Sunlight‐Driven Formation and Dissociation of a Dynamic Mixed‐Valence Thallium(III)/Thallium(I) Porphyrin Complex

Abstract

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. Further exposure of the complex to direct sunlight leads to thallium dissociation and to total recovery of the free base. Hence, the porphyrin plays a key role at all stages of the cycle of the complex: It hosts two metal ions, and by absorbing light, it allows the formation and dissociation of Tl(III). These results constitute the basis for the further design of innovative light-driven bimetallic molecular devices.

HgII‐Mediated TlI‐to‐TlIII Oxidation in Dynamic PbII/Tl Porphyrin Complexes

“…It corresponded to a double translocation of the metal ions that exchange concomitantly between the two sides of the porphyrin, while retaining their coordination modes. We have shown previously that, in complex 1 Tl(III) , the metal ion exchanges between the two sides of the ligand by funneling through the N ‐core of the porphyrin (intramolecular motion), which is based on the markedly different exchange regimes on the NMR timescale for degenerate equilibrium and an equilibrium with free base . Therefore, the double translocation in complex 1 Tl(III) ⋅PbOAc likely follows combined intra‐ and intermolecular exchange processes (funneling vs. dissociation/association, respectively) for Tl III and Pb II ions (Scheme a), in a similar way to that of the related Cd II /Pb II and Hg II /Pb II complexes (non‐compartmentalized exchange process) .…”

“…The two other Tl I cations, Tl3 and Tl4, are bound to the carboxylate groups of the straps that adopt a broken W‐shaped conformation, in contrast to the W‐shaped conformation displayed by related complexes with a hanging‐atop coordination mode . The latter conformation orientates a metal ion towards the porphyrin macrocycle, whereas Tl3 and Tl4 are projected away from it.…”

“…More precisely, the metal ions exchange their position relative to the porphyrin plane and retain their respective coordination modes (coupled translocation processes: HAT up →HAT down coupled to OOP down →OOP up ). Type I‐to‐Type II conversion has been readily achieved by different means (Scheme a): addition of acetate ions or spontaneous evolution of the Hg II /Tl I complex into a mixed valence Tl III /Tl I species . The latter process, an Hg II ‐mediated Tl I ‐to‐Tl III oxidation, is well suited in the aforementioned context.…”

Structural analysis of a dimeric trinuclear zinc(II) complex based on a preorganized yet flexible strap porphyrin

“…We have been able to establish that this through-ring translocation is effective not only for zinc and cadmium [13] but also for thallium(III) [18] whereas it is not possible for lead(II) or bismuth(III) (non-compartimentalized vs. compartimentalized translocations) [19].…”

Adaptable Overhanging Carboxylic Acid Porphyrins: Towards Molecular Assemblies through Unusual Coordination Modes

“…Such a structure was obtained by formally grafting one or two straps on the diametrically opposed meso positions, namely 5,15 or/and 10,20 of the macrocycle (Figure , top line). Based on the study of the resulting homo‐ and heterobimetallic complexes, our group has evidenced a new coordination mode,, , new dynamic processes encompassing compartmentalized and non‐compartmentalized translocations taking place during stereoselective metallation reactions, or dynamic constitutional evolution, and recently controlled by (photo)redox processes , , . Most of the properties of these complexes come from the peculiar hanging‐atop coordination mode in which a metal cation is “overhung” to the intramolecular carboxylate group and is stabilized via hydrogen bond(s) between the amide linkage(s) of the strap and its own acetate ligand .…”