Synthesizing Ag Nanoparticles of Small Size on a Hierarchical Porosity Support for the Carboxylative Cyclization of Propargyl Alcohols with CO2 under Ambient Conditions

Article abstract of DOI:10.1002/chem.201502479

Both immobilization of Ag nanoparticles (AgNPs) of very small size on hierarchical porosity supports and carboxylative cyclization of propargyl alcohols with CO₂ under ambient conditions are very interesting. In this work, we synthesized AgNPs supported on sulfonated macroreticular resin (SMR) with hierarchical pores in water/alcohol solutions. It was shown that the size of the AgNPs on the SMR could be tailored easily by altering the synthetic solutions, and very small AgNPs with narrow size distribution (1-3 nm) could be obtained in water/methanol solution. It was found that the AgNPs/SMR with small AgNPs was highly efficient and an easily recyclable catalyst for the synthesis of α-alkylidene cyclic carbonates by carboxylative cyclization of propargyl alcohols with CO₂ at ambient pressure and temperature, which was the first work to use metal nanoparticles as the catalysts for the reaction.

Full text of DOI:10.1002/chem.201502479

DOI: 10.1002/chem.201502479
Communication
&
Carbon Dioxide Fixation
Synthesizing Ag Nanoparticles of Small Size on a Hierarchical
Porosity Support for the Carboxylative Cyclization of Propargyl
Alcohols with CO under Ambient Conditions
2
Meng Cui, Qingli Qian,* Zhenhong He, Jun Ma, Xinchen Kang, Jiayin Hu, Zhimin Liu, and
[a]
Buxing Han*
[
8]
[9]
polymer-supported Cu or Ag salts were also used to cata-
lyze the reaction at high CO pressure (5–14 MPa) and elevated
Abstract: Both immobilization of Ag nanoparticles
AgNPs) of very small size on hierarchical porosity sup-
2
(
temperature (40–608C). Although many elegant works have
been carried out, design and fabrication of efficient and reus-
able catalysts for the reaction under ambient pressure and
temperature is still highly desirable because, in general, the
catalysts reported for the reactions suffer from some draw-
ports and carboxylative cyclization of propargyl alcohols
with CO under ambient conditions are very interesting. In
2
this work, we synthesized AgNPs supported on sulfonated
macroreticular resin (SMR) with hierarchical pores in
water/alcohol solutions. It was shown that the size of the
AgNPs on the SMR could be tailored easily by altering the
synthetic solutions, and very small AgNPs with narrow size
distribution (1–3 nm) could be obtained in water/metha-
nol solution. It was found that the AgNPs/SMR with small
AgNPs was highly efficient and an easily recyclable cata-
lyst for the synthesis of a-alkylidene cyclic carbonates by
backs, such as high CO pressure and/or difficulty in recycling.
2
Metal nanoparticles immobilized on supports with hierarchi-
cal macro- and mesopores are of obvious advantage in cataly-
sis because they combine the unique features of the nanocata-
[
10]
lysts and hierarchical porosity of the supports.
Functional
polymers are among the most important supports for metal
nanoparticle catalysts, because of good designability and tuna-
bility of polymer chain structure, porosity, and functional
groups. These kinds of supported catalysts have been de-
signed by different researchers. For example, Reiser and co-
carboxylative cyclization of propargyl alcohols with CO at
2
ambient pressure and temperature, which was the first
work to use metal nanoparticles as the catalysts for the re-
action.
[
11]
workers utilized polymer- and dendrimer-coated magnetic
nanoparticles as versatile supports for catalysts, scavengers,
[
12]
and reagents. Hariprasad et al. reported Pd-nanoparticle-em-
bedded polymer thin film “dip catalysts” for Suzuki–Miyaura re-
[
13]
CO2 is an abundant, safe, and renewable carbon resource.
actions. Biswas et al. designed and prepared polymer-assist-
ed chainlike organization of CuNi alloy nanoparticles as sol-
vent-adoptable pseudohomogeneous catalysts for alkyne–
azide click reactions with magnetic recyclability. Herbois
Transformation of CO into value-added products is of great
2
[
1]
importance. a-Alkylidene cyclic carbonates can serve as im-
[2]
portant intermediates in many organic syntheses. One of the
best strategies is carboxylative cyclization of propargyl alcohols
[
14]
et al.
synthesized highly-efficient Ru nanoparticle catalysts
with CO , which is a clean route for the synthesis of a-alkyli-
supported by a water-compatible three-dimensional b-cyclo-
2
dene cyclic carbonates. Different metal-free catalytic systems,
such as tertiary phosphine, bicyclic guanidine, the N-hetero-
dextrin-based polymer for the catalytic hydrogenation of bio-
[
15]
mass-derived furanic compounds. Yang et al.
fabricated
cyclic carbene/CO adduct, and the N-heterocyclic olefin/CO2
water-compatible Pd nanoparticle catalysts supported on mi-
croporous polymers, which showed high activity and extremely
low Pd leaching behavior in the carbon cross-coupling reac-
tions.
2
adduct have been reported as catalysts to synthesize a-alkyli-
[3]
dene cyclic carbonates. However, high-temperature and CO2
pressure were usually needed for the reactions when these
catalysts were used. Various transition-metal salts, including
Both controllable synthesis of Ag nanoparticles of very small
size on supports with hierarchical porosity and efficient carbox-
[4]
[5]
[6]
[7]
Ag, Cu, Co, and Pd, were found to be effective homoge-
nous catalysts for the carboxylative cyclization reactions. Some
ylative cyclization of propargyl alcohols with CO under ambi-
2
ent conditions are very interesting and challenging. Sulfonated
macroreticular resin (SMR) has hierarchical porosity and good
[
a] M. Cui, Dr. Q. Qian, Dr. Z. He, Dr. J. Ma, X. Kang, J. Hu, Prof. Dr. Z. Liu,
Prof. Dr. B. Han
Beijing National Laboratory for Molecular Sciences
CAS Key Laboratory of Colloid, Interface and Chemical Thermodynamics
Institute of Chemistry, Chinese Academy of Sciences
Beijing 100190 (China)
[
16]
chemical and mechanical stability. In this work, we synthe-
0
sized Ag nanoparticles (AgNPs)/SMR composites in aqueous
solutions of alcohols (methanol, ethanol, and propanol) with
different compositions. It was found that the size of the AgNPs
could be tailored successively by altering the synthetic sol-
vents, and the particle size could be very small with narrow
size distribution when water/methanol was used as the sol-
E-mail: qianql@iccas.ac.cn
hanbx@iccas.ac.cn
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201502479.
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ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
vent. Very interestingly, support-
ed AgNPs of small size could be
used as efficient and recyclable
catalysts for producing a-alkyli-
dene cyclic carbonates by cou-
pling of propargyl alcohols and
CO2 at room temperature and
atmospheric pressure. As far as
we know, this is the first work to
use metal(0) nanoparticles as the
catalysts for the reaction.
The pore-size distribution of
the dry SMR was determined by
mercury intrusion porosimetry.
The size of the most pores in the
dry SMR was in the range of 10–
9
0 nm and centered at 26 nm
(
Figure S1, Supporting Informa-
tion). We prepared the AgNPs/
SMR catalysts in the aqueous
solutions of different alcohols,
and the alcohols acted as both
co-solvent and reductant. The
Figure 1. SEM image of SMR cross section (a) and TEM images of the AgNPs/SMR catalysts: Cat-M (b), Cat-E (c),
route is shown sketchily in and Cat-P (d). The insets in (b–d) show the size distribution of the AgNPs. The Ag contents in (b–d) determined
+
by ICP-AES method were 24.9, 25.0, and 26.3 wt%, respectively.
Scheme 1. Briefly, the Ag ions
mation. The size of the AgNPs synthesized could be tailored by
altering the carbon chain of the alcohols and the composition
of the water/alcohol solutions. In general, the size of the
AgNPs synthesized in water/methanol solution was the small-
est. For a fixed alcohol, a solution with 50 vol% alcohol gener-
ated the smallest AgNPs. The sizes of the AgNPs in AgNPs/SMR
catalysts synthesized in water/methanol (50 vol%, Cat-M),
water/ethanol (50 vol%, Cat-E), and water/propanol (50 vol%,
Cat-P) solutions were mainly in the ranges of 1–3, 2–5, and 3–
7
nm, respectively (Figure 1b–d). The EDS study demonstrated
that the Ag was well distributed on the whole resin beads (Fig-
[
10d]
ure S4, Supporting Information). In our previous paper,
we
prepared Pt nanoparticles (2–5 nm) within the SMR by using
water/ethanol as the solvent, and found that water/ethanol
nanoreactors were formed in situ in the resin matrix. The
reason for the strong effect of the solvents on the size of the
AgNPs synthesized in this work is not clear. We believe that
the size of the water/alcohol nanoreactors formed in the resin
may increase with the size of the alcohols in the solution,
which may be one of the main reasons for the size increase of
the Ag particles with the chain length of the alcohols.
Scheme 1. Route of the AgNPs/SMR catalyst synthesis.
were exchanged onto the sulfonic group of the SMR, replacing
+
+
the Na ions. Then the NaOH added reacted with Ag ions to
form Ag O, which was further reduced to Ag atoms by the al-
2
[
17]
cohol in situ. The metallic Ag aggregated to form the AgNPs
on the support. The AgNPs/SMR catalysts were obtained after
The wavenumbers of the peaks in the IR spectrum of the
SMR were nearly the same as those of the SMR in the catalysts
(Figure S5, Supporting Information), which suggests that there
existed mainly physical interactions between the AgNPs and
the resin support. The Cat-M and AgNPs/SMR catalyst pre-
pared in water (Cat-W) were characterized by X-ray diffraction
(XRD) (Figure S6, Supporting Information). Strong metallic Ag
washing and drying. The X-ray photoelectron spectroscopy
0
(
XPS) analysis confirmed the formation of Ag in the resin (Fig-
ure S2, Supporting Information).
The SMR and AgNPs/SMR catalysts synthesized in water/
methanol, water/ethanol, water/propanol solutions of different
alcohol contents were characterized by SEM and TEM, and the
images are given in Figure 1 and Figure S3, Supporting Infor-
[
18]
peaks were observed in the XRD pattern of Cat-W because
larger Ag particles (4–26 nm) existed in the sample (Figure S6a,
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Supporting Information). There was no visible Ag peaks in the
XRD pattern of Cat-M (Figure S6b, Supporting Information),
which indicated the formation of very small Ag particles (1–
[
19]
3
nm).
The uniform AgNPs of very small size on the SMR with hier-
archical porosity may have special properties in catalysis. Car-
boxylative cyclization of propargyl alcohols with CO is a clean
2
route for the synthesis of a-alkylidene cyclic carbonates. We
first selected the carboxylative cyclization of 2-methyl-3-butyn-
2
-ol (1a) with CO to explore the catalytic performance of the
2
AgNPs/SMR catalysts with Ag particles of different sizes, and
the results are given in Figure 2. It is interesting that the cata-
Figure 3. Effect of reaction time on the product yield over Cat-M. Reaction
conditions: 1 mmol substrate (2-methyl-3-butyn-2-ol), 1 mmol DBU, Cat-M
2
(10 mol% Ag based on the substrate), 2 mL DMF, 0.1 MPa CO , 258C.
siderably affect the geometrical structure and electronic prop-
erties of metal nanoparticles, such as binding energy, energy
gap between HOMO and LUMO, ionization potential, and elec-
[
20]
tron affinity. We believe that variations of geometrical struc-
ture and electronic properties of the AgNPs with the size and
the solvents are important reasons for the size and solvent ef-
fects of the catalytic reaction.
Figure 2. Effects of the size of AgNPs on the activity of the AgNPs/SMR cata-
lysts. Reaction conditions: 1 mmol substrate, 1 mmol DBU, catalyst (10 mol%
Table 1. Catalytic performance of the Cat-M for carboxylative cyclization
of various propargyl alcohols with CO .
2
Ag based on the substrate), 2 mL DMF, 0.1 MPa CO
2
, 258C, 10 h.
[a]
lysts with small Ag particles were very active for the reaction
even at ambient temperature and pressure (Cat-M, Cat-E, Cat-
P in Figure 2). In contrast, the activity of Cat-W with large Ag
particles was very low. The yield of the target product in-
creased with the increase of the catalyst loading when the cat-
alyst dosage was low. However, the yield was less sensitive as
the loading exceeded 10 mol% Ag (Figure S7, Supporting In-
formation).
[b]
Entry
1
Substrate
Product
Yield [%]
91
The above results show that catalyst with the smallest Ag
particles (Cat-M) had the highest activity for the reaction. The
effects of solvents and bases on the reaction were studied
using this catalyst with a reaction time of 5 h, and the data are
presented in Table S1, Supporting Information. The results
demonstrate that Cat-M had the best performance when 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU) was used as the promot-
er and DMF as the solvent. Figure 3 illustrates the dependence
of yield on the reaction time. A yield of 91% was obtained at
2
3
93
90
4
87
1
0 h and further increase of reaction time did not change the
5
6
86
96
yield notably. The activity of the catalyst did not decrease no-
ticeably and the Ag content of the catalyst (23.5 wt%) did not
change evidently after the catalyst was reused five times (Fig-
ure S8, Supporting Information). The results above demon-
strate that Cat-M was a highly efficient and easily recyclable
catalyst for the reaction.
[a] Reaction conditions: substrate (1 mmol), Cat-M (10 mol% Ag based
on the substrate), DBU (1 mmol), DMF (2 mL), 0.1 MPa CO , 258C, 10 h.
b] Determined by H NMR methods, using 1,3,5-trioxane as an internal
standard.
As can be seen from the above results, the size of the
AgNPs and solvents influenced the activity of the catalyst sig-
nificantly. DFT studies indicated that the size and solvents con-
2
1
[
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Communication
Acknowledgements
The authors thank the National
Natural Science Foundation of
China. This work was supported
by the National Natural Science
Foundation of China (21373234,
21303224, U1232203, 21321063)
and the Chinese Academy of Sci-
ences (KJCX2.YW.H30).
2
Scheme 2. Proposed mechanism for the reaction of propargyl alcohols and CO catalyzed by AgNPs/SMR catalyst.
To verify the versatility of the catalyst, we tested other sub-
strates of typical structures using Cat-M, and the results are
listed in Table 1. Cat-M is very effective for synthesizing a-alky-
lidene cyclic carbonates of different molecular structures by
carboxylative cyclization of a series of propargyl alcohols with
CO2 at ambient conditions. The catalytic activity (based on
TOF) of Cat-M is comparable to those of some homogeneous
Keywords: carbon dioxide · cyclic carbonates · nanoparticles ·
supported catalysts · silver
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Received: July 1, 2015
Published online on September 14, 2015
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