Syntheses, Properties, and X-ray Crystal Structures of Piano-Stool Iron Complexes Bearing an N-Heterocyclic Carbene Ligand

Piano-stool iron complexes containing the C−C unsaturated IMes or saturated H2-IMes ligand are readily synthesized from [CpFe(CO)2(I)]. Substitution of the iodide ligand affords the cationic species [CpFe(CO)2(L)][[I] (1a + I -) and (1b + I -) (a, L = IMes, b, L = H2-IMes), subsequent decarbonylation of which yields the neutral iodo derivatives 2a,b. Cyclic voltammetry studies of 2a,b show a reversible one-electron oxidation to the corresponding 17-electron radical cation. The mono(acetonitrile) complexes 3a,b are obtained from UV irradiation of 1a,b + PF 6 - in CH3CN, but displacement of the second CO ligand is inhibited by strong metal−CO π-back-donation.