“Oxidative Addition” of Halogens to Uranium(IV) Bis(amidophenolate) Complexes

A series of U­(IV) complexes, (Rap)2U­(THF)2 [R = tert-butyl (t-Bu) (1), adamantyl (Ad) (2), diisopropylphenyl (dipp) (3)], supported by the redox-active 4,6-di-tert-butyl-2-(R)­amidophenolate ligand, have been synthesized by salt metathesis of 2 equiv of the alkali metal salt of the ligand, M2[Rap] [M = K (1 and 2), Na (3)], with UCl4. Exposure of these uranium complexes to 1 equiv of PhICl2 results in oxidative addition to uranium, forming the bis-(4,6-di-tert-butyl-2-(R)­iminosemiquinone) ([Risq]1–) uranium­(IV) dichloride dimer, [(Risq)2UCl]2(μ2-Cl)2 [R = t-Bu (4), Ad (5), dipp (6)]. The addition of iodine to 1 forms (tBuisq)2UI2(THF) (7), while the reactivity of I2 with 2 and 3 results in decomposition. Complexes 1–7 have been characterized by 1H NMR and electronic absorption spectroscopies. X-ray crystallography was employed to elucidate structural parameters of 2, 3, 5, and 7.