The geometric and electronic structure of an oxidized Cu complex ([CuSal] + ; Sal = N, N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-(1R,2R)-diamine) with a non-innocent salen ligand has been investigated both in the solid state and in solution. Integration of information from UV-vis-NIR spectroscopy, magnetic susceptibility, electrochemistry, resonance Raman spectroscopy, X-ray crystallography, X-ray absorption spectroscopy, and density functional theory calculations provides critical insights into the nature of the localization/delocalization of the oxidation locus. In contrast to the analogous Ni derivative

The one-electron oxidized species of a Ni(II)-phenolate complex has been shown to be in the Ni(II)-phenoxyl radical state at room temperature and the Ni(III)-phenolate state at < -120 degrees C, indicating that the oxidation state is temperature dependent.

The oxidation of water in the process of dioxygen evolution is catalyzed by an oxygen-evolving complex (OEC) in photosynthesis, which is one of the most important and fundamental chemical processes in nature. [1][2][3] The active site in a photosynthetic OEC protein contains a tetramanganese cluster, [4] which adopts a Y-shaped geometry as revealed by recent X-ray structure analysis of photosystem II.[5] Though the mechanism of dioxygen evolution has not been determined, the stage of oxygen evolution would involve either a high valent terminal oxo manganese species [3,4,6] or the coupling of bridging oxo units. [2,3] Manganese complexes have been extensively studied as artificial OEC models in structural and functional investigations to understand the mechanism of oxygen evolution from water in photosynthetic OEC.[3] However, only a few Mn complexes that can catalyze homogeneous water oxidation have been reported. [7,8] We have previously reported dimanganese complexes of dimeric tetraarylporphyrins linked by 1,2-phenylene bridge (Scheme 1).[8] The anodic oxidation of an aqueous solution of acetonitrile (5 % v/v H 2 O in CH 3 CN) with the dimanganese tetraarylporphyrin dimer evolved oxygen in the potential range > 1.20 V versus Ag/Ag + . The catalyst can also oxidize olefins such as cyclooctene to form epoxide with stoichiometric amounts of m-chloroperbenzoic acid (mCPBA).[9] We proposed that the oxidation of a dimanganese(iii) tetraarylporphyrin dimer could give the corresponding high valent Mn=O complex, which is the active species in these oxidation. However, the mechanisms of oxygen evolution and epoxidation, especially the formation of a high-valent Mn=O intermediate have not been fully confirmed. Herein, we report on the oxidation of the dimanganese porphyrin dimer by employing mCPBA as an oxidant, and the characterization of the resulting Mn (Figure 1). When one molar equivalent of 1,1-diphenyl-2-picrylhydrazine (DPPHa one-electron reductant for each Mn ion) was added to 2, a Mn IV 2 species 3 was rapidly formed, which has a Soret band centered at 415 nm. Complex 3 was also prepared when one molar equivalent of mCPBA for each Mn ion was added to 1 in CH 2 Cl 2 /CH 3 CN (1:4, v/v) solution in the presence of five equivalents of Bu 4 NOH, confirmed by UV/Vis spectrum. When the solution of 2 was left stand at room temperature, the Soret band at 423 nm gradually disappeared and a 468 nm band accordingly appeared with isosbestic points indicating (1) and a reaction pathway for O 2 formation.