Bis-cyclopentadienyl alkoxides and aryl oxides of uranium(IV). Influence of the steric hindrance of the R groups on the stability of the Cp2U(OR)2, Cp2U(OC6H4R)2 and Cp2U(OC6H3R2)2 derivatives

Reactions of Cp2U(NEt2)2 with the moderately acidic agents ROH and ArOH lead to the cleavage of the UNEt2 bonds and formation of di-cyclopentadienyl dialkoxides and diaryl oxides of uranium(IV). The yields of the new derivatives are strongly dependent on the bulk of the OR or OAr groups; they can undergo disproportionation or decomposition reactions with formation of tris-cyclopentadienyl derivatives of uranium(IV). With the high-sterically crowded 2,6-(But)2C6H3OH ligand only one UNEt2 bond is cleaved, with formation of the stable Cp2U(OAr)(NEt2) complex. The tris-cyclopentadienyl aryl oxides of uranium(IV) formed in the disproportionation reactions of the bis-cyclopentadienyl diaryl oxides have been also obtained by reaction of Cp3UNEt2 with ArOH