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 H-2-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 = H-2- 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 la,b(+)PF(6)(-) in CH3CN, but displacement of the second CO ligand is inhibited by strong metal-CO pi-back-donation.