Novel Complexes trans(Cl)-[Os(bpy)(CO)(CH3CN)Cl2]n (n = 0, +1; bpy = 2,2′-Bipyridine): Photo- and Electrochemical Syntheses and Comparative Study of Their Bonding and Redox Properties

Abstract

Photoirradiation of the complex trans(Cl)-[Os(bpy)(CO)2Cl2] in acetonitrile with λ ⩾ 320 nm light gives rise to substitution of a CO ligand, with the formation of trans(Cl)-[Os(bpy)(CO)(CH3CN)Cl2]. The bonding properties and redox reactions of the novel photoproduct were thoroughly investigated by several methods such as nanosecond time-resolved UV/Vis absorption and resonance Raman spectroscopy, cyclic voltammetry, and IR and UV/Vis spectroelectrochemistry. Its one-electron electrochemical oxidation in acetonitrile produces the stable cation trans(Cl)-[Os(bpy)(CO)(CH3CN)Cl2]+. This complex is also formed as the major product during one-electron oxidation of the dicarbonyl precursor trans(Cl)-[Os(bpy)(CO)2Cl2] in acetonitrile at room temperature. By contrast, the initial dicarbonyl oxidation product trans(Cl)-[Os(bpy)(CO)2Cl2]+ remains stable in dry noncoordinating dichloromethane and in butyronitrile at low temperatures. The CO-loss reactivity of trans(Cl)-[Os(bpy)(CO)2Cl2], induced by the partial oxidation of the formally osmium(II) centre, is dramatically lower compared to the corresponding ruthenium(II) complex due to the stronger Os−CO bonds. Replacement of one CO or Cl ligand in trans(Cl)-[Os(bpy)(CO)2Cl2] by a stronger σ-donor CH3CN or isopropoxycarbonyl [−C(O)OiPr] ligands strengthens the Os−CO bond(s) and results in photostable derivatives. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)