Preparation and Physicochemical Properties of New Linear μ-Oxo Bridged Ruthenium(IV) and Osmium(IV) Porphyrin Dimers

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Abstract
μ-Oxo-bis[(hydroxo)(octaethylporphyrinato)ruthenium(IV)] was prepared by the oxidation of (carbonyl)(octaethylporphyrinato)ruthenium(II) with t-butyl hydroperoxide in good yield. Facile replacement of the hydroxyl group with various anions afforded μ-oxo dimer complexes formulated as [{RuIV(oep)X}2O] (X=Cl, Br, and OCOCH3). The same type of osmium complexes, [{OsIV(oep)(OCH3)}O], {[OsIV(oep)(OCH3)}O{OsIV(oep)(OH)}], and [{OsIV(oep)(OH)}2O] were obtained from the air oxidation product of (carbonyl)(methanol)(octaethylporphyrinato)osmium(II) in the presence of 2,3-dimethylindole. These complexes are diamagnetic. The 1H NMR data are in conformity with the linear oxo-bridged dimer structure which was proved by X-ray crystallography with [{RuIV(oep)(OH)}2O]. The redox potentials were measured by the cyclic voltammetry. These complexes showed three distinct quasi-reversible redox couples assignable to metalII/ metalIII, metalIII/metalIV, and porphyrin ligand oxidation, respectively. Significantly lower redox values and anomalous spectral features indicate a strong pπ-dπ interaction between the bridging oxygen atom and the two quadrivalent metal ions.