Electrochemical studies of tricyclopentadienyl uranium IV chloride complexes: (RCp)3UCl (RCp=RC5H4 with R=H; Me: CH3; tBu: (CH3)3C); TMS: (CH3)3Si)

Abstract

Electrochemical behaviour of tricyclopentadienyl uranium IV complexes (RCp)3UCl (RCp=RC5H4 with R=H; Me: CH3; tBu: (CH3)3C); TMS: (CH3)3Si) was investigated in THF with Bu4NPF6 electrolyte at different size platinum electrodes. Cyclic voltammetry was performed at a conventional size electrode, under unsteady-state diffusion conditions and linear scan voltammetry at a microelectrode, under steady-state diffusion conditions. The different species of uranium IV are reduced according to a reversible one-electron process. The half-wave potentials of the four U(IV)/U(III) systems have been determined and compared. The diffusion coefficients of the U(IV) complexes have been calculated also. For the oxidation reaction, the use of a microelectrode allows the kinetic complications, which are observed at the conventional size electrode, to be eliminated. Thus, the reversible one-electron oxidation process is characterized. It leads to the formation of a U(V) complex which is an unusual oxidation state for organometallic uranium complexes. Cyclic voltammetry shows the instability of (RCp)3UCl+ (U(V) complexes). For the (MeCp)3UCl, the oxidation mechanism agrees with the model described by Savéant for a reversible one-electron process coupled to a disproportionation reaction. This chemical reaction regenerates the U(IV) complex at the electrode. This result has been generalized to the other three uranium (IV) complexes.