Stability and solid-state polymerization reactivity of imidazolyl- and benzimidazolyl-substituted diacetylenes: pivotal role of lattice water

Abstract

International audience1,6-Bis(1-imidazolyl)-2,4-hexadiyne (1) and1,6-bis(1-benzimidazolyl)-2,4-hexadiyne (5) have beenpreparedby a novel method that consists in refluxing excess imidazole and benzimidazole with 2,4-hexadiyne-1,6-diol bis(p-toluenesulfonate),pTS (3). This procedure is a viable alternative to the widely used Hay coupling protocol in case the target diyne possesses substituents capable of deactivating the copper catalyst by complexation. Diyne1crystallizes as a hydrate,1?H2O(2). For this compound, water is essential toachieve a crystalline material, and attempts to obtain crystals without included solvent were unsuccessful. In the structure of2, the organic fragments organize around the water molecule and interact with it through a dense network of hydrogen bonds. The CMC-CMC moieties are not oriented suitably for topochemical polymerization, and when trying to alter the organizationof the crystal by heating so as to induce polymerization, water is lost in an abrupt fashion that leads to instantaneous decomposition into polyaromatic-like species. Similar results were observed when water was removedin vacuo at room temperature. The benzimidazole-containing compound can be crystallized with water molecules (4)orwithout(5). X-ray crystallography shows that the structure of 5is organized by numerous C-H...N, C-H...p,andimidazolyl...imidazolyl p-p interactions. The diacetylene molecules almost have the right arrangement for topochemical polymerization, withpossibly reactingCMC-CMC fragments not beingparallel, a rare situation indiacetylene chemistry. Yet, experiments showthat topochemical polymerizationdoes not occur. Incorporationofwater in the lattice of5leads toa solvate that is topochemically reactive. Unlike2, however, water molecules in 4are not isolated but are organized as ribbons. Spectroscopic characterization of the polymer of4indicates that it is a blue phase polymer, with water coordinated to it. This study shows that it is possible to use water, and more generally solvent molecules, to transform a nonreactive diacetylene into a reactive one, even though this approach is less predictable than the cocrystal approach developed by Fowler, Lauher, and Goroff. The solvate approach is simple to implement, quite versatile because of the large rangeof solvents available, andonedoes not face theproblemof having to remove the host in case one needs to recover the polymer. Previous studies describing a similar approach are scarce

Diacetylene polymerization on a bulk insulator surface

“…The favourable molecule-molecule distance for diacetylene polymerization has been identified to be in the range of 0.47-0.52 nm with an angle of 451 for the molecular axis with respect to the crystal translation, 10 which is perfectly matched in the molecular islands formed prior to annealing: the moleculemolecule distance along the [010] direction is 0.5 nm as indicated in Fig. 2b.…”

“…9 For this reaction, the crystalline arrangement of the precursor monomers has been recognized as being of pivotal importance, as the acetylene units have to be within a distance of no more than 0.4 nm and the molecular backbones of two diacetylene monomers must form an angle close to 451 with respect to the crystal translational vector. 10 On surfaces, suitable precursors have been shown to arrange in a pattern fulfilling the above topochemical requirements. An elegant example of on-surface polymerization initiated by a voltage pulse with the tip of a scanning tunnelling microscope (STM) has been presented by M. Aono and co-worker.…”

Diacetylenes with Ionic‐Liquid‐Like Substituents: Associating a Polymerizing Cation with a Polymerizing Anion in a Single Precursor for the Synthesis of N‐Doped Carbon Materials

“…[19] Evidently,i n the case of 2·N(CN) 2 ,attractive cation-p interactions are modulated by repulsive cation-cation interactions. We note that parallel displaced stacking of imidazolium groups is present in the 173 Kc rystal structure of 1,6-bis(N-methylimidazolium)hexa-2,4-diyne dibromide, [15] andt hat the centroid···centroid distance between these groups is quite large (4.521 ).…”

“…This situation is interesting, asi td iffers from those found in the crystal structures of anhydrous and hydrated 1,6-bis(1-benzimidazolyl)-2,4-hexadiyne. [19] In these pseudopolymorphs, imi-dazole···imidazole and phenyl···imidazole interactions were detected,b ut no head-to-tail arrangementw as recognized. Cer-tainly,t he absence of charges contributes largely to the observed dichotomy,y et the presence of numerous CH···p and OH···p/OH···Ni nteractions in the structures of the neutralc ompound cannot be ignored.…”

“…[20] Interestingly,h owever, the centroid···centroid distances observed in 2·N(CN) 2 are 0.1-0.3 l onger than the imida-zole···phenyl distances measured in hydrated 1,6-bis(1-benzimidazolyl)-2,4-hexadiyne, in the range 3.37-3.50 . [19] Evidently,i n the case of 2·N(CN) 2 ,attractive cation-p interactions are modulated by repulsive cation-cation interactions. We note that parallel displaced stacking of imidazolium groups is present in the 173 Kc rystal structure of 1,6-bis(N-methylimidazolium)hexa-2,4-diyne dibromide, [15] andt hat the centroid···centroid distance between these groups is quite large (4.521 ).…”