Geometries and binding energies of complexes of cations with benzene, [2.2]paracyclophane and a [2.2]paraheterocyclophane are computed and compared using ab initio calculations. [2.2]Paracyclophane is not used for building cation receptors because of its small cavity. Here, we demonstrate that its binding capability toward cations using one aromatic ring is superior to benzene in 10 kcal/mol. This unexpected difference is explained by the reduction, upon complexation, of the repulsive interaction of the pi-systems, which is due to the close proximity of the two benzene rings. Experimental results derived from the analysis of X-ray structures retrieved from the CSD support this explanation.
Counterintuitive affinity of [2.2]paracyclophane to cations
Chem. Phys. Lett. 2005, 408, 59-64.