Understanding Rate Acceleration and Stereoinduction of an Asymmetric Giese Reaction Mediated by a Chiral Rhodium Catalyst

The surprising acceleration of the addition of electron-rich radicals to alpha,beta-unsaturated 2-acyl imidazoles by a chiral-at-metal rhodium catalyst is investigated. M06/Lanl2DZ (Rh),6-31G(d) calculations reproduce the observed rate acceleration and shed light on a catalyst design where a rigid chiral pocket with a steric interaction >5 angstrom from the chiral metal center leads to the observed high stereoinduction. Analysis of the molecular orbitals of two key addition transition states emphasize the role of the catalyst as a Lewis acid without significant charge transfer.