Oxygen activation and transfer catalyzed by ruthenium porphyrins

The author has recently described the preparation and characterization of a trans-dioxo ruthenium (VI) porphyrin complex which has been shown to be an efficient catalyst for the aerobic epoxidation of olefins. It was also shown that this complex catalyzes the hydroxylation of alkanes under appropriate conditions. It is now apparent that the dioxoruthenium (VI) complex is the species responsible for oxygen transfer and that an intermediate oxoruthenium (IV) complex is then reoxidized in air. It was shown that the oxidation of ruthenium (IV) to ruthenium (VI) proceeds via a disproportionation to produce both ruthenium (VI) and ruthenium (II) porphyrin complexes. The ruthenium (II) complex reacts rapidly with oxygen to regenerate the oxoruthenium (IV) intermediate which then continues the catalytic cycle. Experimental results which illuminate this oxygen activation and transfer process are described.