Diborane generation using sodium borohydride

We pointed out that sodium borohydride on a weight basis should be far more efficient than sodium hydroxide and ferrosilicon. Although we had never used it for hydrogen generation, we had no doubt that it would be similar to diborane in reacting readily with water to liberate hydrogen. They asked for a demonstration. 

An alternative diborane source was used by the checker. Diborane was generated by adding boron trifluoride-ethyl ether to sodium tetrahydroborate (sodium borohydride) in ether. The generator was charged to yield a maximum of 0.6 mol of... 

Sodium borohydride reacts with Lewis acids in nonprotic solvents to yield diborane [19287-45-7], B2H6 (18), which can then be used to generate other useful organoboranes such as amine boranes, alkyl boranes, and boron hydride clusters. 

Any of these BH3 compounds adds readily to most alkenes at room temperature or lower temperatures. The reactions usually are carried out in ether solvents, although hydrocarbon solvents can be used with the borane-dimethyl sulfide complex. When diborane is the reagent, it can be generated either in situ or externally through the reaction of boron trifluoride with sodium borohydride ... 

Early reports of hydroboration reactions often recommended in situ generation of diborane from sodium tetrahydroborate (borohydride) and trifluoroborane etherate or some similar mixture. Indeed, it is still reasonable to use this method for simple hydroborations, provided that nothing more complicated than oxidation of the resultant organoborane is intended. Otherwise, the approach should be avoided, particularly since borane is now commercially available in the form of several Lewis base complexes. 

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