Supramolecular structure of enaminones in solid-state

Abstract

The crystalline structure of four enaminones [R 1C(O)CH C(Me)NR 2R 3, where R 1 = CCl 3, R 2 = H, R 3 = Bn ( 1); R 1 = CHCl 2, R 2 = H, R 3 = Bn ( 2); R 1 = CCl 3, R 2, R 3 = (CH 2) 4 ( 3); R 1 = CHCl 2, R 2 , R 3 = (CH 2) 2 O (CH 2) 2 ( 4)] were determined by X-ray diffraction. It was found that compounds 1– 4 adopted the enaminone tautomeric form. Compounds 1 and 2 displayed intramolecular hydrogen bonds (2.658 ⩽ d (N⋯O) ⩾ 2.726), which are associated with the presence of resonance-assisted hydrogen bonds (RABHs). The bond length data implicated that π-delocalization in 3 and 4 was reduced in comparison to 1 and 2 and this can be interpreted as some gain of the aromatic character in the chelate form. In addition, it was shown that the crystal packing of these enaminones is governed by C H⋯O, C H⋯Cl, Cl⋯Cl weak interactions and these interactions presents interatomic distances in accordance with the reported van der Waals radii of the atoms involved. The energy of these intermolecular interactions was calculated as a difference in energy between the complex on the one hand and the sum of isolated monomers on the other. The energetic contributions of each interaction to the stability of the crystalline packing were determined, firstly for each interaction independently and secondly, for all interactions simultaneously. The additive effect was verified by the fact that the sum of all individual energetic contributions resulted in the same stability as that found when the energetic contribution of all interactions was calculated simultaneously.