C O M M U N I C A T I O N S
In summary, the novel nanotube composites consisting of Au or
Pd nanoparticles and polythiophene have been successfully fabri-
cated by the electropolymerization of terthiophene-functionalized
Au or Pd nanoparticles in a nanoporous alumina membrane. The
Pd/polythiophene nanotube composites (2-Pd-PT-NTs) are recy-
clable highly effective catalysts for the carbon-carbon coupling
reaction, although 2-Pd nanoparticles were aggregated during the
reaction. This new method is currently being extended to other metal
and metal oxide nanoparticles/polythiophene nanotube composites
to realize a wide range of hybrid nanomaterials with controllable
surface chemistry. We expect this work to yield a broad range of
potential applications in catalysis, nanoelectrochemistry, chemical/
biological separation, and sensor developments.
Figure 1. 1-Au-PT-NTs: (a) and (b) SEM image [scale bar: (a) 5 µm;
(
b) 1 µm]. Inset (scale bar ) 100 nm): the high-magnification image. (c)
TEM image.
Acknowledgment. This work was supported in part by the
Grant-in-Aid for Scientific Research on Priority Areas (Nos.
7036067 and 18033055 “Chemistry of Coordination Space”) from
the Ministry of Education, Science, Sports and Culture, Japan.
Figure 2. 1-Pd-PT-NTs: (a) SEM image (scale bar ) 5 µm). (b) TEM
image. Inset (scale bar ) 50 nm): the high-magnification image. (c) EDX
spectrum. Cu peaks are from the supporting copper grid.
1
aggregate after the electropolymerization of 1-Pd nanoparticles in
the alumina membrane. These results clearly indicate that the
electropolymerization of 1-Au or 1-Pd nanoparticles in a nanoporous
alumina template led to the formation of the nanotube composites
consisting of Au or Pd nanoparticles and polythiophene as
constituents of nanotubes.
A great interest has been placed on the use of metallic
nanoparticles for nanocatalysis.5,7 To evaluate the catalytic capability
of the nanotubes, we have studied the Stille coupling reaction which
is a very important carbon-carbon bond-forming reaction (eq 1).7,12
Supporting Information Available: Synthesis of 1, 2, 1-Au, 1-Pd,
2-Pd, and the nanotubes, the spectral data, the SEM and TEM images,
and the EDX spectra. This material is available free of charge via the
Internet at http://pubs.acs.org.
References
(
1) (a) Wildgoose, G. G.; Banks, C. E.; Compton, R. G. Small 2006, 2, 182.
(
b) Georgakilas, V.; Gournis, D.; Tzitzios, V.; Pasquato, L.; Guldi, D.
M.; Prato, M. J. Mater. Chem. 2007, 17, 2679.
(
2) (a) Martin, C. R. Acc. Chem. Res. 1995, 28, 61. (b) Hulteen, J. C.; Martin,
C. R. J. Mater. Chem. 1997, 7, 1075. (c) Aleshin, A. N. AdV. Mater.
2006, 18, 17. (d) Xiao, R.; Cho, S., II.; Liu, R.; Lee, S. B. J. Am. Chem.
Soc. 2007, 129, 4483 and references cited therein.
The Stille coupling reaction of methyl-2-iodobenzoate (3) with
(
3) (a) Zhang, X.; Manohar, S. K. J. Am. Chem. Soc. 2005, 127, 14156. (b)
Ko, S.; Jang, J. Angew. Chem., Int. Ed. 2006, 45, 7564.
4) (a) Steinhart, M.; Jia, Z.; Schaper, A. K.; Wehrspohn, R. B.; Gosele, U.;
Wendorff, J. H. AdV. Mater. 2003, 15, 706. (b) Cao, H.; Wang, L.; Qiu,
Y.; Wu, Q.; Wang, G.; Zhang, L.; Liu, X. ChemPhysChem 2006, 7, 1500
and references cited therein.
2-(tributylstannyl)thiophene (4) in the presence of the nanotubes,
(
1-Pd-PT-NTs, in THF at 50 °C for 5 h gave the corresponding
coupling product (5) in a low yield of 30%. In order to improve
the catalytic activity of nanotubes, we have synthesized nanotube
composites of polythiophene and palladium nanoparticles stabilized
by the phosphine ligand instead of the thiol group in 1, since
generally alkyl thiols and thiolates are well-known as poisons that
inhibit the catalysis of reactions by metal nanoparticles.13 Ter-
thiophene-linked oligoethyleneoxy-phosphine (2), the phosphine
(
(
(
5) (a) Schmid, G. Nanoparticles; Wiley-VCH: Weinheim, 2004. (b) Rao,
C. N. R.; Muller, A.; Cheetham, A. K. The Chemistry of Nanomaterials;
Wiley-VCH: Weinheim, 2004; Vol. 1 and 2.
6) (a) Hata, K.; Fujihara, H. Chem. Commun. 2002, 2714. (b) Tamura, M.;
Fujihara, H. J. Am. Chem. Soc. 2003, 125, 15742. (c) Komine, Y.; Ueda,
I.; Goto, T.; Fujihara, H. Chem. Commun. 2006, 302.
7) (a) Roucoux, A.; Schulz, J.; Patin, H. Chem. ReV. 2002, 102, 3757. (b)
Widegren, J. A.; Finke, R. G. J. Mol. Catal. A: Chem. 2003, 198, 317.
(
c) M-Manas, M.; Pleixats, R. Acc. Chem. Res. 2003, 36, 638. (d) Astruc,
2
-stabilized palladium nanoparticles (2-Pd), and the nanotubes (2-
D.; Lu, F.; Aranzaes, J. R. Angew. Chem., Int. Ed. 2005, 44, 7852.
10
Pd-PT-NTs) have been prepared. The catalytic property of 2-Pd
nanoparticles was tested in the Stille coupling reaction (eq 1), i.e.,
the reaction of 3 with 4 in the presence of 2-Pd nanoparticles and
KF in THF at 50 °C for 5 h afforded the product 5, but Pd black
due to aggregation was formed during the reaction.1 In contrast,
significantly, no precipitation of Pd nanoparticles after the reaction
was observed when the nanotubes of 2-Pd-PT-NTs were used for
the Stille reaction. Typically, the reaction of 3 (266 mg, 1 mmol)
and 4 (372 mg, 1 mmol) in the presence of 2-Pd-PT-NTs (4 mg)
and KF (174 mg, 3 mmol) in THF was carried out at 60 °C for 5
h under argon to give the coupling product 5 in a quantitative yield.
The nanotubes as catalyst were reused under the same conditions
with essentially no loss in activity. Importantly, this finding
demonstrates that the surface atoms of the palladium in 2-Pd-PT-
NTs possess catalytic activity.
(8) Compounds (1 and 2) were designed for the following reasons: (i) Since
metal nanoparticles are unstable with respect to aggregation and precipita-
tion to the bulk metal, stabilizers such as thiols and phosphines are used
5
in their preparation to prevent agglomeration. (ii) The oxidation potential
of terthiophene is lower than that of thiophene. (iii) The oligoethyleneoxy
linkage is hydrophilic in nature since the pore walls of the porous alumina
membrane possess hydrophilic sites.
4,15
(
9) Palladium nanoparticles have been of increasing scientific interest as a
7
catalyst for the carbon-carbon coupling reaction.
(10) See the Supporting Information.
(
11) The diameter of the alumina membrane obtained from Whatman Inc. was
found to be 220 ( 15 nm, as revealed by SEM.
(12) (a) Metal-catalyzed Cross-coupling Reactions; Diederich, F., Stang, P.
J., Eds.; Wiley-VCH: New York, 1998. (b) Tsuji, J. Palladium Reagents
and Catalysts; John Wiley & Sons; West Sussex, 2004.
(13) Catalysis from A to Z. A Concise Encyclopedia; Cornils, B., Herrmann,
W. A., Schlogl, R., Wong, C.-H., Eds.; Wiley-VCH: Weinheim, 2000.
14) Pd nanoparticles are known to aggregate easily and form Pd black.
5
,7
(
(15) The catalytic properties of the Pd nanoparticles and their nanotube
composites are discussed in the Supporting Information.
JA7114212
J. AM. CHEM. SOC.
9
VOL. 130, NO. 11, 2008 3241