C-H Bond Activation by a Seven-Coordinate Bipyridine-Bipyrazole Ruthenium(IV) Oxo Complex.

Ruthenium-oxo species with high coordination numbers have long been proposed as active intermediates in catalytic oxidation chemistry. By employing a tetradentate bipyridine-bipyrazole ligand, we herein reported the synthesis of a seven-coordinate (CN7) ruthenium(IV) oxo complex, [Ru IV (tpz)(pic) 2 (O)] 2+ ( Ru IV O ) (tpz = 6,6'-di(1 H -pyrazol-1-yl)-2,2'-bipyridine, pic = 4-picoline), which exhibits high activity toward the oxidation of alkylaromatic hydrocarbons. The large kinetic isotope effects (KIE) for the oxidation of DHA/DHA- d 4 (KIE = 10.3 ± 0.1) and xanthene/xanthene- d 2 (KIE = 17.2 ± 0.1), as well as the linear relationship between log (rate constants) and bond dissociation energies of alkylaromatics, confirmed a mechanism of hydrogen atom abstraction.