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)(3)(2-). 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 Bronsted 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., [nBu(4)N](3)[B{OB(CN)(3)}(3)] and [nBu(4)N][B(OSiPh3)(CN)(3)].