Tailoring the Electronic Structure of Uranium Mono(imido) Species through Ligand Variation.

Uranium mono(imido) species have been prepared via the oxidation of Cp*U(Mes PDIMe )(THF) (1-Cp*) and [CpP U(Mes PDIMe )]2 (1-CpP ), where Cp* = η5 -1,2,3,4,5-pentamethylcyclopentadienide, CpP = 1-(7,7-dimethylbenzyl)cyclopentadienide, Mes PDIMe = 2,6-[(Mes)N═CMe]2 C5 H3 N, and Mes = 2,4,6-trimethylphenyl, with organoazides. Treating either with N3 DIPP (DIPP = 2,6-diisopropylphenyl) formed uranium(IV) mono(imido) complexes, CpP U(NDIPP)(Mes PDIMe ) (2-CpP ) and Cp*U(NDIPP)(Mes PDIMe ) (2-Cp*), featuring reduced [Mes PDIMe ]- . The addition of electron-donating 1-azidoadamantane (N3 Ad) to 1-Cp* generated a dimeric product, [Cp*U(NAd)(Mes HPDIMe )]2 (3), from radical coupling at the p-pyridine position of the pyridine(diimine) ligand and H-atom abstraction, formed through a monomeric intermediate that was observed in solution but could not be isolated. To support this, Cp*U(t Bu-Mes PDIMe )(THF) (1-t Bu), which has a tert-butyl group protecting the para position, was also treated with N3 Ad, and the monomeric product, Cp*U(NAd)(t Bu-Mes PDIMe ) (2-t Bu), was isolated. All isolated complexes were analyzed spectroscopically and structurally, and the dynamic solution behavior was examined using electronic absorption spectroscopy.