Synthesis, crystal structure and reactivity of uranium(iv) complexes with p-tert-butylcalix[4]arene ligands

Abstract

Reactions of UCl₄ with 25,27-dimethoxy-5,11,17,23-tetra-tert-butylcalix[4]arene (H₂Me₂calix) in THF or pyridine at 80 °C gave [UCl₂(Me₂calix)L₂] [L = THF (1) or pyridine (2)]. Similar treatment of U(acac)₄ (acac = MeCOCHCOMe) with H₂Me₂calix in THF or pyridine afforded [U(acac)₂(Me₂calix)] (3). The bis-calixarene compound [U(Me₂calix)(H₂calix)] (4) was obtained by reaction of U(OTf)₄ or U(OTf)₃ with H₂Me₂calix in pyridine at 110 °C. Treatment of UCl₄ with H₂Me₂calix in pyridine at 110 °C gave [Mepy][UCl₂(Hcalix)(py)₂] (5) resulting from demethylation and acid cleavage of the methoxy groups of the calixarene ligand of 2. Adventitious traces of air were responsible for the formation of [Hpy][Mepy]₄[{UCl(calix)}₃(µ₃-O)][UCl₆] (6) during the reaction of UCl₄ and H₂Me₂calix, and of [{U(Me₂calix)(µ₃-O)LiCl(THF)}₂] (7) during the reaction of 2 with ^tBuLi. The X-ray crystal structures of 1·2THF, 2·2py, 3·0.25L (L = THF and py), 4·2py, 5, 6·3py and 7·THF have been determined.