Mimicking the Regulation Step of Fe‐Monooxygenases: Allosteric Modulation of Fe^IV‐Oxo Formation by Guest Binding in a Dinuclear Zn^II–Fe^II Calix[6]arene‐Based Funnel Complex

Abstract

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 Zn at the small rim and Fe in the amine/pyridine ligand has been achieved. The heterodinuclear complex obtained displays an overall cone conformation capped by the tris(imidazole)Zn moiety and bears a non-heme Fe complex at its base. Each of the metal centers exhibits one labile position, allowing the coordination inside the cavity of a guest alkylamine at Zn and the generation of reaction intermediates (Fe (OOH) and Fe O) at the large rim. A dependence between the chain length of the encapsulated alkylamine and the distribution of Fe (OOH) intermediates and Fe (OMe) is observed. In addition, it is shown that the generation of the Fe 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 Fe 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 Fe center towards oxidants.

A Deep Cavitand Receptor Functionalized with Fe(II) and Mn(II) Aminopyridine Complexes for Bioinspired Oxidation Catalysis

“…Remarkably, the new compound [ 2· Fe­(O)] 2+ remains relatively stable at 0 °C ( t 1/2 ∼ 20 min), but it reacts rapidly (within seconds) with excess thioanisole, producing 0.9 equiv of the sulfoxide and regenerating 2 ·Fe­(OTf) 2 (as shown by UV–vis spectroscopy, see SI). Overall, this data indicates that the embedment of the complex in the cavitand stands the formation of high valent iron-oxo species without apparent degradation of the supramolecular vessel, while not compromising its reactivity in oxygen atom transfer reactions against external substrates.…”

“…The selectivities obtained in the oxidation reactions so far tested with substrates that form kinetically stable complexes with the receptor do not significantly differ from those obtained with a model compound, suggesting that the oxidation steps are occurring to a significant extent outside the cavity. To the best of our knowledge, this system represents the first example of a sizable container functionalized with a coordination complex capable of (a) maintaining catalytic activity in selective C–H/CC oxidation reactions, and (b) supporting high valent metal-oxo species typically associated with such transformations . Future developments in this area will address the limitations of the system presented, including the development of conformationally restricted analogues, which prevented free rotation of the ligand scaffold.…”

Hydroxylation of Aromatics by H2O2 Catalyzed by Mononuclear Non‐heme Iron Complexes: Role of Triazole Hemilability in Substrate‐Induced Bifurcation of the H2O2 Activation Mechanism

“…Formation of the Fe V (O)(OH) or Fe V (O)(OAc) motif requires two cis labile sites which are found in complexes derivedfrom tetradentate ligands, [21,25,26] while the {Fe IV (O);O H C}p air is often proposed with pentadentate ones. [13,16,28,29] For this reason,w eh ave developed an ew pentadentate ligandw here one pyridyl group was replacedb yatriazole, knownt ob el ess donating andm ore labile than pyridine, [14,30] with the aim of generating as ystemthat could possibly gather the stability and robustnesso fp entadentate systemsw hile beinga blet oa ccess at etradentate coordination spherei ns itu through triazole labilization.…”

“…For this reason, we have developed a new pentadentate ligand where one pyridyl group was replaced by a triazole, known to be less donating and more labile than pyridine, with the aim of generating a system that could possibly gather the stability and robustness of pentadentate systems while being able to access a tetradentate coordination sphere in situ through triazole labilization.…”