Regioselective hydrosilylation of terminal acetylenes via acetylene-Co 2(CO)4dppm complex: Effects of the ligands in acetylenedicobalt complex

Article abstract of DOI:10.1016/j.tetlet.2004.11.118

The regioselective hydrosilylation of the acetylenedicobalt complex on the terminal acetylene with special reference to the ligands to produce a vinylsilane is described. It was found that the use of the ligands exchanged dicobalttetracarbonyl bis(diphenylphosphino)methane complex dramatically changed the regioselectivity compared to the corresponding dicobalthexacarbonyl complex.

Full text of DOI:10.1016/j.tetlet.2004.11.118

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 381–384
Regioselective hydrosilylation of terminal acetylenes via
acetylene–Co (CO) dppm complex: effects of
the ligands in acetylenedicobalt complex
2
4
Shingo Tojo and Minoru Isobe*
Laboratory of Organic Chemistry, Graduate School of Bioagricultural Sciences, Nagoya University,
Chikusa, Nagoya 464-8601, Japan
Received 29 October 2004; revised 22 November 2004; accepted 24 November 2004
Abstract—The regioselective hydrosilylation of the acetylenedicobalt complex on the terminal acetylene with special reference to the
ligands to produce a vinylsilane is described. It was found that the use of the ligands exchanged dicobalttetracarbonyl bis(diphenyl-
phosphino)methane complex dramatically changed the regioselectivity compared to the corresponding dicobalthexacarbonyl
complex.
Ó 2004 Elsevier Ltd. All rights reserved.
Vinylsilanes are very useful intermediates in synthetic
1
to a dicobalttetracarbonyl bis(diphenylphosphino)-
methane (Co (CO) dppm) complex from a dicobalt-
hexacarbonyl (Co (CO) ) complex in the terminal
2 6
organic chemistry. The hydrosilylation of an acetylenic
compound is one of the general methods to produce a
2
4
2
vinylsilane. We have developed the reductive decom-
plexation of the acetylenedicobalthexacarbonyl complex
with a trialkylsilane to produce the corresponding
acetylene.
The results of hydrosilylations with the Co (CO) com-
2
6
3
5
vinylsilane (hydrosilylation). In the course of the
plexes and Co (CO) dppm complexes are shown in
2 4
syntheses of marine natural products, the hydrosilyla-
tions of the internal acetylenedicobalt complexes such
as 1 and 3 usually exhibited an extremely high regiose-
Table 1. In all cases, the results of the Co (CO) dppm
2 4
complexes exhibited high regioselectivity. The Co (CO)
2
6
complexes of the sugar acetylene derivatives 11, 15, 18,
22, 26, and 30 were readily prepared by mixing the
3
a,4
lectivity (Scheme 1).
However, the same hydrosilyl-
6
–8
ation reaction of the terminal acetylene with an
acetylene–Co (CO) dppm complex. We found a signifi-
cant improvement in the regioselectivity by changing
corresponding sugar acetylene compounds
Co (CO) . The dppm complexes were prepared by the
with
2
4
2
8
following sequence (Scheme 2).
2 6
Scheme 1. Hydrosilylations of internal acetylene Co (CO) complexes.
Keywords: Hydosilylation; Vinylsilane; Acetylenedicobalt complex.
*
Corresponding author. Tel.: +81 52 789 4109; fax: +81 52 789 4111; e-mail: isobem@agr.nagoya-u.ac.jp
0
040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.11.118

382
S. Tojo, M. Isobe / Tetrahedron Letters 46 (2005) 381–384
as a mixture of regioisomers in high yields. However, the
regioselectivity was low, and most of the major products
were vinylsilane A which has an internal silyl group.
2 4
Scheme 2. Preparation of Co (CO) dppm complex.
Next, we investigated the reaction with the ligands
exchanged Co (CO) dppm complexes (Table 1, entries
2, 4, 6, 8, 10, 12, 14, and 16). The reaction of a simple
2
4
The complex 6 could be directly obtained from sugar
6
acetylene 5 by treating with Co (CO) dppm, which
2
aliphatic compound 8 and triethylsilane in 1,2-dichloro-
3d
6
9
was easily prepared by Co (CO) and dppm, therefore
2
ethane with BTMSA at reflux for 16 h gave 9 and 10 as
an inseparable mixture with the ratio of 6:94 in 70%
8
1
0
6
was cleanly produced as a single diastereomer in
9
0% yield.
yield (entry 2). For the sugar acetylene complexes 12,
6
, 19, 23, 27, and 31, which were prepared from the
We first examined the hydrosilylation with the Co (CO)
2
complexes (Table 1, entries 1, 3, 5, 7, 9, 11, 13, and 15).
In every case, the hydrosilylations were completed in 1–
corresponding sugar acetylene, the reactions proceeded
very slowly to give the vinylsilanes with high regioselec-
tivity in moderate yields (entries 4, 6, 8, 10, 12, and 14).
The moderate yields may be responsible for the instabil-
ity of the dppm complexes under the heating conditions.
6
3
h by heating at 65 °C with triethylsilane and bis(tri-
methylsilyl)acetylene (BTMSA) to give the vinylsilanes
3d
Table 1. Hydrosilylations with acetylenedicobalt complexes
a
Entry Substrate
X
Temp
°C)
Time
(h)
Products
Yield Ratio
(%)
b
(
(A:B)
A
B
1
2
7: Co
8: Co
2
(CO)
(CO)
6
65
1
16
99
70
55:45
6:94
d
d
d
d
d
d
d
d
2
4
dppm
Reflux
+
+
1
0
9
3
4
11: Co
12: Co
2
(CO)
6
65
1
27
90
44
56:44
7:93
c
2
(CO)
4
dppm
Reflux
1
4
1
3
5
6
15: Co
2
(CO)
6
65
1.5
23
+
+
+
+
+
+
95
70
63:37
8:92
c
6: Co
2
(CO)
4
dppm
Reflux
1
7
1
6
7
8
18: Co
19: Co
2
(CO)
6
65
2
25
97
49
55:45
6:94
c
c
c
c
2
(CO)
4
dppm
dppm
dppm
dppm
dppm
Reflux
2
1
2
2
0
4
9
22: Co
23: Co
2
(CO)
(CO)
6
65
2
46
83
56
87:13
2:98
10
2
4
Reflux
25
29
33
1
1
2
26: Co
27: Co
2
(CO)
(CO)
6
65
2
64
96
54
71:29
0:100
1
2
4
Reflux
2
8
2
1
3
4
30: Co
31: Co
2
(CO)
(CO)
6
65
2.5
63
97
44
57:43
0:100
1
2
4
Reflux
3
1
5
6
34: Co
35: Co
2
(CO)
(CO)
6
65
3
35
89
80
26:74
15:85
1
2
4
Reflux
3
7
3
6
3
d
BTMSA = bis(trimethylsilyl)acetylene.
a
All products were inseparable mixtures.
b
c
1
The ratios of the products were determined from the H NMR data (400 MHz).
Dppm complexes were unstable under the heating condition.
Reflux temperature is 83 °C.
d

S. Tojo, M. Isobe / Tetrahedron Letters 46 (2005) 381–384
383
The regioselectivity was pronounced in entries 10, 12,
amount of some products should be generated by the
side reactions was observed in entry 2.
1
1
and 14, particularly 27 and 31 afforded 29 and 33 as
a single regioisomer. In the reaction of an aromatic com-
pound 35 (entry 16), no dramatic effect of the ligands
was observed, which might be probably attributed to
an electronic factor of the aromatic ring.
The hydrosilylation mechanism via the acetylenedico-
balt complex has not yet been clarified, however the
significant difference in the selectivity between the
Co (CO) and Co (CO) dppm complexes should be
2
6
2
4
In a hydrosilylation, platinum or rhodium catalysts have
often been used with a trialkylsilane to produce a
explained on the basis of the configuration of the reac-
tant system. The configurations of 8, 26, and 27 were
confirmed by the NOESY spectra (Fig. 1). The terminal
position of the Co (CO) dppm complex in 8 is very
1
,2
vinylsilane. Therefore, we also examined the reaction
of 38, 39, and 40 with a platinate catalyst (Na PtCl )
2
6
2
4
as the most typical catalyst (Table 2). The reactions were
completed in 10–30 min by heating with triethylsilane at
hindered, judging from the NOEÕs correlations between
the ligand-aromatic protons of dppm and the terminal
proton of the cobalt complex. Furthermore, in the case
of 27, the terminal proton had correlations at the ligand-
methylene protons of dppm as well as the C6 position on
the dihydropyrane ring. Thus, as a plausible explana-
tion, the hydride should approach the less hindered
internal carbon to produce a vinylsilane B as 29. While,
the terminal proton of Co (CO) complex in 26 had
6
5 °C to afford the vinylsilanes 9, 10, 24, 25, 36, and 37.
In these cases, the major products were vinylsilane B
which has a terminal silyl group, and the regioselectivity
was low, especially in entry 2. This system was usually
carried out by simple heating of the reaction mixture
1
2
under air atmosphere, but various side reactions
occasionally occurred, such as the intramolecular
isomerization of an olefin, and the silylation of a free
alcohol, thus a mild condition which is applicable to
complex compounds is desired. The fact that the small
2
6
a correlation at the C2 position on the dihydro-
pyrane ring. Thus, the terminal carbon should be
attacked by the hydride in the Co (CO) complexes,
2
6
2 6
Table 2. Hydrosilylations with Na PtCl
b
c
Entry
1
Substrate
Temp (min)
10
Products
Yield (%)
94
Ratio (A:B)
A
B
9
+
10
22:88
3
3
8
9
2
3
30
30
24
36
+
+
25
37
80
89
31:69
13:87
40
a
b
c
Na
All products were inseparable mixtures.
The ratios of the products were determined from the H NMR data (400 MHz).
2 6
PtCl was added as a 0.01 M solution in 2-propanol.
1
Figure 1. NOEÕs correlations observed in 8, 26, and 27.

384
S. Tojo, M. Isobe / Tetrahedron Letters 46 (2005) 381–384
since the internal carbon would be hindered by the
dihydropyrane ring. However, the steric hindrance of
the Co (CO) complex was smaller than that of the
reactions: (d) Kira, K.; Tanda, H.; Hamajima, A.; Baba,
T.; Takai, S.; Isobe, M. Tetrahedron 2002, 58, 6485.
. (a) Kira, K.; Isobe, M. Tetrahedron Lett. 2001, 42, 2821; (b)
Baba, T.; Isobe, M. Synlett 2003, 547, and references therein.
. About the selection of ligand and the other application of
4
2
6
Co (CO) dppm complex, therefore the regioselectivity
2
4
5
of the Co (CO) complex may be slightly lower than
2
6
2 4
Co (CO) dppm complexes, see: Hamajima, A.; Isobe, M.,
that of the Co (CO) dppm complex.
2
4
in preparation.
. Hosokawa, S.; Kirschbaum, B.; Isobe, M. Tetrahedron
Lett. 1998, 39, 1917.
7. Ichikawa, Y.; Isobe, M.; Konobe, M.; Goto, T. Carbo-
hydr. Res. 1987, 171, 193.
8. Tsukiyama, T.; Isobe, M. Tetrahedron Lett. 1992, 33,
6
In conclusion, we have successfully improved the
regioselectivity of the hydrosilylation by using a
Co (CO) dppm complex on the terminal acetylene
2
4
derivatives. Further developments of this reaction, such
as catalytic reactions and synthetic applications, are now
in progress.
7
911.
. (a) Lisic, E. C.; Hanson, B. E. Inorg. Chem. 1986, 25, 812;
b) Chia, L. S.; Cullen, W. R. Inorg. Chem. 1975, 14, 482.
9
(
1
1
0. For compound 6: as a reddish-brown amorphous;
NMR (CDCl , 400 MHz), d 7.44–7.16 (20H, m), 6.16–6.12
(1H, m), 5.79 (1H, br d, J = 10.2 Hz), 5.59–5.52 (2H, m),
.36–5.31 (1H, m), 4.61–4.55 (1H, m), 4.37 (1H, dd,
J = 4.7, 12.0 Hz), 4.27 (1H, dd, J = 2.0, 12.0 Hz), 3.63
1H, td, J = 10.0 (H–P), 13.2 Hz}, 3.09 {1H, td, J = 9.6
H
3
Acknowledgements
5
This study was supported by a Grant of the 21st Century
COE Program and Grant-in-Aid for Specially Promoted
Research (16002007) from the Ministry of Education,
Culture, Sports, Science and Technology (MEXT),
Japan. We are grateful to Mr. K. Koga at Nagoya Uni-
versity for measurement of the NMR spectroscopy.
We also thank Mr. A. Hamajima at our laboratory for
his discussion of the Co (CO) dppm complexes.
{
1
3
(
H–P), 13.2 Hz}, and 2.08 (6H, s); C NMR (CDCl3,
1
1
1
7
00 MHz), d 203.10–202.80 (m), 171.25, 170.61, 137.00–
36.00 (m), 132.69–132.63 (m), 132.00–131.34 (m), 129.71–
29.61 (m), 128.43–128.14 (m), 123.87, 77.20, 76.31,
2.65–72.60 (m), 68.51, 65.08, 63.36, 42.02 (t,
3
1
J = 19.8 Hz), 21.12, and 20.83;
P NMR (CDCl3,
162 MHz), d 40.67 (2P, br s); IR (neat), mmax 3057, 2931,
2
4
2
7
022, 1992, 1965, 1733, 1435, 1371, 1235, 1096, 1042, 782,
39, and 694 cm ; FAB-MS-HR, found: 853.0573, calcd
ꢀ
1
+
37 9 2 2
for C41H O P Co (M+H) : 853.0577.
2
5
References and notes
11. For compound 29: as a colorless oil; ½aꢁ ꢀ 74:6 (c 0.67,
D
1
CHCl ); H NMR (CDCl , 400 MHz), d 6.08 (1H, ddd,
3
3
1
. For reviews, see: (a) Colvin, E. W. Silicon Reagents in
Organic Synthesis; Academic: London, 1988; (b) Hiyama,
T.; Kusumoto, T. In Comprehensive Organic Synthesis;
Trost, M. B., Fleming, I., Eds.; Pergamon: Oxford, 1991;
Vol. 8, p 763.
J = 2.2, 4.9, 10.2 Hz), 6.02–5.94 (3H, m), 5.20–5.17 (1H,
m), 4.58–4.54 (1H, m), 4.49 (1H, br t, J = 3.4 Hz), 4.37
(1H, dd, J = 7.6, 11.7 Hz), 4.05 (1H, dd, J = 3.9, 11.7 Hz),
2.08 (3H, s), 2.03 (3H, s), 0.93 (9H, t, J = 8.1 Hz), and 0.57
1
3
(6H, q, J = 8.1 Hz); C NMR (CDCl , 100 MHz), d
3
2
. For general method, see: Comprehensive Handbook
on Hydrosilylation; Marciniec, B., Ed.; Pergamon: Oxford,
170.76, 170.52, 141.88, 130.29, 129.49, 125.24, 77.23,
73.25, 70.87, 65.36, 63.53, 20.86, 7.29, and 3.30; IR (neat),
1
992.
. (a) Hosokawa, S.; Isobe, M. Tetrahedron Lett. 1998, 39,
609; (b) Isobe, M.; Nishizawa, R.; Hosokawa, S.;
mmax 2954, 2912, 2876, 1748, 1457, 1372, 1232, 1119, 1024,
ꢀ1
3
943, 786, and 722 cm ; Anal. Calcd for C H O Si : C,
67.56; H, 8.50. Found: C, 67.54; H, 8.69; EI-MS-HR,
3
2
48
5
3
2
+
Nishikawa, T. Chem. Commun. 1998, 2665; (c) Isobe,
M.; Nishizawa, R.; Nishikawa, T.; Yoza, K. Tetrahedron
Lett. 1999, 40, 6927; BTMSA was added as a trapping
reagent of active cobalt catalyst to avoid the side
found: 325.1476, calcd for C H O Si (MꢀEt) :
1
6
25
5
325.1471.
12. Tamao, K.; Ishida, N.; Tanaka, T.; Kumada, M. Organo-
metallics 1983, 2, 1694.