Pyrrolic macrocycles : exotic coordination and adaptative systems

Molecular design of multifunctional chelates

Keywords: macrocyclization, bioinspiration, conformational analysis, nitrogen ligand, controlled architecture, molecular platform

The design of new porphyrin based chelates, with precise positioning of ligands around the core of the macrocycle, to achieve high level of control on the metal binding geometry and thus reactivity, is a crucial step to achieve innovative properties. For that purpose, keeping in mind a biomimetic approach, several straightforward methodologies allowing the differentiating of the two sides of the pyrrolic macrocycle have been developed. They take, for instance, advantage of the various atropisomers of the tetra-aminophenylporphyrin that can be separated and interconverted if needed.

multifunctional chelates

Coordination and activation of small molecules

Keywords: dioxygen carrier, reduction catalysis, supramolecular, second coordination sphere

Coordinating molecular oxygen to carry it in a physiological medium, or reducing it to water, or even reducing carbon dioxide remain more than ever processes that we still do not control. We have previously developed a series of porphyrins with overhung carboxylic acid ligands which have shown unexpected properties for the stabilization of molecular oxygen, once metalated by iron. We have widened the initial series to either other ligands of the single strap type to, this time, reduce molecular oxygen (New J. Chem. 2018) or even to other suspended groups in order to change the second coordination sphere of the complex and thus modify the properties of the complex, so as to catalyze the reduction of carbon dioxide (Chem. Commun. 2018,  Angew. Chem. Int. Ed. 2019, collaboration Prof. A. Aukauloo, Université Paris-Saclay). These single-strap analogs, once “embedded” into host molecules should preserve the properties of the original models while forming a soluble adduct in physiological medium and thus allowing us to stabilize the oxygenated adduct (New J. Chem. 2018, Inorg. Chem. 2017, collaboration Prof. T. Hayashi, Osaka University, Dr. H. Kitagishi, Doshisha University, Kyoto).

Coordination and activation of small molecules

Unusual dynamic coordination

Keywords: translocation, compartmentalization, dynamic coordination, redox switch

The discovery, characterization and understanding of new coordination modes in porphyrin ligands functionalized with straps delivering at least one overhung carboxylic acid, as well as the resulting dynamic coordination chemistry, are the basis of this axis. Thus, the exploitation of “out-of-plane” (linked to the nitrogenous core of the macrocycle but out of the plane) and “hanging-atop” (suspended from the carboxylic acid of the strap) coordination modes initially highlighted in our ligands has given birth to a new family of bi-stable molecules opening the way to new molecular switches. A targeted extension concerns obtaining a system under redox control, according to which the gain or loss of an electron by a metal can activate or inhibit the system. Already, an original photo-oxidation process from Tl(I) to Tl(III), leading to the formation of a dynamic bimetallic complex of mixed valence thallium, has been successfully investigated (Angew. Chem. Int. Ed. 2015). Another example is illustrated in the spontaneous oxidation of Tl(I) to Tl(III) in Hg(II)/Tl(I) and Pb(II)/Tl(I) heterobimetallic complexes (Chem. Commun. 2016, Chem. Eur. J. 2019, Eur. J. Inorg. Chem. 2019).

From Bismuth-Lead complexes to double translocation based molecular switch

Expanded porphyrin based adaptative systems

Keywords: (anti)aromaticity, Möbius ring, molecular recognition, conformation, chirality, switch

Over the past decade, expanded porphyrins have attracted considerable interest. In addition to unusual coordination properties, they exhibit a strong interaction between their electronic and conformational properties, making them attractive for the design of complex systems sensitive to stimuli. For example, the switching of (anti)aromaticity can result from a change in conformation (Möbius torsion), a modification of the π system or by promoting an excited state. Recently, our group focused on the use of hexaphyrins in the field of molecular recognition, an under-explored area. In particular, the combination of recognition processes with (anti)aromaticity switching and/or conformational changes could lead to new types of adaptive molecular receptors with innovative functions. For this, we have designed and studied so-called “capped” hexaphyrins, that are decorated with either a hydrophobic cavity (collaboration Dr. M. Ménand, Sorbonne University) or an additional coordination site. The first Möbius ring metallo-receptors, aromatic, with chiroptical properties that can be modulated via host-guest chemistry, have thus emerged (Angew. Chem. Int. Ed. 2016, Chem. Commun. 2016, J. Am. Chem. Soc. 2017, Chem. Eur. J. 2018, Org. Biomol. Chem. 2019, J. Am. Chem. Soc. 2019).

Möbius hexaphyrin-Chiral metalloreceptor