title: Structural rearrangements in triple-decker-like complexes with mixed group 15/16 ligands: synthesis and characterization of the redox couple.
abstract: The reaction of As4Se4 with stoichiometric amounts of [Cp*Fe2(CO)4] (Cp* = C5Me5) in boiling toluene forms [Cp2*Fe2As2Se2] (1) in good yield. X-ray crystallography shows 1 to have a triple-decker structure which comprises a tetraatomic mu,eta4:4-As2Se2 ligand. Density functional theory (DFT) and extended Hückel molecular orbital (EHMO) calculations confirm that the As2Se2 ligand behaves as a four-electron pi donor. Oxidation of 1 with equimolar amounts of [(C5H5)2Fe]PF6, Br2 and I2, respectively, gave compounds 2-4. According to X-ray crystallographic investigations that were carried out on 2 and 4, the oxidation state has a considerable influence on the structure of the Fe2As2Se2 core: significant shortening of the Fe-Fe distance (deltad(Fe-Fe)> 0.3 A) and weakening of the As-As bond length ((deltad(As-As) > 0.3 A) suggests the formal presence of two diatomic AsSe ligands and a Fe-Fe bond. DFT and EHMO calculations confirm that an electron is removed from an occupied Fe-Fe orbital of antibonding character during oxidation. All molecular orbitals lower their energies upon oxidation, but the energy drop is relatively small for those involving the As-As bond. An additional structural feature in 4 consists of an electronic interaction of the iodide with both As atoms which suggests a formally neutral ion pair. Electrochemical studies confirm that the oxidation of 1 is a reversible one-electron process with E(1/2)= +0.07 V (in THF). These studies also reveal that 4 dissociates in polar solvents, such as THF, into [1]+ and I-, which is followed by transformation into 1 and I3.
authors.affiliation: Laboratoire de Synthèse et d'Electrosynthèse Organométalliques (UMR 5632), Université de Bourgogne, Dijon, France.
authors.forename: O
authors.initials: O
authors.lastname: Blacque
authors.forename: H
authors.initials: H
authors.lastname: Brunner
authors.forename: M M
authors.initials: MM
authors.lastname: Kubicki
authors.forename: F
authors.initials: F
authors.lastname: Leis
authors.forename: D
authors.initials: D
authors.lastname: Lucas
authors.forename: Y
authors.initials: Y
authors.lastname: Mugnier
authors.forename: B
authors.initials: B
authors.lastname: Nuber
authors.forename: J
authors.initials: J
authors.lastname: Wachter