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.