Thermally Stable Uranium Dinitrogen Complex with Siloxide Supporting Ligands

A new dinitrogen adduct of a homoleptic uranium tris(siloxide) complex, [U{OSi(Mes)(3)}(3)](2)(mu-eta(2):eta(2)-N-2), is reported. Synthesis of the N-15-labeled isotopomer and Raman spectroscopy confirm the reductive activation of N-2 to a (N-2)(2-) dianion. The N-15 NMR shift of the N-15(2)-labeled isotopomer is also reported. Crystallographic characterization shows a side-on (N-2)(2-) coordinated in either an eclipsed or staggered conformation in different crystals. The U-N-2-U complex is stable to vacuum and shows high thermal stability, retaining the formally reduced dinitrogen at 100 degrees C. The parent three-coordinate uranium(III) [U{OSi(Mes)(3)}(3)] could not be isolated in our hands, with N-2-free syntheses affording only uranium(IV) compounds. The rational synthesis and full characterization of two such U(IV) byproducts, [U{OSi(Mes)(3)}{N(SiMe3)(2)}(3)] and [U{OSi(Mes)(3)}(4)], is also reported.