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(MesPDIMe)(THF) (1-Cp*) and [CpPU(MesPDIMe)]2 (1-CpP), where Cp* = η5-1,2,3,4,5-pentamethylcyclopentadienide, CpP = 1-(7,7-dimethylbenzyl)cyclopentadienide, MesPDIMe = 2,6-[(Mes)N═CMe]2C5H3N, and Mes = 2,4,6-trimethylphenyl, with organoazides. Treating either with N3DIPP (DIPP = 2,6-diisopropylphenyl) formed uranium(IV) mono(imido) complexes, CpPU(NDIPP)(MesPDIMe) (2-CpP) and Cp*U(NDIPP)(MesPDIMe) (2-Cp*), featuring reduced [MesPDIMe]-. The addition of electron-donating 1-azidoadamantane (N3Ad) to 1-Cp* generated a dimeric product, [Cp*U(NAd)(MesHPDIMe)]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(tBu-MesPDIMe)(THF) (1-tBu), which has a tert-butyl group protecting the para position, was also treated with N3Ad, and the monomeric product, Cp*U(NAd)(tBu-MesPDIMe) (2-tBu), was isolated. All isolated complexes were analyzed spectroscopically and structurally, and the dynamic solution behavior was examined using electronic absorption spectroscopy.