ELECTROCHEMICAL AND CHEMICAL OXIDATION OF PI-BONDED [BIS(DIPHENYLARSINO)METHANE]CHROMIUM AND PI-MOLYBDENUM DICARBONYL COMPLEXES

Electrochemical oxidation of the complexes M(CO)2DAM [M = Cr, Mo; DAM = bis(diphenylarsino)methane] in dichloromethane, acetone, and acetonitrile shows some unusual reaction pathways. At mercury electrodes the reversible steps [formula-omitted] [formula-omitted] are seen in all solvents. Controlled potential electrolyses at a potential corresponding to the limiting current of the reversible polarographic wave generate the mercury cations. Under voltammetric conditions at a platinum electrode Cr(CO)2DAM undergoes the reversible one-electron oxidation [formula-omitted] in acetoneand dichloromethane under all conditions and in acetonitrile at low temperature. A further irreversible process[formula-omitted] is also observed. Controlled potential electrolysis at a potential corresponding to the voltammetric one-electron oxidation at 20C indicates a two-electron oxidation. However, in acetone or dichloromethane at -78C, an n value of 1.0 is obtained at platinum and the cation [Cr(CO)2DAM]+ is stable on the synthetic time scale at low temperatures. When the temperature is raised, the cation disproportionates to Cr(CO)2DAM and non-carbonyl-containing species. In contrast to Cr(CO)2DAM, Mo(CO)2DAM undergoes irreversible oxidation at platinum under all conditions and only non-carbonyl-containing products are obtained from controlled potential electrolysis. Chemical reactions with Hg(II), Ag(I), and iodine are consistent withelectrochemical data. In acetonitrile, oxidation with NOPF6 gives the cations [M(C0)2(N0)DAM(CH3CN)2]+ and these can be isolated as hexafluorophosphate salts. For M = Mo, [Mo(CO)jNO(CH3CN)3]+ is also formed. The chemical reactions and electrochemical data can be used to provide a systematic account of reaction pathways for oxidation of the M(CO)2DAM complexes. © 1979, American Chemical Society. All rights reserved.