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Recognizing that the complexes of the type [(IPr)Pt(SiR ) ]
3
2
Table 4. Hydrosilylation of terminal alkynes.
are exceptional hydrosilylation precatalysts, we endeavored to
[12]
explore their potential. However, the single isolated member
of this family, [(IPr)Pt(SiMe Ph) ] 10, cannot be stored for more
2
2
than two days. Longer storage requires it to be kept away
[
13]
from light and under high vacuum in a sealed ampoule. For
this practical reason, we resolved to use the more convenient
activation pathway of the robust [(IPr)Pt(dvtms)] 5 by the
silanes, generating the 3rd generation precatalyst in situ for all
following hydrosilylation reactions.
[
a]
[b]
R’
R
3
SiH
Et
b/a
Yield [%]
1
2
3
4
5
6
7
8
9
1
nHex
nHex
nHex
nHex
nHex
nHex
nHex
nHex
nHex
nHex
Ph
3
SiH
SiO)Me
7:1
>20:1
96:1
41:1
13:1
>20:1
>20:1
>20:1
>20:1
>20:1
>20:1
>20:1
93
94
98
98
92
96
86
96
87
98
91
95
(Me
(Me
(Me
(Me
3
3
3
3
2
SiH
[c]
[c]
[c]
SiO)
SiO)
SiO)
2
MeSiH
2
MeSiH
2
MeSiH
[
[
d]
e]
The results of the hydrosilylation of silylated alkynes by our
new precatalysts are presented in Table 3. For every substrate,
the selectivities and yields were excellent. Interestingly, where-
(Me
PhMe
Ph MeSiH
Ph ClSiH
(EtO) MeSiH
3
SiO)
3
SiH
[
[
f]
2
SiH
2
g]
[
2
d]
h]
0
2
[
11
(Me
(Me
3
SiO)
SiO)
2
MeSiH
MeSiH
Table 3. Hydrosilylation of silylated alkynes.
1
1
1
2
3
4
3
2
(Me
3
SiO)
2
MeSiH
>20:1
>20:1
14:1
98
97
PhMe
PhMe
2
SiH
SiH
[h]
[i]
1
5
2
82
[
a]
[b]
R’
R
3
SiH
b/a
Yield [%]
[
c]
Performed on 3 mmol scale, with the exception of entry 4, which was
performed on 65 mmol scale. [a] Determined by H NMR spectroscopy on
the crude reaction mixture; [b] yield of product isolated by filtration
4
through a plug of silica gel/celite/MgSO , GC purity >95%; [c] deter-
mined by GC/MS on the crude reaction mixture; [d] 0.03 mol% precata-
lyst; [e] 0.01 mol% precatalyst; [f] 0.05 mol% precatalyst; [g] quenched
with ethanol/triethylamine and isolated as ethoxy(hexenyl)diphenylsilane;
1
2
3
4
5
nHex
tBu
Ph
Ph
Ph
(Me
(Me
(Me
PhMe
Ph MeSiH
3
3
3
SiO)
SiO)
SiO)
2
2
2
MeSiH
MeSiH
MeSiH
13:1
1:14
13:1
19:1
>20:1
97
82
97
88
90
1
2
SiH
2
1
Performed on 3 mmol scale. [a] Determined by H NMR spectroscopy on
the crude reaction mixture; [b] yield of product isolated by filtration
[h] 1 mol% precatalyst; [i] yield of product isolated by column
through a plug of silica gel/celite/MgSO
of precatalyst was used.
4
, GC purity >95%; [c] 0.1 mol%
chromatography on silica gel, GC purity>95%. Ts =para-toluenesulfonyl.
as an n-hexyl or a phenyl substituent directed the incoming
silyl group at the b position and afforded the expected (E)-bis-
lenges: a) both unsaturated groups can be hydrosilylated;
b) the 1,6-enyne system might poison the catalyst by chela-
tion; c) the double bond could direct the reversible 1,2-migra-
tory insertion toward the a isomer (see below). Therefore, this
substrate was introduced in one portion (see below) and the
catalyst loading was increased to 1 mol%. We were pleased to
note that there was no trace of hydrosilylation of the double
bond and that the vinylsilane could be obtained with excellent
regioselectivity. The perfect discrimination between both
unsaturations is attributed to the higher coordinating ability of
[7b]
silylvinyl products (Table 3, entries 1, 3–5), a bulky tert-butyl
group led to the opposite regioisomer (entry 2). This is in
agreement with a regioselectivity model governed by steric
effects (see below). Pleasingly, arylsilanes were perfectly
tolerated, leading to improved regioselectivities (Table 3, en-
tries 4 and 5).
The 3rd generation platinum precatalysts proved to be
exceptional promoters for the hydrosilylation of terminal acety-
lenes, affording exquisite selectivities for almost every sub-
strate examined (Table 4). Surprisingly, triethylsilane provided
relatively low regioselectivity levels, although the yields were
excellent (Table 4, entry 1). Notwithstanding this specific case,
every other silane scrutinized, including silyloxy-, aryl-, chloro-,
and alkoxysilanes, achieved high yields and outstanding selec-
tivities (Table 4, entries 2–10). It should be noted that the cata-
lyst loading could be reduced to 0.01 mol% while still main-
taining excellent selectivities (Table 4, entries 3–5). Moreover,
the procedure was scaled up to 65 mmol without any difficul-
[
15]
the alkyne (stronger p-acidity).
Finally, [(IPr)Pt(SiR ) ] precatalysts were evaluated in the
3
2
hydrosilylation of olefins (Table 5). 1-Octene and (+)-b-citronel-
lene were straightforwardly hydrosilylated with complete
regiocontrol (Table 5, entries 1 and 2). Epoxides (readily
opened with Karstedt catalyst 4) as well as alcohols were toler-
ated (Table 5, entries 3 and 4). The hydrosilylation of allyl
ethers and esters was carried out in good yields without
degradation through p-allyl platinum intermediates (Table 5,
entries 3–7), enabling us to easily assemble g-functionalized
propylsilanes, which are highly desired building blocks for
[14]
ties (Table 4, entry 4) and phenylacetylene was also success-
fully hydrosilylated (entry 11). Under these conditions, free al-
cohols were not silylated (Table 4, entries 12–14) and increased
steric hindrance proved not to be detrimental to the selectivity
[
6]
industrial applications.
Although allyl methacrylate was
easily polymerized, introducing a radical inhibitor minimized
this side reaction and the hydrosilylated adduct could be
obtained in good yields (Table 5, entry 7). Furthermore, the hy-
drosilylation of a 1,1-disubstitued alkene was also successfully
(
entry 13). It is important to point out that the reaction of the
tosylamine derivative (Table 4, entry 15) represents three chal-
Chem. Eur. J. 2015, 21, 17073 – 17078
17075
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