AbstractCurrently, the chemistry of carbonyl derivatives of the closo-borate anions is actively developing. It is of great interest to obtain protonated complexes of these types of clusters for further directed functionalization. The aim of this study is to develop an approach to the preparation of the protonated complex of the monocarbonyl derivative [B10H9CO⋅Hfac]0. In the course of the work, the target complex has been obtained by protonation of the [B10H9CO]– anion with an excess of trifluoromethanesulfonic acid CF3SO3OH. In this reaction, the boron cluster is quantitatively protonated. When a base is added, the protonation process becomes reversible.