A new type of lewis acid-base bifunctional M(salphen) (M=Zn, Cu and Ni) catalysts for CO2 fixation

Article abstract of DOI:10.1002/cctc.201500113

A new type of Lewis acid-base bifunctional M(salphen) complexes (M=Zn^II, Cu^II, and Ni^II) pending two N-methylhomo- piperazine groups as nucleophiles were prepared by a one-pot method. The Zn(salphen) complexes proved to be efficient and recyclable homogeneous catalysts towards the solvent-free synthesis of cyclic carbonates from epoxides and CO₂ in the absence of a co-catalyst. The catalysts can be easily recovered and five times reused without significant loss of activity and selectivity. Bifunctional catalysts: A new type of Lewis acid-base bifunctional Zn(salphen) catalysts with an organic base, N-methylhomopiperazine, as a nucleophile were prepared by a one-pot method and successfully applied in the production of cyclic carbonates from CO₂ and epoxides. The catalysts used in this catalytic system are extremely stable and can be recycled at least five times and their activity is almost unchanged.

Full text of DOI:10.1002/cctc.201500113

DOI: 10.1002/cctc.201500113
Communications
A New Type of Lewis Acid–Base Bifunctional M(salphen)
(M=Zn, Cu and Ni) Catalysts for CO2 Fixation
Yanwei Ren, Jungui Chen, Chaorong Qi, and Huanfeng Jiang*[a]
A new type of Lewis acid–base bifunctional M(salphen) com-
plexes (M=ZnII, CuII, and NiII) pending two N-methylhomo-
piperazine groups as nucleophiles were prepared by a one-pot
method. The Zn(salphen) complexes proved to be efficient and
recyclable homogeneous catalysts towards the solvent-free
synthesis of cyclic carbonates from epoxides and CO2 in the
absence of a co-catalyst. The catalysts can be easily recovered
and five times reused without significant loss of activity and
Scheme 1. Cooperative activation of epoxide with bifunctional catalysts.
selectivity.
powerful catalyst mediators. For instance, Kleij and co-workers
The utilization of carbon dioxide (CO2) as a renewable C1 feed-
stock for the synthesis of value added chemicals currently re-
ceives considerable attention.[1] However, the exceptional ki-
netically and thermodynamically stability of CO2 is a major
drawback regarding its economic use as reactant. Many proce-
dures have been developed towards the easy and economical
chemical fixation of CO2. Among them, the catalytic cycloaddi-
tion of CO2 with epoxides to form cyclic carbonates, which are
used as electrolytes in lithium-ion batteries, raw materials for
polycarbonate, and polar aprotic solvents, is one of the most
promising environment-friendly reactions for the large-scale
conversion of CO2.[2] To date, various homogeneous catalytic
systems, including alkali metal halides,[3] metallosalen,[2c,4] met-
alloporphyrins,[5] and metal-free catalyst,[6] and various hetero-
geneous catalytic systems, including ion-exchange resins,[7] and
quaternary ammonium or phosphonium supported on carbon
nanotube or functional polymers,[8] and metallosalen based
metal-organic frameworks,[9] have been developed to promote
this transformation.
have developed a bifunctional Zn(salpyr) [salpyr=N,N’-bis(sali-
cylidene)-3,4-pyridinediamine] catalyst that can be alkylated at
the pyridyl-N atom, providing a complex with a built-in nucleo-
phile (either I or Br).[4a] The catalysis data support the synergis-
tic effect of the Lewis acidic site and the halide anion nucleo-
phile resulting in markedly improved catalytic behavior com-
pared with a system that lacks a Lewis acid activator. Alterna-
tively, a bifunctional Al(salen) in conjunction with intramolecu-
lar quaternary ammonium salts as cocatalysts, has also been
recently prepared and successfully applied in regioselective
ring opening of three-membered heterocyclic compounds (ep-
oxides or N-substituted aziridines) in coupling reactions with
CO2, affording the corresponding five-membered cyclic prod-
ucts with complete configuration retention at the methine car-
bon.[4b]
In addition to common halide anion nucleophiles, previously
Shi and co-workers reported that a binary system involving an
organic base, triethylamine used as nucleophile and binaph-
thyladiamion M(salen)-type complexes can efficiently catalyze
reactions of epoxides with CO2, and they proposed a Lewis
acid and Lewis base cocatalyzed mechanism by isotope-label-
ing experiments.[4l] Combined these results and our interests in
creating bifunctional (rather than binary) catalyst systems that
could be prepared in a few steps from readily available materi-
als, herein we present a new type of bifunctional single-com-
ponent M-salphen [salphen=N,N’-bis(salicyladehyde-o-phenyl-
enediamine)] catalysts system (Scheme 1b) that involves terti-
ary amine moiety as Lewis base and metal center as Lewis acid
within one structure, and examine their catalytic activity for
the cycloaddition of CO2 and various epoxides. This structural
design increases the stability of catalysts compared with the
ionic bifunctional systems, therefore enhances their recycling
performance.
Prominent among these are a variety of metallosalen com-
plexes because of their ease of synthesis, while varying the
steric and electronic properties about the metal centers. Over
the past decades, many successful examples of metallosalen
catalysts that have been developed for the preparation of
cyclic carbonates include both binary[4d–l] and bifunctional sys-
tems,[4a–c] with the latter category being less developed as
a probable result of the more synthetically demanding charac-
teristics of bifunctional catalysts preparation. Nonetheless, bi-
functionality (as shown in Scheme 1a, a Lewis acid (metal
center) and a halide anion XÀ (nucleophile) are required) has
proven to be highly useful in various cases to create more
[a] Dr. Y. Ren, J. Chen, Dr. C. Qi, Prof. Dr. H. Jiang
School of Chemistry and Chemical Engineering
South China University of Technology
Guangzhou, 510640 (P.R. China)
As shown in Scheme 2, via one-pot method, a series of
M(salphen) (Mn=ZnII, CuII, and NiII) catalysts with electron-do-
nating group (1a–1c) and electron-withdrawing group (1d–
1e) were synthesized and characterized by IR spectroscopy,
and mass spectrometry, as well as by elemental analysis (for
E-mail: jianghf@scut.edu.cn
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201500113.
ChemCatChem 0000, 00, 0 – 0
1
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ

Communications
Scheme 2. Synthesis of complexes 1a–1 f and the structures of 2a–2c.
further details see the Supporting Information). These selected
divalent metal ions have been proven to be useful in cyclic car-
bonate synthesis.[2c] Single crystal X-ray diffraction analyses for
1e reveal that the central CuII ion coordinated in a nearly
square-planar geometry with two nitrogen atoms and two
oxygen atoms from the deprotonated salphen ligand and the
seven-membered N-methylhomopiperazine adopts
a ship-
shape conformation locating above and below the salphen
plane (Figure 1), as we expected that the coordinatively un-
saturated metal center can activate the epoxides ring, mean-
while the tertiary amine of N-methylhomopiperazine attacks
the less-hindered carbon atom of the coordinated epoxide.
The activity of various catalysts was tested at 1008C and
2 MPa of CO2 pressure using the cycloaddition reaction of pro-
pylene oxide (PO) with CO2 with 1 mol% catalyst loading. The
yield and selectivity were determined by using gas chromatog-
raphy (GC), and in all examined cases, the selectivity for five-
membered cyclic propylene carbonate (PC) was higher than
99%. Firstly, we found that the PC could be obtained in excel-
lent yields in the presence of ZnII salphen complexes (Table 1,
entries 1 and 4), whereas moderate and lower yields were ach-
ieved in the presence of CuII and NiII salphen complexes under
the same conditions, respectively. This is in accordance with
that ZnII ion in salphen complexes shows increased Lewis-acid
behavior as a result of the constrained geometry imposed by
the ligand scaffold.[4i,10] It should be note that the introduction
of electron-withdrawing group (Br) in the both phenyl sides of
the salphen ligand scaffold turned out to give almost the same
activity (Table 1, entries 1–6). Hence, the catalytic activity of
this kind of catalyst is closely related with the metal center not
the electronic effect of ligand; a recent study also reported
that the catalyst containing a zinc ion was the most active for
CO2 coupling with epoxide owing to its high activity.[4e] For
a better understanding of the role of the tertiary amine moiet-
ies in seven-membered N-methylhomopiperazine, the control
complexes 2a–2c without N-methylhomopiperazine were also
prepared for comparison (Scheme 2). If only 2a–2c or N-meth-
ylhomopiperazine was used as catalyst, no reaction occurred
(entries 7–10), illustrating that the coexistence of organic base
and M(salphen) is essential to promote this reaction. On the
contrary, the binary catalyst system of 2a–2c and N-methylho-
Figure 1. X-ray single crystal structure of 1e. Thermal ellipsoids for the non-
hydrogen atoms are drawn at the 30% probability level. All hydrogen atoms
are omitted for clarity. a) View down crystallographic c axis. b) View down
crystallographic a axis.
mopiperazine in a molar ratio of 1/2 also gave PC in moderate
yields under the same conditions (entries 11–13). The rationale
behind this is the ability of these Lewis acidic complexes to
self-dimerize and thus make the coordination of the substrate
to the metal catalytic center a competitive process. An accu-
rate study on Zn(salphen) self-assembly has been previously
reported and shows that the extent of its strength is depen-
dent on the location and combination of the aromatic ring
substituents.[11] However, as expected in our catalysts 1a–1 f,
two bulky N-methylhomopiperazine locating above and below
the salphen plane (Figure 1b) not only inhibit the intermolecu-
lar self-assembly behavior, but also provide efficient organic
base nucleophile into one structure. On the basis of the above
results, we suggest that the Lewis base and Lewis acid of 1a
(or 1d) work together to open the epoxy ring and then react
with CO2 to give PC via a ring-opening and recyclization pro-
cess, and therefore the conclusion should be that bifunctionali-
ty pays off as there is higher conversion. This is not the same
mechanism in the reported binary catalytic systems composed
of binaphthyladiamion M(salen)-type complexes and triethyla-
mine.[4l] Importantly, PC can be easily separated from 1a (or
&
ChemCatChem 0000, 00, 0 – 0
www.chemcatchem.org
2
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Communications
Besides the catalyst activity, the sustainability and recycling
potential are also decisive criteria for possible large-scale appli-
cation. Therefore, recyclability studies of 1a (or 1d) were per-
formed to evaluate the sustainability of the catalyst. After each
run, 1a (or 1d) could easily be precipitated from the PC solu-
tion by the addition of diethyl ether. After filtration, another
batch of PO was added and the next catalytic run was started.
The results of the recycling experiments showed no obvious
decrease in activity of the catalyst after being used five times
(entries 20 and 21). Furthermore, the catalyst recovered from
the catalytic reaction exhibited the almost same chemical com-
position as the freshly prepared 1a (or 1d), unambiguously
supporting the stability of the catalyst during the catalytic re-
actions.
Table 1. Results of the cycloaddition reaction of propylene oxide (PO)
with CO2 in the presence of various catalysts.[a]
Entry
Catalyst
T [8C]
t [h]
Yield[b] [%]
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1 f
2a
2b
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
25
4
4
4
4
4
4
4
4
4
4
4
4
4
1
2
4
4
4
12
3
3
92
68
27
90
70
32
<5
<5
<5
<5
65
45
22
26
65
0
9
2c
10
11
12
13
14
15
16
17
18[d]
19[d]
20[e]
21[e]
base[c]
2 a +base[c]
2b+base[c]
2c+base[c]
Under optimized reaction conditions, we next examined the
chemical fixation reaction of the other epoxides with CO2
using 1a and 1d, respectively. The results are summarized in
Table 2. It is very clear that, electron-withdrawing and electron-
1a
1a
1a
1a
1a
1a
1a
1d
80
56
52
65
83
78
100
100
100
100
Table 2. Reactions of other epoxides with CO2 catalyzed by 1a and 1d.[a]
Entry
Epoxide
Catalyst
Yield[b] [%]
[a] General reaction conditions: 10 mL stainless-steel autoclave, PO
(10 mmol), catalyst (0.1 mmol), CO2 pressure (2 MPa), [b] The yields were
determined by GC with an internal standard. [c] Base is N-methylhomo-
piperazine, [d] The CO2 pressure is 1 MPa, [e] The catalyst after being
used five times.
1
2
1a
1d
85
84
3
4
5
6
1a
1d
1a
1d
99
98
96
92
7
8
1a
1d
78
73
1d) with diethyl ether. While using 2a and N-methylhomo-
piperazine as co-catalysts, PC can be only separated by distilla-
tion, owing to the good solubility of N-methylhomopiperazine
in the solution of PC. This is a highly energetic process be-
cause of the high boiling point of PC and, therefore, has a neg-
ative effect on the carbon footprint of the reaction. Conse-
quently, 1a (or 1d) offers the possibility of a sustainable
system for the chemical fixation of CO2.
9
10
1a
1d
75
76
11
12
1a
1d
35
30
[a] Reaction conditions: epoxide (10 mmol), catalyst (0.1 mmol), CO2 pres-
sure (2 MPa), reaction temperature (1008C), reaction time (4 h). [b] The
yields were determined by GC with an internal standard.
The reaction time, reaction temperature and CO2 pressure
are important factors for the yields of PC. In a short reaction
period of only 1 h at 1008C, for example, PC is obtained in
only 26% (entries 14). When reaction time was extended to
8 h, a yield of 95% is reached, a very small amount of increase
of the yield compared to that in the reaction time of 4 h. Then
the influence of the temperature on the conversion was also
investigated. By reducing the temperature from 100 to 808C,
the yield of PO decreased drastically from 92 to 56% (en-
tries 17), and no reaction could take place at room tempera-
ture (entries 16). In addition, the yield of PC decreased as CO2
pressure decreased from 2 to 1 MPa (entries 18), even increas-
ing this reaction time to 12 h, only 65% of PC was obtained
(entries 19). It is known that lower CO2 pressure could reduce
the solubilization effect of CO2 in the solution of PO; in turn,
the yield was decreased.[12] The catalyst loading was not ex-
plored in our experiments because of the easy recyclability of
1a (or 1d). Finally, the best reaction conditions involve the 1a
(or 1d) (1 mol%) at 1008C under a high pressure of CO2
(2 MPa) for 4 h.
donating terminal epoxides can be converted to the corre-
sponding cyclic carbonates in good yields. In all experiments,
cyclic carbonates are the sole products. The very good conver-
sions of epichlorohydrin and glycidol (Table 2, entries 5–8) can
be explained by the electron-withdrawing substituents.[13]
These substituents result in facilitated nucleophilic attack of
the N-methylhomopiperazine during the ring opening of the
epoxide. Unfortunately, the internal epoxide, cyclohexene
oxide, which is known to undergo cycloaddition with CO2
poorly, is converted to the corresponding cyclic carbonate
with a yield of 35 and 30% by catalyst 1a and 1d (entries 11
and 12), respectively, presumably due to the high steric hin-
drance.[6a]
In conclusion, we explored a new bifunctional Zn(salphen)
catalysts with an organic base N-methylhomopiperazine as nu-
cleophile for the production of cyclic carbonates from CO2 and
epoxides. The notable features of our protocol include the use
of an abundant, non-toxic metal (Zn) and the ease of synthesis
of the bifunctional catalysts compared with previous ionic bi-
ChemCatChem 0000, 00, 0 – 0
www.chemcatchem.org
3
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ

Communications
[4] a) C. Martꢂn, C. J. Whiteoak, E. Martin, M. M. Belmonte, E. C. Escudero-
Adꢃn, A. W. Kleij, Catal. Sci. Technol. 2014, 4, 1615–1621; b) W. M. Ren,
Y. Liu, X. B. Lu, J. Org. Chem. 2014, 79, 9771–9777; c) R. C. Luo, X. T.
Zhou, S. Y. Chen, Y. Li, L. Zhou, H. B. Ji, Green Chem. 2014, 16, 1496–
1506; d) F. Castro-Gꢄmez, G. Salassa, A. W. Kleij, C. Bo, Chem. Eur. J.
2013, 19, 6289–6298; e) D. W. Tian, B. Y. Lium, Q. Y. Gan, H. R. Li, D. J.
Darensbourg, ACS Catal. 2012, 2, 2029–2035; f) A. Decortes, A. W. Kleij,
ChemCatChem 2011, 3, 831–834; g) R. M. Haak, A. Decortes, E. C. Escu-
dero-Adan, M. M. Belmonte, E. Martin, J. Benet-Buchholz, A. W. Kleij,
Inorg. Chem. 2011, 50, 7934–7936; h) A. Decortes, M. M. Belmonte, J.
Benet-Buchholz, A. W. Kleij, Chem. Commun. 2010, 46, 4580–4582;
i) A. W. Kleij, Dalton Trans. 2009, 4635–4639; j) P. Yan, H. W. Jing, Adv.
Synth. Catal. 2009, 351, 1325–1332; k) H. W. Jing, S. K. Edulji, J. M.
Gibbs, C. L. Stern, H. Y. Zhou, S. T. Nguyen, Inorg. Chem. 2004, 43, 4315–
4327; l) Y. M. Shen, W. L. Duan, M. Shi, J. Org. Chem. 2003, 68, 1559–
1562.
[5] a) T. Ema, Y. Miyazaki, J. Shimonishi, C. Maeda, J. Hasegawa, J. Am.
Chem. Soc. 2014, 136, 15270–15279; b) D. S. Bai, S. H. Duan, L. Hai,
H. W. Jing, ChemCatChem 2012, 4, 1752–1758; c) T. Ema, Y. Miyazaki, S.
Koyama, Y. Yano, T. Sakai, Chem. Commun. 2012, 48, 4489–4491.
[6] a) M. H. Anthofer, M. E. Wilhelm, M. Cokoja, M. Drees, W. A. Herrmann,
F. E. Kꢅhn, ChemCatChem 2015, 7, 94–98; b) K. R. Roshan, A. C. Kathalik-
kattil, J. Tharun, D. W. Kim, Y. S. Won, D. W. Park, Dalton Trans. 2014, 43,
2023–2031; c) Z. Wu, H. Xie, X. Yu, E. Liu, ChemCatChem 2013, 5, 1328–
1333; d) J. Q. Wang, K. Dong, W. G. Cheng, J. Sun, S. J. Zhang, Catal. Sci.
Technol. 2012, 2, 1480–1484; e) J. A. Li, L. G. Wang, F. Shi, S. M. Liu, Y. D.
He, L. J. Lu, X. Y. Ma, Y. Q. Deng, Catal. Lett. 2011, 141, 339–346.
[7] Y. Du, F. Cai, D. L. Kong, L. N. He, Green Chem. 2005, 7, 518–523.
[8] a) S. F. Baj, T. Krawczyk, K. Jasiak, A. Siewniak, M. Pawlyta, Appl. Catal. A
2014, 488, 96–102; b) S. D. Lee, B. M. Kim, D. W. Kim, M. I. Kim, K. R.
Roshan, M. K. Kim, Y. S. Won, D. W. Park, Appl. Catal. A 2014, 486, 69–
76; c) T. Takahashi, T. Watahiki, S. Kitazume, H. Yasuda, T. Sakakura,
Chem. Commun. 2006, 1664–1666; d) T. Sakai, Y. Tsutsumi, T. Ema,
Green Chem. 2008, 10, 337–341; e) Y. Xie, Z. Zhang, T. Jiang, J. He, B.
Han, T. Wu, K. Ding, Angew. Chem. Int. Ed. 2007, 46, 7255–7258; Angew.
Chem. 2007, 119, 7393–7396.
functional systems. More importantly, the catalysts used in this
catalytic system are extremely stable and can be recycled at
least five times and their activity is almost unchanged. Efforts
are underway to elucidate the mechanistic details of the reac-
tion and explore the catalytic activities of other trivalent metal
complexes with this bifunctional ligand.
Experimental Section
General catalytic procedure: A 10 mL stainless steel reactor was
added with catalyst (0.1 mmol) and a magnetic stirring bar. Then
the epoxide (10.0 mmol) was added and the steel reactor was
charged under a constant pressure of CO2 (2 MPa) for 1 min and
heated to the desired temperature. After reaction completion, the
reactor was cooled down to 08C and the excess CO2 was released
carefully. The reaction mixture was collected by adding 5 mL of
chloroform and a sample was taken for GC analysis (using 1,3,5-tri-
methylbenzene as an internal standard) to determine yield and se-
lectivity.
For recycling studies of catalyst 1a (or 1d), propylene carbonate
was separated from the catalyst by adding ether. The catalyst pre-
cipitates was recovered by centrifugation. Afterwards, the catalyst
was dried at 508C for 6 h in vacuo. By adding the same amount of
epoxide (10.0 mmol), the next catalytic run was started.
Acknowledgements
We are grateful to the National Natural Science Foundation of
China (Nos. 21372087 and 21172076), the National Basic Re-
search Program of China (No. 2011CB808600), and the Natural
Science Foundation of Guangdong Province, China (No.
10351064101000000) for the financial support.
[9] a) Y. W. Ren, X. F. Chen, S. R. Yang, C. R. Qi, H. F. Jiang, Q. P. Mao, Dalton
Trans. 2013, 42, 9930–9937; b) Y. W. Ren, Y. C. Shi, J. X. Chen, S. R. Yang,
C. R. Qi, H. F. Jiang, RSC Adv. 2013, 3, 2167–2170.
[10] E. C. Escudero-Adꢃn, J. Bene Buchholz, A. W. Kleij, Chem. Eur. J. 2009, 15,
4233–4237.
Keywords: CO2 fixation · cyclic carbonate · homogeneous
catalysis · salphen · zinc
[11] a) J. A. A. W. Elemans, S. J. Wezenberg, E. C. Escudero-Adꢃn, J. Benet-
Buchholz, D. den Boer, M. J. J. Coenen, S. Speller, A. W. Kleij, S. De Feyter,
Chem. Commun. 2010, 46, 2548–2550; b) M. Martꢂnez Belmonte, S. J.
Wezenberg, R. H. Haak, D. Anselmo, E. C. Escudero-Adꢃn, J. Bene Buch-
holz, A. W. Kleij, Dalton Trans. 2010, 39, 4541–4550.
[12] Y. N. Zhao, Z. Z. Yang, S. H. Luo, L. N. He, Catal. Today 2013, 200, 2–8.
[13] a) M. Ulusoy, E. Cetinkaya, B. Cetinkaya, Appl. Organomet. Chem. 2009,
23, 68–74; b) A. Kilic, A. A. Palali, M. Durgun, Z. Tasci, M. Ulusoy, Spectro-
chim. Acta Part A 2013, 113, 432–438.
[1] a) P. Lanzafame, G. Centi, S. Perathoner, Chem. Soc. Rev. 2014, 43, 7562–
7580; b) N. J. English, M. M. EI-hendawy, D. A. Mooney, J. M. D. MacElroy,
ˇ
Coord. Chem. Rev. 2014, 269, 85–95; c) Z. Tas¸ci, A. Kunduracioglu, I.
Kani, B. C¸etinkaya, ChemCatChem 2012, 4, 831–835; d) R. Angamuthu,
P. Byers, M. Lutz, A. L. Spek, E. Bouwman, Science 2010, 327, 313–315.
[2] a) M. Petrowsky, M. Ismail, D. T. Glatzhofer, R. Frech, J. Phys. Chem. B
2013, 117, 5963–5970; b) B. Schꢁffner, F. Schꢁffner, S. P. Verevkin, A.
Bçrner, Chem. Rev. 2010, 110, 4554–4581; c) A. Decortes, A. M. Castilla,
A. W. Kleij, Angew. Chem. Int. Ed. 2010, 49, 9822–9837; Angew. Chem.
2010, 122, 10016–10032.
[3] a) X. Zhou, Y. Zhang, X. G. Yang, J. Yao, G. Y. Wang, Chin. J. Catal. 2010,
31, 765–768; b) S. R. Jagtap, M. J. Bhanushali, A. G. Panda, B. M. Bhan-
age, Catal. Lett. 2006, 112, 51–55.
Received: February 6, 2015
Published online on && &&, 0000
&
ChemCatChem 0000, 00, 0 – 0
www.chemcatchem.org
4
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

COMMUNICATIONS
Bifunctional catalysts: A new type of
Lewis acid–base bifunctional
Y. Ren, J. Chen, C. Qi, H. Jiang*
&& – &&
Zn(salphen) catalysts with an organic
base, N-methylhomopiperazine, as
a nucleophile were prepared by a one-
pot method and successfully applied in
the production of cyclic carbonates
from CO2 and epoxides. The catalysts
used in this catalytic system are ex-
tremely stable and can be recycled at
least five times and their activity is
almost unchanged.
A New Type of Lewis Acid–Base
Bifunctional M(salphen) (M=Zn, Cu
and Ni) Catalysts for CO2 Fixation
ChemCatChem 0000, 00, 0 – 0
www.chemcatchem.org
5
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ