Highly efficient dehydrogenative coupling of hydrosilanes with amines or amides using supported gold nanoparticles

Article abstract of DOI:10.1002/chem.201405601

Hydroxyapatite-supported gold nanoparticles (Au/HAP) can act as a highly active and reusable catalyst for the coupling of hydrosilanes with amines under mild conditions. Various silylamines can be selectively obtained from diverse combinations of equimola

Full text of DOI:10.1002/chem.201405601

DOI: 10.1002/chem.201405601
Communication
&
Gold Catalysis
Highly Efficient Dehydrogenative Coupling of Hydrosilanes with
Amines or Amides Using Supported Gold Nanoparticles
Takato Mitsudome,[a] Teppei Urayama,[a] Zen Maeno,[a] Tomoo Mizugaki,[a]
Koichiro Jitsukawa,[a] and Kiyotomi Kaneda*[a, b]
lanes or amines for the high-yielding coupling. With regard to
Abstract: Hydroxyapatite-supported gold nanoparticles
(Au/HAP) can act as a highly active and reusable catalyst
the coupling reaction of hydrosilanes with amides, only one
catalytic method has been reported despite the utility of silyla-
for the coupling of hydrosilanes with amines under mild
mides.[3] Furthermore, these above-reported methods are diffi-
conditions. Various silylamines can be selectively obtained
cult to recover and reuse.[4] Therefore, it is evident that the de-
from diverse combinations of equimolar amounts of hy-
velopment of an environmentally benign and highly efficient
drosilanes with amines including less reactive bulky hydro-
catalytic system for the selective coupling of hydrosilanes with
silanes. This study also highlights the applicability of Au/
amines or amides is still an important research target.
HAP to the selective synthesis of silylamides through the
Recently, we first disclosed that hydroxyapatite-supported
coupling of hydrosilanes with amides, demonstrating the
gold nanoparticles (Au/HAP) catalyzed the oxidation of hydro-
first example of an efficient heterogeneous catalyst. More-
silanes with water to the corresponding silanols associated
over, Au/HAP shows high reusability and applicability for
with the formation of H2.[5] This transformation method by
gram-scale synthesis.
using gold NPs has since been explored by other researchers
with respect to size and shape of gold NPs.[6] The activity of
Au/HAP for hydrosilanes was also applicable to the dehydro-
genative coupling of hydrosilanes with alcohols[7] and the de-
SiÀN bond-containing compounds, such as silylamines and
silylamides, are important materials for silylation reagents, li-
gands, and valuable building blocks of silicone polymers.[1]
Conventionally, silylamines or silylamides have been synthe-
sized through stoichiometric reactions of chlorosilanes with
amines or amides in the presence of bases.[1d] However, chloro-
silanes are toxic and unstable in air moisture, and a large
amount of the HCl salt is formed as the by-product, which re-
stricts the applicability of these transformations. In this con-
text, the cross-coupling reaction of hydrosilanes with amines
or amides is an alternative and attractive synthetic method of
silylamines or silylamides. The easy-handling and availability of
hydrosilanes under neutral conditions enable efficient synthesis
of diverse SiÀN bond-containing compounds to produce H2 as
the sole co-product. To date, several catalysts for the cross-cou-
pling reaction of hydrosilanes with amines have been devel-
oped and some improvements have been made in catalytic
performance.[2] However, these catalysts still have suffered
from problems in low activities,[2b–d,h–j,m] limitations of substrate
applicability[2a–l] and necessity of excess amounts of hydrosi-
oxygenation of amides, sulfoxides, and pyridine N-oxides by
using hydrosilanes as reductants.[8]
In the course of our study on the interaction between gold
nanoparticles and hydrosilanes, we herein demonstrate
a green protocol for the selective coupling of hydrosilanes
with amines or amides by using gold nanoparticle catalysts.
Hydroxyapatite-supported gold nanoparticles with a mean di-
ameter of 3.0 nm (Au/HAP) can act as an efficient heterogene-
ous catalyst for the selective coupling of various kinds of hy-
drosilanes with amines or amides.
This catalyst system requires only equimolar amounts of hy-
drosilanes and amines or amides to achieve high-yielding syn-
thesis of the desired SiÀN bond-containing compounds. The
catalytic activity is significantly higher than the previously re-
ported catalysts. Furthermore, the Au/HAP catalyst is recovera-
ble and reusable while maintaining its high catalytic
performance.
The synthesis of Au/HAP followed our previous report.[5] The
characterization was performed by X-ray absorption fine struc-
ture and transmission electron microscope analyses. The highly
dispersed gold nanoparticles with a mean diameter of 3.0 nm
formed on the surface of HAP were confirmed.[9]
[a] Dr. T. Mitsudome, T. Urayama, Dr. Z. Maeno, Dr. T. Mizugaki,
Prof. Dr. K. Jitsukawa, Prof. Dr. K. Kaneda
Department of Materials Engineering Science
Graduate School of Engineering Science, Osaka University
1–3 Machikaneyama, Toyonaka, Osaka 560-8531( Japan)
Fax: (+81)6-6850-6260
Various HAP-supported metal nanoparticles were synthe-
sized, and the catalytic activities were investigated in the cou-
pling reaction of an equimolar amount of dimethylphenylsi-
lane (1) and n-butylamine (2) in THF solvent. Among the metal
nanoparticles tested, Au/HAP exhibited the best activity to
give N-(n-butyl)dimethylphenylsilylamine (3) in 99% yield ac-
companied by the generation of equimolar amounts of H2
(Table 1, entry 1).[10] Ag/HAP and Pd/HAP were also active, but
E-mail: kaneda@cheng.es.osaka-u.ac.jp
[b] Prof. Dr. K. Kaneda
Research Center for Solar Energy Chemistry, Osaka University
1-3 Machikaneyama, Toyonaka, Osaka 560-8531 (Japan)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201405601.
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Table 1. Dehydrogenative coupling of 1 with 2 using various catalysts.[a]
Table 2. Dehydrogenative coupling of hydrosilanes with amines using
Au/HAP.[a]
Entry
Catalyst
d [nm]
Conv. (yield) [%][b]
Entry
Hydrosilane
PhMe2SiH
Amine
T [8C]
t [h]
Yield [%][b]
1
Au/HAP
Au/HAP
Au/HAP
Ag/HAP
Pd/HAP
Cu/HAP
Ru/HAP
Rh/HAP
Pt/HAP
Au/TiO2
AuAl2O3
Au/SiO2
Au/MgO
Au/HAP
Au/HAP
3.0
3.0
3.0
5.4
3.2
4.0
2.4
3.3
4.8
3.6
3.6
2.2
3.1
5.7
6.5
99
99
99
54
48
0
0
0
0
72
63
29
15
83
33
2[c]
3[d]
4
1
2
n-BuNH2
tBuNH2
60
100
4
10
99 (87)
96 (88)
3
60
3
99 (86)
5
6
7
8
4
60
8
99 (86)
5
6
7
8
Et2NH
NH3
R=H
4-Br
100
100
40
40
40
10
1
1
2
2
16
20
12
20
12
2
0.5
2
1
92 (83)
(90)
9
99 (88)
97 (82)
99 (88)
95 (87)
96 (85)
99 (86)
(86)
99 (83)
99 (84)
99 (86)
95 (84)
89 (78)
98 (88)
99 (85)
99[e]
10
11
12
13
14
15
9
4-MeO
n-BuNH2
n-BuNH2
n-BuNH2
NH3
n-BuNH2
n-BuNH2
PhNH2
n-BuNH2
PhNH2
n-BuNH2
PhNH2
PhNH2
PhNH2
10
11[c]
12
13
14
15
16
17
18
19
20
21[d]
22
Ph2MeSiH
Ph3SiH
Et3SiH
60
100
100
100
60
60
25
60
25
60
25
BnMe2SiH
Ph2SiH2
[a] Reaction conditions: Catalyst (metal: 0.83 mol%),
(1 mmol), THF (3 mL). [b] Determined by GC using an internal standard
technique. [c] Reuse 1. [d] Reuse 2.
1 (1 mmol), 2
PhMeSiH2
tBu2SiH2
0.5
1
1
the yields of 3 were much lower than that obtained by Au/
HAP (Table 1, entries 4 and 5). Other metal nanoparticles, such
as Cu, Ru, Rh, and Pt, did not show any activities (Table 1, en-
tries 6–9), revealing that gold nanoparticles had uniquely high
catalytic activity. We then investigated the support effect of
different kinds of inorganic materials to immobilize the gold
nanoparticles, and found that HAP was an effective support
compared to other supports, such as TiO2, Al2O3, SiO2, and
MgO (Table 1, entries 1 vs. 10–13).[11] The size effect of gold
nanoparticles was also studied by using Au/HAP having differ-
ent gold-particle sizes, confirming that smaller gold nanoparti-
cles provided higher catalytic activities (Table 1, entries 1 vs. 14
and 15).
Ph2SiH2
Ph2SiH2
60
60
1
0
[a] Reaction conditions: Au/HAP (Au: 0.83 mol%), hydrosilane (1 mmol),
amine (1 mmol), THF (3 mL), Ar. [b] Determined by GC using an internal
standard technique; values in parenthesis are the yield of the isolated
products. [c] Au/HAP (Au: 1.6 mol%), hydrosilane (0.5 mmol), amine
(0.5 mmol), THF (2 mL), Ar. [d] Aniline (2 mmol). [e] Yield of the monoami-
nosilane.
Selective synthesis of monoaminosilanes from hydrosilanes
containing multiple SiÀH bonds is a challenging issue due to
the easy formation of the undesired silazane by-product. Nota-
bly, the present Au/HAP catalyst system was found to be
useful for the synthesis of monoaminosilanes from dihydrosi-
lanes. The selective coupling of dihydrosilanes with simple
amines in an equimolar ratio successfully proceeded, giving
the desired monoaminosilanes in excellent yields (entries 15–
20). This result is in sharp contrast with previous reports, in
which the delicate modulation of the ratio of silane/amine or
use of bulky amines was required to achieve high selectivity of
monoaminosilanes.[2d,i,k]
With the optimized Au/HAP catalyst having a mean diameter
of 3.0 nm in hand, the scope of hydrosilanes and amines was
explored in this transformation. The results summarized in
Table 2 demonstrate that Au/HAP showed broad applicability
for diverse combinations of hydrosilanes with amines in an
equimolar ratio of hydrosilanes to amines. Compound 1 was
efficiently coupled with aliphatic (entries 1–6) and aromatic
(entries 7–9) amines, providing the corresponding silylamines
in high yields. Functionalized amines, such as allylamine
(entry 3), morpholine (entry 4), and 4-bromoaniline (entry 8),
were also tolerated. It is said that ammonia often causes low
selectivity[12] and low yields[2i] of the corresponding monosilyla-
mines due to the production of disilazane by-products and
poisoning by strong coordination of ammonia to active metal
species, respectively. In contrast, Au/HAP worked well, giving
the monosilylamine in high yields (entries 6 and 13). The high-
yielding coupling reaction of other tertiary hydrosilanes with 2
was also successful (entries 10–12 and 14). Although sterically
hindered hydrosilanes, such as triethylsilane and benzyldime-
thylsilane, are known to be only slightly reactive,[2i] these were
quantitatively coupled with 2 to afford the corresponding silyl-
amines (entries 12 and 14).
To elucidate the high selectivity toward monoaminosilanes,
the following control experiments were investigated. 1) Mono-
aminohydrosilane was solely produced when using two equiv-
alents of amine with hydrosilane (entry 21). 2) When the mono-
aminohydrosilane diphenylsilylaniline was employed as a start-
ing material, no reaction occurred, and diphenylsilylaniline was
quantitatively recovered (entry 22). These results clearly dem-
onstrated that the reason for the high selectivity is due to no
reactivity of the monoaminohydrosilanes under our reaction
conditions.
We also checked the possibility of the participation of ho-
mogeneous gold species leaching from Au/HAP. The coupling
processes were abruptly and completely terminated by the re-
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moval of Au/HAP from the reaction mixtures by filtration, and
no leaching of gold species could be detected by inductively
coupled plasma (ICP) analysis of the filtrate, thus proving that
the observed catalysis of Au/HAP was intrinsically heterogene-
ous. In addition, Au/HAP showed excellent reusability in the re-
cycling experiments (Table 1, entries 2 and 3). Furthermore, the
practical applicability of Au/HAP for the gram-scale synthesis
of silylamines was demonstrated in the coupling of 1 with 2
(Scheme 1). The transformation proceeded efficiently, giving
1.83 g of the silylamine (86% isolated yield), in which the turn-
over number reached 5180. This value is the best among re-
ported catalysts.[13]
er transform infrared study.[15] From these results, the coupling
reaction may occur as follows. First, a cleavage of SiÀH bond
of a hydrosilane adsorbed on Au/HAP by a gold atom occurs.
Next, nucleophilic attack of an amine to the electrophilic Si
atom bound on the gold atom gives the corresponding silyla-
mine together with generation of H2.
In conclusion, we disclosed that hydroxyapatite-supported
gold nanoparticles act as a highly efficient catalyst for the se-
lective coupling of hydrosilanes with amines or amides. A wide
range of silylamines and silylamides can be obtained in good
to excellent yields, in which only an equimolar ratio of hydrosi-
lanes to amines or amides could be utilized. This catalyst
system provides a simple, efficient, and sustainable protocol
for the synthesis of various silylamines and silylamides.
Acknowledgement
Scheme 1. Gram-scale synthesis of silylamine.
This work was supported by JSPS KAKENHI Grant Numbers
26289303, 26630410, 26105003, and 24246129. This work was
also supported by the Program for Creating Future Wisdom,
Osaka University, selected in 2014. We thank Dr. Uruga, Dr.
Nitta, and Dr. Ina (SPring-8) for XAFS measurements. The TEM
experiments were carried out at a facility of the Research
Center for Ultrahigh Voltage Electron Microscopy, Osaka
University.
Next, the catalytic potential of Au/HAP to the selective syn-
thesis of silylamides was investigated in the coupling of 1 with
several amides. The results exemplified in Scheme 2 revealed
Keywords: amides · amines · coupling · gold · nanoparticles ·
silanes
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Scheme 2. Dehydrogenative coupling of 1 with amides using Au/HAP. Reac-
tion conditions: Au/HAP (0.3 g, Au: 0.5 mol%), hydrosilane (5 mmol), amide
(5 mmol), and THF (15 mL).
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activity of Au/HAP was 15-fold higher than that of the reported
homogeneous Ni catalyst, demonstrating the first example of
a highly active heterogeneous catalyst.[3]
To gain insights into the catalytic features of Au/HAP in the
coupling of hydrosilanes with amines, the dependency of reac-
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amount of 1 and independent of the concentration of 2. When
using PhMe2SiD, a kinetic isotope effect (kH/kD=1.5) and gen-
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mining step is the activation step of the SiÀH bond of 1 by Au
nanoparticles. In a separate experiment, the treatment of an
equimolar mixture of PhMe2SiD and n-Bu3SiH in the presence
of Au/HAP in THF under Ar at 608C provided HD-scrambled
PhMe2SiH and n-Bu3SiD, clearly showing that SiÀH cleavage oc-
curred on the gold nanoparticles.[14] The activation of the SiÀH
bond of 1 by gold nanoparticles was also confirmed by a Fouri-
Chem. Eur. J. 2015, 21, 3202 – 3205
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[13] Pd/C (TON=174) [2a], [(Et2N)3U][BPh4] (118) [2 f], tethered ruthenium
complex (100) [2l], Ru3(CO)12 (100) [2j], [Cp(iPr3P)Ru(NCMe)2]+BAF (33)
[2h], [Yb(h2-Ph2CNAr)(hmpa)4] (33) [2e], [areneCr(CO)2(h2-HsiHPh2)] (20)
[2c], [(NHC)Yb(SiMe3)2] (20) [2k], ToMMgÀNR2 (20) [2i], [M{N(SiMe3)2}2]2
(20) [2m] and CuCl (15) [2d].
[14] No formation of the HD-scrambled hydrosilanes was confirmed in the
absence of Au/HAP; see the Supporting Information for detailed
results.
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[9] See the Supporting Information for detailed results.
[10] In Table 1, no by-products other than H2 were observed.
[11] Prominent catalytic activity of Au/HAP may be due to the strong ad-
sorption ability of the HAP support for hydrosilanes. The highly con-
densed hydrosilanes on the HAP surface efficiently interact with active
sites on gold nanoparticles, leading to the high catalytic activity of Au/
HAP; see Ref. [7].
[15] We previously reported that the redshift of an absorption band as-
signed to a SiÀH bond stretching vibration of 1 occurred after the
treatment of 1 with Au/HAP, indicating the activation of the SiÀH bond
of 1 by gold nanoparticles; see Ref. [7].
Received: October 11, 2014
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Published online on January 8, 2015
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