Silver-catalyzed transmetalation between chlorosilanes and aryl and alkenyl Grignard reagents for the synthesis of tetraorganosilanes

Article abstract of DOI:10.1002/anie.200801949

(Chemical Equation Presented) The silver savior: Nucleophilic substitution reactions of chlorosilanes with aryl Grignard reagents have been developed which take place under silver catalysis to afford tetraorganosilanes (see scheme). This transformation is likely to be promoted by diarylargentate reagents that are generated in situ.

Full text of DOI:10.1002/anie.200801949

Angewandte
Chemie
DOI: 10.1002/anie.200801949
Organosilver Reagents
Silver-Catalyzed Transmetalation between Chlorosilanes and Aryl and
Alkenyl Grignard Reagents for the Synthesis of Tetraorganosilanes**
Kei Murakami, Koji Hirano, Hideki Yorimitsu,* and Koichiro Oshima*
The nucleophilic substitution reaction of chlorosilanes with
organometallic reagents is a fundamental method used for
forming carbon–silicon bonds.[1] The reactions of chlorotrior-
ganosilanes with organolithium reagents generally proceed
smoothly at low temperatures (À788C). On the other hand,
reactions with the less reactive, yet readily available, organo-
magnesium reagents often require prolonged reaction times
and high temperatures (solvent b.p.), and result in moderate
yields of tetraorganosilanes.[2] Herein we report that silver
salts can catalyze the reactions of chlorotriorganosilanes with
organomagnesium reagents to yield a variety of tetraorgano-
silanes efficiently; this reveals a new aspect of silver
catalysis.[3–5]
only 13% yield in the absence of silver nitrate (Table 1,
entry 1). Other silver salts, such as silver halides, acetate, and
triflate, accelerated the carbon–silicon bond formation
(Table 1, entries 3–7). Other Group 11 metal halides, such as
copper(I)bromide and gold(I)chloride, also promoted the
reaction with only slightly lower efficiency (Table 1, entries 8
and 9). Nickel and palladium salts failed to catalyze the
reaction (Table 1, entries 10 and 11).
The Grignard reagent scope was studied and the results
are summarized in Table 2.[7] The reactions with 2-naphthyl,
Table 2: Silver-catalyzed reaction of 1a with various Grignard reagents.
Treatment of chlorodimethylphenylsilane (1a)with p-
tolylmagnesium bromide in the presence of a catalytic
amount of silver nitrate in THF at 208C for 1.5 h provided
the corresponding tetraorganosilane 2a in 93% yield
(Table 1, entry 2).[6] The transformation is regarded as a
Entry
R
t [h]
Product
Yield [%][a]
1
2
3
4
5
6
7
8
2-naphthyl
p-FC6H4
p-MeOC6H4
p-(iPr3SiO)C6H4
o-MeC6H4
1.5
1.5
1.5
1.5
24
20
4.5
1.5
2b
2c
2d
2e
2 f
2g
2h
2i
71
92
97
96
88
80
78
0
Table 1: Metal-catalyzed reaction of chlorodimethylphenylsilane with
p-tolylmagnesium bromide.
m-CF3C6H4
=
CH2 C(SiMe3)
iPr
[a] Yield of isolated product.
Entry
Catalyst
Yield [%][a]
Entry
Catalyst
Yield [%][a]
1
2
3
4
5
6
none
AgNO3
AgCl
AgBr
AgI
13
7
8
9
10
11
AgOTf
CuBr
AuCl
NiCl2
Pd(OAc)2
83
75
78
24
9
93 (92)[b]
p-fluorophenyl, p-methoxyphenyl, and p-(triisopropylsiloxy)-
phenyl Grignard reagents (Table 2, entries 1–4)proceeded as
smoothly as those described in Table 1. Sterically hindered o-
tolylmagnesium bromide was less reactive, and a prolonged
reaction time was essential for the reaction to proceed to
completion (Table 2, entry 5). An aryl Grignard reagent
having an electron-withdrawing trifluoromethyl group
reacted with chlorosilane 1a slowly in the presence of silver
nitrate (Table 2, entry 6). A bulky alkenylmagnesium reagent
also participated in the reaction (Table 2, entry 7).[8] Unfortu-
nately, attempts to introduce an alkyl group failed because of
the instability of the alkylsilver species (Table 2, entry 8).
The reactions of bulkier chloromethyldiphenylsilane and
chlorotriethylsilane with p-tolylmagnesium bromide under
silver catalysis proceeded to completion after extended
reaction times (Table 3, entries 1 and 2). Chlorosilanes
having an olefinic moiety (Table 3, entries 3 and 4)or a
chloromethyl moiety (Table 3, entry 5)reacted without any
observable side reactions. Notably, the reaction could be
performed on a scale as large as 50 mmol (with respect to 1 f).
Sterically congested chlorotriisopropylsilane failed to react
(Table 3, entry 6).
86
91
86
91
AgOAc
1
[a] Yield was determined by H NMR spectroscopy. [b] Yield of isolated
product. Tf=trifluoromethanesulfonyl.
silver-catalyzed transmetalation reaction between chlorosi-
lane and the Grignard reagent. Notably, 2a was obtained in
[*] K. Murakami, Dr. K. Hirano, Dr. H. Yorimitsu, Prof. Dr. K. Oshima
Department of Material Chemistry
Graduate School of Engineering, Kyoto University
Kyoto-daigaku Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan)
Fax: (+81)75-383-2438
E-mail: yori@orgrxn.mbox.media.kyoto-u.ac.jp
oshima@orgrxn.mbox.media.kyoto-u.ac.jp
[**] This work was supported by Grants-in-Aid for Scientific Research
from MEXT and JSPS. K.H. acknowledge JSPS for financial support.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200801949.
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Table 3: Scope of chlorosilanes.
Treatment of a mixture of 1j and 1k with an aryl Grignard
reagent under silver catalysis resulted in the predominant
formation of 2g, which is derived from 1j [Eq. (5)]. The
electron density of the silicon atom of 1j is likely to be lower
than that of 1k. The resulting substituent effect for the aryl
group of 1j and 1k can thus eliminate the possibility of the
formation of a silyl cation or cationlike intermediate.
Entry
Chlorosilane, R
t [h]
Product
Yield [%]
1
2
3
4
5
6
1b, MePh2Si
1c, Et3Si
10
9.5
11
18
3
3a
3b
3c
3d
3e[a]
3 f
87
73
80
74
=
1d, (CH2 CHCH2)Me2Si
=
1e, (CH2 CH)Ph2Si
1 f, (ClCH2)Me2Si
1g, iPr3Si
74 (79)[b]
trace
10
[a] PhMgBr was used instead of p-tolylmagnesium bromide. [b] 50 mmol
scale.
We were also able to introduce two different aryl groups
onto dichlorodimethylsilane in a one-pot process [Eq. (1)].
The first arylation proceeded in the absence of the silver
catalyst; silver nitrate was then added along with the second
Grignard reagent to yield 4 in excellent yield.
Generally, uncatalyzed nucleophilic substitution reactions
of chlorosilanes proceed with either retention or inversion of
configuration.[9] However, the silver-catalyzed reaction of
chiral compound 6[10] (60% ee, S configuration)provided the
corresponding product 7 in racemic form [Eq. (6)]. Such
racemization upon nucleophilic substitution of chlorosilanes
is rarely reported.
The silver-catalyzed reaction was highly effective, not only
for chlorosilanes but also for the reaction of silyl triflate 1c’
[Eq. (2)]. This result suggests that silver nitrate does not serve
to capture the chloride ion of 1 by precipitation of silver
chloride.
Based on our results [Eqs. (2)–(6)], we propose the
reaction mechanism depicted in Scheme 1. Initially, diaryl-
argentate species 8 would be generated in situ,[11] followed by
nucleophilic attack of the argentate complex upon the
III
À
chlorosilane to afford silicate 9 or 9’ bearing a Si Ag
bond.[12] Reductive elimination from 9 or 9’ would be
Given that the reaction mechanism would involve a
silicon-centered radical intermediate or a silyl cation species,
5-exo or 6-endo cyclization might occur in the silver-catalyzed
reactions of 1h and 1i [Eq. (3)and (4]). However, the
reactions resulted in simple arylation, and no cyclized
products were observed.
Scheme 1. A proposed mechanism. Intermediates 9’’ and 10 should
have trigonal-bipyramidal structures, although the position of each
substituent is not clear.
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Angewandte
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slow[12] and 9 or 9’ could undergo pseudorotation,[9] resulting
in the loss of the initial stereochemistry. After the scrambling,
reductive elimination from 9’’ would occur to afford silicate 10
with concomitant formation of arylsilver 11. Silicate 10 would
liberate a chloride ion to afford the product. By the action of
the aryl Grignard reagent, 11 would be converted into the
initial argentate 8.
In summary, the protocol described here provides a mild
and efficient method for the preparation of tetraorganosi-
lanes, and will be applicable to the synthesis of organosilicon
reagents and organosilicon-based advanced materials. There
are many effective reactions that employ combinations of
organomagnesium reagents and copper catalysts. On the
other hand, little is known about the useful reactivity of
organomagnesium reagents using silver catalysis.[4a,5] The
present reaction will open up new possibilities for silver-
catalyzed reactions with organometallic reagents.
Chem. 2006, 4313 – 4322; c)A. Yanagisawa, T. Arai, Chem.
Commun. 2008, 1165 – 1172; d)J. G. Noltes, G. van Koten in
Comprehensive Organometallic Chemistry II, Vol. 3 (Ed.: J. L.
Wardell), Pergamon, Oxford, 1995, Chapter 2.
[4] Recent selected examples of silver-catalyzed reactions: a)T.
Schwier, A. W. Sromek, D. M. L. Yap, D. Chernyak, V.
Gevorgyan, J. Am. Chem. Soc. 2007, 129, 9868 – 9878; b)S. Su,
J. A. Porco, Jr., J. Am. Chem. Soc. 2007, 129, 7744 – 7745; c)J. L.
Thompson, H. M. L. Davies, J. Am. Chem. Soc. 2007, 129, 6090 –
6091; d)S. Porcel, A. M. Echavarren, Angew. Chem. 2007, 119,
2726 – 2730; Angew. Chem. Int. Ed. 2007, 46, 2672 – 2676; e)I.
Nakamura, T. Nemoto, Y. Yamamoto, A. de Meijere, Angew.
Chem. 2006, 118, 5300 – 5303; Angew. Chem. Int. Ed. 2006, 45,
5176 – 5179; f)J. Sun, S. A. Kozmin, Angew. Chem. 2006, 118,
5113 – 5115; Angew. Chem. Int. Ed. 2006, 45, 4991 – 4993; g)H.
Yamamoto, M. Wadamoto, Chem. Asian J. 2007, 2, 692 – 698.
[5] Silver-catalyzed coupling reaction of alkyl Grignard reagent and
alkyl halide where the alkyl groups are the same: a)M. Tamura,
J. K. Kochi, Synthesis 1971, 303 – 305; silver-catalyzed oxidative
homocoupling reactions of Grignard reagents: b)T. Nagano, T.
Hayashi, Chem. Lett. 2005, 34, 1152 – 1153; c)M. Tamura, J. K.
Kochi, Bull. Chem. Soc. Jpn. 1972, 45, 1120 – 1127; silver-
catalyzed cross-coupling reactions of allylic Grignard reagents
and alkyl halides: d)H. Someya, H. Ohmiya, H. Yorimitsu, K.
Oshima, Org. Lett. 2008, 10, 969 – 971.
[6] The reaction proceeded with similar efficiency when it was
performed in the presence of triphenylphosphane (10 mol%).
However, the use of tri-tert-butylphosphane as well as an N-
heterocyclic carbene ligand (SIMes·HCl; Mes = 2,4,6-trimethyl-
phenyl)led to decreased yields of 2a, 84% and 78%, respec-
tively.
[7] For each reaction in Tables 2 and 3, we confirmed that the
process was inefficient in the absence of the silver catalyst.
[8] Smaller alkenylmagnesium reagents, such as vinylmagnesium
bromide, reacted smoothly in the absence of the silver salt.
[9] a)R. J. P. Corriu, C. Guerin, J. J. E. Moreau, The Chemistry of
Organic Silicon Compounds (Eds.: S. Patai, Z. Rappoport),
Wiley, New York, 1989, Chapter 4; b)A. R. Bassindale, P. G.
Taylor, The Chemistry of Organic Silicon Compounds (Eds.: S.
Patai, Z. Rappoport), Wiley, New York, 1989, Chapter 13;
c)R. R. Holmes, Chem. Rev. 1990, 90, 17 – 31.
Experimental Section
Typical
procedure
for
silver-catalyzed
reactions:
Chlorodimethylphenylsilane (1a, 85 mg, 0.50 mmol)in THF (5 mL)
was added to AgNO3 (4.2 mg, 0.025 mmol)under argon, followed by
4-methylphenylmagnesium bromide (1.0m solution in THF, 0.75 mL,
0.75 mmol). The reaction mixture was stirred at 208C for 1.5 h before
a saturated aqueous solution of NH4Cl (2 mL)was added. The
mixture was extracted with ethyl acetate and the combined organic
extracts were dried over Na2SO4 and concentrated in vacuo. Purifi-
cation of the residue by column chromatography on silica gel (n-
hexane)afforded dimethyl(4-methylphenpyhl)enylsilane
104 mg, 0.46 mmol)in 92% yield (Table 1, entry 2).
(
2a,
Received: April 25, 2008
Published online: July 4, 2008
Keywords: nucleophilic substitution ·
.
organomagnesium reagents · silanes · silver
[10] L. H. Sommer, C. L. Frye, G. A. Parker, K. W. Michael, J. Am.
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Stuttgart, 2002, Chapter 4.4; b)M. A. Brook, Silicon in Organic,
Organometallic, and Polymer Chemistry, Wiley, New York, 2000,
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Silicon Compounds (Eds.: S. Patai, Z. Rappoport), Wiley, New
York, 1989, Chapter 10.
[2] A different approach for the efficient synthesis of tetraorgano-
silanes with transition metal catalysts: J. Terao, N. Kambe, Chem.
Rec. 2007, 7, 57 – 67.
[11] a)C. M. P. Kronenburg, J. T. B. H. Jastrzebski, J. Boersma, M.
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[12] A similar intermediate that undergoes slow reductive elimina-
tion has been proposed in the reaction of dimethylargentate with
halomethane: W. Nakanishi, M. Yamanaka, E. Nakamura, J.
Am. Chem. Soc. 2005, 127, 1446 – 1453, and references therein.
[3] a)H. Schmidbaur, A. Bayler, The Chemistry of Organic
Derivatives of Gold and Silver (Eds.: S. Patai, Z. Rappoport),
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