"Template Effects and Kinetic Selection in the Self-Assembly of Crown Ether-Cyclobis(paraquat-p-phenylene)[2]Catenanes. Effect of the 1,4-Dioxybenzene and 1,5-Dioxynaphthalene Units"

The template effects exerted by bis(p-phenylene)[34]crown-10 (3) and by 1,5-dinaphto[38]crown-10 (4) in the ring-closure reaction of the trication 2(3+) to yield the [2]catenanes 7(4+) and 8(4+) have been quantitatively evaluated in acetonitrile at 62 C by UV/visible spectroscopy. The rate of ring closure of the trication 2(3+) dramatically increases in the presence of the templates 3 and 4, up iv approximately 230 times at [3] approximate to 0.1 mol L-1. and up to approximately 1900 times at [4] approximate to 0.01 mol L-1. The outcome of kinetic selection experiments, in which the two crown ethers compete for the incorporation into the catenane structure, has been discussed in the light of the obtained results. It has been shown that the product ratio of catenanes obeys the Curtin-Hammett principle only if the concentrations of the templates are equal and much greater than that of the substrate. Analysis of the rate profiles has shown that the 1,5-dioxynaphthalene unit, present in the template 1, has a greater affinity than the 1,4-dioxybenzene unit, present in the template 3, for the electron-deficient pyridinium rings present in both the transition-slats and substrate structures. Ab initio calculations at the 3-21G and 6-31G(d) levels of theory indicate that the greater affinity of the 1,5-dioxynaphthalene unit cannot be explained on the basis of greater pi-pi stacking and [C-H ... pi] interactions, but rather on the basis of the: model of apolar complexation in which the solvent plays a major role.