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Adding HClO4 to [(BnTPEN)MnIII–OO]+ in MeOH generates a short-lived MnIII–OOH species, which converts to a putative MnV＝O species. The potent MnV＝O species in MeCN oxidizes the pendant phenyl ring of the ligand in an intramolecular fashion. The addition of benzene causes the formation of (BnTPEN)MnIII-phenolate. These findings suggest that high valent Mn species have the potential to catalyze challenging aromatic hydroxylation 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]

The reaction of [(L)MnII]2+ (L = neutral polypyridine ligand framework) in the presence of mCPBA (mCPBA = m‐Chloroperoxybenzoic acid) generates a putative MnV=O species at RT. The proposed MnV=O species is capable of performing the aromatic hydroxylation of Cl‐benzoic acid derived from mCPBA to give [(L)MnIII(m‐Cl‐salicylate)]+, which in the presence of excess mCPBA generates a metastable [(L)MnV(O)(m‐Cl‐salicylate)]+, characterized by UV/Vis absorption, EPR, resonance Raman spectroscopy, and ESI‐MS studies. The current study highlights the fact that [(L)MnIII(m‐Cl‐salicylate)]+ formation may not be a dead end for catalysis. Further, a plausible mechanism has been proposed for the formation of [(L)MnV(O)‐m‐Cl‐salicylate)]+ from [(L)MnIII(m‐Cl‐salicylate)]+. The characterized transient [(L)MnV(O)‐m‐Cl‐salicylate)]+ reported in the current work exhibits high reactivity for oxygen atom transfer reactions, supported by the electrophilic character depicted from Hammett studies using a series of para‐substituted thioanisoles. The unprecedented study starting from a non‐heme neutral polypyridine ligand framework paves a path for mimicking the natural active site of photosystem II under ambient conditions. Finally, evaluating the intracellular effect of Mn(II) complexes revealed an enhanced intracellular ROS and mitochondrial dysfunction to prevent the proliferation of hepatocellular carcinoma and breast cancer cells. [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]

Haloperoxidase enzymes utilize metal hypohalite species to halogenate aliphatic and aromatic C–H bonds to C–X (X = Cl, Br, I) in nature. In this work, we report the synthesis and spectroscopic characterization of a unique RuIII-OCl species as a structural mimic of haloperoxidase enzymes. The reaction of [(BnTPEN)RuII(NCCH3)]2+ (BnTPEN = N1-benzyl-N1,N2,N2-tris(pyridine-2-ylmethyl)ethane-1,2-diamine) with hypochlorite in the presence of an acid in CH3CN : H2O mixtures generated a novel [(BnTPEN)RuIII-OCl]2+ species that persists for 4.5 h at room temperature. This new species was characterized by UV–vis absorption, EPR, and resonance Raman spectroscopic techniques, and ESI-MS. The RuIII-OCl species is capable of performing oxygen atom transfer and hydrogen atom abstraction to various organic substrates. [ABSTRACT FROM AUTHOR]

Adding HClO 4 to [(BnTPEN)Mn III -OO] + in MeOH generates a short-lived Mn III -OOH species, which converts to a putative Mn V O species. The potent Mn V O species in MeCN oxidizes the pendant phenyl ring of the ligand in an intramolecular fashion. The addition of benzene causes the formation of (BnTPEN)Mn III -phenolate. These findings suggest that high valent Mn species have the potential to catalyze challenging aromatic hydroxylation reactions.

A simple and atom economic protocol for the construction of C-X/C-C bonds via catalytic aminium radical-cation salt (Magic Blue)-initiated S N 2-type nucleophilic ring-opening transformations of racemic and nonracemic aziridines with different hetero and carbon nucleophiles to afford various amino ethers, thioethers, and amines in up to 99% yield, and with perfect enantiospecificity for some substrates but reduced ee with others (for nonracemic aziridines), is developed. This aminium radical-cation salt-initiated, S N 2-type nucleophilic ring-opening strategy, along with various cyclization protocols, is employed to synthesize various biologically significant compounds.

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.)

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 Ni II (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 Ni III bisphenoxyl diradical species, in CH 3 CN and CH 2 Cl 2 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 Ni III 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 Ni III bisphenoxyl diradical species. This three electron oxidized species can perform hydrogen atom abstraction and oxygen atom transfer reactions., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Haloperoxidase enzymes utilize metal hypohalite species to halogenate aliphatic and aromatic C-H bonds to C-X (X = Cl, Br, I) in nature. In this work, we report the synthesis and spectroscopic characterization of a unique Ru III -OCl species as a structural mimic of haloperoxidase enzymes. The reaction of [(BnTPEN)Ru II (NCCH 3 )] 2+ (BnTPEN = N 1 -benzyl- N 1 , N 2 , N 2 -tris(pyridine-2-ylmethyl)ethane-1,2-diamine) with hypochlorite in the presence of an acid in CH 3 CN : H 2 O mixtures generated a novel [(BnTPEN)Ru III -OCl] 2+ species that persists for 4.5 h at room temperature. This new species was characterized by UV-vis absorption, EPR, and resonance Raman spectroscopic techniques, and ESI-MS. The Ru III -OCl species is capable of performing oxygen atom transfer and hydrogen atom abstraction to various organic substrates.