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The participation of both ligand and the metal center in the redox events has been recognized as one of the ways to attain the formal high valent complexes for the late 3d metals, such as Ni and Cu. Such an approach has been employed successfully to stabilize a Ni(III) bisphenoxyl diradical species in which there exist an equilibrium between the ligand and the Ni localized resultant spin. The present work, however, broadens the scope of the previously reported three oxidized equivalent species by conveying the approaches that tend to affect the reported equilibrium in CH3CN at 233 K. Various spectroscopic characterization revealed that employing exogenous N‐donor ligands like 1‐methyl imidazole and pyridine favors the formation of the Ni centered localized spin though axial binding. In contrast, due to its steric hinderance, quinoline favors an exclusive ligand localized radical species. DFT studies shed light on the novel intermediates′ complex electronic structure. Further, the three oxidized equivalent species with the Ni centered spin was examined for its hydrogen atom abstraction ability stressing their key role in alike reactions. [ABSTRACT FROM AUTHOR]

Lewis acid‐bound high valent Mn‐oxo species are of great importance due to their relevance to photosystem II. Here, we report the synthesis of a unique [(BnTPEN)Mn(III)−O−Ce(IV)(NO3)4]+ adduct (2) by the reaction of (BnTPEN)Mn(II) (1) with 4 eq. ceric ammonium nitrate. 2 has been characterized using UV/Vis, NMR, resonance Raman spectroscopy, as well as by mass spectrometry. Treatment of 2 with Sc(III)(OTf)3 results in the formation of (BnTPEN)Mn(IV)−O−Sc(III) (3), while HClO4 addition to 2 forms (BnTPEN)Mn(IV)−OH (4), reverting to 2 upon Ce(III)(NO3)3 addition. 2 can also be prepared by the oxidation of 1 eq. Ce(III)(NO3)3 with [(BnTPEN)Mn(IV)=O]2+ (5). In addition, the EPR spectroscopy revealed the elegant temperature‐dependent equilibria between 2 and Mn(IV) species. The binding of redox‐active Ce(IV) boosts electron transfer efficiency of 2 towards ferrocenes. Remarkably, the newly characterized Mn(III)−O−Ce(IV) species can carry out O‐atom and H‐atom transfer reactions. [ABSTRACT FROM AUTHOR]

Inspired by copper-based metalloenzymes, we aim to incorporate amino acids into our ligands to facilitate active copper intermediates that serve as functional and structural models for these enzymes. Herein, we report the synthesis of a Cu(II) complex with a C2 symmetric proline-based pseudopeptide LH2 (N,N′-(ethane-1,2-diyl)bis(pyrrolidine-2-carboxamide)), which is capable of supporting an [(L)Cu(III)]+ (3) intermediate in MeOH : CH3CN (1 : 20) at −30 °C. From comparative studies with the pyridine analog Cu(II) complex, it was demonstrated that the incorporation of amino acid in the ligand framework decreased the Cu(III)/Cu(II) redox potential significantly to react readily with mCPBA and CAN. The newly generated [(L)Cu(III)]+ can promote hydrogen atom abstraction reactions with phenolic substrates. [ABSTRACT FROM AUTHOR]

Cytochrome P450s and Galactose Oxidases exploit redox active ligands to form reactive high valent intermediates for oxidation reactions. This strategy works well for the late 3d metals where accessing high valent states is rather challenging. Herein, we report the oxidation of NiII(salen) (salen=N,N′‐bis(3,5‐di‐tert‐butyl‐salicylidene)‐1,2‐cyclohexane‐(1R,2R)‐diamine) with mCPBA (meta‐chloroperoxybenzoic acid) to form a fleeting NiIII bisphenoxyl diradical species, in CH3CN and CH2Cl2 at −40 °C. Electrochemical and spectroscopic analyses using UV/Vis, EPR, and resonance Raman spectroscopies revealed oxidation events both on the ligand and the metal centre to yield a NiIII bisphenoxyl diradical species. DFT calculations found the electronic structure of the ligand and the d‐configuration of the metal center to be consistent with a NiIII bisphenoxyl diradical species. This three electron oxidized species can perform hydrogen atom abstraction and oxygen atom transfer reactions. [ABSTRACT FROM AUTHOR]

The participation of both ligand and the metal center in the redox events has been recognized as one of the ways to attain the formal high valent complexes for the late 3d metals, such as Ni and Cu. Such an approach has been employed successfully to stabilize a Ni(III) bisphenoxyl diradical species in which there exist an equilibrium between the ligand and the Ni localized resultant spin. The present work, however, broadens the scope of the previously reported three oxidized equivalent species by conveying the approaches that tend to affect the reported equilibrium in CH 3 CN at 233 K. Various spectroscopic characterization revealed that employing exogenous N-donor ligands like 1-methyl imidazole and pyridine favors the formation of the Ni centered localized spin though axial binding. In contrast, due to its steric hinderance, quinoline favors an exclusive ligand localized radical species. DFT studies shed light on the novel intermediates' complex electronic structure. Further, the three oxidized equivalent species with the Ni centered spin was examined for its hydrogen atom abstraction ability stressing their key role in alike reactions., (© 2023 Wiley-VCH GmbH.)

Lewis acid-bound high valent Mn-oxo species are of great importance due to their relevance to photosystem II. Here, we report the synthesis of a unique [(BnTPEN)Mn(III)-O-Ce(IV)(NO 3 ) 4 ] + adduct (2) by the reaction of (BnTPEN)Mn(II) (1) with 4 eq. ceric ammonium nitrate. 2 has been characterized using UV/Vis, NMR, resonance Raman spectroscopy, as well as by mass spectrometry. Treatment of 2 with Sc(III)(OTf) 3 results in the formation of (BnTPEN)Mn(IV)-O-Sc(III) (3), while HClO 4 addition to 2 forms (BnTPEN)Mn(IV)-OH (4), reverting to 2 upon Ce(III)(NO 3 ) 3 addition. 2 can also be prepared by the oxidation of 1 eq. Ce(III)(NO 3 ) 3 with [(BnTPEN)Mn(IV)=O] 2+ (5). In addition, the EPR spectroscopy revealed the elegant temperature-dependent equilibria between 2 and Mn(IV) species. The binding of redox-active Ce(IV) boosts electron transfer efficiency of 2 towards ferrocenes. Remarkably, the newly characterized Mn(III)-O-Ce(IV) species can carry out O-atom and H-atom transfer reactions., (© 2023 Wiley-VCH GmbH.)