Cycloaddition of carbon dioxide and epoxides catalyzed by rare earth metal complexes bearing a Trost ligand

Article abstract of DOI:10.1039/d1nj02460d

A series of rare earth metal complexes (Sm (1), Eu (2), Y (3), Yb (4), and Lu (5)) based on Trost ligands were synthesized and well characterized, and catalyzed the cycloaddition of carbon dioxide and epoxides successfully. The combination of 1 mol% Sm-based complex1with 2 mol% tetrabutylammonium bromide (TBAB) was proved to be the optimal catalyst system for the formation of the monosubstituted cyclic carbonate at 70 °C under the atmospheric pressure. While for the more challenging disubstituted epoxides, the adduct cyclic carbonates were successfully obtained when the pressure of CO₂was elevated to 0.7 MPa.

Full text of DOI:10.1039/d1nj02460d

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Cycloaddition of carbon dioxide and epoxides
catalyzed by rare earth metal complexes bearing a
Trost ligand†
Cite this: New J. Chem., 2021,
45, 13096
Jun Cheng, Chengrong Lu* and Bei Zhao
*
A series of rare earth metal complexes (Sm (1), Eu (2), Y (3), Yb (4), and Lu (5)) based on Trost ligands
were synthesized and well characterized, and catalyzed the cycloaddition of carbon dioxide and
epoxides successfully. The combination of
1
mol% Sm-based complex
1
with
2
mol%
Received 19th May 2021,
Accepted 14th June 2021
tetrabutylammonium bromide (TBAB) was proved to be the optimal catalyst system for the formation of
the monosubstituted cyclic carbonate at 70 1C under the atmospheric pressure. While for the more
challenging disubstituted epoxides, the adduct cyclic carbonates were successfully obtained when the
pressure of CO2 was elevated to 0.7 MPa.
DOI: 10.1039/d1nj02460d
rsc.li/njc
compounds to catalyze the cycloaddition of mono- and disubstituted
epoxides and CO2 at atmospheric CO2 pressure, and room
Introduction
In recent years, global warming has caused more and more temperature to 75 1C.6f Capacchione et al. used [OSSO]-type
serious environmental disasters, such as an abnormal climate, iron(III) complexes as catalysts, tetrabutylammonium bromide
melting of glaciers and rising sea levels. The latest research (TBAB) as a co-catalyst, and variously substituted epoxides were
shows that human activities have pushed today’s CO2 content selectively converted into the corresponding cyclic carbonates
in the atmosphere to the highest level during the past 23 at 35 1C under 0.1 MPa CO2.12e Dai et al. reported the conversion
million years, which has exceeded the absorption and conversion of CO2 to cyclic carbonates under ambient conditions (room
capacity of nature. Carbon capture, storage and utilization are the temperature, 0.1 MPa CO2) with highly reactive one-component
main strategies to achieve a carbon neutral status. The utilization organocatalysts – a series of pincer-type compounds possessing
of CO2, a kind of abundant, non-toxic and renewable C1 resource, an N-heterocyclic carbene precursor.13e However, among the
is of great significance in green and sustainable development. The published studies, some harsh reaction conditions were required,
chemical conversion of CO2 has potential economic benefits, such as a relatively high catalyst loading (45 mol%),13a,c
a
since many high value-added products are obtained from relatively higher temperature (4100 1C),5a,13g and a high pressure
CO2.1–3 The cycloaddition reaction of CO2 with epoxides, a (41 MPa).5a,b,6a,b,d,12c,d,13b
commonly used reaction for the chemical conversion of CO2,
Rare earth metals have unique electronic structures, a
has aroused great interest because of its 100% atom efficiency strong oxygen affinity, and high Lewis acidity. Several rare earth
and the biocompatible and biodegradable products— metal complexes containing nitrogen or oxygen proligands were
carbonates.4 A number of catalysts have been developed for synthesized, which showed high reactivities in the cycloaddition
the cycloaddition reactions, including main-group metal reaction of CO2 and epoxide.14 Yao and coworkers developed the
complexes (e.g., Mg,5 Al,6 Ca,7 and Li8), transition-metal first rare earth metal complex bearing a poly(phenolato) ligand
complexes (e.g. Cr,9 Co,10 Zn,11 and Fe12) and organocatalysts.13 to catalyze the cycloaddition reaction of monosubstituted
For example, Kim and coworkers employed dimeric aluminum epoxides under mild conditions (85 1C and 0.1 MPa CO2) in
the presence of tetrabutylammonium iodide (TBAI). Meanwhile,
under 1 MPa CO2, the same catalyst system is good for
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry,
disubstituted epoxides.14a Furthermore, the polyphenol
Chemical Engineering and Materials Science, Dushu Lake Campus,
Soochow University, Suzhou 215123, People’s Republic of China.
E-mail: zhaobei@suda.edu.cn
proligands were modified by changing one of the substituents
on the nitrogen from phenol to a smaller noncoordinating methyl
group, and the desired rare earth metal complexes were synthe-
sized to show excellent catalytic activity in the cycloaddition
reaction of carbon dioxide with epoxides under ambient
conditions, especially in the conversion of disubstituted epoxides
† Electronic supplementary information (ESI) available: Solid state structures,
NMR spectra, and crystallographic data. CCDC 2075317 (complex 1), 2075330
(complex 2), 2074336 (complex 3), 2075334 (complex 4) and 2075318 (complex 5).
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/d1nj02460d
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(room temperature, 0.1 MPa CO2).14f Around the same time,
Otero’s group developed a novel lanthanum heteroscorpionate
catalyst, which showed exceptional catalytic activity for the synthesis
of cyclic carbonates with a low catalyst loading (0.05–0.5 mol%).14c
Different ligands lead to different chemical behaviors of the
corresponding metal complexes, so one of the strategies for
adjusting the effects of the metal-based catalysts is to change
the ligands. In view of the excellent catalytic activity of rare
earth metal complexes, a new type of rare earth metal dichloride
supported by a Trost proligand – an easier to obtain [ONONO]
proligand – was prepared and characterized, and further
investigations of the catalytic reactivities in the cycloaddition
reaction of CO2 and epoxides were conducted.
Fig. 1 Solid-state structure of complex 1 showing 30% probability thermal
ellipsoids; for clarity, all other hydrogen atoms and solvent molecules are
omitted except for alcoholic hydroxyl hydrogen. Selected bond lengths [Å]
and bond angles [deg]: Sm1–O1 2.232(12), Sm1–O2 2.171(19), Sm1–
O3 2.198(17), Sm1–O4 2.466(12), Sm1–Cl1 2.737(6), and Sm1–Cl2 2.739(7);
O1–Sm1–O2 84.4(6), O1–Sm1–O3 86.0(6), O1–Sm1–O4 175.4(6), O2–
Sm1–O3 170.4(5), O1–Sm1–Cl1 93.2(4), O1–Sm1–Cl2 94.7(4), O4–Sm1–
Cl1 87.7(4), and O4–Sm1–Cl2 84.4(4).
Results and discussion
Synthesis of complexes 1–5
According to previous work, a Trost proligand with a semicrown
structure was prepared using the commercially available
prolinol.15 Metathesis reaction of the Trost proligand with rare
earth metal precursors RE[N(SiMe3)2]Cl2 proceeded readily in
THF at room temperature and gave the corresponding rare
earth metal dichlorides 1–5 in high yields of 65–90%
(Scheme 1). The solid-state structures of complexes 1–5 were
characterized by X-ray diffraction analysis, and were determined
to be monomeric and isomorphic. Taking complex 1 as an
example (Fig. 1), the central metal samarium is six-coordinated
with two chlorine atoms and four oxygen atoms, which come
from the Trost ligand and a coordinated THF molecule. The
samarium atom is bonded in three ways, namely, a metal–
aryloxy s bond, a metal–alkoxy coordinate bond and a metal–
chlorine s bond. The average bond length of phenolato–Sm
bonds is 2.232(12) Å, similar to the data reported in the complex
[SmL2]{[(THF)3Li]2(m-Cl)} (H2L = (S)-2,4-di-tert-butyl-6-[[2-(hydroxy-
diphenylmethyl)pyrrolidinlyl]methyl]pheno) (2.239(5), 2.231(4) Å).16a
Considering the difference between the radius of the Sm(III) ion
and the Yb(III) ion, the bond lengths of Sm–alkoxy coordinate
bonds of 2.171(19) Å and 2.198(17) Å are comparable to the same
kind of Yb–O bond length (2.067(5) Å) of the complex [LYb(LH)].16b
The average bond length of Sm–Cl bonds in complex 1 (2.738 Å)
is longer than that of SmCl3(THF)4 (2.683 Å). On account of
the observation of a peak at 3377 cmÀ1, which is ascribed to the
stretching vibration of the hydroxyl O–H bond (Fig. 2), and the
acidity differences between the alcoholic hydroxyl and phenolic
Fig. 2 IR spectrum of complex 1.
hydroxyl groups, the retaining of alcoholic hydroxyl hydrogen
atoms in complex 1 was confirmed.
Catalytic reactivities
With the rare earth metal complexes 1–5 in hand, the cycload-
dition of CO2 and epoxides was investigated. Using epichloro-
hydrin 6a as the template substrate, the addition reaction with
CO2 was conducted neat under atmospheric pressure in the
presence of 1 mol% of the catalyst and 2 mol% of the co-
catalyst. The results are listed in Table 1.
All the complexes catalyzed the cyclic addition of CO2 to
epichlorohydrin at room temperature, when tetrabutylammonium
bromide (TBAB) acted as the co-catalyst. The decreasing order of
reactivity of complexes 1–5 complied with the decreasing ionic
radius (Sm(III) 4 Eu(III) 4 Y(III) 4 Yb(III) 4 Lu(III)), and complex 1
showed the highest reactivity (Table 1, entries 1–5). This is
Scheme 1 Synthesis of rare earth metal complexes 1–5.
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Table 1 Screening of the catalytic conditions of the cycloaddition of CO2
with epichlorohydrin 6aa
Table 2 Cycloaddition of monosubstituted terminal epoxides and CO2
catalyzed by complex 1 and TBABabc
Entry
Cat.
Co-cat.
T/1C
Conv.bc/%
1
2
3
4
5
6
7
8
1
2
3
4
5
—
1
1
1
1
1
1
1
1
—
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAI
TBAC
PPNCl
DMAP
TBAB
TBAB
TBAB
TBAB
TBAB
25
25
25
25
25
25
25
25
25
25
50
60
70
70
70
65
42
36
34
30
16
60
45
49
60
75
92
499
95
9
10
11
12
13
14d
15
62
a
Reaction conditions: 1 mol% catalyst and 2 mol% co-catalyst, for 24 h.
b
c
Determined by 1H NMR spectroscopy. Selectivities for the cyclic
d
carbonate products are all 499%. 18 h.
consistent with the previously reported pattern, that is, rare earth
metal complexes of larger ionic radii showed higher reactivities,
attributed to the larger open coordination sphere suitable for
substrate binding.8a,b,d Different co-catalysts, tetrabutylammonium
chloride (TBAC), bis(triphenylphosphine)iminium chloride
(PPNCl), and 4-dimethylaminopyridine (DMAP) were also tested,
and TBAB was proved to be the best performer (Table 1, entries
7–10). The decreasing reactivities, BrÀ 4 IÀ 4 ClÀ, were observed,
presumably because of the balanced nucleophilicity and leaving
ability of the bromide anion. The reaction time and temperature
were screened subsequently (Table 1, entries 11–14). When the
reaction temperature was raised to 70 1C, quantitative conversion of
epichlorohydrin was achieved after 24 h (Table 1, entry 13). The
a
Reaction conditions: 0.02 mmol complex 1, 0.04 mmol TBAB, 70 1C,
b
c
24 h, 0.1 MPa CO2 pressure, neat. Isolated yield. Selectivities for the
d
cyclic carbonate products are all 499%. Without complex 1, deter-
mined by 1H NMR spectroscopy. 40 h.
e
For epoxides with different alkyloxy substituents, the corres-
yield of carbonate 7a was slightly deceased to 95% if the reaction ponding cyclic carbonates 7h–7k were produced in excellent
time was shortened to 18 h (Table 1, entry 14). Meanwhile, TBAB yields, too, even including the ether subunit containing a
itself was found to have a catalytic effect on the reaction without double or triple bond (7l and 7m). The epoxide containing
the morpholine ring yielded 89% of the cycloaddition product 7o;
meanwhile, the morpholine ring is maintained. Unfortunately,
complex 1. The conversion of epichlorohydrin was 16% at room
temperature and 62% at 70 1C (Table 1, entries 6 and 15). However,
it is undeniable that the improvement was significant when the for sterically hindered substrates, such as glycidyl 4-tert-
combination catalysis of complex 1 and TBAB was tested (Table 1, butylbenzoate, the yield of the corresponding cyclic ester 7p
entries 1 vs. 6, and entries 13 vs. 15). Thus, the optimal conditions is only 42%. When a binary monosubstituted epoxy subunit in
were confirmed as follows: 1 mol% catalyst 1, 2 mol% co-catalyst one molecule, such as 1,2,7,8-diepoxyoctane (6q), was tested,
TBAB, 70 1C, 24 h, and 0.1 MPa CO2.
the cycloaddition occurred at both sides in 65% yield.
To study the scope of the cycloaddition, a series of mono- Furthermore, when the reaction time was prolonged to 40 h,
the yield was increased to 93%. It is of note that substrate 6r, a
compound with a monosubstituted epoxy group together with a
substituted terminal epoxides were examined, and the results
are summarized in Table 2. In addition to the template substrate
epichlorohydrin 6a, simple monosubstituted epoxy compounds 1,2-disubstitued epoxy group, undergoes cycloaddition with
such as epibromohydrin, propylene oxide and 1,2-epoxyhexane CO2 only at the monosubstituted side under the current
(6b–6e) achieved quantitative conversion under the optimal conditions. This indicates that the cycloaddition of the
conditions. When the alkyl group of the epoxide contains a disubstituted epoxide is more challenging. In order to test
double bond (6f), the cycloaddition reaction is also carried out again the necessity of complex 1, the cycloaddition of CO2 with
smoothly, and the yield of cyclocarbonate 7f is as high as 99%. 6g or 6r using TBAB as the catalyst was carried out, respectively.
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Table 3 Cycloaddition of disubstituted epoxides with CO2 catalyzed by
complex 1 and TBABab
Fig. 3 Recycling of complex 1. Reaction conditions: complex 1 (1 mol%),
TBAB (2 mol%), CO2 (0.1 MPa), 70 1C, and 24 h. Conversion of cyclic
carbonate 7a was determined by 1H NMR spectroscopy.
the next catalytic cycle. As shown in Fig. 3, complex 1 was
reused for three successive cycles with a negligible decline of
the conversion of 6a, from 99% to 95%, until the fourth cycle,
which showed a significant decrease in conversion to 86%.
a
Kinetic study
Reaction conditions: 0.06 mmol complex 1, 0.12 mmol TBAB, 70 1C,
b
24 h, 0.7 MPa CO2, neat. Isolated yield.
We conducted a kinetic study to further understand the catalytic
behavior of complex 1 for the cycloaddition reaction of epoxides
and CO2, using epichlorohydrin 6a as a model substrate and
1H NMR monitoring for 12 h (Fig. 4). The kinetic study showed
that the reaction has a first-order relationship between substrate
conversion and time, highlighting the catalyst stability under the
reaction conditions tested.
As expected, the outcomes were very poor, at 20% for 7g and a
trace amount for 7r.
Subsequently, in order to realize the cycloaddition of
disubstituted epoxides with CO2, new catalytic conditions were
investigated. To our delight, by only elevating the CO2 pressure
to 0.7 MPa, the template substrate cyclohexene oxide 8a was
converted to the corresponding cyclic carbonate 9a in 80%
yield. The substrate scope of the disubstituted epoxides was
carried out and the results are listed in Table 3. The outcomes of
both geminal and adjacent disubstituted epoxides are satisfactory.
ortho-Disubstituted epoxides, such as 1,2-epoxy-4-vinyl cyclohexane
epoxy cyclopentane and 3,4-tetrahydrofuran epoxides, produced
the corresponding cyclic carbonates (9b–9d) in high yields
(80–89%). For gem-disubstituted epoxides, the yields of cyclic
carbonates (9e and 9f) are even better than those of the ortho-
disubstituted substrates under the same conditions. Compared
with those of the reported rare earth metal complexes, the
catalytic reactivities of the rare earth metal complexes bearing
the Trost ligand have not been significantly improved, and the
conditions for the synthesis of cyclic carbonates are similar to
those of the rare earth metal phenolates reported by Yao’s
group.14a,b
Fig. 4 Plot of ([6a]0/[6a]) against time. Reactions were carried out at 70 1C
neat in the presence of 0.1 MPa CO2 with 0.04 mmol TBAB and 0.02 mmol
complex 1. ([6a]0, initial concentration of epichlorohydrin 6a; [6a], the
concentration of 6a.).
Catalyst recycling
Mechanism
In the cycloaddition reaction of CO2 and epoxide, the recycl- Based on previous reports on the formation mechanism of
ability of the catalyst is one of the important parameters to cyclic carbonates17 and the present results, a possible mechanism
evaluate the performance of the catalyst. To better understand for the current system is proposed (Scheme 2). The epoxide is
the stability of the catalyst during the reaction, the recyclable activated by the samarium center of catalyst 1, and the bromide
reaction of epichlorohydrin 6a and CO2 catalyzed by complex 1 anion in TBAB subsequently attacks the less hindered side of
was investigated under atmospheric pressure using TBAB as the the epoxide to generate the terminal alkoxide (A). Carbon
co-catalyst. The product was isolated by vacuum distillation dioxide then inserts into the Sm–O bond, forming carbonate
after 24 h; subsequently, the catalyst was separated ready for intermediate (B). Finally, the cyclic carbonate is formed by
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vacuum, the solid residue was washed with hexane to remove
HN(SiMe3)2. Crystals were obtained at room temperature from
a solution in a mixed solvent of DCM and THF.
Characteristic data of complexes 1–5
H2LSmCl2ÁTHF (1). Colorless crystals, 0.71 g, yield 77%; IR
(KBr, cmÀ1) n 3381, 2960, 1477, 1448, 1382, 1066, 883, 748, 703;
anal. calcd for C47H53Cl2N2O4SmÁTHF: C, 60.62; H, 5.74; N,
3.01. Found: C, 60.54; H, 5.69; N, 2.90.
H2LEuCl2Á2THF (2). Colorless crystals, 0.60 g, yield 65%; IR
(KBr, cmÀ1) n 3381, 2972, 1479, 1450, 1380, 1043, 875, 752, 705;
anal. calcd for C47H53Cl2N2O4EuÁ2THF: C, 60.96; H, 6.12; N,
2.79. Found: C, 61.32; H, 6.13; N, 2.86.
Scheme 2 Proposed mechanism cycle for carbonate synthesis catalyzed
by complex 1.
H2LYCl2ÁTHF (3). Colorless crystals, 0.71 g, yield 82%;
1H NMR (400 MHz, DMSO-d6) d 7.96 (d, J = 7.8 Hz, 1H, ArH),
7.69 (d, J = 7.4 Hz, 4H, ArH), 7.58 (d, J = 7.8 Hz, 3H, ArH), 7.22
(m, 8H, ArH), 7.03 (m, 4H, ArH), 6.65–6.32 (m, 2H, ArH), 5.48 (s,
1H, OH), 4.07–3.68 (m, 2H, NCH2Ar), 3.41 (m, 1H, NCH), 3.20
(m, 2H, CH2, NCH2Ar), 2.82 (m, 1H, NCH), 2.65 (m, 2H, NCH2),
2.25 (m, 2H, NCH2), 2.04 (m, 3H, CH3), 1.98–1.77 (m, 2H, CH2),
1.63 (m, 2H, CH2), 1.51–1.35 (m, 4H, CH2). 13C NMR (101 MHz,
DMSO-d6) d 160.0, 154.6, 153.1, 148.8, 148.0, 147.9, 128.5,
128.1, 127.2, 126.6, 126.4, 126.2, 125.8, 125.1, 124.8, 124.2,
120.3, 81.0, 78.9, 77.9, 76.2, 70.7, 57.1, 54.6, 30.0, 29.4, 24.1,
23.8, 20.8, 20.5, 20.1. IR (KBr, cmÀ1) n 3356, 2970, 1485, 1450,
1380, 1049, 881, 748, 707. Anal. calcd for C47H53Cl2N2O4YÁTHF:
C, 64.91; H, 6.14; N, 3.22. Found: C, 64.99; H, 6.22; N, 3.23.
H2LYbCl2ÁTHF (4). Colorless crystals, 0.85g, yield 90%; IR
(KBr, cmÀ1) n 3404, 2970, 1487, 1444, 1382, 1064, 879, 748, 705;
anal. calcd for C47H53Cl2N2O4YbÁTHF: C, 59.18; H, 5.60; N, 2.94.
Found: C, 58.82; H, 5.99; N, 2.55.
H2LLuCl2Á2THF (5). Colorless crystals, 0.76 g, yield 80%;
1H NMR (400 MHz, DMSO-d6) d 7.96 (d, J = 7.7 Hz, 1H, ArH),
7.69 (d, J = 7.5 Hz, 4H, ArH), 7.58 (d, J = 7.8 Hz, 3H, ArH), 7.27
(d, J = 7.5 Hz, 8H, ArH), 7.14–6.92 (m, 4H, ArH), 6.70–6.32 (m,
2H, ArH), 5.47 (s, 1H, OH), 4.08–3.68 (m, 2H, NCH2Ar), 3.44 (m,
1H, NCH), 3.20 (s, 2H, NCH2Ar), 2.86 (m, 1H, NCH), 2.70 (m,
2H, NCH2), 2.33–2.08 (m, 2H, NCH2), 2.05 (m, 3H, CH3), 1.98–
1.79 (m, 2H, CH2), 1.61 (m, 2H, CH2), 1.47 (m, 4H, CH2); 13C
NMR (101 MHz, DMSO-d6) d 160.4, 154.7, 153.1, 148.9, 147.9,
128.1, 127.3, 126.4, 124.2, 120.3, 70.9, 70.7, 57.1, 29.4, 24.1,
20.2; IR (KBr, cmÀ1) n 3384, 2970, 1487, 1448, 1382, 1074, 877,
750, 705; anal. calcd for C47H53Cl2N2O4LuÁ2THF: C, 59.59; H,
5.98; N, 2.73. Found: C, 59.38; H, 5.83; N, 3.01.
intramolecular nucleophilic attack, and complex 1 is released
for the next catalytic cycle.
Conclusions
In summary, a series of rare earth metal complexes (Sm (1), Eu
(2), Y (3), Yb (4), and Lu (5)) based on the Trost proligand were
prepared and well characterized. The investigation of the
catalytic reactivities in the cycloaddition reaction of carbon
dioxide with epoxides was carried out. Under mild conditions
(70 1C, 0.1 MPa CO2), Sm-based complex 1 showed excellent
reactivities in catalyzing the cycloaddition of CO2 and mono-
substituted terminal epoxides bearing different functional
groups in the presence of TBAB. Furthermore, disubstituted
epoxides were successfully transformed to the corresponding
cyclic carbonates at 70 1C, while elevation of pressure to 0.7
MPa CO2 is required. Recyclability tests of the catalytic system
and a kinetic study were conducted as well.
Experimental
Materials and instrumentation
All manipulations were performed under an argon atmosphere
using standard Schlenk techniques, except for ligand precursor
synthesis. Crystal data were collected on Gemini Atlas and Japan
Rigaku Saturn 724+ X-ray diffractometers. Structures were solved
and refined using the OLEX2 program. NMR (1H, 13C) spectra
were recorded using a Bruker Ascend 400 spectrometer. All the
epoxy compounds were purchased and dried with CaH2 and
distilled before use. Solvents, such as THF, DCM, and hexane,
were degassed and distilled over sodium benzophenone ketyl
before use. The Trost proligand was prepared according to
optimization of the literature methods.15
General procedure for cyclic carbonate synthesis under 0.1 MPa
CO2
In a typical experiment, complex 1 (18.6 mg, 0.02 mmol), TBAB
(12.8 mg, 0.04 mmol), and epichlorohydrin (156 mL, 2 mmol)
were added to a 5 mL flask equipped with a magnetic stirring
bar under argon. The round bottomed flask was then degassed
and filled with CO2. The mixture was heated at 70 1C for 24 h.
Experimental procedure
Synthesis of complexes 1–5. To a THF solution of the Trost After the reaction, a drop of the resulting mixture was analyzed
proligand (1 mmol), a solution of RE[N(SiMe3)2]Cl2 (1 mmol) in by 1H NMR spectroscopy to determine the yield and selectivity.
THF was added slowly. The mixture was stirred overnight at Conversion was determined through comparing the integration
room temperature. After THF had been removed under of the product and the yield. The analytically pure product was
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isolated
by
column
chromatography
(petroleum 5.70 (t, J = 8.0 Hz, 1H, OCH), 4.83 (t, J = 8.4 Hz, 1H, OCH2), 4.37
ether : ethyl acetate = 1 : 10) and confirmed by comparison with (t, J = 8.2 Hz, 1H, OCH2).
the literature data.4,6c,13h,14d–f
4-(Phenoxymethyl)-1,3-dioxolan-2-one (7h)6c. White solid,
380.3 mg, yield 99%;1H NMR (400 MHz, CDCl3) d 7.31 (m,
2H, ArH), 7.02 (m, 1H, ArH), 6.91 (m, 2H, ArH), 5.03 (m, 1H,
OCH), 4.66–4.50 (m, 2H, OCH2), 4.28–4.11 (m, 2H, OCH2).
4-((Benzyloxy)methyl)-1,3-dioxolan-2-one (7i)14e. Light yellow
General procedure for the cycloaddition of CO2 to epoxides
under 0.7 MPa CO2
Reactions were carried out in a 100 mL stainless steel Parr
reactor with a stirring bar inside and a needle valve for injection.
Complex 1 (93 mg, 0.1 mmol) and TBAB (64 mg, 0.2 mmol) were
dissolved in the epoxides. The reactor was pressurized to
0.7 MPa with CO2, and heated at 70 1C for 24 h. The analytically
pure product was isolated by column chromatography
(petroleum ether and ethyl acetate) and confirmed by comparison
of 1H NMR spectra with the literature data.6c,14f
1
liquid, 426.6 mg, yield 95%; H NMR (400 MHz, CDCl3) d 7.35
(m, 5H, ArH), 4.87–4.79 (m, 1H, OCH), 4.62 (m, 2H, OCH2),
4.54–4.36 (m, 2H, OCH2), 3.69 (m, 2H, OCH2).
4-(Propoxymethyl)-1,3-dioxolan-2-one (7j)14e. Light yellow
liquid, 334.2 mg, yield 96%; 1H NMR (400 MHz, CDCl3) d
4.80 (m, 1H, OCH), 4.49 (t, J = 8.4 Hz, 1H, OCH2), 4.42–4.36
(t, J = 7.2 Hz, 1H, OCH2), 3.67 (m, 1H, CH2O), 3.61 (m, 1H,
CH2O), 3.51 (t, J = 6.6 Hz, 2H, OCH2), 1.56 (m, 2H, CH2–CH2),
1.36 (m, 2H, CH2–CH2), 0.92 (t, J = 7.4 Hz, 3H, CH3).
Catalyst recycling study
4-(Methoxymethyl)-1,3-dioxolan-2-one (7k)6c. Light yellow
liquid, 261.6 mg, yield 99%; 1H NMR (400 MHz, CDCl3) d
4.87–4.79 (m, 1H, OCH), 4.50 (t, J = 8.4 Hz, 1H, OCH2), 4.41–
4.35 (t, J = 7.2 Hz, 1H, OCH2), 3.65 (m, 1H, OCH2O), 3.57 (m, 1H,
OCH2O), 3.43 (s, 3H, OCH3).
In a typical run, epichlorohydrin (185.0 mg, 2 mmol), complex 1
(18.6 mg, 0.02 mmol), and TBAB (12.8 mg, 0.04 mmol) were
placed in a Schlenk tube, to which a balloon charged with CO2
was connected. The reaction was heated at 70 1C for 24 h.
The resulting sample was analyzed using 1H NMR spectroscopy.
The product and reactant were separated from the catalytic
system by vacuum distillation under 110 1C. Fresh substrate
was added to the residue for the new run.
4-((Allyloxy)methyl)-1,3-dioxolan-2-one (7l)14d. Light yellow
liquid, 309.9 mg, yield 98%; 1H NMR (400 MHz, CDCl3) d
5.86 (m, 1H, CHQCH2), 5.32–5.18 (m, 2H, CH–CH2), 4.82 (m,
1H, OCH), 4.54 (t, J = 8.4 Hz, 1H, OCH2), 4.42–4.36 (t, J = 7.2 Hz,
1H, OCH2), 4.05 (m, 2H, OCH2), 3.65 (m, 2H, OCH2).
4-((Prop-2-yn-1-yloxy)methyl)-1,3-dioxolan-2-one
(7m)14e
.
Characterization data of cyclic carbonates
4-Chloromethyl-1,3-dioxolan-2-one (7a)6c. Light yellow Light yellow liquid, 256.0 mg, yield 82%; H NMR (400 MHz,
liquid, 270.3 mg, yield 99%; 1H NMR (400 MHz, CDCl3) d CDCl3) d 4.91–4.83 (m, 1H, OCH), 4.52 (t, J = 8.4 Hz, 1H, OCH2),
5.00 (m, 1H, OCH), 4.60 (t, J = 8.6 Hz, 1H, OCH2), 4.41 (m, 4.40 (t, J = 7.2 Hz, 1H, OCH2), 4.32–4.18 (m, 2H, CH2O), 3.85–
1
1H, OCH2), 3.78 (m, 2H, ClCH2).
3.71 (m, 2H, CH2C), 2.50 (s, 1H, CCH).
4-Bromomethyl-1,3-dioxolan-2-one (7b)13h
.
Light yellow
4-Hydroxymethyl-1,3-dioxolan-2-one (7n)6c. Light yellow
liquid, 358.3 mg, yield 99%; 1H NMR (400 MHz, CDCl3) d liquid, 158.2 mg, yield 67%; 1H NMR (400 MHz, CDCl3) d
4.97 (m, 1H, OCH), 4.57 (m, 1H, OCH2), 4.32 (m, 1H, OCH2), 4.88–4.77 (m, 1H, OCH), 4.58–4.37 (m, 2H, OCH2), 3.99 (m,
3.60 (m, 2H, Br CH2).
1H, CH2OH), 3.74 (m, 1H, CH2OH).
4-Methyl-1,3-dioxolan-2-one (7c)14d
.
Light yellow liquid,
4-(Morpholinomethyl)-1,3-dioxolan-2-one
(7o)6c.
Light
202.1 mg, yield 99%; 1H NMR (400 MHz, CDCl3) d 4.92–4.82 yellow liquid, 333.2 mg, yield 89%; H NMR (400 MHz, CDCl3)
1
(m, 1H, CHO), 4.62–4.52 (t, J = 8.0 Hz, 1H, OCH2), 4.04 (t, J = d 4.84 (s, 1H, OCH), 4.52 (t, J = 8.3 Hz, 1H, OCH2), 4.27–4.19 (m,
7.8 Hz, 1H, OCH2), 1.50 (m, 3H).
1H, OCH2), 3.67 (d, J = 9.2 Hz, 4H, OCH2CH2N), 2.67 (d, J =
5-Ethyl-1,3-dioxolan-2-one (7d)13h. Light yellow liquid, 285.4 mg, 5.6 Hz, 2H, CH2), 2.55 (d, J = 9.4 Hz, 4H, OCH2CH2N).
1
yield 99%; H NMR (400 MHz, CDCl3) d 4.71 (m, 1H, CHO), 4.54
(2-Oxo-1,3-dioxolan-4-yl)-methyl 4-(tert-butyl)benzoate (7p)6c.
(t, J = 8.0 Hz, 1H, OCH2), 4.08 (t, J = 7.8 Hz, 1H, OCH2), 1.77 (m, 2H, Light yellow liquid, 233.7 mg, yield 42%; 1H NMR (400 MHz,
CH2), 1.39 (m, 4H, CH2), 0.93 (t, J = 7.0 Hz, 3H, CH3).
CDCl3) d 7.96 (d, J = 8.5 Hz, 2H, ArH), 7.48 (d, J = 8.5 Hz,
4-Decylalkyl-1,3-dioxolan-2-one (7e)14e. Light yellow liquid, 2H, ArH), 5.05 (s, 1H, OCH), 4.65–4.55 (m, 2H, OCH2), 4.53
452.0 mg, yield 99%; 1H NMR (400 MHz, CDCl3) d 4.71 (m, 1H, (s, 1H, OCH2), 4.41 (d, J = 8.7 Hz, 1H, OCH2), 1.34 (s, 9H,
OCH), 4.52 (t, J = 8.0 Hz, 1H, OCH2), 4.06 (t, J = 7.8 Hz, 1H, O(CH3)3).
OCH2), 1.89–1.75 (m, 1H,), 1.74–1.64 (m, 1H), 1.50–1.42 (m,
1H), 1.29 (m, 15H), 0.87 (t, J = 7.0 Hz, 3H).
4,4-(Butane-1,4-diyl)-bis-1,3-dioxolan-2-one (7q)6c. Light yellow
1
liquid, 299.2 mg, yield 65%; H NMR (400 MHz, CDCl3) d 4.73
4-(3-Butenyl)-1,3-dioxolan-2-one (7f)4. Light yellow liquid, (s, 2H, OCH2), 4.55 (s, 2H, OCH2), 4.08 (s, 2H, OCH2), 1.78 (d, J =
281.4 mg, yield 99%; 1H NMR (400 MHz, CDCl3) d 5.81 (m, 23.5 Hz, 4H, CH2CH2), 1.53 (d, J = 44.5 Hz, 4H, CH2CH2).
1H, CHQCH2), 5.16–5.02 (t, J = 13.8 Hz, 2H, CHQCH2), 4.75
(m, 1H, OCH), 4.55 (t, J = 8.2 Hz, 1H, OCH2), 4.15–4.05 (t, J = Light yellow liquid, 276.2 mg, yield 75%; H NMR (400 MHz,
7.8 Hz, 1H, OCH2), 2.23 (m, 2H, CH2CH2), 2.04–1.75 (m, 2H, CDCl3) d 4.55–4.29 (m, 2H, OCH2), 4.15–4.02 (m, 1H, OCH),
4-(7-Oxabicyclo[4.1.0]heptan-3-yl)-1,3-dioxolan-2-one (7r)14f
.
1
CH2CH2).
4-Phenyl-1,3-dioxolan-2-one (7g)14d. White solid, 288.9 mg,
3.10 (m 2H, OCH2), 2.17–0.95 (m, 7H, CH2).
1,2-Cyclohexane carbonate (cis-9a)6c. Light yellow liquid,
yield 88%; 1H NMR (400 MHz, CDCl3) d 7.50–7.36 (m, 5H, ArH), 227.4 mg, yield 80%; 1H NMR (400 MHz, CDCl3) d 4.68
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2021
New J. Chem., 2021, 45, 13096–13103 | 13101

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NJC
Paper
Y. Yano and T. Sakai, A bifunctional catalyst for carbon
dioxide fixation: cooperative double activation of epoxides
for the synthesis of cyclic carbonates, Chem. Commun., 2012,
48, 4489.
(m, 2H, OCHCH2), 1.98–1.86 (m, 4H, OCHCH2), 1.67–1.59 (m,
2H, CH2), 1.42 (m, 2H, CH2).
5-Vinylhexahydrobenzo[d][1,3]dioxol-2-one (cis-9b)14f. Light
yellow liquid, 282.5 mg, yield 84%; 1H NMR (400 MHz, CDCl3) d
5.88–5.65 (m, 1H, CHQCH), 5.18–4.96 (m, 2H, CH), 4.934.58
(m, 2H, CHQCH2), 2.49–2.13 (m, 2H, CH2), 1.94 (m, 2H, CH2),
1.75–1.48 (m, 2H, CH2), 1.45–1.16 (m, 1H, CH).
6 (a) C. J. Whiteoak, N. Kielland, V. Laserna, E. C. Escudero-
´
Adan, E. Martin and A. W. Kleij, A powerful aluminum
catalyst for the synthesis of highly functional organic carbo-
nates, J. Am. Chem. Soc., 2013, 135, 1228; (b) W. M. Ren, Y. Liu
and X. B. Lu, Bifunctional aluminum catalyst for CO2 fixa-
tion: regioselective ring opening of three-membered hetero-
cyclic compounds, J. Org. Chem., 2014, 79, 9771; (c) P. F. Gao,
Z. W. Zhao, L. J. Chen, D. Yuan and Y. M. Yao, Dinuclear
aluminum poly(phenolate) complexes as efficient catalysts
for cyclic carbonate synthesis, Organometallics, 2016,
35, 1707; (d) J. Rintjema, R. Epping, G. Fiorani, E. Martin,
Tetrahydro-4H-cyclopenta[d][1,3]dioxol-2-one (cis-9c)6c. Light
1
yellow liquid, 228.0 mg, yield 89%; H NMR (400 MHz, CDCl3) d
5.11 (m, 2H, OCHCH2), 2.15 (m 2H, CH2), 1.86–1.64 (m, 4H, CH2).
Tetrahydrofuro-4H-cyclopenta[d][1,3]dioxol-2-one (cis-9d)6c.
Pale yellow liquid, 217.8 mg, yield 85%; 1H NMR (400 MHz,
CDCl3) d 5.11 (s, 2H, OCH2), 4.23–4.20 (m, 2H, CH2), 3.54–3.51
(m, 2H, CH2).
4,4-Dimethyl-1,3-dioxolan-2-one (9e)6c. Light yellow liquid,
1
´
E. C. Escudero-Adan and A. W. Kleij, Substrate-controlled
229.9 mg, yield 99%; H NMR (400 MHz, CDCl3) d 4.17 (s, 2H,
product divergence: conversion of CO2 into heterocyclic
products, Angew. Chem., Int. Ed., 2016, 55, 3972;
(e) M. Cozzolino, K. Press, M. Mazzeo and M. Lamberti,
Carbon dioxide/epoxide reactions catalyzed by bimetallic
salalen aluminum complexes, ChemCatChem, 2016, 8, 455;
OCH2), 1.54 (s, 6H, CH3).
4-(Chloromethyl)-4-methyl-1,3-dioxolan-2-one (9f)14f. Light
1
yellow liquid, 271.0 mg, yield 90%; H NMR (400 MHz, CDCl3)
d 4.52 (d, J = 8.8 Hz, 1H, OCH2), 4.17 (d, J = 8.8 Hz, 1H, OCH2),
3.74 (d, J = 11.9 Hz, 1H, CH2Cl), 3.61 (d, J = 11.9 Hz, 1H, CH2Cl),
1.64 (s, 3H, CH3).
´
´
´
( f ) D. O. Melendez, A. Lara-Sanchez, J. Martınez, X. Wu,
A. Otero, J. Castro-Osma, M. North and R. S. Rojas, Amidinate
aluminium complexes as catalysts for carbon dioxide fixation
into cyclic carbonates, ChemCatChem, 2018, 10, 2271;
(g) Y. Kim, K. Hyun, D. Ahn, R. Kim, M. H. Park and
Y. Kim, ChemSusChem, 2019, 12, 4211.
Conflicts of interest
There are no conflicts to declare.
7 (a) X. Liu, S. Zhang, Q. W. Song, X. F. Liu, R. Ma and
L. N. He, Cooperative calcium-based catalysis with 1,8
diazabicyclo[5.4.0]-undec-7-ene for the cycloaddition of
epoxides with CO2 at atmospheric pressure, Green Chem.,
2016, 18, 2871; (b) L. Longwitz, J. Steinbauer,
A. Spannenberg and T. Werner, Calcium-based catalytic
system for the synthesis of bio-derived cyclic carbonates
under mild conditions, ACS Catal., 2018, 8, 665.
Acknowledgements
We gratefully acknowledge financial support from the Natural
Science Foundation of the Jiangsu Higher Education Institutions
of China (Grant No. 19KJA320007), the project of scientific and
technologic infrastructure of Suzhou (SZS201708), and PAPD.
8 Z. Q. Guo, Y. Xu, J. B. Chao and X. H. Wei, Lithium
organoaluminate complexes as catalysts for the conversion
of CO2 into cyclic carbonates, Eur. J. Inorg. Chem., 2020,
2835.
Notes and references
1 M. D. Burkart, N. Hazari, C. L. Tway and E. L. Zeitler,
Opportunities and challenges for catalysis in carbon dioxide
utilization, ACS Catal., 2019, 9, 7937.
2 A. Dibenedetto and F. Nocito, The future of carbon dioxide
chemistry, ChemSusChem, 2020, 13, 6219.
3 Z. E. Zhang, S. Y. Pan, H. Li, J. C. Cai, A. G. Olabi,
E. J. Anthony and V. Manovic, Recent advances in carbon
dioxide utilization, Renewable Sustainable Energy Rev., 2020,
125, 109799.
4 L. Y. Hua, B. X. Li, C. P. Han, P. F. Gao, Y. R. Wang, D. Yuan
and Y. M. Yao, Synthesis of homo- and heteronuclear rare
earth metal complexes stabilized by ethanolamine-bridged
bis(phenolato) ligands and their application in catalyzing
reactions of CO2 and epoxides, Inorg. Chem., 2019, 58, 8775.
5 (a) T. Ema, Y. Miyazaki, J. Shimonishi, C. Maeda and
J. Y. Hasegawa, Bifunctional porphyrin catalysts for the
synthesis of cyclic carbonates from epoxides and CO2:
structural optimization and mechanistic study, J. Am. Chem.
Soc., 2014, 136, 15270; (b) T. Ema, Y. Miyazaki, S. Koyama,
9 (a) R. L. Paddock and S. T. Nguyen, Chemical CO2 fixation:
Cr(III) salen complexes as highly efficient catalysts for the
coupling of CO2 and epoxides, J. Am. Chem. Soc., 2001,
123, 11498; (b) X. B. Lu, B. Liang, Y. J. Zhang, Y. Z. Tian,
Y. M. Wang, C. X. Bai, H. Wang and R. Zhang, Asymmetric
catalysis with CO2: Direct synthesis of optically active pro-
pylene carbonate from racemic epoxides, J. Am. Chem. Soc.,
2004, 126, 3732; (c) J. Castro-Osma, K. J. Lamb and
M. North, Cr(salophen) complex catalyzed cyclic carbonate
synthesis at ambient temperature and pressure, ACS Catal.,
2016, 6, 5012.
10 (a) R. L. Paddock and S. T. Nguyen, Chiral (salen)CoIII
catalyst for the synthesis of cyclic carbonates, Chem. Com-
mun., 2004, 1622; (b) C. X. Miao, J. Q. Wang, Y. Wu, Y. Du
and L. N. He, Bifunctional metal-salen complexes as effi-
cient catalysts for the fixation of CO2 with epoxides under
solvent-free, ChemSusChem, 2008, 1, 236.
13102
|
New J. Chem., 2021, 45, 13096–13103
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2021

View Article Online
Paper
NJC
´
11 (a) R. M. Haak, A. Decortes, E. C. Escudero-Adan,
M. M. Belmonte, E. Martin, J. Benet-Buchholz and
A. W. Kleij, Shape-persistent octanuclear zinc salen clusters:
synthesis, characterization, and catalysis, Inorg. Chem., 2011,
C. T. Chen, Z. Y. Guo, M. North and A. C. Whitwood, ACS Catal.,
2019, 9, 1895; (h) Y. H. Hao, D. Yuan and Y. M. Yao, Metal-free
cycloaddition of epoxides and carbon dioxide catalyzed by
triazole-bridged bisphenol, ChemCatChem, 2020, 12, 4346.
50, 7934; (b) A. Decortes, M. M. Belmonte, J. Benet-Buchholza 14 (a) J. Qin, P. Wang, Q. Y. Li, Y. Zhang, D. Yuan and Y. M. Yao,
and A. W. Kleij, Efficient carbonate synthesis under mild
conditions through cycloaddition of carbon dioxide to oxi-
ranes using a Zn(salphen) catalyst, Chem. Commun., 2010,
46, 4580; (c) W. Desens, C. Kohrt, A. Spannenberg and
T. Werner, A novel zinc based binary catalytic system for
CO2 utilization under mild conditions, Org. Chem. Front.,
2016, 3, 156; (d) R. Ma, L. N. He and Y. B. Zhou, An efficient
and recyclable tetraoxo-coordinated zinc catalyst for the
cycloaddition of epoxides with carbon dioxide at atmospheric
pressure, Green Chem., 2016, 18, 226.
Catalytic production of cyclic carbonates mediated by lantha-
nide phenolates under mild conditions, Chem. Commun., 2014,
50, 10952; (b) B. Xu, P. Wang, M. Lv, D. Yuan and Y. M. Yao,
Transformation of Carbon Dioxide into Oxazolidinones and
Cyclic Carbonates Catalyzed by Rare-Earth-Metal Phenolates,
´
´
ChemCatChem, 2016, 8, 2466; (c) J. Martınez, J. Fernandez-
´
´
Baeza, L. F. Sanchez-Barba, J. A. Castro-Osma, A. Lara-Sanchez
and A. Otero, An efficient and versatile lanthanum heteroscor-
pionate catalyst for carbon dioxide fixation into cyclic carbo-
nates, ChemSusChem, 2017, 10, 2886; (d) Z. W. Zhao, J. Qin,
C. Zhang, Y. R. Wang, D. Yuan and Y. M. Yao, Recyclable
single-component rare-earth metal catalysts for cycloaddition
of CO2 and epoxides at atmospheric pressure, Inorg. Chem.,
2017, 56, 4568; (e) L. Y. Qu, I. D. Rosalb, Q. Y. Li, Y. R. Wang,
D. Yuan, Y. M. Yao and L. Maron, Efficient CO2 transformation
under ambient condition by heterobimetallic rare earth com-
plexes: experimental and computational evidences of a syner-
gistic effect, J. CO2 Util., 2019, 33, 413; ( f ) X. Xin, H. W. Shan,
T. Tian, Y. R. Wang, D. Yuan, H. P. You and Y. M. Yao,
Conversion of CO2 into cyclic carbonates under ambient
conditions catalyzed by rare-earth metal complexes bearing
poly(phenolato) ligand, ACS Sustainable Chem. Eng., 2020,
8, 13185; (g) K. Yin, L. Y. Hua, L. Y. Qu, Q. Y. Yao,
Y. R. Wang, D. Yuan, H. P. You and Y. M. Yao, Heterobimetallic
rare earth metal-zinc catalysts for reactions of epoxides and
CO2 under ambient conditions, Dalton Trans., 2021, 50, 1453.
´
12 (a) C. J. Whiteoak, E. Martin, E. Escudero-Adan and A. W. Kleij,
Stereochemical divergence in the formation of organic carbo-
nates derived from internal epoxides, Adv. Synth. Catal., 2013,
355, 2233; (b) F. D. Monica, B. Maity, T. Pehl, A. Buonerba,
A. D. Nisi, M. Monari, A. Grassi, B. Rieger, L. Cavallo and
C. Capacchione, [OSSO]-type iron(III) complexes for the low-
pressure reaction of carbon dioxide with epoxides: catalytic
activity, reaction kinetics, and computational study, ACS
Catal., 2018, 8, 6882; (c) K. A. Andrea, T. R. Brown,
J. N. Murphy, D. Jagota, D. McKearney, C. M. Kozak and
F. M. Kerton, Inorg. Chem., 2018, 57, 13494; (d) E. Fazekas,
G. S. Nichol, M. P. Shaver and J. A. Garden, Stable Fe(III)
phenoxyimines as selective and robust CO2/epoxide coupling
catalysts, Dalton Trans., 2018, 47, 13106; (e) F. D. Monica,
A. Buonerba, V. Paradiso, S. Milione, A. Grassi and
C. Capacchione, [OSSO]-type Fe(III) metallate as single-
component catalyst for the CO2 cycloaddition to epoxides, 15 (a) D. P. Zhao, L. J. Mao, L. Q. Wang, D. X. Yang and
Adv. Synth. Catal., 2019, 361, 283; ( f ) E. Y. Seong, J. H. Kim,
N. H. Kim, K. H. Ahn and E. J. Kang, Multifunctional and
sustainable Fe-iminopyridine complexes for the synthesis of
cyclic carbonates, ChemSusChem, 2019, 12, 409.
R. Wang, Catalytic asymmetric construction of tetrasubsti-
tuted carbon stereocenters by conjugate addition of dialkyl
phosphine oxides to b,b-disubstituted a,b-unsaturated car-
bonyl compounds, Chem. Commun., 2012, 48, 889;
(b) B. M. Trost, C.-I. Hung and G. Mata, Dinuclear metal-
prophenol catalysts: development and synthetic applica-
tions, Angew. Chem., Int. Ed., 2020, 59, 4240; (c) Y. L. Sun,
C. R. Lu, B. Zhao and M. Q. Xue, Enantioselective hydro-
boration of ketones catalyzed by rare-earth metal complexes
containing Trost ligands, J. Org. Chem., 2020, 85, 10504.
13 (a) C. J. Whiteoak, A. Nova, F. Maseras and A. W. Kleij, Merging
sustainability with organocatalysis in the formation of organic
carbonates by using CO2 as a feedstock, ChemSusChem, 2012,
5, 2032; (b) Y. B. Wang, D. S. Sun, H. Zhou, W. Z. Zhang and
X. B. Lu, CO2, COS and CS2 adducts of N-heterocyclic olefins and
their application as organocatalysts for carbon dioxide fixation,
Green Chem., 2015, 17, 4009; (c) L. Wang, G. Y. Zhang, 16 (a) Q. Q. Qian, Y. F. Tan, B. Zhao, T. Feng, Q. Shen and
K. Kodamaa and T. Hirose, An efficient metal- and solvent-free
organocatalytic system for chemical fixation of CO2 into cyclic
carbonates under mild conditions, Green Chem., 2016, 18, 1229;
Y. M. Yao, Asymmetric epoxidation of unsaturated ketones
catalyzed by heyerobimetallic rare earth-lithium complexes
bearing phenoxy functionalized chiral diphenylprolinolate
ligands, Org. Lett., 2014, 16, 4516; (b) C. Zeng, D. Yuan,
B. Zhao and Y. M. Yao, Highly Enantioselective epoxidation
of a,b-Unsaturated ketones catalyzed by rare-earth amides
[(Me3Si)2N]3RE(m-Cl)Li(THF)3 with phenoxy-functionalized
chiral prolinols, Org. Lett., 2015, 17, 2242.
´
(d) S. Sopen, E. Martin, E. C. Escudero-Adan and A. W. Kleij,
Pushing the limits with squaramide-based organocatalysts in
cyclic carbonate synthesis, ACS Catal., 2017, 7, 3532; (e) N. Liu,
Y. F. Xie, C. Wang, S. J. Li, D. H. Wei, M. Li and B. Dai,
Cooperative multifunctional organocatalysts for ambient conver-
sion of carbon dioxide into cyclic carbonates, ACS Catal., 2018, 17 (a) M. North and R. Pasquale, Mechanism of cyclic carbo-
8, 9945; ( f ) J. Y. Hu, J. Ma, H. Z. Liu, Q. L. Qian, C. Xie and
B. X. Han, Dual-ionic liquid system: an efficient catalyst for
chemical fixation of CO2 to cyclic carbonates under mild
conditions, Green Chem., 2018, 20, 2990; (g) X. Wu,
nate synthesis from epoxides and CO2, Angew. Chem., Int.
´
Ed., 2009, 48, 2946; (b) C. Martın, G. Fiorani and A. W. Kleij,
Recent advances in the catalytic preparation of cyclic
organic carbonates, ACS Catal., 2015, 5, 1353.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2021
New J. Chem., 2021, 45, 13096–13103 | 13103