Platinum-Catalyzed Multicomponent Alcoholysis/Hydrosilylation and Bis-hydrosilylation of Alkynes with Dihydrosilanes

Article abstract of DOI:10.1002/cctc.201700390

A new method for the hydrosilylation of alkynes controlled by a platinum catalyst with a monophosphine ligand (called TBSO-MOP) was explored. The platinum-catalyzed multicomponent and sequential silylation reaction involving alkynes, alcohols, and dihydrosilanes resulted in the highly stereoselective and high-yielding construction of functional (E)-vinylsilyl ethers. Moreover, the one-pot bis-hydrosilylation of terminal alkynes with dihydrosilanes was also achieved with the same platinum catalyst system.

Full text of DOI:10.1002/cctc.201700390

Accepted Article
Title: Platinum-Catalyzed Multicomponent Alcoholysis/Hydrosilylation
and Bis-hydrosilylation of Alkynes with Dihydrosilanes
Authors: Li-Wen Xu
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ChemCatChem
10.1002/cctc.201700390
COMMUNICATION
Platinum-Catalyzed Multicomponent Alcoholysis/Hydrosilylation
and Bis-hydrosilylation of Alkynes with Dihydrosilanes
Jian-Xing Xu, Mu-Yi Chen, Zhan-Jiang Zheng, Jian Cao, Zheng Xu, Yu-Ming Cui, Li-Wen Xu*
(
(optional))
Abstract: A new type of hydrosilylation of alkynes controlled by
platinum catalyst with a monophosphine ligand (called as TBSO-
MOP) was presented in this work. The platinum-catalyzed
multicomponent and sequential silylation of alkynes and alcohols
with dihydrosilane, resulted in high stereoselective as well as high-
yield construction of functional (E)-vinylsilyl ethers. Moreover, the
one-pot bis-hydrosilylation of terminal alkynes with dihydrosilane
was also achieved with the same platinum catalyst system in this
work.
multiple bonds. However, the majority of these platinum
[
6]
catalysts deal with mono-hydrosilylation of alkynes. In contrast,
there are few reports on the one-pot bis-hydrosilylations and
related multicomponent alcoholysis/hydrosilylation of alkynes
with alcohols and dihydrosilanes. In fact, such one-pot
multicomponent reaction with general and excellent control in
stereoselectivity is an outstanding and not an easy task due to
the increased difficulty in the chemoselective control and
activation of Si-H bond as well as alkynes or alcohols.
a) Previous work
Catalytic hydrosilylation of carbon-carbon multiple bonds has
been extensively developed and proved to be effective
transformations to obtain synthetically valuable organosilicon
[
Si]-H or [Si]-H2
[Si]
[Si]
R
R
vs
R
R
R
[M] catalyst
R
[Si]
[
1]
compounds. Vinylsilanes, the product of the hydrosilylation of
alkynes, have found widespread applications in advanced
materials and modern organic chemistry as versatile building
[Si]-H or [Si]-H2
[M] catalyst
M] = Pt, Ru, Co, Fe, Rh, Ni, etc.
vs
R
R
[Si]
R
[
[
2]
blocks.
The metal-catalyzed hydrosilylation of alkynes is
b) This work
[Si]-OR'
arguably the most powerful and atom-economical methods for
the synthesis of these reagents in cross-coupling and
nucleophilic additions since it really offers potential for complete
R1
R2
R , R2 = aryl or alkyl
1
[Si]-H2
R1
R2
+
R'OH
[
1,2]
2
R
control of stereoselectivity.
While most of examples reported
[Pt] catalyst
P-Ligand
[
Si]
in the past decades have focused on the hydrosilylation of
R1
R1
[
1-3]
R2
R2 = H
terminal alkynes , only a few examples using transition-metal
catalysts have been used for monohydrosilylation of internal
alkynes without activated groups. Notably as one of hot topics,
rapid and considerable progress has been made in transition-
metal-catalyzed hydrosilylation of internal alkynes during the
Figure 1. From catalytic hydrosilylation of alkynes to multicomponent
silylation/hydrosilylation.
[
4]
past years. Indeed, one important issue in the hydrosilylation
of internal alkynes with hydrosilanes is the low reactivity and the
[4k]
[4,5]
Inspired by Tomooka’s work
reported on the platinum-
inherent difficulty to achieve good stereoselectivity.
It is thus
catalyzed hydrosilyation of internal alkynes, we want to explore
new multicomponent reaction with dihydrosilane, alkyne, with
alcohol. Herein, we reported our effort on the development of
chemoselective bis-hydrosilylation of terminal alkynes and
cascade silylation/hydrosilylation of internal alkynes with
dihydrosilanes and alcohols (Figure 1). Both processes are
highly selective for the formation of alkenylsilyl ethers and bis-
vinylsilanes from internal and terminal alkynes respectively.
of great importance to broaden the hydrosilylation of alkynes to
multicomponent silylation, as it would open up new strategy to
design structurally diverse organosilicon compounds.
Owing to its high catalyst turnovers, platinum complexes, are by
far the well-developed catalysts for the hydrosilylation of C-C
[*]
Mr. J.X. Xu, Dr. Z.J. Zheng, Dr. J. Cao, Dr. Z. Xu, Dr. Y.M. Cui, Prof.
Dr. L.W. Xu
Furthermore,
we
have
developed
a
type
of
Key Laboratory of Organosilicon Chemistry and Material Technology
of Ministry of Education, Hangzhou Normal University, P. R. China
E-mail: liwenxu@hznu.edu.cn
platinum/monophosphine catalyst system with high level of
stereoselective induction, for these catalytic hydrosilylations of
alkynes with dihydrosilane.
Prof. Dr. L.W. Xu
State Key Laboratory for Oxo Synthesis and Selective Oxidation
Lanzhou Institute of Chemical Physics, Chinese Academy of
Sciences, P. R. China
This Project was supported by the National Natural Science
Founder of China (No. and 21472031 and 21503060), and Zhejiang
Provincial Natural Science Foundation of China (LR14B030001 and
LY14B020013). This work is also supported partially by Science and
Technology Department of Zhejiang Province (2015C31138), and
Hangzhou Science and Technology Bureau of China
Our group has recently been interested in the development of
novel P-ligands for transition metal-catalyzed transformations.
To begin this study, we first examined the capacity of TADDOL-
derived monophosphoramidite ligand, BINAP as well as other
phosphine ligands to mediate the platinum-catalyzed
hydrosilylation of diphenylacetylene with methylphenylsilane in
the presence of an equivalent of ethanol (Table 1). The reaction
[**]
was carried out in the presence of 1 mol% Pt
triphenylphosphine (PPh ) in toluene at room temperature to
afford three products 3a, 4a, and 5a, with a ratio of 88:3:9, arise
2 3
(dba) and 2 mol%
(20140432B04).
3
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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ChemCatChem
10.1002/cctc.201700390
COMMUNICATION
from alcoholysis and hydrosilylation reaction (see Table 1, entry
As shown in Table 1, we screened numerous phosphine ligands
(see Table 1, Entries 5-18), including commercially available
phosphine ligands (such as dppp, i-Pr-BPE, BINAP and
4
). And the isolated yield of 3a was quite promising (45%).
[7]
2 3
Notably, Karstedt catalyst or Pt (dba) was not effective under
[
8]
[9]
ligand-free reaction conditions (Entries 2 and 3). These findings
prompted us to further investigate the ligand effect on the
platinum-catalyzed cascade alcoholysis and hydrosilylation.
SegPhos) and our Ar-NNPs (L2) , Fei-Phos (L4) , Xing-Phos
[
10]
[11]
[12]
(L6)
,
Tao-Phos (L7)
,
and other ligands (L8-L12)
.
Pleasingly, a significant increase in the chemoselectivity as well
as the yield was observed when the ligand L9 (simplified as
[
12]
Table 1. Ligand screen of platinum-catalyzed hydrosilylation of
TBSO-MOP)
was used on in this reaction, which gave only
diphenylacetylene with methylphenylsilane in the presence of ethanol:
[
a]
the 3a in excellent chemoselectivity and excellent yield (see
Table 1, entry 15, 3a/4a/5a = >99:<1:<1, 84% isolated yield of
Cascade alcoholysis and hydrosilylation.
Ph
Ph
Ph
Pt2(dba)3 (1 mol%)
Ligand (2 mo%)
(
E)-vinylsilyl ether 3a). In fact, almost no side-product was
O
Ph
+
O
O
Ph
1
+
a
Ph
Si
Si
+
observed in this reaction (>98% yield by HNMR analysis).
Therefore, the reaction conditions would be suitable for facile
preparation of functional vinylsilyl ethers. It is fortunate finding
that we encountered a multicomponent reaction amenable with
sequential alcoholysis and hydrosilylation, in which the
monophosphine, such as TBSO-MOP (L9), the Ar-NNP (L2),
and Xing-Phos (L6), play vital role in controlling the reactivity of
alcohol and methylphenylsilane in the step-by-step alcoholysis
and hydrosilylation reaction (>98:1 chemoselectivity). The other
ligands that are likely to have considerably different coordination
characteristics or other complications were proved to be
disadvantageous ligands in this reaction, which provide useful
information for the controlling of platinum catalyst system in
hydrosilylation. For example, biphosphine ligand (dppp, BINAP,
Fei-Phos) or alcohol-containing phosphine (Tao-Phos) is not
effective in the formation of active platinum(0) catalyst. As a
supplemental experiment, we also investigated the solvent effect
on the Pt (dba) /L9 –catalyzed multicomponent reaction of
Toluene or
other solvent, RT
Ph
Ph
Ph
C2H5OH
SiH2
4a
5a
3a
2
a
O
Ph2P
Me
O
O
N
PAr2
PAr2
PPh2
PPh2
PPh2
N
O
Me
Ph2P
L3
L1
BINAP
L2
Ar-NNPs
L4
Ar = 3,5-di-t-Butyl-4-methoxyphenyl
DTBM-SegPhos
Fei-Phos
PPh2
Ph
Ph
O
H
N
O
O
S
PPh2
IPr
OH
OH
P
N
OTf
PPh2
O
O
Ph
TMS
N
O
Ph
Ph
L5
IPr
L6
Xing-Phos
L7
Tao-Phos
L8
Si
O
O
NH
O
PPh2
Ph
S
2
3
N
H
O
HN
O
diphenylacetylene with methylphenylsilane and ethanol (Entries
9-21, with inferior yields, up to 58%), and thus we were pleased
L9
TBSO-MOP in this work)
1
(
L10
L11
L12
[
b]
to find that the toluene was enough good for the chemoselective
construction of functional silyl ether bearing four different groups.
And interestingly, the use of excess amount of ligand L9
resulted into decreased yield. Notably, the catalytic efficiency of
Entry
Pt cat.
Ligand
Solvent
3a:4a:5a
Yield
[
c]
(%)
1
2
3
none
-
Toluene
Toluene
Toluene
-
-
-
N.R.
N.R.
N.R.
2
Pt (dba)
3
-
Karstedt
Cat.
-
2 3
Pt/L9 is promising when 0.25 mol% Pt (dba) and 0.5 mol% L9
were used in this reaction (See Table S1 of Supporting
Information). In fact, we found that the conversion of substrates
was quite fast and this reaction could be completed within 30
min in the presence of 1 mol% of Pt/L9 (About the kinetic
information, see Figure S1 of Supporting Information). Although
the enantioselectivity for the construction of silicon-stereogenic
center on product 3a is not good in the multicomponent silylation
of alkynes and alcohols with dihydrosilane (4% ee, see Scheme
4
5
6
7
8
9
Pt
Pt
Pt
Pt
Pt
Pt
Pt
Pt
Pt
Pt
Pt
Pt
Pt
Pt
Pt
Pt
Pt
Pt
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
(dba)
(dba)
(dba)
(dba)
(dba)
(dba)
(dba)
(dba)
(dba)
(dba)
(dba)
(dba)
(dba)
(dba)
(dba)
(dba)
(dba)
(dba)
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
PPh
dppp
Pr-BPE
L1
L2
L3
L4
L5
L6
L7
L8
L9
L10
L11
L12
L9
3
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
DCM
88:3:9
-
87:3:10
-
99:<1:1
72:16:12
45
N.R.
77
N.R.
70
i
40
10
11
12
13
14
15
16
17
18
19
20
21
-
-
N.R.
trace
66
N.R.
N.R.
84
98:1:1
-
-
>99:<1:<1
88:2:10
76:4:20
86:2:12
N.D
1), a new type of multicomponent hydrosilylation of alkynes
controlled by platinum catalyst with TBSO-MOP was determined
in this work.
72
54
63
[
d]
36
58
Ph
Ph
Pt (dba)3 (1 mol%)
L9 (2 mo%)
Ph
2
Si
[
d]

Si
O
L9
L9
THF
N.D
N.D
1a
+
O
Ph
PPh2
CH
3
CN
Trace
(0.4
mmol), EtOH (0.4 mmol), platinum complex (1 mol%), ligand (2 mol%), solvent
Toluene or
other solvent, RT
Ph
Ph
C2H5OH
[
a]
SiH2
Note:
Reaction conditions: Diphenylacetylene (0.4 mmol), PhMeSiH
2
2a
3a
8
4
4% yield
% ee (Si)
L9
(TBSO-MOP in this work)
(
2 mL). Reaction time is 12 hours for every case. N.R is no reaction; trace
Scheme 1. The preliminary result for the catalytic construction of Si-
stereogenic vinylsilyl ether 3a.
[
b]
represented <5% yield; N.D is not determined.
Determined by GC-MS
[
c]
[d]
1
analysis. Yields of isolated product 3a. yield was determined by H NMR.
2 3
Utilizing the Pt (dba) as the precatalyst, we examined the
alkyne and alcohol substrate scope of the multicomponent
silylation (Scheme 2). Under the optimal conditions using TBSO-
i
dppp
=
1,3-bis(diphenylphosphino)propane. Pr-BPE
=
1,2-bis(trans-2,5-
diisopropylphospholano)ethane.
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ChemCatChem
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COMMUNICATION
MOP (L9) as ligand, a variety of alkynes bearing electron-
withdrawing or electron-donating substituents on the phenyl ring
underwent the step-by-step alcoholysis and hydrosilylation
reaction with methylphenylsilane and alcohols to afford the
corresponding silyl ethers in high yields and excellent
chemoselectivities (up to 88% isolated yield).
gel chromatography. On the other hand, ortho-substituted alkyne
and heterocycle-containing alkynes also gave the corresponding
products in good yields. Alkyl alkyne was also proved to be
suitable for this method to produce ether-functionalized
vinylsilane in moderate yield in this reaction. The unsymmetric
internal alkyne, such as 1-(prop-1-ynyl)benzene (1n), was also
suitable for platinum-catalyzed multicomponent alcoholysis and
hydrosilylation to give the corresponding product in 60% yield
and 88:12 ratio of 3n/3n′ (Scheme 2). The sequential
alcoholysis/hydrosilylation of diphenylacetylene gave the
corresponding 3o with good yield (73%).
Pt2(dba)3 (1 mol%)
TBSO-MOP (2 mo%)
Ph
Ph
R
R
+
+
O
Ph
R'OH
SiH2
R'
Si
Ph R'
R'
Toluene, RT, 30 min
1
2
R' = Me, Ph
3
Ph
Pt (dba) (0.1 mol%)
2
3
Si
O
H2
Si
Ph O R
Ph
H
TBSO-MOP (0.2 mol%)
+ ROH
Si
+
Si
R
(1)
Pt
Ph
Me
Me
O
P
Ph
Ph
Toluene (2 mL)
r.t., 8 h
Me O R
O
0.4 mmol 0.4 mmol
>
99% conversion
4 (d)
4' (m)
Ph
Ph
Without Pt catalyst: No conversion
Without TBSO-MOP: No conversion
R = Me, m/d = 93:7
R = Et, m/d = 95:5
R = i-Pr, m/d = >99:1
Ph
Ph
Ph
O
Ph
Ph
Ph
O
O
Ph
Si
Ph
O
Ph
Si
Si
Si
Ph
3d
66% yield
Ph
Pt2(dba)3 (2 mol%)
TBSO-MOP (4 mol%)
Me Si
Ph
Ph
H2
Si
H
+
3
c
3a
3b
75% yield
Ph
Me
Toluene (2 mL)
(2)
8
5% yield
8
4% yield
r.t., 48 h
0
.4 mmol
Ph
6
0.4 mmol low conversion
Ph
Ph
Trace product
(<5% yield)
Ph
Si
Si O
Ph
Si O
Fe
O
Scheme 3. The determination of initial step via platinum-promoted alcoholysis
reaction of methylphenylsilane with various alcohols in the absence of internal
alkyne (eq. 1) and hydrosilylation of internal alkyne without alcohol (eq. 2).
Ph
Ph
Ph
Ph
3f
Ph
3
e
3
g
7
6% yield
6
0% yield
8
6% yield
Ph
Et
0 3
Pt (L )
Ph
Et
2
Ph
Et
O
L9
H
Si O
Si O
L0 = dba
Si
Si Pt L9
MeO
OMe
Br
Ph
Ph
Ph
VII
Br
Ph
H
L0 Pt(0) L9
3
i
Ph
I
Ph
3h
F3C
3j
68% yield
CF3
F
Pathway B
(unfavoured)
6
8% yield
7
0% yield
Si Pt L9
F
side product 5a
H
Ph
S
Ph
SiH2
II
SiH2
O
Et
O
Si
S
Si
Ph
Ph
OEt
Si Pt L9
Ph
H
O
O
Ph
3k
Si
Ph
Si Pt L9
3
l
3m
88% yield
Si
Et
4
7% yield
Ph
8
2% yield
Ph
3a
H
Ph
VI
II
Ph
Me
Ph
O
60% yield
n/3n' = 88:12
O
Ph
O
Ph
Me
Si
Si
+
Si
C2H5OH
3
Ph Ph
Ph
H
2 5
C H
Ph
Ph
H
O
Ph
3
o
OEt
Si Pt L9
Pathway A
(favoured)
OEt
Si OEt
Si Pt L9
3n
3n'
73% yield
H
H
III
side product 4a
V
Scheme 2. One-pot multicomponent alcoholysis/silylation of various alkynes.
Reaction conditions: Alkyne (0.4 mmol), PhMeSiH (0.4 mmol ), alcohol (0.4
Pathway C
(
unfavoured)
2
mmol), platinum complex (1 mol%), TBSO-MOP ligand (2 mol%), toluene (2
mL), at room temperature for 30 min..
H
Ph
OEt
Si Pt L9
Si OEt
H
Ph
IV
Figure 2. Proposed mechanism for the platinum-catalyzed cascade
alcoholysis and hydrosilylation of internal alkyne with methylphenylsilane and
alcohol.
As shown in Scheme 2, the catalyst system enabled the
alcoholysis and hydrosilylation of structurally diverse alcohols
and alkynes with methylphenylsilane as an assembled model,
providing the corresponding (E)-vinylsilyl ethers with high
stereoselectivity. The (Z)-isomers and simple vinylsilanes were
never observed. Notably, the conversion of such reaction is
almost quantitative in most of cases and the isolated yield was
slightly lost because of the purification of silyl ethers with silica
[
[
13]
14]
Although both the platinum-catalyzed alcoholysis of silanes
and hydrosilylation of alkynes with monoalkoxyldialkylsilane
were known, it would be interesting to note that the hydrolytic or
alcoholytic oxidation reaction of silanes with water or alcohols is
a hot topic that has been recently described with other transition
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ChemCatChem
10.1002/cctc.201700390
COMMUNICATION
[
15]
metals.
Notably, there is no report for the multicomponent
products is 97:3). And we found that the activity of L9 is better
than that with L8, whereas the hydrosilylation reaction was
completed in the shorter time in the presence of TBSO-MOP
(L9). Notably, the one-pot bis-hydrosilylations of alkynes with
dihydrosilanes have received significantly less attention. Thus
we used the TBSO-MOP (L9) in the further studies on the
platinum –catalzyed bis-hydrosilylation of alkynes with
phenylmethylsilane.
alcoholysis/hydrosilylation of alkyne, alcohol, and dihydrosilane.
A primary reason for this scarcity is that chemoselectivity can be
difficult to control when applying dihydrosilanes as substrates. In
this work, it is interesting to find that the alcoholysis of
dihydrosilane is quite fast (Scheme 3, eq. 1). For example, the
major product is monomethoxymethylphenylsilane (4′, m) but not
dimethoxymethylphenylsilane (4, d) when methanol and
methylphenylsilane was used in this reaction (m/d = 93:7).
Notably, this reaction did not work in the absence of platinum
catalyst or ligand. However, the hydrosilylation of
diphenylacetylene with methylphenylsilane gave only a trace of
the desired product 6 in the absence of alcohol (Scheme 3, eq.
), which supported indirectly that the platinum-catalyzed
hydrosilylation of alkyne, alcohol, and disilane, occurred by step-
by-step alcoholysis and hydrosilylation.
On the basis of the experimental data and precedents regarding
relevant platinum-catalyzed hydrosilylation reaction
propose a multistep mechanism in which the addition of
methylphenylsilane to platinum species I and the subsequent
alcoholysis would be the first step (See Figure 2). Most likely for
steric reasons, the initial reaction of methylphenylsilane with
alcohol would be favorable and resulted into facile alcoholysis of
hydrosilane to form etherified platinum species IV, which then
reacted with internal alkyne to form the desired product by
[
17]
Table 2. Platinum/TBSO-MOP –catalyzed bis-hydrosilylation of terminal
[
a]
alkynes.
PhR'SiH2
R' Ph
Si
R' Ph
Si
Pt2(dba)3 (1 mol%)
R
TBSO-MOP (2 mol%)
+
2
R
Toluene, RT, 2 h
no alcohol)
R
(
7
R
R
6
R' = Me, Ph
1
0
b
c
Entry
R
R'
Yield (%)
7a: 93
7b: 80
7c: 92
7d: 93
7e: 87
7f: 84
7:10
1
2
3
4
5
6
7
[a]
H
4-F
Me
Me
Me
Me
Me
Me
Ph
97:3
97:3
88:12
95:5
95:5
95:5
95:5
[
6,7,16]
, we
4-Cl
4-t-Bu
4-Me
4-MeO
H
7g: 65
2
Note: 1-ethynylbenzene (2 eq.) and PhR'SiH (1 eq.) was used in this
[b]
[c]
reaction. Isolated yields. The ratio of 7:8 was determined by GC-MS and
1
confirmed by H-NMR.
classic hydrosilylation.
Ph
OEt
Pt2(dba)3 (1 mol%)
TBSO-MOP (2 mol%)
Si
Si Pt(0) L9
Ph
Ph
H
Si Pt(0) L9
SiH2
eq.
+
EtOH
1 eq.
+
Toluene, RT
TM
VI'
Ph
Result:
Ph
1
1
eq.
7
a/8a/TM = 63:30:7 (GC data)
V'
Ph
no 9a and 10a in this case
Ph
Si
H
Ph
Ph
Ph
Ph
Si
SiH
Si
Ph
Ph
Si
Ph
+
+
side product
Ph
Pt(0) L9
II'
Si
+
Ph
Me
Ph
Ph
7a
8a
9a
10a
TM
H
H
Scheme 4. Platinum/ TBSO-MOP –catalyzed multicomponent silylation of 1-
ethynylbenzene with methylphenylsilane and ethanol: Desired product TM and
possible side-products 7-10.
Pt(0) L9
Si
Si Pt(0) L9
IV'' (minor)
Pt2(L0)3
(
L0 = dba)
IV'
Encouraged by these results with platinum/TBSO-MOP, we
decided to explore the reactivity of terminal alkynes in this
cascade alcoholysis and hydrosilylation under the optimized
reaction conditions. As shown in Scheme 4, no vinylsilyl ether
PhMeSiH2
L9
Ph
H
Si Pt(0) L9
L0 Pt(0) L9
H
(
TM) was observed according to
a
multicomponent
I'
III'
L0
alcoholysis/silylation analogous to that described in Scheme 2,
and symmetric vinylsilane 7a was a major product. More
interestingly, when 2 equiv. of 1-ethynylbenzene was used in
this reaction, good yield of 7a was obtained (81%) in the
presence of ethanol. In order to clarify the pronounced influence
caused by the phosphine ligand, control and additional
experiments were conducted in the absence of alcohol (See
Table S2 of Supporting Information). Although L4 and L7
Ph
Ph
Pt(0) L9
PhMeSiH2
II'
Figure 3. Proposed mechanism for the platinum-catalyzed bis-hydrosilylation
of terminal alkyne with methylphenylsilane in the absence of alcohol.
Then to delineate the scope of the bis-hydrosilylation, we
studied the bis-hydrosilylation of various terminal alkynes with
methylphenylsilane (Table 2). All reactions were highly selective
for generation of di-(E)-vinylsilanes 7a-g with good to excellent
yields (up to 97:3 and 93% yield), and other side-products or
isomers 8 or 9 were never detected. Notably, regarding the
reactivity and stereochemistry of bis-hydrosilylation, in most
cases the presence of the side-product 10a was detected in the
promote
platinum-catalyzed
monohydrosilylation
of
1-
ethynylbenzene with good chemo- and stereoselectivity to give
di-(E)-vinylsilane 7a in good yield and stereoselectivity, both the
TBSO-MOP (L9) and L8 were still the best ligands in the
platinum-catalyzed bis-hydrosilylation of 1-ethynylbenzene.
Complete conversion as well as excellent chemoselectivity
1
(
>99% conversion and 93% isolated yield, and the ratio of two
H-NMR spectra of the crude mixtures. And the plot of yield
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versus time (min) showing the reaction rate as well as
consumption of phenylmethylsilane for the Pt/L9 –catalyzed bis-
silylation reaction of 1-ethynylbenzene with methylphenylsilane
was provided in Figure S2 (supporting Information), which
revealed the bis-hydrosilylation was performed by cascade
hydrosilylation. These results also suggest that the mechanism
of platinum-catalyzed bis-hydrosilylation is similar to that
previously reported with the usual platinum catalysts , in which
the terminal alkyne bind firstly to the coordinatively unsaturated
Pt(0)-ligand species and thus activate the terminal alkyne for
double hydrosilylation efficiently (See Figure 3, alkyne
coordination followed by oxidative addition).
In summary, we have developed successfully a new type of
hydrosilylation of alkynes controlled by platinum catalyst with a
monophosphine ligand, called as TBSO-MOP. The platinum-
catalyzed multicomponent silylation of alkynes and alcohols with
dihydrosilane, resulted in high stereoselectivity as well as high-
yield construction of functional (E)-vinylsilyl ethers. Moreover,
the one-pot bis-hydrosilylation of terminal alkynes with
dihydrosilane was also achieved with the same platinum catalyst
system. We have shown the powerful potential of phosphine
ligand bearing silicon-based bulky group in chemoselectivity-
controllable platinum-catalyzed multicomponent silylation.
Further studies, such as the detailed mechanism of ligand-
controlled platinum- catalyzed cascade alcoholysis and
hydrosilylation as well as bis-hydrosilyation, are underway in our
group and will be reported in near future.
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Entry for the Table of Contents (Please choose one layout)
Layout 1:
COMMUNICATION
Pt2(dba)3 (1 mol%)
Controllable hydrosilylation: It is
an interesting example to reveal
clearly the powerful potential of
phosphine ligand bearing silicon-
based bulky group, a
R1
R2
TBSO-MOP (2 mol%)
Toluene, RT
Jian-Xing Xu, Zhan-Jiang Zheng, Jian
Cao, Zheng Xu, Yu-Ming Cui, Li-Wen
Xu*
R1
Si OR3
R2
+
Ph
3
SiH2 R OH
Si
O
Page No. – Page No.
PPh2
monophosphine ligand, called as
TBSO-MOP, in chemoselectivity-
controllable platinum-catalyzed
multicomponent hydrosilylations of
alkynes with dihydrosilane, which
gave high yields of (E)-vinylsilyl
ethers and di-(E)-vinylsilanes
respectively.
Platinum-Catalyzed Multicomponent
Alcoholysis/Hydrosilylation and Bis-
hydrosilylation of Alkynes with
Dihydrosilanes
R
TBSO-MOP
Pt2(dba)3 (1 mol%)
TBSO-MOP (2 mol%)
R
R
Si
+
Ph
SiH2
R
Toluene, RT
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