Silylation of aryl iodides with 1,1,1,3,5,5,5-heptamethyltrisiloxane catalyzed by transition-metal complexes

Article abstract of DOI:10.1055/s-2007-980343

The silylation of various kinds of aryl iodides with 1,1,1,3,5,5,5- heptamethyltrisiloxane was achieved by a suitable transition-metal catalyst, such as Pd(0), Pt(0), and Rh(I). These catalytic systems showed dramatically different substrate scope. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-980343

LETTER
1387
Silylation of Aryl Iodides with 1,1,1,3,5,5,5-Heptamethyltrisiloxane Catalyzed
by Transition-Metal Complexes
C
M
atalytic
S
ilylation of
i
A
ryl Io
k
dides with
H
i
eptamethyltr
M
Department of Materials Science, Kitami Institute of Technology, 165 Koencho, Kitami 090-8507, Japan
Fax +81(157)264973; E-mail: muratamk@mail.kitami-it.ac.jp
Received 22 March 2007
Pd(0), Pt(0), or Rh(I) catalyst
KOAc
Abstract: The silylation of various kinds of aryl iodides with
,1,1,3,5,5,5-heptamethyltrisiloxane was achieved by a suitable
transition-metal catalyst, such as Pd(0), Pt(0), and Rh(I). These
catalytic systems showed dramatically different substrate scope.
Me3SiO
Me3SiO Si
Me
1
H
+
I
Ar
DMF
1
2
Key words: silicon, transition metals, catalysis, cross-coupling,
Me3SiO
aryl halides
3
Me SiO Si Ar
+
H Ar
Me
3
4
Arylsilanes and their hypervalent derivatives are versatile Scheme 1
intermediates in modern organic synthesis, particularly
with reactions involving carbon–carbon bond formation
due to the higher stability and lower toxicity of 1 than
triethoxysilane.
through the palladium-catalyzed Hiyama cross-coupling
reaction. Accordingly, the supply of functionalized and
1
reactive arylsilanes has become more necessary. The most An initial screening was performed using representative
common method for the synthesis of arylsilanes is based aryl iodides 2 for the silylation using 1,1,1,3,5,5,5-hep-
on the arylation of halosilanes with aryl Grignard or lithi- tamethyltrisiloxane (1). The results are summarized in
um reagents; however, the protocol has lacked the wide Table 1. Treatment of the electron-rich 4-iodoanisole (2a)
applicability to polyfunctionalized substrates. From the with 1 (2 equiv) and KOAc (3 equiv) in the presence of 3
viewpoints of chemoselectivity, the catalytic silylation of mol% of a transition-metal complex, such as bis(dibenz-
aryl halides would be more attractive. Since aryltriethoxy- ylideneacetone)palladium(0) [Pd(dba)
silanes are one of the most useful coupling reagents,2 neacetone)platinum(0) [Pt(dba)
], and di-m-chlorobis(h -
, in NMP
], bis(dibenzylide-
2
4
2
much attention has been focused on the catalytic silylation 1,5-cyclooctadiene)dirhodium(I) [RhCl(cod)]
2
of aryl halides utilizing triethoxysilane as a silylating re- at room temperature was found to lead to the correspond-
3
agent in the presence of palladium or rhodium complex- ing arylsilane 3a (entries 1–3). The formation of anisole
4
es. The chief drawback of this silylation lies in the high (4a) by reduction of 2a was the major side reaction. Em-
toxicity of triethoxysilane employed as the silylating ploying Pd(dba) was the most preferable choice for
2
5
reagent.
achieving high product selectivity to afford 3a (entry 1).
However, the electronic and steric characteristics of sub-
strates have a significant impact on the reactions; i.e., the
starting halides were restricted to electron-rich aryl io-
Quite recently, triorganosilanes have been used as silylat-
ing reagents to achieve the palladium-, platinum-, or
rhodium-catalyzed silylation of aryl halides. However,
all-carbon-substituted arylsilanes thus obtained are less
reactive for the Hiyama cross-coupling reaction, because
6
7
8
dide, none of which contained ortho substituents (entries
4
and 7).3
,6
electronegative groups, such as fluorine and alkoxy Among several trials using other catalysts, we were
remarkably im-
groups, on the silicon atom are essential for the formation pleased to observe that the use of Pt(dba)
2
1
of a reactive pentacoordinated silicate. Consequently, we proved the selectivity of the silylation of electron-defi-
7
have sought an alternative silylating reagent which pro- cient ethyl 4-iodobenzoate (2b) (entry 5). Therefore, the
vided reactive arylsilanes. In this paper, we report a catalyst system using Pt(dba)
dramatically differs from
catalyst system in the substrate scope, and
the easily available 1,1,1,3,5,5,5-heptamethyltrisiloxane these two systems compensate for each other’s deficien-
2
transition-metal-catalyzed silylation of aryl iodides 2 with the Pd(dba)
2
9
(
1
1; Scheme 1), as well as the synthetic utility of 3-aryl- cies. Very recently, Alami et al. reported on the platinum-
,1,1,3,5,5,5-heptamethyltrisiloxane 3. The present catalyzed silylation of electron-deficient aryl halides with
silylation would be performed without special precautions triethylsilane; however, some of their attempts at the
silylation using other hydrosilanes as silylating reagents
7
were unsuccessful. Unfortunately, neither of these cata-
lysts were suitable for the reaction of sterically hindered
2
c (entries 7 and 8).3
,6,7
SYNLETT 2007, No. 9, pp 1387–1390
Advanced online publication: 23.05.2007
0
1.
0
6.
2
0
0
7
DOI: 10.1055/s-2007-980343; Art ID: U02307ST
©
Georg Thieme Verlag Stuttgart · New York

1
388
M. Murata et al.
LETTER
On the other hand, the [RhCl(cod)] catalyst did not yield cross-coupled with organic electrophiles (Scheme 2). For
2
enough selectivity for any of the selected aryl iodides 2 example, the reaction of 3-phenyl-1,1,1,3,5,5,5-hepta-
(
[
entries 3, 6, and 9). While the product selectivity using methyltrisiloxane (3d) with 4-bromobenzotrifluoride in
RhCl(cod)] catalyst system must be improved, it is note- the presence of a palladium catalyst and TBAF gave the
2
worthy that the rhodium(I)-catalyzed silylation of 2c corresponding unsymmetrical biaryl. In addition, 3d par-
4
,8b
could be carried out in moderate yield (entry 9).
ticipated in rhodium-catalyzed 1,4-addition to a,b-unsat-
urated ester to produce the desired adduct in good yield.13
Table 1 Effect of Substituents on Catalytic Silylation with 1a
CF3
Entry
2
Catalyst
Yield (%)b
(1.0 equiv)
CF3
3
4
Br
PdCl2(PCy3)2 (3 mol%)
TBAF (3 equiv)
1
2
3
4
5
6
7
8
4-MeOC H I (2a)
Pd(dba)2
84
42
57
34
82
25
0
11
52
42
61
17
73
65
87
44
Ph
Ph
6
4
THF–H2O (5:1), 100 °C, 16 h
96%
Pt(dba)2
3
d
(
2 equiv)
1/2 [RhCl(cod)]2
O
(1.0 equiv)
O
4-EtO CC H I (2b) Pd(dba)2
t
2
6
4
O Bu
t
O Bu
[
Rh(OH)(cod)]2 (1.5 mol%)
TBAF (3 equiv)
THF–H2O (5:1), 100 °C, 16 h
Pt(dba)2
80%
1/2 [RhCl(cod)]2
Pd(dba)2
2-MeOC H I (2c)
Scheme 2 Synthetic utility of 3-aryltrisiloxanes 3
6
4
Pt(dba)2
0
In conclusion, we have developed an efficient method for
the transition-metal-catalyzed silylation of aryl iodides 2
with 1,1,1,3,5,5,5-heptamethyltrisiloxane (1).14 The ap-
propriate choice of catalyst controlled the product selec-
tivity and allowed the realization of this silylation. Also,
the synthetic utility of 3-aryl-1,1,1,3,5,5,5-heptamethyl-
trisiloxanes 3 was demonstrated by their coupling with or-
ganic electrophiles. Further investigations to broaden the
scope of this silylation, including that of aryl bromides
and chlorides, as well as to illuminate the reaction mech-
anism, are currently underway in our laboratory.
9
1/2 [RhCl(cod)]2
54
a
Reaction conditions: 2 (0.25 mmol), 1 (0.5 mmol), KOAc (0.75
mmol), and catalyst (3 mol%) in NMP (1 mL) at r.t. for 16 h.
b
GC yields are based on 2 employed.
The results obtained with various aryl iodides 2, giving
arylsiloxanes 3 similarly as above, are listed in Table 2.
Yields reported in this table refer to isolated yields,
whereas those reported in Table 1 are determined by GLC
analysis. The first part of Table 2 involves the application
of palladium-catalyzed silylation to electron-neutral (en-
try 2) and electron-rich aryl iodides (entries 1, 3 and 4). As Acknowledgment
shown in entry 5, heteroaryl iodide 2g was also a good
This work was partially supported by a Grant-in-Aid for Encoura-
gement of Young Scientists (B) from the Ministry of Education,
Culture, Sports, Science and Technology, Japan (No. 16750069).
substrate for the Pd(dba) catalyst system. In the second
part (entries 6–11), the reaction conditions using Pt(dba)2
2
were applied to the silylation of electron-deficient aryl io-
dides. The present methods were extremely tolerant of a
variety of common functional groups. Thus, aryl iodides
References and Notes
2
containing OH (entry 3), NH (entry 4), CO Et (entry 6),
(1) For reviews, see: (a) Hatanaka, Y.; Hiyama, T. Synlett 1991,
845. (b) Hiyama, T. In Metal-Catalyzed Cross-Coupling
Reactions; Diederich, F.; Stang, P. J., Eds.; Wiley-VCH:
Weinheim, 1998, 421. (c) Hiyama, T.; Shirakawa, E. Top.
Curr. Chem. 2002, 219, 61.
2
2
COMe (entry 7), CN (entry 8), and NO (entry 10) groups
2
were all efficiently converted into the corresponding
products 3. In most cases, listed in Table 2, a small
amount of the reduced by-products 4 was identified by
GC analysis of the reaction mixture; but the desired
products 3 and arenes 4 were purely and easily separated
by bulb-to-bulb distillation. Accordingly, the present
reaction would provide a simple and widely available
procedure for 3-aryltrisiloxane 3.
(
2) For a recent review, see: Handy, C. J.; Manoso, A. S.;
McElroy, W. T.; Seganish, W. M.; DeShong, P. Tetrahedron
2005, 61, 12201.
(3) (a) Murata, M.; Suzuki, K.; Watanabe, S.; Masuda, Y. J.
Org. Chem. 1997, 62, 8569. (b) Manoso, A. S.; DeShong, P.
J. Org. Chem. 2001, 66, 7449.
(
4) (a) Murata, M.; Ishikura, M.; Nagata, M.; Watanabe, S.;
Masuda, Y. Org. Lett. 2002, 4, 1843. (b) Murata, M.;
Yamasaki, H.; Ueta, T.; Nagata, M.; Ishikura, M.; Watanabe,
S.; Masuda, Y. Tetrahedron 2007, 63, 4087.
Finally, we turned our attention toward the synthetic ap-
plications of 3-aryltrisiloxanes 3 obtained via the present
silylation. Recently, Denmark, Mori, and Fugami have
(
5) Corriu, R. J. P.; Guérin, C. In Encyclopedia of Reagents for
Organic Synthesis, Vol. 7; Paquette, L. A., Ed.; Wiley: New
York, 1995, 5083.
independently demonstrated the palladium-catalyzed
cross-coupling reactions of oligomeric siloxanes.1
0–12
It
was found that the nonoligomeric arylsiloxanes 3 also
Synlett 2007, No. 9, 1387–1390 © Thieme Stuttgart · New York

LETTER
Catalytic Silylation of Aryl Iodides with Heptamethyltrisiloxane
1389
Table 2 Catalytic Silylation of Various Aryl Iodides 2 with 1,1,1,3,5,5,5-Heptamethyltrisiloxane (1)a
Entry
1
Aryl Iodide 2
Catalyst
Pd(dba)2
Product 3
Yield (%)b
81
I
OMe
(Me3SiO)2MeSi
OMe
2
a
d
e
f
3a
I
(Me3SiO)2MeSi
2
3
4
5
6
7
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pt(dba)2
Pt(dba)2
74
87
90
64
80
80
2
3d
I
OH
(Me3SiO)2MeSi
OH
2
3e
I
NH2
(Me SiO) MeSi
NH2
3
2
2
3f
S
S
I
3 2
(Me SiO) MeSi
2
g
b
3g
I
CO2Et
COMe
(Me SiO) MeSi
CO Et
3
2
2
2
3b
I
(Me SiO) MeSi
COMe
3
2
2
h
3h
I
(Me3SiO)2MeSi
8
9
Pt(dba)2
81
CN
CN
2
i
3i
I
CF3
NO2
Br
(Me3SiO)2MeSi
CF3
NO2
Br
Pt(dba)2
Pt(dba)2
Pt(dba)2
72
82
56
2
j
k
l
3j
I
(Me3SiO)2MeSi
1
1
0
1
2
3k
I
(Me3SiO)2MeSi
2
3l
a
Reaction conditions: 2 (0.5 mmol), 1 (1.0 mmol), KOAc (1.5 mmol), and catalyst (3 mol%) in NMP (2 mL) at r.t. for 16 h.
Isolated yields of 3 are based on 2 employed.
b
(
6) (a) Yamanoi, Y. J. Org. Chem. 2005, 70, 9607. (b) Murata,
M.; Ohara, H.; Oiwa, R.; Watanabe, S.; Masuda, Y.
Synthesis 2006, 1771.
(10) (a) Denmark, S. E.; Wang, Z. Synthesis 2000, 999.
(b) Denmark, S. E.; Wang, Z. J. Organomet. Chem. 2001,
621, 372. (c) Denmark, S. E.; Butler, C. R. Org. Lett. 2006,
8, 63.
(7) Hamze, A.; Provot, O.; Alami, M.; Brion, J.-D. Org. Lett.
2
006, 8, 931.
8) (a) Karshtedt, D.; Bell, A. T.; Tilley, T. D. Organometallics
006, 25, 4471. (b) Yamanoi, Y.; Nishihara, H. Tetrahedron
(11) (a) Mori, A.; Suguro, M. Synlett 2001, 845. (b) Koike, T.;
Mori, A. Synlett 2003, 1850.
(12) Endo, M.; Sakurai, T.; Ojima, S.; Katayama, T.; Unno, M.;
Matsumoto, H.; Kowase, S.; Sano, H.; Kosugi, M.; Fugami,
K. Synlett 2007, 749.
(
2
Lett. 2006, 47, 7157.
(
9) 1,1,1,3,5,5,5-Heptamethyltrisiloxane (1) is commercially
available.
(13) Mori et al. reported a conjugate addition of polymeric
siloxanes to a,b-unsaturated carbonyl compounds. See:
Koike, T.; Du, X.; Mori, A.; Osakada, K. Synlett 2002, 301.
Synlett 2007, No. 9, 1387–1390 © Thieme Stuttgart · New York

1
390
M. Murata et al.
LETTER
(CDCl ): d = 0.12, 1.83, 114.68, 129.82, 135.01, 156.81.
(
14) Silylation of Aryl Iodides; General Procedure: In a glove
3
+
box, the appropriate transition-metal complex (0.015 mmol)
and KOAc (1.5 mmol) were placed in a screw-capped vial.
NMP (2 mL), aryl iodide 2 (0.5 mmol), and 1,1,1,3,5,5,5-
heptamethyltrisiloxane (1; 1.0 mmol) were added
HRMS (EI): m/z [M ] calcd for C H O Si : 314.1190;
13 26 3 3
1
found: 314.1179. 3f: H NMR (CDCl ): d = 0.09 (s, 18 H),
3
0.22 (s, 3 H), 3.72 (br s, 2 H), 6.67 (d, J = 8.5 Hz, 2 H), 7.34
1
3
(d, J = 8.5 Hz, 2 H). C NMR (CDCl ): d = 0.17, 1.86,
3
+
successively. The vial was sealed with a cap and removed
from the glove box. The reaction mixture was then stirred at
r.t. for 16 h. After the reaction was completed, the mixture
was diluted with Et O, washed with H O (3 ×) to remove
114.27, 126.99, 134.61, 147.52. HRMS (EI): m/z [M ] calcd
1
for C H O NSi : 313.1350; found: 313.1317. 3g: H NMR
1
3
27
2
3
(CDCl ): d = 0.11 (s, 18 H), 0.32 (s, 3 H), 7.17 (t, J = 4.0 Hz,
3
1
3
1 H), 7.31 (d, J = 4.0 Hz, 1 H), 7.57 (d, J = 4.0 Hz, 1 H).
C
2
2
NMP, and dried over Na SO . The solvent was removed
under reduced pressure, and the residue was purified by
Kugelrohr distillation to give the desired 3-aryl-
NMR (CDCl ): d = 1.11, 1.77, 127.79, 130.42, 134.46,
2
4
3
+
138.05. HRMS (EI): m/z [M ] calcd for C H O SSi :
304.0805; found: 304.0807. 3h: H NMR (CDCl ): d = 0.11
(s, 18 H), 0.29 (s, 3 H), 2.61 (s, 3 H), 7.65 (d, J = 7.9 Hz, 2
1
1
24
2
3
1
3
1
,1,1,3,5,5,5-heptamethyltrisiloxane 3. The products were
1
13
13
characterized by H and C NMR spectroscopy and HRMS
H), 7.29 (d, J = 7.9 Hz, 2 H). C NMR (CDCl ): d = –0.14,
3
analysis.
1.82, 26.63, 127.19, 133.39, 137.69, 144.68, 198.46. HRMS
1
+
3
a: H NMR (CDCl ): d = 0.10 (s, 18 H), 0.24 (s, 3 H), 3.82
(EI): m/z [M – CH ] calcd for C H O Si : 325.1111;
3
3
14 25
3
3
1
(
s, 3 H), 6.90 (d, J = 8.2 Hz, 2 H), 7.48 (d, J = 8.2 Hz, 2 H).
found: 325.1127. 3i: H NMR (CDCl ): d = 0.12 (s, 18 H),
0.29 (s, 3 H), 7.45 (t, J = 7.6 Hz, 1 H), 7.66 (d, J = 7.6 Hz, 1
H), 7.75 (d, J = 7.6 Hz, 1 H), 7.80 (s, 1 H). C NMR
3
1
3
C NMR (CDCl ): d = 0.16, 1.85, 54.97, 113.25, 129.25,
3
+
13
1
34.75, 160.62. HRMS (EI): m/z [M ] calcd for
1
C H O Si : 328.1347; found: 328.1350. 3b: H NMR
(CDCl ): d = –0.21, 1.80, 111.92, 119.25, 128.22, 132.78,
14
28
3
3
3
+
(
3
(
1
CDCl ): d = 0.10 (s, 18 H), 0.29 (s, 3 H), 1.40 (t, J = 7.2 Hz,
136.83, 137.24, 140.48. HRMS (EI): m/z [M – CH ] calcd
3
3
1
H), 4.38 (q, J = 7.2 Hz, 2 H), 7.62 (d, J = 7.9 Hz, 2 H), 8.01
for C H O NSi : 308.0959; found: 308.0937. 3j: H NMR
1
3
22
2
3
1
3
d, J = 7.9 Hz, 2 H). C NMR (CDCl ): d = –0.15, 1.81,
(CDCl ): d = 0.11 (s, 18 H), 0.28 (s, 3 H), 7.59 (d, J = 7.9 Hz,
3
3
1
3
4.32, 60.91, 128.43, 131.15, 133.13, 144.22, 166.79.
2 H), 7.66 (d, J = 7.9 Hz, 2 H). C NMR (CDCl ): d = –0.13,
1.79, 124.25 (q, J = 4.1 Hz), 124.33 (q, J = 272.1 Hz), 131.45
(q, J = 32.1 Hz), 133.54, 143.22. HRMS (EI): m/z [M –
3
+
HRMS (EI): m/z [M – CH ] calcd for C H O Si :
3
15 27
4
3
1
+
3
(
55.1217; found: 355.1220. 3c: H NMR (CDCl ): d = 0.09
s, 18 H), 0.27 (s, 3 H), 3.79 (s, 3 H), 6.81 (d, J = 7.6 Hz, 1
3
CH ] calcd for C H O F Si : 351.0880; found: 351.0886.
3
13 22
2
3
3
1
H), 6.94 (t, J = 7.6 Hz, 1 H), 7.35 (t, J = 7.6 Hz, 1 H), 7.50
3k: H NMR (CDCl ): d = 0.12 (s, 18 H), 0.31 (s, 3 H), 7.71
(d, J = 8.2 Hz, 2 H), 8.19 (d, J = 8.2 Hz, 2 H). C NMR
3
1
3
13
(
1
(
3
3
1
d, J = 7.6 Hz, 1 H). C NMR (CDCl ): d = 1.06, 1.78, 54.58,
3
09.18, 120.18, 126.00, 131.24, 135.45, 164.00. HRMS
(CDCl ): d = –0.19, 1.81, 117.26, 122.31, 134.09, 147.11.
3
+
+
EI): m/z [M ] calcd for C H O Si : 328.1346; found:
HRMS (EI): m/z [M – CH ] calcd for C H O NSi :
328.0856; found: 328.0866. 3l: H NMR (CDCl ): d = 0.10
(s, 18 H), 0.25 (s, 3 H), 7.40 (d, J = 7.9 Hz, 2 H), 7.49 (d,
J = 7.9 Hz, 2 H). C NMR (CDCl ): d = –0.07, 1.82, 124.22,
130.78, 134.83, 137.30. HRMS (EI): m/z [M – CH ] calcd
1
4
28
3
3
3
12 22
4
3
1
1
28.1384. 3d: H NMR (CDCl ): d = 0.12 (s, 18 H), 0.28 (s,
3
3
1
3
H), 7.30–7.60 (m, 5 H). C NMR (CDCl ): d = 0.02, 1.85,
3
+
13
27.58, 129.39, 133.21, 138.52. HRMS (EI): m/z [M ] calcd
3
1
+
for C H O Si : 298.1241; found: 298.1282. 3e: H NMR
13
26
2
3
3
(
(
CDCl ): d = 0.10 (s, 18 H), 0.24 (s, 3 H), 4.91 (s, 1 H), 6.82
for C H O BrSi : 363.0090; found: 363.0068.
3
12 22
2
3
1
3
d, J = 8.2 Hz, 2 H), 7.43 (d, J = 8.2 Hz, 2 H). C NMR
Synlett 2007, No. 9, 1387–1390 © Thieme Stuttgart · New York