Highly Reactive Uranium(III) Polypyrrolide Complexes:  Intramolecular C−H Bond Activation, Ligand Isomerization, and Solvent Deoxygenation and Fragmentation

Abstract

The reaction of UX 3 (THF) 4 (X ) Cl, I) with the tetraanion of {[(-CH 2 -) 5 ] 4 -calix[4]-tetrapyrrole} gave different compounds depending on the uranium halide, the alkali-metal cation (Li vs K), the stoichiometric ratio of ligand to uranium, and the solvent used. Reaction of the potassium salt of the ligand with uranium iodide in THF and in the ratio 1:1 afforded the dinuclear, tetravalent species 1). The source of the bridging oxygen atom is a THF deoxygenation process. A reaction carried out under identical conditions but with the tetralithium salt of the calix[4]tetrapyrrole afforded instead intractable material unless a stoichiometric ratio of two ligands per uranium was employed. In this event, a new species, the dinuclear tetravalent species [{[(-CH 2 -) 5 ] 4 -calix[4]pyrrole}ULi(THF) 2 ] 2 ‚hexane (2), was isolated. In this complex, the β-C atom of one of the pyrrole rings of the macrocycle was deprotonated and metalated by uranium of a second identical unit, thus assembling the dinuclear structure. The reaction is not accompanied 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 the mononuclear tetravalent species ({[(-CH 2 -) 5 ] 4 -calix[4]tetrapyrrole}ULi(OC 2 H 5 )(THF) 2 ) (3). In this compound one pyrrole ring was isomerized by shifting the attachment of the chain from the R-to the β-position. The LiOCH 2 CH 3 unit was generated by another pathway of THF fragmentation. Finally, a reaction carried out in dimethoxyethane with the purpose of preventing oxidative attack to the metal center, afforded the mononuclear trivalent complex [{[(-CH 2 -) 5 ] 4 -calix[4]tetrapyrrole}U(DME)][K(DME)] (4).

Actinide‐Mediated Cyclization of 1,2,4,5‐Tetracyanobenzene: Synthesis and Characterization of Self‐Assembled Trinuclear Thorium and Uranium Macrocycles

“…The U(1A)N(4) amide bond length of 2.236(12) Å is comparable to that of other structurally characterized uranium( IV ) amide complexes 5. Although actinide isoindolyl complexes are not known, the U(1A)N(3) bond length of 2.464(10) Å is in good agreement with UN bond lengths reported for σ‐bonded uranium( IV ) pyrrolyl6 and pyrazolyl7 complexes.…”

The First Thorium Arene Complex: A Divalent Synthon

“…The formation of 2 is most likely the result of solvent fragmentation, which is a recurrent feature in the chemistry of low‐valent f‐block metals 2a,b. 2j,2k, 7, 11a However, since 1 a and 1 b do not react with DME even on prolonged reflux, the occasional formation of 2 indicates that intermediate species, generated during reduction, are sufficiently reactive to attack the solvent.…”

Multimetallic Cooperative Activation of N2

“…It has only been in the last three years that actinides have started to play a significant role in dinitrogen activation. After the labile fixation8, 9 and two‐electron reduction10 observed with trivalent uranium complexes, the reduction of a trivalent uranium complex of the calix[4]tetrapyrrole ligand system with potassium dihydronaphthylide in 1,2‐dimethoxyethane (DME) under nitrogen afforded the mixed‐valence U IV /U V nitride 33 (Scheme ) 36. 37 The highly reactive species that performs the dinitrogen cleavage in this case was not identified since reactions carried out under an Ar atmosphere promoted solvent deoxygenation, as well as depolymerization of the high‐vacuum, polysilanol grease (Scheme ).…”