A MECHANISTIC STUDY OF THE REDUCTIVE COUPLING OF ACETONE WITH URANIUM-COMPOUNDS

Reaction of acetone with UCl4 and Li(Hg) in the molar ratio 2 : 1 : 2 afforded [Li-2(thf)][UCl4(OCMe2CMe2O)] 4 via the intermediates [{UCl3( thf)(2)}(2)(mu-OCMe2CMe2O)] 1 and [Li-2(thf)][{UCl4(thf)}(2)(mu-OCMe2C Me2O)] 3 (the coupling process). Unequivocal synthesis and characteriz ation of these metallopinacols are presented; [{UCl3(hmpa)(2)}(2)-(mu- 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 t o 1 gave 3 and the latter was transformed in the presence of Li(Hg) in to 4 and UCl3. Tetramethylethylene was liberated after reduction of 4 with Li(Hg) in refluxing thf (the deoxygenation process).