A Uranium Tri-Rhenium Triple Inverse Sandwich Compound
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Salt metathesis between the anionic rhenium(I) compound, Na[Re(η5-Cp)(BDI)] (BDI = N,N′-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate), and the uranium(III) salt, UI3(1,4-dioxane)1.5, generated the triple inverse sandwich complex, U[(μ-η5:η5-Cp)Re(BDI)]3, which was isolated and structurally characterized as the Lewis base adducts, (L)U[(μ-η5:η5-Cp)Re(BDI)]3 (1·L, L = THF, 1,4-dioxane, DMAP). The assignment as one uranium(III) and three rhenium(I) centers was supported by X-ray crystallography, NMR and EPR spectroscopies, and computational studies. An unusual shortening of the rhenium–Cp bond distances in 1·L relative to Na[Re(η5-Cp)(BDI)] was observed in the solid-state and reproduced in calculated structures of 1·THF and the anionic fragment, [Re(η5-Cp)(BDI)]−. Calculations suggest that the electropositive uranium center pulls electron density away from the electron-rich rhenium centers, reducing electron–electron repulsions in the rhenium–Cp moieties and thereby strengthening those interactions, while also making uranium–Cp bonding more favorable.
