Formation of a Ruthenium(V)-Imido Complex and the Reactivity in Substrate Oxidation in Water through the Nitrogen Non-Rebound Mechanism.

A Ru-NH complex, , was oxidized through a proton-coupled electron transfer (PCET) mechanism with a Ce complex in water at pH 2.5 to generate a Ru═NH complex, . Complex was characterized with various spectroscopies, and the spin state was determined by the Evans method to be = 1/2. The reactivity of in substrate C-H oxidation was scrutinized in acidic water, using water-soluble organic substrates such as sodium ethylbenzene-sulfonate (EBS), which gave the corresponding 1-phenylethanol derivative as the product. In the substrate oxidation, complex was converted to the corresponding Ru-NH complex, . The formation of 1-phenylethanol derivative from EBS and that of indicate that complex as the oxidant does not perform nitrogen-atom transfer, in sharp contrast to other high-valent metal-imido complexes reported so far. Oxidation of cyclobutanol by afforded only cyclobutanone as the product, indicating that the substrate oxidation by proceeds through a hydride-transfer mechanism. In the kinetic analysis on the C-H oxidation, we observed kinetic isotope effects (KIEs) on the C-H oxidation with use of deuterated substrates and remarkably large solvent KIE (sKIE) in DO. These positive KIEs indicate that the rate-determining step involves not only cleavage of the C-H bond of the substrate but also proton transfer from water molecules to . The unique hydride-transfer mechanism in the substrate oxidation by is probably derived from the fact that the Ru-NH complex () formed from by 1e/1H reduction is unstable and quickly disproportionates into and .