Synthesis, structure, and C–H bond activation reaction of an iron(IV) terminal imido complex bearing trifluoromethyl groups

Iron terminal imido species featuring electron-withdrawing N-substituents represent an important category of reactive metal-ligand-multiple-bond intermediates in iron-catalyzed reactions. Knowledge of them is very limited, however, as isolable complexes of this type are hard to access. Here, we report an isolable iron(IV) imido complex with trifluoromethyl on nitrogen, namely [(IPr)Fe(NC(CF3)2Ph)2]. We prepared the complex from the reaction of a low-coordinate iron(0) complex with N3C(CF3)2Ph. It has an S = 1 ground spin-state, long Fe-N(imido) bonds, and bent Fe-N(imido)-C(imido) alignments and can undergo intramolecular C–H bond activation reaction to transform into an iron(II) amido complex. Theoretical study suggests that the C–H bond activation reaction involves hydrogen-atom-abstraction mechanism and that the electron-withdrawing nature of trifluoromethyl group renders the imido ligands in [(IPr)Fe(NC(CF3)2Ph)2] and the transition state of the hydrogen-atom-abstraction step structurally close to each other, resulting in a low activation barrier.