A mechanistic study of the reductive coupling of acetone with uranium compounds

Abstract

Reaction of acetone with UCl₄ and Li(Hg) in the molar ratio 2∶1∶2 afforded [Li₂(thf)][UCl₄(OCMe₂CMe₂O)] 4 via the intermediates [{UCl₃(thf)₂}₂(µ-OCMe₂CMe₂O)] 1 and [Li₂(thf)][{UCl₄(thf)}₂(µ-OCMe₂CMe₂O)] 3 (the coupling process). Unequivocal synthesis and characterization of these metallopinacols are presented; [{UCl₃(hmpa)₂}₂(µ-OCMe₂CMe₂O)] (hmpa = hexamethylphosphoramide) was characterized by its crystal structure. Complex 1 was formed by dimerization of the ketyl radical [Cl₃UOCMe₂]˙, obtained itself by electron transfer from UCl₃ to the ketone; the radical was trapped with Ph₃SnH. Addition of LiCl to 1 gave 3 and the latter was transformed in the presence of Li(Hg) into 4 and UCl₃. Tetramethylethylene was liberated after reduction of 4 with Li(Hg) in refluxing thf (the deoxygenation process).