Pyridine Adducts of Tricyano- and Dicyanoboranes

Cyanoborane adducts of the Lewis acids B(CN)(3), BF(CN)(2), and BH(CN)(2) with pyridine and 4-cyanopyridine have been obtained in high yields. The syntheses were accomplished by oxidation of the readily available potassium salts of the cyano(hydrido)borate anions [BH(CN)(3)](-) (MHB), [BFH(CN)(2)](-) (FHB), and [BH2(CN)(2)](-) (DHB) with bromine in the presence of the respective pyridine derivative C5H5N or 4-CN-C5H4N as starting material. All six cyanoborane adducts have been characterized by NMR and vibrational spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The reduction of the cyanoborane adducts has been investigated by cyclic voltammetry and the Lewis acidity of the different cyanoboranes has been assessed using the Gutmann-Beckett method. Selected experimental data and trends are compared to theoretical ones, for example fluoride ion affinities (FIAs).

Automated summary

Cyanoborane adducts of B(CN)(3), BF(CN)(2), and BH(CN)(2) with pyridine and 4-cyanopyridine have been synthesized and characterized. The reduction of the adducts and the Lewis acidity of the cyanoboranes have been investigated. Experimental data and trends have been compared to theoretical ones.