We report the one-pot reactions of the 16e(-) half-sandwich complex CpCoS2C2B10H10 (1), methyl propiolate, and 3e(-)-donor ligands, which lead to selective B-functionalization at carborane with cyclopentadienyl as a functional group at ambient temperature in good yields. Metal-promoted activations of both a B-H bond of the carborane and a C-H bond of the Cp unit take place sequentially in the cooperation of organic ligands. The reaction requires a 3e(-)-donor ligand and an activated alkyne and is therefore suitable for a broad range of substrates. This investigation provides a simple and efficient synthetic route to B-functionalized carborane derivatives.