Tris(trimethylsilyl)aluminum1

(Me3Si)3Al

[65343-66-0]  · C9H27AlSi3  · Tris(trimethylsilyl)aluminum  · (MW 246.61) (.OEt2)

[75441-10-0]  · C13H37AlOSi3  · Tris(trimethylsilyl)aluminum Diethyl Etherate  · (MW 320.75)

(nucleophilic silylation;2,3 silylalumination of terminal alkynes;4 preparation of allyl-, aryl-, and alkenylsilanes5,6)

Physical Data: mp 60 °C (dec).

Solubility: sol ethers, pentane, benzene; reacts violently with protic solvents.

Form Supplied in: white needles; not commercially available.

Preparative Methods: to Aluminum powder and granular aluminum in ether is added Mercury(0) and Chlorotrimethylsilane followed by Lithium wire. After the reaction is complete, the solution is filtered and ether is removed. The solid residue is stirred with pentane, which effects removal of insoluble Li(Me3Si)4Al. Partial concentration and cooling of the pentane solution gives (Me3Si)3Al.OEt2 as white needles.1b,2c

Handling, Storage, and Precautions: ignites spontaneously in air. The reagent can be conveniently handled as a stock solution in pentane, which can be stored under an inert atmosphere in a freezer. The molarity can be determined by titration.2c,6

Carbonyl Additions.

The reagent is a useful nucleophilic trimethylsilyl transfer agent.2a Enones and enals undergo 1,2-addition in ether at room temperature, while 1,4-addition occurs at -78 °C (eq 1).2b Ester carbonyls, which are amenable to attack only in boiling ether in the presence of Aluminum Chloride, give a,a-bis(trimethylsilyl)alkanols.2a

Functionalized acylsilanes are accessible by the reaction of (Me3Si)3Al.OEt2 with (S)-2-pyridyl esters in the presence of stoichiometric Copper(I) Cyanide (eq 2).3

Silylalumination of Alkynes.

Silylalumination of 1-alkynes provides a convenient entry to vinylsilane derivatives in a regio- and stereoselective manner (eq 3).4

Transition Metal Promoted Coupling Reactions.

In the presence of a Ni catalyst, the reagent undergoes cross-coupling reactions with aryl bromides (eq 4).5 Alkenyl iodides are stereospecifically converted to alkenylsilanes in the presence of a Pd catalyst (eq 5).

Allylic acetates are converted to allylsilanes in the presence of Pd0 complexes or Hexacarbonylmolybdenum. The regioselectivity depends on the catalyst. The Mo0 catalyst leads to products with the silyl group attached to the less-hindered end of the allyl group. The regioselectivity of the Pd0-catalyzed reaction depends on the solvent and, in particular, on the ligands. The two catalysts also differ with respect to stereochemistry (eq 6).6


1. (a) Rösch, L. AG(E) 1977, 16, 480. (b) Rösch, L.; Altnau, G. JOM 1980, 195, 47. (c) Rösch, L.; Altnau, G.; Krüger, C.; Tsay, Y.-H. ZN(B) 1983, 38B, 34.
2. (a) Rösch, L.; Altnau, G.; Otto, W. H. AG(E) 1981, 20, 581. (b) Altnau, G.; Rösch, L.; Jas, G. TL 1983, 24, 45. (c) Avery, M. A.; Chong, W. K. M.; Jennings-White, C. JACS 1992, 114, 974.
3. Nakada, M.; Nakamura, S.; Kobayashi, S.; Ohno, M. TL 1991, 32, 4929.
4. Altnau, G.; Rösch, L.; Bohlmann, F.; Lonitz, M. TL 1980, 21, 4069.
5. Trost, B. M.; Yoshida, J. TL 1983, 24, 4895.
6. Trost, B. M.; Yoshida, J.; Lautens, M. JACS 1983, 105, 4494.

Keisuke Suzuki & Tetsuya Nagasawa

Keio University, Yokohama, Japan



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