Palladium-Catalyzed Cross-Coupling of Silanols, Silanediols, and Silanetriols Promoted by Silver(I) Oxide

Article abstract of DOI:10.1021/jo000679p

Palladium-catalyzed cross-coupling of aryl- or alkenylsilanols, silanediols, and silanetriols with a variety of iodoarenes by the catalysis of palladium(0) and in the presence of silver(I) oxide furnished the coupling products in good to excellent yields. The reactions of silanediols or silanetriols under similar conditions proceeded much faster than those of silanols to afford the corresponding coupling products in excellent yields within shorter reaction periods (5-12 h). The measurement of the X-ray diffraction (XRD) pattern of the silver residue after the reaction revealed that silver(I) oxide was converted to silver(I) iodide.

Full text of DOI:10.1021/jo000679p

5342
J . Org. Chem. 2000, 65, 5342-5349
P a lla d iu m -Ca ta lyzed Cr oss-Cou p lin g of Sila n ols, Sila n ed iols, a n d
Sila n etr iols P r om oted by Silver (I) Oxid e
Kazunori Hirabayashi, Atsunori Mori,* J un Kawashima, Masahiro Suguro,
Yasushi Nishihara, and Tamejiro Hiyama†
Chemical Resources Laboratory, Tokyo Institute of Technology, Nagatsuta, Yokohama 226-8503, J apan
amori@res.titech.ac.jp
Received May 2, 2000
Palladium-catalyzed cross-coupling of aryl- or alkenylsilanols, silanediols, and silanetriols with a
variety of iodoarenes by the catalysis of palladium(0) and in the presence of silver(I) oxide furnished
the coupling products in good to excellent yields. The reactions of silanediols or silanetriols under
similar conditions proceeded much faster than those of silanols to afford the corresponding coupling
products in excellent yields within shorter reaction periods (5-12 h). The measurement of the X-ray
diffraction (XRD) pattern of the silver residue after the reaction revealed that silver(I) oxide was
converted to silver(I) iodide.
In tr od u ction
Among versatile synthetic applications of organosilicon
reagents utilization of silanol in organic syntheses have
remained unexplored until recently.1-6 Because partici-
pation of the hydroxy group to a metallic species en-
hances selectivity as well as reactivity in the reactions
of such a metallic reagent to a neighboring functional
group,7 an olefinic substituent of a silanol effects the
Simmons-Smith cyclopropanation,2 Sharpless asym-
metric epoxidation,3 and regioselective dilithiation of
allyl- or alkynylsilanols followed by reactions of the
resulting dianions with electrophiles.4 On the other hand,
nucleophilic attack of a silanol oxygen atom effects allylic
substitution5 or halo-cyclization6 and was utilized for the
introduction of a oxygen-carbon bond into organic mol-
ecules.
In contrast with such synthetic utilization of silanols,
effective transformation of a carbon-silicon bond of
silanols to a carbon-carbon or carbon-heteroatom bond
has not been achieved until recently. We have reported
that aryl- and alkenylsilanols underwent Mizoroki-
Heck-type reaction with an olefin as the first example of
a carbon-carbon bond-forming reaction using silanol as
shown in eq 1.8
Another entry for the carbon-carbon bond-forming
reaction using silanol is the cross-coupling reaction with
organic halides. Although various organosilicon reagents
have been shown to undergo the cross-coupling reac-
tions,9 the reaction with silanol has not been studied so
far.10,11
Herein, we report the palladium-catalyzed cross-
coupling reactions of silanol, silanediol, and silanetriol
with aryl iodide. These reactions were found to proceed
particularly in the presence of silver(I) oxide as an
activator. The role of the silver reagent in the cross-
coupling is also discussed.
Resu lts a n d Discu ssion
In light of the successful Mizoroki-Heck-type carbon-
carbon bond-forming reaction using silanols,8 we envis-
aged that the cross-coupling with an aryl halide would
also be accessible. The reaction was first examined using
tetrabutylammonium fluoride (TBAF) as an activator
under conditions similar to those frequently employed for
† Present address: Department of Material Chemistry, Graduate
School of Engineering, Kyoto University, Yoshida, Kyoto 606-8501,
J apan.
(1) For a review on silanol: Lickiss, P. D. Adv. Inorg. Chem. 1995,
42, 147-262.
(2) (a) Hirabayashi, K.; Mori, A.; Hiyama, T. Tetrahedron Lett. 1997,
38, 461-464. (b) Hirabayashi, K.; Takahisa, E.; Nishihara, Y.; Mori,
A.; Hiyama, T. Bull. Chem. Soc. J pn. 1998, 71, 2409-2417.
(3) (a) Chan, T. H.; Chen, L. M.; Wang, D. J . Chem. Soc., Chem.
Commun. 1988, 1280-1281. (b) Chan, T. H.; Chen, L. M.; Wang, D.;
Li, L. H. Can. J . Chem. 1993, 71, 60-67. (c) Yamamoto, K.; Kawanami,
Y.; Miyazawa, M. J . Chem. Soc., Chem. Commun. 1993, 436-437. (d)
Li, L. H.; Chan, T. H. Tetrahedron Lett. 1997, 38, 101-104.
(4) (a) Takaku, K.; Shinokubo, H.; Oshima, K. Tetrahedron Lett.
1997, 38, 5189-5192. (b) Uehira, S.; Takaku, K.; Shinokubo, H.;
Oshima, K. Synlett 1998, 1096-1098.
(8) (a) Hirabayashi, K.; Nishihara, Y.; Mori, A.; Hiyama, T. Tetra-
hedron Lett. 1998, 39, 7893-7896. See also: (b) Hirabayashi, K.; Ando,
J .; Mori, A.; Nishihara, Y.; Hiyama, T. Synlett 1999, 99-101. (c)
Hirabayashi, K.; Ando, J .; Kawashima, J .; Nishihara Y.; Mori, A.;
Hiyama, T. Bull. Chem. Soc. J pn. 2000, 73, 1409-1417.
(9) (a) Hiyama, T.; Hatanaka, Y. Pure Appl. Chem. 1994, 66, 1471-
1478. (b) Hiyama, T. Organosilicon Compounds in Cross-Coupling
Reactions. In Metal-Catalyzed Cross-Coupling Reactions; Diederich,
F., Stang, P., Eds.; Wiley-VCH: 1998; Chapter 10, pp 421-454. See
also: (c) Mowery, M. E.; DeShong, P. J . Org. Chem. 1999, 64, 1684-
1688. (d) Denmark, S. E.; Choi, J . Y. J . Am. Chem. Soc. 1999, 121,
5821-5822. (e) Denmark, S. E.; Wu, Z. Org. Lett. 1999, 1, 1495-1498.
(10) The preliminary communication: Hirabayashi, K.; Kawashima,
J .; Nishihara, Y.; Mori, A.; Hiyama, T. Org. Lett. 1999, 1, 299-301.
(11) Denmark independently reported the cross-coupling of alkenyl-
silanols using a fluoride ion as an activator: Denmark, S. E.; Wu, Z.
Org. Lett. 2000, 2, 565-568.
(5) Trost, B. M.; Ito, N.; Greenspan, P. D. Tetrahedron Lett. 1993,
34, 1421-1424.
(6) (a) Takaku, K.; Shinokubo, H.; Oshima, K. Tetrahedron Lett.
1996, 37, 6781-6784. (b) Shinokubo, H.; Oshima, K.; Utimoto, K. Bull.
Chem. Soc. J pn. 1997, 70, 2255-2263.
(7) (a) Hoveyda, D. A.; Fu, G. C. Chem. Rev. 1993, 93, 1307-1370.
(b) Snieckus, V. Chem. Rev. 1990, 90, 879-933.
10.1021/jo000679p CCC: $19.00 © 2000 American Chemical Society
Published on Web 07/29/2000

Palladium-Catalyzed Cross-Couplings
J . Org. Chem., Vol. 65, No. 17, 2000 5343
Ta ble 2. Solven t Effect of th e Rea ction of 1a w ith 2a a
Sch em e 1
entry
solvent
T/°C
yieldb/%
1
2
3
4
5
6
7
8
9
THF
Bu2O
60
52
27
63
60
36
34 (40)
64
35 (60)
7 (40)
100
60
dioxane
hexane
toluene
100
DMF
DMSO
a
The reaction was carried out using 1a (0.24 mmol), 2a (0.2
mmol), Pd(PPh3)4 (5 mol %), and Ag2O (0.2 mmol) in THF at 60
°C for 5 h. b In parentheses; % conversion of silanol 1a to disiloxane
((ArylSiMe2)2O).
Sch em e 2
Ta ble 1. Effect of a n Ad d itive in th e Cou p lin g Rea ction
of 1a w ith 2a a
entry
additive (mol %)
yieldb/%
1
2
3
4
5
Ag2O (100)
(50)
(10)
(0)
(200)
80c
61d
17d
0d
84e
0
6
7
CuO (100)
CaO
0
8
BaO
0
9
K2CO3
NaOH
AgOTf
AgBF4
AgNO3
0
0
21
23
16
10
11
12
13
reaction (entry 4). On the other hand, excess amounts of
Ag2O exhibited little effect to improve the yield (entry
5). The attempted cross-coupling reactions using other
additives were revealed to be totally inferior; the use of
other metal oxides, CuO, CaO, or BaO, and inorganic
bases, K2CO3 or NaOH, were found to give no reaction
under similar conditions, and the reaction using an ionic
silver salt, AgOTf, AgBF4, or AgNO3, proceeded to result
in lower yields.
The cross-coupling reactions were then examined in
several solvents as shown in Table 2. The reaction
proceeded in THF at 60 °C in good yield (entry 1). Yields
in other solvents such as Bu2O, 1,4-dioxane, and toluene
at 100 °C were comparable to the result in THF at 60 °C
(entries 3, 4, and 7). In contrast, the use of hexane or an
aprotic polar solvent such as DMF or DMSO appeared
to be inferior (entries 8 and 9).
Scheme 2 shows the cross-coupling of other organo-
silicon reagents arylpentamethyldisiloxane 4a and aryl-
trimethylsilane 4b to furnish the corresponding coupling
products in 4% and 0% yields, respectively, suggesting
the significant role of the hydroxy group of silanol to
undergo the reaction.
The reactions of aryl- and alkenylsilanols with a
variety of organic halides are summarized in Table 3. In
a sharp contrast to the reaction with iodobenzene, the
use of bromobenzene and phenyl triflate resulted in much
lower yields under similar conditions (entries 3 and 4).
It is remarkable that the reactions of 1-bromo-4-iodo-
benzene (2g) and 4-iodophenyl triflate (2h ) afforded 3g
and 3h , respectively (entries 10 and 11), to react at the
carbon-iodine bond with bromide or triflate remaining
intact. The reactions with iodobenzenes bearing an
electron-donating substituent also proceeded in good
yields. In contrast, yields were relatively lower in the
reactions of iodides with an electron-withdrawing sub-
stituent although the reactions proceeded, indeed.
a
The reaction was carried out using 1a (0.24 mmol), 2a (0.2
mmol), Pd(PPh3)4 (5 mol %), and additive in THF at 60 °C for 36
b
h. The yields were estimated by 1H NMR using 1,1,2-trichloro-
ethylene as an internal standard. c Isolated yield. The reaction
d
time was 65 h. e The reaction time was 38 h.
the cross-coupling of difluoro(ethyl)phenylsilane.11,12 How-
ever, treatment of (4-methoxyphenyl)dimethylsilanol (1a )
with iodobenzene (2a ) in the presence of TBAF, 10 mol
% of Pd(OAc)2, and 20 mol % of PPh3 resulted in no
reaction along with the formation of 1,3-di(4-methoxy-
phenyl)-1,1,3,3-tetramethyldisiloxane.
Thus, various additives instead of the fluoride ion were
examined, and we found that the coupling reaction
occurred when Ag2O was employed as an activator.13,14
For example, the reaction of 1a with 2a using Ag2O (100
mol %) in THF at 60 °C for 36 h afforded 4-methoxybi-
phenyl (3a ) in 80% yield (Scheme 1). Table 1 summarizes
the results on the reaction of 1a with 2a in the presence
of Ag2O or other additives. The reaction using less than
an equimolar amount of Ag2O (50 mol % and 10 mol %)
proceeded to give 3a in 61 and 17% yield, respectively
(entries 2 and 3) suggesting that the reaction by the
catalytic use of Ag2O gives the product in a yield
corresponding to a slightly excess amount of Ag2O. In
addition, the reaction without silver resulted in no
(12) (a) Hatanaka, Y.; Fukushima, S.; Hiyama, T. Chem. Lett, 1989,
1711-1714. (b) Hatanaka, Y.; Hiyama, T. J . Org. Chem. 1989, 54, 268-
270.
(13) Ag2O has been used as an activator in the cross-coupling
reactions of organoboron and organosilicon compounds: (a) Uenishi,
J .; Beau, J .-M.; Armstrong, R. W.; Kishi, Y. J . Am. Chem. Soc. 1987,
109, 4756-4758. (b) Gillmann, T.; Weeber, T. Synlett 1994, 649-650.
(c) Malm, J .; Bjo¨rk, P.; Gronowitz, S.; Ho¨rnfeldt, A.-B. Tetrahedron
Lett. 1992, 33, 2199-2202. (d) Mateo, C.; Fera´ndez-Rivas, C.; Echa-
varren, A. M.; Ca´rdenas, D. J . Organometallics 1997, 16, 1997-1999.
(14) Ito, Y.; Konoike, T.; Saegusa, T. J . Am. Chem. Soc. 1975, 97,
649-651.

5344 J . Org. Chem., Vol. 65, No. 17, 2000
Ta ble 3. Cr oss-Cou p lin g Rea ction of a Sila n ol w ith a n Or ga n oh a lid ea
Hirabayashi et al.
a
Unless otherwise noted, the reactions were carried out under the following conditions: 1 (0.24 mmol), halide (0.2 mmol), Pd(PPh3)4
(5 mol %), Ag2O (0.2 mmol), in THF (2 mL) at 60 °C. Yields were estimated by 1H NMR using 1,1,2-trichloroethylene as an internal
b
standard. c The product was 4-MeOC6H4C6H4-4'-Br. The product was 4-MeOC6H4C6H4-4'-OTf.
d
Other silanols similarly underwent the cross-coupling
reactions in moderate to good yields. Arylsilanols with
an electron-withdrawing substituent on their aromatic
rings furnished the coupling products in good yields
(entry 12). However, the reaction with dimethyl(phenyl)-
silanol (1c) showed poor reactivity (entry 13). The reac-
tion with (2-methylphenyl)dimethylsilanol (1d ) was also
ineffective (entry 14). It should be pointed out that
alkenylsilanols generally reacted much faster than aryl-
silanols (entry 15 and 16).9b,15 Indeed, the reactions with
octen-1-yl- and 2-phenylethenylsilanols proceeded within
shorter reaction periods (3-4 h) to afford the correspond-
ing products 3i and 3j in excellent yields. In addition,
benzyl bromide also reacted with 1a to give the diphen-
ylmethane derivative 3k in 55% yield.
Although the coupling of silanol proceeds, the reactions
of arylsilanols, in general, require longer periods to afford
the product in good yield. Hence, we are subsequently
interested in the cross-coupling reaction of silanediols and
silanetriol, which might show higher efficiency due to the
presence of multiple hydroxy groups on silicon.
Syntheses of silanediols were carried out by a careful
hydrolysis of the corresponding dichlorosilane 6.16 The
reaction of dichloro(ethyl)(phenyl)silane (6a ) was hydro-
lyzed with 2 mol amounts of NaHCO3 in diethyl ether/
H2O (method A) or 2 mol amounts of aniline and H2O
(16) (a) George, P. D.; Sommer, L. H.; Whitmore, F. C. J . Am. Chem.
Soc. 1953, 75, 1585-1588. (b) Takiguchi, T. J . Am. Chem. Soc. 1959,
81, 2359-2361.
(15) Such difference of the reactivity was also shown in the reactions
of aryl- and alkenylsilacyclobutanes. See ref 9d,e.

Palladium-Catalyzed Cross-Couplings
J . Org. Chem., Vol. 65, No. 17, 2000 5345
Ta ble 4. Syn th eses of Sila n ed iols
sometimes caused difficulty in the purification due to the
contamination of a small amount of unidentified silicone
impurities.
entry
R
R'
X
methoda
A
yield/%
80
1
2
3
4
5
6
7
Ph
Ph
Ph
Et
Cl (6a )
Cl (6b)
H
Cl (6c)
Cl (6d )
Cl (6e)
Cl (6f)
It should also be pointed out that several coupling
reactions were found to proceed smoothly starting from
the use of dichloro- or trichloroaryl and -alkenyl silicon
reagents via hydrolysis and the cross-coupling sequence
without purifying the formed crude silanediols or a
silanetriol. In sharp contrast to the successful formation
of methyl(phenyl)silanediol (7b) from the corresponding
hydrosilane (method C), the attempted hydrolysis of
dichloro(methyl)phenylsilane with aqueous NaHCO3
(method A) resulted in the formation of a complex
mixture of oligosiloxanes, whose 1H NMR spectrum
clearly indicated that most of the silanediol has been
converted to the oligomers.18 Nevertheless, the cross-
coupling of such a complex mixture with 2j under similar
conditions, indeed, produced the corresponding coupling
product in 77% yield. Attempts to isolate several si-
lanediols and a silanetriol 9b have also been unsuccessful
by methods A-C. However, these crude mixtures were
similarly converted to the coupling products in excellent
yields as summarized in Table 6. Since further purifica-
tion of crude silanediols that are obtained as a liquid is
generally difficult, isolation of (1-hexenyl)methylsi-
lanediol, methyl(2-phenylethenyl)silanediol, and (1-ethyl-
1-butenyl)methylsilanediol in analytically pure form by
the hydrolyses of dichlorosilanes 6g, 6h , and 6i, respec-
tively, has not been achieved to give mixtures whose
NMR measurements suggested contamination of insepa-
rable silicone oligomers in considerable amounts along
with the desired silanediol. The cross-coupling reactions
Me
Me
Et
C
B
90
65
79
74
62
4-MeC6H4
4-MeOC6H4
PhCHdCH
PhCHdCPh
a
Method A: 6 (1 mmol), NaHCO3 (2 mmol), in Et2O/H2O at 0
°C. Method B: 6 (1 mmol), H2O (2 mmol), PhNH2 (2 mmol), in
Et2O at 0 °C. Method C: dihydrosilane (1 mmol), Pd/C (5 mol %),
in dioxane/phosphate buffer (pH ) 6.84) at rt.
(method B) in diethyl ether to yield silanediol 7a in a
good yield (eq 2). In contrast, similar hydrolysis of
dichloro(methyl)(phenyl)silane (6b) gave silanediol 7b in
a very low yield probably along with complex mixture of
silicone oligomers. However, synthesis of 7b was alter-
natively achieved by the Pd/C catalyzed hydrolytic de-
hydrogenation of methyl(phenyl)silane (method C) in 90%
yield.17 Other silanediols were prepared by each of these
methods A-C. The results on the preparation of si-
lanediols are shown in Table 4. All of the synthesized
silanediols given in Table 4 were solid at an ambient
temperature. These produced crude solids were washed
with hexane, to show sufficient purity for further cross-
coupling reactions, and can be stored in a refrigerator
for months under an argon atmosphere. However, the
attempted recrystallization from hexanes-ether with
slight heating resulted in decomposition of silanediols.
The cross-coupling of silanediols with several sub-
strates was performed in the presence of Ag2O as shown
in Table 5. The reaction of ethyl(phenyl)silanediol (7a )
with 4-methoxyiodobenzene (2i) proceeded at 60 °C for
12 h in the presence of 5 mol % of Pd(PPh3)4 and 100
mol % of Ag2O to give 4-methoxybiphenyl (3a ) in 80%
yield (entry 1). Since the reaction using silanol 1c under
similar conditions afforded the coupling product in only
35% yield (Table 3, entry 13), the reactivity of silanediol
was found to be much superior to the corresponding
silanol.
As observed in the cross-coupling of silanol, bromide
and triflate also failed to give the product (entries 4 and
5). However, the reactions of silanediol 7b with several
iodides proceeded; excellent yields were achieved within
a shorter reaction period (12 h) compared with those of
silanols (36 h at 60 °C in THF). In addition, silanetriol
9a also reacted with 4-methoxyiodobenzene in 83% at 60
°C for 12 h (entry 6).
The reactions of other arylsilanediols 7c and 7d
proceeded with aryl iodides 2i and 2a in good yields,
respectively (entries 11 and 12). Alkenylsilanediols 7e
and 7f also effected the cross-coupling reactions (entries
13 and 14). Worthy of note, in addition, is the ease of
purification in the coupling of silanediol and silanetriol
by a simple silica gel column chromatography procedure.
In contrast, the reaction with the corresponding silanol
using these crude mixture with 2i or 2j resulted to give
the coupling products in excellent yields.19 In addition,
trichlorosilane 8b, whose corresponding silanetriol were
also unable to obtain, were similarly subjected to the
hydrolysis-coupling sequence to afford the coupling prod-
ucts in 76% yield. Since an unstable silanediol probably
exist in an equilibrium with the corresponding silicone
oligomers, consumption of the silanediol by the coupling
in the reaction mixture would facilitate further regenera-
tion of the silanediol for the coupling to proceed. In
contrast, the coupling reaction with a disiloxane 4a (see
Scheme 2) or an aged silanol that would reluctantly
converted to the disiloxane did not proceed because
regeneration of a silanol from the corresponding disilox-
ane hardly occurred (Scheme 3).
In view of the cross-coupling of silanols and silanediols,
the role of Ag2O as an activator is of considerable interest.
Hence, analysis of the silver residue, after completion of
(18) See the Supporting Information.
(19) A cross-coupling reaction with chlorosilanes in the presence of
NaOH might also be formation of oligosiloxanes. See: Gouda, K.;
Hagiwara, E.; Hatanaka, Y.; Hiyama, T. J . Org. Chem. 1996, 61, 7232-
7233.
(17) Barnes, G. H., J r.; Daughenbaugh, N. E. J . Org. Chem. 1966,
31, 885-887.

5346 J . Org. Chem., Vol. 65, No. 17, 2000
Hirabayashi et al.
Ta ble 5. Cr oss-Cou p lin g Rea ction of a Sila n ed iol or Sila n etr iol 9a w ith a n Ar yl Ha lid ea
a
The reactions were carried out using 7 or 9 (0.24 mmol), halide (0.2 mmol), Pd(PPh3)4 (5 mol %), Ag2O (0.2 mmol) in THF at 60 °C.
Yields were estimated by 1H NMR using 1,1,2-trichloroethylene as an internal standard. c The reaction was carried out using 7e (6
b
mmol), 2i (5 mmol), Pd(PPh3)4 (3 mol %), and Ag2O (5 mmol), the coupling product 3j was purified by recrystallization.
Ta ble 6. Rea ction s of a Cr u d e Sila n ed iol or a Sila n etr iol
w ith a n Ar yl Ha lid ea
Sch em e 3
of new peaks were found identical with those of AgI (D).
On the other hand, B of Figure 1 is the XRD pattern of
the residue after the reaction using 50 mol % of Ag2O.20
The pattern shows that the relative intensity of the peaks
of Ag2O to those of AgI decreased in comparison with A.
Thus, we consider that the stoichiometry of the Ag2O-
promoted cross-coupling reaction of silanol could be
expressed as eq 4 being indicative that the reaction of a
silicon reagent (1 mol amount) with 0.5 mol amount of
Ag2O give the coupling product along with an equimolar
amount of AgI and 0.5 mol amount of disiloxane.21
Accordingly, the result that the reaction of silanol 1a with
2a using 10 mol % of Ag2O afforded the coupling product
in 17% yield would also be likely (cf. Table 1, entry 3).
a
The reactions were carried out using silanediol or silanetriol
(0.6 mmol), aryl halide (0.5 mmol), Pd(PPh3)4 (5 mmol %), and
Ag2O (0.5 mmol) in THF at 60 °C.
the reaction of silanediol 7a with 2i in the presence of
100 mol % of Ag2O, was carried out by the measurement
of X-ray diffraction (XRD) pattern. The reaction to afford
the corresponding coupling product in 93% yield gave a
crude mixture of gray THF solution along with black
precipitates, which were subjected to the XRD analysis.
The results are summarized in Figure 1. As shown in A
of Figure 1, the spectrum indicated that several new
peaks appeared along with remaining Ag2O (C). Α part
(20) The reaction of 7a with 2i in the presence of 50 mol % of Ag2O
afforded 3a in 43% yield.
(21) We also confirmed the formation of disiloxane in the coupling
of 2-phenylethynyl(dimethyl)phenylsilane with an aryl iodide to give
the corresponing coupling product along with 1,1,3,3-tetramethyl-1,3-
diphenyldisiloxane in an excellent yield: Hirabayashi, K.; Kawashima,
J .; Mori, A. Unpublished results.

Palladium-Catalyzed Cross-Couplings
J . Org. Chem., Vol. 65, No. 17, 2000 5347
Con clu sion
In summary, the palladium-catalyzed cross-coupling
of silanol, silanediol, and silanetriol was revealed to occur
in the presence of Ag2O. A variety of aryl iodides smoothly
reacted with several aryl- and alkenylsilicon reagents.
These reactions were found to be specifically effective
when an aryl iodide was used as a substrate. Silanediols
and silanetriols were found, in general, much reactive
than silanols in the coupling reactions. XRD analyses
revealed that Ag2O was transformed to AgI through the
cross-coupling reaction. These results suggest that orga-
nosilicon reagents bearing hydroxy group(s) on silicon can
also be available as a cross-coupling reaction, which
serves as the second example of the transformation of
carbon-silicon bond of such compounds. Since syntheses
of silanols, silanediols, and silanetriols can be carried out
with simple procedures, synthetic application as a key
reaction for the construction of a variety of natural and
unnatural organic molecules would be available.
Exp er im en ta l Section
Gen er a l Meth od s. All reactions were carried out under an
argon atmosphere. Bu2O, dioxane, toluene, THF, and hexane
were distilled from sodium/benzophenone and DMF and
DMSO from calcium hydride. Hexamethylcyclotrisiloxane (D3)
was kindly donated by Shin-Etsu Chemical Co. Ltd. Ag2O was
purchased from Wako Pure Chemical Inc. and used without
further purification. XRD patterns were measured with Rigaku
X-RAY DIFFRACTIOMETER RINT Ultima+/PC.
F igu r e 1. XRD patterns: (A) The silver residue by the
reaction using 100 mol % of Ag2O; (B) the silver residue by 50
mol % of Ag2O; (C) Ag2O; (D) AgI.
P r ep a r a tion of Ar ylsila n ols. Synthesis of arylsilanols
1a -d were carried out in a manner similar to that described
in the literature.8c
F igu r e 2. Plausible intermediate.
Gen er a l P r oced u r e for th e Cou p lin g Rea ction of a
Sila n ol w ith a n Ar yl Ha lid e. To a solution of Pd(PPh3)4 (11.6
mg, 0.01 mmol) and Ag2O (46.3 mg, 0.2 mmol) in THF (2 mL)
were added sequentially aryl halide (0.2 mmol) and silanol
(0.24 mmol) at room temperature. The mixture was stirred at
60 °C for 36 h. The reaction mixture was diluted with diethyl
ether and then was passed briefly through an alumina pad.
The pad was washed with diethyl ether. The eluate was
washed with 1 M HCl (aq), saturated NaHCO3 (aq), and brine.
The organic layers were dried over anhydrous MgSO4, filtered,
and then concentrated in vacuo. The residue was purified by
flash column chromatography on silica gel (ethyl acetate/
hexanes or toluene/hexanes as eluents) to afford the corre-
sponding product. The following coupling products were
reported: 4-methoxy-4′-methyl-biphenyl (3b),25 4-methoxy-2′-
methyl-biphenyl (3c),26 4-methoxy-4′-trifluoromethyl-biphenyl
(3d ),3c,26 4-acetyl-4′-methoxy-biphenyl (3e),3b,25 4-methoxy-4′-
nitro-biphenyl (3f),27 4-bromo-4′-methoxy-biphenyl (3g),28 1-(4-
methoxyphenyl)-1-octene (3i),29 4-methoxystilbene (3j),30 and
(4-methoxyphenyl)(phenyl)methane (3k ).31
With these results in hand, the role of Ag2O may be
explained as follows: (i) Since the coupling of silanol is
specifically effective for the reaction with aryl iodide, the
silver would interact with intermediary organopalladium-
(II) iodide complex produced by the oxidative addition of
aryl iodide to palladium(0) due to the strong affinity of
iodine with silver.22 The effect may induce abstraction
of iodine to form a cationic palladium species23 that would
induce transmetalation of the organic group on silanol.
(ii) Ag2O or other basic species formed in situ may act as
a nucleophilic activator of silanol to form pentacoordinate
silicate species, which also facilitate the transfer of an
organic group on silicon to palladium (transmetalation).
However, use of other silver salts such as AgOTf,
AgBF4, and AgNO3, which may also be possible to form
the cationic palladium, were less effective (Table 1).
These findings are considerably unlikely to explain the
role (i). On the other hand, the fact that almost no
reaction has occurred in the use of aryl bromide and
-triflate hardly account for the role (ii).24 Thus, we
consider that the role of Ag2O may be cooperative with
both (i) and (ii), interacting with iodine atom and silanols
as shown in Figure 2.
4′-Met h oxyb ip h en yl-4-yl t r iflu or om et h a n esu lfon a t e
(3h ): 1H NMR (CDCl3) δ 3.86 (s, 3H), 6.99 (d, 2H, J ) 9.0 Hz),
7.31 (d, 2H, J ) 8.7 Hz), 7.49 (d, 2H, J ) 8.7 Hz), 7.60 (d, 2H,
J ) 9.0 Hz); 13C NMR (CDCl3) δ 55.4, 114.4, 118.8 (q, J ) 320.9
Hz), 121.5, 128.2, 128.3, 131.7, 141.3, 148.5, 159.7; IR (KBr)
(25) Farina, V.; Krishnan, B.; Marshall, D. R.; Roth, G. P. J . Org.
Chem. 1993, 58, 5434-5444.
(26) Wallow, T. I.; Novak, B. M. J . Org. Chem. 1994, 59, 5034-
5037.
(22) Ag2O is known to serve as an activator in the Williamson ether
synthesis, the reaction of alcohol with alkyl iodide. See: Walker, H.
G., J r.; Gee, M.; McCready, R. M. J . Am. Chem. Soc. 1962, 27, 2100-
2102.
(23) Halide abstraction by silver salt from arylpalladium halide to
give cationic palladium species. For example, see: Grove, D. M.; van
Koten, G.; Louwen, J . N.; Noltes, J . G.; Spec, A. L. J . Am. Chem. Soc.
1982, 104, 6609-6616.
(24) Although aryl bromide or triflate is less reactive in the oxidative
addition by Pd(0), such a drastic change in the yield (52% vs trace)
seems unlikely.
(27) Brune, H. A.; Stapp, B.; Schmidtberg, G. J . Organomet. Chem.
1986, 307, 129-137.
(28) Kelkar, A. A.; Hanaoka, T.; Kubota, Y.; Sugi, Y. Catal. Lett.
1994, 29, 69-75.
(29) Li, G. M.; Kamogawa, T.; Segi, M.; Nakajima, T. Chem. Express
1993, 8, 53-56.
(30) Maccarone, E.; Mamo, A.; Perrini, G.; Torre, M. J . Chem. Soc.,
Perkin Trans. 2 1981, 324-326.
(31) Fukuzawa, S.; Tsuchimoto, T.; Hiyama, T. J . Org. Chem. 1997,
62, 151-156.

5348 J . Org. Chem., Vol. 65, No. 17, 2000
Hirabayashi et al.
1495, 1427, 1297, 1215 cm-1. Anal. Calcd for C14H11F3O4: C,
50.60; H, 3.34. Found: C, 50.48; H, 3.28.
7.02 (m, 2H), 7.09-7.14 (m, 6H), 7.24-7.35 (m, 3H); 13C NMR
(CDCl3) δ -2.6, 126.2, 127.5, 127.8, 127.9, 128.8, 129.8, 136.5,
Eth yl(p h en yl)sila n ed iol (7a ) (Meth od A). To a vigor-
ously stirred solution of NaHCO3 (0.84 g, 10.0 mmol) in diethyl
ether/H2O (10 mL/40 mL) was slowly added a solution of
dichloro(ethyl)(phenyl)silane (1.03 g, 5.0 mmol) in 10 mL of
diethyl ether over 20 min. After being stirred for 5 min, the
phases were separated and the aqueous was extracted with
diethyl ether. The combined organic layers were washed with
brine, dried over sodium carbonate, and concentrated in vacuo.
The residue was washed with hexane to give 0.67 g of 7a (80%
yield): mp 69-70 °C dec; 1H NMR (CDCl3) δ 0.86 (q, 2H, J )
7.5 Hz), 1.04 (t, 3H, J ) 7.5 Hz), 2.65 (br s, 2H), 7.36-7.45
(m, 3H), 7.64-7.69 (m, 2H); 13C NMR (CDCl3) δ 6.3, 6.5, 127.9,
140.2, 140.8, 141.9; IR (KBr) 3250 (br), 968, 926, 908 cm-1
;
HRMS (EI, m/e) calcd for C15H16O2Si (M+) 256.0919, found
256.0904.
P h en ylsila n etr iol (9a ).16b Synthesis of 9a was carried out
in a manner similar to that of 7a (method A), 71% yield (white
solid). The produced 9a was subjected to the coupling reaction
without further purification: mp (dec) 125-126 °C; IR (KBr)
3220 (br), 999, 908, 858 cm-1
.
Gen er a l P r oced u r e for th e Cr oss-Cou p lin g Rea ction
of a Sila n ed iol or a Sila n etr iol w ith a n Ar yl Iod id e
(Rep r esen ta tive a s th e Rea ction of 7e a n d 2i). To a
mixture of silver(I) oxide (1.16 g, 5.0 mmol), 7e (1.16 g, 6.0
mmol), and Pd(PPh3)4 (0.16 g, 0.14 mmol) were successively
added 20 mL of THF and 2i (1.17 g, 5.0 mmol). The resulting
mixture was then heated at 60 °C, and stirring was continued
for 20 h. The mixture was cooled to room temperature, passed
through an alumina pad, and washed with diethyl ether. The
filtrate was washed with 1 M HCl (aq), saturated NaHCO3
(aq), and brine. The organic layer was dried over anhydrous
MgSO4 and concentrated under reduced pressure. The residue
was recrystallized from hexanes to give 0.71 g of 3j (68% yield).
Other reactions were carried out in a similar manner. For the
reactions in smaller scales, the purification could also be
carried out by column chromatography on silica gel using
hexanes/EtOAc or hexanes/toluene as an eluent. The spectro-
scopic data of 1,2-diphenyl-1-(4-methoxyphenyl)ethene
(3n ),33 was identical with those in the literature.
Gen er a l P r oced u r e for th e Cr oss-Cou p lin g th r ou gh
th e Hyd r olysis-Cou p lin g Sequ en ce w ith ou t Isola tion of
th e Cr u d e Sila n ed iols or Sila n etr iols. Dichloro[(E)-1-
hexenyl]methylsilane (0.12 g, 0.6 mmol) were subjected to the
hydrolysis by the method B to leave a liquid, which is a
complex mixture of oligomers (for 1H and 13C NMR; see
Supporting Information). The liquid was used directly to the
cross-coupling reaction in a manner similar to that of a
silanediol. All products obtained were identical with authentic
samples. Specroscopic data of 1-(4-cyanophenyl)-1-hexene
(3o),19 1-(4-methoxyphenyl)-1-hexene (3p ),34 and 1-(4-methoxy-
phenyl)-1-ethyl-1-butene (3q)35 were identical with those of
respective literature references.
P r ep a r a tion of a Sa m p le for XRD An a lysis. The proce-
dure described for the cross-coupling reaction was followed
using 1a (0.19 g, 1.2 mmol), 4-methoxyiodobenzene (0.23 g,
1.0 mmol), Pd(PPh3)4 (58 mg, 0.05 mmol), and Ag2O (0.23 g,
1.0 mmol, or 0.12 g, 0.5 mmol). The mixture involving a black
precipitate was filtered off and washed with ethanol and then
diethyl ether. The resulting solid was dried under reduced
pressure to give a black powder, which was subjected to a glass
plate for the XRD analysis and set in the diffractiometer. The
results were shown below.
Resid u e w ith 100 m ol % of Ag2O: 2θ (rel intensity) 18.582
(87), 20.558 (135), 26.698 (325), 32.841 (14663), 33.700 (795),
38.100 (4211), 47.180 (69), 51.456 (61), 54.981 (1946), 65.521
(1062), 68.879 (381).
Resid u e w ith 50 m ol % of Ag2O: 2θ (rel intensity) 22.359
(1256), 23.701 (3613), 25.321 (507), 32.840 (1431), 38.101
(1444), 39.202 (2553), 42.640 (594), 44.320 (279), 46.321 (1445),
55.001 (183), 59.301 (128), 64.500 (219).
130.2, 133.8, 135.0; IR (KBr) 3250 (br), 959, 878, 830 cm-1
;
HRMS (EI, m/e) calcd for C8H12O2Si (M+) 168.0606, found
168.0599.
Meth yl(p h en yl)sila n ed iol (7b)32 (Meth od C). To a solu-
tion of methyl(phenyl)silane (0.69 mL, 5.0 mmol) in phosphate
buffer (pH ) 6.84)/dioxane (0.9 mL/10 mL) was added 0.10 g
of Pd/C (5%). After being stirred at room temperature for 3 h,
the mixture was poured into diethyl ether/H2O and the phases
were separated. The aqueous layer was extracted with diethyl
ether. The combined organic layers were washed with brine,
dried over anhydrous sodium sulfate, and concentrated under
reduced pressure. The residue was recrystallized from hexane
to afford 0.69 g of 7b (90% yield): mp 85-86 °C dec; 1H NMR
(CDCl3) δ 0.44 (s, 3H), 2.66 (s, 2H), 7.36-7.47 (m, 3H), 7.65-
7.68 (m, 2H); 13C NMR (CDCl3) δ -1.8, 127,9, 130.2, 133.5,
136.0; IR (KBr) 3350 (br), 1028, 885, 787 cm-1
.
Eth yl(4-m eth ylp h en yl)sila n ed iol (7c) (Meth od B). To
a solution of aniline (1.82 mL, 20 mmol) and H2O (0.36 mL,
20 mmol) in 10 mL of diethyl ether was slowly added a solution
of dichloro(ethyl)(4-methylphenyl)silane (2.20 g, 10 mmol)
dissolved in 5 mL of diethyl ether over 20 min to form a white
precipitate, which was filtered off. The filtrate was concen-
trated under reduced pressure to leave a solid. Hexane was
added to the solid, and the suspension was vigorously stirred.
Then the mixture was filtered and dried under reduced
pressure to furnish 1.19 g of 7c (65% yield). The product could
be used for the coupling reaction without further purification,
although the attempted recrystallization was unsuccessful due
1
to the decomposition: mp 70-71 °C dec; H NMR (CDCl3) δ
0.85 (q, 2H, J ) 7.5 Hz), 1.03 (t, 3H, J ) 7.5 Hz), 2.37 (s, 3H),
3.15 (brs, 2H), 7.22 (d, 2H, J ) 8.1 Hz), 7.56 (d, 2H, J ) 8.1
Hz); 13C NMR (CDCl3) δ 6.4, 6.6, 21.6, 128.7, 131.5, 133.8,
140.2; IR (KBr) 3250 (br), 1119, 799 cm-1; HRMS (EI, m/e)
calcd for C9H14O2Si (M+) 182.0762, found 182.0766.
Eth yl(4-m eth oxyp h en yl)sila n ed iol (7d ). Synthesis of 7d
was carried out in a manner similar to that of 7c (method B),
79% yield (white solid). The product was used for the coupling
1
reactions without further purification: mp 69-70 °C dec; H
NMR (CDCl3) δ 0.84 (q, 2H, J ) 8.0 Hz), 1.03 (t, 3H, J ) 8.0
Hz), 3.77 (brs, 2H), 3.82 (s, 3H), 6.84 (d, 2H, J ) 8.7 Hz), 7.53
(d, 2H, J ) 8.7 Hz); 13C NMR (CDCl3) δ 6.4, 6.7, 55.0, 113.6,
126.2, 135.4, 161.2; IR (KBr) 3221 (br), 1283, 1030, 862 cm-1
;
HRMS (EI, m/e) calcd for C9H14O3Si (M+) 198.0711, found
198.0716.
Eth yl[(E)-2-p h en yleth en yl]sila n ed iol (7e). Synthesis of
7e was carried out in a manner similar to that of 7c (method
B), 74% yield (white solid). The product was used for the
coupling reactions without further purification: mp 106-107
Ag2O: 2θ (rel intensity) 7.718 (927), 8.478 (502), 9.640 (221),
12.841 (263), 21.321 (433), 22.360 (757), 23.259 (234), 23.702
(1777), 25.320 (329), 25.905 (136), 28.941 (209), 32.857 (357),
39.200 (1308), 42.640 (284), 46.320 (630),
1
°C dec; H NMR (CDCl3) δ 0.78 (q, 2H, J ) 7.7 Hz), 1.06 (t,
3H, J ) 7.7 Hz), 2.63 (br s, 2H), 6.33 (d, 1H, J ) 19.5 Hz),
7.17 (d, 1H, J ) 19.5 Hz), 7.26-7.39 (m, 3H), 7.43-7.51 (m,
2H); 13C NMR (CDCl3) δ 6.3, 6.8, 122.4, 126.7, 128.5, 128.6,
137.5, 147.5; IR (KBr) 3220, 994, 882, 737 cm-1; HRMS (EI,
m/e) calcd for C10H14O2Si (M+) 194.0762, found 194.0761.
Meth yl[(Z)-1,2-d ip h en yleth en yl]sila n ed iol (7f). Syn-
thesis of 7f was carried out in a manner similar to that of 7c
(method B), 62% yield (white solid). The product was used for
the coupling reactions without further purification: mp (dec)
85-86 °C; 1H NMR (CDCl3) δ 0.35 (s, 3H), 2.45 (br, 2H), 6.99-
AgI:36 2θ (rel intensity) 23.070 (100), 39.133 (60), 46.308
(30), 56.667 (6), 62.258 (8), 71.028 (8), 76.082 (6), 84.285 (4),
89.100 (4), 97.186 (4), 125.101 (4).
(33) Cacchi, S.; Felici, M.; Pietroni, B. Tetrahedron Lett. 1984, 25,
3137.
(34) Negishi, E.; Takahashi, T.; Baba, S.; Van Horn, D. E.; Okukado,
N. J . Am. Chem. Soc. 1987, 109, 2393-2401.
(35) Duboudin, J . G.; J ousseaume, B. J . Organomet. Chem. 1978,
162, 209.
(36) XRD pattern of AgI is available form International Centre for
Diffraction Data (ICDD).
(32) Harris, G. J . Chem. Soc. B 1970, 488-491.

Palladium-Catalyzed Cross-Couplings
J . Org. Chem., Vol. 65, No. 17, 2000 5349
by the hydrolysis of dichloro[(E)-1-hexenyl]silane (6g) and
comparison of 1H NMR spectra of 7b with the hydrolysis
product, giving the mixture of the corresponding oligosiloxanes
from 6b. This material is available free of charge via the
Internet at http://pubs.acs.org.
Ack n ow led gm en t. This work was supported by
Yamada Science Foundation and Asahi Glass Founda-
tion. Organosilicon reagents were kindly donated by
Shin-Etsu Chemical Co. Ltd.
Su p p or tin g In for m a tion Ava ila ble: 1H and 13C NMR
spectra of new silanediols (7a ,c-f) and of the crude silanediol
J O000679P