The Mechanism of Rhodium-Catalyzed Allylic C–H Amination

Herein,
the mechanism of catalytic allylic C–H amination
reactions promoted by Cp*Rh complexes is reported. Reaction kinetics
experiments, stoichiometric studies, and DFT calculations demonstrate
that the allylic C–H activation to generate a Cp*Rh­(π–allyl)
complex is viable under mild reaction conditions. The role of external
oxidants in the catalytic cycle is elucidated. Quantum mechanical
calculations, stoichiometric reactions, and cyclic voltammetry experiments
concomitantly support an oxidatively induced reductive elimination
process of the allyl fragment with an acetate ligand proceeding through
a Rh­(IV) intermediate. Stoichiometric oxidation and bulk electrolysis
of the proposed π–allyl intermediate are also reported
to support these analyses. Lastly, evidence supporting the amination
of an allylic acetate intermediate is presented. We show that Cp*Rh­(III)2+ behaves as a Lewis acid catalyst to complete the allylic
amination reaction.