Mimicking the Regulation Step of Fe-Monooxygenases: Allosteric Modulation of FeIV-Oxo Formation by Guest Binding in a Dinuclear ZnII-FeIICalix[6]arene-Based Funnel Complex

A heteroditopic ligand associated with a calix[6]arene scaffold bearing a tris(imidazole) coordinating site at its small rim and an amine/pyridine ligand at its large rim has been prepared, and its regioselective coordination to ZnII at the small rim and FeII in the amine/pyridine ligand has been achieved. The heterodinuclear complex obtained displays an overall cone conformation capped by the tris(imidazole)ZnII moiety and bears a non-heme FeII complex at its base. Each of the metal centers exhibits one labile position, allowing the coordination inside the cavity of a guest alkylamine at ZnII and the generation of reaction intermediates (FeIII (OOH) and FeIV O) at the large rim. A dependence between the chain length of the encapsulated alkylamine and the distribution of FeIII (OOH) intermediates and FeIII (OMe) is observed. In addition, it is shown that the generation of the FeIV O intermediate is enhanced by addition of the alkylamine guest. Hence, this supramolecular system gathers the three levels of reactivity control encountered in oxidoreductases: i) control of the FeII redox properties through its first coordination sphere, allowing us to generate high valent reactive species; ii) control of guest binding through a hydrophobic funnel that drives its alkyl chain next to the reactive iron complex, thus mimicking the binding pocket of natural systems; iii) guest-modulated reactivity of the FeII center towards oxidants.