Polystyrene-supported N-heterocyclic carbene-silver complexes as robust and efficient catalysts for the reaction of carbon dioxide and propargylic alcohols

Article abstract of DOI:10.1002/adsc.201300007

Three polystyrene-supported N-heterocyclic carbene-silver complexes [PS-NHC-Ag(I)] and a polystyrene-supported N-heterocyclic carbene-copper complex [PS-NHC-Cu(I)] catalyst were synthesized and characterized by elemental analysis, Fourier transform infrared spectroscopy, inductively coupled plasma-atom emission spectrometer, thermogravimetric analysis and scanning electron micrographs. The catalytic activity of the supported catalysts was investigated for the reaction of propargylic alcohols and carbon dioxide. PS-NHC-Cu(I) showed no catalytic activity to the reaction, while PS-NHC-Ag(I) showed a considerable high activity and selectivity for the reaction, yielding the corresponding α-alkylidene cyclic carbonates in high to excellent yields under mild conditions. Most importantly, the supported catalysts could be separated easily from the products and reused up to 15 times without loss of their high catalytic activity, showing excellent stability. The effect of various reaction parameters such as carbon dioxide pressure, temperature, time, and catalyst loading on the reaction was also investigated. Copyright

Full text of DOI:10.1002/adsc.201300007

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DOI: 10.1002/adsc.201300007
Polystyrene-Supported N-Heterocyclic Carbene–Silver Complexes
as Robust and Efficient Catalysts for the Reaction of Carbon
Dioxide and Propargylic Alcohols
Xiaodong Tang,a Chaorong Qi,a,* Haitao He,a Huanfeng Jiang,a,* Yanwei Ren,a
and Gaoqing Yuana
a
School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, Peopleꢀs
Republic of China
Fax : (+86)-20-8711-2906; e-mail: crqi@scut.edu.cn or jianghf@scut.edu.cn
Received: January 10, 2013; Revised: May 10, 2013; Published online: July 12, 2013
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201300007.
Abstract: Three polystyrene-supported N-heterocy- alkylidene cyclic carbonates in high to excellent
clic carbene–silver complexes [PS-NHC-Ag(I)] and yields under mild conditions. Most importantly, the
a
polystyrene-supported N-heterocyclic carbene– supported catalysts could be separated easily from
copper complex [PS-NHC-Cu(I)] catalyst were syn- the products and reused up to 15 times without loss
thesized and characterized by elemental analysis, of their high catalytic activity, showing excellent sta-
Fourier transform infrared spectroscopy, inductively bility. The effect of various reaction parameters such
coupled plasma-atom emission spectrometer, ther- as carbon dioxide pressure, temperature, time, and
mogravimetric analysis and scanning electron micro- catalyst loading on the reaction was also investigat-
graphs. The catalytic activity of the supported cata- ed.
lysts was investigated for the reaction of propargylic
alcohols and carbon dioxide. PS-NHC-Cu(I) showed
no catalytic activity to the reaction, while PS-NHC- Keywords: carbon dioxide fixation; cyclic carbo-
Ag(I) showed a considerable high activity and selec- nates; N-heterocylic carbene complexes; propargylic
tivity for the reaction, yielding the corresponding a- alcohols; supported catalysts.
Introduction
tive catalysts for the preparation of a-alkylidene
cyclic carbonates, including copper,[3] silver,[4] cobalt,[5]
Carbon dioxide (CO2) is the chief greenhouse gas.
Due to human activities, the amount of CO2 released
into the atmosphere has been rising extensively
during and after the industrial revolution, which
began in 1850. This has caused serious environmental
problems such as global warming and climate change.
Thus, the capture, utilization and storage of CO2 have
been attracting extensive attention in the whole
world. Chemical fixation of CO2 is regarded as an ef-
ficient route for the utilization of CO2 because CO2
can be used as a safe and cheap C1 building block for
the synthesis of many useful organic compounds.[1]
One of the promising examples is the synthesis of a-
alkylidene cyclic carbonates from the coupling of
propargylic alcohols and CO2, because a-alkylidene
cyclic carbonates are useful building blocks in organic
synthesis (Scheme 1).[2] Many transition metal salts
Scheme 1. a-Alkylidene cyclic carbonates as useful building
and organic compounds have been found to be effec- blocks in organic synthesis.
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As a part of our program to develop more efficient
and environmentally benign methods for the fixation
of CO2,[13] herein, we wish to report that polystyrene-
supported N-heterocyclic carbene–silver complexes
[PS-NHC-Ag(I), 3] (Scheme 2) can be used as robust,
efficient and environmentally friendly catalysts for
the reaction of CO2 and propargylic alcohols under
mild conditions, offering the corresponding a-alkyli-
dene cyclic carbonates in high to excellent yields.
Scheme 2. Heterogeneous catalysts for the reaction of prop-
argylic alcohols with CO2.
Results and Discussion
ruthenium,[6] palladium,[7] tri-n-butylphosphine,[8] N- A PS-NHC-Cu(I) and three PS-NHC-Ag(I) catalysts
heterocyclic carbenes,[9] and iodine of tert-butyl hypo- were synthesized according to procedures reported in
iodite (t-BuOI).[10] And recently, an electrochemical the literature,[14] and the preparation steps are shown
method for the synthesis of a-alkylidene cyclic carbo- in Scheme 3. The analytical data of the four polystyr-
nates has also been developed by our group with ene-supported catalysts are listed in Table 1. The
a copper anode and a nickel cathode in an undivided copper content of catalyst 2 was 0.38 mmolgÀ1, and
cell containing (n-Bu)4NBr–MeCN electrolyte.[11]
the silver contents of catalyst 3a, 3b and 3c were
Although the coupling of CO2 with propargylic al- found to be 0.70, 0.65 and 0.49 mmolgÀ1, respectively,
cohols has been studied extensively, to date, only one based on inductively coupled plasma-atomic emission
heterogeneous catalyst, (dimethylamino)methyl-poly- spectrometer (ICP-AES) analysis. In comparison with
styrene-supported copper(I) iodide (DMAM-PS-CuI, the nitrogen content in the catalysts, the data indicate
1) (Scheme 2), has been used by our group for the that only a part of imidazolium groups anchored on
production of the five-membered a-alkylidene cyclic
carbonates.[12] Compared with the homogeneous cata-
Table 1. Analytical data of the polymer-supported catalysts.
Catalyst C Metal loading
lytic systems mentioned above, catalyst 1 could work
without organic solvent, be easily separated from the
product and be reused. However, two problems asso-
ciated with the catalyst 1 as a heterogeneous catalyst
are: (i) the need for a high CO2 pressure (14 MPa),
and (ii) the instability of its catalytic capacity. These
drawbacks limit the practical application of catalyst
1 in industrial process heavily. Therefore, there is con-
tinuing motivation for us to develop more robust and
efficient heterogeneous catalysts for this transforma-
tion.
H
N
[wt%][a] [wt%][a] [wt%][a] [mmolgÀ1][b]
2
47.50
58.63
57.65
64.66
4.86
6.26
6.34
5.78
6.36
7.85
6.52
6.33
0.38
0.70
0.65
0.49
3a
3b
3c
[a]
[b]
Determined by elemental analyses.
Determined by inductively coupled plasma-atomic emis-
sion spectrometry (ICP-AES).
Scheme 3. Preparation of polystyrene-supported N-heterocyclic carbene Ag and Cu complexes.
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Polystyrene-Supported N-Heterocyclic Carbene–Silver Complexes as Robust and Efficient Catalysts
Figure 2. TGA curves of supported catalysts 2 and 3.
Figure 1. FT-IR spectra of (A) resin 4, (B) resin 5a, (C) cat-
alyst 2, (D) catalyst 3a, (E) catalyst 3b, and (F) catalyst 3c.
Table 2. TG data of the polymer-supported catalysts.
Compound
Temperature [8C]
Weight loss [%]
the polymeric support 5 took part in the reactions
with the metal Cu or Ag to form metal complexes.
Figure 1 shows the FT-IR spectra of resin 4, poly-
styrene-supported ionic liquid 5a, catalysts 2, and cat-
alyst 3. In the spectrum of resin 4, there are two char-
acteristic absorption bands at 1264 cmÀ1 and 673 cmÀ1
Catalyst 2
35–118
3.5
190–393
393–470
35–120
190–390
390–476
35–108
204–390
390–476
35–102
200–390
390–478
31.5
20.4
8.2
25.8
22.8
4.7
31.3
19.1
4.1
35.8
22.3
Catalyst 3a
Catalyst 3b
Catalyst 3c
À
which correspond to the C Cl bond. However, they
were absent and two strong absorption bands at
1567 cmÀ1 and 1160 cmÀ1 appeared in the spectrum of
5a, which characterize the ring vibration and the posi-
À
tion 2 C H bond bending vibration of the imidazoli-
um groups, respectively, providing clear evidence for
the attachment of the ligands.[15] The presence of the
two strong absorption bands in the spectra of the sup-
ported catalysts also suggests that not all the imidazo-
lium group anchored on the polymeric support 5 re- polymeric chain. The third stage of weight loss (30–
acted with the metal Cu or Ag to form metal carbene 35%) started immediately after completion of second
complexes, which is consistent with the data of ele- stage, which may be due to the decomposition of the
mental analyses. The IR spectra of 1-benzyl-3-methyl- metal complexes.
imidazolium chloride and [1-benzyl-3-methylimidazol-
2-ylidene]AgCl also confirm these results (see Sup- the supported catalysts, SEM photographs were taken
porting Information, Figure S1 and Figure S2). at different synthesis stages (Figure 3). It is clearly
For a better understanding of the morphologies of
The thermal stability of the four supported catalysts visible that the relative smooth surface of the starting
was estimated using TG analysis. TGA curves are polymer 4 changed after immobilization of the ligands
shown in Figure 2, and TGA data are summarized in and metals. Especially, as shown in Figure 3, D, the
Table 2. The TGA curves of these four catalysts are surface of the catalysts 3a appeared to be covered
similar and show three stages of distinct weight loss with a large amount of small particles and thus
between 35 and 7008C. A small decrease in weight became rougher. It should be noted that the sizes of
was observed at less than 1208C, which may corre- the particles were on the nanometer scale although
spond to the loss of the adsorbed and bound water in their shapes were irregular. The surface morphologies
the polymer matrix.[16] The second stage of weight of catalysts 3b and 3c were similar and became looser
loss (25.8–35.8%) started at 1908C and continued up in comparison with those of catalyst 2 and 3a. More-
to 3938C, which occurred either may be due to the over, elemental mapping by energy dispersive X-ray
dissociation of the covalently bonded metal com- absorption spectroscopy (EDS) confirmed a uniform
plexes or may be attributed to partial scission of the distribution of Cu or Ag in the polymer supports.
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Figure 3. SEM and EDS elemental-mapping images of (A) resin 4, (B) resin 5a, (C) catalyst 2, (D) catalyst 3a, (E) catalyst
3b, and (F) catalyst 3c.
The catalytic activities of the four supported cata- was reported that polymer-supported ionic liquids
lysts were first investigated using the coupling of 3- were very active catalysts for the cycloaddition of
ethylpent-1-yn-3-ol with CO2 as the model reaction CO2 to epoxides,[17] the reaction of 3-ethylpent-1-yn-3-
under the same reaction conditions (Table 3). Control ol with CO2 could not occur in the presence of resin
experiments showed that the coupling reaction did 5a (entry 2). It should be noted that catalyst 1, which
not occur without any catalyst (entry 1). Although it could efficiently catalyze the reaction under supercrit-
ical conditions,[12] only gave 12% yield of the product
with 82% selectivity, showing very low activity under
Table 3. Catalytic activity of different catalysts in the reac-
present conditions (entry 3). No product was obtained
when using compound 2 as catalyst, indicating that
catalyst 2 is inactive for the reaction (entry 4). How-
ever, to our delight, in the presence of 2 mol% of 3a,
the reaction proceeded smoothly, producing cyclic
carbonate 7a almost quantitatively (entry 5). These
results indicate the catalytic activity of catalyst 3a is
much higher than that of catalyst 1. Catalysts 3b and
3c were less effective than catalysts 3a, but they could
still yield the desired product in 92% and 89% yields,
respectively (entries 6 and 7).
With these good results at hand, we then examined
the effect of CO2 pressure, temperature, time, and cat-
alyst loading on the reaction between 6a and CO2
with 3a as catalyst. Figure 4 shows the influence of
CO2 pressure on the yield of 7a at 408C with a reac-
tion time of 24 h. It is noteworthy that a 71% yield of
the product 7a could be obtained at 1 MPa of CO2, in-
dicating the reaction could be performed under very
low CO2 pressure. As expected, an increase in CO2
tion of 3-ethylpent-1-yn-3-ol with CO2.[a]
Entry
Catalyst
Selectivity [%][b]
Yield [%][b]
1
2
3
4
5
6
7
–
5a
1
0
0
0
0
12
0
99 (93)
92
89
82
0
>99
>99
97
2
3a
3b
3c
[a]
Reaction condtions: 0.5 mmol 6a, 2 mol% catalyst, 5 MPa
CO2, 408C, 24 h.
Determined by GC analysis; number in parenthesis is
isolated yield.
[b]
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Polystyrene-Supported N-Heterocyclic Carbene–Silver Complexes as Robust and Efficient Catalysts
Figure 6. Effect of reaction time on the yield of 7a. Reaction
conditions: 0.5 mmol 6a, 2 mol% 3a, 5 MPa CO2, 408C.
Figure 4. Effect of CO2 pressure on the yield of 7a. Reaction
conditions: 0.5 mmol 6a, 2 mol% 3a, 408C, 24 h.
pressure resulted in an increase in the yield of 7a,
which reached a maximum value at 5 MPa. Further
increase of pressure showed no effect on the yield.
The dependence of the yield of 7a on the reaction
temperature was investigated at a CO2 pressure of
5 MPa with a reaction time of 24 h. As is easily seen
from Figure 5, the catalytic activity of 3a was strongly
dependent on reaction temperature. In this respect,
the yield of 7a increased sharply with increasing tem-
perature in the lower temperature region from 20 to
408C, while no significant change was observed from
40 to 1008C.
The effect of reaction time on the yield of 7a at
5 MPa CO2 and 408C is shown in Figure 6. It shows
Figure 7. Effect of catalyst concentration on the yield of 7a.
Reaction conditions: catalyst 3a, 0.5 mmol 6a, 5 MPa CO2,
408C, 24 h.
that the yield of 7a increased smoothly with the reac-
tion time, and that 6a could be quantitatively convert-
ed into cyclic carbonate 7a within 24 h. Figure 7
shows the dependence of the yield of 7a on the cata-
lyst concentration. When the concentration of catalyst
3a was increased from 0.5 mol% to 2 mol%, the rate
of the reaction was obviously accelerated and the
yield of 7a was increased dramatically from 41 to
99%. Further increase of the amount of the catalyst
showed no influence on the yield.
The scope of the reaction was further explored with
various propargylic alcohols using 3a as catalyst, and
the results are summarized in Table 4. Under the opti-
mized reaction conditions, other tertiary propargylic
alcohols 6b, 6c, 6h and 6i could also undergo the car-
Figure 5. Effect of reaction temperature on the yield of 7a.
Reaction conditions: 0.5 mmol 6a, 2 mol% 3a, 5 MPa CO2,
24 h.
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Table 4. Synthesis of various cyclic carbonates under the optimized conditions.[a]
[a]
[b]
[c]
[d]
[e]
Reaction conditions: 0.5 mmol propargylic alcohol, 2 mol% 3a, 5 MPa CO2, 408C, 24 h.
Determined by GC analysis.
Isolated yield.
The reaction was carried out at 808C.
The reaction was carried out at 608C.
boxylatic cyclization with CO2 smoothly to give the yield the desired products in excellent yields but at
corresponding products in high yields (entries 1, 2, 10 a higher temperature (808C); when the reactions
and 11). Sterically hindered substrates 6d–6f could were carried out at 408C, only moderate yields were
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Polystyrene-Supported N-Heterocyclic Carbene–Silver Complexes as Robust and Efficient Catalysts
obtained (entries 3–8). It is noteworthy that 2-phenyl-
but-3-yn-2-ol (6g), which showed no reactivity to the
reaction when using DMAM-PS-CuI (1) as catalyst,[12]
could smoothly react with CO2 in the presence of 3a
(2 mol%) to give the expected product 7g in 81%
yield, along with 15% yield of 3-hydroxy-3-phenylbu-
tan-2-one as the major by-product. Secondary propar-
gylic alcohols 6j and 6k showed lower activity under
standard conditions but could yield the corresponding
products in high yields just by changing the reaction
temperature to 608C (entries 12–15). But in the case
of primary or internal propargylic alcohols as sub-
strate, no a-alkylidene cyclic carbonates were ob-
tained even at higher temperature such as 808C, and
the starting materials were recovered (entries 16 and
17). These results also suggested that the present
method seemed to be specific for terminal secondary
and tertiary propargylic alcohols.
One of our most important goals in this work was
to achieve more robust and recyclable catalysts for
the synthesis of a-alkylidene cyclic carbonates from
CO2 and propargylic alcohols. In this experiment, the
catalyst 3a was reused 15 times in the reaction of 6a
and CO2 to investigate the constancy of the catalyst
activity and reusability. In each cycle, the heterogene-
ous catalyst 3a could be easily recovered by filtration
and washed with diethyl ether (3ꢂ5 mL). After
drying, the catalyst was reused directly for the next
run. The yields of 7a for the fifteen repeated runs are
shown in Figure 8. It is notable that the catalytic ac-
tivity of the PS-NHC-Ag(I) catalyst remained un-
changed even after being reused 15 times. The reac-
tions at the 14th and 15th recycled runs gave 7a in 98
and 97% yields, respectively. The leaching of Ag that
occurred during the reaction was also examined. ICP-
AES analysis of the filtrate obtained after filtration
Figure 9. FT-IR spectra of catalyst 3a before (A) and after
being reused 15 times (B).
Figure 10. TGA curves of catalyst 3a before and after being
reused 15 times.
showed that the amount of Ag present in the filtrate
was less than 0.01% of the initial amount. These re-
sults indicate that the catalyst exhibits excellent stabil-
ity. This may be due to the specific coordination
chemistry of the N-heterocyclic carbenes anchored on
the polymers, which could effectively prevent the
leakage of the catalytically active metal Ag from the
supports to the solutions. The recovered catalyst 3a
after being reused 15 times was also characterized by
IR, TGA and SEM-EDS (Figure 9, Figure 10 and
Supporting Information, Figure S3), and no significant
changes have been found in comparison with the
fresh catalyst.
Figure 8. Reusability of 3a. Reaction conditions: 0.5 mmol
6a, 2 mol% 3a, 5 MPa CO2, 608C, 24 h.
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Conclusions
General Procedure for Preparation of Polystyrene-
Supported N-Heterocyclic Carbene–Copper Complex
In conclusion, we have demonstrated that polystyr- (2)
ene-supported N-heterocylic carbene silver complexes
The synthesized resin 5a (2 g), CuI (1.033 g, 5.44 mmol),
can be used as robust and efficient catalysts for the
reaction of various terminal tertiary and secondary
propargylic alcohols with CO2 under mild conditions,
offering the corresponding a-alkylidene cyclic carbo-
nates in high to excellent yields. The significant ad-
vantages of this methodology are mild reaction condi-
tions, low catalyst loadings, high yields, and simple
workup procedures. Most importantly, the supported
catalysts showed excellent stability. They could be
separated easily from the products and reused up to
15 times without loss of their high catalytic activity.
NaO-t-Bu (0.52 g, 5.44 mmol) and dry THF (25 mL) were
added in sequence to an oven-dried Schlenk flask. The re-
sulting suspension was stirred at room temperature under
a nitrogen atmosphere for 24 h. Then the solution was fil-
tered and the resin was washed with H2O (10 mLꢂ3), meth-
anol (10 mLꢂ3) and acetone (10 mLꢂ3), respectively, and
dried under vacuum at 608C overnight. The PS-NHC-Cu(I)
catalyst was obtained as a gray-green resin; yield: 2.15 g.
The copper amount of the PS-NHC-Cu(I) was found to be
0.38 mmolgÀ1 based on ICP-AES analysis.
Representative Procedure for Preparation of
Polystyrene-Supported N-Heterocyclic Carbene–
Silver Complex (3a)
Experimental Section
The synthesized resin 5a (2 g), Ag2O (0.636 g, 2.74 mmol)
and CH2Cl2 (25 mL) were added to an oven-dried Schlenk
flask. The resulting suspension was stirred at room tempera-
ture for 24 h. Then the solution was filtered and the resin
was washed with methanol (10 mLꢂ3) and acetone
(10 mLꢂ3), respectively, and dried under vacuum at 608C
overnight. The PS-NHC-Ag(I) catalyst was obtained as
a light gray resin; yield: 2.17 g. The silver amount of the PS-
NHC-Ag(I) was found to be 0.70 mmolgÀ1 based on ICP-
AES analysis.
General Information
NMR spectra were recorded with a Bruker DRX-400 spec-
trometer; CDCl3 was used as solvent and TMS as an inter-
nal standard. GC analyses were performed on a GC-7900
chromatograph with an FID and equipped with an AT.SE-
30 capillary column (internal diameter: 0.32 mm, length:
30 m). Mass spectra were recorded with a Shimadzu GCMS-
QP5050A mass spectrometer at an ionization voltage of
70 eV and equipped with a DB-WAX capillary column (in-
ternal diameter: 0.25 mm, length: 30 m). IR spectra were re-
corded in KBr disks with a Bruker TENSOR 27 spectrome-
ter. TGA was performed on TAINC-Q600SDT at a heating
rate of 108CminÀ1. Elemental analysis was performed on
a Vario EL elemental analyzer. The amount of metal immo-
bilized on the supports was determined by means of an in-
ductively coupled plasma-atomic emission spectrometer
(ICP-AES). Scanning electron microscope (SEM) and
energy dispersive X-ray absorption spectroscopy (EDS)
were was performed on a QUANTA400F. Carbon dioxide
with a purity of 99.99% was supplied by Guangzhou Gases
Factory Co., Ltd. All the other chemicals including propar-
gylic alcohols and imidazoles were commercially available
and used as received.
General Procedure for the Reaction of CO2 and
Propargylic Alcohols
Propargylic alcohol (0.5 mmol) and catalyst were added to
a 15 mL stainless autoclave reactor with a magnetic stirrer.
CO2 was introduced from a cylinder and the reaction was
carried out at the selected temperature under magnetic stir-
ring for 24 h, and the pressure was kept constant during the
reaction. When the reaction was completed, the vessel was
cooled with an ice bath and the pressure was released slowly
to atmospheric pressure. The residue was extracted with di-
ethyl ether. The resin was filtrated, washed with diethyl
ether (3ꢂ5 mL) and dried at 408C. The collected filtrate
was condensed under reduced pressure. The crude product
was purified by chromatography on a silica gel column using
light petroleum ether/ethyl acetate as eluent and identified
by IR, GC-MS and NMR.
Representative Procedure for Preparation of
Polystyrene-Supported Ionic Liquid (5a)
4,4-Diethyl-5-methylene-1,3-dioxolan-2-one
(7a):[5]
1H NMR (CDCl3, 400 MHz): d=0.91 (t, J=7.2 Hz, 6H),
1.62–1.71 (m, 2H), 1.83–1.92 (m, 2H), 4.19 (d, J=3.2 Hz,
1H), 4.80 (d, J=3.2 Hz, 1H); 13C NMR (CDCl3, 100 MHz):
d=7.0, 31.8, 85.7, 90.8, 151.8, 155.6; MS (70 eV): m/z (%)=
156 [M+], 112, 97, 70, 55 (100).
To a solution of 1-methylimidazole (2.57 g, 31.25 mmol) in
25 mL toluene, 2% DVB cross-linked chloromethylated
polystyrene 4 (ca. 5.0 mmol Cl/g) (5 g) was added. Then the
mixture was heated to 808C with stirring for 24 h under ni-
trogen atmosphere. After completion of the reaction, the so-
lution was filtered and the resin was washed with chloro-
form (10 mLꢂ3), methanol (10 mLꢂ3), and ethyl acetate
(10 mLꢂ3), respectively, and dried under vacuum at 608C.
A white resin was obtained; yield: 6.95 g. The composition
of the polystyrene-supported ionic liquid (5a) was deter-
mined by elemental analysis (C 66.65, H 7.97, N 7.68%) and
indicated that the loading capacity of imidazolium group
was about 2.74 mmolgÀ1 based on nitrogen content.
4,4-Dimethyl-5-methylene-1,3-dioxolan-2-one
(7b):[11]
1H NMR (CDCl3, 400 MHz): d=1.58 (s, 6H), 4.28 (d, J=
4.0 Hz, 1H), 4.73 (d, J=3.6 Hz, 1H); 13C NMR (CDCl3,
100 MHz): d=27.5, 84.6, 85.2, 151.2, 158.7; MS (70 eV): m/z
(%)=128 [M+], 84, 69, 56 (100).
4-Ethyl-4-methyl-5-methylene-1,3-dioxolan-2-one (7c):[11]
1H NMR (CDCl3, 400 MHz): d=0.93 (t, J=7.2 Hz, 3H),
1.53 (s, 3H), 1.67–1.76 (m, 1H), 1.81–1.90 (m, 1H), 4.23 (d,
J=3.2 Hz, 1H), 4.75 (d, J=3.6 Hz, 1H); 13C NMR (CDCl3,
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Polystyrene-Supported N-Heterocyclic Carbene–Silver Complexes as Robust and Efficient Catalysts
100 MHz): d=7.2, 25.8, 33.2, 85.5, 87.5, 151.4, 157.3; MS
(70 eV): m/z (%)=142 [M+], 113, 70, 56 (100).
ence Foundation of China (20932002, 21172078), the Guang-
dong Natural Science Foundation (10351064101000000), and
the Fundamental Research Funds for the Central Universities
(2011ZZ007) for financial support.
4-Isopropyl-4-methyl-5-methylene-1,3-dioxolan-2-one
(7d):[12] 1H NMR (CDCl3, 400 MHz): d=0.97 (d, J=6.8 Hz,
3H), 0.99 (d, J=7.2 Hz, 3H), 1.54 (s, 3H), 1.87–1.94 (m,
1H), 4.24 (d, J=3.2 Hz, 1H), 4.78 (d, J=3.6 Hz, 1H);
13C NMR (CDCl3, 100 MHz): d=16.0, 16.3, 24.0, 36.9, 86.1,
89.8, 151.6, 157.1; MS (70 eV): m/z (%)=156 [M+], 114, 97,
70 (100), 55.
References
4-Isobutyl-4-isopropyl-5-methylene-1,3-dioxolan-2-one
(7e): Colorless liquid. IR (film): n=1831 (C=O), 1685 cmÀ1
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1
(C=C); H NMR (CDCl3, 400 MHz): d=0.91 (d, J=5.2 Hz,
6H), 0.93 (d, J=5.2 Hz, 6H), 1.54–1.58 (m, 2H), 1.78–1.83
(m, 2H), 4.20 (d, J=2.8 Hz, 1H), 4.81 (d, J=2.8 Hz, 1H);
13C NMR (CDCl3, 100 MHz): d=23.8, 23.9, 24.1, 48.3, 86.0,
90.3, 151.6, 157.1; MS (70 eV): m/z (%)=198 [M+], 156,
112, 97 (100), 69, 55; anal. calcd for C11H18O3: C 66.64, H
9.15; found: C 66.46, H 9.18.
4-Hexyl-4-methyl-5-methylene-1,3-dioxolan-2-one (7f):[11]
1H NMR (CDCl3, 400 MHz): d=0.84 (t, J=6.0 Hz, 3H),
1.24–1.37 (m, 8H), 1.54 (s, 3H), 1.62–1.69 (m, 1H), 1.79–
1.86 (m, 1H), 4.23 (d, J=3.6 Hz, 1H), 4.75 (d, J=3.2 Hz,
1H); 13C NMR (CDCl3, 100 MHz): d=13.9, 22.4, 22.8, 26.2,
28.8, 31.4, 40.4, 85.4, 87.2, 151.5, 157.7; MS (70 eV): m/z
(%)=198 [M+], 139, 111, 97, 69, 55 (100).
4-Methyl-5-methylene-4-phenyl-1,3-dioxolan-2-one(7g):[11]
1H NMR (CDCl3, 400 MHz): d=1.95 (s, 3H), 4.45 (d, J=
3.2 Hz, 1H), 4.93 (d, J=3.2 Hz, 1H), 7.38–7.47 (m, 5H);
13C NMR (CDCl3, 100 MHz): d=27.5, 87.1, 88.1, 124.7,
128.9, 129.1, 139.2, 151.1, 157.5; MS (70 eV): m/z (%)=190
[M+], 145, 118 (100), 103, 77.
4-Methylene-1,3-dioxaspiro[4.4]nonan-2-one
(7h):[12]
ACHTUNGTRENNUNG
[4.5]decan-2-one
(7i):[12]
1H NMR (CDCl3, 400 MHz): d=1.54–1.73 (m, 8H), 1.95–
1.98 (m, 2H), 4.25 (d, J=3.6 Hz, 1H), 4.72 (d, J=4.0 Hz,
1H); 13C NMR (CDCl3, 100 MHz): d=21.6, 24.4, 36.5, 85.5,
86.4, 151.5, 158.8; MS (70 eV): m/z (%)=168 [M+], 124,
109, 95, 82, 67 (100), 54.
4-Isopropyl-5-methylene-1,3-dioxolan-2-one
(7j):[12]
1H NMR (CDCl3, 400 MHz): d=0.96 (d, J=6.8 Hz, 3H),
1.05 (d, J=6.8 Hz, 3H), 1.98–2.04 (m, 1H), 4.32 (d, J=
1.6 Hz, 1H), 4.88 (s, 1H), 4.99 (s, 1H); 13C NMR (CDCl3,
100 MHz): d=15.0, 17.6, 32.7, 84.2, 87.5, 152.1, 152.3; MS
(70 eV): m/z (%)=142 [M+], 100, 83, 70, 56 (100).
4-Methylene-5-pentyl-1,3-dioxolan-2-one (7k):[11] 1H NMR
(CDCl3, 400 MHz): d=0.87 (t, J=5.6 Hz, 3H), 1.29–1.45
(m, 6H), 1.73–1.83 (m, 2H), 4.31 (d, J=1.6 Hz, 1H), 4.82
(d, J=1.6 Hz, 1H), 5.10–5.15 m, 1H); 13C NMR (CDCl3,
100 MHz): d=13.8, 22.3, 23.5, 31.1, 34.7, 79.8, 86.6, 152.1,
153.4; MS (70 eV): m/z (%)=170 [M+], 127, 97, 83, 69, 55
(100).
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We thank the National Basic Research Program of China
(973 Program) (2010CB732206), the National Natural Sci-
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2028
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ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2013, 355, 2019 – 2028