Synthesis of Arylsilanes via Palladium(0)-Catalyzed Silylation of Aryl Halides with Hydrosilane

Full text of DOI:10.1021/jo971143f

J . Org. Chem. 1997, 62, 8569-8571
8569
as Et3SiH, tended to form a C-H bond in preference to
a C-Si bond.8,9
Syn th esis of Ar ylsila n es via
P a lla d iu m (0)-Ca ta lyzed Silyla tion of Ar yl
Ha lid es w ith Hyd r osila n e
The results of the reaction of 4-iodoanisole (1) with 1.5
equiv of (EtO)3SiH (2) for 1 h at room temperature under
various conditions are listed in Table 1. The products
were contaminated with the normal cross-coupling
product,1c,9 anisole (4), in each case as a result of a
hydridic behavior of 2. Although we were unable to
completely control the selectivity of the products, the
(EtO)3SiH-base combination provided the predominant
formation of 4-(triethoxysilyl)anisole (3). As for the base,
the tertiary amines, such as Et3N and i-Pr2NEt, proved
to be highly effective (entries 2 and 3). In the absence of
a base or in the presence of other types of bases, the
reactions occurred insufficiently (entries 1, 4, and 5), even
though the cited simultaneous silylation and reduction
of alkyl iodides using Et2SiH2 was caused in the absence
of base.5 The use of amide solvents, such as NMP, DMF,
and DMA, is also essential for this silylation (entries 3
and 6). The reactions in other kind of solvents, such as
DMSO, MeCN, dioxane, and toluene, resulted in quite
low yields (entries 7 and 8).
Miki Murata, Katsuhiro Suzuki, Shinji Watanabe, and
Yuzuru Masuda*
Department of Materials Science, Kitami Institute of
Technology, Kitami 090, J apan
Received J une 24, 1997
Arylsilanes are both valuable intermediates in organic
synthesis1 and useful cross-linking agents.2 Accordingly,
much attention has been paid to their synthesis.3 Among
others, the catalytic cross-coupling reaction of organic
halides using disilanes as silicon sources has proven to
be a versatile method for synthesizing functionalized
organosilanes.4 Kunai and Ishikawa have recently re-
ported on a PdCl2-catalyzed Si-H/C-I exchange reaction
that formed an Si-I bond as well as an Si-C bond,5
indicating the potential use of hydrosilanes as silylating
reagents in the presence of palladium catalyst. To our
knowledge, however, there has been no report of pal-
ladium-catalyzed silicon-aryl carbon bond formation
using hydrosilane derivatives with high chemical selec-
tivity. We describe here the first and advantageous
example of a specific silylation of aryl iodides 1 with
triethoxysilane (EtO)3SiH (2) as a silicon source and
affording the corresponding arylsilanes 3 in high yield
(eq 1).
The reaction was efficiently catalyzed by Pd2-
(dba)3‚CHCl3 with 2 equiv (for Pd atom) of P(o-tol)3 (entry
2). The palladium complex having bulky phosphines may
effectively accelerate the oxidative addition step by ready
formation of a coordinatively unsaturated species.10 The
ratio of Pd2(dba)3‚CHCl3 to a phosphine ligand affected
the rate of the silylation; that is, more than 2 equiv of
P(o-tol)3 slowed the reaction rate extremely. And the
monodentate phosphine ligand was recognized to be more
effective than the bidentate ligand (entries 9 and 10).
Table 2 summarizes the results of the silylation of
representative aryl halides 1 with 2, which was con-
ducted in a manner similar to that above. Since the
desired 3 and reduced arenes 4 were purely and easily
separated by bulb-to-bulb distillation, although 3 was
contaminated with 4 in each case, the present reaction
should provide a simple and available procedure for
synthesizing arylsilanes 3. The rate of the silylation was
also affected by the sort of aryl halides used; that is, aryl
iodides 1 usually exhibited higher reactivity than aryl
bromides (entries 1 and 2). The presence of functional
groups such as MeCO2 in the starting 1 did not interfere
with the outcome of the present reaction, since the
reactants were inert to many functional groups (entry
5). However, although both aryl iodides 1 having electron-
donating groups and heteroaromatic iodides were very
readily silylated with 2 (entries 1, 3-7, 10, and 11), the
presence of electron-withdrawing groups significantly
decreased the yields and the selectivity of this silylation
(entries 8 and 9). Namely, aryl iodides having the latter
groups had a strong tendency to produce competitively
reduced arenes 4 (52 and 60%, GLC yields) as a result of
the respective acceleration both of the oxidative addition
Preliminary investigations indicated that the combina-
tion of 2 as hydrosilane and a tertiary amine was highly
efficient for this silylation of aryl iodides. It is known
that the Cl3SiH-Et3N combination greatly facilitates the
silylation of allyl6 or benzyl chlorides.7 However, the
present use of Cl3SiH was not suitable in the presence
of palladium complex, under which condition it merely
recovered the starting aryl halide. Furthermore, the
trialkylsilanes usually used as reducing reagents, such
(1) For the cross-coupling reaction with organic electrophiles, see:
(a) Hatanaka, Y.; Hiyama, T. Chem. Lett. 1989, 2049. (b) Hatanaka,
Y.; Fukushima, S.; Hiyama, T. Chem. Lett. 1989, 1771. (c) For a recent
review, see: Hatanaka, Y.; Hiyama, T. Synlett 1991, 845.
(2) For examples, see: (a) Loy, D. A.; Shea, K. J . Chem. Rev.
(Washington, D.C.) 1995, 95, 1431. (b) Baney, R. H.; Itoh, M.;
Sakakibara, A.; Suzuki, T. Chem. Rev. (Washington, D.C.) 1995, 95,
1409.
(3) (a) Colvin, E. W. Silicon Reagents in Organic Synthesis; Aca-
demic: New York, 1988; p 39. (b) Colvin, E. W. In The Chemistry of
the Metal-Carbon Bond; Hartley, F. R., Patai, S., Eds.; Wiley: New
York, 1987; Vol. 4, p 562.
(4) (a) Hatanaka, Y.; Hiyama, T. Tetrahedron Lett. 1987, 28, 4715.
(b) Yamamoto, K.; Suzuki, S.; Tsuji, J . Tetrahedron Lett. 1980, 21, 1653.
(c) Matsumoto, H.; Kasahara, M.; Takahashi, M.; Arai, T.; Nakao, T.;
Nagai, Y. J . Organomet. Chem. 1983, 250, 99. (d) Eaborn, C.; Griffiths,
R. W.; Pidcock, A. J . Organomet. Chem. 1982, 225, 331.
(5) Kunai, A.; Sakurai, T.; Toyoda, E.; Ishikawa, M.; Yamamoto, Y.
Organometallics 1994, 13, 3233.
(6) Furuya, N.; Sukawa, T. J . Organomet. Chem. 1975, 96, C1.
(7) Benkeser, R. A.; Gaul, J . M.; Smith, W. E. J . Am. Chem. Soc.
1969, 91, 3666.
(8) A mixture of Pd2(dba)3‚CHCl3 (0.015 mmol), P(o-tol)3 (0.06 mmol),
Et3SiH (1.5 mmol), iodobenzene (1.0 mmol), and i-Pr2NEt (3.0 mmol)
in NMP (4 mL) was stirred at room temperature for 2 h. The GLC
analysis of the reaction mixture indicated the formation of the
corresponding phenylsilane (34% yield).
(9) Boukherroub, R.; Chatgilialoglu, C.; Manuel, G. Organometallics
1996, 15, 1508 and references therein.
(10) Farina, V.; Krishnan, B. J . Am. Chem. Soc. 1991, 113, 9585.
S0022-3263(97)01143-2 CCC: $14.00 © 1997 American Chemical Society

8570 J . Org. Chem., Vol. 62, No. 24, 1997
Notes
intermediate in preference to the hydrosilane.9 However,
the present treatment of isolated Ar-PdII-X with (EtO)3-
SiH (2) and Et3N gave neither 3 nor 4.13,14 Consequently,
a mechanism involving oxidative addition of aryl halides
1 can effectively be ruled out in the present reaction. On
the other hand, Kunai and Ishikawa proposed a mech-
anism for the Si-H/C-I exchange involving oxidative
addition of the hydrosilane followed by σ-bond metathesis
between an Si-Pd bond and a C-I bond.5 In analogy
with this mechanism, the oxidative addition of (EtO)3-
SiH (2) must be a key step in the present silylation.
In conclusion, we found a new and useful synthesis of
arylsilanes 3 in which (EtO)3SiH (2) acted specifically as
a silicon source for the coupling reaction with aryl iodides
1 in the presence of the palladium catalyst and the
tertiary amine. Investigations for further mechanistic
studies and silylations with other organic halides are
currently in progress in our laboratory.
Ta ble 1. Rea ction of 4-Iod oa n isole u n d er Va r iou s
Con d ition sa
yield (%)b
entry
ligand
base
none
solvent
3
4
1
2
3
4
5
6
7
8
9
P(o-tol)3
P(o-tol)3
P(o-tol)3
P(o-tol)3
P(o-tol)3
P(o-tol)3
P(o-tol)3
P(o-tol)3
PPh3
NMP
NMP
NMP
NMP
NMP
DMF
DMSO
toluene
NMP
NMP
5
4
6
7
Et3N
88
92
4
72
82
31
6
i-Pr2NEt
pyridine
KOAc
i-Pr2NEt
i-Pr2NEt
i-Pr2NEt
i-Pr2NEt
i-Pr2NEt
5
23
17
19
5
19
1
76
0
10
dppe
a
Reactions of 4-iodoanisole (1) (1.0 mmol) with 2 (1.5 mmol)
were carried out at room temperature for 1 h in 4 mL of solvent
by using 0.015 mmol of Pd2(dba)3‚CHCl3, phosphine ligand (0.06
b
mmol), and base (3 mmol). GLC yields are based on 1 used.
Ta ble 2. P a lla d iu m -Ca ta lyzed Silyla tion of Ar yl Ha lid esa
Exp er im en ta l Section
Gen er a l. All the experiments were carried out under an
argon atmosphere. NMP was distilled from CaH2 before use. A
commercial triethoxysilane was used directly. NMR spectra
were recorded on a J EOL J NM-FX-200 spectrometer (1H, 199.5
MHz; 13C, 50.1 MHz). EI mass spectra were obtained at an
ionization potential of 70 eV with a J EOL J MS-SX102 spec-
trometer. CAUTION! A hood should be worn while handling
triethoxysilane and all contact with the eyes avoided.16
Syn th esis of tr ieth oxyp h en ylsila n e.17 Typ ica l P r oce-
d u r e. Triethoxyphenylsilane synthesis is used to illustrate the
general procedure for synthesizing arylsilanes. To a solution
of Pd2(dba)3‚CHCl3 (80 mg, 0.08 mmol) and P(o-tol)3 (91 mg, 0.3
mmol) in NMP (20 mL) were added iodobenzene (1.00 g, 4.90
mmol), i-Pr2NEt (2.6 mL, 15 mmol), and triethoxysilane (1.24
g, 7.5 mmol). After being stirred for 1 h at room temperature,
the mixture was extracted with benzene. The extract was
washed three times with water to remove NMP, dried over
MgSO4, and concentrated. The residue was purified by Kugel-
rohr distillation to give 846 mg (72% yield) of analytically and
spectroscopically pure triethoxyphenylsilane: 1H NMR (CDCl3)
δ 1.25 (t, J ) 7.0 Hz, 9 H), 3.88 (q, J ) 7.0 Hz, 6 H), 7.3-7.5 (m,
3 H), 7.6-7.8 (m, 2 H); 13C NMR (CDCl3) δ 18.12, 58.68, 127.78,
130.22, 131.08, 134.74; MS (m/z) 240 (16), 195 (38), 181 (13),
162 (28), 147 (100), 139 (33), 135 (33); HRMS for C12H20O3Si
calcd 240.1182, found 240.1141.
4-(Tr ieth oxysilyl)a n isole:17c,d IR (neat) 2975, 2360, 1598,
1567, 1506, 1459, 1390, 1282, 1250 cm-1 1H NMR (CDCl3) δ
;
1.24 (t, J ) 7.0 Hz, 9 H), 3.86 (q, J ) 7.0 Hz, 6 H), 6.92 (d, J )
8.6 Hz, 2 H), 7.61 (d, J ) 8.6 Hz, 2 H); 13C NMR (CDCl3) δ 18.12,
54.89, 58.55, 113.57, 122.00, 136.37, 161.37; MS (m/z) 270 (52),
255 (53), 225 (38), 211 (25), 181 (28), 169 (27), 149 (22), 147 (100),
135 (32); HRMS for C13H22O4Si calcd 270.1287, found 270.1261.
4-(Tr ieth oxysilyl)-N,N-d im eth yla n ilin e:17c IR (neat) 2973,
2884, 1600, 1517, 1389, 1360, 1167, 1077 cm-1; 1H NMR (CDCl3)
δ 1.23 (t, J ) 7.0 Hz, 9 H), 2.97 (s, 3 H), 3.85 (q, J ) 7.0 Hz, 6
H), 6.71 (d, J ) 8.8 Hz, 2 H), 7.53(d, J ) 8.8 Hz, 2 H); 13C NMR
a
Reactions of aryl halide 1 (1.0 equiv) with 2 (1.5 equiv) were
carried out at room temperature in NMP by using Pd2(dba)3‚CHCl3
(1.5 mol %), P(o-tol)3 (6 mol %), and Pr2NEt (3 equiv). b GLC yields
i
are based on 1 used. Those in parentheses are isolated yield. c The
d
reaction was carried out at 50 °C. At 80 °C.
(13) Benkeser proposed that a silyl anion species was generated by
the Et3N-hydrosilane system.7 It is believed that transmetalation
between an R-PdII-X and
formation of an Si-C bond.4a
a silyl anion analogue provides the
to form an Ar-PdII-X and the following transmetalation
with the hydride.11
(14) To a solution of (4-MeO-C6H4)PdI(PPh3)215 (0.050 mmol) in DMF
(1 mL) were added Et3N (0.30 mmol) and (EtO)3SiH (0.098 mmol). After
being stirred at 50 °C for 6 h, the GLC analysis indicated neither the
formation of the corresponding arylsilane nor that of anisole.
(15) Fitton, P.; Rick, E. A. J . Organomet. Chem. 1971, 28, 287.
(16) Encyclopedia of Reagents for Organic Synthesis; Paquette, L.
A., Ed.; Wiley: New York, 1995; Vol. 7, p 5083.
Bearing in mind the previously described result,12
a
hydrosilane as well as an aryl halide can add oxidatively
to palladium(0) complexes. Chatgilialoglu presented that
the organic halides were the first to be added oxidatively
to the palladium(0) complexes, forming an R-PdII-X
(17) (a) Chappelow, C. C.; Elliott, R. L.; Goodwin, J . T., J r. J . Org.
Chem. 1960, 25, 435. (b) Sobolevskii, M. V.; Kleshchevnikova, S. I.;
Rumyantseva, E. I.; Abramova, E. A; Dubrovskaya, G. A. Plast. Massy
1971, 9. (c) Lutskii, A. E.; Abukhova, E. M.; Voronkov, M. G.; Alksne,
V. Teor. Eksp. Khim. 1973, 9, 123. (d) Ernst, C. R.; Spialter, L.; Buell,
G. R.; Wilhite, D. L. J . Am. Chem. Soc. 1974, 96, 5375. (e) Chuy, N.
D.; Chvalovsky, V.; Schraml, J .; Magi, M.; Lippmaa, E. Collect. Czech.
Chem. Commun. 1974, 40, 875.
(11) (a) Echavarrene, A. M.; Stille, J . K. J . Am. Chem. Soc. 1988,
110, 1557. (b) Baillargeon, V. P.; Stille, J . K. J . Am. Chem. Soc. 1986,
108, 452.
(12) For a recent review of Pd-catalyzed hydrosilylation, see: Horn,
K. A. Chem. Rev. (Washington, D.C.) 1995, 95, 1317.

Notes
J . Org. Chem., Vol. 62, No. 24, 1997 8571
(CDCl3) δ 18.16,39.90, 58.43, 111.57, 115.69, 135.96, 151.76; MS
(m/z) 283 (100), 238 (12), 182 (8), 166 (13), 147 (29), 122 (12);
HRMS for C14H25O3NSi calcd 283.1604, found 283.1630.
4-(Tr ieth oxysilyl)a ceta n ilid e: IR (neat) 3307, 2975, 1669,
14.16, 54.84, 56.96, 124.55, 128.05, 130.70, 132.94, 162.63; MS
(m/z) 312 (5), 267 (100), 253 (15), 239 (61), 223 (16), 195 (22),
183 (17), 163 (25), 147 (20), 135 (8); HRMS for C15H24O5Si calcd
312.1393, found 312.1392.
1
1593, 1525, 1392, 1318, 1291 cm-1; H NMR (CDCl3) δ 1.24 (t,
4-(Tr ieth oxysilyl)ben zon itr ile: IR (neat) 2977, 2231, 1444,
1
J ) 6.8 Hz, 9 H), 2.18 (s, 3 H), 3.85 (q, J ) 6.8 Hz, 6 H), 7.52 (d,
J ) 8.3 Hz, 2 H), 7.64 (d, J ) 8.3 Hz, 2 H); 13C NMR (CDCl3) δ
18.18, 24.46, 58.71, 119.11, 128.64, 135.67, 140.10, 168.97; MS
(m/z) 297 (10), 252 (68), 205 (100), 176 (31), 162 (15), 147 (48);
HRMS for C14H23O4NSi calcd 297.1396, found 297.1399.
4-Acetoxy(tr ieth oxysilyl)ben zen e: IR (neat) 2976, 2887,
1767, 1593, 1499, 1392 cm-1; 1H NMR (CDCl3) δ 1.22 (t, J ) 6.8
Hz, 9 H), 2.28 (s, 3 H), 3.84 (q, J ) 6.8 Hz, 6 H), 7.09 (d, J ) 8.3
Hz, 2 H), 7.67 (d, J ) 8.3 Hz, 2 H); 13C NMR (CDCl3) δ 18.11,
20.98, 58.68, 120.98, 128.55, 136.06, 152.48, 169.00; MS (m/z)
298 (3), 256 (100), 210 (51), 183 (17), 155 (27), 147 (62); HRMS
for C14H22O5Si calcd 298.1237, found 298.1238.
1390, 1296 cm-1; H NMR (CDCl3) δ 1.25 (t, J ) 7.0 Hz, 9 H),
3.88 (q, J ) 7.0 Hz, 6 H), 7.65 (d, J ) 8.3 Hz, 2 H), 7.78 (d, J )
8.3 Hz, 2 H); 13C NMR (CDCl3) δ 18.16, 59.04, 113.93, 131.12,
135.23, 137.88, 159.74; MS (m/z) 265 (43), 250 (17), 220 (100),
206 (46), 192 (20), 176 (34), 164 (62); HRMS for C13H19O3NSi
calcd 265.1134, found 265.1144.
2-(Tr ieth oxysilyl)th iop h en e:18 IR (neat) 2976, 2888, 1695,
1501, 1442, 1407, 1391, 1296, 1216, 1167 cm-1; 1H NMR (CDCl3)
δ 1.25 (t, J ) 7.0 Hz, 9 H), 3.90 (q, J ) 7.0 Hz, 6 H), 7.22 (dd, J
) 3.3, 4.5 Hz, 1 H), 7.48 (d, J ) 3.3 Hz, 1 H), 7.66 (d, J ) 4.5 Hz,
1 H); 13C NMR (CDCl3) δ 19.42, 60.26, 129.37, 130.63, 133.15,
138.12; MS (m/z) 246 (52), 213 (6), 201 (34), 187 (7), 167 (7), 158
(13), 147 (100), 135 (34); HRMS for C10H18O3SiS calcd 246.0765,
found 246.0746.
4-(Tr ieth oxysilyl)tolu en e:17c,d IR (neat) 2975, 2926, 2360,
1
1604, 1443, 1390, 1295, 1167 cm-1; H NMR (CDCl3) δ 1.24 (t,
J ) 7.0 Hz, 9 H), 2.36 (s, 3 H), 3.86 (q, J ) 7.0 Hz, 6 H), 7.19 (d,
J ) 7.9 Hz, 2 H), 7.57(d, J ) 7.9 Hz, 2 H); 13C NMR (CDCl3) δ
18.16, 21.50, 58.59, 127.41, 128.59, 134.82, 140.20; MS (m/z) 254
(23), 209 (38), 181 (5), 165 (16), 162 (30), 153 (19), 147 (100),
135 (17); HRMS for C13H22O3Si calcd 254.1363, found 254.1338.
4-Ch lor o(tr ieth oxysilyl)ben zen e:17d IR (neat) 2975, 2888,
3-(Tr ieth oxysilyl)p yr id in e:19 1H NMR (CDCl3) δ 1.26 (t, J
) 6.8 Hz, 9 H), 3.90 (q, J ) 6.8 Hz, 6 H), 7.2-7.3 (m, 1 H), 7.95
(d, J ) 5.9 Hz, 1 H), 8.65 (d, J ) 4.9 Hz, 1 H), 8.83 (s, 1 H); 13
C
NMR (CDCl3) δ 18.04, 58.80, 123.07, 126.55, 142.36, 151.05,
154.99; MS (m/z) 241 (54), 240 (100), 226 (18), 212 (27), 196 (88),
147 (29), 182 (25); HRMS for C11H19O3NSi calcd 241.1134, found
241.1112.
1
2360, 1699, 1583, 1557, 1485, 1443, 1389, 1296, 1261 cm-1; H
NMR (CDCl3) δ 1.17 (t, J ) 7.0 Hz, 9 H), 3.79 (q, J ) 7.0 Hz, 6
H), 7.28 (d, J ) 8.5 Hz, 2 H), 7.54 (d, J ) 8.5 Hz, 2 H); 13C NMR
(CDCl3) δ 18.12, 58.75, 128.06, 129.53, 136.13, 136.70; MS
(m/z) 274 (3), 239 (27), 229 (44), 185 (15), 173 (25), 162 (31), 147
(100), 135 (9); HRMS for C12H19O3ClSi calcd 274.0792, found
274.0792.
Ack n ow led gm en t. We are grateful to Dr. Tatsuo
Ishiyama and Professor Norio Miyaura of Hokkaido
University for their useful discussions and suggestions.
J O971143F
Eth yl 4-(Tr ieth oxysilyl)ben zoa te: IR (neat) 2977, 2928,
1
2361, 1720, 1558, 1445, 1391, 1367, 1279, 1101 cm-1; H NMR
(18) Voronkov, M. G.; Zelchan, G. I.; Savushkina, V. I.; Tabenko, B.
M.; Chernyshev, E. A. Khim. Geterotsikl. Soedin. 1976, 772.
(19) Rubinsztain, S.; Zeldin, M.; Fife, W. K. Synth. React. Inorg.
Met.-Org. Chem. 1990, 20, 495.
(CDCl3) δ 1.24 (t, J ) 7.0 Hz, 9 H), 1.47 (t, J ) 7.0 Hz, 3 H),
3.88 (q, J ) 7.0 Hz, 6 H), 4.39 (q, J ) 7.0 Hz, 2 H), 7.74 (d, J )
8.2 Hz, 2 H), 8.04 (d, J ) 8.2 Hz, 2 H); 13C NMR (CDCl3) δ 10.29,