Isocyanide adducts of tri- and tetravalent uranium metallocenes supported by tetra(isopropyl)cyclopentadienyl ligands.

Reaction of the uranium(iii) metallocenium salt [(CpiPr4)2U][B(C6F5)4] with tert-butyl isocyanide (tBuNC) yielded the dicationic uranium(iv) complex [(CpiPr4)2U(CNtBu)4][B(C6F5)4]2 (1), which displays a linear metallocene geometry. Use of crude mixtures of [(CpiPr4)2U][B(C6F5)4], which contain a soluble source of iodide, led instead to isolation of the monocationic uranium(iv) iodide complex [(CpiPr4)2U(I)(CNtBu)2][B(C6F5)4] (2). Adduct formation with no change in oxidation state was observed upon addition of tBuNC to the neutral uranium(iii) species (CpiPr4)2UI, resulting in isolation of (CpiPr4)2U(I)(CNtBu) (3). X-ray crystallographic and IR spectroscopic studies both showed effects ascribed to the presence of multiple strongly donating isocyanide ligands in 1.

The Bonding Situation in the Dinuclear Tetra-Hydrido Complex [{5CpFe}2(µ-H)4] Revisited by Hard X-Ray Spectroscopy.

High energy resolution fluorescence detected XANES (HERFD-XANES) and valence-to-core X-ray emission spectroscopy (VtC-XES) are introduced as powerful tools to investigate hydride-iron interaction, the possible iron-iron bond, and iron spin state of the dinuclear tetra-hydrido complex [{5CpFe}2(µ-H)4] (1H, 5Cp = η5-C5 iPr5) by thoroughly accessing the geometric and electronic structure of this complex in comparison to the nonhydride reference [5CpCpFe] (1, Cp = C5H5). The so far observed most intense hydride induced signals in the pre-edge feature of the HERFD-XANES and in the VtC-XES spectra at the iron K-edge allow a precise analysis of the LUMO and HOMO states, respectively, by application of time-dependent density function theory (TD-DFT) and density functional theory (DFT) calculations. The results of these calculations are further employed to understand the oxidation state, spin states, and potential Fe-Fe bonds in this complex.