**2. Results and discussion**

### **2.1 Preparation of benzimidazolium salts**

Nitrogen-containing heterocyclic compounds received great attention because of their wide range of catalytic and pharmacological properties in organometallic chemistry. In this study, benzimidazoles salts (**2a-j**) prepared by the reaction of N-(isobutyl)-benzimidazole (1) with various aryl chloride in DMF at 80°C for 24 h. The reaction pathway is shown in **Figure 1**.

*Novel N-Heterocyclic Carbene Silver (I) Complexes: Synthesis, Structural Characterization… DOI: http://dx.doi.org/10.5772/intechopen.101950*

**Figure 1.** *Synthesis of the benzimidazoles salts (2a-j).*

The NMR spectra of all compounds were run in δ-CDCl3. The acidic protons (NCHN) of the benzimidazolium salts (**2a-j**) were detected in the <sup>1</sup> H NMR spectra at 12.07, 11.81, 11.44, 11.08, 11.29, 10.48, 12.05, 11.34, 11.52, and 11.95 ppm, respectively, as a typical singlet. These are in agreement with values in the associated literature [43–49]. The methyl protons of the isopropyl group on the benzimidazolium salts (**2a-j**) were observed between 0.98 and 1.06 in the form of doublets, whereas the methyl protons of the benzimidazolium salts (**2a-j**) were signaled at 2.24–2.44 ppm as singlets. The isopropyl group H2' protons on all the benzimidazolium salts were visualized as septets in the interval 2.34–2.44 ppm. Also, in the <sup>1</sup> H NMR spectra of (**2a-j**), the H1' protons appeared between 4.32–4.51 ppm while the H1" protons were detected as typical singlet between 5.80–6.90 ppm. The signals detected in the range of 6.94–8.64 ppm are assigned to the aromatic protons of benzimidazolium salts (**2a-j**). In 13C NMR spectra, the N-HCN (C2) carbene peak of benzimidazole salts (**2a**-**j**) was assigned between 141.91–144.02 ppm.

Ag2O and Benzimidazolium salts (**2a-j**) were reacted in dichloromethane at room temperature under dark and Ag(I)-NHC complex (**3a-j**) was obtained in very good yields. The Ag(I) complexes (**3a-j**) have good solubility in polar solvents and are stable in the air and towards the moisture. The synthetic route for the synthesis of Ag(I)-NHC complex (**3a-j**) is shown in **Figure 2**. In the <sup>1</sup> H NMR spectra, the acidic imino proton of benzimidazolium salts (NCHN) were not observed between δ 10.48–12.07 ppm. Similarly, in the 13C NMR spectra, imino carbon of benzimidazolium salts (NCHN) was not observed between δ 141–144 ppm.

**Figure 2.** *Synthesis of silver(I) complexes 3a-j.*

At the same time, the formation of the Ag(I) complexes (**3a-j**) was proven by IR spectra, which showed CN bond vibrations in the range of 1400–1591 cm—1. The antibacterial and antioxidant activities of all the synthesized benzimidazolium salts (**2a-j**) and their corresponding Ag(I) complexes (**3a-j**) were evaluated as per details given in the following text.
