Notes. Geometric effects on the redox properties of complexes [RuX2(R2SO)n(R2S)4-n] and the implications for oxidation catalysis

Abstract

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 E_½versus 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_π) 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 E_½ values range from + 0.72 to 1.42 V. Ligand-additivity theory provides a consistent rational 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.