Dimethylformamide-stabilised palladium nanoclusters catalysed coupling reactions of aryl halides with hydrosilanes/disilanes

Article abstract of DOI:10.1039/c9ra02895a

N,N-Dimethylformamide-stabilised Pd nanocluster (NC) catalysed cross-coupling reactions of hydrosilane/disilane have been investigated. In this reaction, the coupling reaction proceeds without ligands with low catalyst loading. N,N-Dimethylacetamide is a crucial solvent in these reactions. The solvent effect was considered by various techniques, such as transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The Pd NCs can be recycled five times under both hydrosilane and disilane reaction conditions.

Full text of DOI:10.1039/c9ra02895a

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PAPER
Dimethylformamide-stabilised palladium
nanoclusters catalysed coupling reactions of aryl
Cite this: RSC Adv., 2019, 9, 17425
halides with hydrosilanes/disilanes†
Tatsuki Nagata,a Takeru Inoue,a Xianjin Lin,a Shinya Ishimoto,a Seiya Nakamichi,a
a
Hideo Oka,a Ryota Kondo,a Takeyuki Suzukib and Yasushi Obora
*
N,N-Dimethylformamide-stabilised Pd nanocluster (NC) catalysed cross-coupling reactions of hydrosilane/
disilane have been investigated. In this reaction, the coupling reaction proceeds without ligands with low
catalyst loading. N,N-Dimethylacetamide is a crucial solvent in these reactions. The solvent effect was
considered by various techniques, such as transmission electron microscopy, X-ray photoelectron
spectroscopy, and thermogravimetric analysis. The Pd NCs can be recycled five times under both
hydrosilane and disilane reaction conditions.
Received 17th April 2019
Accepted 28th May 2019
DOI: 10.1039/c9ra02895a
rsc.li/rsc-advances
for reactant.13 We have reported a surfactant-free preparation of
dimethylformamide (DMF)-stabilised transition-metal (Au, Fe,
Ir, Cu, and Pd) NPs by the DMF reduction method.14 Among
Introduction
Arylsilanes have attracted a great deal of interest in various
elds. Silicon-containing molecules have unique and specic
properties and various uses, such as in medicine,1 in
photonics,2 and as organic intermediates.3 Conventional
methods for arylsilane synthesis are unsatisfactory because of
byproducts and side reactions.4 Accordingly, considerable
attention has focused on their selective synthesis.5 Transition
metal catalysed cross-coupling reactions between aryl halides
and hydrosilanes or disilanes have emerged as selective and
easy to handle protocols. However, these reactions are generally
achieved using transition metal complexes, such as Pd6 and Rh7
complexes, with 1–5 mol% of the catalyst. In addition, hydro-
silanes act as weak reducing reagents8 and using them as
coupling substrates inhibits reduction of aryl halides. More-
over, owing to the stability of the Si–Si bond, disilanes show low
reactivity for silylation reagents, so the coupling reactions
require bulky phosphorus ligands.9
these NPs, Pd NCs have proven to be highly effective in various
palladium-catalysed cross-coupling reactions, such as Suzuki–
Miyaura, Mizoroki–Heck,15a and Migita–Kosugi–Stille coupling
reactions.15b DMF-stabilised Fe2O3 NPs also show high catalytic
activity for hydrosilylation of unactivated terminal alkenes.16
The Pd–Pt–Fe2O3 nanocatalyst has recently been reported for
coupling aryl halides with hydrosilanes. However, the Pd
monometallic catalyst shows low reactivity and causes
decomposition.17
In this paper, we describe DMF-stabilised palladium NCs
catalysed coupling reactions of aryl halides with hydrosilanes/
disilanes to give arylsilanes with moderate to good yields.
These reactions proceed at low catalyst loading under ligand
and additive free conditions. In addition, the Pd NCs catalysts
in both the hydrosilane/disilane reaction systems can be recy-
cled at least ve times.
Metal nanoparticles (NPs) and nanoclusters (NCs) have
unique physical and chemical properties.10 They are expected to
show high catalytic performance owing to their stability, selec-
tivity, activity, and recyclability.11,12 On the other hand, colloidal
nanocatalysts require removal of capping agent to access cata-
lytically active surface. Stabilizing agents such as thiolates,
phosphines, surfactants, and polymers, behaves a protect shell
Results and discussion
Initially, we chose to study the cross-coupling reaction between
iodobenzene (1a) and dimethylphenylsilane (2a) using LiOAc as
a base in DMF at 100 ꢀC. Aer 16 h, dimethyldiphenylsilane (3a)
was obtained in moderate yield (Table 1, entry 1). When we
changed N-dimethylacetamide (DMAc) solvent to the reaction,
the yield increased to 80% (entry 2). The reaction was achieved
by using low Pd loadings compared with the previously reported
catalytic processes.6b,d During the course of the reaction, small
amount of benzene (<10% yield) was observed as byproduct.
The reaction was not accelerated in N-methyl-2-pyrrolidone
(NMP) and toluene (entries 3 and 4). Various bases were
tested. LiOAc gave the highest yield (entries 5–6). The use of
aDepartment of Chemistry and Materials Engineering, Faculty of Chemistry, Materials
and Bioengineering, Kansai University, Suita, Osaka 564-8680, Japan. E-mail: obora@
kansai-u.ac.jp
bComprehensive Analysis Center, The Institute of Scientic and Industrial Research
(ISIR), Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0057, Japan
† Electronic supplementary information (ESI) available: Characterization and
spectra. See DOI: 10.1039/c9ra02895a
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Table
1 Optimisation of the coupling reaction conditions with
hydrosilanea
Entry
Solvent
Base
Conv. (%)
Yieldb (%)
1
2
3
4
5
6
7
8
9d
DMF
DMAc
NMP
Toluene
DMAc
DMAc
DMAc
DMAc
DMAc
LiOAc
LiOAc
LiOAc
LiOAc
NaOAc
KOAc
KOtBu
None
>99
>99
—
52
80 (75)
Fig. 2 TG analysis of Pd NCs-DMF (blue) and Pd NCs-DMAc (red).
c
41
7
68
57
8
66
curves in the range of 25 ꢀC to 200 ꢀC of the two Pd NCs-
prepared by DMF (Pd NCs-DMF) and the Pd NCs covered by
DMAc (Pd NCs-DMAc) indicated similar charts. A difference was
observed in the TG curves of the both Pd nanoclusters from
>99
>99
>99
>99
97
52
9
LiOAc
ꢀ
above 200 C, suggesting that the two nanoparticles were pro-
a
Reaction conditions: 1a (1.0 mmol), 2a (3.0 mmol), Pd NCs (0.1 mol%),
b
tected by different molecules on the surface on the metal clus-
ters (DMF and DMAc).
and base (1.0 mmol) in solvent (1.0 mL) at 100 ꢀC for 16 h. The
conversion of 1a and yields were determined by gas chromatography
(GC) analysis. The isolated yield is shown in parenthesis. Not
determined due to overlapping of GC peaks. PdCl2 was used as
catalyst precursor.
c
The surface states of the as-prepared Pd NCs and solvent-
displaced Pd NCs with DMAc were determined by XPS. The
binding energy positions of Pd 3d5/2 and Pd 3d3/2 are shown in
Fig. 3. Peak FWHMs are described in Table S1.† The other main
peaks (C, O, and N) are shown in Fig. S4–S6.† The main peaks of
Pd at 338.8, 337.2 eV of 3d5/2 and 344.0, 342.1 of 3d3/2 was higher
than that of bulk Pd (Pd 3d5/2 335.1 eV and Pd 3d3/2 340.3
eV).18,19 The Pd 3d5/2 and 3d3/2 spectrum of Pd NCs with DMF is
shown in Fig. 3a. The DMAc Pd NCs have a broad peak (Pd 3d5/2
343.7, 341.8 eV and Pd 3d3/2 338.5, 336.6 eV) (Fig. 3b). A
signicant peak shi in Pd NCs with DMAc by increase of the
measurement time (Fig. 3d). In contrast, the as-prepared Pd
NCs remain unchanged (Fig. 3c). The changes in the two
samples are caused by removal of the protective molecules on
the surface. With irradiation by X-ray and sample heating, the
protective molecules (DMF rigid protecting layer) are removed
as the number of measurements increases. With elimination of
the protective surface molecules, surface palladium is reduced.
These data are associated with the TG analysis results, where
DMAc displacement of the Pd NCs removes the capping mole-
cules and results in easy access to the active sites.
d
KOtBu under these conditions gave the product in 8% yield
along with intractable byproduct (by GC) (entry 7). The reaction
also occurred in the absence of a base (entry 8). The use of PdCl2
under these conditions shows low catalytic activity (entry 9). To
investigate the specic solvent effect, we prepared Pd NCs in
DMF followed by a replacement of DMF on the Pd NCs by using
DMAc by heating at 100 ꢀC for 24 h. A TEM image and the
particle size distribution of the DMAc-displaced Pd NCs are
shown in Fig. 1. The average particle size of 2 nm is the same as
that of the prepared Pd NCs (Fig. 1).
1H-NMR spectroscopy, Fourier transform-infrared (FT-IR)
spectroscopy, thermogravimetric (TG) analysis, and X-ray
photoelectron spectroscopy (XPS) were performed to analyse
the DMAc-substituted Pd NCs. From H-NMR analysis, several
peaks around 8 ppm in H-NMR assigned to formyl protons of
DMF molecules on the Pd NCs.14f,15a–c The formyl group proton
(d ¼ 8.14 ppm) disappears aer solvent displacement (Fig. S1†).
FT-IR analysis (Fig. S2†) shows a peak at 1670 cmꢁ1, which is
attributed to the n(C]O) stretching vibration and indicates the
presence of DMF and DMAc molecules. The thermal stability of
the Pd NPs was investigated by TG analysis (Fig. 2). The TG
1
1
Fig. 3 XPS spectra of Pd NCs with DMF (a) at first measurement, (b) at
Fig. 1 (a) TEM image (scale bar ¼ 5 nm) and (b) nanoparticle size third measurement, and Pd NCs with DMA which substituted from
distribution of the DMAc-displaced Pd NCs.
DMF (c) at 1st and (d) at 3rd measurement.
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Next, we investigated aryl halides bearing both electron-
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Table
2
Optimisation of the arylsilylation condition with
hexamethyldisilanea
donating and electron-withdrawing substituents (Scheme 1).
Electron-donating substrates (4-methyl and 4-methoxy, and 4-
tert-butyl) gave excellent yields (84%, 97%, and 82% for 3b, 3c,
and 3d, respectively). Electron withdrawing substrates were less
effective (34% and 42% for 3e and 3f, respectively). Various
silanes were investigated. The corresponding arylsilanes
diphenylmethylsilane (3g), triethylsilane (3h), and triethox-
ysilane (3i) were obtained in 38%, 32%, and 25% yield,
respectively.
We wanted to extend the coupling reaction to disilanes.
Hexamethyldisilane is readily available as a Rochow direct
process byproduct.20 The reaction of iodobenzene with hexam-
ethyldisilane at 120 ꢀC afforded 5a in 70% yield (Table 2, entry
1). Various bases were examined. NaOAc showed the best
performance (entries 2–5). The same solvent effect was observed
for DMF and DMAc (entry 6). The presence of a base was
necessary for the reaction (entry 7). The reaction by using PdCl2
as catalyst precursor and gave the product in 38% (entry 8).
Iodobenzene derivatives bearing electron-donating groups,
such as p-methyl, p-methoxy, and p-tert-butyl groups, gave the
corresponding products in good yields (Table 3, entries 2–4).
Electron-withdrawing groups were less effective (entries 5–7).
However, the reaction of bromo/chlorobenzene under these
conditions was sluggish.
Based on the results and those reported in the literature, the
plausible reaction mechanisms are shown in Scheme S7.†21
Iodobenzene or hydrosilane oxidatively adds to the Pd NCs. The
desired coupling product is obtained by the s-bond metathesis
reaction.
We investigated possible reuse of the catalyst.22 Aer the
reaction, we performed annular dark eld scanning trans-
mission electron microscopy (ADF-STEM) and inductively
coupled plasma-atomic emission spectroscopy (ICP-AES) anal-
ysis (Table S2†). The particle size remained the same (Fig. 4).
Entry
Solvent
Base
Conv. (%)
Yieldb (%)
1
2
3
4
5
6
7
8c
DMAc
DMAc
DMAc
DMAc
DMAc
DMF
LiOAc
NaOAc
KF
Na2CO3
KOtBu
NaOAc
None
>99
>99
>99
>99
89
>99
58
78
70
83 (70)
73
78
27
69
32
38
DMAc
DMAc
NaOAc
a
Reaction conditions: 1a (1.0 mmol), 4 (3.0 mmol), Pd NCs (0.1 mol%),
b
and base (1.0 mmol) in solvent (1.0 mL) at 120 ꢀC for 24 h. The
conversion of 1a and yields were determined by GC analysis. The
isolated yield is shown in parenthesis. PdCl2 was used as catalyst
c
precursor.
Based on a previous study, the results suggest that the Pd NCs
possess recyclability in the coupling reaction.
We investigated the recyclability of the Pd NCs (Fig. 5 and 6).
Aer performing the reaction with the disilane system (Table 2,
entry 2), the hexane layer was extracted using 8 mL of hexane
ve times. The hexane layer (containing the starting materials
and products) was removed. The DMAc was evaporated from the
residual DMAc layer containing Pd NCs and the residue was
reused as the catalyst for the reaction under the same condi-
tions (Table 2, entry 2). The Pd NCs gave good yields ve times.
We also tested the coupling reaction of aryl halide with hydro-
silane (reaction conditions as in Table 1, entry 2). In the
hydrosilane coupling reaction, the extraction solvent was
modied. Product 3a and the starting materials were extracted
using a mixed solvent (hexane : ethyl acetate ¼ 95 : 5). The Pd
NCs catalyst tolerated multiple cycles.
Table 3 Coupling Reaction of Aryl halides 1a with hexamethyldisilanea
Entry
X
I
R
Product
Yieldb (%)
1
2
3
4
5
6
7
8
9
H
5a
5b
5c
5d
5e
5f
5g
5a
5a
70
65
73
86
66
59
p-Me
p-OMe
p-tBu
p-COMe
p-COOMe
p-CF3
H
48
Br
Cl
5c
H
Tracec
a
Reaction conditions: 1a (1.0 mmol), 2a (3.0 mmol), Pd NCs (0.1 mol%),
b
and base (1.0 mmol) in DMAc (1.0 mL) at 120 ꢀC for 24 h. Isolated
yield. c GC yield.
Scheme 1 Scope of various substrates.
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Experimental
1. General
GC analysis was performed with a ame ionisation detector
1
using a 0.22 mm ꢂ 25 m capillary column (BP-5). The H and
13C NMR spectra were recorded at 400 and 100 MHz, respec-
tively. The 1H and 13C NMR chemical shis are reported in ppm
with respect to the residual chloroform (1H 7.26 ppm, 13C 77
ppm). The products were characterised by H NMR, 13C NMR,
1
Fig. 4 (a) ADF-STEM image (scale bar ¼ 20 nm) and (b) particle size
and GC-MS. The TEM and STEM images were obtained with
a JEOL JEM-ARM200F instrument at an accelerating voltage of
200 kV. Size distributions of nanoparticles were measured by
counting 100 nanoparticles. ICP-AES was performed with
a Shimadzu ICPS-8100 spectrometer. XPS analysis was per-
formed with a ULVAC-PHI PHI5000 VersaProbe with Al Ka
radiation. The measured spectra were calibrated by the C 1 s
electron peak (284.5 eV). TG analysis was performed with
a Thermo Plus EVO device (Rigaku, Japan) at a heating rate of
distribution of the Pd NCs after the reaction.
10 C minꢁ1 under nitrogen ow.
ꢀ
All of the synthesised compounds (3a,23a 3b,23a 3c,23a 3d,23b
3e,23a 3f,23b 3g,23e 3h,23c 3i,23d 5a,24a 5b,24c 5c,24c 5d, 5e,24b 5f,24d and
5g24b
reported.
All of the starting materials were commercially available and
) are known compounds and have been previously
used without further purication. The DMF-protected Pd NCs
were prepared according to a previously reported method.15a
(A) Preparation of the DMF-stabilised Pd NCs. DMF (50
mL) was added to a 300 mL three-necked round bottom ask.
The solution was preheated to 140 ꢀC (ꢃ2 ꢀC) and stirred at
1500 rpm for 5 min. PdCl2 solution (0.1 M, 500 mL) was then
added to the hot DMF solution, which was allowed to react for
10 h under stirring (1500 rpm) at 140 ꢀC (ꢃ2 ꢀC). The resulting
clear yellow solution was used as the 1 mM Pd NCs solution in
DMF. In prior to the catalytic reaction, DMF solvent was
removed in vacuo, then the residue was dissolved in DMAc (50
mL) and stirred the reaction mixture at 100 ꢀC for 24 h.
Subsequent solvent evaporation in vacuo and the residue was
used as Pd NCs-DMAc for the measurements and coupling
reaction.
Fig. 5 Multiple catalyst recycling for coupling of iodobenzene with
disilane (conditions as in Table 2, entry 2).
2. Typical procedure
(A) Reaction of aryl halides with hydrosilanes. A mixture of
iodobenzene (1a, 204 mg, 1 mmol), dimethylphenylsilane (2a,
409 mg, 3 mmol), LiOAc (67 mg, 1 mmol), Pd NCs in DMAc (1
ꢀ
Fig. 6 Multiple catalyst recycling for coupling of iodobenzene with
hydrosilane (conditions as in Table 1, entry 2).
mL, 1 mM) as a catalyst, and solvent was stirred at 100 C for
16 h in an Ar atmosphere. The product and substrate conver-
sions and yields were estimated by GC from the peak areas
based on an internal standard (n-decane). 3a was obtained in
80% yield. 3a was isolated by column chromatography [silica gel
(230–400 mesh), n-hexane as eluent] in 75% yield (159 mg).
3a dimethyldiphenylsilane: colorless liquid, 1H-NMR (400
MHz; CDCl3; CDCl3) d: 7.57–7.54 (4H, m, Ph), 7.39–7.38 (6H, m,
Ph), 0.59 (6H, s, Me); 13C-NMR (100 MHz; CDCl3; CDCl3) d:
138.22 (C) 134.22 (CH), 129.11 (CH), 127.82 (CH), ꢁ2.42 (CH3);
GC-MS (EI) m/z (relative intensity) 212(23) [M]+, 197(100),
198(19), 105(9).
Conclusions
We have developed Pd NCs catalytic system for silylation of aryl
halides with hydrosilanes. The Pd NCs catalyst can be separated
and reused at least ve times without notable loss of the cata-
lytic activity. The same catalyst can also be used for silylation of
hexamethyldisilane. DMAs displacement enables easy access to
the active sites of the Pd NCs. Further investigation of metal NPs
as catalysts is underway.
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3b dimethyl(phenyl)(p-tolyl)silane: colorless liquid, 1H-NMR
(400 MHz; CDCl3; CDCl3) d: 7.57–7.55 (2H, m, Ph), 7.48–7.46
(2H, m), 7.39–7.38 (3H, m, Ph), 7.23–7.21 (2H, m, Ph), 2.39
(3H, s, SiMe2), 0.58 (6H, s, Me); 13C-NMR (100 MHz; CDCl3;
CDCl3) d: 138.96 (C), 138.50 (C), 134.53 (C), 134.23 (CH), 134.15
(CH), 129.00 (CH), 128.65 (CH), 127.76 (CH), 21.45 (CH3), ꢁ2.32
(CH3); GC-MS (EI) m/z (relative intensity) 226(18) [M]+, 211(100),
212(21), 105(7).
3c (4-ethoxyphenyl)dimethyl(phenyl)silane: colorless liquid,
1H-NMR (400 MHz; CDCl3; CDCl3) d: 7.53–7.44 (7H, m, Ph),
6.97–6.95 (2H, m, Ph), 3.85 (3H, s, OMe), 0.58 (6H, s, SiMe2); 13C-
NMR (100 MHz; CDCl3; CDCl3) d: 160.48 (C), 138.66 (C), 135.62
(CH), 134.11 (CH), 128.97 (CH), 127.75 (CH), 113.58 (CH), 54.97
(CH3), ꢁ2.32 (CH3); GC-MS (EI) m/z (relative intensity) 242(20)
[M]+, 227(100), 135(4).
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(B) Reaction of aryl halides with disilanes. A mixture of
iodobenzene (1a, 204 mg, 1 mmol), hexamethyldisilane (4,
439 mg, 3 mmol), NaOAc (82 mg, 1.0 mmol), and Pd NCs in
DMAc (1.0 mL, 1 mM) as a catalyst was stirred at 120 ꢀC for 24 h
in an Ar atmosphere. Conversion of the substrate and the yield
of the product were estimated by GC from the peak areas based
on an internal standard (n-tridecane). 5a was obtained in 83%.
5a was isolated by column chromatography [silica gel (230–400
mesh), petroleum ether as eluent] in 70% yield (105 mg), 1H
NMR (400 MHz; CDCl3; CDCl3) 7.66–7.46 (2H, m, Ph), 7.40–7.33
(3H, m, Ph), 0.27 (9H, s, SiMe3); 13C-NMR (100 MHz; CDCl3;
CDCl3) d: 140.47 (C), 133.28 (CH), 128.75 (CH), 127.71 (CH),
ꢁ1.16 (CH3).; GC-MS (EI) m/z (relative intensity) 150(18) [M]+,
136(12), 135(100).
5b trimethyl(p-tolyl)silane: colorless liquid, 1H-NMR (400
MHz; CDCl3; CDCl3): d 7.45 (d, J ¼ 8.0 Hz, 2H, Ph), 7.20 (d, J ¼
7.6 Hz, 2H, Ph), 2.37 (s, 3H, Me), 0.27 (s, 9H, SiMe3); 13C-NMR
(100 MHz; CDCl3; CDCl3): d 138.6 (C), 136.8 (C), 133.3 (CH),
128.6 (CH), 21.5 (CH3), ꢁ1.1 (CH3); GC-MS (EI) m/z (relative
intensity) 164(13) [M]+, 149(100), 121(9).
3d (4-(tert-butyl)phenyl)dimethyl(phenyl)silane: colorless
1
liquid, H-NMR (400 MHz; CDCl3; CDCl3) d: 7.21–7.01 (9H, m,
Ph), 0.98 (9H, s, tBu), 0.21 (6H, s, SiMe2); 13C-NMR (100 MHz;
CDCl3; CDCl3) d: 151.98 (C), 138.46 (C), 134.59 (C), 134.15 (CH),
134.04 (CH), 128.99 (CH), 127.75 (CH), 124.77 (CH), 34.62 (C),
31.22 (CH3), ꢁ2.34 (CH3); GC-MS (EI) m/z (relative intensity)
268(16) [M]+, 253(100), 237(6), 105(10).
5c (4-methoxyphenyl)trimethylsilane: colorless liquid, 1H-
NMR (400 MHz; CDCl3; CDCl3): d 7.20 (d, J ¼ 8.8 Hz, 2H, Ph),
6.67 (d, J ¼ 8.4 Hz, 2H, Ph), 3.56 (s, 3H, OMe), 0.00 (s, 9H,
SiMe3); 13C-NMR (100 MHz; CDCl3; CDCl3): d 162.2 (C), 135.7
(CH), 132.2 (C), 114.4 (CH), 55.9 (CH3), 0.00 (CH3); GC-MS (EI)
m/z (relative intensity) 180(16) [M]+, 165(100), 135(9).
5d (4-(tert-butyl)phenyl)trimethylsilane: white solid, m.p.
77.5–78, 1H-NMR (400 MHz; CDCl3; CDCl3): d 7.49 (d, J ¼ 8.4 Hz,
2H, Ph), 7.41 (d, J ¼ 8.0 Hz, 2H, Ph), 1.34 (s, 9H, Me), 0.27 (s, 9H,
SiMe3); 13C-NMR (100 MHz; CDCl3; CDCl3): d 151.7 (C), 136.9
(C), 133.2 (CH), 124.7 (CH), 34.6 (C), 31.2 (CH3), ꢁ1.06(CH3);
GC-MS (EI) m/z (relative intensity) 206(12) [M]+, 191(100), 176(7).
5e 1-(4-(trimethylsilyl)phenyl)ethan-1-one: colorless liquid,
1H-NMR (400 MHz; CDCl3; CDCl3) d: 7.92–7.91 (2H, m, Ph),
7.63–7.61 (2H, m, Ph), 2.60 (3H, s, COMe), 0.29 (9H, s, SiMe3);
13C-NMR (100 MHz; CDCl3; CDCl3) d: 198.33 (C), 147.21 (C),
137.17 (C), 133.48 (CH), 127.19 (CH), 26.58 (CH3), ꢁ1.38 (SiMe3);
GC-MS (EI) m/z (relative intensity) 192(14) [M]+, 177(100), 162(1),
119(7).
3e dimethyl(phenyl)(4-(triuoromethyl)phenyl)silane: 1H-
NMR (400 MHz; CDCl3; CDCl3) d: 7.64–7.61 (4H, m, Ph), 7.53–
7.52 (2H, m, Ph), 7.41–7.38 (3H, m Ph), 0.60 (6H, s, SiMe2); 13C-
NMR (100 MHz; CDCl3; CDCl3) d: 143.36 (q, 4JC–F ¼ 1.0 Hz, CH),
137.03 (CH), 134.41 (CH), 134.10 (CH), 130.99 (q, 2J
¼
C–F
32.2 Hz, CH), 129.45 (CH), 127.97 (CH), 124.29 (q, 3JC–F ¼ 3.7 Hz,
CH), 124.19 (q, 1JC–F ¼ 273.0 Hz, C), ꢁ2.63 (CH3); GC-MS (EI) m/z
(relative intensity) 280(4) [M]+, 265(100), 184(15).
3f methyl 4-(dimethyl(phenyl)silyl)benzoate: colorless liquid,
1H-NMR (400 MHz; CDCl3; CDCl3) d: 8.00 (2H, dd, J ¼ 8.3,
0.7 Hz, Ph), 7.60 (2H, dd, J ¼ 8.3, 0.7 Hz, Ph), 7.51–7.49 (2H, m,
Ph), 7.38–7.37 (3H, m, Ph), 3.92 (3H, s, OMe), 0.58 (6H, d, J ¼
0.6 Hz, SiMe2); 13C-NMR (100 MHz; CDCl3; CDCl3) d: 167.22 (C),
144.63 (C), 137.28 (C), 134.13 (CH), 134.11 (CH), 130.49 (C),
129.34 (CH), 128.51 (CH), 127.91 (CH), 52.12 (CH3), ꢁ2.61
(CH3); GC-MS (EI) m/z (relative intensity) 270(7) [M]+, 256(20),
255(100), 239(2).
3g methyltriphenylsilane: colorless liquid, 1H-NMR (400
MHz; CDCl3; CDCl3) d: 7.56–7.36 (15H, m, Ph), 0.87 (3H, s,
SiMe); 13C-NMR (100 MHz; CDCl3; CDCl3) d: 136.06 (C), 135.25
(CH), 129.37 (CH), 127.83 (CH), ꢁ3.40 (CH3); GC-MS (EI) m/z
(relative intensity) 274(5) [M]+, 259(100), 180(12).
5f methyl 4-(trimethylsilyl)benzoate: colorless liquid, 1H-
NMR (400 MHz; CDCl3; CDCl3) d: 7.99 (2H, d, J ¼ 8.3 Hz, Ph),
7.59 (2H, d, J ¼ 8.2 Hz, Ph), 3.92 (3H, s, OMe), 0.29 (9H, s,
SiMe3); 13C-NMR (100 MHz; CDCl3; CDCl3) d: 167.28 (C), 146.84
(C), 133.27 (CH, s), 130.19 (C), 128.44 (CH), 52.09 (CH3), ꢁ1.34
(CH3); GC-MS (EI) m/z (relative intensity) 208(5) [M]+, 193(100),
133(14).
3h triethyl(phenyl)silane: colorless liquid, 1H NMR (400
MHz; CDCl3; CDCl3): d 7.50–7.35 (m, 2H, Ph), 7.34–7.25 (m, 3H,
Ph), 0.96 (t, J ¼ 8.0 Hz, 9H, Me), 0.79 (q, J ¼ 7.2 Hz, 6H, SiCH2);
13C-NMR (100 MHz; CDCl3; CDCl3): d 137.8 (C), 134.5 (CH),
129.0 (CH), 127.9 (CH), 7.7 (CH3), 3.6 (CH2); GC-MS (EI) m/z
(relative intensity) 192(6) [M]+, 163(59), 135(100), 107(77).
3i triethoxy(phenyl)silane: colorless liquid, 1H NMR (400
MHz; CDCl3; CDCl3): d 7.68 (d, J ¼ 6.4 Hz, 2H, Ph), 7.34 (m, 3H,
Ph), 3.87 (q, J ¼ 7.2, 6H, OCH2), 1.25 (t, J ¼ 6.8 9H, Me); 13C-NMR
(100 MHz; CDCl3; CDCl3): d 134.8 (C), 130.9 (CH), 130.4 (CH),
127.9 (CH), 58.7 (CH2), 18.2 (CH3); GC-MS (EI) m/z (relative
intensity) 240(23) [M]+, 195(42), 145(100), 135(36).
5g trimethyl(4-(triuoromethyl)phenyl)silane: 1H-NMR (400
MHz, CDCl3; CDCl3): d 7.64 (d, J ¼ 7.6 Hz, 2H, Ph), 7.59 (d, J ¼
8.0 Hz, 2H, Ph), 0.30 (s, 9H, SiMe3); 13C-NMR (100 MHz; CDCl3;
CDCl3): d 145.6 (C), 133.8 (CH), 130.8 (q, J ¼ 31.6 Hz, C), 124.3
(q, J ¼ 270.2 Hz, C), 124.2 (q, J ¼ 3.9 Hz CH), ꢁ1.41(CH3) GC-MS
(EI) m/z (relative intensity) 218(6) [M]+, 203(100), 189(0.60).
3. Preparation of the TEM sample
(A) Pd NCs-DMAc (before the reaction). Aer preparation
the Pd NCs, Solvent DMF was displaced DMAc. The DMAc Pd
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NCs solution was stirred at 100 ꢀC, 24 h, then they were diluted
with 3 mL of ethanol and added dropwise onto the TEM grid
(Cu).
(B) Pd NCs-DMAc (aer the reaction). Aer the reaction
under the conditions given in Table 2, entry 2, the reaction
mixture was extracted with a mixed solvent [hexane : ethyl acetate
(99 : 1), 5 mL, 5 times] to remove 5a. DMAc was removed by
evaporation under high vacuum and then redispersed in ethanol.
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The Pd NCs remained in the DMAc solvent (bottom phase).
Conversion of the substrate and the yield of the product were
calculated from their GC peak areas based on an internal
standard (n-decane). The DMAc solution containing the Pd NCs
was ltered through a cotton plug to remove the Pd NCs from
the DMAc solution. DMAc was removed under vacuum and the
residue was redissolved in DMAc (1 mL). Pd NCs in DMF were
used for the next catalytic reaction under the reaction condi-
tions given in Table 1, entry 2 by adding iodobenzene (1a,
109 mg, 1.0 mmol), dimethylphenylsilane (2a, 409 mg, 3.0
mmol), and LiOAc (67 mg, 1.0 mmol).
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(bottom phase). Conversion of the substrate and the yield of the
product were calculated from their GC peak areas based on an
internal standard (n-tridecane). The DMAc solution containing
the Pd NCs was ltered through a cotton plug to remove the Pd
NCs from the DMAc solution. DMAc was removed under vacuum
and the residue was redissolved in DMAc (1 mL). The Pd NCs in
DMAc were used for the next catalytic reaction under the reaction
conditions given in Table 2, entry 2 by adding iodobenzene (1a,
204 mg, 1.0 mmol), hexamethyldisilane (4, 409 mg, 3.0 mmol),
and NaOAc (82 mg, 1.0 mmol).
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Conflicts of interest
There are no conicts to declare.
Acknowledgements
This work was supported by the “Development of Innovative
Catalytic Processes for Organosilicon Functional Materials”
project (PL: K. Sato, AIST) from the New Energy and Industrial
Technology Development Organization (NEDO). We thank the
members of the Comprehensive Analysis Center, SANKEN
(ISIR), Osaka University, for TEM, ICP-AES analyses.
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