Monomeric Bis(anilido)iron(II)
Complexes with <i>N</i>‑Heterocyclic Carbene Ligation:
Synthesis, Characterization, and Redox Reactivity toward Aryl Halides
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Abstract
Using monodentate <i>N</i>-heterocyclic carbenes
as the ancillary ligands, seven monomeric bis(anilido)iron(II) complexes
[(IPr<sub>2</sub>Me<sub>2</sub>)<sub>2</sub>Fe(NHAr)<sub>2</sub>]
(IPr<sub>2</sub>Me<sub>2</sub> = 2,5-diisopropyl-3,4-dimethylimidazol-1-ylidene;
Ar = Ph, C<sub>6</sub>H<sub>4</sub>-2-Pr<sup><i>i</i></sup>, Mes, C<sub>6</sub>H<sub>3</sub>-2,6-Cl<sub>2</sub>, Dipp) and [(IPr)Fe(NHAr)<sub>2</sub>] (IPr = 2,5-di(2,6-diisopropylphenyl)imidazol-1-ylidene;
Ar = C<sub>6</sub>H<sub>3</sub>-2,6-Cl<sub>2</sub>, Dipp) have been
prepared by the one-pot reactions of [Fe(Mes)<sub>2</sub>]<sub>2</sub> with the corresponding <i>N</i>-heterocyclic carbenes,
and anilines. These high-spin diamido complexes have been fully characterized
by <sup>1</sup>H NMR, solution magnetic susceptibility, UV–vis,
IR, X-ray diffraction, cyclic voltammetry, as well as elemental analysis.
The strong affinity of the <i>N</i>-heterocyclic carbene
ligands toward ferrous centers, and the steric protection exerted
by the NHC ligands are the key factors to stabilize these bis(anilido)iron
complexes in a monomeric manner. Reactivity studies revealed the four-coordinate
complex [(IPr<sub>2</sub>Me<sub>2</sub>)<sub>2</sub>Fe(NHMes)<sub>2</sub>] can react with 1 equiv of 1-iodo-3,5-dimethylbenzene or
1-bromo-3,5-dimethylbenzene in C<sub>6</sub>D<sub>6</sub> and THF-d<sub>8</sub> to furnish 1-C<sub>6</sub>D<sub>5</sub>-3,5-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>, and 5-D-1,3-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>, respectively. Under similar conditions, the three-coordinate
compound [(IPr)Fe(NHDipp)<sub>2</sub>] is inert toward these halides
