Structures and Oxidation Properties of Phenylene-Bridged Diazacycloalkanes: Ring Size Effects on Structures and...

Phenylenediamine derivatives have been investigated as functional molecules because of their characteristic oxidation properties. In this study, phenylene-bridged diazacycloalkanes, that is, C10, C12, and C14, in which numbers indicate the lengths of a side chain, were synthesized, and the effects of the macroring size on their structures and oxidation properties were investigated. X-ray crystallography revealed that the structures around the nitrogen atoms were remarkably dependent on the chain lengths. The benzene plane of C10 is arranged almost perpendicular to the macroring to avoid steric contact. However, the benzene plane of C14 and alkyl frame were co-planar. Stabilization resulting from conjugation was comparable to destabilization caused by macroring strain according to DFT calculations. Structural differences between C10 and C14 caused changes in the NMR chemical shifts of the inner methylene protons and first oxidation potentials in solution. Notably, the properties of C12 can be analyzed as those of distributed structures, which is of interest with respect to exploiting the metastable structure of the molecules. The observed relationships between the steric structures and properties can facilitate the design of functional molecules containing phenylenediamine moieties.