Boryl-Mediated Reversible H₂ Activation at Cobalt: Catalytic Hydrogenation, Dehydrogenation, and Transfer Hydrogenation

We describe the synthesis of a cobalt­(I)–N2 complex (2) supported by a meridional bis-phosphino-boryl (PBP) ligand. Complex 2 undergoes a clean reaction with 2 equiv of dihydrogen to afford a dihydrido­borato­cobalt dihydride (3). The ability of boron to switch between a boryl and a dihydrido­borate conformation makes possible the reversible conversion of 2 and 3. Complex 3 reacts with HMe2N–BH3 to give a hydrido­borane cobalt tetra­hydrido­borate complex. We explore this boryl–cobalt system in the context of catalytic olefin hydrogenation as well as amine–borane dehydrogenation/transfer hydrogenation.