Selective hydrosilylation of alkynes with a nanoporous gold catalyst

Article abstract of DOI:10.1039/c3cy00242j

The hydrosilylation of acetylenic compounds proceeded smoothly in the presence of a reusable nanoporous gold catalyst under mild conditions and the β-(E)-cis-addition products were obtained in good to high yields regio- and stereoselectively.

Full text of DOI:10.1039/c3cy00242j

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Selective hydrosilylation of alkynes with a nanoporous
gold catalyst†
Cite this: DOI: 10.1039/c3cy00242j
a
ab
a
Yoshifumi Ishikawa, Yoshinori Yamamoto and Naoki Asao*
Received 13th April 2013,
Accepted 18th May 2013
DOI: 10.1039/c3cy00242j
www.rsc.org/catalysis
The hydrosilylation of acetylenic compounds proceeded smoothly
in the presence of a reusable nanoporous gold catalyst under mild
conditions and the b-(E)-cis-addition products were obtained in
good to high yields regio- and stereoselectively.
Scheme 1 Hydrosilylation of alkynes giving three possible isomeric vinylsilane
Introduction
compounds.
The hydrosilylation of acetylenic compounds is a powerful
1
synthetic method for vinylsilane compounds, which are
proceeded with these catalysts, but they often have some draw-
backs, such as formation of side-products, low substrate generality,
and low selectivity. A thin gold film on the surface of glass
synthetically versatile organosilicon reagents in organic synth-
2
esis. Since three isomeric products, a-, b-(E)-, and b-(Z)-isomers,
8
can possibly be formed with terminal alkynes (Scheme 1), the
control of regio- and stereoselectivity in this process is highly
desirable for selective preparation of these vinylsilane com-
pounds. Generally, the selectivity is mainly affected by the
nature of catalysts, alkynes, hydrosilanes, and reaction conditions.
We have previously reported the selective trans-hydrosilylation with
Lewis acid catalysts, such as AlCl and EtAlCl , leading to the b-(Z)-
capillaries also exhibits the activity for this reaction in a
continuous-flow reactor, for which cumbersome microwave
9
irradiation is necessary. Recently, we were successful in using a
monolithic nanoporous gold material (AuNPore) as an effective
10,11
unsupported catalyst for some molecular transformations.
In
this communication, we report that the AuNPore, fabricated
from an Au–Al alloy, is an effective green catalyst for hydrosilyla-
tion of terminal alkynes, leading to b-(E)-products with high
3
2
3
product exclusively. On the other hand, most of the reactions
with homogeneous and heterogeneous transition metal cata-
lysts, such as Pt, Co, Ni, and Pd, proceed in a cis-fashion
1
2
regio- and stereoselectivities.
4
stereoselectively. But they often gave low regioselectivity
between a- and b-(E)-products. We are particularly focusing on Results and discussion
the development of heterogeneous green catalysis because a
The requisite nanoporous gold materials were fabricated from
heterogeneous catalytic system has many advantages compared
to the homogeneous one, such as easy separation of catalysts
from the reaction mixture, easy recycling, and enhanced stabi-
two kinds of alloys, AuAl and AuAg. The selective removal of
aluminum from an Au20Al80 alloy ribbon was conducted with
1
3
5,6
20% NaOH to obtain AuNPore-1. On the other hand, the silver
from a Au30Ag70 alloy thin film was dissolved in 70% HNO
lity. Recently, supported-gold nanoparticles have emerged as
efficient catalysts with considerable synthetic potential for many
3
1
4
7
(AuNPore-2). The scanning electron microscopy (SEM) study
revealed that both materials exhibited an open bicontinuous
interpenetrating ligament-channel structure with a length scale
of 10–30 nm. The energy dispersive X-ray (EDX) spectra showed
that small amounts of less noble metals, aluminum (4 at%) and
silver (2 at%), remained, respectively.
types of molecular transformations. The hydrosilylation also
a
WPI-Advanced Institute of Materials Research, Tohoku University,
Sendai 980-8577, Japan. E-mail: asao@m.tohoku.ac.jp; Fax: +81-22-217-6165;
Tel: +81-22-217-6165
b
State Key Laboratory of Fine Chemicals, Dalian University of Technology,
Dalian 116012, China
The hydrosilylation of phenylacetylene 1a with triethylsilane
2a was carried out with these catalysts and the results are
†
Electronic supplementary information (ESI) available: SEM micrographs, CV,
and experimental section. See DOI: 10.1039/c3cy00242j
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a
3
Table 1 Hydrosilylation of phenylacetylene with Et SiH with a AuNPore catalyst
catalytic turnover frequencies (TOFs, number of converted
molecules per surface site and hour) are shown in Table 2.
Obviously, AuNPore-1 has a higher TOF than AuNPore-2
(entries 1 and 2). One might think that the fabrication process
of AuNPore-2 with HNO would deactivate the materials. How-
ever, the catalytic activity of AuNPore-1 did not change upon
3
b
Yield (%)
3
treatment with 70% HNO although the surface area of the
Entry
1
Solvent
Time (h)
3a
4a
resulting AuNPore-3 slightly decreased as reported previously
AcOEt
AcOEt
AcOEt
Dioxane
1
1
1
1
1
1
1
3
74
21
50
66
55
48
43
98
1
2
1
1
1
1
1
1
15
c
(entry 3). These results suggested that two plausible synergistic
2
3
d
effects generated by the residual metals should be considered.
One is the activation effect by aluminum, and the other is the
deactivation effect by silver.
4
5
6
7
8
CH
(CH
3
CN
Cl)
2
2
Toluene
AcOEt
Then, we next fabricated a new nanoporous gold catalyst,
including both Al and Ag, from the Au19Ag
The chemical etching was carried out with 20% NaOH for the
Al (AuNPore-4).
1
Al80 alloy ribbon.
a
Reactions were carried out with 1a (1 mmol) and 2a (1.5 mmol) in the
b
presence of 2 mol% of AuNPore-1 catalyst at 70 1C. Determined by selective removal of aluminum to obtain Au93Ag
3
4
1
c
H NMR analysis with p-xylene as an internal standard. Reaction was
d
We found that the catalytic activity of AuNPore-4 was quite low
and 3a was produced in only 2% yield (entry 4). In comparison
with the activity of AuNPore-1 in entry 1, this result revealed that
the residual silver has the inhibition effect in this process.
conducted with AuNPore-2 derived from an AuAg alloy. Reaction was
conducted in the presence of 10 mol% of BHT.
summarized in Table 1. The reaction proceeded smoothly with Indeed, after immersion of AuNPore-4 in HNO , the resulting
3
a catalytic amount of AuNPore-1, derived from the AuAl alloy, at AuNPore-5, having a lower amount of silver, exhibited compar-
7
0 1C for 1 h, and gave the b-(E)-product 3a in 74% yield able catalytic activity with that of AuNPore-2 (entries 2 and 5). At
selectively and small amounts of a-isomer 4a was produced the same time, this result also indicated that aluminum had no
1%, entry 1). In contrast, the chemical yield of 3a dramatically special activation effect on this reaction. As a blank test, the
(
decreased to 21% when AuNPore-2 was used, which was reaction was conducted with Au powder, the average diameter of
fabricated from the AuAg alloy (entry 2). The reaction proceeded particles of which is 3 mm, but it was ineffective (entry 6).
even in the presence of 10 mol% of BHT as a radical inhibitor
The substrate generality was examined and the results are
and 3a was obtained in 50% yield (entry 3). This result suggested summarized in Table 3. In every case, the reactions gave the
that the reaction is not likely to proceed through the radical desired products 3 in high yields together with less than 3%
mechanism. Besides AcOEt, 1,4-dioxane and CH
solvents for this reaction (entries 4 and 5), but less polar phenylacetylene 1b was more reactive and 3b was obtained in
solvents, such as (CH Cl) and toluene, were less effective 97% yield in 2 h (entry 2). On the other hand, the reaction of
entries 6 and 7). Finally, optimization experiments revealed that p-methoxy-phenylacetylene 1c needed longer reaction times
3
CN are suitable of 4. Compared to the phenylacetylene 1a (entry 1), p-fluoro-
2
2
(
the chemical yield of 3a increased up to 98% when the reaction (entry 3). These results clearly showed that electron-withdrawing
was conducted in AcOEt for 3 h (entry 8).
Further studies were conducted focusing on the difference
in the catalytic activity between AuNPore-1 and 2. The specific
surface area (SSA) was electrochemically measured and the
Table
3
AuNPore-catalyzed hydrosilylation with
a
variety of alkynes and
a
hydrosilanes
a
Table 2 Catalytic activity of AuNPores in the hydrosilylation
b
Yield (%)
Cat
Time
0
Entry
R
C
R
3
SiH
SiH
(mol%) (h)
3
4
2
ꢀ1
b,c
ꢀ1
Entry Catalyst
Composition SSA (m g ) Yield (%) TOF (h )
1
2
3
4
5
6
7
8
9
6
H
5
1a Et
1b Et SiH
3
2a
2a
2a
2a
2a
2a
2
2
2
2
2
2
2
5
3
2
6
3
3
3
6
12
12
18
98
97
97
99
97
97
96
85
98
80
1
2
2
2
1
1
3
3
2
2
1
2
3
4
5
6
AuNPore-1 Au96Al
AuNPore-2 Au98Ag
AuNPore-3 Au98Al
AuNPore-4 Au93Ag
AuNPore-5 Au96Ag
Au powder
4
10.5
12.0
8.4
11.3
8.3
74
21
62
2
16
1
757
189
789
19
207
22
6
p-FC H4
p-MeOC H4 1c Et SiH
C6H13
PhCH2
c-C H
3
2
6
3
3
3
3
2
1d Et SiH
1e Et SiH
1f Et SiH
1a PhMe SiH 2b
1a (EtO)
1a Bu SiH
1a (i-Pr)
3
Al
Al
4
1
3
6
11
d
0.1
C6H5
2
C
C
C
6
6
6
H
H
H
5
5
5
3
SiH 2c
a
Reactions were carried out with 1a (1 mmol) and 2a (1.5 mmol) in the
presence of 2 mol% of AuNPore catalyst at 70 1C for 1 h unless
otherwise noted. Determined by H NMR analysis with p-xylene as
an internal standard. a-Isomer 4a was produced in less than 1% yield
3
2d 10
10
3
SiH 2e 20
b
1
c
a
Reactions were carried out with 1 (1 mmol) and 2 (1.5 mmol) in the
b 1
d
in each case. Reaction was conducted with 2 mol% of Au powder at presence of AuNPore catalyst at 70 1C. Determined by H NMR
7
0 1C for 2 d.
analysis with p-xylene as an internal standard.
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Notes and references
1
2
3
B. Marciniec, Silicon Chem., 2002, 1, 155; B. M. Trost and
Z. T. Ball, Synthesis, 2005, 853.
E. Langkopf and D. Schinzer, Chem. Rev., 1995, 95, 1375;
D. S. W. Lim and E. A. Anderson, Synthesis, 2012, 983.
N. Asao, T. Sudo and Y. Yamamoto, J. Org. Chem., 1996,
Scheme 2 Hydrosilylation with the recovered catalyst.
61, 7654; T. Sudo, N. Asao, V. Gevorgyan and Y. Yamamoto,
J. Org. Chem., 1999, 64, 2494; T. Sudo, N. Asao and
Y. Yamamoto, J. Org. Chem., 2000, 65, 8919.
A. K. Roy, Adv. Organomet. Chem., 2008, 55, 1.
K. Kaneda, K. Ebitani, T. Mizugaki and K. Mori, Bull. Chem.
Soc. Jpn., 2006, 79, 981.
Selected examples of hydrosilylation with heterogeneous
catalysts, see: P. Boudjouk, B. H. Han, J. R. Jacobsen and
B. J. Hauck, J. Chem. Soc., Chem. Commun., 1991, 1424;
C. Polizzi, A. M. Caporusso, G. Vitulli, P. Salvatori and
M. Pasero, J. Mol. Catal., 1994, 91, 83; M. A. Brook,
H. A. Ketelson, F. J. LaRonde and R. Pelton, Inorg. Chim.
Acta, 1997, 264, 125; Z. M. Michalska, K. Strzelec and
J. W. Sobczak, J. Mol. Catal. A: Chem., 2000, 156, 91;
R. Jim ´e nez, J. M. Lopez and J. Cervantes, Can. J. Chem.,
groups on the phenyl group promoted the present reaction.
Not only aromatic alkynes but also aliphatic alkynes are sui-
table substrates (entries 4–6). Besides Et SiH 2a, other hydro-
3
4
5
silanes 2b–d were available (entries 7–9). Even with sterically
bulky (i-Pr) SiH 2e, the reaction proceeded to give the corre-
3
6
sponding vinylsilane 3j in 80% yield although increased loading
amounts of catalyst and longer reaction time were required
(entry 10).
The catalyst can be recovered easily by tweezers and any
cumbersome separation procedures, such as filtration and
centrifugation, are not required. We conducted the reaction
of 1b several times with the recovered catalyst, but no signifi-
cant loss of the catalytic activity was observed even after 5 times
(Scheme 2). The SEM image of the recovered catalyst after five
2000, 78, 1491; M. Chauhan, B. J. Hauck, L. P. Keller and
uses has no differences compared to that of the fresh one and
these results clearly demonstrate that the catalyst has high
reusability and stability due to its robust nanoporous structure.
We next investigated the leaching test. The hydrosilylation
of triethylsilane 2a to phenylacetylene 1a was carried out for
P. Boudjouk, J. Organomet. Chem., 2002, 645, 1;
M. Okamoto, H. Kiya, H. Yamashita and E. Suzuki, Chem.
Commun., 2002, 1634; R. Jim ´e nez, J. M. Mart ´ı nez Rosales
and J. Cervantes, Can. J. Chem., 2003, 81, 1370; H. Hagio,
M. Sugiura and S. Kobayashi, Synlett, 2005, 813; E. Ram ´ı rez-
Oliva, A. Hern ´a ndez, J. M. Mart ´ı nez-Rosales, A. Aguilar-
Elguezabal, G. Herrera-P ´e rez and J. Cervantes, ARKIVOC,
1
2
5 min under the standard conditions, and 3a was produced in
2% yield at this time. Then, the catalyst was removed from the
reaction vessel. Even after stirring for 2 h in the absence of
the catalyst, further generation of 3a was not detected at all.
The reaction restarted when the removed catalyst was put back
into the mixture, and finally 3a was obtained in 96% yield.
Furthermore, leaching of the gold into the reaction mixture
was not detected by inductively coupled plasma (ICP) analysis
2006, V, 126; A. Hamze, O. Provot, J.-D. Brion and M. Alami,
Synthesis, 2007, 2025; M. Okamoto, H. Kiya, A. Matsumura
and E. Suzuki, Catal. Lett., 2008, 123, 72; H.-H. Shih,
D. Williams, N. H. Mack and H.-L. Wang, Macromolecules,
2009, 42, 14; F. Alonso, R. Buitrago, Y. Moglie, J. Ruiz-
Mart ´ı nez, A. Sep u´ lveda-Escribano and M. Yus,
J. Organomet. Chem., 2011, 696, 368; R. Cano, M. Yus and
D. J. Ram o´ n, ACS Catal., 2012, 2, 1070.
(
o1 ppm). These results clearly indicated that the current
transformation was really heterogeneous.
7
8
A. Corma, A. Leyva-P ´e rez and M. J. Sabater, Chem. Rev.,
2011, 111, 1657; Y. Zhang, X. Cui, F. Shi and Y. Deng, Chem.
Conclusions
Rev., 2012, 112, 2467; M. Stratakis and H. Garcia, Chem.
Rev., 2012, 112, 4469.
A. M. Caporusso, L. A. Aronica, E. Schiavi, G. Martra,
G. Vitulli and P. Salvadori, J. Organomet. Chem., 2005,
In conclusion, we have disclosed that the AuNPore exhibited a
remarkable catalytic activity in the hydrosilylation of alkynes as
a non-supported nanostructured catalyst. The reaction does not
need any additives, such as bases, stabilizers, and ligands, as
well as any cumbersome work-up procedures like filtration or
centrifugation. Further applications of the AuNPore catalyst in
other transformations are currently under investigation in our
laboratory.
6
90, 1063; A. Corma, C. Gonz ´a lez-Arellano, M. Iglesias and
F. S ´a nchez, Angew. Chem., Int. Ed., 2007, 46, 7820;
L. A. Aronica, E. Schiavi, C. Evangelisti, A. M. Caporusso,
P. Salvadori, G. Vitulli, L. Bertinetti and G. Martra, J. Catal.,
2009, 266, 250; A. Psyllaki, I. N. Lykakis and M. Stratakis,
Tetrahedron, 2012, 68, 8724.
9
G. Shore and M. G. Organ, Chem.–Eur. J., 2008, 14, 9641.
Acknowledgements
1
0 N. Asao, Y. Ishikawa, N. Hatakeyama, M. Bateer,
Y. Yamamoto, M. Chen, W. Zhang and A. Inoue, Angew.
Chem., Int. Ed., 2010, 49, 10093; N. Asao, N. Hatakeyama,
Menggenbateer, T. Minato, E. Ito, M. Hara, Y. Kim,
Y. Yamamoto, M. Chen, W. Zhangi and A. Inouei, Chem.
This work was partially supported by the Grant-in-Aid for
Scientific Research on Innovative Areas ‘‘Reaction Integration’’
(No. 2105) from the MEXT, Japan. Y.I. thanks the Research
Fellowships of JSPS for Young Scientists.
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Commun., 2012, 48, 4540; N. Asao, Menggenbateer, Y. Seya,
Y. Yamamoto, M. Chen, W. Zhang and A. Inoue, Synlett,
group, see: T. Fujita, P. F. Guan, K. McKenna, X. Y. Lang,
A. Hirata, L. Zhang, T. Tokunaga, S. Arai, Y. Yamamoto,
N. Tanaka, Y. Ishikawa, N. Asao, Y. Yamamoto and
M. W. Chen, Nat. Mater., 2012, 11, 775.
2012, 66; M. Yan, T. Jin, Y. Ishikawa, T. Minato, T. Fujita,
L.-Y. Chen, M. Bao, N. Asao, M.-W. Chen and Y. Yamamoto,
J. Am. Chem. Soc., 2012, 134, 17536.
1 N. Asao, T. Jin, S. Tanaka and Y. Yamamoto, Pure Appl.
Chem., 2012, 84, 1771.
13 Z. Zhang, Y. Wang, Z. Qi, W. Zhang, J. Qin and J. Frenzel,
J. Phys. Chem. C, 2009, 113, 12629.
14 A. J. Forty, Nature, 1979, 282, 597; J. Erlebacher, M. Aziz and
A. Karma, Nature, 2001, 410, 450.
1
1
2 Atomic insights of the nanoporous gold catalyst fabricated
from the Au–Ag alloy and its preliminary result on the catalytic 15 Y. Ding, Y.-J. Kim and J. Erlebacher, Adv. Mater., 2004,
properties in the hydrosilylation have been reported by our 16, 1897.
Catal. Sci. Technol.
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