C–H Bond Activation via U(II) in the Reduction of Heteroleptic Bis(trimethylsilyl)amide U(III) Complexes

Reduction of (C5Me5)2UIII(NR2) and (C5Me5)­UIII(NR2)2 (R = SiMe3) with potassium graphite in the presence of 2.2.2-cryptand (crypt) generates dark solutions that have UV–visible spectra consistent with time-dependent density functional theory (TDDFT) calculations on the U­(II) products, [(C5Me5)2UII(NR2)]− and [(C5Me5)­UII(NR2)2]−. However, the solutions quickly change color and form the U­(III) C–H bond activation products [K­(crypt)]­[(C5Me5)2UIII(CH2SiMe2NSiMe3-κC,κN)] (1) and [K­(crypt)]­[(C5Me5)­UIII(NR2)­(CH2SiMe2NSiMe3-κC,κN)] (2), which were identified by X-ray crystallography. DFT calculations on the putative [(C5Me5)2UII(NR2)]− and [(C5Me5)­UII(NR2)2]− complexes revealed 5f36d1 ground-state electron configurations, as previously found in isolable [(C5H4SiMe3)3UII]−, which indicated that these low-symmetry heteroleptic complexes are reasonable precursors for new U­(II) complexes.