Binuclear molybdenum alkoxide as the versatile catalyst for the conversion of carbon dioxide

Article abstract of DOI:10.1039/c7gc03372a

The triply bonded dimolybdenum compound, Mo₂(O^tBu)₆ (1), was investigated as a homogeneous catalyst for the conversion of CO₂. The compound 1 acted as a rare example of a versatile catalyst with an impressive ability to transform CO₂ into various valuable products, including propiolic acids, cyclic carbonates, and benzo[d]thiazole- and benzo[d]oxazolecarboxylic acids, in high yields with short reaction times and excellent selectivity at ambient pressure and low temperatures (25-75 °C). This is the first report of the application of a metal-metal bond-containing species in the catalytic conversion of CO₂.

Full text of DOI:10.1039/c7gc03372a

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Binuclear molybdenum alkoxide as the versatile catalyst for the
conversion of carbon dioxide†
Jing-Huo Chen,a Cheng-Hua Deng,a Sheng Fang,a Jian-Gong Ma*a and Peng Cheng*a,b
Received 00th January 20xx,
Accepted 00th January 20xx
The triply-bonded dimolybdenum compound, Mo2(OtBu)6 (1), was investigated as homogeneous catalyst for the
conversion of CO2. 1 acted as a rare example of versatile catalyst with impressive activity to transform CO2 into various
valuable products including propiolic acids, cyclic carbonates, benzo[d]thiazole and benzo[d]oxazole carboxylic acids in
high yield, short reaction time and excellent selectivity at ambient pressure and low temperatures (25-75 °C). This is the
first report on applying metal-metal-bond-containing species in catalytically CO2 conversion.
DOI: 10.1039/x0xx00000x
www.rsc.org/
Binuclear molybdenum alkoxides with metal-metal bond
were intensively explored by Cotton, Chisholm and the other
groups, which exhibited special electronic configuration, broad
Introduction
reaction types and rich reactivity towards certain substrates.5
However, the application of such compounds in catalysis is
barely studied.6 The triply-bonded Mo2(OR)6-type (R = Me3Si,
The massive emission of CO2 and subsequent series
environmental problems such as greenhouse effect, glacier
melting and a rise in sea level, are one of the global challenges
confronting us in this century.1 Alternatively, CO2 is also a non-
toxic, renewable, and low-cost C1 resource, which can be used
by chemical methods to provide high-value products.2 Several
methods and catalysts, including both homo- and hetero-
generous catalytic systems, have been developed in this area,
such as nanoparticles, metal clusters, organometallic
compounds, metal-organic frameworks and composite
materials.2,3 Nevertheless, most of the reported catalysts
convert CO2 to only one type of product, and the materials
suitable for activating CO2 in different progresses and
productions are quite rare. As a homogeneous catalytic
system, N-heterocyclic carbene (NHC) exhibits significant
activity for the activation of CO2 in several procedures,3d,4
while different central metal ions, substituents and/or ancillary
ligands are demanded for each catalytic reaction to obtain the
optimal efficiency and result. The development of efficient,
inexpensive, and easily prepared versatile catalysts for
converting CO2 into different types of high value-added
products is just at the beginning, which could supply a new
strategy to reduce the cost, save the energy-consuming and
expand the application prospect of CO2 fixation and
conversion.
t
iPr, Bu, Ne) compounds were reported to react with CO2 via a
Mo-OR bond insertion reaction leading to products of the type
Mo2(OR)4(O2COR)2 (Scheme 1).7 This reversible reaction
indicated the potential of Mo2(OR)6 compounds in activating
CO2, thus we selected such compound as catalyst to explore
new system for CO2 conversion.
Herein, we reported the first attempt to apply metal-metal-
bond-containing species for catalyzing CO2 transformation. We
investigated the binuclear molybdenum alkoxide, Mo2(OtBu)6
(1
), as a homogeneous catalyst for the conversion of CO2.
Under ambient pressure, CO2 was converted by into multiple
1
products including propiolic acids, cyclic carbonates,
benzo[d]thiazole and benzo[d]oxazole carboxylic acids in high
yield, short reaction time, low energy-consuming, good
tolerance of substrates and excellent selectivity.
1 exhibited a
rare example as highly efficient versatile catalyst for CO2
conversion.
Results and discussion
According to the reported method,
1 can be synthesized as
orange crystals from MoCl5 in at least four steps.5b,8 We
simplified the procedure into two steps including a “one-pot”
reaction of MoCl5 with Sn in ether and subsequent reaction
with LiOtBu (see the experimental section for details), which
reduced the complicity and saved synthesis time and cost.
aDepartment of Chemistry and Key Laboratory of Advanced Energy Material
Chemistry, College of Chemistry, Nankai University, Tianjin 300071 (P. R. China).
E-mail: mvbasten@nankai.edu.cn.
bState Key Laboratory of Elemento-Organic Chemistry and Collaborative Innovation
Center of Chemical Science and Engineering (Tianjin), Nankai University, Tianjin
300071 (P. R. China).
E-mail: pcheng@nankai.edu.cn.
†Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See DOI:
10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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Journal Name
DMViFew Artic6le5O.8nline
6
7
8
9
1.5
1.5
1.5
1.5e
3.0b
3.0c
1.5d
1.5
10
10
10
10
50
50
50
50
DMF
DMF
DMF
DOI: 10.1039/C7GC30433.472A
21.5
98.2
a Reaction conditions: 1-ethynylbenzene (1.0 mmol), catalyst 1, CO2
b
c
d
(1.0 atm, using a balloon), solvent (5 mL). K(OtBu). Li(OtBu).
Scheme 1 The reversible reaction of Mo2(OR)6 with CO2.
Firstly, we determined the catalytic activity of
e
f
1 for the
K2CO3. 1·CO2. Yields of gas chromatography. For a full condition
survey, See Table S1 in ESI†.
fixation of CO2 with terminal alkynes into propiolic acids, which
served as important synthetic intermediates in medical and
organic synthesis to give coumarins, flavones, aminoalkynes,
alkynylarenes, and arylideneoxindoles.2b,c,3a,9 As shown in
Table 1, we carried out generation of 3-phenylpropiolic acid
Table 2 Synthesis of propiolic acid derivatives from CO2 and
terminal alkynes with catalyst 1.a
from CO2 (1 atm) and 1-ethynylbenzene at 50 °C by
1 in DMF
as the model. With only 1.5 mol% of , we obtained the
1
product in a high yield of 93.2% within 10 h (Entry 1, Table 1),
3a, 93.2%
3b, 94.5%
3c, 93.8%
The TON and TOF were 62.1 and 6.21 h-1 respectively. It should
be noted that the performance of
1 is outstanding for the mild
condition and short reaction time in comparison with most of
the reported catalysts (Table S3, ESI†): for most of the
reported catalysts working at 1 atm, 16-24 hours are required
to complete the reactions, while at least a time of 37.5% is
3d, 96.6%
3e, 95.2%
saved when using
the dosage of
1
as catalyst. Either increasing or decreasing
3f, 73.8%
1
(Table S1, ESI†) led to the decrease of the
3g, 74.0%
3h, 66.6%
yield. The process could hardly run without catalyst or base
(Entries 2 and 3, Table 1). The catalytic effect was sensitive to
temperature (Entries 4 and 5, Table 1): At 25 °C, less than 5%
yield was obtained, because lower temperature was unfavorite
for the activation of 1-ethynylbenzene and the release of the
product from the dimolybdenum center; when the
temperature was 75 °C, the yield of 3-phenylpropiolic acid
decreased to 87.6% in comparison of 93.2% at 50 °C, probably
because high temperature could reverse the reaction direction
3i, 82.7% (>99%b)
3j, 77.2% (>99%b)
a
Reaction conditions: terminal alkyne (1.0 mmol), catalyst 1 (1.5
mol%), Cs2CO3 (1.5 mmol), CO2 (1.0 atm, using a balloon), 50 °C,
b
DMF (5 mL), 10 h. Selectivities for diethynylbenzene substrates,
confirmed by thin-layer chromatography, column chromatography
and crystal structures of the products. Yields of isolated products
were obtained by column chromatography separation.
of CO2 with
1 and hinder the efficient activation of CO2. The
influence of organic solvents was surveyed on the catalytic
system, which confirmed DMF as a superior solvent for this
system (Table S1, ESI†) because DMF as a weak base was a
better solvent for both Cs2CO3 and CO2 than the other
solvents.10 Variation of Cs2CO3 to the other bases under
otherwise identical conditions led to the decrease of the yield
into 65.8-21.5% (Entries 6-8, Table 1), indicating that Cs2CO3
was the suitable base for deprotonation of terminal
alkynes.2c,11
We further subjected several important aromatic alkyne
substrates with electron-donating (CH3, OCH3) or electron-
withdrawing (Cl) substituents to react with CO2 under the
standard condition (1.5 equiv Cs2CO3, 1 atm CO2, DMF, 50 °C),
and corresponding products in excellent yields (93.8-96.6%)
were obtained, as shown in Table 2. Even for an alkyne with a
heterocyclic group (thiophene), 95.2% yield was achieved. As
catalyst,
1 showed good hindrance tolerance as well, which
Table 1 Synthesis of 3-phenylpropiolic acid from CO2 and 1-
catalyzed carboxylation of aromatic alkynes with substituents
as large as naphthalene, anthracene and pyrene in a yield of
ethynylbenzene with catalyst 1.a
ca. 70% respectively (Entries 3f
-
3h, Table 2).
Importantly, we found that
1 exhibited excellent selectivity
Catalyst
(mol%)
Base
(mmol)
Time Temp
Yieldf
(%)
for the carboxylation of diethynylbenzenes (Entries 3i and 3j
Table 2). When reacting either 1,3 or 1,4-diethynylbenzene
with CO2 by , we obtained the asymmetric compounds with
,
Entry
Solvent
(h)
10
10
10
10
10
(°C)
50
50
50
25
75
1
1
2
3
4
5
1.5
0
1.5
1.5
0.0
1.5
1.5
DMF
DMF
DMF
DMF
DMF
93.2
5.8
<5
>99% selectivity and yields of 77.2% and 82.7%, respectively,
as confirmed by thin-layer chromatography, column
chromatography and crystal structures of the products (Fig. S2,
Fig. S3 and Table S2, ESI†). As far as we know, most of the
other catalysts reported till now can only convert these
diethynylbenzene compounds into corresponding symmetric
1.5
1.5
1.5
<5
87.6
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dicarboxylic acids (Table S4, ESI†).9c,12 Although Ag2WO4 could
gave some production of 3i, while poor yield (24%) and barely
selectivity was reported (Table S4, ESI†). In comparison with
symmetric dicarboxylic acids, the asymmetric products could
participate in more extensive subsequent modifications and
progresses, such as polymerization, Diels-Alder reaction,
reductive addition and so on, to form more types of industrial
and/or pharmaceutical products. This asymmetric selectivity
View Article Online
DOI: 10.1039/C7GC03372A
7a, 94.2%
7d, 92.5%
7b, 89.9%
7e, 87.5%
7c, 91.8%
7f, 92.7%
Reaction conditions: heterocycle (1.0 mmol), catalyst 1 (3.0 mol%),
Cs2CO3 (1.2 mmol), CO2 (1.0 atm, using a balloon), 75 °C, DMF (3
mL), 10 h. Yields of isolated products were obtained by column
chromatography separation.
makes
1 an outstanding catalyst for CO2 conversion.
Table 3. Carboxylation of aromatic heteroarenes catalysed by 1.a
To further explore the characteristic of 1 as the versatile catalyst
for CO2 conversion, we performed the third model reaction of CO2
with propylene oxide, which is an attractive strategy of CO2 fixition,
because the products, cyclic carbonates, are one of the most
important materials as degreaser, electrolytes in lithium ion
batteries, raw materials for plastics, precursors for pharmaceutical
intermediates, eco-friendly nonprotic solvents, and so on.14
Catalytic systems for the conversion of CO2 into cyclic carbonates
have been investigated in recent decades, including Schiff base,
NHC complex, Salen-metal compound and metal-organic
frameworks as well as organic/inorganic salts.2a,14,15 However,
development of new catalytic materials with mild condition and
short reaction time is still highly-demanded till now.
At 1 atm and room temperature (25 °C), we carried out the
catalytic CO2 insertion of propylene oxide with 1 in the presence of
tetrabutylammonium bromide (nBu4NBr). The reaction process was
attentively monitored, as shown in Fig. 1. Impressively, we achieved
a yield as high as 86.0% with 1.0 mol% loading of 1 within a short
time of 2 h (TON, 86.0 and TOF, 43.0 h-1). Further reducing the
loading of 1 to 0.5 mol% still afforded 78% yield during the first 2 h
(TON, 156.0 and TOF, 78.0 h-1). As far as we know, there is barely
observation of a catalyst exhibiting such high efficiency under
ambient temperature and pressure for this reaction (Table S4, ESI†),
which confirms the unique activity of 1 for the activation and
conversion of CO2.
Catalyst
(mol%)
Temperature
(°C)
Yieldd
(%)
Entry
Time (h)
1
2
1.5
3.0
4.5
3.0
3.0
3.0
3.0
10
10
10
5
75
75
75
75
50
75
75
68.9
95.3
94.8
61.4
19.8
82.1
71.7
3
4
5
10
10
10
6b
7c
a
Reaction conditions: benzothiazole (1.0 mmol), catalyst 1, base
(Cs2CO3, 1.2 mmol), CO2 (1.0 atm, using a balloon), solvent (DMF, 3
b
c
d
mL). K(OtBu). Li(OtBu). Yield of Isolated product obtained by
column chromatography separation.
Secondly, we applied
1 for the C-C coupling of heteroarenes
with CO2 to afford 1,3-benzo[d]thiazole-2-carboxylic acid, 1,3-
benzo[d]oxazole-2-carboxylic acid and their derivatives. Till
now the type of catalysts for such reactions is quite limited,
and relatively high temperature, long reaction time and/or
extra pressure are normally demanded.3b,d,4b,c,13 As the model
reaction, we catalyzed the reaction of 1.0 atm CO2 with
After the first 2 h, the reaction slowed down, owing to the
decreasing concentrition of substrate present in the reaction
system.24 A yield as high as 97.5% was obtained in 24 h.
nBu4NBr is important in the catalysis process for the ring-open
of epoxides,14,15,19 while only 14% yield was observed with
benzo[d]thiazole by 1 under the presence of Cs2CO3 in DMF. At
50 °C, the carboxylation product yield was only 19.8%, which
was enhanced significantly to 95.3% at 75 °C (Table 3; TON,
31.8 and TOF 3.2 h-1). Under the optimized condition, we
subjected typical derivatives of both benzo[d]thiazole and
benzo[d]oxazole to the C-C coupling reaction, and observed
excellent yields (85.4-95.3%), as shown in Table 4. All of these
carboxylations were completed in 10 h, indicating the high
nBu4NBr solely without
epoxide substrates,
1
(Condition f, Fig. 1). For the terminal
1
exhibited good substituent tolerance as
well with the yields of 93.1-96.8% even for the substrate
containing naphthalene unit (Entries 9b-9e, Table 5). Although
cyclohexene oxide was much less reactive compared to the
aromatic substrates, we still observed 61.2% yield under such
mild condition (Entry 9f, Table 5).
activity of
1.
Table 4 The carboxylation of heteroarenes catalyzed by 1.
6a, 95.3%
6d, 85.4%
6c, 91.3%
6f, 93.5%
6b, 89.2%
6e, 91.2%
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characterized 1·CO2 as intermediate at the begiVnienwinAgrticolefOntlhinee
reaction (Figure S1, ESI†). The formation of 1·CO2
DOI: 10.1039/aCs7GtCh0e33fi7r2sAt
step could be further confirmed by the fact that even higher
yield was obtained with
Fig. 1 Optimal experiments: CO2 (1 atm in a balloon), 25 °C,
a
b
propylene oxide (50.0 mmol). 1 (1.0 mol%), nBu4NBr (3.6 mmol).
1 (1.0 mol%), nBu4NBr (1.8 mmol). 1 (0.5 mol%), nBu4NBr (3.6
c
mmol). d 1 (1.0 mol%), Bu4NBr (5.0 mmol). 1 (0.1 mol%), Bu4NBr
n
e
n
(3.6 mmol). f 1 (0 mmol), nBu4NBr (3.6 mmol).
Scheme 2 Proposed catalytic process of
CO2 with terminal alkynes and heteroarenes.
1·CO2 instead of as catalyst for the generation of 3-
1 for the reactions of
Table 5 Synthesis of cyclic carbonates from CO2 and epoxides with 1
and nBu4NBr.
1
phenylpropiolic acid (Entry 9, Table 1). Bases are inevitable in
these catalytic process, because Cs2CO3 is important for the
activation and deprotonation of alkynes2c,11,12,18 or
heteroarenes,13 respectively. We have separated CsHCO3 from
the former two reactions, confirming the deprotonation role of
Cs2CO3 (Figure S4, ESI†). Subsequently, 1·CO2 could react with
the activated substrates leading to intermediates with both
CO2 and corresponding substrates connected on the Mo-Mo
center. Based on the crystal structure (Figure S1, ESI†), two
tBu-O-COO bridges in 1·CO2 are at a cis-position of each other,
thus for the reaction of diethynylbenzenes, the intermediate
formed by the reaction of X* with one 1·CO2 molecule could
hardly react further with another molecule of 1·CO2 due to the
stereo hindrance effect, and asymmetric products are
obtained instead of the dicarboxylic acids. According to the
meta-stability of the bonding between O2C- and -OtBu unit, an
intramolecular rearrangement is possible to form C-C bonds
between CO2 and corresponding substrates, after which the
final products are released from the Mo-Mo center, and
9c, 93.1%
9f, 61.2%
9a, 97.5%
9d, 94.2%
9b, 96.8%
9e, 93.8%
Reaction conditions: 9a-9b, epoxide (50.0 mmol), catalyst 1 (1.0
n
mol%), Bu4NBr (3.6 mmol), CO2 (1 atm, using a balloon), 25 °C; 9c-
9f, epoxide (10.0 mmol), catalyst 1 (1.0 mol%), nBu4NBr (0.72 mmol),
CO2 (1 atm, using a balloon), 25 °C, CH2Cl2 (3 mL). Yields of isolated
product obtained by column chromatography separation.
In the basis of the results above, we considered the
mechanism for
for CO2 versatile conversion, and following three unique
features of should be noticed: i) can activate CO2 molecule
1 to exhibit such outstanding catalytic activity
1
1
catalyst
1 could be recovered. The reaction mechanism of CO2
with the Mo-Mo center very fast, but can also release it easily
instead of forming strong bonding, which is of benefit for
with epoxides catalyzed by
1
could be similar as that of the
reaction for alkynes or heteroarenes, while nBu4NBr is used
instead of Cs2CO3 for the ring-open of epoxides,14,15,19 as
presented in Scheme S1 (ESI†).
completing the catalytic circle efficiently; ii) besides CO2,
1 can
also interact with other molecules or units with the Mo-Mo
center, such as alkynes16 and organometallic anions,17 in order
to connect both -CO2 and other groups to the same Mo-Mo
Conclusions
center and enhance the possibility of bond-forming between
t
them; and iii) the proper steric effect of Bu groups render
1
In summary, we establish a new catalytic system, and
thoroughly discrete in solution, which could lead to the unique
selectivity of towards the diethynyl substrates.
Based on these facts, we proposed the general catalytic
process of for converting CO2 in the C-H bond activation
investigate the dimolybdenum alkoxide catalyst
example of versatile catalyst to convert CO2 into various high
value-added products. For each model reaction, exhibits its
own peculiarities: i) At ambient pressure and 50 °C,
catalytically converts CO2 into propiolic acids efficiently, and
affords >99% selectivity for the carboxylation of
diethynylbenzenes to give the asymmetric products, which is
1 as a rare
1
1
1
1
reactions, as shown in Scheme 2. The first step is
unambiguously CO2 insertion into Mo-O bonds to form
Mo2(O2COtBu)2(OtBu)4
(1·CO2), since we have separated and
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barely reported. ii) Outstanding activity of
1
is observed for the became colorless. The filtrate was combined evapVoierwatAertdiclteoOnglienet
t
DOI: 10.1039/C7GC03372A
C-C coupling of heteroarenes with CO2 under
1
atm and 75 °C the product Mo2(O Bu)6 3.20 g under pressure. Yield: 55.5%
in excellent yields within 10 h. iii) Excellent yields are achieved (based on MoCl5). 1H NMR (300 MHz, C6D6):
by for the production of cyclic carbonates from CO2 within 2
 1.59 (s) ppm.
1
h, which is an exceptional efficiency under ambient pressure
and temperature compared with the known catalysts for this
Preparation of Mo2(OtBu)4(OOCOtBu)2 (1·CO2)
reaction. This contribution could supply new route for the CO2 (20 Mpa) was transfered into a high pressure reactor
circulation of carbon in environment and sustainable containing a block sample of Mo2(OtBu)6 (1.0 g). After one day,
production in industry, pharmacy and chemical engineering. all the red solid had become a blue solid which was identified
Catalytically conversion of CO2 by
ongoing in our lab.
1
to other products is as Mo2(OtBu)4(OOCOtBu)2 by 1H NMR and single crystal
1
diffraction. H NMR (300 MHz, C6D6):
18H) ppm.
 1.63 (s, 36H), 1.49 (s,
Experimental section
General experimental procedure for carboxylation of
terminal alkynes
General procedures
The terminal alkynes (1.0 mmol), Cs2CO3 (489 mg, 1.5 mmol)
and Mo2(OtBu)6 (10 mg, 1.5 mol%) were placed in a 10 mL
Schlenk reaction tube. The reaction tube was degassed, the
CO2 (balloon) and DMF (5 mL) were then introduced in to the
reaction mixture under stirring. After this, the reaction mixture
was stirred at 50 °C for 10 h, then the reaction mixture was
cooled to room temperature. Water (10 mL) was added to
dilute the reaction mixture and it was washed with CH2Cl2 (3
times, 10 mL each). Then the water phase was acidified with
concentrated HCl to pH = 1 and stirred for 0.5 h. The alkynes
acid was extracted with ethyl acetate (3 times, 10 mL each).
The organic phase was dried with Na2SO4, filtered and the
solvent was evaporated under vacuum to afford the alkynes
acid. The product was purified by a flash chromatography and
characterized by NMR.
Unless otherwise noted, all manipulations were performed
under a dry argon or carbon dioxide atmosphere using
Schlenk-line techniques or under an argon atmosphere in an
Mbraun glovebox. All the reagents employed were
commercially available and used without further purification.
Acetonitrile
was
distilled
from
calcium
hydride;
tetrahydrofuran, n-hexane and ether were distilled from
sodium piece; Superdry N,N-Dimethylformamide with
molecular sieves and 2.2 M LiOtBu of THF solution were used
without further purification. NMR spectra were recorded on a
Varian Inc Mercury Vx-300 type (1H NMR, 300 MHz; 13C NMR,
75 MHz) spectrometer and a Bruker Ascend-400 spectrometer
(1H NMR, 400 MHz; 13C NMR, 101 MHz). Data were reported in
the following order: chemical shift in ppm (multiplicity was
indicated by s (singlet), d (doublet), t (triplet), q (quartet), m
(multiplet)).
General experimental procedure for carboxylation of
aromatic heteroarenes and then esterification
The simplified synthetic method of Mo2(OtBu)6 (1)
The heterocycle (1.0 mmol), Cs2CO3 (391 mg, 1.2 mmol) and
Mo2(OtBu)6 (20 mg, 3.0 mol%) were placed in a 10 mL Schlenk
reaction tube. The reaction tube was degassed, the CO2
(balloon) and DMF (5 mL) were then introduced in to the
reaction mixture under stirring. After this, the reaction mixture
was stirred at 75 °C for 10 h, then the reaction mixture was
cooled to 50 °C, and MeI (188 µL, 3 mmol) was added with a
syringe. The reaction mixture was stirred for 2 hours at 50 °C.
Then the reaction mixture was cooled to room temperature
and the solvent was evaporated. Water (10 mL) was added to
make a suspension, and the organic product was extracted
with CH2Cl2 (3 times, 10 mL each). The organic phase was dried
with Na2SO4, filtered and the solvent was evaporated under
vacuum. The product was purified by a flash chromatography
and characterized by NMR.
The molybdenum pentachloride (5.0 g, 18.0 mmol) and tin
particles (2.3 g, 23.0 mmol) were mixed together in a Schlenk
bottle. Then the bottle was taken outside the glovebox and
connected to a Schlenk line, and 50.0 mL ether was transferred
to the bottle. The mixture was stirred for 10 h at room
temperature, afterwards orange solid and orange liquid were
formed. The reaction mixture except excess tin particles was
transferred into another Schenk bottle under pressure. The
orange solid was filtered through a Celite and washed with 5
mL ether for three times, then the orange solid was dried
under vacuum and obtained with 3.8g.
The orange solid (3.8 g) obtained from the previous step was
mixed with 22.0 mL 2.2 M LiOtBu of THF solution (LiOtBu 48.0
mmol). The mixture was stirred for 18 h to give a red-black
solution and a black solid. The reaction mixture was filtered
through a Celite and the black solid was washed with THF until
the solid became colorless. The filtrate was evaporated to get
a red solid under pressure. The red solid and 50.0 mL ether
were mixed in a Schlenk bottle, then the mixture was stirred
for 15 minutes. The reaction mixture was filtered through a
Celite and the residue was washed with ether until the solid
General experimental procedure for cycloaddition of CO2
with epoxides
Mo2(OtBu)6 (0.317 g, 1 mol%) and Co-catalyst (Bu4NBr, 3.6
mmol) were added into the Schlenk reaction tube (10 mL) that
was then capped with a septum and taken outside the
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J. Name., 2013, 00, 1-3 | 5
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glovebox. The flask was connected to the Schlenk line and (m, 2H), 3.99 (s, 3H) ppm; 13C NMR (101 MHz, CDCl3): δ 160.93,
View Article Online
vacuumed. Then, CO2 (balloon) and 50 mmol of epoxides were 157.87, 152.99, 136.63, 127.52, 127.05, D1O2I5:.1306.1,01392/2C.70G0C,05333.7523A
introduced into the reaction mixture under stirring. The ppm.
reaction mixture was stirred at 25 °C for 24 h. The product was Methyl 4-bromobenzo[d]thiazole-2-carboxylate (6b). 1H NMR
extracted by silica gel flash chromatography and characterized (400 MHz, CDCl3):
by NMR.
 7.93-7.90 (dd, 1H), 7.80-7.77 (dd, 1H),
7.41-7.37 (t, 1H), 4.08 (s, 3H) ppm; 13C NMR (101 MHz, CDCl3):
δ 161.03, 158.89, 151.75, 137.73, 130.77, 128.50, 121.43,
119.21, 53.92 ppm.
Methyl 5-bromobenzo[d]thiazole-2-carboxylate (6c). 1H NMR
(400 MHz, CDCl3):  8.28-8.27 (d, 1H), 7.77-7.75 (d, 1H), 7.58-
NMR data for all products
3-phenylpropiolic acid (3a). 1H NMR (300 MHz, DMSO-d6):

7.64-7.62 (d, 2H), 7.56-7.53 (t, 1H), 7.49-7.45 (t, 2H) ppm; 13C 7.55 (dd, 1H), 4.03 (s, 3H) ppm; 13C NMR (101 MHz, CDCl3): δ
NMR (75 MHz, DMSO-d6): δ 154.35 (-COOH), 132.61, 130.92, 160.59, 159.50, 154.08, 135.42, 130.84, 128.04, 123.18,
129.06, 119.00, 84.33, 81.81 ppm.
120.84, 53.83 ppm.
3-p-tolylpropiolic acid (3b). 1H NMR (300 MHz, DMSO-d6):

Methyl 5-chlorobenzo[d]thiazole-2-carboxylate (6d). 1H NMR
7.52-7.48 (m, 2H), 7.29-7.25 (m, 2H), 2.35 (s, 3H) ppm; 13C (400 MHz, CDCl3):

8.10-8.09 (d, 1H), 7.82-7.80 (d, 1H), 7.44-
NMR (75 MHz, DMSO-d6): δ 153.04 (-COOH), 140.01, 131.50, 7.41 (dd, 1H), 4.02 (s, 3H) ppm; 13C NMR (101 MHz, CDCl3): δ
128.64, 115.10, 84.33, 80.89, 21.18 ppm. 160.61, 159.71, 153.75, 134.90, 133.25, 128.25, 124.90,
3-(4-methoxyphenyl)propiolic acid (3c). 1H NMR (300 MHz, 122.88, 53.79 ppm.
DMSO-d6):
7.59-7.54 (m, 2H), 7.03-6.98 (m, 2H), 3.80 (s, 3H) Methyl 6-bromobenzo[d]thiazole-2-carboxylate (6e). 1H NMR
ppm; 13C NMR (75 MHz, DMSO-d6): δ 159.92 (-COOH), 153.12, (400 MHz, CDCl3):
8.07-8.02 (t, 2H), 7.64-7.62 (d, 1H), , 4.05
133.45, 113.87, 109.89, 84.69, 80.54, 55.14 ppm.
(s, 3H) ppm; 13C NMR (101 MHz, CDCl3): δ 160.75, 158.47,
3-(4-chlorophenyl)propiolic acid (3d). 1H NMR (300 MHz, 151.91, 138.28, 130.96, 126.57, 124.71, 121.91, 53.87 ppm.
DMSO-d6):
7.66-7.62 (m, 2H), 7.55-7.50 (m, 2H) ppm; 13C Methyl 6-chlorobenzo[d]thiazole-2-carboxylate (6f). 1H NMR
NMR (75 MHz, DMSO-d6): δ 153.10 (-COOH), 135.04, 133.54, (400 MHz, CDCl3): 8.14-8.12 (d, 1H), 7.94 (d, 1H), 7.54-7.51




128.53, 117.35, 82.87, 82.33 ppm.
(dd, 1H), 4.07 (s, 3H) ppm; 13C NMR (101 MHz, CDCl3): δ
3-(thiophen-3-yl)propiolic acid (3e). 1H NMR (300 MHz, 160.86, 158.57, 151.72, 137.97, 134.12, 128.39, 126.39,
DMSO-d6): δ 8.17 (d, 1H), 7.69-7.66 (m, 1H), 7.32-7.30 (d, 1H) 121.79, 53.90 ppm.
ppm; 13C NMR (75 MHz, DMSO-d6): δ 153.13 (-COOH), 133.67, Methyl benzo[d]oxazole-2-carboxylate (7a). 1H NMR (400
128.94, 126.74, 117.17, 81.11, 79.89 ppm.
MHz, CDCl3):  7.91-7.89 (d, 1H), 7.68-7.66 (d, 1H), 7.56-7.45
3-(naphthalene-2-yl)propiolic acid (3f). 1H NMR (300 MHz, (m, 2H), 4.10 (s, 3H) ppm; 13C NMR (101 MHz, CDCl3): δ 157.03,
DMSO-d6): δ 8.31 (s, 1H), 8.00-7.95 (t, 3H), 7.64-7.57 (m, 3H) 152.66, 151.04, 140.62, 128.38, 125.97, 122.31, 111.89, 53.81
ppm; 13C NMR (75 MHz, DMSO-d6): δ 153.00 (-COOH), 132.59, ppm.
132.33, 131.31, 127.68, 127.12, 126.92, 126.82, 126.21, Methyl 5-methylbenzo[d]oxazole-2-carboxylate (7b). 1H NMR
115.41, 84.28, 81.43 ppm.
(400 MHz, CDCl3):  7.48 (s, 1H), 7.36-7.34 (d, 1H), 7.17-7.15
3-(phenanthren-9-yl)propiolic acid (3g). 1H NMR (300 MHz, (m, 2H), 3.95 (s, 3H), 2.34 (s, 3H) ppm; 13C NMR (101 MHz,
DMSO-d6): δ 8.94-8.86 (m, 2H), 8.42 (s, 1H), 8.31-8.28 (m, 1H), CDCl3): δ 156.68, 152.34, 148.92, 140.44, 135.66, 129.41,
8.10-8.07 (d, 1H), 7.83-7.78 (m, 3H) 7.74-7.69 (t, 1H) ppm; 13C 121.41, 110.85, 53.39, 21.26 ppm.
NMR (75 MHz, DMSO-d6): δ 152.97 (-COOH), 133.97, 129.55, Methyl 5-bromobenzo[d]oxazole-2-carboxylate (7c). 1H NMR
129.24, 128.92, 128.63, 128.19, 126.95, 126.60, 124.74, (400 MHz, CDCl3):
 7.97 (d, 1H), 7.61-7.58 (dd, 1H), 7.52-7.50
122.64, 122.13, 114.44, 85.49, 82.04 ppm.
(d, 1H), 4.06 (s, 3H) ppm; 13C NMR (101 MHz, CDCl3): δ 156.49,
3-(pyren-1-yl)propiolic acid (3h). 1H NMR (300 MHz, DMSO- 153.43, 149.82, 141.92, 131.49, 124.99, 118.75, 113.10, 53.93
d6): δ 8.43-8.34 (m, 4H), 8.29-8.26 (t, 3H), 8.19-8.09 (m, 2H) ppm.
ppm; 13C NMR (75 MHz, DMSO-d6): δ 153.00 (-COOH), 131.47, Methyl 5-chlorobenzo[d]oxazole-2-carboxylate (7d). 1H NMR
131.37, 129.61, 129.52, 129.19, 128.55, 128.36, 126.00, (400 MHz, CDCl3):
 7.78 (s, 1H), 7.54-7.52 (d, 1H), 7.44-7.41
125.84, 125.49, 123.82, 122.97, 122.40, 122.09, 111.97, 86.56, (d, 1H), 4.04 (s, 3H) ppm; 13C NMR (101 MHz, CDCl3): δ 156.44,
82.99 ppm.
153.59, 149.34, 141.39, 131.45, 128.75, 121.83, 112.60, 53.85
3-(4-ethynylphenyl)propiolic acid (3i). 1H NMR (300 MHz, ppm.
DMSO-d6): δ 7.64-7.61 (m, 2H), 7.55-7.53 (m, 2H), 4.47 (s, 1H) Methyl 6-methylbenzo[d]oxazole-2-carboxylate (7e). 1H NMR
ppm; 13C NMR (75 MHz, DMSO-d6): δ 152.81 (-COOH), 131.72, (400 MHz, CDCl3):
 7.65-7.63 (d, 1H), 7.34 (s, 1H), 7.18-7.16
131.17, 123.10, 118.52, 83.24, 82.94, 82.72, 82.06 ppm.
(d, 1H), 4.00 (s, 3H), 2.43 (s, 3H) ppm; 13C NMR (101 MHz,
3-(3-ethynylphenyl)propiolic acid (3j). 1H NMR (300 MHz, CDCl3): δ 156.88, 151.99, 151.14, 139.16, 138.28, 127.29,
DMSO-d6): δ 7.70-7.60 (m, 3H), 7.50-7.45 (m, 1H), 4.35 (s, 1H,) 121.34, 111.49, 53.49, 21.94 ppm.
ppm; 13C NMR (75 MHz, DMSO-d6): δ 152.68 (-COOH), 134.03, Methyl 6-bromobenzo[d]oxazole-2-carboxylate (7f). 1H NMR
132.77, 131.76, 128.49, 121.72, 118.82, 82.50, 81.64, 81.39 (400 MHz, CDCl3):
ppm.
(d, 1H), 4.07 (s, 3H) ppm; 13C NMR (101 MHz, CDCl3): δ 156.56,
Methyl benzo[d]thiazole-2-carboxylate (6a). 1H NMR (400 152.88, 151.26, 139.62, 129.65, 123.16, 121.75, 115.28, 53.93
MHz, CDCl3): 8.15-8.13 (d, 1H), 7.87-7.85 (d, 1H), 7.50-7.26 ppm.
 7.80 (s, 1H), 7.73-7.71 (d, 1H), 7.56-7.54

6 | J. Name., 2012, 00, 1-3
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Page 7 of 9
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4-methyl-1,3-dioxolan-2-one (9a). 1H NMR (300 MHz, DMSO-
d6): δ 4.95-4.84 (m, 1H), 4.60-4.54 (m, 1H,), 4.08-4.03 (m, 1H),
1.40-1.38 (d, 3H) ppm; 13C NMR (75 MHz, DMSO-d6): δ 153.74,
73.33, 70.14, 18.78 ppm.
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3676; (f) N.-N. Zhu, X.-H. Liu, T. Li, J.-GD. OMI:a1,0P.1.0C39h/eCn7gGCa0n3d37G2.A-
M. Yang, Inorg. Chem., 2017, 56, 3414-3420.
3. (a) D. Yu and Y. Zhang, Proc. Natl Acad. Sci. USA., 2010, 107
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4-(chloromethyl)-1,3-dioxolan-2-one (9b). 1H NMR (300 MHz,
DMSO-d6): δ 5.13-5.12 (m, 1H), 4.62-4.58 (t, 1H), 4.30-4.26 (m,
1H), 4.03-3.91 (d, 2H) ppm; 13C NMR (75 MHz, DMSO-d6): δ
154.51, 74.97, 66.90, 45.33 ppm.
20184-20189; (b) W. Wang, G. Zhang, R. Lang, C. Xia and F.
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, 962-998;
4-phenyl-1,3-dioxolan-2-one (9c). 1H NMR (300 MHz, DMSO-
d6): δ 7.50-7.41 (m, 5H), 5.88-5.83 (t, 1H), 4.91-4.85 (t, 1H),
4.44-4.39 (t, 1H) ppm; 13C NMR (75 MHz, DMSO-d6): δ 153.40,
135.27, 128.29, 127.87, 125.54, 77.19, 70.32 ppm.
(b) I. I. F. Boogaerts, G. C. Fortman, M. R. L. Furst, C. S. J.
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74, 3109-3113; (b) M. H. Chisholm, F. A. Cotton, C. A. Murillo
and W. W. Reichert, Inorg. Chem., 1977, 16, 1801-1808. (c)
M. H. Chisholm and N. J. Patmore, In Molecular Metal-Metal
Bonds, Chapt. 6 (Ed.: S.T. Liddle), Wiley-VCH, Weinheim,
4-(phenoxymethyl)-1,3-dioxolan-2-one (9d). 1H NMR (300
MHz, DMSO-d6): δ 7.33-7.29 (t, 2H), 7.00-6.95 (t, 3H), 5.16-
5.15 (m, 1H), 4.66-4.61 (t, 1H), 4.41-4.37 (t, 1H), 4.30-4.27 (d,
1H), 4.22-4.18 (m, 1H) ppm; 13C NMR (75 MHz, DMSO-d6): δ
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ppm.
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4-((naphthalen-1-yloxy)methyl)-1,3-dioxolan-2-one (9e). 1H
NMR (300 MHz, DMSO-d6): δ 8.09-8.06 (t, 1H), 7.91-7.88 (t,
1H), 7.56-7.52 (m, 3H), 7.46-7.42 (m, 1H), 7.01-6.99 (d, 1H),
5.34-5.2 (m, 1H), 4.75-4.71 (t, 1H), 4.60-4.56 (m, 1H), 4.50-4.46
(m, 1H), 4.40-4.37 (m, 1H) ppm; 13C NMR (75 MHz, DMSO-d6):
δ 155.13, 153.30, 134.03, 127.59, 126.65, 126.13, 125.63,
124.69, 121.08, 120.70, 105.51, 74.83, 67.86, 66.46 ppm.
Hexahydrobenzo-1,3-dioxolan-2-one (9f). 1H NMR (300 MHz,
DMSO-d6): δ 4.83-4.77 (m, 2H), 1.94-1.81 (m, 2H), 1.76-1.65
(m, 2H), 1.52-1.31 (m, 4H) ppm; 13C NMR (75 MHz, DMSO-d6):
δ 153.71, 75.00, 26.09, 18.78 ppm.
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Conflicts of interest
There are no conflicts of interest to declare.
10. D. Yu and Y. Zhang, Green Chem., 2011, 13, 1275-1279.
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Acknowledgements
This project was financially supported by the National Key R&D
Program of China (2016YFB0600902), the NSFC (21671110),
and the NSF of Tianjin (16JCZDJC36700).
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Polyhedron, 1994, 13, 2035-2042; (d) T. A. Budzichowski, M.
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DOI: 10.1039/C7GC03372A
Table of contents
CO2 were transformed into different products in mild condition, high yield and
excellent selectivity with single catalyst.