Copper-catalyzed arylation of chlorosilanes with grignard reagents

Article abstract of DOI:10.1246/bcsj.82.1012

Nucleophilic substitution reactions of chlorosilanes with aryl Grignard reagents take place efficiently in the presence of copper(I) iodide to afford tetraorganosilanes.

Full text of DOI:10.1246/bcsj.82.1012

1012 Bull. Chem. Soc. Jpn. Vol. 82, No. 8, 1012–1014 (2009)
Short Articles
Table 1. Scope of Grignard Reagents
Copper-Catalyzed Arylation
of Chlorosilanes with
Grignard Reagents
5 mol% CuI
1.5 equiv
BrMg Ar
Me2PhSi Cl
Me2PhSi Ar
THF, 20 °C
2
1a
Entry
Ar
Time/h
2
Yield/%a)
1
2
3
4
5
6
7
8
p-MeC6H4
2-Naphthyl
2
0.5
3
3
3
50
3
18.5
2a
2b
2c
2d
2e
2f
81 (13)
84 (3)
81 (33)
87 (48)
98 (9)
80 (21)
81 (0)
76 (0)
Eiji Morita, Kei Murakami, Masayuki Iwasaki,
Koji Hirano, Hideki Yorimitsu,*
and Koichiro Oshima*
p-MeOC6H4
p-(i-Pr3SiO)C6H4
p-FC6H4
m-CF3C6H4
o-MeC6H4
Department of Material Chemistry, Graduate School of
Engineering, Kyoto University, Kyoto-daigaku Katsura,
Nishikyo-ku, Kyoto 615-8510
2g
2h
[CH2=C(SiMe3)]
a) Isolated yield. Yields obtained in the absence of CuI are in
parentheses.
Received April 1, 2009; E-mail: yori@orgrxn.mbox.media.
kyoto-u.ac.jp, oshima@orgrxn.mbox.media.kyoto-u.ac.jp
Table 2. Scope of Chlorosilanes
5 mol% CuI
+
BrMg
1.5 equiv
Si
Si Cl
1
Nucleophilic substitution reactions of chlorosilanes
with aryl Grignard reagents take place efficiently in the
presence of copper(I) iodide to afford tetraorganosilanes.
THF, 20 °C, 3 h
3
Entry
Si
3
Yield/%a)
1b)
2
3
4
5
6c)
7
MePh2Si (1b)
Et3Si (1c)
3b
3c
3d
3e
3f
76 (0)
75 (0)
70 (43)
85 (65)
81 (31)
91 (69)
0
The reactions of chlorotriorganosilanes with organomagne-
sium reagents that yield tetraorganosilanes are generally slow
despite the seeming simplicity.1 We have reported that silver(I)
nitrate and zinc chloride are efficient catalysts for the reaction
of chlorosilanes with organomagnesium reagents.2 We wish to
report herein that copper(I) iodide is also effective for the
reaction.3
(CH2=CHCH2)Me2Si (1d)
(CH2=CH)Ph2Si (1e)
(ClCH2)Me2Si (1f)
(ClCH2)Me2Si (1f)
i-Pr3Si (1g)
3f
3g
a) Isolated yield. Yields obtained in the absence of CuI are in
parentheses. b) Performed for 2 h. c) Performed for 0.5 h at
reflux.
The reactions of chlorodimethylphenylsilane (1a) with
arylmagnesium bromides are summarized in Table 1. Treat-
ment of 1a with p-methylphenylmagnesium bromide in the
presence of 5 mol % of copper(I) iodide in THF at 20 °C for 2 h
afforded the corresponding tetraorganosilane 2a in 81% yield
(Table 1, Entry 1). Electron-rich arylmagnesium reagents re-
acted with 1a smoothly (Entries 3 and 4). Electron-deficient
m-trifluoromethylphenylmagnesium bromide required a pro-
longed reaction time due to the low nucleophilicity (Entry 6).
The methyl group of the o-methylphenylmagnesium bromide
did not retard the reaction (Entry 7). 1-Trimethylsilylethenyl-
magnesium bromide as well as arylmagnesium bromide
participated in the reaction (Entry 8). In the absence of
copper(I) iodide, the reactions with electron-rich arylmagne-
sium reagents proceeded moderately (Entries 3 and 4). Without
copper(I) iodide, electronically neutral, electron-deficient, and
sterically demanding Grignard reagents reacted sluggishly
(Entries 1, 2, and 5-8).
presence of the catalyst, in spite of the bulky nature of the silyl
group (Entry 4). Arylation of chloro(chloromethyl)dimethyl-
silane (1f) proceeded on silicon without loss of the chloro-
methyl moiety, even at an elevated temperature (Entries 5 and
6). Bulky chlorotriisopropylsilane (1g) resisted the reaction
(Entry 7).
Unfortunately, the dramatic effect of copper(I) iodide in
the arylation was not applicable to reactions with other
Grignard reagents. An attempt to benzylate t-butylchlorodi-
methylsilane failed, and no benzylation took place (eq 1). An
attempted synthesis of allyltriisopropylsilane led to a moderate
yield (eq 2). The reaction of chloromethyldiphenylsilane with
butylmagnesium bromide yielded the corresponding product in
44% yield irrespective of the presence or absence of copper(I)
iodide (eq 3).
The scope of chlorosilanes is shown in Table 2. Although no
arylation took place in the reactions of chloromethyldiphenyl-
silane (1b) and chlorotriethylsilane (1c) in the absence of
copper(I) iodide, addition of copper(I) iodide dramatically
improved the yields (Entries 1 and 2). The effect of copper(I)
iodide was not drastic in the reaction of allylchlorodimethyl-
silane (1d) (Entry 3) probably because of small allyl and
methyl groups. Surprisingly, the reaction of chlorodiphenyl-
vinylsilane (1e) proceeded smoothly in the absence as well as
5 mol% CuI
t-BuMe2Si
Ph
BrMg
Ph
t-BuMe2SiCl +
ð1Þ
ð2Þ
ð3Þ
THF, 20 °C, 5 h
5 mol% CuI
0%
1.5 equiv
BrMg
i-Pr3Si
+
i-Pr3SiCl
THF, 20 °C, 5 h
(5 mol% CuI)
THF, 20 °C, 5 h
36%
1.5 equiv
+
BuMgBr
1.5 equiv
Ph2MeSiBu
44%
Ph2MeSiCl
Published on the web August 7, 2009; doi:10.1246/bcsj.82.1012

E. Morita et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 8 (2009) 1013
R1
The copper-catalyzed transmetalation was applicable to the
synthesis of 4 from dichlorodimethylsilane by sequential
arylation (eq 4). The first arylation proceeded without copper(I)
iodide. Copper(I) iodide and the second arylmagnesium reagent
were then added in the same pot to yield 4 in excellent yield.
The absence of copper(I) iodide for the second arylation
significantly decreased the yield of 4 (<30%).
Cl−
Si
R3
Ar
R2
Ar
R3
R1
-
Si
R2 Cl
ArMgBr
2 ArMgBr
8
ArCu
9
1) 1.2 equiv p-MeC6H4MgBr
THF, 0 °C, 1 h
CuI
Ar2CuMgBr
p-MeC6H4
Me2SiCl2
Me2Si
Ar Cu Ar
-
ð4Þ
2) 1.4 equiv p-MeOC6H4MgBr
5 mol% CuI, THF, 20 °C, 3 h
R3
R1
p-MeOC6H4
Si
6
4 84%
R2 Cl
7''
R1
Si
The silver-catalyzed reaction of optically enriched chloro-
silane 1h resulted in the loss of chirality.2a This was also the
case for the copper catalysis (eq 5).
R3
R2
Cl
5 mol% CuI
p-MeOC6H4MgBr
R1
R2 Si
Ar Cu Ar
Me
Me
1-naphthyl
1-naphthyl
R3
Cl
Ar Cu Ar 7
-
R3
-
Si
Si
Ph p-MeOC6H4
ð5Þ
Si R1
or
R2
THF, 20 °C, 17 h
Ph Cl
7'
1h 58%ee of (S)
5 26%, 0%ee
Cl
Thus, we are tempted to propose a reaction mechanism that
is quite similar to the silver-catalyzed reaction2a (Scheme 1).
Diarylcuprate4 6 would react with chlorosilane to form silicate
7 or 7¤ bearing a Si-CuIII bond. Reductive elimination from 7
or 7¤ would be slow enough to allow 7 or 7¤ to undergo
pseudorotation5 that leads to the loss of the initial stereo-
chemistry.6 Reductive elimination from 7¤¤ would then occur to
yield silicate 8 and arylcopper 9. Departure of chloride from
8 would afford tetraorganosilane. Remaining aryl Grignard
reagent would convert 9 to initial cuprate 6.
Scheme 1. Plausible reaction mechanism.
phenylsilane (2a, 183 mg, 0.81 mmol) in 81% yield.
Procedure for the Synthesis of Diaryldimethylsilane (eq 4).
Dichlorodimethylsilane (129 mg, 1.0 mmol) was placed in a 20-mL
reaction flask under argon in THF (5 mL). The flask was cooled to
0 °C. p-Methylphenylmagnesium bromide (1.0 M THF solution,
1.2 mL, 1.2 mmol) was slowly introduced to the flask. The reaction
mixture was stirred for 1 h at 0 °C. p-Methoxyphenylmagnesium
bromide (1.0 M THF solution, 1.4 mL, 1.4 mmol) and CuI (9.5 mg,
0.05 mmol) were sequentially added at 20 °C. The mixture was
stirred for 3 h at 20 °C. A saturated aqueous solution of NH4Cl
(2 mL) was added. The organic compounds were extracted with
ethyl acetate three times. The combined organic part was dried
over Na2SO4 and concentrated in vacuo. Silica gel column purifi-
cation with hexane/ethyl acetate = 50:1 afforded (p-methoxy-
phenyl)dimethyl(p-methylphenyl)silane (4, 214 mg, 0.84 mmol) in
84% yield.
Experimental
Instrumentation and Chemicals. 1H NMR (300 MHz) and
13C NMR (75 MHz) spectra were taken on a Varian Mercury 300
spectrometer and were obtained in CDCl3 with tetramethylsilane as
an internal standard. TLC analyses were performed on commercial
glass plates bearing a 0.25-mm layer of Merck Silica gel 60F254
.
Characterization of Products.
All the products showed
Silica gel (Wakogel 200 mesh) was used for column chromatog-
raphy.
spectra identical with those reported in the literature.2a
Unless otherwise noted, materials obtained from commercial
suppliers were used without further purification. CuI was pur-
chased from Wako Pure Chemicals. Arylmagnesium bromide was
prepared from magnesium turnings (Nacalai Tesque, Inc.) and
the corresponding bromoarene in THF. THF was purchased from
Kanto Chemical Co., stored under nitrogen, and used as is.
Chlorosilanes were purchased from Shin-Etsu Chemical Co., Ltd.
and Tokyo Chemical Industry Co., Ltd. Optically enriched 1h was
prepared according to the literature.7
Typical Procedure for Copper-Catalyzed Reactions. The
reaction of 1a with p-methylphenylmagnesium bromide (Table 1,
Entry 1) is representative. CuI (9.5 mg, 0.05 mmol) was placed in a
20-mL reaction flask under argon. Chlorodimethylphenylsilane
(170 mg, 1.0 mmol) in THF (5 mL) was added to the flask. Then,
p-methylphenylmagnesium bromide (1.0 M THF solution, 1.5 mL,
1.5 mmol) was added. The mixture was stirred at 20 °C for 2 h.
A saturated aqueous solution of NH4Cl (2 mL) was added. The
organic compounds were extracted with ethyl acetate three times.
The combined organic part was dried over Na2SO4 and concen-
trated in vacuo. Chromatographic purification on silica gel by
using hexane as an eluent afforded dimethyl(p-methylphenyl)-
The work is supported by Grants-in-Aid for Scientific
Research. M.I. and K.H. acknowledge JSPS for financial
support.
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1014 Bull. Chem. Soc. Jpn. Vol. 82, No. 8 (2009)
© 2009 The Chemical Society of Japan
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5
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