Preparation of a microporous organic polymer by the thiol-yne addition reaction and formation of Au nanoparticles inside the polymer

Article abstract of DOI:10.1039/c5cc02269j

A microporous polymer with sulfide and thiol groups was synthesized using the thiol-yne reaction. Au nanoparticles were prepared by in situ reduction reaction inside the polymer and were found to be well dispersed. The Au-containing polymer showed catalytic activity in the reduction of 4-nitrophenol.

Full text of DOI:10.1039/c5cc02269j

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DOI: 10.1039/C5CC02269J
ARTICLE TYPE
Preparation of a microporous organic polymer by the thiol-yne addition
reaction and formation of Au nanoparticles inside the polymer
Hyunpyo Lee, Hyungwoo Kim, Tae Jin Choi, Hyun Woo Park and Ji Young Chang*
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
A microporous polymer with sulfide and thiol groups was
monomer according to the literature (Scheme S1, Fig. S1,
1
7
synthesized by the thiol-yne reaction. Au nanoparticles were 50 ESI†).
Tetraphenyladamantane was synthesized from the
prepared by in-situ reduction reaction inside the polymer and
were found to be well dispersed. The Au-containing polymer
showed catalytic activity in a reduction of 4-nitrophenol.
Fridel-Crafts reaction of 1-bromoadamantane with benzene in the
1
8
presence of
ethynylphenyl)adamantane was obtained from the Sonogashira-
Hagihara cross-coupling reaction of tetrakis(4-
Significant interest has been shown in microporous organic 55 iodophenyl)adamantane with trimethylsilylacetylene and
AlCl3
and then iodized.
Tetrakis(4-
1
0
polymers with highly cross-linked network structures as
promising metal catalyst supports. The porous structures and
large surface areas of the microporous organic polymers facilitate
the ease of access of reactants to catalytic sites. A metal catalyst
subsequent deprotection reaction under basic conditions.
The microporous polymer was prepared using the thiol-yne
reaction
as
shown
in
Scheme
1.
Tetrakis(4-
1
2
2
3
3
4
4
5
0
5
0
5
0
5
ethynylphenyl)adamantane was reacted with a two-fold excess of
can be incorporated into the microporous polymer in the form of 60 1,3,5-benzenetrithiol in the presence of AIBN in DMF. The
1
2
an ion complex or as a nanoparticle.
Highly cross-linked microporous organic polymers are usually
prepared by the coupling reactions of multi-functional organic
addition of a thiyl radical formed with AIBN to an ethynyl group
yielded a vinyl linker. The disulfide linkages were also produced
from an oxidative reaction between the unreacted thiol groups.
The structure of the microporous polymer was investigated using
3-6
building blocks. Transition metal-mediated coupling reactions,
3
4
13
13
such as Yamamoto coupling, Suzuki coupling, Ullmann 65 C solid state NMR and FT-IR spectroscopy. In the C solid
5
6
coupling, and Sonogashira-Hagihara coupling have been used
extensively for polymer synthesis. Among metal catalyst free
reactions, the condensation reactions of multiamino-
state NMR spectrum (Fig. S2, ESI†), aromatic carbon peaks were
observed at 124, 133, 137 and 148 ppm. The peak of acetylene C-
C triple carbon at around 90 ppm was not visible, indicating that
all acetylene groups reacted with thiol groups. The peaks of the
7
8
functionalized monomers with aldehydes, carboxylic acids, and
9
anhydrides have been successfully employed to prepare highly 70 vinyl carbons overlapped with those of the aromatic carbons. The
cross-linked microporous polymers.
The thiol-yne reaction between a thiol and an alkyne is another
interesting metal catalyst free coupling reaction, which can be
useful for the synthesis of a highly crosslinked polymer network.
adamantane carbon peaks were observed at 44 and 38 ppm. FT-
IR spectroscopy also confirmed the consumption of acetylene
groups in the polymerization (Fig. S3, ESI†), showing that a
carbon stretching vibration peak of the acetylene group at 2100
10
-1
-1
The thiol-yne reaction proceeds in a high yield via a radical 75 cm did not occur. The weak peak at 2550 cm was assigned to
mechanism with the aid of a radical initiator or UV light. A
the stretching vibration of a thiol group. While the thiol groups
that did not participate in the thiol-yne reaction were converted to
the disulfide units, some of these remained due to the steric
hindrance.
11
number of multibranched polymers such as dendrimers,
1
2
13
hyperbranched polymers, and star polymers have been
synthesized using this reaction.
In this study, we prepared a microporous organic polymer
containing sulfide and thiol groups using the thiol-yne reaction of
a tetraethynyl compound with trithiol. Gold nanoparticles (Au
NPs) were incorporated into the microporous polymer using an
in-situ reduction reaction of HAuCl with NaBH . We expected
4
4
that the sulfide and thiol groups would prevent the aggregation of
Au NPs by interacting with their surfaces. Au NPs attracted
considerable attention for their catalytic activities in organic
1
4
reactions such as the reduction of nitro groups or the oxidation
of alcohols and CO. Here, we present the synthesis of an Au
NPs loaded microporous polymer and its use for the amination
8
0
1
5
16
Scheme 1 Synthesis of the microporous polymer.
reaction of 4-nitrophenol in the presence of NaBH
4
.
To gain more information about the polymer structure, a model
Tetrakis-(4-ethynylphenyl)adamantane was prepared as
a
reaction for the polymerization was performed with
a
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Page 2 of 4
phenylacetylene and two-fold excess of thiophenol in DMSO-d
6
The microporous polymer was found to have amorphous
1
(
Fig. 1a). The reaction mixture was analysed in situ using H 40 spherical structures with diameters ranging from 20 to 30 nm
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NMR spectroscopy (Fig. 1b-1d). Immediately after mixing of the
two chemicals (Fig. 1b), a new small peak appeared at 6.68 ppm
for vinylic protons in addition to the thiol and acetylene proton
peaks at 5.36 and 4.18 ppm, respectively, and aromatic proton
according to scanning electron microscopy (SEM) and wide angle
DOI: 10.1039/C5CC02269J
X-ray diffraction (WXRD) measurements (Fig. S5, ESI†). The
porosity of the microporous polymer was investigated by nitrogen
adsorption-desorption experiment. Hysteresis was observed in the
5
0
5
0
5
0
peaks at from 7 to 7.6 ppm. This result suggested that an aromatic 45 pressure range from 0.75 to 1.0, suggesting that the polymer
acetylene group had high reactivity with a thiol group in the
swelled at high pressure. The Brunauer-Emmet-Teller (BET)
surface area and total pore volume of the microporous polymer
determined by nitrogen adsorption-desorption isotherms were
1
9
o
hydrothiolation reaction. After stirring at 100 C for 3 h in the
presence of AIBN, the acetylene proton peak completely
disappeared and two types of vinylene peaks noticeably
1
1
2
2
3
2
3
575.8 m /g and 1.76 cm /g, respectively (Fig. S6, ESI†). The
developed (Fig. 1c). The integration ratio between the vinylene 50 thermogravimetric analysis (TGA) of the polymer showed good
proton peaks at 6.69-6.83 ppm and the aromatic proton peaks was
calculated to be approximately 1 : 15, indicating that an acetylene
group reacted almost quantitatively with a thiol group through the
thermal stability with the 5% weight loss temperature of around
300 °C in nitrogen (Fig. S7, ESI†).
Au nanoparticles (Au NPs) were loaded in the microporous
thiol-yne reaction.
A
mechanism study of the thiol-yne
4
polymer using the in-situ reduction of HAuCl precursor with
photopolymerization by Fairbanks et al. showed that each ethynyl 55 NaBH
4
. The polymer was dispersed in ethanol, followed by the
2
0
group reacted with two thiol groups because the reaction of a
thiyl radical with an alkyne group produced a vinyl unit, which
was still reactive against another thiyl radical. In the thermal
reaction, however, excess thiol groups were consumed due to the
addition of aqueous solutions of HAuCl4 and NaBH . The
disulfide bonds of the polymer would be also reduced to yield
4
2
2
thiol groups in this process. After the reaction, the polymer was
isolated by filtration and washed with water and ethanol. After
60 incorporating Au NPs, the BET surface area decreased from
575.8 m /g to 103.5 m /g because Au NPs occupied some pores,
which reduced the porosity and increased the total weight of the
polymer. The pore size distribution determined by non-local
density functional theory (NLDFT) broadened after Au NPs were
1
9
reaction between the thiol groups to yield disulfide bonds.
1
2
2
When the solution was diluted with CDCl
3
(90 % CDCl
3
, v/v), H
NMR spectroscopy showed vinylene doublets of the trans
configuration at 6.90 and 6.72 ppm (J = 15.6 Hz) and those of the
cis configuration at 6.60 and 6.51 ppm (J = 10.8 Hz) (Fig. 1d).
The trans isomer was found to be 88 % of the resulting vinyl 65 loaded. The average loading capacity of Au determined by TGA
2
1
sulfide products, comparable to the reported data. In the mass
spectrum, the most intense peak appeared at m/z 212, indicating
the vinyl sulfide adduct with a molecular weight of 212 was a
major product in the hydrothiolation reaction (Fig. S4, ESI†).
was about 7 wt%.
The formation of Au NPs was confirmed by high resolution
transmission electron microscopy (TEM). The Au NPs were well
dispersed in the microporous polymer, probably bound to sulfide
or thiol end groups (Fig. 2). The average diameter of Au NPs was
7
0
7
.0 nm. The X-ray diffraction pattern of the Au NPs loaded
microporous polymer is shown in Fig. S8 (ESI†). Two strong
diffraction peaks were observed at 2θ = 38.1° and 44.1°,
corresponding to the (111) and (200) planes of a typical fcc Au
2
3
7
5
crystal phase, respectively. The size of the Au NPs was further
estimated from the peak width of the (111) Bragg reflection using
the Debye–Scherrer formula. The average diameter of Au NPs
was calculated to be 7.3 nm, which was consistent with the result
from the TEM image.
Fig. 1 (a) Schematic description for the model reaction of thiophenol and
1
phenylacetylene. (b) H NMR spectrum of the reaction mixture of
1
3
5
thiophenol and phenylacetylene in DMSO-d
6
. (c-d) H NMR spectra of
the reaction mixture of thiophenol and phenylacetylene after heating at
8
0
o
1
00 C for 3 h in the presence of AIBN, measured in DMSO-d
6
(c) and
Fig. 2 HR-TEM image of the Au NPs loaded microporous polymer.
measured in DMSO-d /CDCl (1/9, v/v) (d).
6
3
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The elemental states of the Au NPs were investigated using X- 45 government (MSIP) (No. 2010-0017552).
ray photoelectron spectroscopy (XPS) (Fig. S9, ESI†). In the XPS
spectrum, the peaks of Au 4d binding energy showed at 334 and
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DOI: 10.1039/C5CC02269J
Notes and references
3
51 eV. In the high-resolution XPS spectrum, we observed peaks
Department of Materials Science and Engineering, College of
Engineering, Seoul National University, Seoul 151-744, Korea. Fax: +82
2 885 1748; Tel+82 2 880 7190; E-mail: jichang@snu.ac.kr
5
0
5
0
5
at 84.4 and 88.2 eV corresponding to the Au 4f and Au 4f5/2
7
/2
24
binding energies, respectively. These energies were slightly
higher than the bulk Au 4f levels (4f7/2 = 84.0 eV and 4f5/2 = 87.6 50 † Electronic Supplementary Information (ESI) available: Experimental
eV). The peaks of the Au binding energies (86 and 90 eV) were
3
+
details and characterization data of the monomer and the polymers. See
DOI: 10.1039/b000000x/
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4
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55
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4
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Wavelength (nm)
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95
In summary, we demonstrated an efficient way to incorporate a
metal nanoparticle catalyst into a microporous polymer in a well
dispersed form. A sulfur-containing microporous polymer was
prepared using the thiol-yne addition reaction. Au NPs were
loaded in the microporous polymer using the in-situ reduction of
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4
2
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This research was supported by the National Research
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