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A Uranium Tri-Rhenium Triple Inverse Sandwich Compound

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posted on 20.03.2019, 14:49 by Michael A. Boreen, Trevor D. Lohrey, Guodong Rao, R. David Britt, Laurent Maron, John Arnold
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-η55-Cp)­Re­(BDI)]3, which was isolated and structurally characterized as the Lewis base adducts, (L)­U­[(μ-η55-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.