Facile H/D Exchange at (Hetero)Aromatic Hydrocarbons Catalyzed by a Stable Trans-Dihydride N-Heterocyclic Carbene (NHC) Iron Complex

Abstract

Earth-abundant metal pincer complexes have played an important role in homogeneous catalysis during the last ten years. Yet, despite intense research efforts, the synthesis of iron PC_carbeneP pincer complexes has so far remained elusive. Here we report the synthesis of the first PC_NHCP functionalized iron complex [(PC_NHCP)FeCl₂] (<b>1</b>) and the reactivity of the corresponding <i>trans</i>-dihydride iron(II) dinitrogen complex [(PC_NHCP)Fe(H)₂N₂)] (<b>2</b>). Complex <b>2</b> is stable under an atmosphere of N₂ and is highly active for hydrogen isotope exchange at (hetero)aromatic hydrocarbons under mild conditions (50 °C, N₂). With benzene-<i>d</i>₆ as the deuterium source, easily reducible functional groups such as esters and amides are well tolerated, contributing to the overall wide substrate scope (e.g., halides, ethers, and amines). DFT studies suggest a complex assisted σ-bond metathesis pathway for C(sp²)-H bond activation, which is further discussed in this study.