221 J. Electroanal. Chem., 313 (1991) 227-241 Elsevier Sequoia S.A., Lausanne JEC 01564 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Electrochemical study of uranium( Iv> and uranium( Iv) organometallic compounds in tetrahydrofuran by means of conventional microelectrodes and ultramicroelectrodes Part I. Application to the Na(Hg) reduction of Cp&JCl (CP = TC5H5) D. Hauchard l , M. Cassir l * and J. Chivot Institut National des Sciences et Techniques Nuc%aires, Centre d’Etudes Nucleaires de &clay, 91 I91 Gif-sur- Yvette Cedex (France) M. Ephritikhine Service de Chimie Molkdaire, DSM, DPhG, Centre d’Etudes NuclPnires de Saclay, 91191 Gif-sur- Yvette Cedex (France) (Received 4 January 1991; in revised form 14 March 1991) Abstract Complementary information on the voltammetric behaviour of CpsUCl in NBu,PFs +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 CpsUCl leads to CpsUCl-, which is stable even at slow scan rates. The diffusion coefficient of CpsUCl has been determined (Dcp,uc, =lO-’ cm2/s). The oxidation of CpsUCl leads to an unusual U(” organometallic compound: CpsUCl+; it is shown that this oxidation process is followed by the disproportionation of Cp,UCl+ (ECE mechanism). The Na(Hg) reduction of CpsUCl was followed electrochemically at a Pt UME (with high or low concentrations of the supporting electrolyte). CpsU(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, CpsUClJ, stabilized by the formation of a stable ion pair with zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJI NBu: , was formed as a major product. l To whom correspondence should be addressed. Present address: Laboratoire de Chimie Nucleaire et Industrielle, Ecole Centrale, Grande Voie des Vignes, 92295 ChBtenay-Malabry Cedex, France. ** Present address: Laboratoire d’Electrochimie, Prof. B. Tremillon, (U.R.A. 216 du C.N.R.S.) Ecole Nationale Superieure de Chimie, 11 Rue Pierre et Marie Curie, F 75231 Paris Cedex 05, France. 0022-0728/91/$03.50 0 1991 - Elsevier Sequoia S.A. All rights reserved