Synthesis and Characterization of a Series of Uranium(IV) Species: Investigating Coordination With a Redox Innocent Triamine Ligand

摘要

Investigation of uranium(IV) complexes chelated by a tridentate amine, H3RITA (H3RITA = (MesNHCH2CH2)2NH, Mes = 2,4,6-trimethylphenyl), has afforded novel new compounds with the potential for small molecule activation. Deprotonation of H3RITA with two equivalents of benzyl potassium affords K2HRITA, which upon reaction with uranium tetrachloride forms (THF)2UCl2(HRITA) (THF = tetrahydrofuran). The labile THF molecules are easily substituted for triphenylphosphine oxide (OPPh3), a much stronger ligand, forming (Ph3PO)UCl2(HRITA). Installation of a cyclopentadienyl ligand, Cp* (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl), was achieved by the metathesis of (THF)2UCl2(HRITA) with KCp* to form Cp*UCl(HRITA). For Cp*UCl(HRITA), full deprotonation of the RITA ligand was possible by using the strong base, methyllithium. The reaction of methyllithium with Cp*UCl(HRITA) affords Cp*U(RITA)(LiCl(THF)2)—a uranium species containing a weakly bound lithium chloride ligand. Replacement of the lithium chloride with triphenylphosphine oxide forms the neutral species, Cp*U(RITA)(OPPh3), which contains a rare trianionic RITA ligand. All complexes have been characterized by 1H NMR and IR spectroscopies, and where possible, their electronics were probed by electronic absorption spectroscopy. The molecular structures of (THF)2UCl2(HRITA), (Ph3PO)UCl2(HRITA), Cp*UCl(HRITA), and Cp*U(RITA) (LiCl(THF)2) were determined by single X-ray diffraction studies.