Chiral titanium(IV) and vanadium(V) salen complexes as catalysts for carbon dioxide and epoxide coupling reactions

Article abstract of DOI:10.1016/j.tet.2021.131929

Chiral titanium(IV) and vanadium(V) salen complexes were found to catalyse the synthesis of cyclic carbonates from carbon dioxide and epoxides. Reactions could be conducted at room temperature and 50 bar pressure of carbon dioxide or at 100 °C and atmospheric pressure with catalyst concentrations as low as 0.1 mol% and co-catalyst (tetrabutylammonium bromide) concentrations as low as 0.5 mol%. The cyclic carbonates formed were racemic and a mechanism is proposed which relies on Lewis base catalysis to activate the carbon dioxide rather than Lewis acid catalysed activation of the epoxide as more commonly proposed for catalysis by metal complexes.

Full text of DOI:10.1016/j.tet.2021.131929

Tetrahedron 82 (2021) 131929
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Chiral titanium(IV) and vanadium(V) salen complexes as catalysts for
carbon dioxide and epoxide coupling reactions
,
c
Svetlana A. Kuznetsova a, Ilia V. Gorodishch b, Alexander S. Gak a
,
Valeria V. Zherebtsova d, Igor S. Gerasimov e, Michael G. Medvedev d
,
,
e
Dinara Kh. Kitaeva a, Ekaterina A. Khakina a, Michael North f *, Yuri N. Belokon a
,
, **
a Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov Street 28, 119991, Moscow, Russian Federation
b Moscow State University, Chemistry Department, Leninskiye Gory, 1/3, 119234, Moscow, Russian Federation
c Moscow State University, Faculty of Material Science, Leninskie Gory, 1/73, 119991, Moscow, Russian Federation
d D. Mendeleev University of Chemical Technology of Russia, Higher Chemical College of the Russian Academy of Sciences, Zelinskogo Street 38-8, 80, 11733,
Moscow, Russian Federation
e N.D. Zelinsky Institute of Organic Chemistry RAS, Leninsky Prospect, 47, 119991, Moscow, Russian Federation
f Green Chemistry Centre of Excellence, Department of Chemistry, University of York, Heslington, YO10 5DD, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Chiral titanium(IV) and vanadium(V) salen complexes were found to catalyse the synthesis of cyclic
carbonates from carbon dioxide and epoxides. Reactions could be conducted at room temperature and
50 bar pressure of carbon dioxide or at 100 ꢀC and atmospheric pressure with catalyst concentrations as
low as 0.1 mol% and co-catalyst (tetrabutylammonium bromide) concentrations as low as 0.5 mol%. The
cyclic carbonates formed were racemic and a mechanism is proposed which relies on Lewis base catalysis
to activate the carbon dioxide rather than Lewis acid catalysed activation of the epoxide as more
commonly proposed for catalysis by metal complexes.
Received 15 October 2020
Received in revised form
22 December 2020
Accepted 5 January 2021
Available online 13 January 2021
Dedicated to Professor Richard J. K. Taylor in
appreciation of his tenure as editor of
Tetrahedron.
© 2021 Elsevier Ltd. All rights reserved.
Keywords:
Salen ligand
Carbon dioxide
Cyclic carbonate
Vanadium
Titanium
1. Introduction
epoxides 1 to form cyclic carbonates 2 (Scheme 1) [1], a class of
commodity chemicals finding applications as solvents, electrolytes
Combustion of fossil fuels is likely to remain as a source of en-
ergy for the foreseeable future. This, along with the continued need
for products such as cement whose manufacture produces large
amounts of waste carbon dioxide, means that harmful carbon di-
oxide emissions will continue to increase. One way to turn this
waste carbon dioxide into valuable chemicals is its reaction with
for lithium ion batteries, monomers for polymer synthesis, and as
chemical starting materials [2].
There is a large volume of publications on the catalysis of this
reaction using either metal complexes (salen complexes, in
particular) [3,4] or organocatalysts, amongst which quaternary
ammonium halides feature prominently [5,6]. The most catalyti-
cally efficient systems usually consist of a combination of quater-
nary ammonium halides and Lewis acids (LA), which function
cooperatively as illustrated in Scheme 2A [3,7]. The key stage of the
reaction is nucleophilic opening of the Lewis acid activated epoxide
ring by the halide anion, generating an oxyanion species. Subse-
quently, the negatively charged oxygen atom reacts with carbon
* Corresponding author.
** Corresponding author.
E-mail addresses: ilia.gorodishch@chemistry.msu.ru (I.V. Gorodishch),
alexandrg03@gmail.com
(A.S.
Gak),
valeriazerebcova00@gmail.com
dioxide to form
a Lewis acid coordinated carbonate anion.
(V.V. Zherebtsova), medvedev.m.g@gmail.com (M.G. Medvedev), michael.north@
york.ac.uk (M. North), yubel@ineos.ac.ru (Y.N. Belokon).
https://doi.org/10.1016/j.tet.2021.131929
0040-4020/© 2021 Elsevier Ltd. All rights reserved.

S.A. Kuznetsova, I.V. Gorodishch, A.S. Gak et al.
Tetrahedron 82 (2021) 131929
cyclic carbonate.
Amongst the abundant metals employed as catalysts for cyclic
carbonate synthesis, complexes of aluminium and iron feature
prominently [6,7]. Titanium is also one of the six highly abundant
metals in the Earth’s crust and is readily available [8]. However, the
use of molecular titanium-based complexes as catalysts for cyclic
carbonate synthesis is under-developed [9]. Therefore, we decided
to investigate the applicability of titanium complexes for this re-
action. Salen ligands belong to the so-called ‘privileged ligands’ and
are easily available and inexpensive, giving them great potential as
ligands for catalysts for a wide range of chemical transformations.
We have previously employed chiral titanium(IV) and vanadium(V)
salen complexes (Fig. 1) as efficient catalysts for the asymmetric
synthesis of cyanohydrins (Scheme 3) [10,11], so the use of chiral
titanium(IV) salen complexes was of particular interest. Since
variously ligated vanadium(V) complexes have previously been
used for carbon dioxide and epoxide couplings [12], vanadium(V)
salen complexes were also included in this study. In a preliminary
study, we showed that at room temperature and atmospheric
pressure, both titanium(IV) and vanadium(V) salen complexes have
only very poor catalytic activity for cyclic carbonate synthesis [13].
However, titanium(IV) salen complexes did have high catalytic
activity for the closely related reaction between epoxides and car-
bon disulphide [13] and vanadium(V) salen complexes were sub-
sequently shown to be active catalysts for the reaction between
epoxides and isocyanates (Scheme 3) [14]. Wang et al. also reported
that a titanium(IV) salophen complex would catalyse the synthesis
of cyclohexene carbonate 2h from cyclohexene oxide 1h under
much harsher reaction conditions (120 ꢀC and 40 bar pressure) [15].
In view of this precedent and the recent demonstration that the
mechanism of cyclic carbonate synthesis by a given catalyst could
change as the reaction conditions were changed [16], we decided to
investigate the synthesis of cyclic carbonates from epoxides and
carbon dioxide catalysed by titanium(IV) and vanadium(V) salen
complexes under a wider range of conditions and herein report the
results of this study.
Scheme 1. Synthesis of cyclic carbonates 2.
Scheme 2. General mechanisms for cyclic carbonate synthesis. A: Lewis acid catalysed
epoxide activation. B: Lewis base catalysed carbon dioxide activation.
Intramolecular nucleophilic substitution results in elimination of
the halide anion, formation of the cyclic carbonate product and
regenerates the Lewis acid and ammonium halide [7]. These binary
catalyst systems can be highly efficient and in some cases are able
to promote cyclic carbonate formation at ambient temperatures
and low carbon dioxide pressure [3].
Some organocatalyst systems however do not possess an acidic
group within their structure [5]. In these cases an alternative
mechanism is generally proposed (Scheme 2B) in which a Lewis
base within the catalyst reacts with carbon dioxide to form a
carboxylate anion. This carboxylate then acts as the nucleophile
which ring-opens the epoxide and the resulting alkoxide cyclizes
onto the carbonyl with elimination of the Lewis base to form the
Fig. 1. Structures of the titanium(IV) and vanadium(V) complexes and the halide salts
used in this work.
2

S.A. Kuznetsova, I.V. Gorodishch, A.S. Gak et al.
Tetrahedron 82 (2021) 131929
Table 1
Initial experiments on CO2 and styrene oxide coupling promoted by complex 3 and
TBAB.a
Entry
3 (mol%)
TBAB (mol%)
T (oC)
Pressure (bar)
Yield (%)b
1
2
3c
4
5
6
7
4
4
4
4
2
2
2
8
8
8
8
8
4
4
50
25
25
50
50
50
25
50
50
1
1
1
95
95
17
98
98
99
75
50
50
a
Reaction conditions: 1.83 mmol of styrene oxide, solvent free for 24 h.
b
Yields were determined by 1H NMR spectroscopy with an internal standard. No
side products were detected in the reaction.
c
The styrene carbonate was racemic as determined by chiral HPLC.
50 bar pressure and 50 ꢀC (compare Table 1, entries 1 and 6).
However, lowering the temperature to 25 ꢀC did result in a
measurable decrease of the yield (to 75%) when these lower
amounts of catalyst components were used (Table 1, entry 7).
From the results in Table 1, it is apparent that both the carbon
dioxide pressure and the temperature of the reaction had a sig-
nificant effect on the reaction rate. The coupling could be efficiently
conducted either at 25 ꢀC and 50 bar pressure or at 50 ꢀC and at-
mospheric pressure. It seemed that a two-fold temperature in-
crease had the same effect as a fifty-fold increase in the pressure
(Table 1, entries 2 and 4). The concentration of the catalyst com-
ponents seemed to have a much lower effect on the catalytic per-
formance, at least in the concentration range studied in Table 1.
Thus, a two-fold decrease in the concentration of complex 3 had no
negative effect on the product yield (Table 1, entries 4 and 5).
Simultaneously halving the concentration of TBAB at 50 ꢀC and
50 bar pressure also did not result in any reduction in the yield
(Table 1, entries 1 and 6), though when the reaction temperature
was reduced to 25 ꢀC, the yield did drop to 75%. These results
suggested that to assess the real catalytic potential of complex 3, a
more thorough search for the optimal reaction conditions was
needed. Table 2 summarises the results of changing the concen-
tration of complex 3 and the nucleophilic components (TBAB or Cv-
X) at atmospheric pressure and temperatures of 50e100 ꢀC.
As entries 1, 2 and 4 of Table 2 indicate, halving the concen-
tration of complex 3 and TBAB had no effect on the catalytic per-
formance under these reaction conditions either. After 3 h at 50 ꢀC
and 1 bar pressure of carbon dioxide, the yields were consistently
8e10%. Extending the reaction time to 24 h (Table 2, entry 3),
increased the yield of styrene carbonate 2a to 68%, showing that the
catalyst system had not died. Further reducing the TBAB concen-
tration to 1 mol% whilst keeping the concentration of complex 3 at
0.5 mol% led to an almost proportional fall in the styrene carbonate
yield (Table 2, entries 5 and 6). A further decrease in the amount of
complex 3 to 0.2 mol% (using 4 mol% of TBAB) partially restored the
yield of styrene carbonate (Table 2, entries 7 and 8) although the
catalytic performance was still meager. Increasing the reaction
temperature to 100 ꢀC greatly improved the performance of the
two-component catalyst (Table 2, entries 9e12). At this tempera-
ture, almost quantitative yields of styrene carbonate could be
achieved using just 0.1 mol% of complex 3 and a ratio of TBAB/3
between 5:1 and 1:1 after 24 h (Table 2, entries 11 and 12).
Scheme 3. Previous and current work on the use of complexes 3 and 4 as catalysts.
2. Results and discussion
2.1. Catalyst and reaction condition optimisation studies
Titanium(IV) and vanadium(V) salen complexes 3 and 4 were
prepared as previously described [10,11a]. Complex 3 has previ-
ously been shown to be bimetallic in the solid state, but in solution
is in equilibrium with monometallic species [17]. For ease of com-
parison with complex 4, in this manuscript all mol% of complex 3
assume that it is completely dissociated into monometallic species.
The two-component catalysts were prepared by mixing complex 3
or 4 with different proportions of nucleophilic agents (TBAB, TBAI,
Cv-Br or Cv-I; Fig. 1) and used as catalysts for the synthesis of cyclic
carbonates 2a-h from epoxides 1a-h. The initial screening of the
catalysts was made with styrene oxide 1a as reactant.
The results summarised in Table 1 indicate that complex 3 could
catalyse the carbon dioxide/epoxide coupling reaction. The reaction
was successfully carried out within 24 h using 4 mol% of complex 3
and 8 mol% of TBAB at 50 ꢀC and 50 bar pressure of carbon dioxide
(Table 1, entry 1). The reaction went almost to completion even at
25 ꢀC under the otherwise same conditions (Table 1, entry 2).
However, at atmospheric pressure and 25 ꢀC the yield of styrene
carbonate 2a was only 17% (Table 1, entry 3), a result which is
consistent with the 13% conversion previously reported under
almost identical conditions [13]. Notably, the styrene carbonate
formed in entry 3 was racemic. The chemical yield of styrene car-
bonate could be increased to 98% by increasing the reaction tem-
perature (Table 1, entry 4). Halving the concentration of complex 3
(to 2 mol%) had no effect on the product yield under these condi-
tions (Table 1, entry 5). Simultaneously halving the concentration of
complex 3 and TBAB (to 2 mol% and 4 mol% respectively) also had
no adverse effect on the product yield from a reaction carried out at
Additional improvements in the catalytic performance of the
3

S.A. Kuznetsova, I.V. Gorodishch, A.S. Gak et al.
Tetrahedron 82 (2021) 131929
Table 2
Table 3
Experiments on CO2 and styrene oxide coupling at 1 bar CO2 pressure varying the
Experiments on CO2 and styrene oxide coupling promoted by complex 4 and hal-
concentration of complex 3 and using various halide sourcesa.
ides.a
Entry
3 (mol%)
Halide source (mol%)
T (oC)
time (h)
Yield (%)b
Entry 4 (mol%) Halide source (mol%) T (oC) P (bar) time (h) Yield (%)b
1
2
3
4
1
TBAB (8)
TBAB (8)
TBAB (8)
TBAB (4)
TBAB (1)
TBAB (1)
TBAB (4)
TBAB (4)
TBAB (2)
TBAB (0.5)
TBAB (0.5)
TBAB (0.1)
Сv-Br (2)
Сv-I (2)
50
50
50
50
50
50
50
50
100
100
100
100
100
100
100
100
100
3
3
24
3
3
24
3
24
3
8
1
2
3
4
2
2
2
2
2
2
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
e
50
50
50
50
25
25
50
100
100
100
100
100
100
100
100
100
100
100
50
50
1
1
50
1
1
1
1
1
1
1
1
1
1
1
1
1
24
24
3
24
24
24
24
24
3
0
>99
34
97
>99
21
42
>99
49
>98
62
42
22
>98
97
47
7e10
18
0.5
0.5
0.5
0.5
0.5
0.2
0.2
0.2
0.1
0.1
0.1
0.2
0.2
0.2
0.2
0.1
10
68
9
3
17
5
30
45
25
98
90
73
69
57
20
28
TBAB (8)
TBAB (8)
TBAB (8)
TBAB (8)
TBAB (8)
TBAB (8)
TBAB (4)
TBAB (2)
TBAB (2)
TBAI (2)
TBAB (1)
TBAB (0.5)
TBAB (0.5)
Cv-Br (8)
Cv-Br (2)
Cv-Br (0.5)
Cv-I (0.5)
5
5
6c
7
6c
7
8c
9
8c
9
10c
11
12
13
14
15
16
17
3
10c
11
12
13
14
15
16
17
18
24
3
3
24
24
3
3
3
3
24
24
3
3
3
Сv-Br (1)
Сv-Br (0.5)
Сv-Br (0.5)
3
3
a
Reaction condition: 1.83 mmol of epoxide, solvent free at atmospheric pressure.
Yields were determined by 1H NMR spectroscopy with an internal standard. No
b
a
Reaction condition: 1.83 mmol of epoxide, solvent free.
b
side products were detected in the reaction.
Yields were determined by 1H NMR spectroscopy with an internal standard. No
c
The styrene carbonate was racemic as determined by chiral HPLC.
side products were detected in the reaction.
c
The styrene carbonate was racemic as determined by chiral HPLC.
catalyst system were achieved by using CV-Br instead of TBAB
(Table 2, compare entries 9,10 with 13,17). With this halide source,
lowering of the concentration of complex 3 actually improved the
catalytic performance of the catalyst system (Table 2, entries 16 and
17). The use of Cv-I did not improve the catalyst activity (Table 2,
entry 14). However, the use of TBAB was more convenient than use
of intensely coloured Cv-Br.
Vanadium salen complex 4 has the potential to catalyse the
coupling of epoxides and carbon dioxide without the addition of
any nucleophilic components as it already contains a nucleophilic
chloride ion. However, complex 4 displayed no catalytic activity in
the reaction between styrene oxide and carbon dioxide even at
high pressure (Table 3, entry 1). In contrast, a two-component
catalyst system based on complex 4 and TBAB was almost as
active as the corresponding titanium complex 3 and TBAB catalyst
system as shown by comparison of the data in Tables 1e3.
entries 13, 17 and 18). However, Cv-I was twice as efficient as Cv-Br
(Table 3, entries 17 and 18), again confirming the preference for
iodide rather than bromide based nucleophiles in the vanadium
catalysed system.
Although decreasing the nucleophile concentration was gener-
ally detrimental to the activity of the catalyst system, a change from
2 mol% to 1 mol% of TBAB had only a small influence on the catalytic
performance (Table 3, entries 9 and 12). However, a further halving
of the concentration of TBAB led to an almost twofold reduction in
the styrene carbonate yield (Table 3, entries 12 and 13). In other
words there is a saturation effect of the added co-catalyst on the
reaction yield as Table 4 illustrates (entries 1e3 and 4e6). The io-
dide salt is an exception to this rule (Table 4, entries 7e9) and a
rational for this is discussed below.
Under the optimised reaction conditions (Table 2, entry 11 or
Table 3, entry 14) the use of complexes 3 and 4 to catalyse the
synthesis of cyclic carbonates 2aem from epoxides 1aem and
carbon dioxide was investigated. The results are summarised in
Table 5. As can be seen from the data, styrene oxides 1a,b and 3-
chloropropylene oxide 1c reacted at atmospheric pressure
(Table 5, entries 1e3) whereas the reactions of propylene oxide 1d,
butylene oxide 1e and hexylene oxide 1f (Table 5, entries 4e6) had
to be carried out at 25 bar pressure of carbon dioxide due to
volatility of these substrates. Ether derivatives 1gei were also
excellent substrates under these conditions (Table 5, entries 7e9).
Predictably, cyclohexene oxide 1j was the least reactive substrate,
giving cis-cyclohexene carbonate 2j in only 23 and 32% yields from
reactions catalysed by complexes 3 and 4 respectively after 24 h at
100 ꢀC and 25 bar pressure (Table 5, entry 10). Fluorinated epoxides
1kem were also excellent substrates especially for titanium based
catalyst 3 (Table 5, entries 11e13).
The catalyst system based on vanadium complex 4 and TBAB
had good activity at high concentrations of TBAB and complex 4
(Table 3, entries 2e5) and it even promoted the synthesis of styrene
carbonate in 99% yield at 25 ꢀC and 50 bar pressure within 24 h
(Table 3, entry 5). However, at 25 ꢀC and 1 bar carbon dioxide
pressure, the yield of styrene carbonate 2a dropped to just 21%
(Table 3, entry 6), a result which is consistent with the 12% con-
version previously reported under the same conditions except for a
lower TBAB concentration [13]. A twenty-fold decrease of the
concentration of complex 4 to 0.1 mol% expectedly led to sub-
stantial decrease in the catalytic activity at 50 ꢀC and 1 bar pressure
(Table 3, entry 7). However, increasing the reaction temperature to
100 ꢀC (Table 3, entries 8e14) allowed the reaction to go to
completion within 24 h using just 0.1 mol% of complex 4 and
0.5 mol% of TBAB (Table 3, run 14). For the vanadium based catalyst
system, TBAI was more efficient than TBAB (Table 3, compare en-
tries 9 and 11). The use of Cv-Br or Cv-I did not improve the activity
of the catalyst system compared to use of TBAB (Table 3, compare
4

S.A. Kuznetsova, I.V. Gorodishch, A.S. Gak et al.
Tetrahedron 82 (2021) 131929
Table 4
oxidation state which was reliably shown by an increase in the
catalytic activity of the complex when the reaction was conducted
under an oxygen containing atmosphere rather than an inert at-
mosphere [11c]. An attempt to carry out a similar study during
cyclic carbonate synthesis catalysed by complex 4 and TBAB did not
give conclusive results as the atmosphere above the reaction is
inevitably predominantly carbon dioxide. However, there is indi-
rect evidence that the catalytically active species for cyclic car-
bonate synthesis has vanadium in the þ4 oxidation state. Thus, Cv-I
was twice as active as Cv-Br when used in the catalytic system with
vanadium complex 4 (Table 3, entries 17 and 18). In addition, no
saturation effects of the added co-catalyst on the performance of 4
were observed in the case of Cv-I (Table 4). However, Cv-Br and Cv-I
had very similar activity when used in the catalytic system with
titanium complex 3 (Table 2, entries 13 and 14). This can be
explained if, in the case of catalysis by vanadium complex 4, iodide
reduces vanadium(V) to vanadium(IV) and the latter is the more
active catalyst for cyclic carbonate synthesis. No such reduction
could occur in case of titanium(IV) complex 3 which explains the
similar activity of Cv-Br and Cv-I in this case. A recent publication
reported a closely related vanadium-based catalyst and argued in
favour of vanadium(IV) rather than vanadium(V) as the more active
catalyst for the synthesis of cyclic carbonates from epoxides and
carbon dioxide [12b]. It is also notable that the specifically prepared
vanadium(IV) analogue of complex 4 was more active than the
initially vanadium(V) form of 4 (Table 4, entry 1).
Experiments on CO2 and styrene oxide coupling promoted by complex 4 and hal-
ides.a
Entry
Halide source (mol%)
Yield (%)b
1
2
3
4
5
6
7
8
9
TBAB (0.5)
TBAB (1)
TBAB (2)
Cv-Br (0.5)
Cv-Br (1)
Cv-Br (2)
Cv-I (0.5)
Cv-I (1)
22 (27)c
42
49
18
40
47
10
39
62
Cv-I (2)
a
Reaction condition: 1.83 mmol of epoxide, 0.1 mol % of 4, 100ꢀ C, 1 bar CO2
pressure, neat epoxide for 3 h.
b
Yields were determined by 1H NMR spectroscopy with an internal standard. No
side products were detected in the reaction.
c
The result of an experiment using the V(IV) version of complex 4.
2.2. Mechanistic discussion
Quantum chemical calculations at PBE0 [18]-D3 [19,20]/def2-
TZVP [21] level of theory showed that reduction of vanadium(V)
to vanadium(IV) increased the negative charge (calculated within
the QTAIM framework [22]) on the doubly bonded oxygen by 0.14
and 0.16 electrons in the case of complexes with and without a
The results summarised in Tables 1e5 pose questions related to
the mechanism of the reaction. It was not clear what oxidation state
the vanadium ion had during the reaction. In cyanohydrin syn-
theses promoted by complex 4, the vanadium was in the þ5
Table 5
The coupling of epoxides with CO2 promoted by 3/TBAB or 4/TBAB at 100 ꢀC.a
Entry
Epoxide
Pressure (bar)
Yield (%)b
1
2
3
4
5
6
7
8
Styrene oxide 1a
4-Chlorostyrene oxide 1b
3-Chloropropylene oxide 1c
Propylene oxide 1d
Butylene oxide 1e
1
1
1
>98(98)
>98(98)
>98(96)
87(98)
92(96)
>98(98)
94(98)
>98(98)
>98(98)
23(32)
98(98)
98(98)
25
25
25
25
25
25
25
25
25
25
Hexylene oxide 1f
3-Phenoxypropylene oxide 1g
3-Benzyloxypropylene oxide 1h
3-Allyloxypropylene oxide 1i
Cyclohexene oxide 1j
2-((1,1,2,3,3,3-hexafluoro-propoxy)methyl)oxirane 1k
2-(fluoromethyl)oxirane 1l
2-(2,2,3,3,4,4,5,5,6,6,7,7,7-tridecafluoroheptyl)oxirane 1m
9
10
11
12
13
90(70)
a
Reaction conditions: 1.83 mmol of epoxide, 0.1 mol% of 3 or 4 and 0.5 mol% of TBAB, solvent free for 24 h.
b
Yields were determined by 1H NMR spectroscopy with an internal standard. No side products were detected in the reaction. The yield obtained using the vanadium based
catalyst system is given in brackets.
5

S.A. Kuznetsova, I.V. Gorodishch, A.S. Gak et al.
Tetrahedron 82 (2021) 131929
bromine ligand, respectively (Table 6). Changing vanadium(IV) to
titanium(IV) increases the negative charge on this oxygen by
another 0.1 electrons. Introduction of the bromine ligand has only a
minor effect on the oxygen charge, but a major effect on the carbon
dioxide-adduct stability, vide infra. Thus, vanadium(IV) complexes
can be expected to be more active as Lewis bases than vanadium(V)
complexes.
catalysed by complex 3 gave the products with 40% enantiomeric
excess [23]. Another closely related titanium(IV) complex catalysed
epoxide ring-opening with trimethylsilyl cyanide, giving the
product with 90% enantiomeric excess [23]. Therefore, had the
main function of chiral catalysts 3 and 4 been the activation of the
epoxide (Scheme 2A), the cyclic carbonates prepared at a room
temperature would be expected to be enantiomerically enriched
which was not the case. Hence it appears that complexes 3 and 4
function not as Lewis acid catalysts, but as Lewis base catalysts and
that they catalyse the formation of cyclic carbonates by a mecha-
nism similar to that shown in Scheme 2B with the oxygen of the
M ¼ O group acting as the Lewis base. In this mechanism, the key
stereo-determining epoxide ring-opening step occurs with a sig-
nificant distance between the chiral salen ligand and the epoxide
which explains why the cyclic carbonate product is racemic.
To verify the ability of the metal-salen complexes to bind carbon
dioxide through their Lewis basic oxygens, the molecular structures
of the corresponding adducts were optimised at the same
computational level of theory as above, additionally accounting for
the solvation effects of propylene oxide (ε ¼ 16.0, εinf ¼ 1.866) with
PCM [24]. Computed free energies of the corresponding carbon
dioxide addition reactions are shown in Fig. 2. Calculations on the
vanadium(IV) complex coordinated to bromine showed that it
eliminated bromide when optimised with PCM, but the other
starting complexes were successfully optimised. Among the carbon
dioxide-containing complexes, only those for titanium(IV) (both
with and without Br) and one with Br-vanadium(IV) could be
located. Their free energies relative to the starting materials are 7.8,
15.1 and 26.6 kcal/mol, respectively. All these energies are accept-
able for intermediates of reactions proceeding at 50 ꢀC [25] and are
The previously studied catalytic activity of complex 3 in asym-
metric cyanohydrin synthesis was strongly concentration depen-
dent, showing the bimetallic nature of the catalytically active
species [10]. If a bimetallic species was responsible for catalysis of
cyclic carbonate synthesis, a decrease in the concentration of the
catalyst would have had a highly negative effect on the yield of
cyclic carbonate. In fact, an insignificant variation of the product
yield as the catalyst concentration was reduced was observed for
both catalysts 3 and 4 (Tables 1e3). The same was true when the
TBAB concentration was varied. These results can be explained in
the case of complex 3 by the known equilibrium between mono-
metallic and bimetallic forms of the complex (Fig. 1) [17]. This
equilibrium is both concentration and solvent dependent, with low
concentrations and polar solvents favoring the monometallic spe-
cies. Thus, if the monometallic form is catalytically active, there will
be proportionately more of it present at lower concentrations
which will, at least partially, offset the overall lower concentration
of the catalyst. In addition, cyclic carbonates are much more polar
than epoxides [2], so the polarity of the solvent mixture will in-
crease as the reaction progresses and this will also perturb the
equilibrium shown in Fig. 1 in favour of the monometallic species.
As a result, a complex variation of product yield with catalyst 3
concentration would be expected as shown by the results in Table 2.
The monometallic form of complex 3 [(salen)Ti]O] is Lewis acidic
at titanium, but also possesses a highly Lewis basic oxygen. Vana-
dium(V) complex 4 also possesses a highly Lewis basic oxygen, but
this will become even more Lewis basic if the vanadium is reduced
in situ to vanadium(IV) as discussed above (see Table 6). Hence,
both complexes 3 and 4 can generate species of the form (salen)
M¼O in the reaction mixture and these species possess both Lewis
acidity and Lewis basicity. The presence of bromide ions in solution
should additionally increase the basicity of the oxygen atoms by
forming halide-metal bonds and, consequently, negatively charged
complexes [Br(salen)M¼O]e (Table 6). The saturation effect
observed when the bromide containing cocatalyst concentration
was increased in the case of complex 4 (Table 4) could then be
explained by the almost complete formation of such a complex at
higher concentrations of bromide.
Another feature of the catalysis was the formation of racemic
styrene carbonate 2a from styrene oxide 1a and carbon dioxide in
reactions promoted by chiral complexes 3 and 4 (Table 1, entry 3,
Table 2, entry 6, 8 and10, Table 3 entry 7). Both complexes 3 and 4
efficiently catalyse the synthesis of cyanohydrins from aldehydes
and trimethylsilyl cyanide at ambient temperature, giving products
with enantiomeric purities in the region of 60e90% [10,11]. In
addition, the ring-opening of epoxides with trimethylsilyl cyanide
Table 6
Calculated QTAIM charges of the doubly bonded oxygen atoms (shown in bold) in
various complexes.
Metal
Ti
Catalytic center
M(IV)
M(V)
Ti¼O
ꢁ0.94a
ꢁ0.96
ꢁ0.84
ꢁ0.86
e
BreTi]O
V¼O
e
V
ꢁ0.68
BreV]O
ꢁ0.72b
a
Compound 3.
Compound 4, but with Br instead of Cl.
b
Fig. 2. Computed free energies of CO2-binding reactions.
6

S.A. Kuznetsova, I.V. Gorodishch, A.S. Gak et al.
Tetrahedron 82 (2021) 131929
consistent with the proposed interaction of carbon dioxide with
Lewis basic M¼O groups. According to the calculated free energies,
introduction of bromine into the titanium(IV) complex stabilizes
the intermediate by 7 kcal/mol, which explains the necessity of a
bromide source in this reaction. The relatively high free energy of
the BreV(IV)eOeCO2 intermediate is likely associated with loss of
the translational entropy [26] accompanying the reaction due to
the need to combine three freely moving species (carbon dioxide,
bromide and the complex).
the initially five coordinate Ti(IV) or V(IV) salen complexes. This
creates six-coordinate metal(IV)(salen) complexes with further
reduced Lewis acidity, but significantly enhanced Lewis basicity
associated with the M¼O group as shown in Scheme 4.
3. Conclusions
Readily available salen complexes of titanium and vanadium are
shown to act as catalysts for cyclic carbonate synthesis from carbon
dioxide and epoxides. The reaction could be carried at atmospheric
pressure and 100 ꢀC or at higher pressure and ambient temperature
with the amount of the catalyst and co-catalyst as low as 0.1% mol.
On the basis of the formation of racemic cyclic carbonate and the
retention of relative stereochemistry during the reaction, a mech-
anism, is proposed which involves the metal(salen) complexes
acting as Lewis bases to active the carbon dioxide rather than as
Lewis acids to activate the epoxide.
Based on the above evidence, it is apparent that complexes 3
and 4 catalyse cyclic carbonate synthesis by a mechanism which
involves them acting as Lewis bases to activate carbon dioxide.
However, the mechanism shown in Scheme 2B involves a single
step which would invert the stereochemistry of a 1,2-disubstituted
epoxide. As such it would be expected to give trans-cyclohexene
carbonate from cyclohexene oxide, whilst the IR [27], 1H NMR and
13C NMR spectra [28] of the product indicated that cis-cyclohexene
carbonate was actually formed. Therefore, we propose the catalytic
cycle shown in Scheme 4. This is a modified version of the mech-
anism shown in Scheme 2B in which the alkoxide formed by ring-
opening of the epoxide reacts with carbon dioxide to form a second
carbonate (shown in purple in Scheme 4) which can then ring-close
to form the cyclic carbonate product with elimination of the Lewis
base-carbonate adduct which carried out the epoxide ring-opening
(shown in green and blue in Scheme 4). This modified mechanism
involves two potentially stereo-inverting steps at the same carbon
atom and hence would be expected to result in the formation of cis-
cyclohexene carbonate from cyclohexene oxide. The intermolecular
reaction of the alkoxide with carbon dioxide is favoured over its
intramolecular reaction with the Lewis base-carbonyl group due to
the high carbon dioxide pressure (25 bar) needed when using
cyclohexene oxide as substrate. A similar mechanism involving
reaction of a ring-opened epoxide intermediate with carbon diox-
ide has previously been proposed to explain the stereochemistry of
cyclic carbonate synthesis catalysed by metal-free salophen ligands
[29].
4. Experimental section
CH2Cl2 was distilled under an argon atmosphere from calcium
hydride and methanol was distilled under an argon atmosphere
from magnesium turnings/iodine. All chemicals were purchased
from Sigma-Aldrich or P&M Invest and used without further pu-
rification. If not stated otherwise, column chromatography was
performed with silica gel 60 M from Macherey-Nagel. Proton, car-
bon and fluorine nuclear magnetic resonance spectra were recor-
ded on a Bruker Avance 400 (operating at 400, 101 and 376 MHz,
respectively, for 1H, 13C and 19F nuclei) and a Bruker Avance 300
(operating at 300, 75 and 282 MHz, respectively, for 1H, 13C and 19
F
nuclei) NMR spectrometers. Chemical shifts for 1H and 13C nuclei
are reported in ppm relative to the residual solvent peak (CDCl3:
d
¼ 7.26 ppm for 1H NMR,
d
¼ 77.2 for 13C NMR; C6D6:
¼ 7.16 ppm
d
for 1H NMR,
d
¼ 128.06 for 13C NMR; acetone-d6:
¼ 2.05 ppm for
d
A final issue relates to the role of the tetrabutylammonium
bromide co-catalyst in these reactions as it is not involved in a
reaction with the epoxide in the mechanism shown in Scheme 4.
Instead, the co-catalyst can act as a halide source to coordinate to
1H NMR,
to CF3Cl (
d
¼ 29.84, 206.26 for 13C NMR) and for 19F nuclei e relative
¼ 0 ppm).
d
HRMS were run in positive ion mode on a Bruker micrOTOF II by
electrospray ionization (ESI). The capillary voltage was 4500 V. The
range of detected masses was m/z 50 to 3000. Elemental analyses
were carried out in the Laboratory of Microanalysis of the A.N.
Nesmeyanov Institute of Organoelement Compounds of the
Russian Academy of Sciences.
4.1. Titanium(IV) catalyst (3) [10]
Ti(OiPr)4 (0.55 g, 1.9 mmol) was added with stirring to a solution
of (1R,2R)-N,N,-bis[3,5-di(tert-butyl)salicyliden] cyclohexane-1,2-
diamine (1.0 g, 1.8 mmol) in dry CH2Cl2 (50 mL). After stirring for
3 h under argon, H2O (33 mg, 1.8 mmol) was added. Then, the re-
action mixture was stirred at ambient temperature under argon for
2 h. The solution was then evaporated under reduced pressure to
give titanium complex 3 (1.0 g,1.7 mmol) as a yellow powder in 90%
yield. Found: C, 70.9; H, 8.5; N, 4.6. C72H104N4O6Ti2 requires C, 71.0;
25
H, 8.6; N, 4.6%; mp 314e316 ꢀC (lit.10 315 ꢀC); [
a]
e311 (c 0.01,
D
CHCl3); nmax (KBr) 2942, 2862, 1634, 1591, 1199, 1171, 1038,
637 cmꢁ1;. dH (C6D6) 7.86 (s, 1H), 7.61 (s, 1H), 7.41 (s, 1H), 7.31 (s,
1H), 6.99 (s, 1H), 6.87 (s, 1H), 4.2e4.1 (m, 1H), 2.3e2.2 (m, 1H),
2.0e1.8 (m, 1H), 1.6e1.5 (m, 1H), 1.4e1.3 (m, 2H), 1.27 (s, 9H), 1.47 (s,
9H), 1.22 (s, 9H), 1.19 (s, 9H), 0.9e0.5 (m, 4H); dC (C6D6) 163.1, 161.9,
160.9, 157.0, 139.9, 139.3, 138.0, 137.6, 128.6, 128.5, 128.0, 125.9,
122.3, 69.8, 65.9, 36.0, 35.4, 34.1, 34.0, 31.7, 31.6, 30.4, 30.0, 29.9,
27.9, 24.9, 24.8.
Scheme 4. Proposed catalytic cycle for cyclic carbonate synthesis catalysed by com-
plexes 3 and 4.
7

S.A. Kuznetsova, I.V. Gorodishch, A.S. Gak et al.
Tetrahedron 82 (2021) 131929
4.2. Vanadium(V) catalyst (4) [11a]
EtOAc:hexane to separate the catalyst. Column chromatography on
silica, eluting with 1:3 EtOAc:hexane was then used to purify the
cyclic carbonates.
VOCl3 (0.090 ml, 0.95 mmol) was added with stirring to a so-
lution of (1R,2R)-N,N,-bis[3,5-di(tert-butyl)salicyliden] cyclo-
hexane-1,2-diamine (0.34 g, 0.63 mmol) in THF (20 ml). The
reaction was stirred for 0.5 h at ambient temperature, then evap-
orated under reduced pressure. The product was purified by silica
gel chromatography eluting first with CHCl3, then 99:1
CHCl3:MeOH, then 9:1 CHCl3:MeOH. The dark green fractions were
collected and evaporated in vacuo to give vanadium(V) complex 4
(0.25 g, 0.39 mmol) in 62% yield. Found: C, 66.9; H, 8.1; N, 4.3; V, 8.1.
4.6. General procedure for the addition of CO2 to epoxides at
elevated pressures
To a 7 ml autoclave was added an epoxide (1.83 mmol) and the
required amounts of catalyst 3 or 4 and a nucleophile. The autoclave
was then sealed and pressurised with CO2 at the desired temper-
ature. The reaction was stirred for the specified time, then the
reactor was cooled to ambient temperature and CO2 was released
slowly. The reaction mixture was analysed by 1H NMR spectroscopy
using 1,4-dinitrobenzene as internal standard, then passed through
a pad of silica gel eluting with 1:2 EtOAc:hexane to separate the
catalyst. Column chromatography on silica, eluting with 1:3
EtOAc:hexane was then used to purify the cyclic carbonates.
4-Phenyl-1,3-dioxolan-2-one (2a) [4b]. Obtained in 98% yield
C
36H52N2O3VCl requires C, 66.8; H, 8.1; N, 4.3; V, 7.9%; mp > 190 ꢀC
25
(decomp.); [
a
]
e1280 (c 0.01, CHCl3); nmax (KBr) 1621, 1250,
D
597 cmꢁ1
;
dH (CDCl3) 8.71 (s, 1H), 8.54 (s, 1H), 7.77 (s, 1H), 7.73 (s,
1H), 7.57 (s, 1H), 7.51 (s, 1H), 4.5e4.4 (m, 1H), 3.9e3.7 (m, 1H), 2.74
(d J 9.6 Hz, 1H), 2.56 (d J 9.6 Hz, 1H), 2.3e1.9 (m, 5H), 1.9e1.7 (m,
1H), 1.56 (s, 9H), 1.55 (s, 9H), 1.40 (s, 9H), 1.38 (s, 9H); dC (CDCl3)
164.9, 161.5, 160.9, 159.9, 143.9, 143.7, 135.9, 135.1, 132.0, 131.4,
129.2, 128.3, 122.0, 120.8, 70.3, 69.5, 35.8, 35.6, 34.5, 34.4, 31.4, 30.4,
30.3, 30.0, 29.7, 29.3, 24.5, 24.1; HRMS: found m/z 611.3412;
calculated for C36H52N2O3V [M]þ 611.3412.
using catalyst 4. IR (KBr):
y
(C]O) 1813, 1797 cmꢁ1; 1H NMR (CDCl3,
400 MHz) dH 7.5e7.3 (m, 5H), 5.7e5.6 (m, 1H), 4.8e4.4 (m, 2H); 13
C
NMR (CDCl3, 101 MHz) 155.1, 136.0, 129.7, 129.2, 126.1, 78.1, 71.2;
HRMS: found m/z 187.0368; calculated for C9H8O3Na [MþNa]þ
187.0366.
4.3. Vanadium(IV) catalyst [11b]
4-(Chlorophenyl)-1,3-dioxolan-2-one (2b) [4b]. Obtained in 98%
This complex was synthesised by a literature procedure.[11b] IR
(KBr): 1604 cmꢁ1, 983 cmꢁ1. Anal. calc. for C36H52N2O3V: C 70.68; H
8.57; N 4.58; found: C 70.33; H 8.40; N 4.53; HRMS: found m/z
611.3408; calculated for C36H52N2O3V [M]þ 611.3412.
yield using catalyst 4. IR (KBr): y
(C]O) 1800 cmꢁ1; 1H NMR (CDCl3,
400 MHz) dH 7.42e7.32 (m, 4H), 5.68 (m, 1H), 4.82e4.31 (m, 3H);
13C NMR (CDCl3, 101 MHz) 154.6, 135.7, 134.3, 129.5, 127.2, 77.3,
70.9; HRMS: found m/z 220.9980 (100%), 222.9953; calculated for
C9H7ClO3Na [MþNa]þ 220.9976 (35Cl), 222.9947 (37Cl).
4.4. Exchange of chloride counter anion in crystal violet by bromide
or iodide
4-(Chloromethyl)-1,3-dioxolan-2-one (2c) [4b]. Obtained in 96%
yield using catalyst 4. IR (KBr):
y
(C]O) 1799 cmꢁ1; 1H NMR (CDCl3,
400 MHz) dH 5.1e5.0 (m, 1H), 4.6e4.3 (m, 2H), 3.8e3.7 (m 2H); 13
C
Crystal violet (0.60 g, 1.5 mmol) was dissolved in EtOH (3 ml)
and the solution was passed through a column filled with Amberlite
CG-400 ion exchange resin in its iodide or bromide form. Then, the
resin was flushed with a water/EtOH solvent mixture. The solution
was evaporated and the residue dried in vacuo. Crystal violet bro-
mide (0.58 g, 1.3 mmol) was obtained in 87% yield. No chloride was
detected in the product by X-ray fluorescence. Found: C, 64.2; H,
6.7; N, 9.1; Br, 16.7. C25H30N3Br.H2O requires C, 63.8; H, 6.8; N, 8.9;
Br, 16.9%; mp 120e122оС; IR (KBr) ῦ ¼ 2919, 2854, 2806, 1584, 1362,
NMR (CDCl3, 101 MHz) 154.5, 74.5, 67.0, 44.1; HRMS: found m/z
136.9998 (100%), 138.9969; calculated for C4H6ClO3 [MþH]þ
137.0000 (35Cl), 138.9971 (37Cl).
4-Methyl-1,3-dioxolan-2-one (2d) [4b]. Obtained in 98% yield
using catalyst 4. IR (KBr): y ;
(C]O) 1781 cmꢁ1 1H NMR (CDCl3,
400 MHz) dH 4.7e4.6 (m, 1H), 4.4e4.3 (m, 1H), 3.9e3.8 (m, 1H), 1.31
(d J 6.4 Hz, 3H); 13C NMR (CDCl3, 101 MHz) 155.1, 73.8, 70.7, 19.1;
HRMS: found m/z 125.0214; calculated for C4H6O3Na [MþNa]þ
125.0209.
1172 cmꢁ1
;
dH (CDCl3) 7.20 (d J 9.1 Hz, 6H), 6.73 (d J 9.1 Hz, 6H), 3.20
4-Ethyl-1,3-dioxolan-2-one (2e) [4b]. Obtained in 96% yield
(s, 18H); dC (CDCl3) 178.1, 155.5, 139.7, 126.5, 112.4, 40.7; HRMS:
found m/z 372.2436; calculated for C25H30N3 [M]þ 372.2434.
Crystal violet iodide [4b] (0.65 g, 1.3 mmol) was obtained in 88%
yield. No chloride was detected in the product by X-ray fluores-
cence. Found: C, 60.0; H, 6.2; N, 8.4; I, 25.3. C25H30N3I requires C,
60.1; H, 6.0; N, 8.4; I, 25.4%; mp 192e194оС; IR (KBr) ῦ ¼ 2913, 2852,
using catalyst 4. IR (KBr): y ;
(C]O) 1791 cmꢁ1 1H NMR (CDCl3,
400 MHz) dH 4.7e4.6 (m, 1H), 4.5e4.4 (m, 1H), 4.1e4.0 (m, 1H),
1.9e1.7 (m, 2H), 1.05 (t J 7.5 Hz, 3H); 13C NMR (CDCl3, 101 MHz)
155.3, 78.2, 69.1, 26.7, 8.3; HRMS: found m/z 139.0385; calculated
for C5H8O3Na [MþNa]þ 139.0366.
4-Butyl-1,3-dioxolan-2-one (2f) [4b]. Obtained in 98% yield us-
2808, 1582, 1368, 1174 cmꢁ1
;
dH (CDCl3) 7.27 (d J 9.0 Hz, 6H), 6.82
ing catalyst 4. IR (KBr): y ;
(C]O) 1796 cmꢁ1 1H NMR (CDCl3,
(d J 9.0 Hz, 6H), 3.24 (s, 18H); dC (CDCl3) 178.1, 155.5, 139.6, 126.5,
112.4, 40.7; HRMS: found m/z 372.2436; calculated for C25H30N3
[M]þ 372.2434.
400 MHz) dH 4.8e4.6 (m, 1H), 4.5e4.4 (m, 1H), 4.1e4.0 (m, 1H),
1.9e1.8 (m, 1H), 1.8e1.6 (m, 1H), 1.5e1.3 (m, 4H), 0.94 (t J 6.9 Hz,
3H); 13C NMR (CDCl3, 101 MHz) 155.2, 77.2, 69.4, 33.4, 26.3, 22.1,
13.7; HRMS: found m/z 167.0678; calculated for C7H12O3Na
[MþNa]þ 167.0679.
4.5. General procedure for the addition of CO2 to epoxides at
atmospheric pressure
4-(Phenoxymethyl)-1,3-dioxolan-2-one (2g) [4b]. Obtained in
98% yield using catalyst 4. IR (KBr): y ;
(C]O) 1804, 1780 cmꢁ1 1H
To a 10 ml round bottom flask fitted with a septum was added
catalyst 3 or 4 (1.83 ꢂ 10ꢁ3 mmol) and a nucleophile (0.910 ꢂ 10ꢁ2
mmol). The flask was evacuated and filled with CO2 using a balloon.
Epoxide (1.83 mmol) was added and the reaction was placed into a
pre-heated oil bath and stirred at atmosphere pressure. After the
specified reaction time, the reaction was cooled to room tempera-
ture and the mixture was analysed by 1H NMR spectroscopy using
1,4-dinitrobenzene as internal standard. The reaction mixture was
NMR (CDCl3, 400 MHz) dH 7.4e7.2 (m, 2H), 7.0e6.9 (m, 1H), 6.92 (d J
8.0 Hz, 2H), 5.1e5.0 (m, 1H), 4.7e4.5 (m, 2H), 4.3e4.1 (m, 2H); 13C
NMR (CDCl3, 101 MHz) 157.8, 154.9, 129.6, 122.0, 114.6, 74.3, 66.9,
66.2; HRMS: found m/z 217.0469; calculated for C10H10O4Na
[MþNa]þ 217.0471.
4-(Benzyloxymethyl)-1,3-dioxolan-2-one (2h) [30]. Obtained in
98% yield using catalyst 4. IR (KBr): y ;
(C]O) 1791 cmꢁ1 1H NMR
(CDCl3, 400 MHz) dH 7.5e7.3 (m, 5H), 4.9e4.8 (m, 1H), 4.7e4.6 (m,
then passed through
a pad of silica gel eluting with 1:2
2H), 4.6e4.3 (m, 2H), 3.6e3.5 (m, 2H); 13C NMR (CDCl3, 101 MHz)
8

S.A. Kuznetsova, I.V. Gorodishch, A.S. Gak et al.
Tetrahedron 82 (2021) 131929
154.8, 137.1, 128.1, 127.8, 74.8, 73.7, 66.8, 66.3; HRMS: found m/z
231.0630; calculated for C11H12O4Na [MþNa]þ 231.0628.
References
[1] For reviews see:. a) E.A. Quadrelli, G. Centi, J.-L. Duplan, S. Perathoner,
4-(Allyloxymethyl)-1,3-dioxolan-2-one (2i) [30]. Obtained in
ChemSusChem 4 (2011) 1194e1215;
b) M. Peters, B. Kohler, W. Kuckshinrichs, W. Leitner, P. Markewitz, T.E. Müller,
98% yield using catalyst 4. IR (KBr): y ;
(C]O) 1794 cmꢁ1 1H NMR
€
(CDCl3, 400 MHz) dH 5.9e5.7 (m, 1H), 5.4e5.1 (m, 2H), 4.8e4.7 (m,
1H), 4.5e4.2 (m, 2H), 4.0e3.9 (m, 2H), 3.7e3.4 (m, 2H); 13C NMR
(CDCl3, 101 MHz) 155.2, 137.9, 117.2, 75.33, 72.1, 68.9, 66.1; HRMS:
found m/z 181.0482; calculated for C7H10O4Na [MþNa]þ 181.0477.
cis-Cyclohexene carbonate (2j) [4b]. Obtained in 32% yield using
ChemSusChem 4 (2011) 1216e1240;
c) I. Omae, Coord. Chem. Rev. 256 (2012) 1384e1405;
d) B. Hu, C. Guild, S.L. Suib, J. CO2 Util. 1 (2013) 18e27;
e) M. Aresta, A. Dibenedetto, A. Angelini, J. CO2 Util. 3e4 (2013) 65e73;
f) A.A. Olajire, J. CO2 Util. 3e4 (2013) 74e92;
g) M. Aresta, A. Dibenedetto, A. Angelini, Chem. Rev. 114 (2014) 1709e1742;
h) A. Otto, T. Grube, S. Schiebahn, D. Stolten, Energy Environ. Sci. 8 (2015)
3283e3297;
catalyst 4. IR (KBr): y ;
(C]O) 1799, 1733 cmꢁ1 1H NMR (CDCl3,
400 MHz) dH 4.8e4.6 (m, 2H), 2.0e1.8 (m, 4H), 1.7e1.5 (m, 2H),
1.5e1.3 (m, 2H); 13C NMR (CDCl3, 101 MHz) 155.5, 75.7, 26.8,
19.2 ppm; HRMS: found m/z 165.0529; calculated for C7H10O3Na
[MþNa]þ 165.0522.
ꢀ
ꢀ
i) A.J. Martín, G.O. Larrazabal, J. Perez-Ramírez, Green Chem. 17 (2015)
5114e5130;
j) Q. Liu, L. Wu, R. Jackstell, M. Beller, Nat. Commun. 6 (2015) 5933;
k) M. Poliakoff, W. Leitner, E.S. Streng, Faraday Discuss 183 (2015) 9e17;
l) B. Yu, L.-N. He, ChemSusChem 8 (2015) 52e62.
€
[2] B. Schaffner, F. Schaffner, S.P. Verevkin, A. Borner, Chem. Rev. 110 (2010)
4-((1,1,2,3,3,3-hexafluoropropoxy)methyl)-1,3-dioxolan-2-one
4554e4581.
(2k) [31]. Obtained in 98% yield using catalyst 4. IR (KBr): y(C]O)
[3] For reviews see:. a) A. Decortes, A.M. Castilla, A.W. Kleij, Angew. Chem. Int. Ed.
49 (2010) 9822e9837;
1801 cmꢁ1; 1H NMR (CDCl3, 300 MHz) dH 5.1e4.8 (m, 2H), 4.6e4.5
(m, 1H), 4.4e4.3 (m, 2H), 4.2e4.1 (m, 1H); 19F {1H}NMR (СDCl3,
282 MHz) ꢁ75.6e76.6 (m, 3F), ꢁ81.16 (ddt, J 146.7, 25.6, 9.9 Hz,
1F), ꢁ84.08 (dq J 146.7, 9.6 Hz, 1F), ꢁ212.84e213.42 (m, 1F); 13C
NMR (CDCl3, 75 MHz) 154.8, 125.7e114.1 (m, 2xC), 86.9e81.9 (m),
73.5, 65.4, 63.3e63.1 (m). HRMS: found m/z 291.0056; calculated
for C7H6F6O4Na [MþNa]þ 291.0062.
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Declaration of competing interest
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
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Acknowledgements
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5 (2017)
This work was supported by the Ministry of Science and Higher
Education of the Russian Federation. Quantum chemical calcula-
tions were supported by the Russian Science Foundation grant #
17-13-01526. The authors acknowledge the computational re-
sources provided by the Moscow State University’s Faculty of
Computational Mathematics and Cybernetics (IBM Blue Gene/P,
Polus). The research was carried out using the equipment of the
shared research facilities of HPC computing resources at Lomono-
sov Moscow State University [33]. The Siberian Branch of the
Russian Academy of Sciences (SB RAS) Siberian Supercomputer
Center is gratefully acknowledged for providing supercomputer
facilities. This work has been carried out using computing resources
of the federal collective usage centre Complex for Simulation and
Data Processing for Mega-science Facilities at NRC “Kurchatov
Institute”, http://ckp.nrcki.ru/.
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