Masked Low-Coordinate Fe(–I) Species: NHC- and Alkene-Supported Fe(–I)-Dinitrogen Complexes

Iron(-I) remains among the least understood oxidation states of iron due to the scarcity of structurally well-defined iron(-I) complexes. Herein, we demonstrate that a combined ligand set of N-heterocyclic carbene (NHC) with divinyltetramethyldisiloxane (dvtms) can effectively stabilize iron(-I) complexes [K(18-C-6)(THF)n][(NHC)Fe(N₂)(η:²η²-dvtms)] behaving like masked low-coordinate iron(-I) species in reactions. The series of iron(-I) complexes [K(18-C-6)(THF)n][(NHC)Fe(N₂)(η:²η²-dvtms)] bearing different NHC ligands (NHC = IiPr, 1a; ICy, 1b; IMesCy, 1c; IMes, 1d; IDep, 1e; IPr, 1f; Me₂-cAAC, 1g) were prepared from the reactions of the iron(0) complexes [(NHC)Fe(η:²η²-dvtms)] with KC₈ and 18-C-6 in THF under a dinitrogen atmosphere. These iron(-I) complexes have been characterized by ¹H NMR, solution magnetic susceptibility measurement, electron paramagnetic resonance spectroscopy, elemental analysis, and single-crystal X-ray diffraction study. Reactivity studies established their conversions to the iron(I) complexes [(NHC)Fe(NNSiiPr₃)(η:²η²-dvtms)] (2), [(18-C-6)K(μ-σ:σ-dIDep)Fe(σ:η²-MeCHSiMe₂OSiMe₂CH = CH₂)] (3), and [K(18-C-6)(THF)₂][Fe(σ:σ:η:²η²-CH₂=CHSiMe₂OSiMe₂CHCH₂CH₂CHMe₂SiOMe₂SiCH = CH₂)] (4) under corresponding reaction conditions, showing the capability of low-coordinate iron(-I) species in mediating two-electron reductive transformations of dinitrogen and alkenes. Furthermore, these iron(-I) complexes facilitate the hydrodehalogenation of nonactivated organic halides upon one-electron redox reactions, yielding iron(0) complexes and hydrodehalogenated organic products. The straightforward synthesis and rich reactivity of these iron(-I) complexes highlight their potential utility as reagents and catalysts for challenging chemical transformations.