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 (μ-η 2:η 2 -N 2 ), is reported. Synthesis of the 15 N-labeled isotopomer and Raman spectroscopy confirm the reductive activation of N 2 to a (N 2 ) 2– dianion. The 15 N NMR shift of the 15 N 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 °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(SiMe 3 ) 2 } 3 ] and [U{OSi(Mes) 3 } 4 ], is also reported.