Weak interactions between resorcinarenes and diquaternary alkyl ammonium cations

The interactions of resorcin[4]arenes 1 with alkyl ammonium cations bearing a 1,4-diazabicyclo[2.2.2]octane (DABCO) scaffold (3(2+), 4(2+) and 5(2+)) were analyzed in the solid state by X-ray crystallography, in solution by H-1 NMR spectroscopy, and in the gas phase by ESI-TOF mass spectrometry. The results are complemented with AM1 calculations and compared to previous reports on complexation studies of resorcinarenes with quaternary alkyl ammonium cations. The NMR titration results indicate that there are hardly any differences in the binding of the quaternary tetramethyl ammonium cation 2(+) and the diquaternary N, N'-dimethyl DABCO dication 4(2+). The large N, N'-dibenzyl DABCO dication 5(2+) has two potential sites for inclusion, that is, the aryl groups and the central cationic part, and the complexation and interactions of both sites with 1 were verified in the NMR studies as well as in the solid state structures.