Unlocking nucleophilic reactivity in Co-MHAT catalysis: Stereospecific backside-backside displacement by...

The recent renaissance of olefin hydrofunctionalization based on cobalt-catalyzed hydrogen atom transfer (Co-MHAT) has primarily focused on two pathways: the homolytic cleavage of the alkyl-Co^III intermediate and its electrophilic reaction upon oxidation. In contrast, a third pathway, which leverages the two-electron nucleophilic potential of alkyl-Co^III, has remained unexplored because of the inherently low polarization of the C-Co bond. Here, we report an axial-coordination activation strategy to unlock this reactivity space in Co-MHAT catalysis. Through stoichiometric organometallic studies using well-defined alkyl-Co^III complexes, we demonstrate that an alkoxide ligand can render alkyl-Co^III sufficiently nucleophilic to displace a suitable leaving group, via a stereospecific backside-backside approach. This pathway is further applied in catalysis, enabling a diastereoselective redox neutral Co-MHAT cyclopropanation reaction.