The d4 ML6 bis-boryl complex OsH(Bcat)2Cl(PiPr3)2 (Bcat = catecholborate) has been prepared by the reaction of OsH2Cl2(PiPr3)2 with HBcat, via the monoboryl intermediate OsH2(Bcat)Cl(PiPr3)2, and its structure determined by X-ray diffraction analysis. The Os–B bonds and the stability and disposition of the boryl ligands have been analyzed by DFT calculations. The bis-boryl complex loses HBcat to give Os(Bcat)Cl(CO)2(PiPr3)2, under a CO atmosphere.