Synthetic, structural, and computational investigations of N-alkyl benzo-2,1,3-selenadiazolium iodides and their supramolecular aggregates

Abstract

Despite their versatility, the application of telluradiazoles as supramolecular building blocks is considerably constrained by their sensitivity to moisture. Albeit more robust, their selenium analogues form weaker supramolecular interactions. These, however, are enhanced when one nitrogen atom is bonded to an alkyl group. Here we investigate general methods for the synthesis of such derivatives. Methyl, iso-propyl and tert-butyl benzo-2,1,3-selenadiazolium cations were prepared by direct alkylation or cyclo-condensation of the alkyl-phenylenediamine with selenous acid. While the former reaction only proceeds with the primary and tertiary alkyl iodides, the latter is very efficient. Difficulties reported in earlier literature are attributable to the formation of adducts of benzoselenadiazole with its alkylated cations and side reactions initiated by aerobic oxidation of iodide. However, the cations themselves are resilient to oxidation and stable in acidic to neutral aqueous medium. X-ray crystallography was used in the identification and characterization of the following compounds: [C6H4N2(R)Se](+)X(-), (R = CH(CH3)2, C(CH3)3; X = I(-), I3(-)], [C6H4N2(CH3)Se](+)I(-), and [C6H4N2Se][C6H4N2(CH3)Se]2I2. Formation of SeN secondary bonding interactions (chalcogen bonds) was only observed in the last structure as anion binding to selenium is a strong competitor. The relative strengths of those forces and the structural preferences they enforce were assessed with DFT-D3 calculations supplemented by AIM analysis of the electron density.

Chalcogen Bonding “2S–2N Squares” versus Competing Interactions: Exploring the Recognition Properties of Sulfur

“…[53] 2,1,3-Benzothiadiazole (1b;F igure 1a)a nd its derivatives serve as an effective test-case because of their affinity for crystallization, relevance to medicinal chemistry [54][55][56] and materials science. [57][58][59][60][61][62][63][64][65][66][67][68] Furthermore, many structural derivatives are capable of forming2 S-2N square dimeric [69,70] or polymerici nteractions within their crystalline lattices ( Figures 1b,c), and the scaffold allows for the systematic substitution of positions 4-7 on the benzo ring.…”

Synthesis and Applications of 5‐Membered Chalcogen‐Nitrogen π‐Heterocycles with Three Heteroatoms

“…Notably, the Lewis acidity of 1,2,5‐chalcogenadiazoles can be increased by their transformation into N ‐substituted cationic derivatives, particularly via alkylation ,. This can also be used in anion recognition and sensing …”

Effect of Aromatic System Expansion on Crystal Structures of 1,2,5-Thia- and 1,2,5-Selenadiazoles and Their Quaternary Salts: Synthesis, Structure, and Spectroscopic Properties

“…It is worth noticing that two main factors, i.e., the size and nature of the alkyl group and the anion play a crucial role in self-association of N-alkylated cationic rings in solid. So far a few motifs recurring in crystals of chalcogenadiazolium salts have been identified [26] (Figure 2). For example, pattern number I has been observed in N-methyl-2,1,3-benzothiadiazolium triflate and pattern III in N-methyl-2,1,3-benzoselenadiazolium triflate described by Risto and co-workers Recently, it has been proved that blocking one of the nitrogen atoms in a molecule of 2,1,3-benzochalcogenadiazole, either by attachment of a transition metal ion (Hg [20], Cu, Ag, Co [21]) or N-alkylation, shortens the E•••N intermolecular distance and consequently strengthens chalcogen bonding [22].…”

“…It is worth noticing that two main factors, i.e., the size and nature of the alkyl group and the anion play a crucial role in self-association of N-alkylated cationic rings in solid. So far a few motifs recurring in crystals of chalcogenadiazolium salts have been identified [26] (Figure 2). decades.…”