Ni-Catalyzed Enantioconvergent Kumada–Corriu Cross-Coupling between β‑Bromostyrenes and Secondary Grignard Reagents: Reaction Development, Scope and Mechanistic Investigations

A Ni-catalyzed enantioconvergent cross-coupling between
β-bromostyrenes
and secondary Grignard reagents is reported. This C(sp2)–C(sp3) cross-coupling is applicable to a broad
range of electrophilic and nucleophilic partners and affords the products
in good to high levels of enantio-induction. Experimental mechanistic
investigations revealed an unexpected binding mode of the chiral (P,N)
ligand and support a radical rebound mechanism involving in-cage radicals.
Kinetic experiments provide evidence for an off-cycle resting state
featuring
dinuclear species. Computational analyses are in line with this hypothesis
and coherent with a catalytic cycle proceeding via a Ni(I)/Ni(III)
manifold. They further suggest an enantio-determining radical capture
event and shed light on the origin of the Dynamic Kinetic Resolution
process.