Dinuclear Iron–Imido Complexes with N-Heterocyclic Carbene Ligation: Synthesis, Structure, and Redox Reactivity

The introduction of an N-heterocyclic carbene ligand (NHC) to iron–imido chemistry has led to the successful preparation of a series of iron–imido complexes featuring rhombic [Fe­(μ2-NDipp)2Fe]n (n = 0, 1+, 2+) cores. The dimeric iron­(II)–imido complex [(IPr2Me2)­Fe­(μ2-NDipp)2Fe­(IPr2Me2)] (1) was prepared by protonolysis of the ferrous precursor [(IPr2Me2)­Fe­(Mes)2] with the aniline derivative DippNH2. Complex 1 has a rhombic [Fe­(μ2-NDipp)2Fe] core in which the iron sites adopt trigonal-planar geometry and have a formal Fe­(II) oxidation state. Oxidation of 1 with 1 or 2 equiv of [Cp2Fe]­[BF4] resulted in the formation of the dinuclear iron­(III) complex [F­(IPr2Me2)­Fe­(μ2-NDipp)2Fe­(IPr2Me2)­F] (2) or [F­(IPr2Me2)­Fe­(μ2-NDipp)2Fe­(IPr2Me2)­(BF4)] (3), respectively. However, the reaction of 1 with benzyl chloride could give either the diferric complex [Cl­(IPr2Me2)­Fe­(μ2-NDipp)2Fe­(IPr2Me2)­Cl] (4) or the mixed-valent complex [(IPr2Me2)­Fe­(μ2-NDipp)2Fe­(IPr2Me2)­Cl] (5), depending on the reaction stoichiometry. Complex 5 is also accessible upon the reaction of 1 with 4. Complexes 1–5 have been fully characterized by 1H NMR, UV–vis spectroscopy, single-crystal X-ray diffraction studies, and elemental analysis. The successful preparation of these complexes revealed the potential of the iron–imido rhomb for mediating electron transfer.