Remarkably selective recognition of iodobenzene derivatives by a macrocyclic bis-Pt(II) metallohost.

We designed and synthesized self-assembled bis-Pt-II dimer 1.4BF(4) with quino[8,7-b][1,10] phenanthroline as an extended pi-face contact area, which acts as the first artificial receptor with high affinity toward iodinated aromatic compounds significantly based on noncovalent iodine...aromatic-plane interactions in a "side-on" fashion. Despite their structural similarity to a previously reported metallohost 2(4+) that bears 2,2':6',2 "-terpyridine units, a dramatic change in selectivity toward substituted benzene derivatives was observed for 1(4+). H-1 NMR spectroscopic titration revealed a high affinity of 1(4+) towards haloarenes, with exceptionally large association constants for 2-iodophenol (K-a = 16 000 M-1) and 1,2-diiodobenzene (K-a = 21 000 M-1), which are 93- and 140-fold higher, respectively, than the values obtained for 2(4+). In addition, 1(4+) showed a remarkably high affinity and selectivity toward 2,6-diiodophenol (K-a = 35 000 M-1), which is an important substructure of the thyroid hormone T-4. X-ray crystallography and theoretical calculations strongly suggest that " side-on" iodine...aromatic-plane interactions and pi-pi stacking contribute to the strong 1,2-diiodobenzene and 2,6-diiodophenol binding. The results obtained here give unique and valuable insight into the nature of halogen atom interactions in their "side-on" region with an electropositive aromatic plane, which may provide useful guidance for designing artificial receptors for iodinated biomolecules.