Bond Dissociation Energy-Controlled Regioselectivity in Hydrofunctionalization

The bond dissociation energy (BDE) in reactants was found
to be
critical for determining the tunable pathways of low-valent tungsten-catalyzed
chain-walking hydroboration and hydrogermylation of β,γ-unsaturated
amides, which is considered to be the key factor in the regioselective
determination. Computational results revealed that the higher BDE
of the H–B bond hampers the oxidative hydrogen migration, leading
to borane reacting with tungsten later than alkenes. Thus, the generation
of a β-borylated product was found to be favorable through H–Cβ bond oxidative addition, H–Cδ bond reductive elimination, H–B bond oxidative hydrogen migration,
and B–Cβ bond reductive elimination. As a
comparison, the lower BDE of H–Ge leads to a facile oxidative
hydrogen migration of the H–Ge bond, which finally results
in the formation of an α-germylated product after germyl-assisted
olefin walking. Further distortion–interaction analysis confirmed
that the weak H–Ge bond was easier to distort for its reactions.