Weak interactions between resorcinarenes and diquaternary alkyl ammonium cations

Abstract

The interactions of resorcin[4]arenes 1 with alkyl ammonium cations bearing a 1,4-diazabicyclo[2.2.2]octane (DABCO) scaffold (3²⁺, 4²⁺ and 5²⁺) were analyzed in the solid state by X-ray crystallography, in solution by ¹H 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 4²⁺. The large N,N’-dibenzyl DABCO dication 5²⁺ 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.