Supramolecular architectures of conformationally controlled 1,3-phenyl-dioxalamic molecular clefts through hydrogen bonding and steric restraints

Abstract

In this contribution the supramolecular architecture of a series of six 1,3-phenyl-dioxalamic molecular clefts is described. The conformation was controlled by the use of Me and OMe group substitution in the phenyl spacer. The structural and conformational study was carried out by X-ray diffraction analysis, DFT calculations at PBEPBE 6-31+G (3df, 3pd) theory level and variable temperature ¹H NMR in solution. The C2-Me group exerts a dual influence on the conformation adopting the endo(sc) or exo(ac) conformations in the oxalamic arms, meanwhile the C2-OMe group leads to the adoption of the exo(ap) conformation. DFT study results showed that the exo(ap)–exo(ap) conformation is more stable than the other conformations due to the conjugation that stabilizes the molecule and minimizes the conformational energy. Supramolecular arrays in oxalamate/oxalamide derivatives of 1,3-diaminobenzene, 2-methyl-benzene-1,3-diamine and 2,4,6-trimethyl-benzene-1,3-diamine are directed by self-complementary N–H⋯O hydrogen bonding interactions, whose organization in the crystal depends on the twist of the oxalamic arms, meanwhile in oxalamate/oxalamide derivatives of 5-tert-butyl-2,6-diamineanisol with an exo(ap)–exo(ap) conformation, the supramolecular arrays are directed by π-stacking, dipolar carbonyl–carbonyl interactions and C–H⋯O soft contacts. N¹,N¹′-(1,3-(2,4,6-Trimethyl)-phenyl)-bis-(N²-(2-(2-hydroxyethoxy)ethyl)oxalamide) adopts the form of a supramolecular meso-helix, which is the first example of helical 1,3-phenyl-dioxalamide.