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. 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 1-Hg·PbOAc and 1-Cd·PbOAc exist as two degenerate states in equil. controlled by a chem. effector (AcO-). The process corresponds to a double translocation of the metal ions according to an intramol. migration of Hg(II) or Cd(II) through the N-core, oscillating between the two equiv. overhanging carbonyl groups, coupled to an intermol. pathway for PbOAc exchanging between the two equiv. overhanging carboxylate groups (N-coreup ↹ N-coredown coupled to strapdown ↹ strapup, i.e., coupled motion #1 in the abstr. graphic). The third is library-level (constitutional dynamics), where a dynamic constitutional evolution of the system was achieved by the successive addn. of two chem. effectors (DMAP and then AcO-). It allowed shifting equil. forward and backward between 1-Hg·PbOAc and the corresponding homobimetallic complexes 1Hg2·DMAP and 1-Pb·PbOAc. The latter displays a different ligand-level dynamics, as an intraligand coupled migration of the Pb(II) ions (N-coreup ↹ strapup coupled to strapdown ↹ N-coredown, i.e., coupled motion #2 in the abstr. graphic). In addn., 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 supramol. coordination chem., 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. [on SciFinder(R)]