A Uranium Tri-Rhenium Triple Inverse Sandwich Compound

Salt metathesis between the anionic rhenium(I) compound, Na[Re(η 5 -Cp)(BDI)] (BDI = N, N ′-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate), and the uranium(III) salt, UI 3 (1,4-dioxane) 1.5, generated the triple inverse sandwich complex, U[(μ-η 5:η 5 -Cp)Re(BDI)] 3, which was isolated and structurally characterized as the Lewis base adducts, (L)U[(μ-η 5:η 5 -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(η 5 -Cp)(BDI)] was observed in the solid-state and reproduced in calculated structures of 1·THF and the anionic fragment, [Re(η 5 -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.