Dioxygen Activation and O–O Bond Formation Reactions by Manganese Corroles

Abstract

Activation of dioxygen (O2) in enzymatic and biomimetic reactions has been intensively investigated over the past several decades. More recently, O–O bond formation, which is the reverse of the O2-activation reaction, has been the focus of current research. Herein, we report the O2-activation and O–O bond formation reactions by manganese corrole complexes. In the O2-activation reaction, Mn(V)-oxo and Mn(IV)-peroxo intermediates were formed when Mn(III) corroles were exposed to O2 in the presence of base (e.g., OH−) and hydrogen atom (H atom) donor (e.g., THF or cyclic olefins); the O2-activation reaction did not occur in the absence of base and H atom donor. Moreover, formation of the Mn(V)-oxo and Mn(IV)-peroxo species was dependent on the amounts of base present in the reaction solution. The role of the base was proposed to lower the oxidation potential of the Mn(III) corroles, thereby facilitating the binding of O2 and forming a Mn(IV)-superoxo species. The putative Mn(IV)-superoxo species was then converted to the corresponding Mn(IV)-hydroperoxo species by abstracting a H atom from H atom donor, followed by the O–O bond cleavage of the putative Mn(IV)-hydroperoxo species to form a Mn(V)-oxo species. We have also shown that addition of hydroxide ion to the Mn(V)-oxo species afforded the Mn(IV)-peroxo species via O–O bond formation and the resulting Mn(IV)-peroxo species reverted to the Mn(V)-oxo species upon addition of proton, indicating that the O–O bond formation and cleavage reactions between the Mn(V)-oxo and Mn(IV)-peroxo complexes are reversible. The present study reports the first example of using the same manganese complex in both O2-activation and O–O bond formation reactions.

Significantly improved electrocatalytic oxygen reduction by an asymmetrical Pacman dinuclear cobalt(ii) porphyrin–porphyrin dyad

“…Efficient and selective catalysts for the oxygen reduction reaction (ORR) are required in many kinds of energy conversion and storage devices, such as fuel cells and metal-air batteries, because the kinetically slow ORR is the key cathode reaction in these systems. [1][2][3][4][5][6][7] Research on molecular catalysts is signicant to provide fundamental knowledge on reaction mechanisms and structure-function relationships, [8][9][10][11] which is essential for the development of new catalysts with improved performance.…”

Boosting Molecular Complexity with O2: Iron‐Catalysed Oxygenation of 1‐Arylisochromans through Dehydrogenation, Csp3−O Bond Cleavage and Hydrogenolysis

“…In a polar protic medium, Fe IV –oxo complexes behave as strong oxidants, capable of oxidising inert C−H bonds –. As no oxidation of the solvent was observed and on the basis of the X‐ray structure of the [Fe(thf)(OTf) 2 L] complex, it might be plausible that the ligand somehow is involved in the reduction of such Fe IV –oxo species, which could eventually lead to O−O bond formation . The use of non‐innocent ligands that actively participate in the catalytic cycle is nowadays well acknowledged and several examples have also been shown in the area of iron catalysis and in catalytic oxidations .…”

“…[7a-c] As no oxidation of the solvent was observed and on the basis of the X-ray structure of the [Fe(thf)(OTf) 2 L] complex, [21a] it might be plausible that the ligand somehow is involved in the reduction of such Fe IV -oxo species, which could eventually lead to OÀOb ond formation. [40] The use of non-innocent ligandst hat actively participate in the catalytic cyclei sn owadays well acknowledged [41] ands everale xamples have also been shown in the area of iron catalysis [42] and in catalytic oxidations. [43] Unfortunately,t he oxygen acceptor of this reaction has not been identified and thus, the mechanism postulated (Scheme 7) is merely speculative.…”

An In‐Depth Look at the Reactivity of Non‐Redox‐Metal Alkylperoxides

“…Metal alkylperoxides are of fundamental and practical importance owing to their remarkable structural diversity and versatility in applications . For example, they have been widely used as very efficient oxidants in a variety of oxygen‐transfer organic processes and postulated as key intermediates in many biological systems . Despite extensive research in the field, there is still relatively limited knowledge of the factors tuning their reactivity and stability, which seems to be the largest barrier in the further development of reagents and catalytic systems based on metal alkylperoxides.…”

“…[1,2] Fore xample,t hey have been widely used as very efficient oxidants in av ariety of oxygentransfer organic processes [3][4][5][6] and postulated as key intermediates in many biological systems. [7][8][9] Despite extensive research in the field, there is still relatively limited knowledge of the factors tuning their reactivity and stability,which seems to be the largest barrier in the further development of reagents and catalytic systems based on metal alkylperoxides. Over the last two decades,systematic studies on the chemistry of metal alkylperoxides have mostly been focused on model compounds involving transition metals ( T M), [10][11][12][13][14][15][16][17] whereas that based on non-redox-active metals ( NR M) has been paid much less attention.…”