 12, 1514–1539;
c) A. Decortes, A. M. Castilla, A. W. Kleij, Angew. Chem. Int. Ed. 2010, 49,
9822–9837; Angew. Chem. 2010, 122, 10016–10032.
[14] C. Zhao, Z. Huang, W. Rodrꢂguez-Cꢃrdoba, A. L. Kaledin, Y. Yang, Y. V. Ge-
letii, T. Lian, D. G. Musaev, C. L. Hill, Inorg. Chem. 2013, 52, 13490–
13495.
[15] a) P. Wasserscheid, W. Keim, Angew. Chem. Int. Ed. 2000, 39, 3772–3789;
Angew. Chem. 2000, 112, 3926–3945; b) R. Sheldon, Chem. Commun.
2001, 2399–2407; c) H. Kawanami, A. Sasaki, K. Matsui, Y. Ikushima,
Chem. Commun. 2003, 896–897.
[16] C. Cadena, J. L. Anthony, J. K. Shah, T. I. Morrow, J. F. Brennecke, E. J.
Maginn, J. Am. Chem. Soc. 2004, 126, 5300–5308.
[17] J. M. Sun, S. Fujita, M. J. Arai, Organomet. Chem. 2005, 690, 3490–3497.
[18] a) I. D. Brown, D. Altermatt, Acta Crystallogr. Sect. B 1985, 41, 244–247;
b) N. E. Brese, M. O’Keeffe, Acta Crystallogr. Sect. B 1991, 47, 192–197;
c) M. O’Keeffe, N. E. Brese, Acta Crystallogr. Sect. B 1992, 48, 152–154.
Experimental Section
Details on the synthetic process of compound 1, reaction proce-
dures, the recycling process, additional experiments, powder XRD
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 0000, 00, 1 – 5
&
4
&
ÞÞ
These are not the final page numbers!

CHEMCATCHEM
COMMUNICATIONS
www.chemcatchem.org
[19] V. Calꢃ, A. Nacci, A. Monopoli, A. Fanizzi, Org. Lett. 2002, 4, 2561–2563.
[20] F. Castro-Gꢃmez, G. Salassa, A. W. Kleij, C. Bo, Chem. Eur. J. 2013, 19,
6289–6298.
c) D. S. Bai, G. H. Nian, G. J. Wang, Z. Z. Wang, Appl. Organomet. Chem.
2013, 27, 184–187.
[23] a) F. Wang, C. Z. Xu, Z. Li, C. G. Xia, J. Chen, J. Mol. Catal. A 2014, 385,
133–140; b) C. J. Whiteoak, N. Kielland, V. Laserna, F. C. Gꢃmez, E.
Martin, E. C. Escudero-Adꢄn, C. Bo, A. W. Kleij, Chem. Eur. J. 2014, 20,
2264–2275.
[21] a) Q. X. Han, C. He, M. Zhao, B. Qi, J. Y. Niu, C. Y. Duan, J. Am. Chem. Soc.
2013, 135, 10186–10189; b) K. Surendra, N. S. Krishnaveni, K. R. Rao, Tet-
rahedron Lett. 2004, 45, 6523–6526.
[22] a) M. North, R. Pasquale, Angew. Chem. Int. Ed. 2009, 48, 2946–2948;
Angew. Chem. 2009, 121, 2990–2992; b) F. W. Chen, X. F. Li, B. Wang,
T. G. Xu, S. L. Chen, P. Liu, C. W. Hu, Chem. Eur. J. 2012, 18, 9870–9876;
Received: July 24, 2014
Published online on && &&, 0000
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 0000, 00, 1 – 5
&
5
&
ÞÞ
These are not the final page numbers!

COMMUNICATIONS
Z. Huo, J. Zhao, Z. Bu, P. Ma, Q. Liu,
J. Niu,* J. Wang*
Vacant looks all around: A monovacant
Keggin-type polyoxometalate-supported
trirhenium carbonyl derivate is synthe-
sized. It is an efficient and recyclable
catalyst in the synthesis of cyclic
&& – &&
Synthesis of Cyclic Carbonates from
Carbon Dioxide and Epoxides
Catalyzed by a Keggin-Type
Polyoxometalate-Supported Rhenium
Carbonyl Derivate in Ionic Liquid
carbonates from carbon dioxide and ep-
oxides under mild reaction conditions in
pyrrolidinium bromide ionic liquid. DFT
calculations indicate that the derivate
acts as a Lewis acid center.
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 0000, 00, 1 – 5
&
6
&
ÞÞ
These are not the final page numbers!