Unveiling the Origins of Enantioconvergence in Cobalt-Catalyzed Asymmetric Hydrogenation of Minimally Functionalized Isomeric Olefins

Enantioconvergent hydrogenation of E/Z-mixed olefins represents a highly efficient and economically advantageous strategy in modern stereoselective synthesis. However, the origins of the stereochemical outcomes remain ambiguous due to the paucity of mechanistic studies. In this work, we systematically investigated the mechanisms and underlying origins of enantioconvergence in the cobalt-catalyzed enantioconvergent hydrogenation of minimally functionalized E/Z-mixed olefins. Our findings unveil a compelling synergistic cocatalytic mechanism involving cobalt and Ph2SiH2. The isomerization of E/Z-mixed olefins into a 1,1-disubstituted alkene enables the enantioconvergence, diverging from conventional explanations that are directly governed by steric hindrance or chelation effects. Subsequent alkene reinsertion forms a primary alkyl-cobalt intermediate, which exhibits markedly easier σ-bond metathesis compared to secondary or tertiary alkyl-cobalt species. This characteristic fundamentally drives the enantioconvergent hydrogenation process. Structural analysis reveals that the lower energy of the σ-bond metathesis transition state associated with primary alkyl-cobalt species is primarily attributed to the substantially reduced steric hindrance between the IIP ligand and the primary alkyl moiety, as compared to secondary or tertiary alkyl-cobalt counterparts. Enantioselectivity is determined by both the alkene reinsertion and σ-bond metathesis steps, and is induced by the chiral IIP ligand, which preferentially accommodates the most sterically demanding olefin substituent in the I quadrant. Furthermore, these mechanisms well elucidated the observed enhancement in conversion with Ph2SiH2. Based on the computational findings, an intriguing chiral induction model is proposed. This improved mechanistic understanding provides practical insights for the future design of substrate-independent enantioconvergent transformations.