Sodium Triethylhydroborate

At room temperature sodium hydride reacts exothermally with triethylborane in diethyl ether. The complex formation in hydrocarbons requires temperatures over 50°. The preparation of sodium triethylhydroborate is best carried out in boiling benzene. The salt, which is readily soluble in benzene, is generally obtained in pure form after filtration of unreacted materials (e.g., sodium) and distillation of the solvent. 

The reaction of sodium hydride with trimethylborane under similar conditions gives sodium hydrotrimethylborate. 

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The reaction of diethylmagnesium with sodium triethylhydroborate in ether at -78 C gives a solution of Mg(H)Et, which disproportionates to MgEt2 and MgH2 above -20 °C [29] (eq (14)). The reaction of MgR2 (R Et, Ph) with lithium aluminum hydride produces insoluble MgH2 accompanied by Li[AlH4 RJ n ==1-4) [30] (eq (15)). 

SODIUM TRIETHYLHYDROBORATE, SODIUM TETRAETHYLBORATE, AND SODIUM TRIETHYL-1-PROPYNYLBORATE... 

Caution. Triethylborane is spontaneously flammable, and sodium triethylhydroborate is easily hydrolyzed. The synthesis must be carried out in a protective gas N2, Ar) atmosphere with exclusion of air and moisture. 

Sodium triethylhydroborate is very air- and moisture-sensitive and must be handled in an inert atmosphere. In completely pure form, it is a colorless crystalline solid, m.p. 30°. However, the salt is often obtained as a brown-black oil because of impurities in the sodium hydride. Nevertheless, such products can be used without further purification in reactions such as preparation of sodium tetraethylborate. 

Sodium tetraethylborate is obtained from sodium triethylhydroborate 140-180° under ethylene pressure (65-100 atmospheres).7,8 The addition of triethylborane7 is desirable but not absolutely necessary.8 ( Caution. The entire operation must be carried out in an inert gas atmosphere with strict exclusion of moisture.)... 

A 500-ml. steel autoclave (suitable for use at 500 atmospheres at 300°) with manometer is charged with 201 g. (1.65 moles) of sodium triethylhydroborate and pressured to 80 atmospheres with ethylene. The mixture is heated with shaking at 140-150° for 2 hours. The pressure falls from 100 to 30 atmospheres at 150°. After cooling to 20°, an additional 60 atmospheres of ethylene pressure is added, and the mixture is agitated a further 2 hours at 140-150°. 

Sodium triethylhydroborate reacts with propyne (methylacetylene) with hydrogen evolution even at room temperature.4 In place of pure propyne, a hydrocarbon mixture containing ca. 30% propyne and ca. 30% allene can also be used.4 Only the propyne reacts. 

When using MAPP gas, no cold finger (— 78°) is used in order to avoid retention of the mixed gases. From 244 g. (2 moles) of sodium triethylhydroborate in 300 ml. of benzene and 280 g. of MAPP gas, the foregoing procedure gives 44.3 1. (S.T.P.) of hydrogen and 280 g. (88%) of sodium triethyl-1-propynylborate. In addition, the 500-ml. -78° cold trap contains 165 g. of colorless liquid. [Gas chromatographic analysis 13.4% propene, 33.6% propane, 39.2% allene, 2.5% isobutane, and 11.3% of 1-butene and isobutene.]... 

Alper and his co-workers have reported two new methods for the desulphurization of aliphatic, aromatic, and benzylic thiols. In one method thiols are treated with hexacarbonylmolybdenum, either in acetic acid or following pre-adsorption on silica/ An alternative and milder procedure uses anhydrous ferrous chloride and sodium triethylhydroborate in THF at -78 The 2-benzothiazolylthio-group, useful for stabilizing carbanions, is conveniently removed by electroreduction at a carbon electrode in a cathode cell (e.g. Scheme 4). ... 

Solvents were dried over sodium (light petroleum, bp 40-60°C, toluene) or sodium-benzophenone (diethyl ether, THF). Sodium amide, hexamethyl-disilazane, lithium triethylhydroborate(l —), and hydrogen tetrafluoro-borate(l —) diethyl ether complex were obtained from Aldrich and used as supplied. 

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