C–H and C–F bond activation of fluorinated propenes at Rh: enabling cross-coupling reactions with outer-sphere C–C coupling

Abstract

The reaction of [Rh{(E)-CFCHCF₃}(PEt₃)₃] with Zn(CH₃)₂ results in the methylation of the alkenyl ligand to give [Rh{(E/Z)-C(CH₃)CHCF₃}(PEt₃)₃]. Variable temperature NMR studies allowed the identification of a heterobinuclear rhodium–zinc complex as an intermediate, for which the structure [Rh(CH₃)(ZnCH₃){(Z)-C(CH₃)CHCF₃}(PEt₃)₂] is proposed. Based on these stoichiometric reactions, unique Negishi-type catalytic cross-coupling reactions of fluorinated propenes by consecutive C–H and C–F bond activation steps at room temperature were developed. The C–H bond activation steps provide a fluorinated ligand at Rh and deliver the fluorinated product, whereas the C–F bond activation and C–C coupling occur via outer-sphere nucleophilic attack at the fluorinated alkenyl ligand.