Diborane s. a. Borane

Complexes with Electrophiles An ether s nonbonding electrons also stabilize borane, BH3. Pure borane exists as a dimer called diborane, B2H6. Diborane is a toxic, flammable, and explosive gas, whose use is both dangerous and inconvenient. Borane forms a stable complex with tetrahydrofuran. The BH3 THF complex is commercially available as a 1 M solution, easily measured and transferred like any other air-sensitive liquid reagent. The availability of BH3 THF has contributed greatly to the convenience of hydroboration (Section 8-7). 

There are many advantages to the use of NH3 as hydrogen source for vehicular fuel cell vehicle applications. However, a major drawback is ammonia s extreme toxicity and adverse health effects. By complexing NH3 with diborane, a stable, non-toxic and non-cryogenic material (H3BNH3) can be prepared. This ammonia-borane complex is stable in water and ambient air and when heated liberates H2 in a sequence of reactions between 137°C and 400°C that reaches about 20% of the initial mass of H3BNH3. Successfiil implementation of ammonia-borane as a potential future transportation fuel, however, requires new chemical techniques and/or processes for its s mthesis that promise substantial reduction in its production costs. 

Because diborane (B2Hg), the source of borane, is a flammable, toxic, explosive gas, a solution of borane—prepared by dissolving diborane in an ether such as THF— is a more convenient and less dangerous reagent. One of the ether oxygen s lone pairs satisfies boron s requirement for an additional two electrons The ether is a Lewis base... 

Parry, R.W. Edwards, L.J. J. Am. Chem. Soc. 1959, 81, 3554. Snow, S.A. Studies of Boranes and MetaUa Boranes I. Metal Con lexes(fBis(trimethylphosphine)-Diborane(4). II. Synthesis and Characterization of 2-(Dichloroboryl)pentdborane(9) Ph.D. Dissertation, University of Utah Salt Lake City, UT, 1985 see Abstract. 

Diborane(6), B2H. This spontaneously flammable gas is consumed primarily by the electronics industry as a dopant in the production of siHcon wafers for use in semiconductors. It is also used to produce amine boranes and the higher boron hydrides. Gallery Chemical Co., a division of Mine Safety AppHances Co., and Voltaix, Inc., are the main U.S. producers of this substance. Several hundred thousand pounds were manufactured worldwide in 1990. 

Enantioselective reduction of ketones.1 The ability of diborane in combination with the vic-amino alcohol (S)-2-amino-3-methyl-l,l-diphenyl-l-butanol (12, 31) to effect enantioselective reduction of alkyl aryl ketones involves formation of an intermediate chiral oxazaborolidine, which can be isolated and used as a catalyst for enantioselective borane reductions (equation I). 

Aromatic boranes are synthesized from diborane and arylmagnesium halides [i 5], arylmercury halides [iS5], or diarylmercury compounds [/S i]. Their oxidation furnishes phenols in variable yields. A large excess (up to 16 mol) of BH3 is necessary for high yields (equations 604 and 605). 

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