Complexes of Iron(II) and Iron(III) Containing Aryl-Substituted N-Heterocyclic Carbene Ligands

Iron(II) and iron(III) complexes containing the 1,3-dimesitylimidazole-2-ylidene (IMes) and 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) ligands have been prepared and characterized. Four-coordinate iron(II) carbene species are sensitive to the steric bulk of the carbene ligand and can adopt both monomeric and halide-bridged dimeric structures with 2:1 and 1:1 carbene to iron stoichiometries, respectively. Iron(III) carbene complexes bind a single carbene ligand, which is easily exchanged in solution. The structural and solution phase characterization of all compounds is reported, and their relevance to iron-catalyzed C–C coupling reactions is discussed.