Hydroxytricyanoborate Anion: Synthetic Aspects and Structural, Chemical, and Spectroscopic Properties.

In recent years, salts of the hydridotricyanoborate anion [BH(CN)3]- (MHB) have become readily available. In spite of the unusually high stability of the MHB anion, it can be used as a valuable starting material for the preparation of selected tricyanoborates, for example, the boron-centered nucleophile B(CN)32-. A further unprecedented example is the hydroxytricyanoborate anion [B(OH)(CN)3]- that is accessible by oxidation of (H3O)MHB with elemental bromine in water. The Brønsted acid (H3O)[B(OH)(CN)3] was isolated as a crystalline solid. It serves as a versatile starting material for the synthesis of coordination compounds, metal salts, and ionic liquids. The [B(OH)(CN)3]- anion shows a rich coordination chemistry and a high tendency to form hydrogen-bonded motifs as demonstrated by a series of salts with different types of cations. Furthermore, the [B(OH)(CN)3]- anion itself serves as starting material for new tricyanoborates such as the unusual trianion [B{OB(CN)3}3]3- and the silylated anions [B(OSiR3)(CN)3]- (R = Me, Et, Ph). Some of these follow-up products have been characterized by single-crystal X-ray diffraction, e.g., [nBu4N]3[B{OB(CN)3}3] and [nBu4N][B(OSiPh3)(CN)3].