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Heterobimetallic Porphyrin Complexes Displaying Triple Dynamics: Coupled Metal Motions Controlled by Constitutional Evolution

par Le Gac, Stéphane ;Fusaro, Luca ;Roisnel, Thierry;Boitrel, Bernard
Référence Journal of the American Chemical Society, 136, 18, page (6698-6715), http://pubs.acs.org/doi/pdf/10.1021/ja501926f
Publication Publié, 2014

Article révisé par les pairs

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Résumé :

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, 1Hg·PbOAc and 1Cd·PbOAc, display three levels of dynamics. The first is strap-level (interactional dynamics), where the PbOAc moiety swings between the left and right side of the strap owing to a second sphere of coordination with lateral amide functions. The second is ligand-level (motional dynamics), where 1Hg·PbOAc and 1 Cd·PbOAc exist as two degenerate states in equilibrium controlled by a chemical effector (AcO-). The process corresponds to a double translocation of the metal ions according to an intramolecular migration of Hg(II) or Cd(II) through the N-core, oscillating between the two equivalent overhanging carbonyl groups, coupled to an intermolecular pathway for PbOAc exchanging between the two equivalent overhanging carboxylate groups (N-coreup⇆ N-coredown coupled to strap down⇆ strapup, i.e., coupled motion #1 in the abstract graphic). The third is library-level (constitutional dynamics), where a dynamic constitutional evolution of the system was achieved by the successive addition of two chemical effectors (DMAP and then AcO-). It allowed shifting equilibrium forward and backward between 1Hg·PbOAc and the corresponding homobimetallic complexes 1Hg2·DMAP and 1Pb·PbOAc. The latter displays a different ligand-level dynamics, in the form of an intraligand coupled migration of the Pb(II) ions (N-coreup⇆ strapup coupled to strap down⇆ N-coredown, i.e., coupled motion #2 in the abstract graphic). In addition, the neutral bridged complexes 1HgPb and 1CdPb, with the metal ions on opposite sides both bound to the N-core and to a carboxylate of a strap, were structurally characterized. These results establish an unprecedented approach in supramolecular coordination chemistry, by considering the reversible interaction of a metal ion with the porphyrin N-core as a new source of self-organization processes. This work should provide new inspirations for the design of innovative adaptative materials and devices. © 2014 American Chemical Society.