The thiaboranes closo-1-SB11H11 (1a) and 12-I-closo-1-SB11H10 (1b) react with 4-(dimethylamino)pyridine under inert conditions upon the formation of the nido-type thiaboranes 9-B{(4-Me2N)C5NH4}2(H)-7-SB10H11 and 9-B{(4-Me2N)C5NH4}2(H)-5-I-7-SB10H10 containing an exoskeletal B-H group. The same type of B-H moiety is also stabilised by one bipyridine molecule in a chelating fashion. These complexes are unstable in solution, and in air and hydrolyse to monodeboronated ionic compounds having [nido-7-SB10H11]- or [5-I-nido-7-SB10H10]- anions which are also products of the reactions of 1a and 1b with other N-bases such as pyridine, ammonia and DABCO. The extrusion of one boron and one sulphur atom takes place when 1a reacts with 2,6-di-tert-butylpyridine to yield decaborane.