C–H Bond Addition across a Transient Uranium–Nitrido Moiety and Formation of a Parent Uranium Imido Complex

Uranium complexes
in the +3 and +4 oxidation states were prepared
using the anionic PN– (PN– = (N-(2-(diisopropylphosphino)-4-methylphenyl)-2,4,6-trimethylanilide)
ligand framework. New complexes include the halide starting materials,
(PN)2UIIII (1) and (PN)2UIVCl2 (2), which both yield (PN)2UIV(N3)2 (3)
by reaction with NaN3. Compound 3 was reduced
with potassium graphite to produce a putative, transient uranium–nitrido
moiety that underwent an intramolecular C–H activation to form
a rare example of a parent imido complex, [K­(THF)3]­[(PN)­UIV(NH)­[iPr2P­(C6H3Me)­N­(C6H2Me2CH2)]] (4). Calculated reaction energy profiles
strongly suggest that a C–H insertion becomes unfavorable when
a reductant is present, offering a distinctively different reaction
pathway than previously observed for other uranium nitride complexes.