Cross coupling on gold nanoparticles. Effect of reinforced affinity of organic group with bipedal thiol

Article abstract of DOI:10.1246/cl.2011.1450

Bipedal thiol, whose end is modified with iodoarene, is synthesized and introduced onto the surface of gold nanoparticles. The obtained nanoparticles allow the SuzukiMiyaura and Sonogashira cross-coupling reactions to form the carboncarbon bond on the sur

Full text of DOI:10.1246/cl.2011.1450

doi:10.1246/cl.2011.1450
1450
Published on the web December 5, 2011
Cross Coupling on Gold Nanoparticles. Effect of Reinforced Affinity
of Organic Group with Bipedal Thiol
Atsushi Sugie,1 Kenta Kumazawa,1 Tomomi Hatta,1 Kiyoshi Kanie,2 Atsushi Muramatsu,2 and Atsunori Mori*1
1Department of Chemical Science and Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe, Hyogo 657-8501
2Institute of Multidisciplinary Research for Advanced Materials, Tohoku University,
2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577
(Received September 6, 2011; CL-110743; E-mail: amori@kobe-u.ac.jp)
Bipedal thiol, whose end is modified with iodoarene, is
results show that the cross-coupling reaction of aryl iodide at the
end of alkanethiol is difficult due to the insufficient stability of
AuNP toward aggregation as well as low reactivity.
synthesized and introduced onto the surface of gold nano-
particles. The obtained nanoparticles allow the Suzuki-Miyaura
and Sonogashira cross-coupling reactions to form the carbon-
carbon bond on the surface of the nanoparticle without serious
aggregation under harsh conditions.
We then envisaged the use of multifunctional capping thiol
for improved stabilization on the gold surface. Such unfunc-
tionalized bidentate or tridentate thiols have been synthesized
by Lee9 and physical properties of thus obtained AuNP are
characterized; however, studies on their tolerance for organic
reactions have not been performed so far. Accordingly, our
interest has been focused on the coupling reactions of the AuNP
stabilized by bipedal 1,3-dithiol bearing iodoarene functionality
by transition-metal catalysis.
Synthesis of bipedal thiol 8 was carried out as outlined
in Scheme 2. The reaction of 11-bromo-1-undecanol with p-
iodophenol in the presence of K2CO3 afforded 3 in 89% yield.
Tosylation of 3 with p-toluenesulfonyl chloride leads to 4, which
was subjected to the reaction of diethyl malonate to afford
diester 5 in 85% yield. Reduction of ester with DIBAL-H
at ¹15 °C furnished the corresponding diol 6 in 87% yield.
Treatment of 6 with tosyl chloride lead to the ditosylate 7 (74%).
Introduction of thioacetyl group, following methanolysis, and
reduction with NaBH4 afforded bipedal thiol 8 in 96% yield.
Preparation of AuNP was carried out with the obtained 8
with H[AuCl4]. It was found that the use of t-BuNH2¢BH3 was
effective to afford the corresponding AuNP 9 after treatment at
55 °C for 3.5 h in THF (Scheme 3).10 Characteristics of AuNP 1
and 9 were compared by TEM observation and TGA measure-
ment (Table 1). The particle size of the AuNP 9 was found to be
smaller than that of the AuNP 1. The adsorption density of thiol
moiety on the AuNP was estimated by the particle size and the
mass loss by TGA. The higher adsorption density of -CH2S of 9
compared to 1 suggested that bipedal thiol 8 effectively covered
the AuNP surface.
Organic transformation over organic/inorganic interfaces is
a new frontier in synthetic organic chemistry. A reaction that
smoothly proceeds under homogeneous conditions in an organic
solvent does not necessarily occur in a similar manner on the
surface. Accordingly, our continuing studies on the development
of new synthetic protocols for alkanethiol-capped gold nano-
particles (AuNP) based on organic synthesis1,2 lead our further
concern toward the reaction at the organic functional group
introduced into the end of the thiol. AuNP recently attracts much
attention as advanced material showing electronic, electroop-
tical, and bioactive properties.3,4 It is thus intriguing to introduce
such organic functionalities by an organic bond-forming reaction
on the surface of AuNP.5,6 We herein report our efforts for
transition-metal-catalyzed cross coupling7 on the surface of
AuNP, in which use of bipedal thiol bearing 1,3-dithiol moiety
at the end of long-chained alkanethiol and a functional group to
be transformed at the other end is highly effective.
We first envisaged the Suzuki-Miyaura coupling8 reaction
on an alkanethiol-capped AuNP. We designed and prepared an
alkanethiol-capped AuNP 1,2 whose terminal is modified with
iodoarene. The reaction of 1 and boronate 2a in the presence
of [Pd(t-Bu3P)2] was performed in THF/aq. K2CO3 at room
temperature for 6 h. Aggregation of the AuNP was not observed
during the reaction; however, the isolated AuNP was not
dispersed again in chloroform or THF, suggesting that aggre-
gation took place in isolation. In addition, the 1H NMR spectrum
of the organic moiety, which was removed from Au by treatment
with iodine, exhibited a ca. 1:1 mixture of the desired biaryl and
unreacted aryl iodide. On the other hand, the reaction at elevated
temperature (40-60 °C) resulted to form black precipitates in
the reaction mixture suggesting aggregation (Scheme 1). These
K2CO3
HO (CH2)11
O
I
HO (CH2)11 Br
HO
I
+
DMSO
50 °C, 44 h
3
89%
EtOOC
TsCl
Et3N
DMAP
EtOOC
NaH
EtOOC
TsO (CH2)11
O
I
(CH2)11
O
I
CH2Cl2
rt, 45 h
DMF/THF
0 °C to reflux
9 h
4
5
85%
EtOOC
90%
TsCl
Et3N
DMAP
O
Au
HO
HO
S
B
Me
TsO
TsO
(CH2)11
O
I +
DIBAL-H
THF
(CH2)11
6
O
I
(CH2)11
O
I
O
CH2Cl2
rt, 19 h
1
2a
7
74%
-15 °C, 26 h
87%
[Pd(t-Bu3P)2]
K2CO3(aq)
S
(CH2)11
O
I
1) AcSK
MeCN
70 °C, 3 h
2) NaOH
THF/MeOH
rt, 4 h
Au
S
HS
HS
NaBH4
THF
(CH2)11
O
Me
(CH2)11
O
I
THF/MeOH
0 °C, 2 h
rt, 40, or 60 °C, 6 h
8
low conversion or aggregation
96%
Scheme 1.
Scheme 2.
Chem. Lett. 2011, 40, 1450-1452
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

1451
HS
HS
t-BuNH2·BH3
A
B
H[AuCl4]·4H2O +
I
(CH2)11
O
THF
40 to 55 °C
3.5 h
8
2a
[Pd(t-Bu3P)2]
K2CO3(aq)
S
Au
I
(CH2)11
O
THF
25-60 °C
S
9
S
S
Figure 2. TEM images of AuNP 9 (A) and 10a (B).
Au
Me
(CH2)11
O
10a
Table 2. Coupling reaction of aryl iodide on AuNP with
arylboronatesa
Scheme 3.
Table 1. Characteristics of AuNP
Temp.
/°C
Yield (-C6H4Aryl/
/mg
Reagent
Time
-C6H4I)/%b
Particle size TGA mass loss Adsorption density
O
B
O
AuNP
CF3
/nm
at 800 °C/%
(-CH2S/nm2)a
rt
rt
3 h
17.1
>95
(2b)
1
9
7.8 « 0.97
5.4 « 0.87
9.65
15.31
3.98
7.88
O
B
OMe
O
3 h
6 h
6 h
17.6
18.0
10.0
>95
93
aCalculated from particle size and TGA mass loss.
(2c)
Me
O
B
O
rt
rt
Me
(2d)
O
B
O
O
80
(2e)
2a
rt
60
60
6 h
10 min
3 h
13.0
16.6
15.7
>95
>95
>95
aThe reaction was carried out with AuNP 9 (20.0 mg) and
arylboronic acid ester (0.1 mmol) in the presence of [Pd(t-
Bu3P)2] (0.01 mmol) and K2CO3 aq. (2 M, 2 mL) in THF
Figure 1. 1H NMR of AuNP 9 (A) and 10a (B) (500 MHz,
CDCl3).
b
(10 mL). Conversion of aryl iodide to biaryl on AuNP was
1
estimated by measurement of H NMR of the nanoparticle or
With the obtained bipedal-thiol-protected AuNP 9 in hand,
the Suzuki-Miyaura coupling was carried out. The reaction of
AuNP 9 and aryl boronate 2a in the presence of [Pd(t-Bu3P)2] in
THF/aq. K2CO3 was found to proceed smoothly to afford the
corresponding biaryl 10a after stirring at room temperature for
6 h. The purple color of the reaction mixture was maintained
during the coupling reaction suggesting no problematic aggre-
gation of AuNP. Addition of ethanol to the resulting mixture
formed a precipitate and successive centrifugation and precip-
itation with ethanol afforded the AuNP as a dark brown solid,
which was easily redispersed in chloroform and THF.
after treatment of AuNP with iodine.
reaction with boronic acid esters bearing 4-(trifluoromethyl)-
phenyl 2b and 4-methoxyphenyl 2c groups proceeded within 3 h
at room temperature to afford the corresponding gold nano-
particles. The use of sterically hindered aryl boronate bearing
2,6-dimethylphenyl 2d and 4-acetylphenyl 2e groups also
furnished the coupling products. It should be pointed out that
the reaction with 2a at 60 °C completed within a short reaction
period (10 min). No significant aggregation was observed also in
the reaction for a longer period (3 h) to afford the corresponding
cross-coupled AuNP 10a. The results clearly show that the
bipedal thiol is much more stable thermally and chemically than
monodentate thiol.
The present protocol would be effective for diversity-
oriented synthesis of AuNPs to introduce a functional group
that is available as advanced materials. The place exchange
method,11 which is the reaction of unfunctionalized-alkanethiol-
capped nanoparticle with a thiol bearing a functional group, is an
alternative choice to form functionalized AuNPs; however, it is
not easy to replace with the intended amount of functionality
onto the particle. Although the reaction of a gold salt (H[AuCl4])
Figure 1 shows 1H NMR spectra of the AuNP 9 (A) and 10a
(B). A new singlet signal at ca. 2.3 ppm, which corresponded to
the methyl group, and additional signals of arylene groups (6.8-
7.6 ppm) were observed in 10a. The signal at 6.66 ppm, which
is assigned as protons of the iodophenoxy group of 9 of A,
disappeared in the spectrum B. The results suggested complete
consumption of the iodophenoxy group of 9 during the reaction.
TEM observation revealed that the obtained AuNP was also
spherical, and no morphological change was observed after cross
coupling (5.6 « 0.86 nm) (Figure 2).
The Suzuki-Miyaura coupling of AuNP 9 with several aryl
boronates was examined under similar conditions (Table 2). The
Chem. Lett. 2011, 40, 1450-1452
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

1452
Table 3. Coupling reaction of aryl iodide on AuNP with
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2
3
[Pd(t-Bu3P)2], CuI
S
i-Pr2NH
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Au
9
R
+
R
(CH2)11
O
THF
25 °C, 24 h
S
11a-e
Yield
/mg
-R
-C6H5
-C6H4-Me-4
-n-C6H13
-SiMe3
Product
(-C6H4Aryl/-C6H4I)/%b
4
5
11a
11b
11c
11d
11e
18.0
12.7
19.6
19.2
19.0
>95
85
84
>95
>95
-Sii-Pr3
aThe reaction was carried out with AuNP 9 (20.0 mg) and
alkyne (0.05 mmol) in the presence of [Pd(t-Bu3P)2] (0.01
mmol), CuI (0.01 mmol), and i-Pr2NH (0.5 mmol) in THF
(2.5 mL). bConversion of aryl iodide to alkynylarene on AuNP
was estimated by measurement of 1H NMR of the nanoparticle.
with a capping thiol bearing a functional group at the end in the
presence of a reducing agent, representative as the Brust-
Schiffrin method,12 the conditions may limit available organic
functional groups. In contrast, the cross-coupling reaction on
AuNP quantitatively proceeded with several arylboronates 2 and
would be a powerful tool to introduce a wide range of
functionality through carbon-carbon-bond formation.
6
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It was also found that the Sonogashira coupling proceeded
with AuNP 9.6b,6c,13 The reaction of AuNP 9 with phenyl-
acetylene in the presence of [Pd(t-Bu3P)2], CuI, and diisopropyl-
amine in THF afforded the corresponding coupling product 11a
after stirring at room temperature for 24 h (Table 3). The similar
reaction of AuNP 9 with terminal alkynes bearing aryl, alkyl,
and trialkylsilyl groups proceeded smoothly to furnish nano-
particle 11b-11e. Accordingly, AuNPs bearing a carbon-carbon-
triple bond, which are available for several further transforma-
tion reactions, were obtained by the coupling protocol.
In summary, we have shown that cross coupling occurs on
the AuNP. The reaction proceeded highly efficiently when
bipedal thiol was employed as a surface-modifying agent to
tolerate the reaction temperature up to 60 °C, whereas the
reactions with monodentate thiol have been less effective. The
coupling reaction allows introduction of organic functional
groups onto nanoparticles, thus, the method would lead to
organic-reaction inspired microfabrication of nanomaterials.14
7
8
9
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AS acknowledges a JSPS Research Fellowship for a Young
Scientist. The authors thank Professor Kiyomi Kakiuchi of Nara
Institute of Science and Technology (NAIST) for measurements
of high-resolution mass spectra.
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3782.
This paper is in celebration of the 2010 Nobel Prize
awarded to Professors Richard F. Heck, Akira Suzuki, and
Ei-ichi Negishi.
12 M. Brust, M. Walker, D. Bethell, D. J. Schiffrin, R. Whyman,
J. Chem. Soc., Chem. Commun. 1994, 801.
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14 Supporting Information is available electronically on the CSJ-
Journal Web site, http://www.csj.jp/journals/chem-lett/index.
html.
References and Notes
1
a) A. Sugie, T. Somete, K. Kanie, A. Muramatsu, A. Mori,
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A. Muramatsu, A. Mori, Chem. Lett. 2009, 38, 562. c) A. Sugie,
T. Yamanaka, K. Kumazawa, T. Hatta, Y. Ueda, K. Kanie, A.
Chem. Lett. 2011, 40, 1450-1452
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/