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Dipole-Promoted and Size-Dependent Cooperativity between Pyridyl-Containing Triazolophanes and Halides Leads to Persistent Sandwich Complexes with Iodide
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2008
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Inorganic ChemistryPersistent Sandwich ComplexesEngineeringSandwich ComplexesNatural SciencesCoordination ComplexChemical BondMolecular BiologyPyridyl-containing TriazolophanesOrganic ChemistrySize-dependent CooperativityMolecular ComplexChemistryH NmrPi-stacked TriazolophanesInorganic Compound
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.