Dipole-Promoted and Size-Dependent Cooperativity between Pyridyl-Containing Triazolophanes and Halides Leads to Persistent Sandwich Complexes with Iodide

Authors:
  • MPMaren Pink
    Maren Pink
  • JKJonathan A. Karty
    Jonathan A. Karty
  • AFAmar H. Flood
    Amar H. Flood
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Abstract
Triazolophanes that incorporate pyridyl subunits in place of phenylenes show a heightened propensity to form 2:1 sandwich complexes with halides. Persistent iodide-based sandwiches are observed. Binding constants confirm that the inward-facing electron pairs on the pyridyls destabilize the 1:1 complexes with halides. The 1H NMR spectra verify that the sandwich complexes have two π-stacked triazolophanes rotated to allow registration between opposite dipoles on the pyridyls (directed inward) and triazoles (directed outward). These dipolar interactions cooperate to lower the pyridyl-based repulsions, therefore, increasing K2. Modest cooperative effects are observed for the snugly fitting F−, Cl−, and Br− halides while the too-large I− shows highly positive cooperativity.