Publication de l'équipe S2OMaF dans Account of Chemical Research
Electron-rich Coordination Receptors Based on Tetrathiafulvalene Derivatives: Controlling the Host–Guest Binding
|ABSTRACT: The coordination-driven self-assembly methodology has emerged over the last few decades as an extraordinarily versatile synthetic tool for obtaining discrete macrocyclic or cage structures. Rational approaches using large libraries of ligands and metal complexes have allowed researchers to reach more and more sophisticated discrete structures such as interlocked, chiral, or heteroleptic cages, and some of them are designed for guest binding applications. Efforts have been notably produced in controlling host–guest affinity with, in particular, an evident interest in targeting substrate transportation and subsequent delivering. Recent accomplishments in this direction were described from functional cages which can be addressed with light, pH, or through a chemical exchange. The case of a redox-stimulation has been much less explored. In this case, the charge state of the redox-active cavity can be controlled through an applied electrical potential or introduction of an appropriate oxidizing/reducing chemical agent. Beyond possible applications in electrochemical sensing for environmental and medical sciences as well as for redox catalysis, controlling the cavity charge offers the possibility to modulate the host–guest binding affinity through electrostatic interactions, up to the point of disassembly of the host–guest complex, i.e., releasing of the guest molecule from the host cavity. This Account highlights the key studies that we carried out at Angers, related to discrete redox-active coordination-basedarchitectures (i.e., metalla-rings, -cages, and -tweezers). These species are built upon metal-driven self-assembly between electron-rich ligands, based on the tetrathiafulvalene (TTF) moiety (as well as some of its S-rich derivatives), and various metal complexes.Given the highπ-donating character of those ligands, the corresponding host structures exhibit a high electronic density on thecavity panels. This situation is favorable to bind complementary electron-poor guests, as it was illustrated withbis(pyrrolo)tetrathiafulvalene (BPTTF)-based cavities, which exhibit hosting properties for C60or tetrafluorotetracyanoquinodi-methane (TCNQ-F4). In addition to the pristine tetrathiafulvalene, which was successfully incorporated into palladium- orruthenium-based architectures, the case of the so-called extended tetrathiafulvalene (exTTF) appears particularly fascinating. A seriesof related polycationic and neutral M4L2ovoid containers, as well as a M6L3cage, were synthesized, and their respective bindingabilities for neutral and anionic guests were studied. Remarkably, such structures allow to control of the binding of the guest upon aredox-stimulation, through two distinctive processes: (i) cage disassembling or (ii) guest displacement. As an extension of thisapproach, metalla-assembled electron-rich tweezers were designed, which are able to trigger the guest release through an originalprocess based on supramolecular dimerization activated through a redox stimulus. This ensemble of results illustrates the remarkableability of electron-rich, coordination-based self-assembled cavities to bind various types of guests and, importantly, to trigger theirrelease through a redox-stimulus.