ELECTROCHEMICAL STUDY OF URANIUM(IV) AND URANIUM(IV) ORGANOMETALLIC COMPOUNDS IN TETRAHYDROFURAN BY MEANS OF CONVENTIONAL MICROELECTRODES AND ULTRAMICROELECTRODES .1. APPLICATION TO THE NA(HG) REDUCTION OF CP3UCL (CP=ETA-C5H5)

Complementary information on the voltammetric behaviour of Cp3UCl in NBu4PF6 + THF medium is given at a conventional Pt microelectrode and especially at a Pt ultramicroelectrode (UME) (allowing the concentration of the supporting electrolyte to be minimized) with the purpose of studying the Na(Hg) reduction of this compound. The reduction of Cp3UCl leads to Cp3UCl-, which is stable even at slow scan rates. The diffusion coefficient of Cp3UCl has been determined (D(Cp3UCl) = 10(-5) cm2/s). The oxidation of Cp3UCl leads to an unusual U(v) organometallic compound: Cp3UCl+; it is shown that this oxidation process is followed by the disproportionation of Cp3UCl+ (ECE mechanism). The Na(Hg) reduction of Cp3UCl was followed electrochemically at a Pt UME (with high or low concentrations of the supporting electrolyte). Cp3U(THF) compound was obtained quantitatively when very dilute solutions of the supporting electrolyte were used. The oxidation of this species was characterized by voltammetry. When high concentrations of the supporting electrolyte were added, Cp3UCl-, stabilized by the formation of a stable ion pair with NBu4+, was formed as a major product.