Synthesis and redox chemistry of high-valent uranium aryloxides.
Alcoholysis of U(O(t)Bu)(6) with 1 or 2 equiv of C(6)F(5)OH generates U(O(t)Bu)(5)(OC(6)F(5)) (1) and U(O(t)Bu)(4)(OC(6)F(5))(2) (2) in 70% and 65% yields, respectively. Complexes 1 and 2 have been fully characterized, and their solution redox properties have been determined by cyclic voltammetry. Complex 1 exhibits a reversible reduction feature at E(1/2) = -0.60 V (vs [Cp(2)Fe](0/+)), while 2 exhibits a reversible reduction feature at -0.24 V (vs [Cp(2)Fe](0/+)). Attempts to isolate the other tert-butoxide/pentafluorophenoxide complexes, U(O(t)Bu)(6-n)(OC(6)F(5))(n) (n = 3-6), did not generate the intended products. For instance, reaction of U(O(t)Bu)(6) with 6 equiv of C(6)F(5)OH in CH(2)Cl(2) results in the formation [Li(HO(t)Bu)(2)][U(OC(6)F(5))(6)] (3). The source of the lithium cation in 3 is likely LiI, which is present from the initial synthesis of the U(O(t)Bu)(6). However, reaction of LiI-free U(O(t)Bu)(6) with 6 equiv of C(6)F(5)OH results in the formation of a uranyl complex, UO(2)(OC(6)F(5))(2)(HO(t)Bu)(2) (4), along with isobutylene and (t)BuOC(6)F(5). To probe the mechanism of this transformation, U(O(t)Bu)(6) was reacted with C(6)F(5)(18)OH.0.5DME. This produces UO(2)((18)OC(6)F(5))(2)(DME) (5-(18)O) along with (t)Bu(18)OC(6)F(5) as determined by GC/MS, which suggests that oxo formation only occurs by tert-butyl cation elimination and not aromatic nucleophilic substitution. Several other synthetic pathways to U(VI)(OC(6)F(5))(6) were also investigated. Thus, addition of 10 equiv of C(6)F(5)OH to [Li(THF)](2)[U(O(t)Bu)(6)] in Et(2)O followed by addition of DME results in the formation of [Li(DME)(3)](2)[U(OC(6)F(5))(6)] (7). Oxidation of 7 with 2 equiv of AgOTf in CH(2)Cl(2) or toluene generates [Li(DME)(3)][U(OC(6)F(5))(6)] (8) or [Ag(eta(2)-C(7)H(8))(2)(DME)][U(OC(6)F(5))(6)] (9), respectively. However, no evidence for the formation of U(VI)(OC(6)F(5))(6) was observed during these reactions.
Fortier
Skye
S
Department of Chemistry and Biochemistry, University of California Santa Barbara, California 93106, USA.
Wu
Guang
G
Hayton
Trevor W
TW
D018360:Crystallography, X-Ray; D004563:Electrochemistry; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D014501:Uranium / Q000737:chemistry*
D008024:Ligands; D009942:Organometallic Compounds; D010087:Oxides; D014501:Uranium