Mechanism of Co(iii)-catalyzed annulation of N-chlorobenzamide with styrene and origin of cyclopentadienyl ligand-controlled enantioselectivity

The mechanism of Co(iii)-catalyzed annulation of N-chlorobenzamide with styrene was computationally studied and the effects of chiral cyclopentadienyl (Cp) ligands on enantioselectivity were investigated by using energy decomposition analysis (EDA). The spin-crossover event of Co complexes is observed in the computed energy profile. The triplet state of Co species is favored in most of the intermediates and transition states except for the styrene migratory insertion step which prefers the singlet state. The irreversible styrene migratory insertion is the enantioselectivity-determining step of the reaction. EDA results indicate that the steric effect is the dominant factor for the high-level enantiocontrol, which highlights the importance of the additional bulky substituents on the Cp ring of trisubstituted BINOL-Cp ligands.