Synthesis of Anionic Iron(II) Complex Bearing an N-Heterocyclic Carbene Ligand and Its Catalysis for Aryl Grignard Cross-Coupling of Alkyl Halides

The reaction of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) with one equivalent of a novel imidazolium salt of iron(II), [FeBr3(C4H8O)](HIPr)·C4H8O (1), afforded the anionic iron(II) complex bearing an N-heterocyclic carbene ligand [Fe(IPr)Br3](HIPr)·C7H8 (2), which shows extremely high activity in comparison with the other iron(II)-based precatalysts in the cross-coupling reaction of 4-tolylmagnesium bromide with cyclohexyl bromide.