| Abstract
| - Attempts to prepare trivalent uranium derivatives of the calix[4]tetrapyrrolide tetraanion resolved in a variety of transformations involving THF fragmentation and ligand reorganization.
- The reaction of UX3(THF)4 (X = Cl, I) with the tetraanion of {[(−CH2−)5]4-calix[4]tetrapyrrole} gave different compounds depending on the uranium halide, the alkali-metalcation (Li vs K), the stoichiometric ratio of ligand to uranium, and the solvent used. Reactionof the potassium salt of the ligand with uranium iodide in THF and in the ratio 1:1 affordedthe dinuclear, tetravalent species {[{[(−CH2−)5]4-calix[4]tetrapyrrole}UK(THF)3]2(μ2-O)}·2THF (1). The source of the bridging oxygen atom is a THF deoxygenation process. A reactioncarried out under identical conditions but with the tetralithium salt of the calix[4]tetrapyrroleafforded instead intractable material unless a stoichiometric ratio of two ligands per uraniumwas employed. In this event, a new species, the dinuclear tetravalent species [{[(−CH2−)5]4-calix[4]pyrrole}ULi(THF)2]2·hexane (2), was isolated. In this complex, the β-C atom ofone of the pyrrole rings of the macrocycle was deprotonated and metalated by uranium of asecond identical unit, thus assembling the dinuclear structure. The reaction is notaccompanied by loss of hydrogen gas, while the excess ligand is acting as a Brønsted base.An identical reaction carried out by using uranium trichloride afforded instead themononuclear tetravalent species ({[(−CH2−)5]4-calix[4]tetrapyrrole}ULi(OC2H5)(THF)2) (3).In this compound one pyrrole ring was isomerized by shifting the attachment of the chainfrom the α- to the β-position. The LiOCH2CH3 unit was generated by another pathway ofTHF fragmentation. Finally, a reaction carried out in dimethoxyethane with the purpose ofpreventing oxidative attack to the metal center, afforded the mononuclear trivalent complex[{[(−CH2−)5]4-calix[4]tetrapyrrole}U(DME)][K(DME)] (4).
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