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

The reaction of [Rh{( E )-CF[double bond, length as m-dash]CHCF 3 }(PEt 3 ) 3 ] with Zn(CH 3 ) 2 results in the methylation of the alkenyl ligand to give [Rh{( E / Z )-C(CH 3 )[double bond, length as m-dash]CHCF 3 }(PEt 3 ) 3 ]. Variable temperature NMR studies allowed the identification of a heterobinuclear rhodium-zinc complex as an intermediate, for which the structure [Rh(CH 3 )(ZnCH 3 ){( Z )-C(CH 3 )[double bond, length as m-dash]CHCF 3 }(PEt 3 ) 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.