Metalloenzymes perform highly efficient and selective biotransformation at mild conditions. Synthetic models should ideally present the metal ion with its primary ligands and mimic a selective substrate-binding pocket. In this context, supramolecular platforms allow the combination of a metal binding site with a macrocyclic cavity. In order to function as a molecular receptor, the calix[6]arene core has been rigidified by covalently grafting a coordinating aza cap (tren or tacn) at the small rim, and the corresponding Zn2+ and Cu+/2+ complexes have been previously studied in depth in our group. To further evaluate the role of the cavity, we recently introduced amido or pyridine spacers between the small rim and the coordinating cap. Metal complexes of these “two-story” receptors were synthesized and fully characterized. These systems show a higher flexibility, resulting in the participation of the spacers in metal binding, the modification in the 1st and 2nd coordination sphere, and hence in a change of the reactivity toward exogenous guests compared to the classical “one-story” systems. This new design results, for instance, in the possibility to observe at low temperature an end-on Cu(II)-superoxo intermediate which has never been observed in the corresponding “one-story” complex.

Metal complexes of “two-story” calix[6]arene ligands: Structure and reactivity

255th National Meeting (2018)

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