Abstract Lithium- and potassium cyanodihydropyrrolylborates 1 1 In this paper “pyrrolyl” means pyrrolyl-1 throughout. (made from monopyrrolylborane by reaction with the appropriate cyanide) as well as sodium- and potassium cyanohydrodipyrrolylborates (made from sodium hydrotripyrrolylborate with HCN and from pyridine-dipyrrolylborane with KCN, respectively) were prepared. The hydrolysis of the BH(NC 4H 4) 2CN − ion in acidic media is approximately 250 times faster than that of the BH 3CN − ion. On the other hand the BH 2(NC 4H 4)CN − ion is easily protonated ( pK a = 1.84) at the α-position of the pyrrolyl ring, and is hydrolyzed very slowly even in strongly acidic media. Reaction of the NaBH(NC 4H 4) 2CN with pyridine- and with 4-picoline hydrochlorides (AHCl) results in the formation of compounds A·BH(NC 4H 4)CN containing tetracoordinated chiral boron. Considerable amounts of C 5H 5N·BH(NC 4H 4)CN are also formed in a complex reaction which took place between KBH 2(NC 4H 4)CN and pyridine hydrochloride. These base—borane complexes also undergo α-protonation on the pyrrolyl ring in strongly acidic medium. The boronium ions ABH(NC 4H 5)CN + formed in this way are stable even in concentrated mineral acids.