Chiral Bisphosphine BINAP-Stabilized Gold and Palladium Nanoparticles with Small Size and Their Palladium Nanoparticle-Catalyzed Asymmetric Reaction

Full text of DOI:10.1021/ja0369055

Published on Web 12/02/2003
Chiral Bisphosphine BINAP-Stabilized Gold and Palladium Nanoparticles with
Small Size and Their Palladium Nanoparticle-Catalyzed Asymmetric Reaction
Masaru Tamura and Hisashi Fujihara*
Department of Applied Chemistry and Molecular Engineering Institute, Kinki UniVersity, Kowakae,
Higashi-Osaka 577-8502, Japan
Received June 26, 2003; E-mail: h-fuji@apch.kindai.ac.jp
The synthesis and characterization of metal nanoparticles have
attracted great attention due to their potential applications in
optoelectronics, electronics, and catalysis.1 The property of the
protective ligands greatly influences the particle size and the
dispersity of metal nanoparticles. For the preparation of metal
nanoparticles with small sizes, narrow size distributions, and high
,2
3
a
1,3b
stability, the use of various stabilizers such as amine, phosphine,
and thiols,3 has been extensively studied. As such an example,
c-e
Schmid and co-workers reported that Ph
particles were obtained by a reduction of Ph
Recently, Hutchison and co-workers described a convenient
synthesis of Ph P-stabilized gold nanoparticles obtained from a
reduction of HAuCl with sodium borohydride in the presence of
P. However, much less attention has been paid to the prepara-
3
P-stabilized gold nano-
PAuCl with diborane.3b
3
3
4
4
Ph
3
tion of gold and palladium nanoparticles stabilized by bisphosphine,
and to related optically active metal nanoparticles. Moreover, their
chiral metal nanoparticle-catalyzed asymmetric reactions have not
been developed thus far.
Figure 1. (a) TEM micrograph of BINAP-Au. Circular dichroism spectra
of (b) (R)-BINAP-Au and (c) (S)-BINAP-Au in CHCl3.
Here we report the first synthesis of optically active 2,2′-bis-
diphenylphosphino)-1,1′-binaphthyl [BINAP]-protected gold nano-
particles (BINAP-Au) and palladium nanoparticles (BINAP-Pd)
with smaller cores (diameter < 2 nm) and narrower size distribution,
3
and the difference in the particle size between monophosphine Ph P-
1
remained, as detected by TLC and H NMR spectroscopy. Similarly,
(
BINAP-Pd was prepared by the same procedures as for BINAP-
Au using K
both in solution and in the solid state. At high concentration of
phosphine-stabilized gold nanoparticles in CHCl , BINAP-Au was
more stable than Ph P-Au.
2 4 4
PdCl instead of HAuCl . They are remarkably stable
7
3
stabilized Pd and bisphosphine BINAP-stabilized Pd nanoparticles.
Optically active BINAP represents the most important class of chiral
biaryl ligands and has found very extensive applications in
3
The core size and size distribution of BINAP-Au were examined
by transmission electron microscopy (TEM) (Figure 1a). The TEM
picture of BINAP-Au showed narrowly disperse nanoparticles 1.7
8
5
asymmetric catalysis. Most remarkably, we have found that novel
chiral BINAP-Pd catalyzed the asymmetric hydrosilylation of
styrene with trichlorosilane under mild conditions. This is the first
example for the asymmetric hydrosilylation of styrene catalyzed
by chiral palladium nanoparticles such as chiral BINAP-Pd. In
contrast, a palladium complex coordinated with a chelating bis-
phosphine ligand such as BINAP did not catalyze the hydrosily-
lation of olefins with trichlorosilane even upon elevation of the
reaction temperature.6 Catalytic asymmetric hydrosilylation of
alkenes is an important method for the preparation of optically active
alcohols.6
(
0.4 nm in diameter. The UV-vis spectrum of BINAP-Au
solution in toluene exhibited no significant plasmon resonance at
∼520 nm, which is consistent with its smaller particle size and
9
narrower distribution. The X-ray photoelectron spectroscopy (XPS)
spectrum of BINAP-Au showed the Au 4f binding energies at
84.1 and 87.8 eV, corresponding to the Au state. There was a
feature at 285 eV due to C 1s and 132 eV due to P 2p.
The optically active BINAP-stabilized gold nanoparticles were
prepared by a reduction of HAuCl with NaBH in the presence of
(R)-(+)- or (S)-(-)-BINAP. The circular dichroism spectra (CD)
of optically active (R)-BINAP-Au in CHCl3 showed positive
Cotton effects, while (S)-BINAP-Au showed negative Cotton
effects, as shown in Figure 1, b and c. These (R)- and (S)-BINAP-
Au nanoparticles were stable against racemization. Thus, new
optically active gold nanoparticles in which the chiral center is very
close to the surface of the gold nanoparticles have been prepared.
Although a number of studies on palladium nanoparticle-
catalyzed reactions have been reported,1 no clear-cut example of
asymmetric reactions catalyzed by chiral phosphine-stabilized
palladium nanoparticles has been hitherto known. New phosphine
0
b,c
4
4
Synthesis and purification of mono- or bisphosphine-stabilized
metal nanoparticles were carried out using a slight modification of
4
the procedure reported by Hutchison et al. To a vigorously stirred
solution of tetraoctylammonium bromide (372 mg, 0.68 mmol) in
1
0 mL of CH
in 15 mL of deionized water. A solution of BINAP (1.09 g, 1.75
mmol) in 200 mL of CH Cl was added, and the resulting solution
was stirred at room temperature. NaBH (388 mg, 10.3 mmol) in
mL of deionized water was then added. The mixture was stirred
2
Cl
2
was added HAuCl
4
‚4H
2
O (323 mg, 0.78 mmol)
2
2
,2
4
5
for 3 h at room temperature under an argon atmosphere. After
reaction the mixture was washed with water, and the filtrate was
evaporated in vacuo to yield BINAP-Au. Purification of BINAP-
Au was repeated until no free phosphine or phase-transfer catalyst
ligand-stabilized palladium nanoparticles (BINAP-Pd, Ph P-Pd)
were synthesized. The XPS spectrum of BINAP-Pd displayed that
the binding energies for the Pd 3d doublet are 336.0 and 341.3 eV.
3
15742
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J. AM. CHEM. SOC. 2003, 125, 15742-15743
10.1021/ja0369055 CCC: $25.00 © 2003 American Chemical Society

C O MMU N I C A T I O N S
Scheme 1
of styrene. Thus, a new chiral BINAP-Pd acts as both promoter
and asymmetric induction reagent for the hydrosilylation of styrene.
In summary, we have demonstrated the synthesis of the chiral
BINAP-Au and BINAP-Pd, and a new type of catalytic asym-
metric induction by the chiral BINAP-Pd. The chiral BINAP-
Au and BINAP-Pd showed the small core with narrow size
distribution and remarkably high stability. A new chiral BINAP-
Pd is an efficient catalyst for the asymmetric hydrosilylation of
olefin under mild conditions. We have found a significant difference
in the catalytic activity between BINAP-Pd nanoparticles and Pd-
BINAP complex. This finding indicates a new aspect in the field
of asymmetric reactions catalyzed by chiral phosphine-stabilized
metal nanoparticles and transition metal-phosphine complexes. The
work reported here points toward a new direction in the design of
chiral metal nanoparticle catalysts for asymmetric synthesis. Further
work is currently in progress in this and related areas.
Figure 2. (a) TEM micrograph of BINAP-Pd. Circular dichroism spectra
of (b) (R)-BINAP-Pd and (c) (S)-BINAP-Pd in CHCl3.
Interestingly, BINAP-Pd has a small core size with a narrow
dispersity of 2.0 ( 0.5 nm (Figure 2a), while, Ph P-Pd has a larger
3
and less narrow dispersed core (2.6 ( 0.7 nm) compared with
BINAP-Pd. These findings indicate that the core size and dispersity
are significantly affected by use of mono- and bisphosphines as
protective ligands. There is no obvious surface plasmon band in
the UV-vis spectrum of BINAP-Pd or Ph
3
P-Pd in CHCl
3
. The
absence of a plasmon band for BINAP-Pd and Ph
3
P-Pd is in
10
accord with theoretical predictions and experimental observations
for 2.2-nm alkanethiolate-stabilized Pd nanoparticles,11 but not with
the report of a 302-nm surface plasmon band for 2.2-nm octade-
canethiolate-protected Pd nanoparticles.12
Acknowledgment. This work was supported by the Grant-in-
Aid for Scientific Research Nos. 12042279 and 15550044 from
the Ministry of Education, Science and Culture, Japan.
2 4 4
Reduction of K PdCl with NaBH in the presence of chiral (R)-
or (S)-BINAP afforded the chiral BINAP-Pd. The CD spectra of
the chiral palladium nanoparticles in chloroform are presented in
Figure 2, b and c, showing positive Cotton effects for (R)-BINAP-
Pd and negative Cotton effects for (S)-BINAP-Pd. Most signifi-
cantly, these chiral BINAP-Pd showed the capability of promoting
hydrosilylation of styrene and its asymmetric induction (vide infra).
To confirm asymmetric catalytic activity of the chiral BINAP-
Pd, we have investigated the hydrosilylation of styrene with
trichlorosilane in which the hydrosilylation did not proceed in the
absence of a catalyst such as palladium-monophosphine complexes.
Catalytic asymmetric hydrosilylation is a very useful method for
the asymmetric synthesis of optically active alcohols because the
carbon-silicon bond in some organosilicon compounds is readily
oxidized into a carbon-oxygen bond with retention of configuration
at the carbon center.13 It has been known that the palladium
complexes coordinated with a chelating bisphosphine ligand, 1,2-
bis(diphenylphosphino)ethane or BINAP, did not catalyze the
hydrosilylation of olefins with trichlorosilane.6 Surprisingly,
however, new chiral BINAP-Pd nanoparticles catalyzed the
hydrosilylation of styrene (Scheme 1).14 Typically, the hydrosilyl-
ation of styrene (6.19 mL, 53.3 mmol) with trichlorosilane (5.33
mL, 53.3 mmol) in the presence of chiral (S)-BINAP-Pd (53 mg)
at room temperature for 5 h gave 1-phenyl-1-trichlorosilylethane
References
(
1) Schmid, G. Clusters and Colloids; VCH: Weinheim, 1994.
2) Feldheim, D. L.; Foss, C. A., Jr. Metal Nanoparticles; Marcel Dekker:
New York, 2002.
3) (a) Leff, D. V.; Brandt, L.; Heath, J. R. Langmuir 1996, 12, 4723. (b)
Schmid, G.; Pfeil, R.; Boese, R.; Bandermann, F.; Meyer, S.; Calis, G.
H. M.; van der Velden, J. W. A. Chem. Ber. 1981, 114, 3634. (c) Brust,
M.; Walker, M.; Bethell, D.; Schiffrin, D. J.; Whyman, R. J. Chem. Soc.,
Chem. Commun. 1994, 801. (d) Templeton, A. C.; Wuelfing, W. P.;
Murray, R. W. Acc. Chem. Res. 2000, 33, 27. (e) Hata, K.; Fujihara, H.
Chem. Commun. 2002, 2714.
(
(
(
4) Weare, W. W.; Reed, S. M.; Warner, M. G.; Hutchison, J. E. J. Am. Chem.
Soc. 2000, 122, 12890.
(
5) Pu, L. Chem. ReV. 1998, 98, 2405.
(
6) (a) Kitayama, K.; Uozumi, Y.; Hayashi, T. J. Chem. Soc., Chem. Commun.
1995, 1533. (b) Uozumi, Y.; Tsuji, H.; Hayashi, T. J. Org. Chem. 1998,
63, 6137. (c) Hayashi, T. Acc. Chem. Res. 2000, 33, 354 and references
therein. (d) Nishiyama, H.; Itoh, K. In Catalytic Asymmetric Synthesis,
2nd ed.; Ojima, I. Ed.; VCH: New York, 2000; pp 111-143.
7) The particle size and the UV-vis spectra of the nanoparticles did not
change for several months.
(
(8) A total of 300 particles were counted.
(
9) (a) Hermann, M.; Kreibig, U.; Schmid, G. Z. Phys. D 1993, 26, 1. (b)
Alvarez, M. M.; Khoury, J. T.; Schaaff, T. G.; Shafigullin, M. N.; Vezmar,
I.; Whetten, R. L. J. Phys. Chem. B 1997, 101, 3706.
b,c
(
10) Creighton, J. A.; Eadon, D. G. J. Chem. Soc., Faraday Trans. 1991, 87,
3881.
(11) (a) Chen, S.; Huang, K.; Stearns, J. A. Chem. Mater. 2000, 12, 540. (b)
Zamborini, F. P.; Gross, S. M.; Murray, R. W. Langmuir 2001, 17, 481.
(
12) Yee, C. K.; Jordan, R.; Ulman, A.; White, H.; King, A.; Rafailovich, M.;
Sokolov, J. Langmuir 1999, 15, 3486.
(
13) Tamao, K. In AdVances in Silicon Chemistry; Larson, G. L., Ed.; JAI
Press: Greenwich, CT, 1996; Vol. 3, pp 1-62.
16
(
1) as a single isomer in 81% yield. The oxidation of 1 with
(14) Although the hydrosilylation of styrene catalyzed by palladium-mono-
15
13
3 4
phosphine complex, Pd(PPh ) , at 100 °C gave 1, none of 1 was obtained
hydrogen peroxide in the presence of potassium fluoride gave
at room temperature as a condition. In contrast, BINAP-Pd catalyzed
22
(
(
S)-1-phenylethanol (2) {[R]
D
2 2
-36.3 (c 3.0, CH Cl )} of 75% ee
the hydrosilylation of styrene even at 0 °C to give 1.
enantiomeric excess)17 in 89% yield. The enantiomeric excess was
(15) Tsuji, J.; Hara, M.; Ohno, K. Tetrahedron 1974, 30, 2143.
16) The hydrosilylation was carried out without solvent.
(
increased to 95% ee when the hydrosilylation was carried out at 0
C, while an optically active (R)-1-phenylethanol (2) was obtained
when (R)-BINAP-Pd was used for the asymmetric hydrosilylation
(17) The determination for the absolute configuration and ee of 2 is based on
6a
the reported data.
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