Geometrical Preference of Ruthenium Oxidation States: Metal Redox and Isomerisation of (0,+)

Article abstract of DOI:10.1039/DT9950001543

Reaction of Na with (L = S2CNEt2), which upon oxidation by cerium(IV) furnished trans-(1+), isolated as its PF6(1-) salt.Both complexes are obtained in nearly quantitative yields.The trivalent complex displays one-electron paramagnetism and a rhombic frozen-solution EPR spectrum which has been analysed affording axial and rhombic distortion parameters of ca. 8000 and ca. 1700 cm^-1 respectively.A ligand-field transition within the Kramers doublets is observed at 6450 cm^-1, the predicted value being ca. 7000 cm^-1.Variable-temperature (253-303 K) voltammetric studies have revealed that electrode reactions proceed in a stereoretentive fashion 1/2(cis), 0.23 and E_1/2(trans), -0.09 V vs. saturated calomel electrode (SCE)> but the species cis-(1+) and trans- are unstable and spontaneously isomerise affording the stable trans-trivalent and cis-bivalent complexes respectively, the equilibrium concentration of the unstable isomers being very small.The rates and activation parameters of these isomerisation reactions presumably proceeding by the twist mechanism (ΔS(excit.)) highly negative) have been determined.The factors controlling geometrical preference of oxidation states viz., metal-phosphorus back-bonding and PPh3...PPh3 steric repulsion are considered in relation to the osmium analogues reported previously.

Full text of DOI:10.1039/DT9950001543

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