title: Examining the Effects of Ligand Variation on the Electronic Structure of Uranium Bis(imido) Species.
abstract: Arylazide and diazene activation by highly reduced uranium(IV) complexes bearing trianionic redox-active pyridine(diimine) ligands, [CpPU(MesPDIMe)]2(1-CpP), Cp*U(MesPDIMe)(THF) (1-Cp*) (CpP= 1-(7,7-dimethylbenzyl)cyclopentadienide; Cp* = η5-1,2,3,4,5-pentamethylcyclopentadienide), and Cp*U(tBu-MesPDIMe) (THF) (1-tBu) (2,6-((Mes)N═CMe)2-p-R-C5H2N, Mes = 2,4,6-trimethylphenyl; R = H,MesPDIMe; R = C(CH3)3,tBu-MesPDIMe), has been investigated. While 1-Cp* and 1-CpPreadily reduce N3R (R = Ph, p-tolyl) to form trans-bis(imido) species, CpPU(NAr)2(MesPDIMe) (Ar = Ph, 2-CpP; Ar = p-Tol, 3-CpP) and Cp*U(NPh)2(MesPDIMe) (2-Cp*), only 1-Cp* can cleave diazene N═N double bonds to form the same product. Complexes 2-Cp*, 2-CpP, and 3-CpPare uranium(V) trans-bis(imido) species supported by neutral [MesPDIMe]0ligands formed by complete oxidation of [MesPDIMe]3-ligands of 1-CpPand 1-Cp*. Variation of the arylimido substituent in 2-Cp* from phenyl to p-tolyl, forming Cp*U(NTol)2(MesPDIMe) (3-Cp*), changes the electronic structure, generating a uranium(VI) ion with a monoanionic pyridine(diimine) radical. The tert-butyl-substituted analogue, Cp*U(NTol)2(tBu-MesPDIMe) (3-tBu), displays the same electronic structure. Oxidation of the ligand radical in 3-Cp* and 3-tBu by Ag(I) forms cationic uranium(VI) [Cp*U(NTol)2(MesPDIMe)][SbF6] (4-Cp*) and [Cp*U(NTol)2(tBu-MesPDIMe)][SbF6] (4-tBu), respectively, as confirmed by metrical parameters. Conversely, oxidation of pentavalent 2-Cp* with AgSbF6affords cationic [Cp*U(NPh)2(MesPDIMe)][SbF6] (5-Cp*) from a metal-based U(V)/U(VI) oxidation. All complexes have been characterized by multidimensional NMR spectroscopy with assignments confirmed by electronic absorption spectroscopy. The effective nuclear charge at uranium has been probed using X-ray absorption spectroscopy, while structural parameters of 1-CpP, 3-Cp*, 3-tBu, 4-Cp*, 4-tBu, and 5-Cp* have been elucidated by X-ray crystallography.
authors.affiliation: H.C. Brown Laboratory, Department of Chemistry, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: John J
authors.initials: JJ
authors.lastname: Kiernicki
authors.affiliation: Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Maryline G
authors.initials: MG
authors.lastname: Ferrier
authors.affiliation: Stanford University , Stanford, California 94305, United States.
authors.forename: Juan S
authors.initials: JS
authors.lastname: Lezama Pacheco
authors.affiliation: Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Henry S
authors.initials: HS
authors.lastname: La Pierre
authors.affiliation: Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Benjamin W
authors.initials: BW
authors.lastname: Stein
authors.affiliation: H.C. Brown Laboratory, Department of Chemistry, Purdue University , West Lafayette, Indiana 47907, United States.|Department of Chemistry, Youngstown State University , Youngstown, Ohio 44555, United States.
authors.forename: Matthias
authors.initials: M
authors.lastname: Zeller
authors.affiliation: Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Stosh A
authors.initials: SA
authors.lastname: Kozimor
authors.affiliation: H.C. Brown Laboratory, Department of Chemistry, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Suzanne C
authors.initials: SC
authors.lastname: Bart