The active site of particulate methane monooxygenase (pMMO) and its mechanism of action are not known. Recently, the Cu C site emerged as a potential active site, but to date it lacks any study on biomimetic resemblance of the coordination environment provided by the enzyme. Here, the synthesis of a cage ligand providing such an environment is reported. Copper is incorporated, and coordination occurs by the two imidazole and one carboxylate group offered by the ligand. Depending on the oxidation state, it can adopt different coordination modes, as evidenced by the solidstate structures and computational investigation. The copper(I) state readily reacts with dioxygen and thereby undergoes CH activation. Moreover, the catalytic aerobic oxidation of hydroquinones as ubiquinol mimics is shown. Clean one-electron oxidation occurs under mild conditions and EPR analysis of the copper(II) state in the presence of water reveals striking similarities to the data obtained from pMMO.
Hypervalent bromine(III) reagents possess a higher electrophilicity and a stronger oxidizing power compared to their iodine(III) counterparts. Despite the superior reactivity, bromine(III) reagents have a reputation of hard-to-control and difficult-to-synthesize compounds. This is partly due to their low stability, and partly because their synthesis typically relies on the use of the toxic and highly reactive BrF 3 as a precursor. Recently, we proposed chelation-stabilized hypervalent bromine(III) compounds as a possible solution to both problems. First, they can be conveniently prepared by electro-oxidation of the corresponding bromoarenes. Second, the chelation endows bromine(III) species with increased stability while retaining sufficient reactivity, comparable to that of iodine(III) counterparts. Finally, their intrinsic reactivity can be unlocked in the presence of acids. Herein, an in-depth mechanistic study of both the electrochemical generation and the reactivity of the bromine(III) compounds is disclosed, with implications for known applications and future developments in the field.
A masked amine building block is used to synthesize an organic cage that is exo-functionalized with one terpy group. Two exo-functionalized cages can be combined via iron-terpy coordination resulting in a cage dumbbell.
Das aktive Zentrum der partikulären Methan-Monooxygenase (pMMO) und ihr Wirkungsmechanismus sind nicht bekannt. In den letzten Jahren trat die Cu C -Seite als potentielles aktives Zentrum auf, jedoch fehlt es bisher an biomimetischen Studien zu dieser vom Enzym bereitgestellten Koordinationssphäre. Hier wird über die Synthese eines Käfigliganden berichtet, welcher solch eine Koordinationssphäre bereitstellt. Die Koordination an Kupfer erfolgt durch die beiden Imidazol-und eine Carboxylatgruppe des Liganden. Abhängig von der Oxidationsstufe kann der Ligand unterschiedliche Koordinationsmodi annehmen, was durch Festkörperstrukturen und computerchemische Untersuchungen belegt wurde. Der Kupfer(I)-Komplex reagiert leicht mit Sauerstoff und geht dadurch eine CH-Aktivierung ein. Darüber hinaus wird die katalytische aerobe Oxidation von Hydrochinonen als Ubichinol-Nachahmungen gezeigt. Eine saubere Ein-Elektronen-Oxidation findet unter milden Bedingungen statt. Die EPR-Analyse des Kupfer(II)-Komplexes zeigt in Gegenwart von Wasser bemerkenswerte Ähnlichkeiten zu Daten, welche von pMMO erhalten wurden.
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