Efficient preparation of monohydrosilanes using palladium-catalyzed Si-C bond formation

Article abstract of DOI:10.1021/ol701820j

(Chemical Equation Presented) The arylation of dihydrosilanes with aryl iodides or heteroaryl iodides in the presence of a palladium catalyst provides the corresponding monohydrosilanes in good to high yield. Moderate to good yields are obtained even in the presence of a variety of reactive functional groups, such as -NH₂, -OH, or -CN, without their protection.

Full text of DOI:10.1021/ol701820j

ORGANIC
LETTERS
2007
Vol. 9, No. 22
4543-4546
Efficient Preparation of
Monohydrosilanes Using
Palladium-Catalyzed Si
Formation
−C Bond
Yoshinori Yamanoi,* Takafumi Taira, Jun-ichi Sato, Ikuse Nakamula, and
Hiroshi Nishihara*
Department of Chemistry, School of Science, The UniVersity of Tokyo, 7-3-1 Hongo,
Bunkyo-ku, Tokyo 113-0033, Japan
yamanoi@chem.s.u-tokyo.ac.jp; nisihara@chem.s.u-tokyo.ac.jp
Received August 11, 2007
ABSTRACT
The arylation of dihydrosilanes with aryl iodides or heteroaryl iodides in the presence of a palladium catalyst provides the corresponding
monohydrosilanes in good to high yield. Moderate to good yields are obtained even in the presence of a variety of reactive functional groups,
such as
−NH2, −OH, or −CN, without their protection.
The transition-metal-catalyzed cross-coupling reaction has
become an important method for carbon-heteroatom bond
formation.1 In particular, there have been significant devel-
opments in the formation of carbon-silicon bonds due to
the recent interest in organosilane compounds as intermedi-
ates for Hiyama coupling2 and in advanced materials such
as ultrahigh energy gap hosts in deep blue organic electro-
phosphorescent devices.3 In particular, monohydrosilanes are
extremely useful intermediates to construct novel organo-
silicon compounds. Although their preparation has been
traditionally accomplished by the treatment of Grignard or
organolithium reagents with dichlorosilanes followed by the
treatment of LiAlH4 (Scheme 1, Route A), this method is a
multistep process and is available only for a limited number
of substrates.4 A recent strategy is the direct conversion of
carbon-halogen bonds to carbon-silicon bonds with hy-
drosilanes in the presence of transition-metal catalysts.5-7
During the course of our studies, we have developed a
method for palladium- and rhodium-catalyzed silylation of
(1) For representative reviews, see: (a) Hartwig, J. F. Pure Appl. Chem.
1999, 71, 1417. (b) Beletskaya, I. P. Pure Appl. Chem. 2005, 77, 2021. (c)
Hassan, J.; Se´vignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M. Chem. ReV.
2002, 102, 1359. (d) Denmark, S. E.; Sweis, R. F. In Metal-Catalyzed Cross-
Coupling Reactions, 2nd ed.; de Meijere, A., Diederich, F., Eds.; Wiely-
VCH: Weinheim, 2004. (e) Tsuji, J. Palladium Reagents and Catalysts;
John Wiley & Sons: Chichester, 2004. (f) Prim, D.; Campagne, J.-M.;
Joseph, D.; Andrioletti, B. Tetrahedron 2002, 58, 2041.
(2) (a) Nakao, Y.; Sahoo, A. K.; Imanaka, H.; Yada, A.; Hiyama, T.
Pure Appl. Chem. 2006, 78, 435. (b) Denmark, S. E.; Ober, M. H. Aldrichim.
Acta 2003, 36, 75. (c) Hiyama, T.; Shirakawa, E. Top. Curr. Chem. 2002,
219, 61. (d) Horn, K. A. Chem. ReV. 1995, 95, 1317. (e) Hatanaka, Y.;
Hiyama, T. Synlett 1991, 845.
(3) (a) Ren, X.; Li, J.; Holmes, R.; Djurovich, P.; Forrest, S.; Thompson,
M. Chem. Mater. 2004, 16, 4743. (b) Liu, X.-M.; He, C.; Huang, J.; Xu, J.
Chem. Mater. 2005, 17, 434.
(4) Patai, S., Rappoport, Z., Eds. The Chemistry of Organic Silicon
Compounds; John Wiley & Sons: New York, 1989.
10.1021/ol701820j CCC: $37.00
© 2007 American Chemical Society
Published on Web 09/29/2007

Scheme 1. Preparation of Monohydrosilanes
Table 1. Optimization of the Preparation of
4-Methoxyphenyldiphenylsilanea
entry
cat.
base
Et3N
Et3N
Et3N
solvent
yieldb (%)
1
2
3
4
5
6
7
8
9
Pd(P(t-Bu)3)2
Pd(PPh3)4
Pd(PCy3)2
Pd(P(t-Bu)3)2
Pd(P(t-Bu)3)2
Pd(P(t-Bu)3)2
Pd(P(t-Bu)3)2
Pd(P(t-Bu)3)2
Pd(P(t-Bu3)2
THF
THF
THF
THF
THF
THF
THF
dioxane
toluene
79
35
trace
d
63
23
5
c
i-Pr2EtN
K3PO4
Na2CO3
Et3N
47
43
aryl halides with monohydrosilanes in the presence of
K3PO4.8 To expand the application of this method, we have
developed a convenient and efficient approach (only one
step!) to the preparation of monohydrosilanes (Scheme 1,
Route B).9
Et3N
a Reaction conditions: 4-iodoanisole (1.0 mmol), diphenylsilane (1.5
mmol), triethylamine (1.5 mmol), palladium catalyst (0.05 mmol), THF
(1.0 mL) at rt for 2 d. b Isolated yield. c No base was added. d No appreciable
reaction.
Initially, the effects of catalysts, solvents, and bases in
the monoarylation of diphenylsilane with 4-iodoanisole were
examined. The results are shown in Table 1. Among the
several transition-metal catalysts screened, Pd(P(t-Bu3))2 was
a quite effective palladium source.10 The reaction proceeded
smoothly at 5 mol % catalyst loading. The phosphine ligand
of palladium catalyst affected the silylation markedly; i.e.,
Pd(PCy3)2 and Pd(PPh3)4 did not show good catalytic activity.
After screening bases, we recognized Et3N as being the most
effective. The desired product was obtained in low yield
without base. Among the solvents examined, the use of THF
was essential for this silylation. Room temperature was found
to be optimal for the reaction. The optimized conditions for
the monoarylation were 4-iodoanisole (1.0 equiv), diphenyl-
silane (1.5 equiv), Et3N as base (1.5 equiv), and 5 mol % of
Pd(P(t-Bu)3)2 in THF at room temperature under an argon
atmosphere, which afforded the monoarylated product in 79%
isolated yield.
We next focused our attention on the scope of the leaving
group on the aromatic ring. As outlined in Table 2, iodide,
Table 2. Effect of Leaving Groupa
(5) Hydrosilanes generally work as reducing reagents in the presence of
palladium catalyst. For example, see: (a) Boukherroub, R.; Chatgilialoglu,
C.; Manuel, G. Organometallics 1996, 15, 1508. (b) Fuwa, H.; Sasaki, M.
Org. Bio. Chem. 2007, 5, 1849.
entry
X
additive
yieldb (%)
(6) For example, see: (a) Murata, M.; Ota, K.; Yamasaki, H.; Watanabe,
S.; Masuda, Y. Synlett 2007, 1387. (b) Murata, M.; Yamasaki, H.; Ueta,
T.; Nagata, M.; Ishikura, M.; Watanabe, S.; Masuda, Y. Tetrahedron 2007,
63, 4087. (c) Murata, M.; Ohara, H.; Oiwa, R.; Watanabe, S.; Masuda, Y.
Synthesis 2006, 1771. (d) Hamze, A.; Provot, O.; Alami, M.; Brion, J.-D.
Org. Lett. 2006, 8, 931. (e) Karshtedt, D.; Bell, A. T.; Tilley, T. D.
Organometallics 2006, 25, 4471. (f) Denmark, S. E.; Kallemeyn, J. M. Org.
Lett. 2003, 5, 3483. (g) Komuro, K.; Ishizaki, K.; Suzuki, H. Touagousei-
kenkyu-nenpo 2003, 6, 24. (h) Gu, W.; Liu, S.; Silverman, R. B. Org. Lett.
2002, 4, 4171. (i) Murata, M.; Ishikura, M.; Nagata, M.; Watanabe, S.;
Masuda, Y. Org. Lett. 2002, 4, 1843. (j) Manoso, A. S.; Deshong, P. J.
Org. Chem. 2001, 66, 7455. (k) Murata, M.; Watanabe, S.; Masuda, Y.
Tetrahedron Lett. 1999, 40, 9255. (l) Murata, M.; Suzuki, K.; Watanabe,
S.; Masuda, Y. J. Org. Chem. 1997, 62, 8569.
1
2
3
4
5
I
c
c
79
trace
14
d
Br
Br
Cl
OTf
Et4NI
c
c
d
a Reaction conditions: aryl halide or triflate (1.0 mmol), diphenylsilane
(1.5 mmol), triethylamine (1.5 mmol), palladium catalyst (0.05 mmol), THF
(1.0 mL), at rt for 2 days. b Isolated yield. c No additive. d Almost full
recovery of starting material.
(7) Although the transition-metal-catalyzed hydrogenative coupling of
Si-H bonds with aromatic C-H bonds has been reported, the reaction is
a little problematic with regard to the control of selectivity due to the drastic
conditions. For recent representative reports, see: (a) Tsukada, N.; Hartwig,
J. F. J. Am. Chem. Soc. 2005, 127, 5022. (b) Ezbiansky, K.; Djurovich, P.
I.; LaForest, M.; Sinning, D. J.; Zayes, R.; Berry, D. H. Organometallics
1998, 17, 1455.
(8) (a) Yamanoi, Y. J. Org. Chem. 2005, 70, 9607. (b) Yamanoi, Y.;
Nishihara, H. Tetrahedron Lett. 2006, 47, 7157.
(9) Fujiwara et al. reported the selective preparation of monohydrosilanes
by the reactions of dihydrosilanes with an equivalent amount of organo-
lanthanide iodides. (a) Jin, W.-S.; Makioka, Y.; Kitamura, T.; Fujiwara, Y.
Chem. Commun. 1999, 955. (b) Makioka, Y.; Fujiwara, Y.; Kitamura, T.
J. Organomet. Chem. 2000, 611, 509.
bromide, chloride, and triflate were all tested as leaving
groups. Unfortunately, bromide, chloride, and triflate did not
have enough reactivity; i.e., there was almost complete
recovery of starting materials. In the case of aryl bromide,
we then examined a treatment with an additional equal
amount of tetraethylammonium iodide, and the yield of
silylation slightly increased.
On the basis of these results, we examined the applicability
of this catalytic system to other aryl iodides and dihydro-
4544
Org. Lett., Vol. 9, No. 22, 2007

silanes. A variety of triorganosilanes were synthesized in a
one-step process in good to high yields in the presence of
Pd(P(t-Bu)3)2 with Et3N in THF at rt for 2 d.11 The
representative results are shown in Table 3. Substituents on
substituted aryl halides gave corresponding arylsilanes in
good yields (entries 3, 7, 13, 14, 19, and 20). However, it
was difficult to couple 2,6-disubstituted aryl iodide with
diphenylsilane because of the large steric effect (entry 11).
Furthermore, heteroaromatic iodides were also coupled with
dihydrosilanes without any difficulty (entries 8, 9, and 17).
As a whole, the silylated products were contaminated with
a small amount of the reduced byproducts in every case.
However, their separation was very easy. Accordingly, the
present reaction provides a simple and widely available
procedure for the preparation of monohydrosilane.12,13
Although the mechanistic details of the reaction are not
yet clear, we envisaged the pathway for Si-C bond forma-
tion as depicted in Scheme 2. Initially, dihydrosilanes would
Table 3. Arylation of Dihydrosilanes Mediated by Palladium
Catalyst
yieldb
(%)
entry
R
Ar
conditionsa product
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
4-MeOC6H4
Ph
A
A
A
A
A
A
A
A
A
A
A
A
A
A
B
C
A
A
A
A
1
2
3
4
5
6
7
8
9
79
63
78
62
63
66
60
66
77
67
c
91
79
84
46
64
60
76
65
70
Scheme 2. Reaction Mechanism
2-MeOC6H4
4-MeC6H4
3-MeC6H4
3-H2NC6H4
1-naphthyl
2-C4H4S
3-C4H4S
4-F3CC6H4
2,6-Me2C6H3
10
-
1-naphthyl 4-MeOC6H4
1-naphthyl 2-MeOC6H4
1-naphthyl 2,4-Me2C6H3
1-naphthyl 4-HOC6H4
1-naphthyl 4-NCC6H4
1-naphthyl 2-C4H4S
1-naphthyl 4-F3CC6H4
Me
Me
11
12
13
14
15
16
17
18
19
add oxidatively to Pd(0) to generate the H-PdII-SiHR2
species. Then, a pathway through σ-bond metathesis14,15
between the Pd(II) species and aryl iodide would lead to the
arylsilanes (Scheme 2(a)). However, we cannot completely
rule out a pathway through further oxidative addition of Ar-I
2-MeOC6H4
2-MeC6H4
a Reaction conditions. A: aryl iodide (1.0 mmol), dihydrosilane (1.5
mmol), triethylamine (1.5 mmol), Pd(P(t-Bu)3)2 (0.05 mmol), THF (1.0 mL),
at rt for 2 d. B: aryl iodide (1.0 mmol), dihydrosilane (3.0 mmol),
triethylamine (3.0 mmol), Pd(P(t-Bu)3)2 (0.05 mmol), THF (1.0 mL), at rt
for 2 d. C: aryl iodide (1.0 mmol), dihydrosilane (3.0 mmol), triethylamine
(3.0 mmol), Pd(P(t-Bu)3)2 (0.05 mmol), THF (1.0 mL), at 0 °C for 5 d.
b Isolated yield. c Not obtained.
(11) Typical Experimental Procedure for a Palladium-Catalyzed
Monoarylation Reaction. The general procedure for palladium-catalyzed
silylation is illustrated by the synthesis of (4-methoxyphenyl)diphenylsilane.
To a solution of Pd(P(t-Bu)3)2 (25 mg 0.049 mmol) in THF (1.0 mL) were
added diphenylsilane (0.32 mL, 1.5 mmol), 4-iodoanisole (234 mg 1.0
mmol), and triethylamine (0.40 mL, 3.0 mmol). After being stirred for 2 d
at room temperature, the reaction mixture was quenched with water,
extracted with CH2Cl2 three times, and dried over Na2SO4. The solvent
was evaporated under reduced pressure, and column chromatography on
slica gel (eluent: hexane/EtOAc ) 10/1) afforded (4-methoxyphenyl)-
diphenylsilane (229 mg, 79%).
(12) In all cases, reduced products (arenes) were observed as side
products, and no double- arylated products were observed by GC-MS
measurement of the reaction mixture. However, double-arylated products
were obtained in the presence of an excess amount of aryl iodides for a
prolonged reaction time. For the preparation of double- arylated products,
see ref 13.
(13) Typical Experimental Procedure for Palladium-Catalyzed
Double-Arylation Reactions. The procedure for palladium-catalyzed
silylation is illustrated by the synthesis of di(4-methoxyphenyl)diphenyl-
silane. To a solution of Pd(P(t-Bu)3)2 (12.8 mg, 0.025 mmol) in THF (1.0
mL) were added diphenylsilane (94 µL, 0.5 mmol), aryl iodide (1.5 mmol),
and triethylamine (0.2 mL, 1.5 mmol). After being stirred for 4 d at room
temperature, the reaction mixture was quenched with water, extracted with
CH2Cl2 three times, and dried over Na2SO4. The solvent was evaporated
under reduced pressure, and fractionated column chromatography was
carried out on silica gel to afford the double-arylated product: tetra-
phenylsilane (20), 49%; di(4-methoxyphenyl)diphenylsilane (21), 72%; and
di(4-methylthiophenyl)diphenylsilane (22), 58%.
the aromatic ring little influenced the yield of silylated
products. This arylation has proved to be compatible with
reactive functional groups such as the free amine (-NH2),
phenolic moiety (-OH), or nitrile group (-CN) (entries 6,
15, and 16) on the aromatic ring. In contrast, the traditional
methods through Grignard or organolithium reagents require
protection of the functional group.4 In addition, ortho-
(10) For representative studies on the use of P(t-Bu)3 in palladium-
catalyzed coupling reactions, see: (a) Nishiyama, M.; Yamamoto, T.; Koie,
Y. Tetrahedron Lett. 1998, 39, 617. (b) Yamamoto, T.; Nishiyama, M.;
Koie, Y. Tetrahedron Lett. 1998, 39, 2367. (c) Watanabe, M.; Nishiyama,
M.; Koie, Y. Tetrahedron Lett. 1999, 40, 8837. (d) Watanabe, M.;
Nishiyama, M.; Yamamoto, T.; Koie, Y. Tetrahedron Lett. 2000, 41, 481.
(e) Littke, A. F.; Fu, G. C. Angew. Chem., Int. Ed. 1998, 37, 3387. (f)
Shaughnessy, K. H.; Kim, P.; Hartwig, J. F. J. Am. Chem. Soc. 1999, 121,
2123. (g) Littke, A. F.; Fu, G. C. J. Org. Chem. 1999, 64, 10. (h) Netherton,
M. R.; Fu, G. C. Org. Lett. 2001, 3, 4295. (i) Hundertmark, T.; Littke, A.
F.; Buchwald, S. L.; Fu, G. C. Org. Lett. 2000, 2, 1729. (j) Dai, C.; Fu, G.
C. J. Am. Chem. Soc. 2001, 123, 2719. (k) Littke, A. F.; Dai, C.; Fu, G. C.
J. Am. Chem. Soc. 2000, 122, 4020. (l) Littke, A. F.; Fu, G. C. J. Am.
Chem. Soc. 2001, 123, 6989. (m) Fu, G. C. J. Org. Chem. 2004, 69, 3245.
(14) Kunai and his co-workers reported that the PdCl2-catalyzed reaction
of alkyl iodides with Et2SiH2 afforded REt2SiI and Et2SiI2 through σ-bond
metathesis. Kunai, A.; Sakurai, T.; Toyoda, E.; Ishikawa, M.; Yamamoto,
Y. Organometallics 1994, 13, 3233.
(15) For a review, see: Perutz, R. N.; Sabo-Etienne, S. Angew. Chem.,
Int. Ed. 2007, 46, 2578.
Org. Lett., Vol. 9, No. 22, 2007
4545

to form a Pd(IV) intermediate (Scheme 2(b)).16 The present
experimental studies cannot ascertain which mechanism is
actually taking place.
reaction mechanism and to extend the application of the
system are underway in our laboratory.
In summary, an inexpensive and highly efficient catalytic
system for the preparation of monohydrosilanes has been
developed. Compared with traditional methods, several
interesting features are apparent on the basis of the present
results, including the following: (1) The catalytic system is
efficient and general for a variety of aryl iodides. (2) Several
functional groups, including amino, hydroxy, or cyano
groups, could be well-tolerated. (3) The inexpensive catalytic
system emerged as an attractive alternative to the Grignard
or organolithium method. Further efforts to reveal the
Acknowledgment. We thank Prof. Koichi Narasaka and
Dr. Motoki Yamane, the University of Tokyo (present
address: Nanyang Technological University, Singapore), for
their discussion and suggestions. We also thank Ms. Kimiyo
Saeki, the Analytical Center at the University of Tokyo, for
the measurement of elemental analysis. This work was
financially supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Science, Sports,
and Culture and CREST, JST, Japan.
Supporting Information Available: General information,
(16) For reviews of organopalladium(IV) chemistry, see: (a) Canty, A.
J. Acc. Chem. Res. 1992, 25, 83. (b) Canty, A. J. In ComprehensiVe
Organometallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G.,
Eds.; Pergamon: Oxford, 1995; Vol. 9. (c) Canty, A. J. Palladium
Complexes Containing Pd(I), Pd(III), or Pd(IV). In Handbook of Organo-
palladium Chemistry for Organic Synthesis; Negishi, E.-i., Ed.; Wiley-
Interscience: New York, 2002; pp 189-211.
1
compound characterization data, and copies of the H and
13C NMR spectra. This material is available free of charge
via the Internet at http://pubs.acs.org.
OL701820J
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Org. Lett., Vol. 9, No. 22, 2007