ANODIC-OXIDATION OF THE COMPLEXES NET(4)[CR(X)(CO)(5)] (X=CN,I) - REACTIVITY OF THE ELECTROGENERATED NEUTRAL SPECIES

The cyclic voltammograms in DMF or acetonitrile of[Cr(CN)(CO)(5)](-) ( Ia) and [Cr(I)(CO)(5)](-) (IIa) show two anodic waves. Under an inert atmosphere, only the first one corresponding to a one-electron-transfe r appears reversible for scan rates of 0.1 V s(-1). In DMF, in the pre sence of oxygen, the reversibility totally disappears. Macroscale elec trolysis in a batch cell at a potential corresponding to the plateau o f the first wave involves two moles of electrons per mole of starting material; during electrolysis, decomposition with CO evolution is obse rved for both complexes while in the case of IIa, additional formation of iodine takes place. In the presence of oxygen, CO2 is produced dur ing electrolysis. The chemical transformations in MeCN of the two neut ral species Cr(CN)(CO)(5) (Ib) and Cr(I)(CO)(5) (IIb) were studied by cyclic voltammetry immediately after their generation by one-electron oxidation in a flow cell of the parent complexes Ia and IIa. A compara tive study of solutions in MeCN of Ia, IIa and Cr(CO)(6) which have be en subject to uv irradiation for approximate to 15 min shows that in b oth cases the first step of the chemical transformation consists in a ligand exchange with formation of [Cr(CN)(NCMe)(CO)(4)] or [Cr(NCMe)(C O)(5)], respectively. Ib (Ia) and IIb (IIa) also proved to be efficien t redox catalysts for the electrooxidation of the cyanide ion and of t riphenylphosphine. (C) 1997 Elsevier Science Ltd.