Synthesis of Amine Derivatives of the Polyhedral Borane Anion [B20H18]4

Ethylenediamine (en) reacts with the polyhedral borane anion [n-B20H18]2-, in the presence or absence of strong nonnucleophilic auxiliary bases, to produce the [ae-B20H17(en)]3- anion. In either case, substitution is accompanied, to an approximately equal extent, by reduction of the starting material to form [a 2 -B20H18]4-. As found with similar substituted systems derived from this 20-boron structure, [ae-B20H17(en)]3- may be conveniently rearranged to the [a 2 -B20H17(en)]3- anion. A more convenient synthesis of the known [ae-B20H17NH3]3- ion, which employs acetonitrile as the source of the NH3 ligand instead of liquid ammonia, is also described.