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J Am Chem Soc. 2008 Dec 24;130(51):17293-5. doi: 10.1021/ja8077329.

Dipole-promoted and size-dependent cooperativity between pyridyl-containing triazolophanes and halides leads to persistent sandwich complexes with iodide.

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  • 1Department of Chemistry, Indiana University, Bloomington, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, USA.


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 (1)H NMR spectra verify that the sandwich complexes have two pi-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 I(-) shows highly positive cooperativity.

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