Nano-SiO 2 : An Efficient Catalyst for the Synthesis of Some new Benzimidazoles - NMR Spectral Characterization

Some benzimidazoles were designed and synthesized by a new route using nano-SiO2 as a highly efficient catalyst. Synthesized compounds were characterized by 1H and 13C-NMR spectral studies. The significant features of this nanocatalyst are high yield of products, short reaction times, green reaction media and a vast range of substrates usage. Proton and 13C chemical shift of the synthesized compounds were calculated. To further confirm the compound formation single crystal XRD analysis was made and discussed for 2-(1H-benzimidazol-2-yl) phenol (1). The crystal packing features four π– π stacking interactions involving the imidazole ring, fused benzene ring and attached benzene ring system [centroid–centroid distances = 3.6106 (17), 3.6108 (17), 3.6666 (17) and 3.6668 (17) A]. Optimization of compound 1 was performed by DFT at B3LYP/6-31G (d, p) using Gaussian-03. All these XRD data are in good agreement with the theoretical values. However, from the theoretical values it is found that most of the optimized bond lengths, bond angles and dihedral angles are slightly higher than the XRD values.