Reduction of (C 5 Me 5 ) 2 U III (NR 2 ) and (C 5 Me 5 )-U III (NR 2 ) 2 (R = SiMe 3 ) 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, [(C 5 Me 5 ) 2 U II (NR 2 )] − and [(C 5 Me 5 )U II (NR 2 ) 2 ] − . However, the solutions quickly change color and form the U(III) C−H bond activation products [K(crypt)][(C 5 Me 5 ) 2 U III (CH 2 SiMe 2 NSiMe 3κ C , κ N ) ] ( 1 ) a n d [ K ( c r y p t ) ] [ ( C 5 M e 5 ) U I I I ( N R 2 ) -(CH 2 SiMe 2 NSiMe 3 -κC,κN)] ( 2), which were identified by X-ray crystallography. DFT calculations on the putative [(C 5 Me 5 ) 2 U II (NR 2 )] − and [(C 5 Me 5 )U II (NR 2 ) 2 ] − complexes revealed 5f 3 6d 1 ground-state electron configurations, as previously found in isolable [(C 5 H 4 SiMe 3 ) 3 U II ] − , which indicated that these low-symmetry heteroleptic complexes are reasonable precursors for new U(II) complexes.
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