Diborane reactions

As can be seen in Fig. 2.1, if the temperature is raised sufficiently, AG becomes negative and the diborane reaction proceeds at a much lower temperature than the boron trichloride reaction. 

Safety considerations are paramount in any boron hydride synthesis. The energy yield from the oxidations of boron hydrides is too high for any cavalier treatment of boron hydrides. Exclusion of air is the critical consideration in diborane reactions. Decaborane(14) is less reactive, generally, in a kinetic sense, but the thermodynamic potential is comparable. In addition, all volatile boron hydrides are toxic. The procedures described in the latter two preparations are within our experience non-hazardous. These procedures should be followed in every detail improvisation is not recommended. 

The configuration of the produced diol is influenced by the relative stabilities of the benzyl- or alkylcarbonium ions formed during the reaction. Similar reactions were investigated earlier. The rate and stereochemistry of the diborane reaction is altered by a small quantity of LiCl. Wide-ranging research has been performed with regard to the mechanism and stereochemistry of the diborane reduction in connection with cyclic and aliphatic a, 3-unsaturated and allylic epoxides, on diterpene models, " and by study of the reduction of epoxy-methylenecyclohexane and 2,3-epoxy-3-methylcyclohexanone. ... 

The sodium-diborane reaction (72) provides another example of unsym-metrical cleavage of a double bridge bond. 

Figure 1. The classical diborane reactions of unsymmetrical and symmetrical cleavage, seen as ligand displacement reactions involving NH3 or the sterically more demanding NMe3...

Pyrolysis of ethylene-diborane and trimethylborane-diborane mixtures (271, 272) yields 2-alkylpentaboranes, as well as mixtures of polyalkylated pentaboranes and alkylated decaboranes. The B NMR data for the alkylated pentaboranes obtained from the ethylene-diborane reaction (271) should be reinterpreted in favor of a downfield chemical shift effect of the alkyl group. 

Hough WV et al (1956) The sodium-diborane reaction. J Am Chtan Soc 78 689 Ortega JV et al (2005) Triborohydride salts as hydrogen storage materials and preparation thereof. Patent US 2005/0135996 Al... 

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