Hydrotris(mesitylpyrazol-1-yl)borate uranium(IV) compounds: synthesis, structure, and ligand isomerization

Abstract

Reaction of UCl₄ with one equivalent of the thallium salt of [HB(3-Mspz)₃]⁻ (=Tp^Ms, Ms = mesityl) afforded UCl₃Tp^Ms*1, due to isomerization of the Tp^Ms ligand to give [HB(3-Mspz)₂(5-Mspz)]⁻ (=Tp^Ms*). Crystals of UCl₃Tp^Ms2 were obtained fortuitously in one particular instance, but a real synthetic route to this compound was not achieved. 1 adds THF to afford UCl₃Tp^Ms*·THF 3. Derivatization of 1 allowed the synthesis of UCl₂[N(SiMe₃)₂]Tp^Ms*4 and UCl₂[C₆H₄CH₂NMe₂-o]Tp^Ms*5. The X-ray analysis of 1, 2 and 4 revealed that the uranium centre is in an octahedral configuration, while in 5 the uranium is seven-coordinated by an additional U–N donor bond due to the chelating nature of the hydrocarbyl ligand. Nitriles and isocyanides do not insert into the U–C bond of 5, but reaction with acetone leads to formation of the uranium aldolate UCl₂[η²-OC(Me₂)₂CH₂C(O)Me]Tp^Ms*6.

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