Protonation versus Oxonium Salt Formation: Basicity and Stability Tuning of Cyanoborate Anions

摘要

Anhydrous HBH2(CN)(2) crystallizes from acidic aqueous solutions of the dicyanodihydridoborate anion. The formation of HBH2(CN)(2) is surprising as the protonation of nitriles requires strongly acidic and anhydrous conditions but it can be rationalized based on theoretical data. In contrast, BX(CN)(3)(-) (X= H, F) gives the expected oxonium salts (H3O)BX(CN)(3) while (H3O)BF2(CN)(2)/HBF2(CN)(2) is unstable. HBH2(CN)(2) forms chains via N-H . . . N bonds in the solid state and melts at 54 degrees C. Solutions of HBH2(CN)(2) in the room-temperature ionic liquid EMImBH2(CN)(2) contain the (NC)H2BCN-H . . . NCBH2(CN)(-) anion and are unusually stable, which enabled the study of selected spectro-scopic and physical properties. (NC)H2BCN-H . . . NCBH2( CN)(-) slowly gives H-2 and (NC)H2BCN-BH(CN)(2)(-). The latter compound is a source of the free Lewis acid BH(CN)(2), as shown by the generation of BHF(CN)(2)(-) and BH(CN)(2) py.