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Synthesis,structure, spectroscopy and redox energetics of a series of uranium(IV) mixed-ligand metallocene complexes
Authors:Robert K Thomson  Brian L Scott  David E Morris  Jaqueline L Kiplinger
Institution:Los Alamos National Laboratory, Los Alamos, NM 87545, USA
Abstract:A series of uranium(IV) mixed-ligand amide–halide/pseudohalide complexes (C5Me5)2UN(SiMe3)2](X) (X = F (1), Cl (2), Br (3), I (4), N3 (5), NCO (6)), (C5Me5)2U(NPh2)(X) (X = Cl (7), N3 (8)), and (C5Me5)2UN(Ph)(SiMe3)](X) (X = Cl (9), N3 (10)) have been prepared by one electron oxidation of the corresponding uranium(III) amide precursors using either copper halides, silver isocyanate, or triphenylphosphine gold(I)azide. Agostic U?H–C interactions and η3-(N,C,C′) coordination are observed for these complexes in both the solid-state and solution. There is a linear correlation between the chemical shift values of the C5Me5 ligand protons in the 1H NMR spectra and the UIV/UIII reduction potentials of the (C5Me5)2UN(SiMe3)2](X) complexes, suggesting that there is a common origin, that is overall σ-/π-donation from the ancillary (X) ligand to the metal, contributing to both observables. Optical spectroscopy of the series of complexes 16 is dominated by the (C5Me5)2UN(SiMe3)2] core, with small variations derived from the identity of the halide/pseudohalide. The considerable π-donating ability of the fluoride ligand is reflected in both the electrochemistry and UV-visible-NIR spectroscopic behavior of the fluoride complex (C5Me5)2UN(SiMe3)2](F) (1). The syntheses of the new trivalent uranium amide complex, (C5Me5)2UN(Ph)(SiMe3)](THF), and the two new weakly-coordinating electrolytes, Pr4N]B{3,5-(CF3)2C6H3}4] and Pr4N]B(C6F5)4], are also reported.
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