Molecular engineering. Part 5.1 Tuning the constrictive binding of container host by the atomic order of portal pillars

Abstract

Two D_4h container hosts 12 and 13 with 4(CH₂–O–bridge–O–CH₂) portal pillars were obtained in good yields by stepwise synthetic routes and showed complementary complexation behaviors to their analogues with (O–CH₂–bridge-CH₂–O)₄ portal pillars. ¹H NMR spectral chemical shifts of host’s inward-turned OCH₂O protons were sensitive to guest change. The stability orders of hemicarceplexes were 12–p-(CH₃CH₂)₂C₆H₄ > 12–p-(CH₃O)₂C₆H₄  12–o-(CH₃O)₂C₆H₄ > 12–m-(CH₃O)₂C₆H₄ and 13–CH₃COCH₂CH₃ > 13–CH₃COCH₂CH(CH₃)₂ > 13–CH₃CON(CH₃)₂ > 13–CH₃COOCH₂CH₃ > 13–CH₃CH₂CON(CH₃)₂ in terms of the activation energy barrier for decomplexation. Large solvent effects on the activation energy for decomplexation of hemicarceplexes were observed.