Preparation and characterization of stable ruthenium(IV)-oxo complexes that contain tertiary phosphine ligands

The chemistry of high-valent ruthenium-oxo complexes has received much attention recently due to the potential applications of these complexes as oxidation catalysts and as oxygen atom transfer agents. In contrast, tertiary phosphine ligands have been primarily utilized in the syntheses of low-valent organometallic complexes, including those that have been used as both homogeneous and heterogeneous catalysts. Through the combination of these two dissimilar types of chemistry, the authors wish to report the first successful syntheses and characterization of ruthenium(IV)-oxo complexes that contain tertiary phosphine ligands in a position cis to the oxo ligand. In the syntheses of these phosphine-ruthenium(IV)-oxo complexes, oxidation of the tertiary phosphine ligand by the ruthenium(IV)-oxo moiety is avoided by initial generation of the ruthenium(II)-aquo-phosphine species, followed by cerium(IV) oxidation to the phosphine-ruthenium(IV)-oxo species. In this manner, no free tertiary phosphine ligand is exposed to a ruthenium(IV)-oxo complex, which would result in rapid phosphine oxidation. In addition, the coordinated phosphine ligands do not undergo any intramolecular or intermolecular oxidation upon formation of the ruthenium(IV)-oxo species. Notably, the reactivity of these complexes as oxidants toward organic substrates is substantially affected by simple variation of the substituents on the cis-phosphine ligand. 12 references, 1 figure.