Parallel Chirality Inductions in Möbius Zn(II) Hexaphyrin Transformation Networks.

Networked chemical transformations are key features of biological systems, in which complex multicomponent interactions enable the emergence of sophisticated functions. Being interested in chirality induction phenomena with dynamic Möbius π-systems, we have designed a pair of Möbius [28]hexaphyrin ligands in order to investigate mixtures rather than isolated molecules. Thus, a hexaphyrin bearing a chiral amino arm was first optimized and found to bind a ZnOAc moiety, triggering an impressive quasi-quantitative chirality induction over the Möbius π-system.

Möbius Zn -Hexaphyrins Bearing a Chiral Coordinating Arm: A Chiroptical Switch Featuring P/M Twist Inversion Controlled by Achiral Effectors.

By their conformational flexibility, Möbius aromatic hexaphyrins provide a dynamic chirality attractive to develop stimuli responsive systems such as chiroptical switches. A regular [28]hexaphyrin has been equipped with a chiral coordinating arm to achieve transfer of chirality from a fix stereogenic element to the dynamic Möbius one. The arm allows straightforward formation of labile monometallic Zn complexes with an exogenous ligand, either a carboxylato or an amino with opposite inwards/outwards orientations relative to the Möbius ring.

Functional Myoglobin Model Composed of a Strapped Porphyrin/Cyclodextrin Supramolecular Complex with an Overhanging COOH That Increases O/CO Binding Selectivity in Aqueous Solution.

A water-soluble strapped iron(III)tetraarylporphyrin () bearing two propylpyridinium groups at the side chains and a carboxylic acid group at the overhanging position of the strap was synthesized to mimic the function of myoglobin with the distal polar functionality in aqueous solution. forms a stable 1:1 inclusion complex with a per--methylated β-cyclodextrin dimer having a pyridine linker (), providing a hydrophobic environment and a proximal fifth ligand to stabilize the O-complex. The ferrous complex () binds both O and CO in aqueous solution.

Interconversion between Möbius chiroptical states sustained by hexaphyrin dynamic coordination.

Harnessing the chiroptical properties of molecular Möbius rings is motivated by fundamental aspects while challenged by synthetic difficulties. Focusing on Möbius aromatic Zn(ii) hexaphyrin complexes, interconversion between two chiral states was achieved through binding and release of an amino ligand (forward/backward stimuli), leading to different chiroptical switching phenomena (amplification, on-off, inversion). The amine either supplies the chirality or behaves as an achiral effector regulating the Zn(ii)-binding of a second (chiral) carboxylato ligand.

Match-mismatch effects in two-fold transfer of chirality within a Möbius metallo-receptor.

Two-fold transfer of chirality has been investigated in a Möbius Zn(ii) hexaphyrin metallo-receptor able to bind simultaneously two different chiral molecules. Match/mismatch effects influence the dynamic stereoselective twisting of the π-system, and allow tuning of the induced chiroptical activity. Such allosteric control is attractive for building chirality sensing systems.

Orchestrating Communications in a Three-Type Chirality Totem: Remote Control of the Chiroptical Response of a Möbius Aromatic System.

Among the various types of chirality (central, axial, helical, planar, etc.), that inherent to Möbius topology remains almost unexplored, partly due to the difficulty to access Möbius compounds. Over the past decade, [28]hexaphyrins have been revealed to be among the best candidates to build on Möbius aromaticity.

Acid-base controlled multiple conformation and aromaticity switches in tren-capped hexaphyrins.

Upon protonation, a tren-capped hexaphyrin undergoes successive rectangular-to-Möbius and Möbius-to-triangular conformational isomerizations, with concomitant antiaromaticity-to-aromaticity reversal. This affords different cage environments leading ultimately to a "crypto-bowl-shape" hexaphyrin hosting a trifluoroacetate counterion.

Hg -Mediated Tl -to-Tl Oxidation in Dynamic Pb /Tl Porphyrin Complexes.

Compared with their purely organic counterparts, molecular switches that are based on metal ion translocations have been underexplored, and more particularly, it remains challenging to control the translocation of several particles in multisite receptors. Recently, bimetallic complexes that undergo double translocation processes have been developed with bis-strapped porphyrin ligands. To implement a redox control for these systems, we have investigated the formation of heterobimetallic lead/thallium complexes, with thallium in the +I and +III oxidation states.

Cyclodextrin-Sandwiched Hexaphyrin Hybrids: Side-to-Side Cavity Coupling Switched by a Temperature- and Redox-Responsive Central Device.

Access to allosteric enzyme mimics that ideally associate communicating compartments for catalysis and regulation is still challenging. Whereas a sandwich "cavity-catalyst-cavity" approach, developed mainly with cyclodextrins and porphyrins, appears promising, its counterpart with hexaphyrins featuring rich conformation, aromaticity, and coordination behavior has not been prospected at all. We thus developed sandwich hybrids made of two cyclodextrins triply linked on each side of a hexaphyrin.

Tren-Capped Hexaphyrin Zinc Complexes: Interplaying Molecular Recognition, Möbius Aromaticity, and Chirality.

Over the past decade, the hexaphyrin skeleton has emerged as a multifaceted frame exhibiting strong interplay between topology, aromaticity, and metal coordination, opening new research areas beyond porphyrins. However, molecular recognition with hexaphyrins has been underexplored, mainly because of the lack of general synthetic strategies leading to sophisticated molecular hosts. Here we have developed a straightforward approach for capping the heteroannulene frame with tripodal units (e.

Designing 'Totem' C2 -Symmetrical Iron Porphyrin Catalysts for Stereoselective Cyclopropanations.

The catalytic activity of the iron(III) C2 chiral porphyrin Fe(2)(OMe) in alkene cyclopropanation is herein reported. The catalyst promoted the reaction of differently substituted styrenes with diazo derivatives with trans-diastereoselectivities and enantioselectivities up to 99:1 and 87 %, respectively. In addition, high TON and TOF values (up to 10 000 and 120 000 h(-1) , respectively) were observed indicating good activity and stability of the catalyst in optimized experimental conditions.

Protonated hexaphyrin-cyclodextrin hybrids: molecular recognition tuned by a kinetic-to-thermodynamic topological adaptation.

Protonation study of [26/28]hexaphyrin-capped cyclodextrins revealed a temperature controlled conformational transition of the cap. The hexaphyrin undergoes a rectangular-to-triangular shape-shifting which strongly modifies the shape of the confined environment featured by the hybrids, and ultimately affects the encapsulation of the counterions. It provides an attractive access to innovative allosteric host-guest systems.

Spontaneous Tl(I)-to-Tl(III) oxidation in dynamic heterobimetallic Hg(II)/Tl(I) porphyrin complexes.

Strapped heterobimetallic Hg(II)/Tl(I) porphyrin complexes, with both metal ions bridged by the N-core in a dynamic way, undergo spontaneous Tl(I)-to-Tl(III) oxidation leading to a mono-Tl(III) complex and a mixed valence Tl(I)/Tl(III) bimetallic complex. It provides a new opportunity to tune metal ion translocations in bimetallic porphyrin systems.

Sunlight-driven formation and dissociation of a dynamic mixed-valence thallium(III)/thallium(I) porphyrin complex.

Inspired by a Newton's cradle device and interested in the development of redox-controllable bimetallic molecular switches, a mixed-valence thallium(III)/thallium(I) bis-strap porphyrin complex, with Tl(III) bound out of the plane of the N core and Tl(I) hung to a strap on the opposite side, was formed by the addition of TlOAc to the free base and exposure to indirect sunlight. In this process, oxygen photosensitization by the porphyrin allows the oxidation of Tl(I) to Tl(III). The bimetallic complex is dynamic as the metals exchange their positions symmetrically to the porphyrin plane with Tl(III) funneling through the macrocycle.

A pentanuclear lead(II) complex based on a strapped porphyrin with three different coordination modes.

We have previously described Pb(II) and Bi(III) bimetallic complexes with overhanging carboxylic acid strapped porphyrins in which one metal ion is bound to the N-core ("out-of-plane", OOP), whereas the second one is bound to the strap ("hanging-atop", HAT). In such complexes, the hemidirected coordination sphere of a HAT Pb(II) cation provides sufficient space for an additional binding of a neutral ligand (e.g.

Heterobimetallic porphyrin complexes displaying triple dynamics: coupled metal motions controlled by constitutional evolution.

A bis-strap porphyrin ligand (1), with an overhanging carboxylic acid group on each side of the macrocycle, has been investigated toward the formation of dynamic libraries of bimetallic complexes with Hg(II), Cd(II), and Pb(II). Highly heteroselective metalation processes occurred in the presence of Pb(II), with Hg(II) or Cd(II) bound out-of-plane to the N-core and "PbOAc" bound to a carboxylate group of a strap on the opposite side. The resulting complexes, 1(Hg)·PbOAc and 1(Cd)·PbOAc, display three levels of dynamics.

Highly diastereoselective cyclopropanation of α-methylstyrene catalysed by a C2-symmetrical chiral iron porphyrin complex.

A new chiral iron porphyrin-based catalyst performed α-methylstyrene stereoselective cyclopropanation with excellent yields (up to 99%), enantio- and diastereoselectivities (ee(trans) up to 87%, trans/cis ratios up to 99 : 1) and outstanding TON and TOF values (up to 20,000 and 120,000 h(-1) respectively).

Formation and dynamic behavior of mono- and bimetallic cadmium(II) porphyrin complexes: allosteric control of coupled intraligand metal migrations.

The complexation behavior of a bis-strapped porphyrin ligand (1) towards Cd(II) has been investigated by (1)H and (113)Cd NMR spectroscopy with the help of X-ray diffraction structures. The presence of an overhanging carboxylic acid group on each side of the macrocycle is responsible for the instantaneous insertion of the metal ion(s) at room temperature, and allows the formation of bimetallic species with unusual coordination modes at the origin of unique dynamic behaviors. In the absence of base, a C2-symmetric bimetallic complex (1Cd2 ) is readily formed, in which the porphyrin acts as a bridging ligand.

Acid-base-controlled stereoselective metalation of overhanging carboxylic acid porphyrins: consequences for the formation of heterobimetallic complexes.

Overhanging carboxylic acid porphyrins have revealed promising ditopic ligands offering a new entry in the field of supramolecular coordination chemistry of porphyrinoids. Notably, the adjunction of a so-called hanging-atop (HAT) Pb(II) cation to regular Pb(II) porphyrin complexes allowed a stereoselective incorporation of the N-core bound cation, and an allosterically controlled Newton's cradle-like motion of the two Pb(II) ions also emerged from such bimetallic complexes. In this contribution, we have extended this work to other ligands and metal ions, aiming at understanding the parameters that control the HAT Pb(II) coordination.

Metal migration processes in homo- and heterobimetallic bismuth(III)-lead(II) porphyrin complexes: emergence of allosteric Newton's cradle-like devices.

Metal ion migration in a bis-strapped porphyrin ligand with overhanging carboxylate groups has been investigated in solution. Two types of homobimetallic complexes are generated with Pb(II) and Bi(III) cations, which stand on both sides of the macrocycle: (i) a dissymmetric complex with one cation bound to the porphyrin N core and the other cation hung over the N core through bonding with a carboxylate of a strap; (ii) a C(2)-symmetric complex with both cations coordinated to the N core and to the carboxylate groups of the straps. Variable-temperature NMR studies and 2D rotational Overhauser effect spectroscopy NMR experiments have shown that in the former dissymmetric complexes, the two cations undergo a coupled intramolecular migration resulting in exchange of their coordination modes.

Translocation-coupled transmetalation at the origin of a dinuclear lead porphyrin complex: implication of a hanging-atop coordination mode.

Translocation of a lead cation from the N-core of a porphyrin to a hanging carboxylate group is coupled to a transmetalation process with a second lead cation, leading to a dinuclear species. A novel hanging-atop coordination mode is responsible for the dynamic and stereocontrolled binding of lead to the porphyrin core.

What does the future hold for photo-oxidizing Ru(II) complexes with polyazaaromatic ligands in medicinal chemistry?

Since the discovery of cisplatin, the search for diagnostic or therapeutic agents based on other metals, has expanded intensively owing to the numerous possibilities offered by coordination chemistry. This mini-review focuses on recent advances in the search for Ru(II) polyazaaromatic complexes of potential interest as molecular tools applied to cellular diagnostics or as specific cellular photo-reagents for future biomedical applications. The interaction of Ru(II) polyazaaromatic complexes with living cells is reported, as well as the photo-reaction mechanisms of photo-oxidizing Ru(II) complexes with nucleic acids.

Unprecedented incorporation of α-emitter radioisotope 213Bi into porphyrin chelates with reference to a daughter isotope mediated assistance mechanism.

For the first time, α-emitter radioisotope (213)Bi has been incorporated into porphyrin chelates, with rates matching with the short period of the radionuclide. An in situ transmetalation mechanism involving the daughter isotope (209)Pb is expected to boost the (213)Bi radiolabeling process.

Allosterically driven self-assemblies of interlocked calix[6]arene receptors.

The construction of self-assembled receptors based on flexible concave subunits is a challenging task and constitutes an interesting approach to mimic binding processes occurring in biological systems. The receptors studied herein are based on flexible calix[6]arene skeletons bearing three (or more) acid-base functionalities at their narrow rim. When complementary, they self-assemble in a tail-to-tail manner to give a diabolo-like complex, provided that each calixarene subunit hosts a guest.