Origins of Selectivity in Molecular and Supramolecular Entities: Solvent and Electrostatic Control of the Translational Isomerism in [2]Catenanes†

The fundamental basis for the stabilization of molecular complexes of various dioxyarenes and/or dithiaarenes and a tetracationic cyclophane was established by empirical force field and ab initio quantum mechanical calculations. The more stable translational isomers of the related [2]catenanes do not necessarily correspond to the more stable complexes involving the individual components. The origin of this anomaly was investigated using the AMBER* force field. Each [2]catenane is composed of cyclobis(paraquat-p-phenylene)the tetracationic cyclophaneand one constitutionally unsymmetrical macrocyclic polyether, incorporating 1,4-dioxybenzene and a dioxyarene or a dithiaarene unit as its two π-electron rich recognition sites. The calculated and experimental isomer ratios at equilibrium for these [2]catenanes are in good agreement. In two instances, the calculated ratios invert as a result of changing the solvation model from H2O to CHCl3. There is a correlation between the experimental and theoretical observ...