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Abstract The reduction of dioxygen to produce selectively H₂O₂or H₂O is crucial in various fields. While platinum‐based materials excel in 4H⁺/4e⁻oxygen reduction reaction (ORR) catalysis, cost and resource limitations drive the search for cost‐effective and abundant transition metal catalysts. It is thus of great importance to understand how the selectivity and efficiency of 3d‐metal ORR catalysts can be tuned. In this context, we report on a Co complex supported by a bisthiolate N2S2‐donor ligand acting as a homogeneous ORR catalyst in acetonitrile solutions both in the presence of a one‐electron reducing agent (selectivity for H₂O of 93 % and TOFi=3 000 h⁻¹) and under electrochemically‐assisted conditions (0.81 V <η<1.10 V, selectivity for H₂O between 85 % and 95 %). Interestingly, such a predominant 4H⁺/4e⁻pathway for Co‐based ORR catalysts is rare, highlighting the key role of the thiolate donor ligand. Besides, the selectivity of this Co catalyst under chemical ORR conditions is inverse with respect to the Mn and Fe catalysts supported by the same ligand, which evidences the impact of the nature of the metal ion on the ORR selectivity. 

Abstract High‐valent Fe(IV)=O intermediates of metalloenzymes have inspired numerous efforts to generate synthetic analogs to mimic and understand their substrate oxidation reactivities. However, high‐valent M(IV) complexes of late transition metals are rare. We have recently reported a novel Co(IV)−dinitrate complex (1‐NO₃) that activates sp³C−H bonds up to 87 kcal/mol. In this work, we have shown that the nitrate ligands in1‐NO₃can be replaced by azide, a more basic coordinating base, resulting in the formation of a more potent Co(IV)−diazide species (1‐N₃) that reacts with substrates (hydrocarbons and phenols) at faster rate constants and activates stronger C−H bonds than the parent complex1‐NO₃. We have characterized1‐N₃employing a combination of spectroscopic and computational approaches. Our results clearly show that the coordination of azide leads to the modulation of the Co(IV) electronic structure and the Co(IV/III) redox potential. Together with the higher basicity of azide, these thermodynamic parameters contribute to the higher driving forces of1‐N₃than1‐NO₃for C−H bond activation. Our discoveries are thus insightful for designing more reactive bio‐inspired high‐valent late transition metal complexes for activating inert aliphatic hydrocarbons. 

The reaction of a mononuclear Mn^III–hydroxo complex with hydrogen peroxide under different reaction conditions yields bis(μ-oxo)dimanganese(iii,iv), Mn^III–hydroperoxo, and Mn^III–peroxo intermediates. 

Synthetic manganese catalysts that activate hydrogen peroxide perform a variety of hydrocarbon oxidation reactions. The most commonly proposed mechanism for these catalysts involves the generation of a manganese(iii)-hydroperoxo intermediate that decays via heterolytic O–O bond cleavage to generate a Mn( v)-oxo species that initiates substrate oxidation. Due to the paucity of well-defined Mn(III)-hydroperoxo complexes, Mn(III)-alkylperoxo complexes are often employed to understand the factors that affect the O–O cleavage reaction. Herein, we examine the decay pathways of the Mn(III)-alkylperoxo complexes [Mn(III)(OOtBu)(6Me dpaq)]+ and [Mn(III)(OOtBu)(N4S)]+, which have distinct coordination environments (N5− and N4S− , respectively). Through the use of density functional theory (DFT) calculations and comparisons with published experimental data, we are able to rationalize the differences in the decay pathways of these complexes. For the [Mn(III)(OOtBu)(N4S)]+ system, O–O homolysis proceeds via a two-state mechanism that involves a crossing from the quintet reactant to a triplet state. A high energy singlet state discourages O–O heterolysis for this complex. In contrast, while quintet–triplet crossing is unfavorable for [Mn(III)(OOtBu)(6Medpaq)]+, a relatively low-energy single state accounts for the observation of both O–O homolysis and heterolysis products for this complex. The origins of these differences in decay pathways are linked to variations in the electronic structures of the Mn(III)-alkylperoxo complexes.