GEOMETRIC EFFECTS ON THE REDOX PROPERTIES OF COMPLEXES [RUX2(R2SO)N(R2S)4-N] AND THE IMPLICATIONS FOR OXIDATION CATALYSIS

The electrochemistry of ruthenium(II) complexes of the type [RuX2(R2SO)n(R2S)4-n] (where n = 1-4) have been studied with examples for fourteen of the fifteen possible isomers for this system. Cyclic voltammograms in CH2Cl2 reveal that a plot of E1/2 versus n is linear with a slope of +0.22 V, indicating that each replacement of a sulphoxide ligand with a thioether donor increases the energy of the highest occupied molecular orbital (d-pi) by ca. 4.8 kcal (ca. 20.08 kJ). When n = 2 five different structural isomers are possible, all of which have been synthesized. Their E1/2 values range from + 0.72 to 1.42 V. Ligand-additivity theory provides a consistent rationale for interpretation of the results. Catalytic studies are described which reveal that only one structure, all-trans-[RuX2(R2SO)2(R2S)2], is catalytically active for O2 oxidations of alcohol. A discussion of the relationship between structure and redox catalysis is included.