Chemistry Letters 2001
1217
Rev., 145, 75 (1995). c) J. Belzner and U. Dehnert, “The
Chemistry of Organic Silicon Compounds,” ed. by Z. Rappoport
and Y. Apeloig, John-Wiley & Sons, Chichester (1998), Vol. 2,
pp 779–826.
The reaction of bis(silyl)zinc, -cadmium, and -mercury with
lithium is almost the sole method using hydrocarbon solvents: a)
K. W. Klinkhammer, Chem. Eur. J., 3, 1418 (1997). b) M.
Nanjo, A. Sekiguchi, and H. Sakurai, Bull. Chem. Soc. Jpn., 71,
2
3
7
41 (1998), and references cited therein.
a) A. Kawachi and K. Tamao, Bull. Chem. Soc. Jpn., 70, 945
1997). b) A. Kawachi and K. Tamao, J. Am. Chem. Soc., 122,
919 (2000). c) A. Kawachi, H. Maeda, H. Nakamura, N. Doi,
(
1
This boron–metal exchange methodology could be extend-
ed to prepare other silyl–metal compounds, as shown in
Scheme 3. The reaction of 2a with t-BuOK (1.0 mol dm in
and K. Tamao, J. Am. Chem. Soc., 123, 3143 (2001). d) M.
Omote, T. Tokita, Y. Shimizu, I. Imae, E. Shirakawa, and Y.
Kawakami, J. Organomet. Chem., 611, 20 (2001).
Pauling’s electronegativity: J. Emsley, “The Elements,” 2nd ed.,
Clarendon Press, Oxford (1992).
Examples of preparations and reactions of silylboranes; a) W.
Biffar and H. Nöth, Angew. Chem., Int. Ed. Engl., 19, 58 (1980).
b) J. D. Buynak and B. Geng, Organometallics, 14, 3112 (1995).
c) E. Bonnefon, M. Birot, J. Dunogues, J.-P. Pillot, C.
Courseille, and F. Taulelle, Main Group Metal Chem., 19, 761
–
3
4
5
THF, 2 mol amt.) in THF at –78 °C afforded the silylpotassium
8a
compound 10, being trapped as 4a in 50% yield. The reaction
–
3
of 2a with MeMgBr (0.9 mol dm in THF, 3 mol amt.) in THF
at 0 °C afforded the silylmagnesium compound 11, being
trapped as 4a in 75% yield. The [(alkoxy)silyl]magnesium
compound 12 was obtained from 6 in a similar manner (74%
yield of 8). It is noted that only a few methods have been
(
1996). d) M. Suginome, H. Nakamura, T. Matsuda, and Y. Ito,
J. Am. Chem. Soc., 120, 4248 (1998). e) M. Suginome, T.
Matsuda, and Y. Ito, Organometallics, 19, 4647 (2000). f) S.
Onozawa, Y. Hatanaka, and M. Tanaka, Chem. Commun., 1997,
1
2
reported for preparation of silylmagnesium compounds.
1
229. g) T. Hata, H. Kitagawa, H. Masai, T. Kurahashi, M.
Shimizu, and T. Hiyama, Angew. Chem. Int. Ed., 40, 790 (2001).
Studies on nucleophilic substitution at boron atoms: a) A.
Cowley and J. L. Mills, J. Am. Chem. Soc., 91, 2911 (1969). b)
B. Glavincevski and S. K. Brownstein, Can. J. Chem., 59, 3012
6
7
(
1980). c) E. Müller and H.-B. Bürgi, Helv. Chim. Acta, 70, 511
(
1987). d) S. Toyota, T. Futawaka, M. Asakura, H. Ikeda, and
M. Oki, Organometallics, 17, 4155 (1998). e) M. Yamashita, Y.
Yamamoto, K.-y. Akiba, and S. Nagase, Angew. Chem. Int. Ed.,
3
9, 4055 (2000), and references cited therein.
Typical procedure: To a solution of 2a (173 mg, 0.45 mmol) in
–
3
THF (3 mL) was added methyllithium in Et O (1.14 mol dm ,
2
0
.78 mL, 0.9 mmol) at –78 °C. The reaction mixture was stirred
at the same temperature for 30 min to give 3a. To the solution of
a was added trimethylchlorosilane (0.14 mL, 1.1 mmol) at –78
C, and the reaction mixture was warmed to the ambient temper-
3
°
ature. After usual workup, 4a was obtained in 87% yield after
column chromatography on silica gel.
a) E. Buncel, T. K. Venkatachalam, B. Eliasson, and U. Edlund,
J. Am. Chem. Soc., 107, 303 (1985). b) U. Edlund, T. Lejon, T.
K. Venkatachalam, and E. Buncel, J. Am. Chem. Soc., 107, 6408
In summary, we have found that the boron–metal exchange
reactions of the (arylsilyl)boranes with MeLi, n-BuLi, t-BuOK,
and MeMgBr are useful for the preparation of arylsilyl anions.
Especially, the boron–lithium exchange reaction occurs even in
the hydrocarbon solvents. This may be useful for elucidation of
structures of silyllithiums in hydrocarbon solvents, study of sol-
vent effect on the reaction of silyllithiums, and tuning of the
reactivity of silyllithiums for selective organic synthesis.
Variation of the substituents on the silicon atom in this method-
ology and application to organic synthesis are now under inves-
tigation.
8
9
(1985). c) H. V. R. Dias, M. M. Olmstead, K. Ruhlandt-Senge,
and P. P. Power, J. Organomet. Chem., 462, 1 (1993).
The choice of the solvent depends on the solubility of the silyl-
boranes.
10 A similar downfield shift was reported in the 29Si resonance of
2a in THF-d8 (δ –9.0) and that in toluene-d8 (δ 9.28) (∆δ 18.28),
see ref 8.
1
1 The starting material 9 was recovered in 55% yield and the side
product, (MeO)Mes Si-SnMe n-Bu, was obtained in 34% yield.
2
2
1
2 Reaction of chlorosilanes with magnesium: a) R. Goddard, C.
Krüger, N. A. Ramadan, and A. Ritter, Angew. Chem., Int. Ed.
Engl., 34, 1030 (1995). b) K. Tamao, M. Asahara, T. Saeki, and
A. Toshimitsu, Angew. Chem. Int. Ed., 38, 3316 (1999).
Lithium–magnesium exchange reaction between silyllithiums
and Grignard reagents: c) H. Hayami, M. Sato, S. Kanemoto, Y.
Morizawa, K. Oshima, and H. Nozaki, J. Am. Chem. Soc., 105,
We thank the Ministry of Education, Culture, Sports,
Science and Technology, Japan, for the Grant-in-Aids for COE
Research on Elements Science, No. 12CE2005 and for
Scientific Research Nos. 12042241 and 12750763.
4
491 (1983). d) D. L. Comins and M. O. Killpack, J. Am. Chem.
Dedicated to Prof. Hideki Sakurai on the occasion of his
0th birthday.
Soc., 114, 10972 (1992). e) A. Kawachi and K. Tamao, J.
Organomet. Chem., 601, 259 (2000). Cobalt–magnesium
exchange reaction of silylcobalt compounds and Grignard
reagents: f) E. Colomer and R. J. P. Corriu, J. Organomet.
Chem., 133, 159 (1977).
7
References and Notes
Reviews: a) K. Tamao and A. Kawachi, Adv. Organomet. Chem.,
8, 1 (1995). b) P. D. Lickiss and C. M. Smith, Coord. Chem.
1
3