Carbocation/Polyol Systems as Efficient Organic Catalysts for the Preparation of Cyclic Carbonates

Article abstract of DOI:10.1002/cssc.201601246

Carbocation/polyol systems are shown to be highly efficient catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide at 50 °C and 5 MPa CO₂ pressure. The best activity was shown by the combination of crystal violet and

Full text of DOI:10.1002/cssc.201601246

DOI: 10.1002/cssc.201601246
Full Papers
Carbocation/Polyol Systems as Efficient Organic Catalysts
for the Preparation of Cyclic Carbonates
Yuri A. Rulev,[a] Zalina T. Gugkaeva,[a] Anastasia V. Lokutova,[a] Victor I. Maleev,[a]
Alexander S. Peregudov,[a] Xiao Wu,[b] Michael North,*[b] and Yuri N. Belokon*[a]
Carbocation/polyol systems are shown to be highly efficient
catalysts for the synthesis of cyclic carbonates from epoxides
and carbon dioxide at 508C and 5 MPa CO2 pressure. The best
activity was shown by the combination of crystal violet and
1,1’-bi-2-naphthol (BINOL), which could be recycled five times
with no loss of activity. The presence of specific interactions
between the amino groups of the carbocation and the hydrox-
yl protons was confirmed by NMR experiments. The Job plots
for the crystal violet iodide/BINOL and brilliant green iodide/
BINOL systems showed that the catalytic systems consist of
one molecule of the carbocation and one molecule of BINOL.
Mechanistic studies using a deuterated epoxide indicate that
there was some loss of epoxide stereochemistry during the re-
action, but predominant retention of stereochemistry is ob-
served. On this basis, a catalytic cycle is proposed.
Introduction
The search for valorization technologies for emitted carbon di-
oxide (CO2) is one of the most rapidly growing fields of chemi-
cal research.[1] The coupling of CO2 with epoxides is a highly
atom economical process, leading to the production of cyclic
carbonates (Scheme 1), which are an important class of indus-
trial intermediates and solvents.[1–4] This methodology is highly
sustainable and is already utilized in industry; the volume of
cyclic carbonates produced is expected to grow substantially
in the near future owing to their use as electrolytes in lithium–
ion batteries. The best catalysts for the synthesis of cyclic car-
bonates are based on a two-component metal complex/
nucleophile catalyst combination.[2,3] Recently, purely organic
catalysts have become the focus of studies[4] because their use
can be more cost-effective, the catalysts are commercially
available, usually more sustainable, and less toxic than metal
complexes. In particular, quaternary ammonium and phospho-
nium salts have been widely utilized as catalysts.[4–8] There are
also examples of imidazolium salts[9–15] and imidazolium-based
ionic liquids[16] used as catalysts for cyclic carbonate synthesis.
In addition, two-component systems comprising an alcohol
(e.g., phenol) and a quaternary ammonium salt have been suc-
cessfully tested.[17,18] This system represents a promising class
of organic catalysts with the potential for further improve-
ment.[4] Unfortunately, the efficiency of the organic catalysts is
no match for metal-based catalysts.[4] This justifies the search
for novel classes of organic catalysts.
We have previously developed several catalytic systems for
the synthesis of cyclic carbonates by coupling of CO2 and ep-
oxides. These included highly efficient and robust aluminum
(salen) complexes,[19,20] and stereochemically inert CoIII com-
plexes that function as “Brønsted acids in disguise” with the
central metal ion only serving as an activator of the catalytical-
ly active Brønsted acidic NH groups.[21]
Scheme 1. Synthesis of cyclic carbonates.
Herein, we describe the use of well-known, commercially
available, and stable carbocations in the form of triarylmethane
dyes (Figure 1) as catalysts for the synthesis of cyclic carbo-
nates. We tested the iodide salt form of malachite green (MGI),
brilliant green (BGI), and crystal violet (CVI) as bifunctional cat-
alysts, the activities of which were augmented by the addition
of Brønsted acids.
[a] Y. A. Rulev, Dr. Z. T. Gugkaeva, A. V. Lokutova, Dr. V. I. Maleev,
Dr. A. S. Peregudov, Prof. Y. N. Belokon
Nesmeyanov Institute of Organoelement Compounds
Moscow 19991 (Russia)
E-mail: yubel@ineos.ac.ru
[b] Dr. X. Wu, Prof. M. North
Green Chemistry Centre of Excellence, Department of Chemistry
University of York
Heslington, YO10 5DD (UK)
E-mail: michael.north@york.ac.uk
Results and Discussion
Supporting Information for this article can be found under:
http://dx.doi.org/10.1002/cssc.201601246.
Although rare, the use of triarylmethylium (trityl) carbocations
as catalysts for organic transformations such as Diels–Alder
and Michael reactions has been reported.[22] However, to the
This publication is part of a Special Issue around the “1st Carbon Dioxide
Conversion Catalysis” (CDCC-1) conference. A link to the issue’s Table of
Contents will appear here once it is complete.
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mation). Moreover, the 13C NMR spectra showed a shift of the
carbocation’s carbon signal (178.02 ppm) to higher field, which
correlated with increasing epoxide concentration (Figure 2).
Thus, the spectra indicated that the epoxide did coordinate
with the carbocation of CVI.
Figure 1. Carbocation dyes used as catalysts for cyclic carbonate synthesis.
best of our knowledge, the use of triarylmethane dyes as or-
ganic catalysts has not been previously reported. The reason
for this seems to be because the activity of a carbocation is in-
versely related to its stability.[22–25] However, carbocations exist
as halide salts; therefore, they are bifunctional systems that in-
clude a Lewis acidic center and a nucleophilic counterion. As
such, they are similar to ammonium salts, which are a well-
known class of catalysts for the synthesis of cyclic carbo-
nates.[4–8] In addition, the amino substituents of triarylmethane
dyes could interact with a Brønsted acid catalyst component.
The resulting formation of a hydrogen bond would increase
the Lewis acidity of the dyes.
Figure 2. Shifts of the signals of the central carbon atom of CVI upon the
addition of increasing concentrations of PO in CD2Cl2. a) pure CVI (0.33m),
b) CVI/PO=2:1, c) CVI/PO=1:1, d) CVI/PO=1:2, e) CVI/PO=1:3, and f) CVI/
PO=1:10. The splitting of the 13C signal in the spectra of e) and f) probably
suggests that at low CVI/PO ratios, two PO molecules may interact with
each CVI.
Based on the accepted mechanism of bifunctional Lewis
acid/halide ion catalysis, a potential mechanism of CO2 addi-
tion to epoxides promoted by the dyes is shown in Scheme 2.
The Lewis acidic carbocation could activate the epoxide to-
wards nucleophilic attack by the iodide anion. Subsequent ad-
dition of CO2 and the elimination of iodide bring the reaction
to completion and regenerate the catalyst.
The addition of CO2 to neat styrene oxide (SO) was selected
as a benchmark reaction to test the activities of the dyes. As
the dyes were commercially available in their chloride form,
both MG and CV were tested in their original (Table 1, en-
tries 1,2) and iodide forms (Table 1, entries 3,5). The chloride to
iodide exchange was easily achieved in a two-phase CH2Cl2/
H2O system using a twentyfold excess of potassium iodide. As
expected, the iodide form was much more active; therefore,
the iodide form of all the dyes was used for further testing.
NMR analysis of mixtures of CVI and propylene oxide (PO)
was used to demonstrate the Lewis acidic interaction of the
1
carbocations with epoxides. Both the H and 13C NMR spectra
revealed significant shifts of the signals of the dimethylamino
groups of CVI and the methyl group of the epoxide to higher
fields as the PO concentration increased (see Supporting infor-
Table 1. Comparison of the catalytic activities of MGI, BGI, CVI, and
TBAI.[a]
Entry
Catalyst
Conversion[b] [%]
Selectivity [%]
1[c]
2[c]
3
4
5
6[d]
7
MG
CV
<1
<1
8
28
45
32
41
not determined
not determined
MGI
BGI
CVI
CVI
TBAI
>99
>99
>99
>99
>99
[a] Reaction conditions: 2 mol% catalyst unless specified otherwise, neat
SO. [b] Conversions were determined by 1H NMR using the catalyst sig-
nals as an internal standard. [c] The dyes were used in their chloride
forms. [d] The catalyst loading was 1% mol.
Scheme 2. Proposed mechanism of the formation of cyclic carbonates pro-
moted by triarylmethane dyes.
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CVI was the most active dye. Its catalytic activity was similar
to that of tetrabutylammonium iodide (TBAI) (Table 1, entries 5
and 7). The catalytic activity of MGI and BGI was inferior to CVI
and TBAI (Table 1, runs 3, 4, 5, and 7). The relative order of ac-
tivity of the dyes was unexpected. If the Lewis acidity of the
cations was the most important factor, the opposite trend
would have been expected as the pKRþ values for MGI and CVI
are 6.9 and 9.4, respectively.[22] This suggests that a compensat-
ing effect influences the catalytic activity of the dye/iodide ion
bifunctional catalyst. The observed catalytic activity trend of
MGI<BGI<CVI can be explained by stronger association of
ion pairs resulting in lower catalytic activity. The dissociation of
the ion pairs should lead to a better catalytic performance,
which was supported by experiments. Thus, halving the CVI
concentration led to a relatively small change in the conver-
sion of SO (Table 1, entries 4 and 6), consistent with greater ion
pair dissociation resulting from dilution of the CVI.
Table 2. Activity of polyol additives in the reaction of styrene oxide with
CO2.[a]
Entry
Polyol
Catalyst
Conversion[b] [%]
1
2
3
4
5
6
TADDOL
TBAI
TBAI
TBAI
BGI
BGI
BGI
70
71
76
41
55
64
meta-bis-TADDOL
CH2-bis-TADDOL
TADDOL
meta-bis-TADDOL
CH2-bis-TADDOL
[a] Reaction conditions: 1.25 mol% of bis-TADDOLs (or 2.5 mol%
TADDOL), 2.5 mol% of TBAI (or BGI), neat SO, 508C, 5 MPa CO2, 24 h.
1
[b] Conversions were determined using H NMR spectroscopy.
number of available hydroxyl groups is kept constant. The re-
sults are shown in Table 2. In the case of TBAI, no significant
difference in catalytic activities was detected between the TAD-
DOLs (Table 2, entries 1–3). However, in the case of BGI, the
TADDOLs were found to have markedly different activities
(Table 2, entries 4–6). The best activator was found to be CH2-
bis-TADDOL, which has the greatest distance between its two
pairs of hydroxyl groups (Table 2, entry 6). This observation
supports the hypothesis that there are activating interactions
between the amino groups of the carbocations and hydroxyl
protons of the polyols.
The introduction of anion complexing agents should lead to
better catalytic performance because of separation of the ion
pairs into Lewis acidic and nucleophilic parts, revealing the
hidden potential of their activity. For this purpose, several poly-
alcohols and carboxylic acids (Figure 3) were investigated.
These can simultaneously coordinate with iodide, form hydro-
gen bonds with the amino groups of the dyes, and coordinate
an alcoholic oxygen to the cationic center of the dye.
Initially, a,a,a’,a’-tetraaryl-2,2 disubstituted-1,3-dioxolane-
4,5-dimethanol (TADDOL) additives were tested with TBAI and
BGI to investigate if there were any cooperative interactions
between the two catalysts. In these experiments, twice as
much TADDOL as bis-TADDOL was used so that the total
Table 3 summarizes the activities of the dyes relative to TBAI
using other types of polyol additives. The polyols themselves
were not catalytically active (Table 3, entry 1). The activity of
TBAI was increased in the order BIMBOL<TADDOL<
H8-BINOL<BINOL, where BIMBOL: 3,3’-bis(hydroxydiphenyl-
methyl)-[1,1’-binaphthalene]-2,2’-diol,
H8BINOL
is
5,5’,6,6’,7,7’,8,8’-octahydro-[1,1’-binaphthalene]-2,2’-diol,
and
Table 3. Catalytic activity of TBAI, MGI, BGI and CVI in the presence of ad-
ditives.[a]
Entry Catalyst
Additive
Conversion[b] Selectivity
(amt. [mol%]) (amt. [mol%])
[%]
[%]
1
–
BINOL, BIMBOL,
H8-BINOL, TADDOL (1.0)
BIMBOL (1.25)
H8-BINOL (2.5)
BINOL (2.5)
BINOL (2.5)
BINOL (1.0)
BIMBOL (1.25)
H8-BINOL (2.5)
BINOL (1.0)
<1
–
2
3
4
5
6
7
8
9
10
11
12
13
14
TBAI (2.5)
TBAI (2.5)
TBAI (2.5)
TBAI (1.0)
MGI (1.0)
BGI (2.5)
BGI (2.5)
BGI (1.0)
BGI (2.5)
BGI (2.5)
CVI (1.0)
CVI (1.0)
CVI (1.0)
53
82
88
69
12
58
82
49
100
0
>99
>99
>99
>99
>99
>99
>99
>99
>99
BINOL (2.5)
terephthalic acid (2.5)
TADDOL (1.0)
BIMBOL (0.5)
48
57
82
>99
>99
>99
BINOL (1.0)
[a] Reaction conditions: neat SO, 508C, 5 MPa CO2, 24 h. [b] Conversions
1
were determined by H NMR using the catalyst signals as an internal stan-
dard.
Figure 3. Compounds used as Brønsted acid additives and an example of
their postulated mode of action.
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BINOL is [1,1’-binaphthalene]-2,2’-diol (Table 1, entry 7; Table 2,
entries 1–3; and Table 3, entries 2–5). The addition of BINOL
also led to an increase in the activities of the carbocation dyes,
even for the least reactive MGI (Table 1, entry 3, Table 3,
entry 6). The effect was even more pronounced in the case of
BGI (Table 1, entry 4, Table 2 entries 4–6, and Table 3, entries 7–
10). The order of efficiency of the additives was TADDOL<
BIMBOL<H8-BINOL<BINOL. At higher concentrations, the cat-
alyst system of BGI/BINOL became more active than that of
TBAI/BINOL (Table 3, entries 4,5 and 9,10). Finally, the most effi-
cient catalyst was CVI/BINOL (Table 1, entries 5,6 and Table 3,
entries 12–14). The order of the efficiency was TADDOL<
BIMBOL<BINOL. Notably, the inexpensive diol BINOL was
more active than the TADDOL derivatives. The greater acidity
of BINOL (pKa =13.2[26] in DMSO) and its lower steric bulk com-
pared to TADDOL (pKa =19.2[26] in DMSO) could explain this
observation. The use of terephthalic acid with BGI (Table 3,
run 11) resulted in complete inhibition of the activity of BGI.
1H and 13C NMR spectra of mixtures of BGI with different
concentrations of BINOL were recorded to investigate the
nature of the interactions between BINOL and a dye molecule
(Figure 4). A significant shift of the peaks attributed to the hy-
droxyl protons of BINOL to lower fields was the most conspicu-
ous change in the spectra of BINOL (Figure 4, b-e). An upfield
shift of the CH2 protons of the ethylamino groups and the aro-
matic protons ortho to the amino groups were also observed
with increasing BINOL concentration (Figure 4, a-d). In addition,
a 0.2 ppm upfield shift of the 13C NMR signal of the carbocat-
ion was observed in the spectrum with a 1:3 ratio of BGI/
BINOL (see Supporting Information). These spectra indicated
that the Lewis acidic central carbon atom of BGI interacted
with BINOL through a lone pair of an OH group in a similar
way to its interaction with PO (Figure 2). Such an interaction
should lead to higher acidity of the hydroxyl group and a shift
of the proton resonance to a lower field.
Job plots of the activity of BGI/BINOL or CVI/BINOL were
constructed to determine the optimal ratio between the dyes
and BINOL (Figure 5). The total loading of the BINOL–
carbocation system was kept constant at 2 mol%. As shown in
Figure 5, the highest yields of styrene carbonate were achieved
in the BGI/BINOL ratio range of 2:1 to 1:1. A similar depend-
ence was observed for CVI, with the best CVI/BINOL ration of
1:1.
Figure 5. Job plots of the BGI/BINOL and CVI/BINOL systems in the synthesis
of styrene carbonate from SO and CO2. Reaction conditions: neat SO,
2 mol% BINOL+carbocation, 508C, 5 MPa CO2, 24 h.
The 1:1 CVI/BINOL system was used for the synthesis of ten
cyclic carbonates 2a–j from terminal epoxides 1a–j (Table 4,
entries 1–13). Good conversions of the more reactive epoxides
1a,d,e were obtained using only 1 mol% of each catalyst com-
ponent (Table 4, entries 1,6,7). However, other aromatic and ali-
phatic epoxides 1b,c,f gave rather low conversions when
1 mol% of each catalyst component was used; much better re-
sults were obtained with 2 mol% of each catalyst (Table 4, en-
tries 2–5,8,9). Therefore, 2 mol% of each catalyst was used
with the remaining substrates. Under these conditions, high
conversions were obtained with substrates possessing long
alkyl chains, ethers, and alcohols in their sidechains (Table 4,
entries 7–11). These results show that the CVI/BINOL system
has general applicability and tolerates functional groups within
the epoxide substrate. Cyclic disubstituted epoxides 1k and 1l
were also investigated as substrates. Cyclohexene oxide 1k
failed to react when a catalyst loading of 1 mol% of each com-
ponent was used (Table 4, entry 14). Increasing the catalyst
loading to 5 mol% of each component resulted in the forma-
tion of cis-cyclohexene carbonate in only 10% yield (Table 4,
entry 15). No polycarbonate was formed in these reactions.
The reaction of cyclopentene oxide 1l was slightly more suc-
cessful, giving cyclopentene carbonate 2l in 31% yield when
5 mol% of each catalyst component was used.
Figure 4. 1H NMR spectra of different ratios of BGI/BINOL in CD2Cl2. a) pure
BGI; b) BINOL/BGI=1:1; c) BINOL/BGI=2:1; d) BINOL/BGI=3:1; and e) pure
BINOL.
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Table 4. CVI/BINOL catalyzed synthesis of cyclic carbonates.
Scheme 3. Use of deuterated epoxides 3a,b to study the stereochemistry of
the cyclic carbonates.
Entry Cyclic car-
bonate
CVI+BINOL
[mol%]
Yield[a] Conversion[b] Selectivity
[%]
[%]
[%]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
2a
2b
2b
2c
2c
2d
2e
2 f
2 f
2g
2h
2i
1+1
1+1
2+2
1+1
2+2
1+1
1+1
1+1
2+2
2+2
2+2
2+2
2+2
1+1
5+5
5+5
72
48
54
82
54
100
76
100
100
100
37
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
the reaction (Scheme 3). In both cases, deuterated cyclic carbo-
nates 4a,b were formed with predominant retention of the ep-
oxide stereochemistry. However, some epimerization was ob-
served, which depended on the amount of catalyst used, as
shown in Table 6. A control experiment in which epoxide 3b
was heated to 508C under nitrogen in the presence of 2 mol%
of both CVI and BINOL showed that it did not epimerize under
these conditions.
70
70
65
60
56
79
71
61
0
78
100
100
100
100
2j
2k
2k
2l
10
31
20
70
>99
>99
Table 6. Synthesis of deuterated cyclic carbonates 4a,b.[a]
Entry Epoxide Catalyst system concentration [mol%] Ratio of 4a/4b
[a] The cyclic carbonates were isolated by flash chromatography on silica.
[b] Conversions were determined by 1H NMR using the catalyst signals as
an internal standard.
1
2
3
3b
3b
3a
2
6
6
11:89
22:78
73:27
[a] Reaction conditions: 2–6 mol% BINOL, 2–6 mol% CVI, neat epoxide
3a or 3b, 508C, 5 MPa CO2, 24 h.
The stability of the CVI/BINOL catalytic system was investi-
gated by reusing the catalysts in the reaction of PO at 508C
and 5 MPa CO2 pressure with a reaction time of 24 h. After the
first 24 h period, the yield of the cyclic carbonate 2d was de-
termined by 1H NMR spectroscopy, then another portion of
propylene oxide was added to the reaction mixture. The re-
sults are shown at Table 5. The system could be recharged five
times with no loss of activity.
On the basis of the spectroscopic and stereochemical stud-
ies, a possible mechanism for the reaction is proposed in
Scheme 4. The carbocation acts as a Lewis acid, activating the
BINOL to become a stronger Brønsted acid. The increase in the
acidity of the BINOL OH group allows it to form a stronger hy-
drogen bond with the epoxide and triggers the epoxide ring
opening by the iodide ion to give intermediate 5. The iodide
ion itself may be positioned in space by the second OH group
of BINOL. The remaining OH group in intermediate 5 could co-
ordinate to CO2, both activating and organizing it towards in-
tramolecular carbonate formation to give intermediate 6,
which can then cyclize to form the cyclic carbonate product
and regenerate the catalyst components.
To investigate the mechanism of the reaction, deuterated
epoxides 3a,b[26] were used to study the stereochemistry of
Table 5. Reusability of the CVI-BINOL catalytic system.[a]
Entry Cycle Catalyst system concentration [mol%] Conversion[b] [%]
1
2
3
4
5[c]
1
2
3
4
5
2
1
0.67
0.5
2
100
100
95
74
100
Intermediates 5 and 6 could also undergo a non-productive
SN2 reaction of the alkyl iodide with external iodide. This reac-
tion would only be visible (as a loss of stereochemical purity)
in deuterated epoxides such as 3a,b, and the relative rate of
reaction with iodide to intramolecular cyclization of the car-
bonate is expected to increase as the concentration of iodide
in the reaction increases, i.e., with increased catalyst loading,
which accounts for the results presented in Table 6.
[a] Reaction conditions: 1 mol% BINOL, 1 mol% CVI, neat PO (50 mg,
0.06 mL, 0.86 mmol), 508C, 5 MPa CO2, 24 h. The second and subsequent
cycles included the addition of a fresh 50 mg portion of epoxide 1d to
the reaction mixture after each 24 h reaction period. [b] Conversions
were determined using 1H NMR spectroscopy. [c] Reaction conditions:
1 mol% BINOL, 1 mol% CVI, both recovered from the experiment of
entry 4 following distillation of 2d, neat PO (50 mg, 0.06 mL, 0.86 mmol),
508C, 5 MPa CO2, 24 h.
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(d, J=8.8 Hz, 4H), 7.34 (d, J=7.6 Hz, 2H), 7.00 (d, J=8.9 Hz, 4H),
3.40 ppm (s, 12H); 13C NMR (101 MHz, CDCl3) d=177.68, 156.98,
141.00, 139.50, 134.73, 133.13, 128.61, 127.38, 113.98, 41.43 ppm.
X-ray fluorescence data: no Cl was detected.
Brilliant green iodide. Brilliant green mono-oxalate (1.0 g,
2.0 mmol) dissolved in CH2Cl2 (10 mL) was added to a solution of
KI (7.0 g, 42 mmol) in water (10 mL). The resulting suspension was
stirred at room temperature for 4 h, then was neutralized by the
addition of aqueous NaOH. The organic layer was separated, dried
over MgSO4, and evaporated under reduced pressure to give bril-
liant green iodide (0.92 g, 90%) as green crystals. M.p. 186–1898C;
IR (KBr) n˜ =3060, 2972, 2928, 1580, 1341, 1186 cmꢀ1 1H NMR
;
(400 MHz, CDCl3) d=7.73–7.68 (m, 1H), 7.56 (t, J=7.6 Hz, 2H), 7.41
(d, J=8.8 Hz, 4H), 7.34 (d, J=7.6 Hz, 2H), 7.00 (d, J=8.9 Hz, 4H),
3.40 ppm (s, 12H); 13C NMR (101 MHz, CDCl3) d=177.68, 156.98,
141.00, 139.50, 134.73, 133.13, 128.61, 127.38, 113.98, 41.43 ppm.
X-ray fluorescence data: no Cl was detected.
Crystal violet iodide. Crystal violet chloride (1.0 g, 2.4 mmol) dis-
solved in CH2Cl2 (10 mL) was added to a solution of KI (7.0 g,
42 mmol) in water (10 mL). The resulting suspension was stirred at
room temperature for 4 h, then the organic layer was separated,
dried over MgSO4, and evaporated under reduced pressure to give
crystal violet iodide (0.94 g, 92%) as green crystals. M.p. 192–
1948C; IR (KBr) n˜ =3087, 2913, 2852, 2808, 1581, 1358, 1171 cmꢀ1
;
1H NMR (400 MHz, CDCl3) d=7.03 (d, J=9.0 Hz, 6H), 6.60 (d, J=
9.0 Hz, 6H), 3.03 ppm (s, 18H); 13C NMR (101 MHz, CDCl3) d=
177.57, 155.32, 139.44, 126.25, 112.32, 40.76 ppm. X-ray fluores-
cence data: no Cl was detected. Calculated for C25H30IN3.H2O: C,
58.03; H, 6.23; N, 8.12. Found: C, 57.95; H, 6.19; N, 7.99.
Scheme 4. A possible mechanism rationalizing the synergistic effect of
BIMBOL on the activity of the dyes in the synthesis of cyclic carbonates.
Synthesis of cyclic carbonates
Experimental Section
All cyclic carbonate syntheses were performed in autoclaves with
5 MPa carbon dioxide starting pressure. The reactions were heated
to 508C and magnetically stirred. After completion of the reaction,
the autoclave was cooled to room temperature before the pressure
Materials
Commercial reagents were used as received unless stated other-
wise. Column chromatography was performed using Silica Gel Kie-
selgel 60 (Merck).
1
was released. The reaction mixture was analyzed by H NMR spec-
troscopy and passed through a pad of silica to separate the cata-
lyst. Column chromatography (SiO2, EtOAc/hexane, 1:3) was then
used to purify the cyclic carbonates.
Instrumentation
Styrene carbonate 2a: M.p. 50–528C; IR (ATR): n˜ =3037, 2921,
1
1782, 1160, 1050 cmꢀ1; H NMR (400 MHz, CDCl3) d=7.44–7.32 (m,
1H and 13C NMR spectra were recorded on Bruker Avance 300,
Bruker Avance III-400, and Bruker Avance 600 spectrometers. Melt-
ing points were determined in open capillary tubes and are uncor-
rected. Elemental analysis was performed at the elemental analysis
laboratory of the Nesmeyanov Institute of Organoelement Com-
pounds of Russian Academy of Sciences (INEOS RAS). All solvents
were purified according to standard procedures.
5H), 5.66 (t, J=8.0 Hz, 1H), 4.82–4.73 (m, 1H), 4.37–4.26 ppm (m,
1H); 13C NMR (101 MHz, CDCl3) d=155.00, 135.88, 129.80, 129.31,
126.00, 78.11, 71.28 ppm.
4-Chlorostyrene carbonate 2b: M.p. 67–708C; IR (ATR) n˜ =3087,
2964, 2912, 1789, 1162, 1048 cmꢀ1 1H NMR (400 MHz, CDCl3) d=
;
7.48–7.25 (m, 4H), 5.65 (t, J=8.0 Hz, 1H), 4.79 (t, J=8.2 Hz, 1H),
4.29 ppm (dd, J=8.6, 7.9 Hz, 1H); 13C NMR (101 MHz, CDCl3) d=
154.65, 135.85, 134.35, 129.59, 127.37, 77.34, 71.10 ppm.
Synthesis of carbocations
4-Bromostyrene carbonate 2c: M.p. 70–728C; IR (ATR) n˜ =2951,
Malachite green iodide. Malachite green chloride (1.0 g, 2.7 mmol)
dissolved in CH2Cl2 (10 mL) was added to a solution of KI (7.0 g,
42 mmol) in water (10 mL). The resulting suspension was stirred at
room temperature for 4 h, then the organic layer was separated,
dried over MgSO4, and evaporated under reduced pressure to give
malachite green iodide (0.95 g, 94%) as green crystals. M.p. 100–
1
2522, 2161, 2017, 1981, 1801, 1771 cmꢀ1; H NMR (400 MHz, CDCl3)
d=7.59 (d, J=8.0 Hz, 2H), 7.25 (d, J=8.0 Hz, 2H), 5.64 (t, J=
8.0 Hz, 1H), 4.80 (t, J=8.0 Hz, 1H), 4.30 ppm (t, J=8.0 Hz, 1H);
13C NMR (100 MHz, CDCl3) d=154.5, 134.8, 132.5, 127.4, 123.9, 77.2,
70.9 ppm.
1028C; IR (KBr): n˜ =2920, 2851, 1583, 1363, 1167 cmꢀ1
;
1H NMR
3-Chloropropylene carbonate 2d: IR (ATR) n˜ =2967, 1779, 1159,
(400 MHz, CDCl3) d=7.73–7.68 (m, 1H), 7.56 (t, J=7.6 Hz, 2H), 7.41
1055 cmꢀ1
;
1H NMR (400 MHz, CDCl3) d=5.02–4.93 (m, 1H), 4.60–
&
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Full Papers
metal based systems,[20] which have been extensively devel-
oped over more than a decade.
4.53 (m, 1H), 4.37 (dd, J=8.9, 5.7 Hz, 1H), 3.82–3.67 ppm (m, 2H);
13C NMR (101 MHz, CDCl3) d=154.49, 74.48, 67.06, 44.03 ppm.
Propylene carbonate 2e: IR (ATR) n˜ =2988, 2924, 1781, 1174,
1044 cmꢀ1 1H NMR (400 MHz, CDCl3) d=4.92–4.67 (m, 1H), 4.64–
;
4.38 (m, 1H), 4.07–3.89 (m, 1H), 1.43 ppm (d, J=6.3 Hz, 3H);
13C NMR (101 MHz, CDCl3) d=155.22, 73.74, 70.78, 19.45 ppm.
Acknowledgements
The authors gratefully acknowledge the financial support from
a RFBR research grant No. 15-03-05648, a Russian Science Foun-
dation grant No. 16-14-00112 and a RAS Presidium grant of basic
research No. P-8 and from the European Union Seventh Frame-
work Programme FP7-NMP-2012 under grant agreement number
309497.
1,2-Decylene carbonate 2 f: IR (ATR) n˜ =2931, 2835, 1796 cmꢀ1
;
1H NMR (400 MHz, CDCl3) d=4.71–4.68 (m, 1H), 4.52 (t, J=8.0 Hz,
1H), 4.06 (t, J=8.0 Hz, 1H), 1.83–1.63 (m, 2H), 1.47–1.26 (m, 12H),
0.87 ppm (t, J=8.0 Hz, 3H); 13C NMR (100 MHz, CDCl3) d=155.1,
77.0, 69.4, 33.9, 31.8, 29.3, 29.1, 29.0, 24.3, 22.6, 14.1 ppm.
1,2-Hexylene carbonate 2g: IR (ATR) n˜ =2941, 2922, 2899,
1796 cmꢀ1 1H NMR (400 MHz, CDCl3) d=4.73–4.66 (m, 1H, OCH),
;
4.52 (t, J=8.0 Hz, 1H), 4.06 (t, J=8.0 Hz, 1H), 1.86–1.65 (m, 2H),
1.49–1.35 (m, 4H), 0.92 ppm (t, J=8.0 Hz, 3H); 13C NMR (100 MHz,
CDCl3) d=155.1, 76.8, 69.4, 33.5, 26.4, 22.2, 13.8 ppm.
Keywords: carbocations · carbon dioxide · catalysts · cyclic
carbonates · phenols
1,2-Dodecylene carbonate 2h: IR (ATR) n˜ =2931, 2832, 1798 cmꢀ1
;
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1H NMR (400 MHz, CDCl3) d=4.73–4.66 (m, 1H), 4.52 (t, J=8.0 Hz,
1H), 4.06 (t, J=8.0 Hz, 1H), 1.84–1.70 (m, 2H), 1.63–1.26 (m, 16H),
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1
3429, 3061, 2989, 2924, 2328, 1791 cmꢀ1; H NMR (400 MHz, CDCl3)
d=7.30 (t, J=8.0 Hz, 2H), 7.02 (t, J=8.0 Hz, 1H), 6.91 (d, J=8.0 Hz,
2H), 5.06–5.01 (m, 1H), 4.62–4.55 (m, 2H), 4.24 (dd, J=11.0, 4.0 Hz,
1H), 4.16 ppm (dd, J=11.0, 4.0 Hz, 1H); 13C NMR (100 MHz, CDCl3)
d=157.7, 154.6, 129.7, 122.0, 114.6, 74.0, 66.8, 66.2 ppm.
1
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Conclusions
Catalytic systems consisting of commercially available carboca-
tions and polyols were found to be active as catalysts for the
synthesis of cyclic carbonates. Carbocations in these systems
act as activators of polyol hydroxyl groups, increasing their
Brønsted acidity. Malachite green, brilliant green, and crystal
violet have been used as antiseptic, antibacterial and fungicidal
agents to treat both humans and animals.[27] As such, they can
be considered as greener and safer catalysts than those based
on complexes of toxic metals such as cobalt, chromium, and
aluminum. The catalytic activity of the dye based catalysts is
comparable to those often reported for metal-based cata-
lysts,[2,3] although not as good as the activity of the very best
ChemSusChem 2016, 9, 1 – 9
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Received: September 7, 2016
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Published online on && &&, 0000
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FULL PAPERS
Double team! Triarylmethane dyes and
1,1’-bi-2-naphthol are combined to form
an organocatalytic system for the syn-
thesis of cyclic carbonates from epox-
ides and carbon dioxide. A catalytic
cycle is proposed based on mechanistic
studies using a deuterated epoxide as
a substrate.
Y. A. Rulev, Z. T. Gugkaeva, A. V. Lokutova,
V. I. Maleev, A. S. Peregudov, X. Wu,
M. North,* Y. N. Belokon*
&& – &&
Carbocation/Polyol Systems as
Efficient Organic Catalysts for the
Preparation of Cyclic Carbonates
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