An Efficient Synthesis of Benzimidazole Derivatives Using a New Binuclear Cu-Bis-Salen Complex at Room Temperature

Benzimidazole derivatives have attracted a significant attention in recent years because oftheir medicinal applications as antiviral, antiulcer, antifungal, antihypertensive, anticancer,and antihistamine compounds [1]. Apart from therapeutic applications, benzimidazoles alsoplay an important role as intermediates in different organic reactions. Two general methodsare reported for the synthesis of 2-substituted benzimidazoles; (1) coupling of phenylenediaminesand carboxylic acids or their derivatives (nitriles, imidates, or orthoesters) as well as (2)a two-step procedure that consists of the oxidative cyclodehydrogenation of aniline Schiff’sbases, which are often generated in situ from the condensation of phenylenediamines with aldehydes[2]. However, most of these methods involve drastic reaction conditions, tediouswork-up procedures and low yields [3]. The additional serious drawbacks relate to the use ofhomogeneous catalysts that are somewhat modified in the work-up procedure and cannot berecovered. In continuation of our work on the development of low loaded, environmentallysound, affordable, stable and selective catalysts for greener organic reactions, herein we reportthe use homogeneous effective catalytic system based on bis-Cu(II)-salen complex forthe synthesis of benzimidazole compounds under mild reaction conditions. This homogeneouscatalytic system possesses inherent advantages for benzimidazole synthesis including highactivity, low metal loading in the catalyst as well as the use of a relatively inexpensive transitionmetal (Cu) system that prepared by accessible and cheap starting materials.