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Naphthalene oxidation by metal-oxygen intermediates is one of difficult reactions in environmental and biological chemistry. Herein, we report that a MnIV-bis(hydroxo) complex, which was fully characterized by various physicochemical methods, such as UV-vis, ESI-MS, EPR, X-ray and XAS, shows the naphthalene oxidation in the presence of acid to afford 1,4-naphthoquinone. Redox titration of the MnIV-bis(hydroxo) complex exhibits one electron reduction potential of 1.09 V, which is the most positive potential for the previously reported nonheme MnIV-bis(hydroxo) species as well as MnIV-oxo analogues. Kinetic studies including kinetic isotope effect suggest that the naphthalene oxidation by the MnIV-bis(hydroxo) complex in the acid-promoted reaction occurs via a rate-determining electron transfer process.

A mononuclear side-on peroxocobalt(III) complex with a tetradentate macrocyclic ligand, [Co(TBDAP)(O)] (1), shows a novel and facile mode of dioxygenase-like reactivity with nitriles (R-C≡N; R = Me, Et, and Ph) to produce the corresponding mononuclear hydroximatocobalt(III) complexes, [Co(TBDAP)(R-C(═NO)O)], in which the nitrile moiety is oxidized by two oxygen atoms of the peroxo group. The overall reaction proceeds in one-pot under ambient conditions (ca. 1 h, 40 °C). O-Labeling experiments confirm that both oxygen atoms are derived from the peroxo ligand. The structures of all products, hydroximatocobalt(III) complexes, were confirmed by X-ray crystallography and various spectroscopic techniques. Kinetic studies including the Hammett analysis and isotope labeling experiments suggest that the mechanistic mode of 1 for activation of nitriles occurs via a concerted mechanism. This novel reaction would be significantly valuable for expanding the chemistry for nitrile activation and utilization.

Copper(II)-hydroperoxo species are often detected as key intermediates in metalloenzymes and biomimetic compounds containing copper. However, the only reactivity has previously been observed for the copper(II)-hydroperoxo complexes is electrophilic, occurring through O-O bond cleavage. Here we report that a mononuclear end-on copper(II)-hydroperoxo complex, which has been successfully characterized by various physicochemical methods including UV-vis, rRaman, CSI-MS and EPR, is a reactive oxidant that utilizes a nucleophilic mechanism. In addition, DFT calculations fully support the electronic structure of this complex as a copper(II)-hydroperoxo complex with trigonal bipyramidal coordination geometry. A positive Hammett ρ value (2.0(3)) is observed in the reaction of copper(II)-hydroperoxo complex with para-substituted acyl chlorides, which clearly indicates nucleophilic character for the copper(II)-hydroperoxo complex. The copper(II)-hydroperoxo complex is an especially reactive oxidant in aldehyde deformylation with 2-PPA and CCA relative to the other metal-bound reactive oxygen species reported so far. The observation of nucleophilic reactivity for a copper(II)-hydroperoxo species expands the known chemistry of metal-reactive oxygen species.

Copper(ii)-alkylperoxo adducts, [Cu(CHDAP)(OOR)] (CHDAP = N,N'-dicyclohexyl-2,11-diaza[3,3](2,6)pyridinophane; R = C(CH)Ph and Bu), were prepared and characterized using various physicochemical methods. These are the first synthetic Cu(ii)-alkylperoxo complexes that can perform aldehyde deformylation (i.e., nucleophilic reactivity) under the stoichiometric reaction conditions, which was confirmed by kinetic studies.

Transition metal−iodosylarene complexes have been proposed to be key intermediates in the catalytic cycles of metal catalysts with iodosylarene. We report the first X-ray crystal structure and spectroscopic characterization of a mononuclear nonheme manganese-(III)−iodosylarene complex with a tetradentate macrocyclic ligand, [Mn III (TBDAP)(OIPh)(OH)] 2+ (2). The manganese(III)−iodosylarene complex is capable of conducting various oxidation reactions with organic substrates, such as C−H bond activation, sulfoxidation and epoxidation. Kinetic studies including isotope labeling experiments and Hammett correlation demonstrate the electrophilic character on the Mn−iodosylarene adduct. This novel intermediate would be prominently valuable for expanding the chemistry of transition metal catalysts.