Amide-based [12]-, [12.12]- and [12.12.12.12]paracyclophanes: non-planarity of amide and phenyl groups in the [12]cyclophane

Abstract

A reaction between ethylenediaminetetraacetic dianhydride and p-xylene-α,α′-diamine has given three amide-based cyclophanes with different ring sizes; the (1∶1)-reaction product is 3,10-dioxo-5,8-bis(carboxymethyl)-2,5,8,11-tetraaza[12]paracyclophane, the (2∶2)-product is 3,10,21,28-tetraoxo-5,8,23,26-tetrakis(carboxymethyl)-2,5,8,11,20, 23,26,29-octaaza[12.12]paracyclophane, and the (4:4)-product is 3,10,21,28,39,46,57,64-octaoxo-5,8,23,26,41,44, 59,62-octakis(carboxymethyl)-2,5,8,11,20,23,26,29,38,41,44,47,56,59,62,65-hexadecaaza[12.12.12.12]paracyclophane. These amide paracyclophanes have been characterized by NMR, infrared, absorption and electrospray mass spectroscopies. Ab initio calculations have shown that the amide and phenyl groups in the (1∶1)-product, i.e., amide[12]paracyclophane, are distorted from the planar structures owing to the strain of the small cyclophane ring. This unusual structure results in physical properties different from those of the other cyclophanes having larger ring sizes: for example, (1) a low acidity of the amide hydrogen and (2) a low basicity of the amino nitrogen.