Structure and Reactivity of Nonporphyrinic TerminalManganese(IV)-Hydroxide Complexes in the Oxidative Electrophilic Reaction br

Abstract

High-valent transition metal-hydroxide complexes havebeen proposed as essential intermediates in biological and syntheticcatalytic reactions. In this work, we report the single-crystal X-raystructure and spectroscopic characteristics of a mononuclear non-porphyrinic MnIV-(OH) complex, [MnIV(Me3-TPADP)(OH)-(OCH2CH3)]2+(2), using various physicochemical methods. Likewise,[MnIV(Me3-TPADP)(OH)(OCH2CF3)]2+(3), which is thermally stableat room temperature, was also synthesized and characterized spectroscopically. The MnIV-(OH) adducts are capable of performingoxidation reactions with external organic substrates such as C-H bond activation, sulfoxidation, and epoxidation. Kinetic studies,involving the Hammett correlation and kinetic isotope effect, and product analyses indicate that2and3exhibit electrophilicoxidative reactivity toward hydrocarbons. Density functional theory calculations support the assigned electronic structure and showthat direct C-H bond activation of the MnIV-(OH) species is indeed possible.