| Abstract
| - The reactions of the bis(tpa) complex of U(III) with methanol and water result in the one-electron oxidation of the metal center leading to the formation of a mononuclear bis(methoxide) complex and of a trimeric oxo species.
- The crystal structure of the complex [U(tpa)2]I3, 1 (tpa = tris[(2-pyridyl)methyl]amine), has been elucidated. Thecomplex exists as only one enantiomer in the crystal leading to the chiral space group P212121. The coordinationgeometry of the metal can be described as a distorted cube. Accidental oxidation of [U(tpa)2]I3 led to the isolationof the unusual mononuclear bishydroxo complex of uranium(IV) [U(tpa)2(OH)2]I2·3CH3CN, 2, which was structurallycharacterized. The controlled reaction of [U(tpa)2]I3 with water resulted in the oxidation of the metal center and ledto the formation of protonated tpa and of the trinuclear U(IV) oxo complex {[U(tpa)(μ-O)I]3(μ3-I)}I2, 3. The solidstate and solution structures of this trimer are reported. The pathway suggested for the formation of this complexis the oxidation of the [U(tpa)2]I3 complex by H2O to form a U(IV) hydroxo complex which then decomposes,eliminating mono-protonated tpa. The comparison with the reported reaction with water of cyclopentadienyl derivativespoints to a higher reactivity toward water reduction of the bis(tpa) complex with respect to the cyclopentadienylderivatives. The reaction of U(III) with methanol in the presence of the supporting ligand tpa leads to formation ofalkoxo complexes similarly to what is found for amide or cyclopentadienyl derivatives. The monomethoxide complex[U(tpa)I3(OMe)], 4, has been prepared in good yield by alcoholysis of the U(III) mono(tpa) complex. The crystalstructure of this complex has been determined. The reaction of [U(tpa)2]I3 with 2 equiv of methanol in acetonitrileallows the isolation of the bismethoxo complex of U(IV) [U(tpa)I2(OMe)2], 5, in 35−47% yield, which has been fullycharacterized. To account for the oxidation of U(III) to U(IV) the suggested mechanism assumes that hydrogen isevolved in both reactions.
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