Selective synthesis of halosilanes from hydrosilanes and utilization for organic synthesis

Article abstract of DOI:10.1016/S0022-328X(03)00254-7

Selective synthesis of halosilanes has been examined. Various types of halosilanes and halohydrosilanes, such as R₃SiX, R₂SiHX, R₂SiX₂, RSiH₂X, RSiHX₂ (X=Cl, Br, F), were obtained by the reactions of the corresponding hydrosilanes with Cu(II)-based reagents selectively in high yields. This method could be also applied to the synthesis of chlorofluorosilanes and chlorohydrogermanes. On the other hand, iodo- and bromosilanes and germanes were obtained by Pd- or Ni-catalyzed hydride-halogen exchange reactions of hydrosilanes with alkyl or allyl halides. Their synthetic applications have been demonstrated by using iodo- and bromosilanes and chlorofluorosilanes.

Full text of DOI:10.1016/S0022-328X(03)00254-7

Journal of Organometallic Chemistry 686 (2003) 3ꢁ15
/
www.elsevier.com/locate/jorganchem
Selective synthesis of halosilanes from hydrosilanes and utilization for
organic synthesis
Atsutaka Kunai *, Joji Ohshita
Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Kagamiyama 1-4-1, Higashi, Hiroshima 739-8527, Japan
Received 13 February 2003; received in revised form 28 March 2003; accepted 28 March 2003
Abstract
Selective synthesis of halosilanes has been examined. Various types of halosilanes and halohydrosilanes, such as R3SiX, R2SiHX,
R2SiX2, RSiH2X, RSiHX2 (Xꢀ
reagents selectively in high yields. This method could be also applied to the synthesis of chlorofluorosilanes and chlorohy-
drogermanes. On the other hand, iodo- and bromosilanes and germanes were obtained by Pd- or Ni-catalyzed hydrideꢁhalogen
/Cl, Br, F), were obtained by the reactions of the corresponding hydrosilanes with Cu(II)-based
/
exchange reactions of hydrosilanes with alkyl or allyl halides. Their synthetic applications have been demonstrated by using iodo-
and bromosilanes and chlorofluorosilanes.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Hydrosilane; Halosilane; Halohydrosilane; Copper reagent; H-halogen exchange; Synthetic utilization
1. Introduction
reactive halosilanes such as bromo- or iodosilanes, while
upon introduction of an silyl group into highly hindered
molecules, striking improvement in yields is often
resulted by using fluorosilanes instead of chlorosilanes.
Thus, molecular design would be much easier if various
halosilanes including halohydrosilanes and mixed halo-
silanes could be readily obtained in hands.
Organohalosilanes are useful starting materials or
reagents in the field of organosilicon chemistry [1] as
well as synthetic organic chemistry [2], as illustrated in
Chart 1. Among halosilanes, chlorosilanes are supplied
by an industrial process, so-called ‘the direct process’ [3],
and are widely used for the synthesis of organosilicon
compounds or polymers. Thus, enormous examples for
the synthetic utility of chlorosilanes have been reported
to date.
However, for building up a desired organosilicon
molecule, we sometimes require organosilanes having
multiple functional groups different in reactivity on the
same silicon atom, such as chlorohydro- or chlorofluor-
osilanes as the starting materials. An example is shown
in Eq. (1), where poly[(disilanylene)ethylene] was ob-
tained by Pt-catalyzed hydrosilylation of chlorohydro-
ð1Þ
In this paper, we would like to review our recent work
on the selective synthesis of such halosilanes from
hydrosilanes, together with some examples for their
utilization. As summarized in Chart 2, the chlorination
and bromination processes include oxidative halogena-
tion of a hydrosilyl bond with copper(II) chloride or
bromide in the presence of a catalytic amounts of CuI to
give the chloro- or bromosilyl bond. The characteristic
aspect of the reaction is that only one hydrogen on the
silicon atom is replaced by a chlorine or bromine atom
with the use of 2 equiv of CuCl2 or CuBr2. The
chlorosilyl bond thus formed can be converted in situ
to the fluorosilyl bond with the simultaneous use of KF,
which provides also a synthetic route to fluorohydrosi-
silane
with
chlorovinylsilane,
followed
by
electroreductive coupling of the product [4]. There
may be also needed in some cases the use of more
* Corresponding author. Tel.:
245494.
E-mail address: akunai@hiroshima-u.ac.jp (A. Kunai).
ꢂ81-824-247727; fax:
/
ꢂ81-824-
/
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00254-7

4
A. Kunai, J. Ohshita / Journal of Organometallic Chemistry 686 (2003) 3ꢁ15
/
In early 1990s, when we were examining electrore-
ductive coupling of chlorosilanes on a Pt cathode in
dimethoxyethane using Cu as a sacrificial anode [14], we
found a curious phenomenon that a small amount of
dichlorosilane was formed from chlorohydrosilane
along with the expected product, dihydrodisilane (Eq.
(2)). We thus assumed that chlorination of the Siꢀ
/H
bond in the starting silane took place with copper salts
generated anodically. Actually, stirring MePhSiH2 with
CuCl2 in the electrolytic cell without a charge overnight
afforded an appreciable amount of MePhSiCl2.
Chart 1.
PtꢀCu
2R2SiHClꢂ2eꢃ 0R2HSiꢀSiHR2(ꢂR2SiCl2)
(2)
We examined about the chlorination ability of CuCl2
towards triorganosilanes in diethyl ether [15], but the
reaction did not proceed with CuCl2 alone unless a
catalyst like Pt surface is present. When a catalytic
amount of CuI was added to CuCl2, however, the
reaction in ether proceeded very smoothly to give
chlorosilanes [16]. Thus, treatment of Me2PhSiH (1)
with 2 equiv molar of CuCl2 in the presence of a
catalytic amount of CuI at room temperature for 13 h
produced Me2PhSiCl (1a) in 82% isolated yield (Eq. (3)).
A trace of disiloxane formed from hydrolysis of the
product was observed, but no other products were
detected by either GLC or spectrometric analysis. The
mixture of CuCl2 and a catalytic amount of CuI is
Chart 2.
lanes in one pot. Moreover, chlorofluorosilanes and
chlorofluorohydrosilanes could be obtained by subse-
quent chlorination of the primary product, fluorohy-
drosilane.
On the other hand, transformation of hydrosilanes to
iodosilanes was achieved by Pd-catalyzed hydrogenꢁ
iodine exchange reaction between alkyl iodide and the
hydrosilyl group, though exhaustive exchange of silyl
hydrogens is inevitable. This approach was modified,
also for the production of bromosilanes and bromoger-
manes. The reaction system could be utilized as reagents
for ring-opening halosilylation of oxygen-containing
ring compounds to give a,v-halosiloxyalkanes.
/
hereafter named as the ‘CuCl2ꢁ
of other triorganohydrosilanes like MePh2SiH (2) and
Bu2MeSiH (3) with 2 equiv of the CuCl2ꢁCuI reagent
/
CuI’ reagent. Treatment
/
also afforded the respective chlorosilanes 2a and 3a in
high yields. In a case of bulky hydrosilane, t-BuMe2SiH
(4), the reaction rate was very slow in ether, but the use
of tetrahydrofuran (THF) as the co-solvent accelerated
markedly the reaction, leading to a 73% yield of t-
BuMe2SiCl (4a) after 60 h of the reaction.
2. Results and discussion
2CuCl2; CuI
2.1. Selective chlorination of hydrosilanes and germanes
with copper reagent
R2R?SiꢀH
R2R?SiꢀCl
(3)
ether
1ꢃ4
1a; R ꢀ Me; R?ꢀPh; 82%
2a; RꢀPh; R?ꢀMe; 77%
2.1.1. Chlorination of hydrosilanes
For the synthesis of chloro-silanes, hydrosilanes are
often used as the starting compounds. In fact, several
methods are available to date for the synthesis of
3a; RꢀBu; R?ꢀMe; 87%
4a; RꢀMe; R?ꢀt-Bu; 73%
chlorosilanes from hydrosilanes [5ꢁ
the reaction of hydrosilanes with CCl4 in the presence of
a catalytic amount of PdCl2 affords chlorosilanes in
/
11]. For example,
The facts that a trace amount of CuI catalyzes the
present reaction and 2 equiv of CuCl2 is necessary for
replacing one Siꢀ
/
H by Siꢀ/Cl suggests that a certain
high yields [9,10]. Radical-induced hydrogenꢁ
/halogen
reactive species such as CuICl or CuI2 might be formed
and plays a role in the present reaction [15], although the
detailed mechanism is not clear yet.
exchange between hydrosilanes and CCl4 also produces
chlorosilanes in good yields [12,13]. All methods includ-
ing these two, however, cannot be applied for the
selective synthesis of the silicon compounds that contain
The present method can be applied to the selective
chlorination of hydrosilyl bonds to give chlorohydrosi-
lanes, such as R2SiHCl, RSiH2Cl, and RSiHCl2, from
the corresponding hydrosilanes. For example, the reac-
both Siꢀ
/
Cl and Siꢀ/H bonds. Even if the reaction is
performed under controlled conditions, the reaction of
polyhydrosilanes always results in a mixture of chlori-
nated products at each stage.
tion of Et2SiH2 (5) with 2 equiv of CuCl2ꢁ
/
CuI in diethyl
ether at room temperature for 43 h yielded Et2SiHCl

A. Kunai, J. Ohshita / Journal of Organometallic Chemistry 686 (2003) 3ꢁ
/
15
5
2CuCl2; CuI
(5a) in 68% yield as the sole product, while similar
reaction of MePhSiH2 (6) for 36 h afforded MePhSiHCl
(6a) in 77% yield (Eq. (4)). In both cases, the mono-
chloro derivatives were formed selectively. Neither the
dichlorosilanes nor other products were observed.
Rf CH2CH2SiRH2
10ꢃ13
Rf CH2CH2SiRHCl
(9)
ether
10a; Rf ꢀ CF3; RꢀMe; 57%
11a; Rf ꢀC4F9; RꢀMe; 49%
12a; Rf ꢀC8F17; RꢀMe; 61%
13a; Rf ꢀC8F17; RꢀH; 65%
2CuCl2; CuI
RR?SiH2
RR?SiHCl
(4)
ether
5; 6
5a; R ꢀ R?ꢀEt; 68% 6a; RꢀMe; R?ꢀPh; 77%
Selective chlorination of trihydrosilane is also possi-
ble. Thus, treatment of PhSiH3 (7) with 2 equiv of
CuCl2ꢁ
afforded PhSiH2Cl (7a) in 70% yield (Eq. (5)), in
addition to a trace amount (B2%) of PhSiHCl2 (7b).
Similar treatment of 7 with 4 equiv of CuCl2ꢁ
/
CuI in ether at room temperature for 72 h
ð10Þ
/
/CuI for 94
h gave only 7b in 66% yield (Eq. (6)).
2CuCl2; CuI
2.1.2. Chlorination of hydrogermanes
PhSiH3
7
PhSiH2Cl 7a; 70%
(5)
Halogermanes are useful reagents in the synthesis of a
variety of organogermanium compounds [18]. Of these,
halohydrogermanes are of high importance, as exempli-
fied by dehydrohalogenative coupling of chlorohydro-
ether
4CuCl2; CuI
PhSiHCl2 7b; 66%
(6)
ether
germanes forming a Geꢀ/Ge bond [19]. A few methods
for the synthesis of halohydrogermanes, including
redistribution reactions of organohydrogermanes with
tetrachlorogermane [20] and selective monohalogena-
tion of dihydrogermanes with HgCl2, ClCH2OCH3 in
the presence of AlCl3 as the catalyst, or N-bromosucci-
nimide, have been published to date [21]. However, these
monohalogenation reactions involve the use of toxic or
costly reagents. Although partial hydrogenation of
dihalogermanes has been also reported, it may be
applied to only some special cases [22].
1,2-Dihydrodisilanes also react with 2 equiv of
CuCl2ꢁCuI under the same conditions to give mono-
/
chlorinated disilanes as the main product (Eq. (7)).
Thus, treatment of HMePhSiSiPhMeH (8) with 2 equiv
of the reagent afforded ClMePhSiSiPhMeH (8a) in 59%
yield, together with a 4% yield of dichlorodisilane 8b,
while the reaction of HEt2SiSiEt2H (9) produced
ClEt2SiSiEt2H (9a, 57%), along with 1,2-dichlorodisi-
lane (9b) (16%) and 9 (11%). Although the selectivity
decreased a little for dihydrodisilanes, the desired
products 8a and 9a could be readily isolated from
byproducts by fractional distillation. On the other
As the extension of selective chlorination of hydro-
silanes with the CuCl2ꢁCuI reagent, we found that this
/
reagent system works also well in the case of hydro-
germanes [23]. Thus, when Et2GeH2 was treated with 2
hand, treatment of 8 and 9 with 4 equiv of CuCl2ꢁCuI
gave 8b (79%) and 9b (90%), respectively, as the sole
product (Eq. (8)).
/
equiv of CuCl2ꢁCuI in ether at room temperature for 1
/
h, Et2GeHCl was obtained in 73% yield (Eq. (11) and
Table 1), while the reaction with 4 equiv of the reagent
for 8 h gave Et2GeCl2 in 85% yield (Eq. (12)). Hex2GeH2
also reacted with 2 equiv of the reagent within 3 h to
give Hex2GeHCl in 65% yield. In this case, however, a
trace of Hex2Ge(OEt)Cl was formed. The ethoxy group
would come from the solvent, ether. The reaction of
Hex2GeH2 in toluene was found to be much slow, but
under reflux for 5 h, Hex2GeHCl was obtained in 91%
yield as the sole product. Monochlorination of Hex2-
GeH2, Ph2GeH2, and PhGeH3 took place in the absence
of CuI, although a longer reaction time was required to
complete the chlorination. This is in marked contrast to
the chlorination of hydrosilanes, which occurs only in
the presence of the CuI catalyst. These hydrogermanes
were also converted to dichlorogermanes in high yields
by heating with 4 equiv of CuCl2 in the presence of CuI
in toluene under reflux for several days (Eq. (12)).
2CuCl2; CuI
HRR?SiꢀSiRR?H
CIRR?SiꢀSiRR?H
(7)
ether
8; 9
8a; R ꢀ Me; R?ꢀPh; 59% 9a; RꢀR?ꢀEt; 57%
4CuCl2; CuI
CIRR?SiꢀSiRR?Cl
(8)
ether
8b; R ꢀ Me; R?ꢀPh; 79% 9b; RꢀR?ꢀEt; 90%
The other examples are demonstrated for the chlor-
ination of dihydro- and trihydrosilanes 10ꢁ
fluoroalkyl group (Eq. (9)) [17]. All these reactions
proceeded selectively with 2 equiv of CuCl2ꢁCuI, and
the corresponding monochlorinated silanes 10aꢁ13a
were obtained as the sole volatile products. Moreover,
the reactions of m- and p-bissilylbenzenes (14, 15) with 4
equiv of the reagent produced bis(chlorosilyl)benzenes,
in which each silyl group was monochlorinated (Eq.
(10)).
/13 bearing a
/
/

6
A. Kunai, J. Ohshita / Journal of Organometallic Chemistry 686 (2003) 3ꢁ15
/
Table 1
Selective chlorination of hydrogermanes with copper reagent
Germane
CuCl2 (equiv)
CuI (equiv)
Conditions
Product (isolated yield)
Et3GeH
Hex3GeH
Et2GeH2
2
2
2
4
2
2
2
4
2
4
2
4
0.03
0.03
0.02
0.02
0.03
0.03
none
0.11
none
0.14
none
0.17
Et2O, rt, 3 h
Et2O, rt, 5 h
Et3GeCl (76%)
Hex3GeCl (88%)
Et2GeIICl (73%)
Et2GeCl2 (85%)
Hex2GeHCl (65%) a
Hex2GeHCl (91%)
Hex2GeHCl (90%)
Hex2GeCl2 (87%)
Ph2GeHCl (87%)
Ph2GeCl2 (86%)
PhGeH2Cl (84%)
PhGeHCl2 (88%)
Et2O, rt, 1 h
Et2O, rt, 8 h
Et2O, rt, 3 h
Hex2GeH2
toluene, reflux, 5 h
toluene, reflux, 19 h
toluene, reflux, 4 days
toluene, reflux, 31 h
toluene, reflux, 6 days
toluene, reflux, 19 h
toluene, reflux, 9 days
Ph2GeH2
PhGeH3
a
A trace of Hex2Ge(OEt)Cl was formed.
2CuCl2; CuI
sole product after distillation of the resulting mixture
(Eq. (13)). No other products were detected by GLC and
spectrometric analysis. Similar reaction of MePh2SiH
R4ꢃnGeHn
R4ꢃnGeHnꢃ1Cl
(11)
(12)
ether or toulene
4CuCl2; CuI
R4ꢃnGeHnꢃ2Cl2
ether or toulene
(2) with 2 equiv of the CuCl2ꢁ
/
CuIꢁKF reagent in THF
/
for 5 h gave MePh2SiF (2c) selectively in 78% isolated
yield.
The present reaction is oxidative in nature and CuCl2
acts as the oxidant. Presumably, replacement of the
hydrogen atom of hydrogermanes with an electronega-
tive chlorine atom suppresses the further chlorination to
provide the high selectivities in the present reactions.
The lower reaction rate of the chlorination of phenyl-
germanes than that of the respective hexylgermanes also
seems to reflect the electronegative nature of the phenyl
group compared to the hexyl group.
2CuCl ꢃCuI; KF R2R?SiF
(13)
2
R2R?SiH
0
THF
1; 2
1c; R ꢀ Me; R?ꢀPh; 82%
2c; RꢀPh; R?ꢀMe; 78%
For these reactions, the use of 2 equiv of CuCl2 as the
oxidant for one HꢀSi bond is essential. When hydro-
/
silanes were treated with an excess amount of KF and
the CuI catalyst in the absence of CuCl2 in THF, the
reaction did not proceed, which suggests that the
starting hydrosilane is first converted to a chlorosilane
2.2. Selective fluorination of hydrosilanes with copper
reagent
with the CuCl2ꢁCuI reagent, and then the resulting Cl
atom is replaced by a fluoride ion to form fluorosilanes
(Eq. (14)). Such Cl/F exchange on a silicon atom is well
/
Fluorosilanes can be used for the synthesis of high
coordinated silicon compounds [24] and highly hindered
organosilanes [25]. To date, several methods are avail-
able for the synthesis of fluorosilanes. The methods
involve the reactions of siloxy compounds with NH4F in
H2SO4 [26], hydrofluoric acid [27], and BF3 etherate
[28], halogen exchange of chlorosilanes with SbF3 [29],
ZnF2 [30], NH4F [31], CuF2 [32], Na2SiF6 [33], NaPF6,
NaSbF6, NaBF4 [34], and Me3SnF [35], and fluorination
of hydrosilanes with AgF [36], PF5 [37], Ph3CBF4 [38],
known [29ꢁ/34].
2CuCl2ꢃCuI
KF
MePh2SiCl 0 MePh2SiF
MePh2SiH
2
(14)
THF
2
a
2c
We applied these reactions to the synthesis of
fluorodiorganosilanes (R2SiHF) from the corresponding
diorganosilanes (R2SiH2). Practically, complete conver-
sion of the starting dihydrosilanes is desirable to get
high purity of the products. Moreover, the formation of
difluoro compounds must be avoided, because it is hard
to separate the desired R2SiHF from R2SiF2 as well as
R2SiH2 by distillation.
SbF3 [39], NOBF4 or NO2BF4 [40], and CuF2ꢁCCl4
/
[41]. Although these methods give fluorosilanes in good
yields, it is difficult to prepare the fluorosilanes bearing
an Siꢀ/H bond from hydrosilanes.
In our continuing study on halogenation of hydro-
silanes, we found that the hydrosilyl group can be
transformed into a fluorosilyl group with the use of the
As expected, dialkyl-, alkylaryl-, and diarylsilanes
could be readily transformed into the corresponding
monofluorosilanes (Eq. (15)). When n-Hex2SiH2 (16)
CuCl2ꢁ
when Me2PhSiH (1) was treated with a mixture of 2
equiv of the CuCl2ꢁCuI reagent and 1 equiv of KF (thus
CuCl2ꢁCuIꢁKF reagent) in THF at room temperature
for 5 h, Me2PhSiF (1c) was obtained in 82% yield as the
/CuI reagent in the presence of KF [42]. Thus,
was treated with 2 equiv of the CuCl2ꢁ
/
CuIꢁKF reagent
/
/
in THF at room temperature, the starting silane
disappeared within 1 h, and distillation of the resulting
mixture afforded n-Hex2SiHF (16c) in 81% yield as the
/
/

A. Kunai, J. Ohshita / Journal of Organometallic Chemistry 686 (2003) 3ꢁ
/
15
7
7d; R ꢀ Ph; 70% 19d; RꢀHex; 54%
sole product. Similar treatment of Ph2SiH2 (17) for 1 h
afforded Ph2SiHF (17c) in 81% isolated yield, while the
reaction of MeMesSiH2 (18) for 24 h produced MeM-
esSiHF (18c) in 75% isolated yield. Rather slow reaction
rate of MeMesSiH2 may be caused by steric hindrance
due to the mesityl substituent. In all cases, the mono-
fluoro derivatives were obtained as the sole product.
Neither difluorosilanes nor other products were detected
in the distillates.
6CuCl2ꢃCuI; 3KF
RSiF3
(19)
THF
7e; R ꢀ Ph; 53%
We extended the present method to the synthesis of
mixed halosilanes. When MePhSiHF (6c) prepared from
MePhSiH2 in the manner described above was treated
with 2 equiv of the CuCl2ꢁCuI reagent in THF at room
/
2CuCl2ꢃCuI; KF
temperature for 10 h, MePhSiClF (6f) was obtained in
74% yield after distillation of the resulting mixture (Eq.
(20)). Similar treatment of Ph2SiHF (17c) with 2 equiv
RR?SiH2
RR?SiHF
(15)
THF
16ꢃ18
16c; R ꢀ R?ꢀHex; 81%
17c; RꢀR?ꢀPh; 81%
of the CuCl2ꢁCuI reagent in THF at 40 8C for 24 h
/
afforded Ph2SiClF (17f) in 67% isolated yield. In both
cases, no other products were detected in the reaction
mixture. The same reactions in ether proceeded much
slower and afforded 6f and 17f in a little higher yields
(83 and 70%).
18c; RꢀMe; R?ꢀMes; 75%
Similar treatment of MePhSiH2 (6) with 2 equiv of the
CuCl2ꢁCuIꢁKF reagent in THF at room temperature
/
/
for 1 h produced MePhSiHF (6c) in 72% yield after
distillation, together with an 8% yield of MePhSiF2,
while the reaction with 4 equiv of the reagent for 48 h
gave MePhSiF2 as the sole product in 61% yield. In
order to obtain only the monofluorosilane as the
product, we carried out the reaction of 6 under milder
conditions. Thus, when the reaction of 6 was carried out
using 2 equiv of the reagent including CsF instead of KF
in refluxing ether for 1 week, 6c was obtained as the sole
product in 68% yield after distillation (Eq. (16)). On the
other hand, the use of CuF2 as the fluoride salt in THF
formed mainly MePhSiF2 [41], together with a disilox-
ane which was presumably resulted by water in the
highly hygroscopic CuF2 salt.
2CuCl2ꢃCuI
RR?SiHF
RR?SiClF
(20)
THF (or ether)
6c; 17c
6f; R ꢀ Me; R?ꢀPh; 74% (83%)
17f; RꢀR?ꢀPh; 67% (70%)
Chlorofluorohydrosilanes can be also synthesized
from trihydrosilanes. Thus, when PhSiH2F (7c) pre-
pared from PhSiH3 was treated with 2 equiv of the
CuCl2ꢁCuI reagent in ether at room temperature for 58
/
h, PhSiHClF (7f) was obtained in 61% yield, while
similar treatment of n-HexSiH2F (19c) with 2 equiv of
this reagent for 48 h afforded n-HexSiHClF (19f) in 59%
yield (Eq. (21)). All these mixed halosilanes and
halohydrosilanes are thermally stable and could be
obtained in pure forms by fractional distillation after
filtration of the reaction mixture to remove copper salts.
No redistribution reactions of halogens were observed
during the distillation.
2CuCl2ꢃCuI; CsF
MePhSiH2
6
MePhSiH 6c; 68%
(16)
ether; reflux
The present method is not restricted to the dihydro-
silanes, but can be applied to the partial fluorination of
trihydrosilanes, RSiH3 (Eq. (17)). In this case, it is
desirable to add KF after the end of the chlorination
step, since simultaneous addition of these salts produces
a mixture of RSiH2F and a small amount of RSiHF2.
Thus, treatment of PhSiH3 (7) for 77 h and n-HexSiH3
2CuCl2ꢃCuI
RSiH2F
RSiHClF
(21)
ether
7c; 19c
7f; R ꢀ Ph; 61% 19f; RꢀHex; 59%
(19) for 42 h with 2 equiv of the CuCl2ꢁCuI reagent in
/
Interestingly, PhSiCl2F and n-HexSiCl2F were not
produced, even when 7c, 7f, 19c, and 19f were treated
this manner afforded PhSiH2F (7c) and n-HexSiH2F
(19c) in 64 and 58% yield, respectively, as the sole
volatile product, while PhSiHF2 (7d) and n-HexSiHF2
(19d) could be obtained when 4 equiv of the reagent was
used (Eq. (18)). PhSiF3 (7e) was obtained also by the
reaction with 6 equiv of the reagent for 1 week (Eq.
(19)).
with the excess of the CuCl2ꢁCuI reagent under similar
/
conditions for several days. In all cases, the reaction
stopped at the stage of monochlorofluorosilanes, prob-
ably because accumulation of electronegative fluorine
and chlorine atoms on the silicon center make an
increase in oxidation potential of these halosilanes,
leading to the decrease in reactivity and the increase in
selectivity. Similarly, the reaction of 7d and 19d with the
2CuCl2ꢃCuI; KF
RSiH3
7; 19
RSiH2F
(17)
ether
7c; R ꢀ Ph; 64% 19c; RꢀHex; 58%
CuCl2ꢁCuI reagent under similar conditions did not
afford the corresponding chlorosilanes, and the starting
materials were recovered unchanged.
/
4CuCl2ꢃCuI; 2KF
RSiHF2
ether
(18)

8
A. Kunai, J. Ohshita / Journal of Organometallic Chemistry 686 (2003) 3ꢁ15
/
2.3. Selective bromination of hydrosilanes with copper
reagent
derivatives [54]. To suppress undesired reactions, we
changed the solvent from ether to benzene. When 16 was
treated with 4 equiv of the CuBr2ꢁCuI reagent in
/
As to bromosilanes, there have been reported several
synthetic methods, such as reactions of polybromosi-
benzene under reflux for 34 h, n-Hex2SiBr2 was
obtained in 70% isolated yield.
lanes with Grignard reagents [43], cleavage of Siꢀ
bonds with PBr3 [44], cleavage of SiꢀPh bonds [26b,45]
or SiꢀSi bonds [46] with Br2, Cl/Br exchange of
chlorosilanes with AlBr3 [44a] or MgBr2 [47], bromina-
tion of polyhydrosilanes with Br2 [44a,48], HBr [49],
HgBr2 [50], or NBS [51], and partial reduction of 1,2-
dibromodisilanes with trialkyltin hydrides [52], but it is
difficult to obtain selectively a desired type of bromohy-
drosilane by these methods.
In our continuing study on halogenation of hydro-
silanes, we found that hydrosilyl groups can be trans-
formed into bromosilyl groups with the use of CuBr2,
instead of CuCl2, in the presence of a catalytic amount
/
O
Mono- and dibrominations of trihydrosilanes are also
possible (Eqs. (24) and (25)). When n-HexSiH3 (19) was
/
/
treated with 2 equiv of the CuBr2ꢁCuI reagent in ether
/
at room temperature for 12 h, n-HexSiH2Br (19g) was
obtained in 64% yield as the sole product after distilla-
tion. When 19 was treated with 4 equiv of the CuBr2ꢁ
/
CuI reagent in benzene at room temperature for 1 week,
n-HexSiHBr2 (19h) was obtained in 55% isolated yield.
Moreover, the reaction of PhSiH3 (7) with 2 equiv of the
reagent in benzene at room temperature for 6 h afforded
PhSiH2Br (7g) in 72% yield, while treatment with 4
equiv of the reagent in benzene at room temperature for
40 h produced PhSiHBr2 (7h) in 67% yield.
of CuI (thus CuBr2ꢁ
analogous to chlorination [16]. When Et3SiH (20) was
treated with 2 equiv of the CuBr2ꢁCuI reagent in diethyl
/
CuI reagent) [53], in a way
2CuBr2ꢃCuI
RSiH3
7; 19
RSiH2Br
(24)
ether (19) or benzene (7)
/
ether at room temperature for 1.5 h, Et3SiBr (20g) was
obtained in 82% yield after distillation of the reaction
mixture (Eq. (22)).
7g; R ꢀ Ph; 72% 19g; Rꢀn-Hex; 64%
4CuBr2ꢃCuI
RSiHBr2
benzene
(25)
2CuBr2ꢃCuI
Et3SiH
Et3SiBr 20g; 82%
(22)
ether
20
7h; R ꢀ Ph; 67% 19h; Rꢀn-Hex; 55%
This reagent could be applied for the monobromina-
tion of dihydrosilanes (Eq. (23)). Thus, when n-Hex2-
SiH2 (16) was treated in diethyl ether with 2 equiv of the
On the other hand, attempted tribromination with
this reagent did not take place. When 7 was heated
under reflux in benzene with 6 equiv of the CuBr2ꢁCuI
/
CuBr2ꢁCuI reagent at room temperature, the starting
/
reagent, dibromination completed within 3 h, much
faster than the case using 4 equiv of the reagent at room
temperature. However, the reaction stopped at this
stage, and no tribromide would be formed even after 1
week. Presumably, accumulation of electronegative
bromine atoms on the same silicon center decreases
the reactivity of the silicon center, as has been observed
previously for the chlorination of fluorohydrosilanes
[42].
silane disappeared within 1 h, and distillation of the
resulting mixture afforded n-Hex2SiHBr (16g) in 73%
yield as the sole volatile product. Similar treatment of
MePhSiH2 (6) for 9 h afforded MePhSiHBr (6g) in 68%
yield, while the reaction of Ph2SiH2 (17) in toluene for
7.5 h produced Ph2SiHBr (17g) in 64% yield.
2CuBr2ꢃCuI
RR?SiH2
R2SiHBr
(23)
ether (6; 16) or toluene (17)
6; 16; 17
We also performed selective bromination of 1,2-
dihydrodisilanes. Thus, when HEt2SiSiEt2H (9) was
treated with 2 equiv of the reagent in benzene at room
temperature for 4 h, HEt2SiSiEt2Br (9g) was obtained in
58% isolated yield, together with a 10% yield of
Et2SiHBr (Eq. (26)).
6g; R ꢀ Me; R?ꢀPh; 68%
16g; RꢀR?ꢀn-Hex; 73%
17g; RꢀR?ꢀPh; 64%
To obtain further information, we carried out dibro-
mination of dihexylsilane and monitored the progress by
GLC. When 16 was treated with 4 equiv of the CuBr2ꢁ
/
2CuBr2ꢃCuI
CuI reagent in ether at room temperature, 16 disap-
peared soon after to generate 16g as the primary
product. This monobromide then diminished slowly
and disappeared after 44 h, during which n-Hex2-
Si(OEt)H and n-Hex2Si(OEt)Br began to increase and
became the final products, indicating that the mono-
bromination proceeds quite fast, while dibromination
requires much longer time, and the bromide once
formed reacts gradually with ether to give ethoxy
HEt2SiSiEt2H
9
HEt2SiSiEt2Br
benzene
(26)
9g; 58%
The selectivity of the bromodisilane diminished in this
case, but two products could be readily separated by
distillation. The monosilane may be produced by the
cleavage of an Siꢀ
generated during the reaction.
/
Si bond of disilane with HBr

A. Kunai, J. Ohshita / Journal of Organometallic Chemistry 686 (2003) 3ꢁ
/
15
9
3i; Rꢀn-Bu; R?ꢀMe; 77%
4i; RꢀMe; R?ꢀt-Bu; 97%
20i; RꢀR?ꢀEt; 85%
2.4. Halogenation by metal-catalyzed hydrogenꢁhalogen
exchange reaction
/
2.4.1. Iodination of hydrosilanes
21i; RꢀR?ꢀPh; 94%
Organic iodosilanes have been shown to be useful
reagents in organic synthesis due to their high reactivity.
However, the synthesis of the iodosilanes, except for
Me3SiI has not been extensively studied. The method for
the synthesis of Me3SiI reported to date involves the
reaction of hexamethyldisilane [55], trimethylphenylsi-
lane [26b], allyltrimethylsilane [56], and 1,4-bis(tri-
methylsilyl)cyclohexa-2,5-diene [57] with I2, and the
reaction of Me3SiCl with NaI in acetonitrile [58].
Organoiodosilanes other than Me3SiI have been pre-
The reaction rate for the Siꢁ
/
H/Cꢁ
/
I exchange is quite
slow for the hydrosilanes bearing a bulky substituent on
the silicon atom, but increased reaction temperature
brings about a considerable reduction in time. For
example, the reaction of t-BuMe2SiH (4) with MeI at
room temperature requires 24 h for completion of the
reaction, while at 60 8C, 4 is completely consumed
within 2.5 h to give a 97% yield of t-BuMe2SiI (4i).
It should be stressed that the present reaction can be
used for the synthesis of phenyl-substituted iodosilanes.
Thus, the reaction of Me2PhSiH (1) with 2.2 equiv of
MeI in the presence of 0.4 mol% of PdCl2 at room
temperature for 4 h gave Me2PhSiI (1i) in 83% isolated
yield. Similarly, the Pd-catalyzed reaction of MePh2SiH
(2) with MeI produced MePh2SiI (2i) in 91% yield.
The reaction of Ph3SiH (21) with MeI is somewhat
different from the others. In this case, the product
Ph3SiI (21i) was produced as solids, and therefore the
reaction was carried out in benzene under reflux. When
PdCl2 was added to the solution, the reaction began
smoothly, but the activity of PdCl2 decreased gradually.
By adding the catalyst twice, finally 21i was obtained in
94% yield.
pared by the methods involving cleavage of Phꢀ
HꢀSi bonds by I2 and HI [59], an SeꢀSi bond by I2 [60],
and an NꢀSi bond by HI [61]. It has also been reported
/Si and
/
/
/
that the reaction of triorganosilanes with iodobenzene in
the presence of a colloidal Ni catalyst at high tempera-
ture produces organoiodosilanes [62].
As an extension of our previous observation for the
chlorination of hydrosilanes with the CuCl2ꢁCuI re-
/
agent, we first examined iodination of Et3SiH using a
small excess of iodine in the presence of CuI in benzene
at room temperature, and obtained Et3SiI in high yield.
Similar CuI-catalyzed reaction of PhMe2SiH with
iodine, however, produced PhMe2SiI only in low yield,
because a Phꢀ
/
Si bond is readily cleaved by the action of
Diiodomethane, iodoform, or iodobenzene can also
be used as the iodide source, though the reactivity of
them seems more sensitive to the substituents on Si,
compared to MeI. For example, the reaction of 1 with
PhI at room temperature for 1 h yielded Me2PhSiI in
91% yield. In contrast to this, the reactions of 20 and 4
with PhI were quite slow even at 80 8C and most of the
starting hydrosilane was recovered unchanged after 19 h
of reaction.
HI generated from the H/I exchange reaction. More-
over, the products were always contaminated with a
trace of I2. Therefore, we attempted to prepare the
iodosilanes by the method that involves no iodine, and
found that Siꢁ
/
H/CꢁI exchange readily takes place in the
/
presence of a palladium chloride catalyst under mild
conditions to give a high quality of iodosilanes.
It is known that treatment of organohydrosilanes with
chlorocarbons in the presence of a catalytic amount of
palladium chloride afforded chlorosilanes in high yields
[63]. We modified this method to be used for the
synthesis of various types of the iodosilanes [64]. Thus,
the reaction of Et3SiH (20) with 1.8 equiv of methyl
iodide in the presence of 0.5 mol% of palladium chloride
at room temperature for 1.5 h afforded Et3SiI (20i) in
85% isolated yield (Eq. (27)). The reaction proceeded
cleanly without solvent and 20i could be readily isolated
as a colorless liquid by simple distillation. No other
products were detected in the distillate. Similar PdCl2-
catalyzed reaction of n-Bu2MeSiH (3) at room tempera-
ture for 7 h with MeI produced n-Bu2MeSiI (3i) in 77%
yield. The formation of methane was verified by mass
spectrometric analysis of the gaseous product.
The present method can be applied to the preparation
of Et2SiI2 (5i) from Et2SiH2 (5). When methyl iodide is
used as the iodine source, a novel alkylꢁhydrogen
/
exchange reaction takes place along with the iodination
reaction (Eq. (28)). Thus, when 5 was treated with 3
equiv of MeI in the presence of 4 mol% of PdCl2 at
60 8C for 24 h, 5i was obtained in 37% isolated yield,
together with a 20% yield of Et2MeSiI. The reaction of 5
with 3 equiv of ethyl iodide for 12 h led to a similar
result. In order to avoid the formation of trialkyliodo-
silanes, we tried to use a bulkier alkyl iodide. Thus,
when 5 was treated with 2.0 equiv of isopropyl iodide in
the presence of 0.5 mol% of PdCl2 at 70 8C for 24 h, the
diiodosilane 5i was formed as a sole volatile product in
74% yield. Moreover, the reaction of MePhSiH2 (6) with
i-PrI proceeded cleanly at 100 8C and afforded MePh-
SiI2 (6i) in 87% yield after 12 h of the reaction (Eq. (29)).
NiCl2 also served as the catalyst, though less active, and
the reaction with NiCl2 under similar conditions for 18 h
cat: PdCl2
R2R?SiꢀHꢂCH3ꢀI
R2R?SiꢀIꢂCH3ꢀH (27)
room temp:
1ꢃ4; 20; 21
1i; R ꢀ Me; R?ꢀPh; 83%
2i; RꢀPh; R?ꢀMe; 91%

10
A. Kunai, J. Ohshita / Journal of Organometallic Chemistry 686 (2003) 3ꢁ15
/
produced 6i in 87% yield [64b].
Me2PhSiBr (1g) in 88% yield. Similar NiCl2-catalyzed
bromination of 1 with allyl bromide required a larger
amount of the catalyst and a longer reaction period to
complete the conversion, compared to the reaction with
PdCl2. Lower activity of NiCl2 relative to PdCl2 is
evident for tribromination of PhSiH3 (21), in which the
Ni catalyst was deactivated during the reaction progress
and continuous addition of the catalyst was necessary to
promote further the reaction. In contrast to this,
PhSiBr3 (21g) was obtained in 88% yield from 21 with
only 1 mol% of the PdCl2-catalyst.
cat: PdCl2
Et2SiH2ꢂ2RI
Et2SiI2ꢂEt2RSiIꢂRH
(28)
60ꢃ70 ꢀC
5
5i
20i
R ꢀ Me:5i; 37%ꢂ20i; 20%
RꢀEt:5i; 31%ꢂ20i; 36%
Rꢀi-Pr:5i; 74%
PdCl2 or NiCl2
MePhSiH2ꢂ2i-C3H7I cat:
100 ꢀC
6
MePhSiI2ꢂ2C3H8
6i; 87%
(29)
Although partially brominated products were found
Trihydrosilanes such as PhSiH3 (7) and n-HexSiH3
(19) were also iodinated nicely with the use of i-PrI at
90 8C to give the corresponding triiodosilanes 7i and 19i
in high yields (Eq. (30)).
to be formed by GCꢁMS analyses of the reaction
/
mixtures in low yields in the bromination of di- and
trihydrosilanes, they were readily separated from the
perbrominated products by fractional distillation.
cat: PdCl2
RSiH3ꢂ3i-C3H7I
7; 19
RSiI3 ꢂ3C3H8
(30)
90 ꢀC
2.4.3. Halogenation of hydrogermanes
It has been reported that heating hydrogermanes with
7i; R ꢀ Ph; 80% 19i; Rꢀn-Hex; 86%
alkyl halides at 80ꢁ90 8C for several hours leads to the
/
formation of halogermanes in high yield [65]. In contrast
to this, PdCl2-catalyzed halogenaton of hydrogermanes
with allyl halides proceeded even at room temperature
(Table 3) [64b]. In these reactions, allyl halide must be
used as the halogen source. Indeed, no reactions
occurred when Hex3GeH (22) was treated with EtBr at
50 8C in the presence of the PdCl2 catalyst, while
Hex3GeBr (22j) was obtained in 80% yield by the
reaction with allyl bromide at room temperature.
Similarly, the reactions of Et3GeH (23), Ph3GeH (24),
Hex2GeH2 (25), and Ph2GeH2 (26) proceeded readily
with allyl bromide to give high yields of bromogermanes
2.4.2. Bromination of hydrosilanes
The HꢁBr exchange reactions of hydrosilanes with
/
alkyl or allyl bromides in the presence of a catalytic
amount of PdCl2 or NiCl2 also proceeded with the
liberation of alkanes to give brominated products in
good to high yields (Table 2) [64b]. The reactions
proceeded more rapidly when allyl bromide, rather
than ethyl and propyl bromide, was used as the halide.
Typically, PdCl2-catalyzed bromination of Me2PhSiH
(1) with EtBr or n-PrBr completed by refluxing the
mixture without solvent for 12 h, while with allyl
bromide, 1 was wholly consumed within 1 h to give
23jꢁ26j, respectively. On the other hand, a longer
/
reaction period was required to complete the tribromi-
nation of HexGeH3 (27) and the product HexGeBr3
(27j) was isolated in rather low yield (58%).
Table 2
Metal-catalyzed bromination of hydrosilanes
a
Silane
Bromide Catalyst b,
conditions
Product
(isolated yield)
Table 3
PdCl2-catalyzed halogenation at room temperature a
Me2PhSiH (1) EtBr
n-PrBr
PdCl2, 50 8C, 12 h Me2PhSiBr (1g, 88%)
PdCl2, 80 8C, 12 h 1g (94%)
b
Silane
Halide
Time (h) Product (isolated yield)
allylBr
allylBr
PdCl2, 80 8C, 1 h 1g (88%)
NiCl2, 80 8C, 16 h 1g (91%)
Et3GeH (23)
allylBr
allylBr
allylBr
allylBr
allylBr
allylBr
allylI
3
3
Et3GeBr (23j, 84%)
Hex3GeBr (22j, 80%)
Ph3GeBr (24j, 72%)
Hex2GeBr2 (25j, 92%)
Ph2GeBr2 (26j, 81%)
HexGeBr3 (27j, 58%)
Et3GeI (23k, 83%)
Hex3GeH (22)
Ph3GeH (24)
Hex2GeH2 (25)
Ph2GeH2 (26)
HexGeH3 (27)
Et3GeH (23)
MePh2SiH (2) EtBr
PdCl2, 50 8C, 36 h MePh2SiBr (2g, 76%)
PdCl2, 80 8C, 1 h 2g (91%)
NiCl2, 80 8C, 24 h 2g (78%)
3
allylBr
allylBr
6
4
53
6
Et2SiH2 (5)
EtBr
allylBr
PdCl2, 50 8C, 72 h Et2SiBr2 (5g, 61%)
NiCl2, 80 8C, 24 h 5g (85%)
Hex3GeH (22)
Ph3GeH (24)
Hex2GeH2 (25)
Ph2GeH2 (26)
HexGeH3 (27)
allylI
allylI
12
12
3
Hex3GeI (22k, 84%)
Ph3GeI (24k, 98%) c
Hex2GeI2 (25k, 80%)
Ph2GeI2 (26k, 75%)
HexGeI3 (27k, 87%)
MePhSiH (6) allylBr
allylBr
PdCl2, 80 8C, 36 h MePhSiBr2 (6g, 79%)
NiCl2, 80 8C, 50 h 6g (80%)
allylI
allylI
allylI
PhSiH3 (21)
allylBr
allylBr
PdCl2, 80 8C, 60 h PhSiBr3 (21g 88%)
NiCl2, 80 8C, 90 h 21g (65%) c
5
12
a
a
Bromide 1.4ꢁ
PdCl2 1 mol% or NiCl2 2ꢁ
NiCl2 (11 mol%) was added in eight portions in every 10ꢁ
/
4 equiv.
PdCl2 1ꢁ
/
3 mol%.
Halide 1.5ꢁ4 equiv.
Benzene was added after 6 h to dissolve the product Ph3GeI.
b
b
c
/
6 mol%.
/
c
/12 h.

A. Kunai, J. Ohshita / Journal of Organometallic Chemistry 686 (2003) 3ꢁ
/
15
11
The use of allyl iodide is also effective for the
iodination of hydrogermanes, compared to MeI. Thus,
when 22 was treated with an excess of MeI and a
catalytic amount of PdCl2 at 60 8C for 70 h, Hex3GeI
(22k) was found to be formed only in 25% yield,
together with 22 remaining in 70% yield. On the other
hand, similar reaction with allyl iodide for 12 h
produced 22k in 84% yield. In contrast to bromination,
the reaction of 27 with allyl iodide proceeded smoothly
to afford 27k in 87% yield. The use of NiCl2 as the
catalyst did not obviously accelerate the halogenation of
hydrogermanes.
the respective aliphatic ketones with the Me3SiNEt2ꢁ
/
MeI reagent [68].
More recently, we found in cooperation with Yama-
moto that treatment of 1:1 mixtures of hydrosilanes and
alkyl iodides with a catalytic amount of PdCl2 (R3SiHꢁ
/
R?IꢁPdCl2) produces high yields of iodosilanes by
/
hydride/iodide exchange [64]. In order to explore further
the scope of synthetic utilities of these reaction systems,
we studied ring-opening halosilylation of cyclic ethers
[69], acetals [70], and lactones [71], which are less
strained than epoxides, with Et3SiHꢁ
/
RXꢁPdCl2 and
/
Me3SiNEt2ꢁRX (RXꢀMeI, EtI, EtBr, AllylBr). The
/
/
In the present halogenation of hydrosilanes and
germanes, the formation of fine black precipitates was
observed, immediately after the contact of the reactants
with the catalysts. At the same time, the corresponding
reactions led to the one step synthesis of bifunctional v-
halo-a-siloxyalkanes (Eq. (31)). They may be potentially
useful in organic synthesis as silyl-protected hydro-
xyalkyl [72] or carboxyalkyl halides.
chlorosilanes were found to be formed by GCꢁMS
/
analysis of the reaction mixtures. This seems to indicate
that the actual active species in these reactions may be
metallic Pd and Ni, formed from the reduction of the
chlorides with hydrosilanes or germanes. Although we
have no clear evidences concerning the reaction mechan-
ism, we tentatively assume that the reaction proceeds via
ð31Þ
Some representative results are picked up in Table 4,
where four kinds of the reagent systems, Et3SiHꢁ
PdCl2 (A), Et3SiHꢁAllylBrꢁPdCl2 (A?), Me3SiNEt2ꢁ
MeI (B), and Me3SiNEt2ꢁAllylBr (B?) are employed.
/
MeIꢁ
/
/
/
/
homolytic Mꢀ
/
H (MꢀSi or Ge) bond cleavage on the
/
/
Pd (or Ni) surface to induce radical chain reactions, or
alternatively, via metathesis type reactions on the metal,
as estimated by occurrence of H/Me exchange in the
reaction of diethylsilane with MeI [16].
When THF was treated with 1 equiv of reagent A at
room temperature for 5 h, 1-iodo-4-triethylsiloxybutane
was obtained in 70% yield as the sole volatile product,
while the reaction with reagent A? at 80ꢁ90 8C for 10 h
/
afforded the corresponding bromosilylation product in
82% yield. The reaction of THF with reagent B (or B?)
also proceeded cleanly to give the similar products in
high yields. Similarly, tetrahydropyran underwent
smooth iodosilylation with reagent A (or B) to afford
1-iodo-5-(triethylsiloxy)pentane in 74% yield. Iodosily-
lation of 2-MeTHF and 2-tetrahydrofurfuryl alcohol
also proceeded smoothly to give the expected ring-
opened products (not shown in the table).
The reactions of cyclohexanone ethylene acetal with 1
equiv of reagent B proceeded smoothly to afford a ring-
opened siloxyethyl enol ether as the sole volatile product
in 76% yield, while N-methy-1,3-oxazolidine ring re-
acted with reagent B to give an enamine in 72% yield.
The formation of siloxyethyl enol ether is in contrast to
the fact that the reactions of ketone acetals with Me3SiI
give the corresponding deprotected ketones [73]. Similar
reactions have been reported for ketone dimethyl
acetals, whose reactions with Me3SiI in the presence of
a slight excess of hexamethyldisilazane give methyl enol
ethers by the loss of one methoxy group and an a-
hydrogen [74]. On the other hand, the reaction of
cyclohexanone ethylene acetal with reagent A proceeded
in a quite different manner and produced a dimeric
product in 63% yield. We tentatively assume that in this
case, dimerization of the acetal followed by Pd-assisted
2.5. Utility of halosilanes
2.5.1. Iodosilanes and bromosilanes
Iodo- and bromosilanes play a unique role in organic
synthetic chemistry and their synthetic utilities have
been demonstrated [2]. Interaction of cyclic ethers with
iodo- or bromotrimethylsilane affords the respective
ring opened iodo- or bromosilation products in good
yields [25c]. Iodo- and bromosilanes, however, exhibit
high tendency to undergo hydrolytic cleavage of the Siꢀ
/
halogen bond with atmospheric moisture leading to the
formation of the respective silanols, unless the silicon
atom is substituted by protecting substituent(s) with
appropriate steric bulkiness, and therefore, iodo- and
bromosilanes are usually difficult to handle as compared
with the other halosilanes, chloro- and fluorosilanes.
Yamamoto et al. reported that 1:1 mixtures of diethy-
laminotrimethylsilane with methyl iodide (Me3SiNEt2ꢁ
MeI) and allyl bromide (Me3SiNEt2ꢁAllylBr) behave as
synthetic equivalent reagents of Me3SiI and Me3SiBr,
respectively, and the reactions with epoxides afford the
corresponding ring-opened 1,2-halosilylation products
/
/
[66]. The Me3SiNEt2ꢁMeI reagent reacts also with alkyl
/
esters to give high yields of trimethylsilyl esters with
liberation of iodoalkanes [67]. It is also demonstrated
that silyl enol ethers are obtained from the reactions of
Cꢀ/C bond cleavage might be involved [70].

12
A. Kunai, J. Ohshita / Journal of Organometallic Chemistry 686 (2003) 3ꢁ15
/
Table 4
Ring-opening halosilyation of cyclic compounds at 80ꢁ90 8C
/
The ring-opening iodo- and bromosilylation of g-, d-,
and o-lactones with reagent A took place smoothly to
give respective O-silyl-protected v-haloalkanoic acids in
high yields, whereas reagent B was inactive towards
these lactones and the starting lactones were recovered
unchanged, probably bcause of steric hindrance of
reagent B. For reagent B, a silylammonium salt may
act as the active species (Eq. (32)).
reagents in two steps (Eq. (20)). The silanes have Siꢀ
/
Cl
and SiꢀF bonds, being different in reactivity, and
/
therefore, selective introduction of a nucleophile may
be possible. To demonstrate this, we carried out the
reaction of n-Hex2SiClF (19f) with organometallic
reagents, RM (Eq. (34)). As expected, when 19f was
treated with organolithium (Rꢀ
organomagnesium reagents (RꢀEt, Vi, Allyl) at ꢃ
50 8C, only the SiꢀCl bond reacted selectively to afford
fluorosilanes 28fꢁ32f. The SiꢀCl bonds in n-HexSiCl2F
/
Bu or PhCꢁ/C) or
/
/
/
Me3SiNEt2 ꢂMeIXMe3Si(NEt2Me)ꢂIꢃ
To demonstrate synthetic utility of the halosilylation
products, we examined conversion of Cꢀhalogen bonds
to CꢀN bonds as an example (Eq. (33)). Thus, treatment
(32)
/
/
(19f?), which was obtainable from 19c, also reacted
selectively with BuLi or AllylMgBr to give fluorosilanes
28g and 32g (Eq. (35)). Fluorosilanes thus obtained still
/
/
of the bromosilylated products with 2 equiv of diethyl-
or dibutylamine at 60 8C for 5 h produced the corre-
sponding O-silyl-protected amino acids in good yields.
keep a reactive Siꢀ
/
F bond, and thus, introduction of
another nucleophile is possible. They may be also
utilized as the reagent for building up sterically hindered
silicon-containing molecules.
The above findings have enabled us to design silicon
polymers with regular alternating arrangement of an Si
unit and p-electron system, in which different p-systems
could be introduced (Eq. (36)). Thus, the reaction of 19f
with a dilithio-p reagent afforded bis(fluorosilylethyny-
l)arenes selectively, which then reacted with another
dilithio-p reagent to give the desired alternating poly-
mers in moderate to good yields.
ð33Þ
RM
2.5.2. Chlorofluorosilanes
As discussed in Section 2.2, chlorofluorosilanes could
be obtained from hydrosilanes by using the copper
n-HexSiClF
19f
n-Hex2SiRF
(34)
ether; ꢃ50 ꢀC
28f; 82% (BuLi; 1 h) 31f; 89% (ViMgBr; 2:5 h)

A. Kunai, J. Ohshita / Journal of Organometallic Chemistry 686 (2003) 3ꢁ
/
15
13
28g; 76% (RM ꢀ BuLi; 1 h)
29f; 86% (PhCꢀCLi; 1 h)
some examples for their application have been demon-
strated using iodosilanes and chlorofluorosilanes.
Further studies on utilization of halosilanes are under
progress.
30f; 83% (EtMgBr; 5 h)
cat: PdCl2
n-HexSiH2F
n-HexSiCl2F
19f?
CCl4
19c
4. Experimental conditions
2RM
ether; ꢃ50 ꢀC
ꢁ
n-HexSiR2F
(35)
32f; 89% (AllylMgCl; 6 h)
4.1. General remarks
32g; 78% (RM ꢀ AllylMgCl; 6 h)
Representative procedures are shown below. All
reactions were carried out under an inert atmosphere.
(36)
3. Summary
Other reactions were also performed in similar manners.
For the purpose of bromination and fluorination with
copper reagents, CuBr2 or a 2:1 mixture of CuCl2 and
KF were used, respectively, in place of CuCl2 used in
chlorination.
We have discussed novel strategies for the synthesis of
various halosilanes from hydrosilanes. With the use of
Cu(II)-based reagents, selective chlorination, bromina-
tion, and fluorination of hydrosilanes could be achieved
to give various types of halosilanes, such as R3SiX,
R2SiHX, R2SiX2, RSiH2X, RSiHX2 (XꢀCl, Br, F),
/
4.2. Chlorination of MePhSiH2 with copper reagent
selectively in high yields. Mixed halosilanes like chloro-
fluorosilanes could be also obtained by applying this
method. The present method is also applicable to
selective chlorination of hydrogermanes. On the other
hand, iodo- and bromosilanes and germanes could be
To a pre-dried mixture of CuCl2 (252 mmol) and CuI
(6 mmol) in a 500-mL flask were added MePhSiH2 (6,
125 mmol) and dry ether (300 mL), and the mixture was
stirred at room temperature for 36 h. The resulting
mixture was filtered to remove copper salts, concen-
trated, and distilled to give MePhSiHCl (6a, 77% yield),
obtained in good yields by Pd- or Ni-catalyzed hydrideꢁ
/
halogen exchange reactions between hydrosilanes and
alkyl or allyl halides. Halosilanes and halogermanes
thus obtained may be utilized as useful starting materi-
als or reagents in fields of organometallic chemistry and
synthetic organic chemistry, for examples, as the build-
ing units for constructing silicon- or germane-containing
functionality materials and high coordination silicon
derivatives, and as the reagents for protecting labile
functional groups, hydrosilylating unsaturated bonds,
boiling point (b.p.) 76ꢁ78 8C/21 mmHg.
/
4.3. Chlorination of MePhSiHF with copper reagent
A mixture of CuCl2 (72 mmol), CuI (0.26 mmol),
MePhSiHF (6c, 37 mmol), and 100 mL of THF in a 200-
mL flask was stirred at room temperature for 10 h. The
mixture was filtered, concentrated, and distilled to give
cleaving Cꢀ
/
O bonds, introducing a silyl unit as the
synthetic auxiliary, and so on. In this point of view,
MePhSiClF (6f, 74% yield), b.p. 75ꢁ77 8C/30 mmHg.
/

14
A. Kunai, J. Ohshita / Journal of Organometallic Chemistry 686 (2003) 3ꢁ15
/
4.4. Pd-catalyzed iodination of Et3SiH
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77 8C/
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/
ꢃ
/
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