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We report on the synthesis and characterization of three iron(III) phosphasalen complexes, [FeIII(Psalen)(X)] differing in the nature of the counter‐anion/exogenous ligand (X−=Cl−, NO3−, OTf−), as well as the neutral iron(II) analogue, [FeII(Psalen)]. Phosphasalen (Psalen) differs from salen by the presence of iminophosphorane (P=N) functions in place of the imines. All the complexes were characterized by single‐crystal X‐ray diffraction, UV/Vis, EPR, and cyclic voltammetry. The [FeII(Psalen)] complex was shown to remain tetracoordinated even in coordinating solvent but surprisingly exhibits a magnetic moment in line with a FeII high‐spin ground state. For the FeIII complexes, the higher lability of triflate anion compared to nitrate was demonstrated. As they exhibit lower reduction potentials compared to their salen analogues, these complexes were tested for the coupling of 2‐naphthol using O2 from air as oxidant. In order to shed light on this reaction, the interaction between 2‐naphthol and the FeIII(Psalen) complexes was studied by cyclic voltammetry as well as UV/Vis spectroscopy. [ABSTRACT FROM AUTHOR]

A strategy is presented to improve the excited state reactivity of homoleptic copper–bis(diimine) complexes CuL2+ by increasing the steric bulk around CuI whereas preserving their stability. Substituting the phenanthroline at the 2‐position by a phenyl group allows the implementation of stabilizing intramolecular π stacking within the copper complex, whereas tethering a branched alkyl chain at the 9‐position provides enough steric bulk to rise the excited state energy E00. Two novel complexes are studied and compared to symmetrical models. The impact of breaking the symmetry of phenanthroline ligands on the photophysical properties of the complexes is analyzed and rationalized thanks to a combined theoretical and experimental study. The importance of fine‐tuning the steric bulk of the N–N chelate in order to stabilize the coordination sphere is demonstrated. Importantly, the excited state reactivity of the newly developed complexes is improved as demonstrated in the frame of a reductive quenching step, evidencing the relevance of our strategy. [ABSTRACT FROM AUTHOR]

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 FeIVO) 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 FeIVO 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. [ABSTRACT FROM AUTHOR]

Two new polytopic ligands based on a calix[6]arene scaffold were synthesized. The truncated coneshaped calixarene was functionalized at its small rim by a trisimidazole site, aimed at generating a tetrahedral ZnII complex, where a fourth labile site inside the cavity is accessible through the funnel provided by its large rim. Tridentate aza ligands (either two or three) were then grafted at this large rim (the entrance of the cavity). ZnII coordination studies, monitored by ¹H NMR spectroscopy, showed unprecedented behavior in this family of heteropolytopic ligands. Indeed, it gives access to complexes of various nuclearities in acetonitrile, where zinc binding is under the supramolecular control of the guest. It is first shown that, in the absence of a good guest donor (a primary amine), ZnII binding is favored at the large rim where two tridentate nitrogenous groups can form an octahedral complex. The addition of a long guest such as heptylamine induces the quantitative translocation of the ZnII ion from the large rim octahedral (Oh) site to the small rim tetrahedral (Td) site provided by the trisimidazole core and the guest ligand. With 2 equiv of ZnII, welldefined dinuclear complexes were obtained and isolated, with one ZnII ion bound at each rim. Interestingly, it is shown that the binding mode at the large rim is under the supramolecular control of the guest bound at the small rim (with short guests, the Oh, environment is obtained at the large rim, whereas long guests disrupt this core through an induced-fit process); the partially included and dangling alkyl chain opens the large rim (entrance of the cavity) and pushes apart the tridentate moieties. As a result, a guest-induced switch of ZnII binding mode occurs and frees one of the tridentate groups from coordination, allowing further extension of the complex nuclearity. [ABSTRACT FROM AUTHOR]