New ferrocenyl chalcogenated (Se, Te) benzimidazoles, benzimidazolium salts and chalcogenones: Structure, electrochemistry, thermal investigation and antioxidant activity

Synthesis of new ferrocenylated benzimidazoles containing organochalcogen donor (Se and Te) atoms in the pendant arm, their corresponding ferrocenylated-NHCs salts and their thione and selenone derivatives have been described. All these compounds were characterized by Infrared (IR), multinuclear (¹H, ¹³C, ⁷⁷Se and ¹²⁵Te) 1D and 2D NMR spectroscopy and mass spectrometry. The molecular structures of five compounds, viz. 1-(1-(ferrocenylselenyl)methyl)-benzimidazole (1), 1-(2-(ferrocenylselenyl)ethyl)-benzimidazole (3), 1-(2-(ferrocenyltelluro)ethyl)-benzimidazole (4), 3-ferrocenyl methyl-1-(2-(ferrocenylselenyl)ethyl)benzimidazolium iodide (8) 3-methyl-1-(2-(ferrocenylselenyl)ethyl)-benzimidazolin-2-selenone (11) were determined by X-ray crystallography. In these compounds, multiple intermolecular hydrogen bonding interactions, CH⋯N, CH⋯C, CH⋯S, CH⋯Se, CH⋯I, CH⋯O, and OH⋯I contribute to the formation of supramolecular structures. Cyclic voltammetric (CV) and thermogravimetric (TGA) studies of these ferrocenyl chalcogenated benzimidazole derivatives have also been carried out. The cyclic voltammogram for all the compounds (1-7) shows one well-defined ferrocene-based wave at a higher positive potential while in the selenated benzimidazoles (1) and (3) and their benzimidazolium salts (5) and (6) present another irreversible single-electron redox wave. The TGA curves of chalcogenated benzimidazolium salts show three steps of decomposition for compounds (6) and (7), and four steps of decomposition for compound (8). The antioxidant activity of benzimidazole precursors (1-4) and benzimidazolium salts (5-7) have been evaluated by conducting a thiobarbituric acid reactive substance (TBARS) assay. The IC₅₀ value of all the compounds has been determined. The toxicity assay of all these compounds against Artemia Salina model at three different concentrations (1, 10 and 100 μM) was also studied.