[129552-42-7]  · C15H19NSi  · (2-Dimethylaminomethylphenyl)phenylsilane  · (MW 241.41)

(hydrosilylating agent; selective reducing agent for carbonyls, acyl chlorides, carboxylic acids, and heterocumulenes under neutral conditions)

Physical Data: bp 115 °C/0.05 mmHg.

Solubility: sol ether, THF, alkanes, aromatics, chlorinated solvents.

Preparative Methods: to 67 g (0.5 mol) of N,N-dimethylbenzylamine in 300 mL of anhydrous ether are added dropwise under nitrogen 200 mL (0.5 mol) of n-Butyllithium (2.5 M in hexane). After being stirred for 48 h at 25 °C, the yellow suspension is transferred into a dropping funnel and added at 0 °C to 54 g (0.5 mol) of phenylsilane in 200 mL of ether. The mixture is stirred for 16 h, then filtered over celite. Solvents are removed under vacuum, and the residue is diluted in pentane, filtered again and fractionally distilled to give 82 g (68%) of 2-(dimethylaminomethylphenyl)phenylsilane (1).1

Related aminoarylsilanes are similarly prepared2 from 1-(dimethylaminomethyl)naphthalene and 1-(dimethylamino)naphthalene, giving [8-(dimethylaminomethyl)-1-naphthyl]phenylsilane (2) and [8-(dimethylamino-1-naphthyl]phenylsilane (3), respectively.

General Discussion.

The reducing properties of silicon hydrides are enhanced by intramolecular pentacoordination.1,3 Solvolysis is observed with alcohols and phenols, and addition to carbonyls occurs without the requirement of external catalysts. Some previous reports concerned the reduction of aroyl chlorides to aldehydes using organosilanes under catalytic conditions with Pd/C4 or tributyltin hydride with catalytic Pd0,5 but incompatible functional groups on the substrate must be avoided. Such problems are overcome with organosilicon hydrides activated by intramolecular coordination of an aminoaryl group. These reagents react with acyl chlorides in carbon tetrachloride, affording chlorosilanes and aldehydes (eq 1).6 The reactions are fast and quantitative. The aldehydes are either isolated by direct distillation from the crude product mixture, or trapped after filtration over wet silica. The organosilanes can be recycled after separation and treatment with Lithium Aluminum Hydride. Halogen, methoxy, and nitroaryl substituents, heteroaryl groups, and alkenes remain unchanged. The method is also suitable for the conversion of dicarboxylic acid chlorides into dialdehydes.

Hydrosilylation of isocyanates and isothiocyanates (eq 2) is readily achieved under mild conditions. Treatment of the adducts through the one-pot addition of acyl chlorides gives N-acylformamides and N-acylthioformamides.7 N,N-Dialkyl C-acylamidines result from the acylation8 of C-silylamidines, obtained (eq 3) by hydrosilylation of alkylcarbodiimides with (2).

Pentacoordinated hydrosilanes react with excess aryl isocyanates to give isocyanurates.9 Carboxylic acids are directly reduced to aldehydes in a one-pot process10 through the thermal decomposition of pentacoordinated silyl carboxylates (eq 4). The aldehydes are extracted from the crude product mixture by distillation, or separated from the trisiloxane by column chromatography over Florisil. The reaction is selective, since fluoro, nitro, cyano, methoxy and heteroaryl substituents do not react with the silane. The present method also permits the reduction of a,b-unsaturated acids. The efficiency follows the order (2) > (1) > (3).

Related Reagents.

Triethylsilane; Triethylsilane-Trifluoroacetic Acid.

1. Arya, P.; Corriu, R. J. P.; Gupta, K.; Lanneau, G. F.; Yu, Z. JOM 1990, 399, 11.
2. Boyer, J.; Brelière, C.; Carré, F.; Corriu, R. J. P.; Kpoton, A.; Poirier, M.; Royo, G.; Young, J. C. JCS(D) 1989, 43.
3. Boyer, J.; Brelière, C.; Corriu, R. J. P.; Kpoton, A.; Poirier, M.; Royo, G. JOM 1986, 311, C39.
4. (a) Jenkins, J. W.; Post, H. W. JOC 1950, 15, 556. (b) Citron, J. D. JOC 1969, 34, 1977. (c) Dent, S. P.; Eaborn, C.; Pidcok, A. JCS(C) 1970, 1703.
5. (a) Four, P.; Guibe, F. JOC 1981, 43, 4439. (b) Guibe, F.; Four, P.; Rivière, H. JCS(C) 1980, 432.
6. Corriu, R. J. P.; Lanneau, G. F.; Perrot, M. TL 1988, 29, 1271.
7. Corriu, R. J. P.; Lanneau, G. F.; Perrot-Petta, M.; Mehta, V. D. TL 1990, 31, 2585.
8. Corriu, R. J. P.; Lanneau, G. F.; Perrot-Petta, M. S 1991, 11, 954.
9. Corriu, R. J. P.; Lanneau, G. F.; Mehta, V. D. HC 1991, 2, 461.
10. Corriu, R. J. P.; Lanneau, G. F.; Perrot, M. TL 1987, 28, 3941.

Robert J. P. Corriu & Gérard F. Lanneau

Université Montpellier II, France

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