Synthesis, Characterization, and Stoichiometric U–O Bond Scission in Uranyl Species Supported by Pyridine(diimine) Ligand Radicals
datasetposted on 02.09.2015, 00:00 by John J. Kiernicki, Dennis P. Cladis, Phillip E. Fanwick, Matthias Zeller, Suzanne C. Bart
Two uranium(VI) uranyl compounds, Cp*UO2(MesPDIMe) (3) and Cp*UO2(tBu-MesPDIMe) (3-tBu) (Cp* = 1,2,3,4,5-pentamethylcyclopentadienide; MesPDIMe = 2,6-((Mes)N=CMe)2C5H3N; tBu-MesPDIMe = 2,6-((Mes)N=CMe)2-p-C(CH3)3C5H2N; Mes = 2,4,6-trimethylphenyl), have been synthesized by addition of N-methylmorpholine N-oxide to trianionic pyridine(diimine) uranium(IV) precursors, Cp*U(MesPDIMe)(THF) (1), Cp*U(MesPDIMe)(HMPA) (1-HMPA), and Cp*U(tBu-MesPDIMe)(THF) (1-tBu). These uranyl complexes contain singly reduced pyridine(diimine) ligands suggesting formation occurs via cooperative ligand/metal oxidation. Treating 3 or 3-tBu with stoichiometric equivalents of Me3SiI results in stepwise oxo silylation to form (Me3SiO)2UI2(MesPDIMe) (5) or (Me3SiO)UI2(tBu-MesPDIMe) (5-tBu), respectively. Additional equivalents result in full uranium–oxo bond scission and formation of UI4(1,4-dioxane)2 with extrusion of hexamethyldisiloxane. The uranium complexes have been characterized via multinuclear NMR, vibrational, and electronic absorption spectroscopies and, in some cases, X-ray crystallography.