Homogenous catalyst for the synthesis of 2-substituted benzimidazoles by dioxomolybdenum(VI) Schiff base complex

A new hydrazone Schiff base, (E)-N′-(3-methoxy-2-hydroxybenzylidene)nicotinohydrazide (H2L), and the corresponding dioxomolybdenum(VI) complex was synthesized and characterized by FI-IR, 1H NMR and 13C NMR spectroscopic methods. The hydrazone Schiff base ligand coordinates to molybdenum through the phenolate O, imine N, and enolic O. The complex was used as a catalyst for the synthesis of 2-substituted benzimidazoles from the reaction of a wide variety of benzaldehydes and o-phenylenediamine under agitation with magnetic stirring. The reaction parameters such as catalyst amount and kind of solvent were optimized. First, the amount of catalyst was optimized in the synthesis of the p-chlorobenzimidazole. The highest yield was obtained in the presence of 3 mg of catalyst. Then, the effect of different solvents was investigated for choosing the reaction media. The results show that the C2H5OH is the best solvent for the synthesis of 2-substituted benzimidazoles. The results showed the nature of substituent on the aromatic ring of the benzaldehyde has no significant effect on the catalytic activity.

Keywords:

Homogenous catalyst , Schiff base , Molybdenum complex , Benzimidazole