Efficient Pd(O)-catalyzed hydrosilylation of alkynes with triorganosilanes

Article abstract of DOI:10.1055/s-2002-33535

An electron-rich Pd(0) complex, a Pd₂(dba)₃·CHCl₃- tricyclohexylphosphine combination catalyzes highly efficient hydrosilylation of alkynes at room temperature with Ph₃SiH or Ph₂MeSiH without solvents

Full text of DOI:10.1055/s-2002-33535

LETTER
1529
Efficient Pd(0)-Catalyzed Hydrosilylation of Alkynes with Triorganosilanes
Efficient
P
d(0)-C
a
a
talyzed Hyd
i
rosilylation
o
M
f
A
lkynes otoda, Hiroshi Shinokubo, Koichiro Oshima*
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
Fax +81(75)7534863; E-mail: oshima@fm1.kuic.kyoto-u.ac.jp
Received 20 May 2002
Abstract: An electron-rich Pd(0) complex, a Pd2(dba)3 CHCl3–tri-
cyclohexylphosphine combination catalyzes highly efficient hy-
drosilylation of alkynes at room temperature with Ph3SiH or
Ph2MeSiH without solvents. The regioselectivity of this process is
higher than that with the conventional Pt(0)-catalyzed hydrosilyl-
ation.
Key words: hydrosilylation, palladium, phosphine, alkyne, alkene
Scheme 1
Transition metal-catalyzed hydrosilylation of alkenes and
alkynes has been extensively investigated, and have found
widespread application ranging from asymmetric synthe-
sis to material science.1 Most of hydrosilylation exploit
transition metal catalysts based on platinum and rhodium
complexes.2–5 Palladium catalysts also effect hydrosilyla-
tion with Cl3SiH,6 and they are particularly important for
enantioselective hydrosilylation with chiral phosphine
ligands.7 However, palladium–phosphine complexes are
not generally employed for hydrosilylation with
triorganosilane because of low catalytic activity. Herein
we wish to report that an electron rich Pd(0)-catalyst,8 a
combination of Pd2(dba)3 CHCl3–trialkylphosphine, effi-
ciently catalyzes stereoselective hydrosilylation of
alkynes with triorganosilanes at room temperature. The
regioselectivity with this protocol is superior to that with
the reported procedure under Pt(0)-catalysis.9
forded unsatisfactory regiocontrol (1a/2a = 79:21). After
several experiments, we found tricyclohexylphosphine
furnished 1-alkenylsilanes with high regioselectivity (1a/
2a = 98:2) (Scheme 1). Unfortunately, no reaction pro-
ceeded with tri(tert-butyl)phosphine. As the palladium
source, Pd2(dba)3 CHCl3 proved to be the best among
3
Pd2(dba)3 CHCl3, Pd(OAc)2, PdCl2(PhCN)2, [PdCl( -
C3H5)]2, and PdCl2(Ph3P)2.
With the optimized catalytic system in our hand, we ex-
amined the hydrosilylation reaction of various alkynes
with Ph3SiH, Ph2MeSiH, and PhMe2SiH. Table 1 summa-
rizes the results.10 Several characteristics of this process
are noteworthy. A variety of alkynes afforded the desired
products in good yields. Olefin, ester, and silyl ether func-
tionalities are compatible under the reaction conditions.
Triphenylsilane is the most reactive among three silanes,
and afforded excellent yields except for phenylacetylene
(entry 1). As for regiocontrol, both Ph3SiH and Ph2MeSiH
exhibited almost the same selectivity. The reaction of 3,3-
dimethyl-1-butyne required the use of 5.0 equiv of the
alkyne because of the low solubility of Ph3SiH in 3,3-di-
methyl-1-butyne (entry 8). Hydrosilylation with
PhMe2SiH is not so efficient as Ph3SiH and Ph2MeSiH
(entry 13).11 Unfortunately, the use of internal alkynes
such as 6-dodecyne yielded none of the alkenylsilane un-
der the same conditions (entry 14).
A mixture of Pd2(dba)3 CHCl3 (0.005 mmol), tribu-
tylphosphine (0.02 mmol), and 1-octyne (1.2 mmol) was
stirred for 10 min. To the mixture, triphenylsilane (1.0
mmol) was introduced at room temperature. After 10 min,
purification of the reaction mixture provided (E)-1-octe-
nylsilane 1a in 89% yield (Scheme 1). The Z-isomer was
not detectable in the reaction mixture. A small amount of
the regioisomer 2a, 2-silyl-1-octene, was also obtained
(9%). The palladium catalyst can be reduced to 0.05
mol%. The low catalyst loading also achieved quantitative
conversion within 10 min at room temperature.
To enhance the regioselectivity, we examined various
phosphine ligands in the reaction with 1-octyne as the
substrate. Triarylphosphines such as triphenylphosphine
exhibited low catalytic activity. Although tris(2,4,6-tri-
methoxyphenyl)phosphine had improved activity, the re-
gioselectivity was not acceptable (vide infra). Triethyl-
phosphite achieved quantitative conversion in 6 h, but af-
In the course of the optimization study, we found an in-
triguing phenomenon: the use of water as a reaction sol-
vent enhances the reactivity of Pd(0)-catalyzed
hydrosilylation of 1-octyne (Scheme 2).12 A better yield
was achieved in water than even the neat conditions with
a
Pd2(dba)3 CHCl3–tris(2,4,6-trimethoxyphenyl)phos-
phine combination as the catalyst.13,14 No observable reac-
tion proceeded in CH2Cl2. We also observed the similar
enhancement in hydrosilylation with Pd(Ph3P)4. Howev-
er, the difference in the yield of the product was not sig-
Synlett 2002, No. 9, Print: 02 09 2002.
Art Id.1437-2096,E;2002,0,09,1529,1531,ftx,en;U00402ST.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0936-5214

1530
D. Motoda et al.
LETTER
R = n-C6H13
+ R
nificant under the optimized conditions with the Pd(0)/
Cy3P system.
R
R
Pd(0) cat.
r. t., 6 h
SiH
Si = Ph3Si
+
+
SiH
The Pd2(dba)3 CHCl3–tributylphosphine combination al-
lows efficient hydrosilylation of alkenes at room temper-
ature (Scheme 3). None of 1-alkenylsilanes, which could
Si
Si
1a
2a
9%
trace
32%
in H2O
34%
89%
a
Pd(Ph3P)4
11%
Neat
Table 1 Hydrosilylation Reaction of Various Alkynes
in CH2Cl2
No reaction
69%
37%
in H2O
13%
7%
17%
49%
b
Pd2(dba)3•CHCl3
/
Neat
((MeO)3C6H2)3Pc
in CH2Cl2
No reaction
a 5 mol% b 0.5 mol% c 2 mol%
Entry Alkyne
Si
Yield Selectivi-
(%)
ty (1/2)
Scheme 2
1
Ph3Si
Ph3Si
Ph3Si
55
95/5
2b
3
95
>99/1
97/3
0.5 mol %
R = n-C6H13
90
Pd2(dba)3•CHCl3
n-Bu3P
R
+
Ph3SiH
SiPh3
R
r. t., 1 h
87%
4
5
Ph3Si
Ph3Si
89
88
97/3
97/3
Scheme 3
be derived via dehydrogenative silylation, was detected in
the reaction mixture.
6
Ph3Si
91
97/3
In conclusion, we have developed an efficient hydrosilyl-
ation protocol with Pd2dba3 CHCl3–tricyclohexylphos-
phine combination. This catalytic system effects rapid
hydrosilylation with excellent regiocontrol at room tem-
perature, and tolerates a variety of functionalities.
7c
8d
9e
Ph2MeSi
Ph2MeSi
Ph2MeSi
82
98
85
98/2
>99/1
94/6
Acknowledgement
This work was supported by Grants-in-Aids for Scientific Research
(No. 14703026) from the Ministry of Education, Culture, Sports,
Science and Technology, Government of Japan.
10
Ph2MeSi
Ph2MeSi
68
91
>99/1
95/1
11e
References
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b 1 min.
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e 2 h.
Synlett 2002, No. 9, 1529–1531 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Efficient Pd(0)-Catalyzed Hydrosilylation of Alkynes
1531
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yne with Ph3SiH is representative. In a 30 mL round-
bottomed flask, Pd2(dba)3 CHCl3 (5.2 mg, 0.005 mmol) and
tricyclohexylphosphine (5.6 mg, 0.02 mmol) were placed
under argon atmosphere, and dodec-1-en-11-yne (0.26 mL,
1.2 mmol) was introduced via a syringe. The mixture was
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room temperature. Triphenylsilane was soon dissolved and
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mixture was submitted on silica gel purification to provide
(E)-1-triphenylsilyl-dodeca-1,11-diene (369 mg, 0.87
mmol) in 87% yield along with a minor amount of 2-
triphenylsilyl-dodeca-1,11-diene (3%).
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mmol), tris(2,4,6-trimethoxyphenyl)phosphine (10.7 mg,
0.02 mmol), and 1-octyne (0.30 mL, 2.0 mmol) were mixed
well. To the mixture, distilled water (5 mL, non-degassed)
was introduced and the mixture was stirred vigorously (1500
rpm) for 5 min. Triphenylsilane (260 mg, 1.0 mmol) was
then added, and the heterogeneous mixture was stirred
vigorously for 6 h. Extractive workup and purification
provided (E)-1-triphenylsilyl-1-octene (256 mg, 0.69 mmol)
along with 2-triphenylsilyl-1-octene (13%).
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amount of water is essential.
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Synlett 2002, No. 9, 1529–1531 ISSN 0936-5214 © Thieme Stuttgart · New York