ELECTROCHEMICAL-BEHAVIOR OF COBALT(I) HYDRIDES

The electrochemical behaviour of hydrides [CoHL4][L = P(OEt)3, PPh(OEt )2, or PPh2(OEt)] in CH2Cl2 and MeCN was examined and the relevant oxi dation mechanisms elucidated by cyclic voltammetry and coulometry. Dif ferent behaviours were observed depending on the nature both of the so lvent and of the phosphite ligands. In CH2Cl2 the stepwise oxidation o f Co(I) to Co(III) was observed, involving a first reversible one-elec tron oxidation step to [CoHL4]+, followed, at more positive potentials , by a second one-electron step, chemically irreversible, for all the phosphite ligands employed. In MeCN, for L = P(OEt), or PPh(OEt)2, the first reversible oxidation to cobalt(II) hydrides was followed by a s econd step complicated by associated chemical reactions involving the solvent to give cobalt(III) cations, [CoH(MeCN)L4]2+. For L = PPh2(OEt ) the electrochemical behaviour was complicated by chemical reactions both of the starting cobalt(I) compound and of its oxidation products with the MeCN solvent. Preparative electrolysis allowed the synthesis of a new cobalt(II) derivative characterized as [CoH{P(OEt)3}4] BPh4 b y spectroscopic techniques.