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)(2)(UI)-I-III (1) and (PN)(2)(UCl2)-Cl-IV (2), which both yield (PN)(2)U-IV(N-3)(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)U-IV(= NH)[(Pr2P)-Pr-i(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.