In an effort to isolate diborane(4) derivatives, we have developed an efficient and uncatalyzed approach using [BH$_3$·THF] and the mercaptopyridine ligand. Thermolysis of 2-mercaptopyridine, in the presence of [BH$_3$·THF], afforded a doubly base-stabilized diborane(4) species 1, [HB(μ-C$_5$H$_4$NS)]$_2$, along with the formation of its isomeric species 2, [HB(μ-C$_5$H$_4$NS)]$_2$, albeit in less yield. Based on the coordination of the boron with the mercaptopyridine ligand in 2 and its spectroscopic data, compound 2 has been designated as a borato-boronium species, in which the anionic borate and cationic boronium units are covalently bonded to each other. Furthermore, we have demonstrated the oxidative insertion of chalcogen atoms (S and Se) through the B–B bond of the base-stabilized diborane(4), 1, that yielded chalcogenido-diboron species, 3(S) and 4(Se).