Layered Compounds. XXXVI. Structure and Properties of Triple-layered Metaparacyclophanes

The geometrical structures of triple-layered metaparacyclophanes are discussed on the basis of the chemical shifts of the NMR spectra and their temperature dependence. [2.2]Metacyclo(4,7)[2.2]paracyclophane 1 and [2.2]metacyclo(12,15)[2.2]metaparacyclophane 2 proved to be mixtures of conformational isomers due to arrangement of meta-substituted ring. [2.2]Paracyclo(4,6)[2.2]metaparacyclophane 3 was confirmed to be a staircase-shape (anti-form), in contrast to a platform-shape (syn-form) of [2.2]metacyclo(4,6)[2.2]metaparacyclophane 5. In their electronic spectra, 1 and 2 exhibit a transannular electronic interaction between the benzene rings similar to that of multilayered [2.2]paracyclophanes; 3 and 5 show one similar to that of multilayered [2.2]metacyclo-phanes. The difference between the former and the latter groups seems to arise from the substitution modes of methylene bridges attached to the inside benzene of triple-layered metaparacyclophanes.