Journal of the American Chemical Society, Vol.130, No.51, 17293-17293, 2008
Dipole-Promoted and Size-Dependent Cooperativity between Pyridyl-Containing Triazolophanes and Halides Leads to Persistent Sandwich Complexes with Iodide
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 H-1 NMR spectra verify that the sandwich complexes have two TT-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 K-2. Modest cooperative effects are observed for the snugly fitting F-, Cl-, and Br- halides while the too-large l(-) shows highly positive cooperativity.