Angewandte
Communications
Chemie
corresponding chlorosilanes. Importantly, di- and trihydrosi-
lanes can be selectively chlorinated in a stepwise manner
when 2 is used as the catalyst. A mechanism for these
chlorination reactions is proposed on the basis of both
competition experiments and DFT calculations.
presence of 2 (10 mol%) and HCl, Me Si(Cl)H was chlori-
2
nated to give Me SiCl at room temperature in 16 h (Table 1,
2
2
entry 2). The chlorination of Ph Si(Cl)H was significantly
2
slower, and after 6 days in presence of 2 (10 mol%) had
reached only 61% conversion into Ph SiCl (Table 1, entry 3).
2
2
We first attempted the stoichiometric reaction of Me Si-
The silyl-substituted hydrosilane tBuMe Si(Me) SiH under-
2 2
2
(
Cl)H with 1 and excess LiCl as the chloride source in toluene.
went chlorination to give tBuMe Si(Me) SiCl cleanly in 18 h
2 2
However, this reaction did not lead to the chlorination of the
(Table 1, entry 4). This method is also compatible with silanes
bearing a siloxy group; thus, Ph (Et SiO)SiH was converted
SiÀH bond, and Me Si(Cl)H remained intact. We assumed
2
2
3
that the low solubility of LiCl was the reason for the lack of
reactivity in this system. Therefore, to increase its solubility,
into the corresponding silyl chloride in 16 h (Table 1, entry 5).
Interestingly, in many of these catalytic reactions, donor-
1
9
Et O was added to the reaction mixture. Immediately after-
2
free 1 was observed by F NMR spectroscopy after the
wards, an NMR spectrum of the mixture showed the partial
conversion of Me Si(Cl)H into Me SiCl and the formation of
reaction. To check whether Et O had any effect on these
2
reactions, we performed the chlorination of Et SiH with 1. We
2
2
2
3
the salt [Li][HB(C F ) ] (Scheme 1). The addition of HCl to
found that, in contrast to the reaction with LiCl, in which
Et O was necessary, this reaction yielded Et SiCl quantita-
6
5 3
this reaction mixture resulted in the evolution of H gas and
2
2
3
the regeneration of 1 (Scheme 1). We therefore decided to
attempt the catalytic chlorination of hydrosilanes with HCl
and a catalytic amount of 2.
tively in 15 min (Table 1, entry 6). The reaction of Ph SiH
2 2
with HCl and 2 (1 mol%) gave the product of monochlori-
nation, Ph Si(H)Cl, with complete conversion after 16 h
2
(
(
(
Table 1, entry 7). The chlorination of PhMeSiH2 with 2
1 mol%) yielded the monochlorination product, PhMeSi-
Cl)H, after 12 min (Table 1, entry 8). The product of
dichlorination was obtained quantitatively from PhMeSiH2
upon stirring for 16 h with 2 (10 mol%; Table 1, entry 9).
Even though Et O in 2 did not have an effect on the
2
chlorination reactions of Et SiH and Me Si(Cl)H, it had
a very substantial effect on the selectivity of the chlorination
3
2
Scheme 1. Stoichiometric chlorination of Me Si(Cl)H with 1 and LiCl
as the chloride source.
2
of PhSiH . Hence, PhSiH in the presence of 2 (10 mol%) and
3
3
HCl gave PhSi(Cl)H and PhSi(H)Cl in an 84:16 ratio after
2
2
1
0 min (Table 1, entry 10). However, when 1 (10 mol%) was
First, we treated Et SiH with 2 (1 mol%) in toluene and
used as the catalyst for the same reaction, an 87:13 mixture of
PhSi(H)Cl2 and PhSi(Cl)H2 was obtained after 10 min.
(Table 1, entry 13). The reaction of PhSiH3 with 2
3
[
24]
HCl. After 15 min, the chlorination product, Et SiCl, was
3
1
29
observed by H– Si HMBC NMR spectroscopy as the only
silicon-containing product (Table 1, entry 1). A control
(10 mol%) gave a mixture of mono- and dichlorinated
products, PhSi(H)Cl (88%) and PhSi(Cl)H (12%), after
experiment in which Et SiH was treated with HCl without
3
2
2
a catalyst did not give any conversion into Et SiCl. In the
16 h (Table 1, entry 12). In contrast, only the dichlorinated
product PhSi(H)Cl2 was obtained
3
Table 1: Chlorination of Si
ÀH bonds under the catalysis of 1 (or 2).
upon stirring with 1 (10 mol%) at
room temperature for 16 h (Table 1,
entry 15). When a smaller amount
of 2 (1 mol%) was used for the
chlorination of PhSiH , the reaction
led to the selective formation of the
monochlorinated product, PhSi-
[
a]
3
Entry
R4 SiHn
Catalyst (mol%)
t [h]
0.25
16
150
18
Product (yield )
Àn
1
2
Et SiH
2 (1)
Et SiCl (99)
3
3
Me Si(Cl)H
2 (10)
2 (10)
2 (10)
2 (1)
1 (1)
2 (1)
Me SiCl (90)
2
2
2
(Cl)H2 (Table 1, entry 11). The
[
b]
3
4
5
6
7
8
9
0
1
2
3
4
5
Ph Si(Cl)H
Ph SiCl (61)
2 2
2
same amount of 1 led to the for-
tBuMe Si(Me) SiH
tBuMe Si(Me) SiCl (99)
2 2
Ph (Et SiO)SiCl (ca. 90)
2 3
2
2
mation of PhSi(Cl)H in 94% yield
2
Ph (Et SiO)SiH
16
2
3
(Table 1, entry 14). Notably, no
Et SiH
0.25
16
0.20
16
0.17
0.17
16
0.17
0.17
16
Et SiCl (99)
3
3
Ph SiH2
Ph Si(Cl)H (99)
PhMeSi(Cl)H (99)
PhMeSiCl (99)
PhSi(Cl)H (84), PhSi(Cl) H (16)
PhSi(Cl)H (>99.5), PhSi(Cl) H (<0.5)
2 2
PhSi(Cl)H (12), PhSi(Cl) H (88)
2 2
PhSi(Cl)H (13), PhSi(Cl) H (87)
2 2
PhSi(Cl)H (94), PhSi(Cl) H (6)
alkylÀSi, ArÀSi, SiÀSi, or SiOÀSi
2
2
[
b]
PhMeSiH2
PhMeSiH2
2 (1)
bond cleavage, which often occurs
2 (10)
2 (10)
2 (1)
2 (10)
1 (10)
1 (1)
2
when previously reported halogen-
1
1
1
1
1
1
PhSiH3
[6,25]
2
2
ation methods are used,
was
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
[
[
c]
observed in these catalytic reac-
tions.
We believe that, similarly to
2
2
b]
[4–7,26]
1 (10)
PhSi(Cl) H (99)
hydrosilylation catalyzed by 1,
2
1
the activation of SiÀH bonds by 1 is
the key step in the chlorination of
hydrosilanes with HCl. Thus, the
[
a] Yields were calculated by H NMR spectroscopy. [b] PhMeSiCl , Ph SiCl , and PhSi(Cl) H were also
2 2 2 2
obtained selectively in a stepwise chlorination reaction. [c] Full conversion into PhSi(Cl) H was observed
after the addition of another portion of HCl and stirring for another 10 h.
2
2
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Angew. Chem. Int. Ed. 2017, 56, 1 – 6
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